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  • Toivonen, Suvi (Helsingin yliopisto, 2002)
  • Plihtari, Riia (Helsingin yliopisto, 2010)
    Atherosclerosis is an inflammatory disease characterized by accumulation of lipids and fibrous connective tissue in the arterial wall. Recently, it has been suggested that decrease in the pH of extracellular fluid of the arterial intima may enhance LDL accumulation by increasing binding of the LDL to matrix proteoglycans and also by making the plaque more favorable for acidic enzymes to be active. Many lysosomal acidic enzymes have been found in atherosclerotic plaques. In this thesis, we were able to induce secretion of lysosomal acidic cathepsin F from human monocyte-derived macrophages by stimulation with angiotensin II. We also showed that LDL pre-proteolyzed with cathepsin S was more prone to subsequent hydrolytic modifications by lipases. Especially acidic secretory sphingomyelinase was able to hydrolyze pre-proteolyzed LDL even at neutral pH. We also showed that the proteolyzed and lipolyzed LDL particles were able to bind more efficiently to human aortic proteoglycans. In addition, the role of extracellular acidic pH on the ability of macrophages to internalize LDL was studied. At acidic pH, the production of cell surface proteoglycans in macrophages was increased as well as the binding of native and modified LDL to cell surface proteoglycans. Furthermore, macrophages cultured at acidic pH showed increased internalization of modified and native LDL leading to foam cell formation. This thesis revealed various mechanisms by which acidic pH can increase LDL retention and accumulation in the arterial intima and has the potential to increase the progression of atherosclerosis.
  • Skwarek-Maruszewska, Aneta (Helsingin yliopisto, 2009)
    In every cell, actin is a key component involved in migration, cytokinesis, endocytosis and generation of contraction. In non-muscle cells, actin filaments are very dynamic and regulated by an array of proteins that interact with actin filaments and/or monomeric actin. Interestingly, in non-muscle cells the barbed ends of the filaments are the predominant assembly place, whereas in muscle cells actin dynamics was reported to predominate at the pointed ends of thin filaments. The actin-based thin filament pointed (slow growing) ends extend towards the middle of the sarcomere's M-line where they interact with the thick filaments to generate contraction. The actin filaments in muscle cells are organized into a nearly crystalline array and are believed to be significantly less dynamic than the ones in other cell types. However, the exact mechanisms of the sarcomere assembly and turnover are largely unknown. Interestingly, although sarcomeric actin structures are believed to be relatively non-dynamic, many proteins promoting actin dynamics are expressed also in muscle cells (e.g ADF/cofilin, cyclase-associated protein and twinfilin). Thus, it is possible that the muscle-specific isoforms of these proteins promote actin dynamics differently from their non-muscle counterparts, or that actin filaments in muscle cells are more dynamic than previously thought. To study protein dynamics in live muscle cells, I used primary cell cultures of rat cardiomyocytes. My studies revealed that a subset of actin filaments in cardiomyocyte sarcomeres displays rapid turnover. Importantly, I discovered that the turnover of actin filaments depends on contractility of the cardiomyocytes and that the contractility-induced actin dynamics plays an important role in sarcomere maturation. Together with previous studies those findings suggest that sarcomeres undergo two types of actin dynamics: (1) contractility-dependent turnover of whole filaments and (2) regulatory pointed end monomer exchange to maintain correct thin filament length. Studies involving an actin polymerization inhibitor suggest that the dynamic actin filament pool identified here is composed of filaments that do not contribute to contractility. Additionally, I provided evidence that ADF/cofilins, together with myosin-induced contractility, are required to disassemble non-productive filaments in developing cardiomyocytes. In addition, during these studies we learned that isoforms of actin monomer binding protein twinfilin, Twf-1 and Twf-2a localise to myofibrils in cardiomyocytes and may thus contribute to actin dynamics in myofibrils. Finally, in collaboration with Roberto Dominguez s laboratory we characterized a new actin nucleator in muscle cells - leiomodin (Lmod). Lmod localises towards actin filament pointed ends and its depletion by siRNA leads to severe sarcomere abnormalities in cardiomyocytes. The actin filament nucleation activity of Lmod is enhanced by interactions with tropomyosin. We also revealed that Lmod expression correlates with the maturation of myofibrils, and that it associates with sarcomeres only at relatively late stages of myofibrillogenesis. Thus, Lmod is unlikely to play an important role in myofibril formation, but rather might be involved in the second step of the filament arrangement and/or maintenance through its ability to promote tropomyosin-induced actin filament nucleation occurring at the filament pointed ends. The results of these studies provide valuable new information about the molecular mechanisms underlying muscle sarcomere assembly and turnover. These data offer important clues to understanding certain physiological and pathological behaviours of muscle cells. Better understanding of the processes occurring in muscles might help to find strategies for determining, diagnosis, prognosis and therapy in heart and skeletal muscles diseases.
