We previously showed that monoterpenoid (1R,2R,6S)-3-methyl-6-(prop-1-en-2-yl)cyclohex-3-ene-1,2-diol 1 alleviates motor manifestations of Parkinson's disease in animal models. In the present study, we designed and synthesized monoepoxides of (1R,2R,6S)-3-methyl-6-(prop-1-en-2-yl)cyclohex-3-ene-1,2-diol 1 and evaluated their biological activity in the MPTP mouse model of Parkinson's disease. We also assessed the ability of these compounds to penetrate the blood-brain barrier (BBB). According to these data, we chose epoxide 4, which potently restored the locomotor activity in MPTP-treated mice and efficiently penetrated the BBB, to further explore its potential mechanism of action. Epoxide 4 was found to robustly promote the survival of cultured dopamine neurons, protect dopamine neurons against toxin-induced degeneration, and trigger the mitogen-activated protein kinase (MAPK) signaling cascade in cells of neuronal origin. Meanwhile, neither the survival-promoting effect nor MAPK activation was observed in non-neuronal cells treated with epoxide 4. In the MPTP mouse model of Parkinson's disease, compound 4 increased the density of dopamine neuron fibers in the striatum, which can highlight its potential to stimulate striatal reinnervation and thus halt disease progression. Taken together, these data indicate that epoxide 4 can be a promising compound for further development, not only as a symptomatic but also as a neuroprotective and neurorestorative drug for Parkinson's disease.

Neurotrophic factors (NTF) are a subgroup of growth factors that promote survival and differentiation of neurons. Due to their neuroprotective and neurorestorative properties, their therapeutic potential has been tested in various neurodegenerative diseases. Bioavailability of NTFs in the target tissue remains a major challenge for NTF-based therapies. Various intracerebral delivery approaches, both protein and gene transfer-based, have been tested with varying outcomes. Three growth factors, glial cell-line derived neurotrophic factor (GDNF), neurturin (NRTN) and platelet-derived growth factor (PDGF-BB) have been tested in clinical trials in Parkinson?s Disease (PD) during the past 20 years. A new protein can now be added to this list, as cerebral dopamine neurotrophic factor (CDNF) has recently entered clinical trials. Despite their misleading names, CDNF, together with its closest relative mesencephalic astrocyte-derived neurotrophic factor (MANF), form a novel family of unconventional NTF that are both structurally and mechanistically distinct from other growth factors. CDNF and MANF are localized mainly to the lumen of endoplasmic reticulum (ER) and their primary function appears to be modulation of the unfolded protein response (UPR) pathway. Prolonged ER stress, via the UPR signaling pathways, contributes to the pathogenesis in a number of chronic degenerative diseases, and is an important target for therapeutic modulation. Intraputamenally administered recombinant human CDNF has shown robust neurorestorative effects in a number of small and large animal models of PD, and had a good safety profile in preclinical toxicology studies. Intermittent monthly bilateral intraputamenal infusions of CDNF are currently being tested in a randomized placebo-controlled phase I?II clinical study in moderately advanced PD patients. Here, we review the history of growth factor-based clinical trials in PD, and discuss how CDNF differs from the previously tested growth factors.

Glial cell line-derived neurotrophic factor (GDNF) supports function and survival of dopamine neurons that degenerate in Parkinson's disease (PD). Ectopic delivery of GDNF in clinical trials to treat PD is safe but lacks significant therapeutic effect. In pre-clinical models, ectopic GDNF is effective but causes adverse effects, including downregulation of tyrosine hydroxylase, only a transient boost in dopamine metabolism, aberrant neuronal sprouting, and hyperactivity. Hindering development of GDNF mimetic increased signaling via GDNF receptor RET by activating mutations results in cancer. Safe and effective mode of action must be defined first in animal models to develop successful GDNF-based therapies. Previously we showed that about a 2-fold increase in endogenous GDNF expression is safe and results in increased motor and dopaminergic function and protection in a PD model in young animals. Recently, similar results were reported using a novel Gdnf mRNA-targeting strategy. Next, it is important to establish the safety of a long-term increase in endogenous GDNF expression. We report behavioral, dopamine system, and cancer analysis of five cohorts of aged mice with a 2-fold increase in endogenous GDNF. We found a sustained increase in dopamine levels, improvement in motor learning, and no side effects or cancer. These results support the rationale for further development of endogenous GDNF-based treatments and GDNF mimetic.