  • Välimäki, Elina (Helsingin yliopisto, 2015)
    Pathogenic micro-organisms have the potential to invade the body and damage the host. The innate immune system is the first defense mechanism to respond in such case. Principal innate immune effector cells macrophages detect the presence of microbe-derived, or endogenous molecules in inappropriate compartments. This recognition leads to the activation of macrophages triggering their defense reactions including secretion of proteins. Inflammasome is an intracellular protein complex that is assembled in macrophages promoting the secretion of an important inflammatory cytokine, interleukin(IL)-1β. Activation of the innate immune response is crucial in immediate host defense, and it also regulates the activation of the adaptive immune response later in infection. However, secretory responses from activated macrophages, or molecular signaling pathways leading to the activation of the inflammasome have not been fully characterized. This study aimed for exploring proteins secreted from human macrophages exposed to endogenous danger signals alone, and in combination with microbe-derived signals. Macrophages were activated with endogenous molecules monosodium urate (MSU) and adenosine triphosphate (ATP). MSU and ATP encountered in extracellular environment are both danger signals to the innate immune system, indicating tissue damage or metabolic dysfunction. The results show that exposing macrophages to MSU or ATP induces a robust protein secretion. Simultaneous detection of MSU with bacteria-derived lipopolysaccharide activates the secretion of inflammatory and defense proteins. Macrophages exposed to ATP display a rapid secretion of vesicles, and this secretion is dependent on the activity of proteins called calpains. Calpains are also required for ATP-induced inflammasome activation in macrophages. Second aim of this study was to explore inflammatory response of macrophages from healthy subjects with a history of reactive arthritis (ReA), an inflammatory joint disease, upon detection of microbe-derived signals. The results show that inflammasome activation is normal, but the secretion of two inflammatory cytokines, tumor necrosis factor and IL-23, is lower from macrophages of former ReA subjects compared to the release of these cytokines from cells of healthy controls. Thirdly this study aimed for unraveling signaling pathways activated by fungal-derived trichothecene mycotoxins in human macrophages. Trichothecene mycotoxins represent an exogenous danger signal to the innate immune system evoking an inflammatory response. The results of this study reveal that trichothecene mycotoxins activate the NLRP3 inflammasome in macrophages. This study provides new information about early innate immune responses that is useful in the discovery of treatments for diseases whose pathogenesis is associated to disturbances in the innate immune system.
  • Miettinen, Juho (Helsingin yliopisto, 2014)
    Innate immunity provides the first line of defence against invading pathogens, and can also be activated by endogenous danger signals released upon tissue damage or injury. Macrophages play an important role in innate immunity. They perform the immune surveillance of their immediate surroundings seeking out tissue damage and/or invading pathogens via pattern recognition receptors. Macrophages are activated upon detection of an invading pathogen or tissue damage, leading to the expression, and secretion of the proteins required for an efficient innate immune response. Herpes simplex virus-1 (HSV-1) is a common human pathogen. It is a master of evading the host immune response leading to its ability to cause a life-long infection in its host. In most cases, HSV-1 does not cause any symptoms in the host, or causes nothing more than an occasional painful blister in the orofacial region. However, in certain cases when the host immune system is compromised, it can cause severe, even lethal, infections. Uric acid can act as an endogenous danger signal that cells can produce and release into the extracellular space after encountering a stress, including that caused by certain viral infections. A high amount of uric acid in cells can also be attributed to certain dietary habits. In the extracellular space if present at high enough concentrations and in the presence of sodium, uric acid can become crystallized into monosodium urate (MSU). MSU is the causative of gouty inflammation in the joints and is known to be phagocytosed by macrophages. In this work, human monocyte-derived macrophages infected with HSV-1, or stimulated with MSU were studied using several proteomic methods combined with functional assays. The main goals were: to characterize the protein secretion pathways and the proteins being secreted from macrophages upon (1) HSV-1 infection, and (2) MSU stimulation; and (3) to characterize the functional mechanisms of HSV-1 infected cell protein 27 (ICP27) in the inhibition of the interferon (IFN) response and also inhibition of apoptosis during HSV-1 infection. The results revealed that robust extracellular vesicle-mediated unconventional protein secretion is induced by IFN-beta priming in HSV-1-infected, and by MSU stimulation in Toll-like receptor 4 ligand, bacterial cell wall component lipopolysaccharide-primed human macrophages. The secreted proteins included endogenous danger signal proteins, and interferon-stimulated gene-encoded proteins. In addition, HSV-1 ICP27 protein requires both the nuclear localization sequence (NLS) and nuclear export sequence (NES) in order to inhibit the IFN response, whereas the NES, but not NLS, is required for the inhibition of apoptosis. The results also demonstrate that pattern recognition receptors RIG-I and/or MDA5 are involved in the HSV-1-induced activation of apoptosis. To conclude, this thesis provides new information on the innate immune response induced by HSV-1 infection, and MSU stimulation, and also on the evasion mechanisms deployed by HSV-1 to avoid the innate immune response in human macrophages. These new results presented in this thesis may be exploited in several ways; in the development of new therapies against viral infections, and in the treatment of autoinflammatory diseases.
  • Latvala, Sinikka (Helsingin yliopisto, 2014)
    The human body is continuously interacting with microbes. Cells of the immune system protect the host from microbes some of which can occasionally cause diseases. Macrophages and dendritic cells (DC) play a central role in innate and adaptive immune responses and they are activated in response to microbial stimulation. During activation these cells produce cytokines, soluble mediators that regulate host immune responses. Recognition of microbes is regulated by multiple host cell receptor systems which activate intracellular signalling pathways ultimately leading to the expression of genes involved in innate and adaptive immune responses. In this thesis the interactions between human leukocytes and various bacteria were studied using human macrophages and DCs. The innate immune responses induced by probiotic and other non-pathogenic bacteria in macrophages and DCs were compared with the responses induced by a pathogenic bacterium Streptococcus pyogenes. The differences in the gene expression profiles of cytokine and chemokine genes and the activation of different signalling pathways were analysed. Although both cell types effectively destroy invading microbes the cytokine patterns they produced in response to bacterial stimulation varied significantly. Macrophages responded to bacterial stimulation in a nearly similar fashion whether the bacteria had probiotic, non-pathogenic, or pathogenic characteristics. Interestingly, DCs showed a much wider variability in their responses to different bacteria. Some non-pathogenic bacteria did not induce detectable levels of cytokines in DCs while others were even more efficient than S. pyogenes in inducing cytokine responses. DC maturation marker molecules were induced in response to non-pathogenic bacteria with relatively weak cytokine production patterns. This led to a semi-mature DC phenotype, which could be involved in tolerogenic responses seen in host cell interactions with commensal bacteria. The other focus of this work was to evaluate the role of dynamin-dependent endocytosis and streptococcal virulence factors, streptolysins, in the immune responses induced by S. pyogenes in macrophages. Streptolysins were not critical for the inflammatory responses induced by this bacterium, suggesting a cooperation of various virulence factors in bacterial pathogenesis. This work provides better understanding of the functions of the innate immune system upon contact with non-pathogenic and pathogenic bacteria. The results may provide useful information for the interpretation of the results obtained from probiotic clinical trials and help to select new candidate probiotic strains for clinical use. In addition, this work identifies new details on the mechanisms of S. pyogenes -induced inflammatory responses.
  • Mäkelä, Sanna (Helsingin yliopisto, 2016)
    Influenza viruses are human respiratory pathogens that cause seasonal epidemics and pandemics. The host restricts the virus infection by inducing immune responses aiming at virus clearance. The immune response has two arms. The innate immunity is the first line defense mechanism that is activated immediately after the recognition of the pathogen. The adaptive immunity, which consists of humoral and cell-mediated immunity, takes more time to develop. The epithelial cells of the respiratory tract and innate immune cells, such as macrophages and dendritic cells, are equipped with a plethora of receptors and signaling molecules that are designed for pathogen recognition. These receptors include Toll-like receptors (TLRs) and RIG-I-like receptors (RLRs). The pathogen recognition by these receptors leads to the activation of complex cellular signaling cascades that culminate in the production of cytokines, small proteins that mediate the communication between cells. In influenza infection, one important class of cytokines is interferons (IFNs) which induce the production of antiviral proteins that are able to inhibit virus infection. On the other hand, influenza viruses are capable of evading innate immune surveillance and there are differences between influenza virus types or strains in their immune evasion mechanisms. In this thesis work influenza virus-induced IFN responses were studied in human macrophages and dendritic cells in vitro. Firstly, we showed that in macrophages influenza B virus infection induced a very early IFN-β and IFN-λ1 gene expression that coincided with the nuclear entry of the virus and the activation and nuclear import of IFN regulatory factor 3 (IRF3). This early activation did not take place in influenza A virus-infected cells. Furthermore, our study indicated that RIG-I receptor was essential for the early IFN gene expression. Secondly, we compared the cytokine responses induced by pandemic H1N1 influenza A virus to the ones induced by seasonal influenza A viruses in human macrophages and dendritic cells. We showed that the pandemic influenza A virus induced weak IFN responses but was highly sensitive to the antiviral actions of IFNs. During the infection, different types of microbial structures are present and can be recognized by different cellular receptors. Another aim of this thesis was to elucidate the mechanism of receptor cooperation in inducing synergistic cytokine production. We confirmed the previous findings that TLR3 or TLR4 together with TLR7/8 induces synergistic interleukin (IL)-12 and IFN gene expression in human dendritic cells. We studied, which regulatory factors bound to IL-12 and IFN-λ1 gene promoters during a synergistic stimulation and which cell signaling pathways took part in the cytokine production. We conclude that at the transcriptional level, several different IRF proteins and cell signaling pathways cooperate in the synergistic IL-12 and IFN-λ gene expression. In addition, we propose that IFNs produced after stimulation of the TLR3 pathway induce the expression of TLR7 receptor and other cell signaling components that create a positive feedback loop that further augments the cytokine and IFN production during synergistic stimulation. This thesis discusses the host-pathogen interactions in the human system and clarifies the cell signaling pathways leading to synergistic cytokine gene expression. Moreover, the early events in influenza B virus infection and IFN responses induced by pandemic H1N1 influenza A virus are described. More detailed knowledge of the human innate immune responses induced by host-pathogen interactions is needed for the development of effective vaccines and antiviral treatments against influenza virus.