Addictive drugs enhance dopamine release in the striatum, which can lead to compulsive drug-seeking after repeated exposure. Glial cell line-derived neurotrophic factor (GDNF) is an important regulator of midbrain dopamine neurons, and may play a mechanistic role in addiction-related behaviors. To elucidate the components of GDNF-signaling that contribute to addiction-related behaviors of place preference and its extinction, we utilized two genetically modified GDNF mouse models in an amphetamine induced conditioned place preference (CPP) paradigm and evaluated how the behavioral findings correlate with dopamine signaling in the dorsal and ventral striatum. We utilized two knock-in mouse strains to delineate contributions of GDNF and Ret signaling using MEN2B mice (constitutively active GDNF receptor Ret), and GDNF hypermorphic mice (enhanced endogenous GDNF expression). The duration of amphetamine-induced CPP was greatly enhanced in MEN2B mice, but not in the GDNF hypermorphic mice. The enhanced duration of CPP was correlated with increased tyrosine hydroxylase (TH) expression and dopamine content in the ventral striatum. Together, our results suggest that downstream components of GDNF signaling, in this case Ret, may mediate persistent drug-seeking behavior through increased TH expression and dopamine levels in the mesolimbic dopamine neurons. (C) 2017 Elsevier Ltd. All rights reserved.

In Parkinson's disease midbrain dopaminergic neurons degenerate and die. Oral medications and deep brain stimulation can relieve the initial symptoms, but the disease continues to progress. Growth factors that might support the survival, enhance the activity, or even regenerate degenerating dopamine neurons have been tried with mixed results in patients. As growth factors do not pass the blood-brain barrier, they have to be delivered intracranially. Therefore their efficient diffusion in brain tissue is of crucial importance. To improve the diffusion of the growth factor neurturin (NRTN), we modified its capacity to attach to heparan sulfates in the extracellular matrix. We present four new, biologically fully active variants with reduced heparin binding. Two of these variants are more stable than WT NRTN in vitro and diffuse better in rat brains. We also show that one of the NRTN variants diffuses better than its close homolog GDNF in monkey brains. The variant with the highest stability and widest diffusion regenerates dopamine fibers and improves the conditions of rats in a 6-hydroxydopamine model of Parkinson's disease more potently than GDNF, which previously showed modest efficacy in clinical trials. The new NRTN variants may help solve the major problem of inadequate distribution of NRTN in human brain tissue. (C) 2016 Elsevier Inc. All rights reserved.

Literature review: The plasma membrane DA transporter (DAT) belongs to the family of Na+/ClÙÄÉ≠ dependent neurotransmitter transporters. DAT is the primary mechanism for clearance of dopamine from the extracellular space and transporting it back to the presynaptic nerve terminals. There's a great interest in the DAT and its regulation as its substrate, dopamine, mediates a wide array of physiological functions e.g. locomotor activity, cognition and the control of motivated behaviors. With selective transport DAT limits the intensity and the duration of dopaminergic signal. Its function is regulated by several kinases, phosphatase and protein-protein interactions. The altered expression of DAT may be related to several neurological diseases such as Parkinson's disease, addiction and ADHD. To study DAT's function, several genetically modified mouse lines including DAT knockout mice, DAT knockdown mice and DAT knock in mice with elevated DAT levels have been generated. Experimental part: Glial cell line-derived neurotrophic factor (GDNF) plays important role in the survival and function of dopaminergic neurons, learning, memory and synaptic plasticity. More recently, several studies have shown that GDNF can also negatively regulate the actions of abused drugs. The aim of this study was to investigate GDNF's role and mechanism of action in plasticity and function of the dopaminergic neurons projecting to striatum. For that purpose, we used in vivo microdialysis in freely moving mice. We chose two different mouse lines: MEN2B mice with constitutive active Ret-signaling and elevated striatal dopamine concentrations, and GDND-cKO mice that lack GDND in the central nervous system. Microdialysis guide cannula was implanted in the dorsal striatum in the stereotaxic surgery and the mice were allowed to recover for 5-7 days. The concentrations of dopamine and its metabolites DOPAC and HVA and also 5-HIAA were determined from the samples by highperformance liquid chromatography. Microdialysis was performed twice for every mouse on days 1 and 4. Between microdialysis days, the mice were given amphetamine 1 mg/kg i.p. on days 2 and 3. In the microdialysis experiment, the mice received amphetamine stimulation (100 µM/60 min) via microdialysis probe. The placements of microdialysis probes were verified from fixed brain sections after the experiments. Amphetamine increased the dopamine output in both mouse lines, but there were no statistically significant differences in striatal dopamine concentrations between genotypes neither after acute nor chronic administration. However, there was a difference between the dopamine outputs in days 1 and 4 in both MEN2B and GDNF-cKO mice: The striatal dopamine concentrations were significantly lower on the second microdialysis day. This may be a sing from tolerance to the drug. However, without more research, it is not possible, by this experiment, to draw direct conclusions of GDNF's role in addiction and in plasticity in striatum. It is possible that the differences between genotypes are too small to be seen with microdialysis. Development of compensatory mechanisms in mice cannot be ruled out either. Effects may also vary between different brain areas.