  • Haapasaari, Päivi (Helsingin yliopisto, 2012)
    The complexity, ambiguity and various sources of uncertainty related to fisheries systems are increasingly acknowledged. This has led to questioning the conventional practices of producing the knowledge base for fisheries policy. The prevailing practice relies on biological stock assessments, whereas uncertainties stemming from the behavior of humans are usually ignored. Focusing on biological management advice has further led to defining management objectives and related reference points in biological terms only. Currently, both scientists and managers call for expanding the practical science-policy cycles to incorporate social sciences and economics and to analyze the different types of knowledge in integrated frameworks. In this thesis, the potential of Bayesian belief networks (BBNs) to broaden the knowledge base of fisheries management is discussed. Applications to social sciences and to interdisciplinary settings are demonstrated in relation to Baltic salmon and Central Baltic herring fisheries. BBNs are based on the idea of structuring problems into acyclic cause-effect relationships and quantifying the relationships with values expressing subjective degree of belief. With their subjective perspective to knowledge, BBNs have features in common with the constructivist and hermeneutic theories of social sciences. This facilitates applications of BBNs to social sciences, and further enables combining social knowledge with biological and economic knowledge. An interdisciplinary model provides a framework to examine interactions between various uncertainties, objectives, and stakeholder interests, and thereby to anticipate consequences of decisions prior to their implementation. Addressing implementation uncertainty by quantifying fishers potential reactions to management measures can question decisions calculated optimal by biological or bio-economic models and turn attention to options that fishers support. BBNs provide a decision tool and a device for participatory problem framings, and an illustrative focus of discussion for adaptive co-management processes. The probabilistic basis of the approach implies that it does not involve a claim for truth but provides a framework to address variables and interrelationships that are considered relevant by scientists and other stakeholders, and further to update a model in order to learn about the system that it represents. The thesis acknowledges the difficulty related to interdisciplinary collaboration caused by the differences in disciplinary practices and paradigms and the scarcity of integrative tools. Through a focus on our research process related to Baltic salmon management, the thesis analyzes what kind of interdisciplinarity between natural scientists, environmental economists and social scientists grew from the need to better understand the complexity and uncertainty inherent to the Baltic salmon fisheries and how divergent knowledge was integrated to support science-based decision making. It is concluded, that interdisciplinarity is an extensive learning process that takes place on three levels: between individuals, between disciplines, and between types of knowledge. Such a learning process is facilitated by formulating a global question and by agreeing a common approach at the outset of a process.
  • Suikkanen, Sanna (Helsingin yliopisto, 2008)
    Eutrophication and enhanced internal nutrient loading of the Baltic Sea are most clearly reflected by increased late-summer cyanobacterial blooms, which often are toxic. In addition to their toxicity to animals, phytoplankton species can be allelopathic, which means that they produce chemicals that inhibit competing phytoplankton species. Such interspecific chemical warfare may lead to the formation of harmful phytoplankton blooms and the spread of exotic species into new habitats. This is the first report on allelopathic effects in brackish-water cyanobacteria. The experimental studies presented in this thesis showed that the filamentous cyanobacteria Anabaena sp., Aphanizomenon flos-aquae and Nodularia spumigena are capable of decreasing the growth of other phytoplankton species, especially cryptophytes, but also diatoms. The detected allelopathic effects are rather transitory, and some co-occurring species show tolerance to them. The allelochemicals are excreted during active growth and they decrease cell numbers, chlorophyll a content and carbon uptake of the target species. Although the more specific modes of action or chemical structures of the allelochemicals remain to be studied, the results clearly indicate that the allelopathic effects are not caused by the hepatotoxin, nodularin. On the other hand, cyanobacteria stimulated the growth of bacteria, other cyanobacteria, chlorophytes and flagellates in a natural phytoplankton community. In a long-term data analysis of phytoplankton abundances and hydrography of the northern Baltic Sea, a clear change was observed in phytoplankton community structure, together with a transition in environmental factors, between the late 1970s and early 2000s. Surface water salinity decreased, whereas water temperature and the concentration of dissolved inorganic nitrogen increased. In the phytoplankton community, the biomass of cyanobacteria, chrysophytes and chlorophytes significantly increased, and the late-summer phytoplankton community became increasingly cyanobacteria-dominated. In contrast, the biomass of cryptophytes decreased. The increased temperature and nutrient concentrations probably explain most of the changes in phytoplankton, but my results suggest that the possible effect of chemically mediated biological interactions should also be considered. Cyanobacterial allelochemicals can cause additional stress to other phytoplankton in the nutrient-depleted late-summer environment and thus contribute to the formation and persistence of long-lasting cyanobacterial mass occurrences. On the other hand, cyanobacterial blooms may either directly or indirectly promote the growth of some phytoplankton species. Therefore, a further increase in cyanobacteria will probably shape the late-summer pelagic phytoplankton community by stimulating some species, but inhibiting others.
  • Suntio, Taina (Helsingin yliopisto, 2008)
    The diversity of functions of eukaryotic cells is preserved by enclosing different enzymatic activities into membrane-bound organelles. Separation of exocytic proteins from those which remain in the endoplasmic reticulum (ER) casts the foundation for correct compartmentalization. The secretory pathway, starting from the ER membrane, operates by the aid of cytosolic coat proteins (COPs). In anterograde transport, polymerization of the COPII coat on the ER membrane is essential for the ER exit of proteins. Polymerization of the COPI coatomer on the cis-Golgi membrane functions for the retrieval of proteins from the Golgi for repeated use in the ER. The COPII coat is formed by essential proteins; Sec13/31p and Sec23/24p have been thought to be indispensable for the ER exit of all exocytic proteins. However, we found that functional Sec13p was not required for the ER exit of yeast endogenous glycoprotein Hsp150 in the yeast Saccharomyces cerevisiae. Hsp150 turned out to be an ATP phosphatase. ATP hydrolysis by a Walker motif located in the C-terminal domain of Hsp150 was an active mediator for the Sec13p and Sec24p independent ER exit. Our results suggest that in yeast cells a fast track transport route operates in parallel with the previously described cisternal maturation route of the Golgi. The fast track is used by Hsp150 with the aid of its C-terminal ATPase activity at the ER-exit. Hsp150 is matured with a half time of less than one minute. The cisternal maturation track is several-fold slower and used by other exocytic proteins studied so far. Operative COPI coat is needed for ER exit by a subset of proteins but not by Hsp150. We located a second active determinant to the Hsp150 polypeptide s N-terminal portion that guided also heterologous fusion proteins out of the ER in COPII coated vesicles under non-functional COPI conditions for several hours. Our data indicate that ER exit is a selective, receptor-mediated event, not a bulk flow. Furthermore, it suggests the existence of another retrieval pathway for essential reusable components, besides the COPI-operated retrotransport route. Additional experiments suggest that activation of the COPI primer, ADP ribosylation factor (ARF), is essential also for Hsp150 transport. Moreover, it seemed that a subset of proteins directly needed activated ARF in the anterograde transport to complete the ER exit. Our results indicate that coat structures and transport routes are more variable than it has been imagined.
  • Kuja-Panula, Juha (Helsingin yliopisto, 2014)
    The purpose for this PhD research is to find a novel gene induced by neurite outgrowth on amphoterin substrate. The finding was a gene that codes type-I transmembrane protein with six leucine-rich repeat (LRR) motifs and one immunoglobulin domain followed by a short cytoplasmic tail. We named this gene as amphoterin-induced gene and ORF (Amigo). Further characterization of AMIGO protein revealed that AMIGO itself is a neurite outgrowth promoting factor and it is also required for the fasciculation of neurites both in vitro and in vivo. The mode of these functions was shown to be homophilic, which puts AMIGO in a group of homophilic cell adhesion molecules. We crystallized the extracellular domain of AMIGO to elucidate the mechanism for its functions. AMIGO crystallized as a homophilic dimer where the concave face of the LRR domain was the interface for dimerization. The isolation of Amigo allowed us to characterize two other homologous genes called Amigo2 and Amigo3 and together they form the novel Amigo gene family. AMIGO protein was found to be an auxiliary subunit of the voltage-gated potassium channel Kv2.1 in adult animals. AMIGO mediates the regulation of the voltage-gating properties of Kv2.1. This AMIGO/Kv2.1 interaction was also studied at the whole animal level by using Amigo knockout mice whereby the lack of Amigo changed voltage-gated potassium currents and resulted in behavioral problems related to human schizophrenia. All these findings suggest that AMIGO has two separate roles in the central nervous system (CNS). First, AMIGO is a homophilic adhesion molecule that supports neurite outgrowth and fasciculation of the neurites during development. Second, the AMIGO regulates the properties of the voltage-gated potassium channel Kv2.1 in the mature CNS.