Literature review part: The enteric nervous system (ENS) often called “the second brain” is considered its own autonomic division that can independently regulate gut function. The ENS is derived from enteric neural crest-derived cells (ENCCs), which colonize the gut during development. Development of the ENS is a complex process, and many signalling pathways are required for a properly functioning ENS, especially GDNF/Gfrα1/RET signalling controlling survival, proliferation, migration, and differentiation of ENCCs. Hirschsprung’s disease (HSCR) is the most common congenital disease affecting gut motility. The prevalence of HSCR is 1:5000, and it is characterized by a complete lack of enteric neurons (aganglionosis) in the distal colon. Due to impaired intestinal motility, infants may have constipation, emesis, abdominal pain or distention, and, in some cases, diarrhea. The most life-threatening symptom is HSCR-associated enterocolitis (HAEC), which occurs in 30-50% of patients. Routine treatment for HSCR is a surgical operation called “pull through” in which the aganglionic segment is removed, and the remaining ganglionic segment is joined to the anus. However, the risk of developing HAEC after successful surgery still exists. Histopathological analysis has revealed that HAEC is accompanied by various changes in the gut epithelium, especially in mucin-producing goblet cells. These changes include hyperplasia of the goblet cells, altered mucin profile, retention of mucin, damaged and disorganized epithelium structure, inflammation, and bacterial adherence to the epithelium. However, a lack of suitable postnatal HSCR mouse models has partially hindered the progress of pinpointing the exact order of these events. A RET mutation found in half of the patients is overwhelmingly the biggest risk factor for HSCR. RET is a receptor on the cell membrane that mediates the effects in GDNF/Gfrα1/RET signaling pathway. of Knock-out mice of Gdnf, Gfra1 and Ret all have intestinal aganglionosis, resembling HSCR. However, to date, no mouse models of HSCR affecting GDNF/Gfrα1/RET signalling exist because pups are born without kidneys and die soon after birth. Experimental part: The GFRa1 hypomorphic mouse line (Gfra1hypo/hypo) created by Dr. Jaan-Olle Andressoo is the first successful model that survives past birth while manipulating GDNF-Gfrα1-RET signalling and phenocopying HSCR. These mice have 70-80% reduction in the expression of Gfrα1 in the developing gut and kidneys, which is sufficient to cause aganglionosis in the distal colon, yet not enough to impair kidney development.These mice are sacrificed between P7-P25 because of welfare problems yet giving a time window for analysis of the development of HAEC. Histological analyses revealed that Gfra1hypo/hypo mice had goblet cell hyperplasia and a shift away from acidic mucin production in the distal colon. Goblet cell hyperplasia was first observed at P10, but the shift in mucin profile already appeared at P5. It is not known what causes goblet cells to change their mucin production, but it seems to be the earliest histopathological change in HAEC preceding goblet cell hyperplasia. qPCR-analysis revealed that Muc2, the main secreted mucin that protects epithelium from invading pathogens, was upregulated at both P5 and P10. mRNA levels of Tnfa were also upregulated at P10. The aforementioned changes were not observed in the duodenum where the ENS had developed normally despite the reduction in Gfra1 expression. This indicates that the changes observed in the colon are likely due to the lack of ENS innervation, rather than a direct effect from GDNF-GFRa1-RET signalling itself. Finally, serum analysis indicated that systemic inflammation did not occur from P10-P16, although one Gfra1hypo/hypo animal had high levels of IL6 and TNFa at P14-16. This indicates that inflammation is not an early stage event and it is preceded by goblet cells related changes. In conclusion, changes in goblet cells seems to be earliest histopathological findings preceeding HAEC.

The receptor tyrosine kinase RET is essential in a variety of cellular processes. RET gain-of-function is strongly associated with several cancers, notably multiple endocrine neoplasia type 2A (MEN 2A), while RET loss-of-function causes Hirschsprung's disease and Parkinson's disease. To investigate the activation mechanism of RET as well as to enable drug development, over-expressed recombinant protein is needed for in vitro functional and structural studies. By comparing insect and mammalian cells expression of the RET extracellular domain (RETECD), we showed that the expression yields of RETECD using both systems were comparable, but mammalian cells produced monomeric functional RETECD, whereas RETECD expressed in insect cells was non-functional and multimeric. This was most likely due to incorrect disulfide formation. By fusing an Fc tag to the C-terminus of RETECD, we were able to produce, in HEK293T cells, dimeric oncogenic RETECD (C634R) for the first time. The protein remained dimeric even after cleavage of the tag via the cysteine disulfide, as in full-length RET in the context of MEN 2A and related pathologies. Our work thus provides valuable tools for functional and structural studies of the RET signaling system and its oncogenic activation mechanisms. (C) 2020 Published by Elsevier B.V.