  • Peltola, Marjaana (Helsingin yliopisto, 2016)
    Schizophrenia is a devastating psychiatric illness afflicting approximately 1% of the world s population. Currently, the disease mechanism is poorly understood and the pharmacological interventions relieve only some of the symptoms. Schizophrenia is highly heritable and genetic factors contribute to about 65-80% of the liability to the illness. However, the genetic etiology is complex and remains largely unknown. Potassium channels are key determinants of neuronal excitability. Kv2.1 is a widely-expressed voltage-gated potassium channel α-subunit. Kv2.1 channels constitute an essential component of the somatodendritic delayed rectifier current (IK) in several neuronal types and regulate excitability, especially during periods of high-frequency firing. This study outlines the identification and characterization of a novel neuronal transmembrane protein AMIGO, which contains extracellular immunoglobulin (Ig) and leucine-rich repeat (LRR) domains. AMIGO was shown to be widely expressed in cerebral neurons and localized to distinctive clusters in the neuronal plasma membrane, restricted to the cell soma and proximal part of neurites. AMIGO was further identified as an auxiliary subunit of the Kv2.1 potassium channel. AMIGO and Kv2.1 were shown to display extensive spatial and temporal colocalization and association in brain. AMIGO was also shown to modify the voltage-dependent activation of Kv2.1 and neuronal delayed rectifier current (IK). To further understand the physiological role of AMIGO in brain, a mouse line lacking the Amigo gene was created and characterized as part of this study. Absence of AMIGO clearly reduced the amount of the Kv2.1 channel protein in mouse brain and altered the voltage-dependent activation of neuronal IK. These changes were accompanied by behavioral and pharmacological abnormalities reminiscent of those identified in schizophrenia. Concomitantly, the rare KV2.1 variant was found to be associated with human schizophrenia. These findings demonstrate the involvement of the AMIGO-Kv2.1 channel complex in schizophrenia-related behavioral domains in mice and establish KV2.1 as a susceptibility gene for schizophrenia spectrum disorders in humans. In the current study, AMIGO was identified as an integral component of the Kv2.1 channel complex in brain. The convergent findings in humans and mice suggest a role for the AMIGO-Kv2.1 potassium channel complex in the pathophysiology of schizophrenia. Furthermore, these findings suggest AMIGO and Kv2.1 may represent potential new targets for schizophrenia treatment development.
  • Saikku, Laura (Helsingin yliopisto, 2010)
    Industrial ecology is an important field of sustainability science. It can be applied to study environmental problems in a policy relevant manner. Industrial ecology uses ecosystem analogy; it aims at closing the loop of materials and substances and at the same time reducing resource consumption and environmental emissions. Emissions from human activities are related to human interference in material cycles. Carbon (C), nitrogen (N) and phosphorus (P) are essential elements for all living organisms, but in excess have negative environmental impacts, such as climate change (CO2, CH4 N2O), acidification (NOx) and eutrophication (N, P). Several indirect macro-level drivers affect emissions change. Population and affluence (GDP/capita) often act as upward drivers for emissions. Technology, as emissions per service used, and consumption, as economic intensity of use, may act as drivers resulting in a reduction in emissions. In addition, the development of country-specific emissions is affected by international trade. The aim of this study was to analyse changes in emissions as affected by macro-level drivers in different European case studies. ImPACT decomposition analysis (IPAT identity) was applied as a method in papers I III. The macro-level perspective was applied to evaluate CO2 emission reduction targets (paper II) and the sharing of greenhouse gas emission reduction targets (paper IV) in the European Union (EU27) up to the year 2020. Data for the study were mainly gathered from official statistics. In all cases, the results were discussed from an environmental policy perspective. The development of nitrogen oxide (NOx) emissions was analysed in the Finnish energy sector during a long time period, 1950 2003 (paper I). Finnish emissions of NOx began to decrease in the 1980s as the progress in technology in terms of NOx/energy curbed the impact of the growth in affluence and population. Carbon dioxide (CO2) emissions related to energy use during 1993 2004 (paper II) were analysed by country and region within the European Union. Considering energy-based CO2 emissions in the European Union, dematerialization and decarbonisation did occur, but not sufficiently to offset population growth and the rapidly increasing affluence during 1993 2004. The development of nitrogen and phosphorus load from aquaculture in relation to salmonid consumption in Finland during 1980 2007 was examined, including international trade in the analysis (paper III). A regional environmental issue, eutrophication of the Baltic Sea, and a marginal, yet locally important source of nutrients was used as a case. Nutrient emissions from Finnish aquaculture decreased from the 1990s onwards: although population, affluence and salmonid consumption steadily increased, aquaculture technology improved and the relative share of imported salmonids increased. According to the sustainability challenge in industrial ecology, the environmental impact of the growing population size and affluence should be compensated by improvements in technology (emissions/service used) and with dematerialisation. In the studied cases, the emission intensity of energy production could be lowered for NOx by cleaning the exhaust gases. Reorganization of the structure of energy production as well as technological innovations will be essential in lowering the emissions of both CO2 and NOx. Regarding the intensity of energy use, making the combustion of fuels more efficient and reducing energy use are essential. In reducing nutrient emissions from Finnish aquaculture to the Baltic Sea (paper III) through technology, limits of biological and physical properties of cultured fish, among others, will eventually be faced. Regarding consumption, salmonids are preferred to many other protein sources. Regarding trade, increasing the proportion of imports will outsource the impacts. Besides improving technology and dematerialization, other viewpoints may also be needed. Reducing the total amount of nutrients cycling in energy systems and eventually contributing to NOx emissions needs to be emphasized. Considering aquaculture emissions, nutrient cycles can be partly closed through using local fish as feed replacing imported feed. In particular, the reduction of CO2 emissions in the future is a very challenging task when considering the necessary rates of dematerialisation and decarbonisation (paper II). Climate change mitigation may have to focus on other greenhouse gases than CO2 and on the potential role of biomass as a carbon sink, among others. The global population is growing and scaling up the environmental impact. Population issues and growing affluence must be considered when discussing emission reductions. Climate policy has only very recently had an influence on emissions, and strong actions are now called for climate change mitigation. Environmental policies in general must cover all the regions related to production and impacts in order to avoid outsourcing of emissions and leakage effects. The macro-level drivers affecting changes in emissions can be identified with the ImPACT framework. Statistics for generally known macro-indicators are currently relatively well available for different countries, and the method is transparent. In the papers included in this study, a similar method was successfully applied in different types of case studies. Using transparent macro-level figures and a simple top-down approach are also appropriate in evaluating and setting international emission reduction targets, as demonstrated in papers II and IV. The projected rates of population and affluence growth are especially worth consideration in setting targets. However, sensitivities in calculations must be carefully acknowledged. In the basic form of the ImPACT model, the economic intensity of consumption and emission intensity of use are included. In seeking to examine consumption but also international trade in more detail, imports were included in paper III. This example demonstrates well how outsourcing of production influences domestic emissions. Country-specific production-based emissions have often been used in similar decomposition analyses. Nevertheless, trade-related issues must not be ignored.
  • Lindén, Eveliina (Helsingin yliopisto, 2006)
    Predation is an important source of mortality for most aquatic animals. Thus, the ability to avoid being eaten brings substantial fitness benefits to individuals. Predator detection abilities and antipredator behaviour were examined in various planktivores, i.e. the littoral mysids Neomysis integer and Praunus flexuosus, three-spined stickleback Gasterosteus aculeatus larvae, pelagic mysids Mysis mixta and M. relicta, and the predatory cladoceran Cercopagis pengoi, with cues from their respective predators European perch Perca fluviatilis and Baltic herring Clupea harengus membras. The use of different aquatic macrophytes as predation refuges by the littoral planktivores was also examined. All pelagic planktivores and stickleback larvae were able to detect the presence of their predator by chemical cues alone. The littoral mysids N. integer and P. flexuosus responded only when chemical and visual predator cues were combined. The responses of stickleback larvae were stronger to the combined cues than the chemical cue alone. A common antipredator behaviour in all of the planktivores studied was decreased ingestion rate in response to predator cues. N. integer and stickleback larvae also decreased their swimming activity. Pelagic mysids and C. pengoi altered their prey selectivity patterns in response to predator cues. The effects of predator cues on the swarming behaviour of N. integer were examined. Swarming brings clear antipredator advantages to N. integer, since when they feed in a swarm, they do not significantly decrease their feeding rate. However, the swarming behaviour of N. integer was not affected by predation risk, but was instead a fixed strategy. Despite the presence or absence of predator cues, N. integer individuals attempted to associate with a swarm and preferred larger to smaller swarms. In studies with aquatic macrophytes, stickleback larvae and P. flexuosus utilized vegetation as a predation refuge, spending more time within vegetation when under predation threat. The two macroalgal species studied, bladderwrack Fucus vesiculosus and stonewort Chara tomentosa, were preferred by P. flexuosus, whereas Eurasian watermilfoil Myriophyllum spicatum was strongly avoided by N. integer and stickleback larvae. In fact, when in dense patches in aquaria, M. spicatum caused acute and high mortality (> 70%) in littoral mysids, but not in sticklebacks, whereas C. tomentosa and northern watermilfoil M. sibiricum did not. In contrast, only 2-4% mortality in N. integer was observed with intact and broken stems of M. spicatum in field experiments. The distribution of littoral mysids in different vegetations, however, suggests that N. integer avoids areas vegetated by M. spicatum.
  • Anttila, Saku (Helsingin yliopisto, 2013)
    Spatial and temporal variation within water bodies causes uncertainties in freshwater monitoring programmes that are surprisingly seldom perceived. This poses a major challenge for the representative sampling and subsequent assessment of water bodies. The sources of variability in lakes are relatively well known. The majority of them produce consistent patterns in water quality that can be statistically described. This information can be used in calibrating the sampling intervals, locations and monitoring methods against the typical variation in a water body as well as the accuracy requirements of monitoring programmes. Similarly, understanding of ecosystem history and functioning in different states can help in contextualizing the collected data. Specifically, studies on abrupt transitions and the interactions involved produce a framework against which recent water quality information can be compared. This thesis research aimed to facilitate water quality monitoring by examining 1) feasible statistical tools to study spatial and temporal uncertainty associated with sampling efforts, 2) the characteristics of variation and 3) ecosystem interactions in different states. Research was conducted at Lake Vesijärvi, southern Finland. Studies of uncertainty utilized data-rich observations of surface water chlorophyll a from flow-through, automated and remote sensing systems. Long-term monitoring information of several trophic levels was used in the analysis of ecosystem interactions. Classical sample size estimates, bootstrap methodology, autocorrelation and spatial standard score analyses were used in spatio-temporal uncertainty analysis. A general procedure to identify abrupt ecosystem transitions was applied in order to characterize lake interactions in different states. The results interlink variability at the study site with information required in sampling design. Sampling effort estimates associated with the spatial and temporal variance were used to derive precision information for summary statistics. The structure of the variance illustrated with an autocorrelation model revealed the low spatial representativeness of discrete sampling in the study area. A generalized autocorrelation model and its parameters from the monitoring area were found applicable in sampling design. Furthermore, areas with constantly higher chlorophyll a concentrations, which had an effect on the water quality information derived with remote sensing, were identified from the study area. Characterization of the interactions between the main trophic levels in different ecosystem states revealed the key role of zooplankton in maintaining the current state as well as the resilience of the studied pelagic ecosystem. The results are brought into a broader context by discussing the applicability of presented methods in sampling design of water quality monitoring programmes. According to this thesis research, sampling design in individual monitoring regimes would benefit from the characterization of variance and subsequent uncertainty analysis of different data sources. This approach allows the calibration of sampling frequency and locations on the observed variance, as well as a quantitative comparison between the abilities of different monitoring methods. The derived precision information also supports the joint use of several monitoring methods. Furthermore, analysis of long-term records can reveal the key elements of freshwater ecosystem functioning and how it has responded to earlier pressures, to which recent monitoring data can be compared. This thesis thus highlights analysis of the variance and history of the monitored system in developing a rationalized and adaptive monitoring programme
  • Kulesskiy, Evgeny (Helsingin yliopisto, 2015)
    Syndecans are cell surface heparan sulfate proteoglycans which are present in all tissues and cell types and have distinct temporal and spatial expression patterns. They play important roles in embryonic development of the organism and control relocation and alteration of extracellular matrix components. Syndecans regulate cell migration, adhesion and proliferation and are engaged in tissue injury, inflammation processes, pathogenesis of infectious diseases and tumor biology. This thesis summarizes the results of studies on one of the syndecan family receptors syndecan-3 (also known as N-syndecan). This proteoglycan is abundantly expressed in developing brain. Syndecan-3 acts as a signaling receptor upon binding of its ligand, heparin-binding growth associated molecule (HB-GAM; also known as pleiotrophin), which activates the cortactin c-Src signaling pathway. This leads to rapid neurite extension in neuronal cells, which makes syndecan-3 an interesting transmembrane receptor in neuronal development and regeneration. However, little is known about the signaling mechanism of syndecan-3. Here I show formation of ligand-syndecan-3 signaling complexes at the cell surface using fluorescence resonance energy transfer (FRET) and bioluminescence resonance energy transfer (BRET). Ligand binding leads to dimerization of syndecan-3 at the cell surface. The dimerized syndecan-3 colocalizes with actin in the filopodia of cells. Lysine 383 in the juxtamembrane (ERKE) sequence and G392 and G396 from GXXXG canonical motif are shown to be important for the ligand-induced dimerization, whereas the cytosolic domain are not required for the dimerization. In addition to acting as a signaling receptor, syndecan-3 acts as a co-receptor in epidermal growth factor receptor (EGFR) ligand binding. FRET analysis suggests that interactions of syndecan-3 and EGFR depend on a shared ligand such as heparin-binding EGF-like growth factor (HB-EGF). Furthermore, it was shown that syndecan-3 may act as a receptor for other ligands, like glial cell line-derived neurotrophic factor (GDNF). In addition, I have found a new receptor for HB-GAM glypican-2 which may be involved in regulation of HB-GAM signaling by competing with syndecan-3 for ligand binding.