Background Parkinson's disease (PD) is associated with proteostasis disturbances and accumulation of misfolded alpha-synuclein (alpha-syn), a cytosolic protein present in high concentrations at pre-synaptic neuronal terminals. It is a primary constituent of intracellular protein aggregates known as Lewy neurites or Lewy bodies. Progression of Lewy pathology caused by the prion-like self-templating properties of misfolded alpha-syn is a characteristic feature in the brains of PD patients. Glial cell line-derived neurotrophic factor (GDNF) promotes survival of mature dopamine (DA) neurons in vitro and in vivo. However, the data on its effect on Lewy pathology is controversial. Objectives We studied the effects of GDNF on misfolded alpha-syn accumulation in DA neurons. Methods Lewy pathology progression was modeled by the application of alpha-syn preformed fibrils in cultured DA neurons and in the adult mice. Results We discovered that GDNF prevented accumulation of misfolded alpha-syn in DA neurons in culture and in vivo. These effects were abolished by deletion of receptor tyrosine kinase rearranged during transfection (RET) or by inhibitors of corresponding signaling pathway. Expression of constitutively active RET protected DA neurons from fibril-induced alpha-syn accumulation. Conclusions For the first time, we have shown the neurotrophic factor-mediated protection against the misfolded alpha-syn propagation in DA neurons, uncovered underlying receptors, and investigated the involved signaling pathways. These results demonstrate that activation of GDNF/RET signaling can be an effective therapeutic approach to prevent Lewy pathology spread at early stages of PD. (c) 2020 International Parkinson and Movement Disorder Society

Review of the literature: The purpose of the review is to go through what is known about mechanisms of actions of different neurotrophic factors (GDNF, neurturin, CDNF and MANF) and how they are transported within the brain. Neurotrophic factors are endogenous and secreted proteins which have a pivotal role in the development and maintenance of neurons. They support the survival of neurons and they can help them to recover from different injuries. Due to these functions neurotrophic factors might be beneficial for the treatment of neurodegenerative disorders like Parkinson's disease. There are a great deal of studies that clearly show the neuroprotective and neurorestrorative function of GDNF and neurturin on dopaminergic neurons. They are also studied in clinical studies with Parkinson's patients but the results have been partly contradictory. The signalling route of GDNF and neurturin via RET tyrosinekinasereceptor is fairly well known but the other mechanisms of action of these factors needs to be studied further. CDNF and MANF constitute a novel, evolutionarily conserved family of neurotrophic factors. They are shown to have neuroprotective and neurorestrorative actions on dopaminergic neurons both in vitro and in vivo in a rodent model of Parkinson's disease. The mechanisms of action of CDNF and MANF are not quite clear at the moment. There are two different domains in their structure both of which are likely to carry different functions. The N-terminal domains of these proteins are close to saposins, lipid and membrane binding proteins, some of which are shown to have neurotrophic and anti-apoptotic effects. The C-terminal domain of MANF, in turn, is structurally close to the SAP-domain of Ku70-protein which binds Bax in the cytoplasm and thus inhibits apoptosis mediated by Bax. CDNF and MANF might protect neurons both via intracellular mechanisms and extracellularly acting like a secreted neurotrophic factor. CDNF and GDNF are transported retrogradially from striatum to substantia nigra. MANF, unlike the others, is transported from striatum to the frontal cortex. MANF and CDNF are shown to have better diffusion properties in the brain parenchyma than GDNF. Experimental part: We studied, by means of microdialysis, the effects of CDNF, MANF and GDNF on the dopaminergic neurotransmission of naive rats within the striatum. Neurotrophic factors (10 µg) and PBS as a negative control were injected into the left striatum in stereotaxic surgery. After this rats recovered one week before the first mircodialysis. The second mircodialysis was performed three weeks after the surgery. The samples were collected from the left striatum of freely moving rats. During the microdialysis neurotransmission was stimulated by replacing the perfusion solution with hypertonic potassium solution and with amphetamine solution. The concentration of dopamine, DOPAC, HVA and 5-HIAA was measured from the dialysate samples. In vivo TH-activity experiment was carried out for three rats in each group. NSD1015 was injected i.p.after which rats were decapitated and their striatums were dissected. The concentration of L-DOPA, dopamine and metabolites on the treated and untreated hemisphere were analyzed from the tissue samples. The amount of L-DOPA in the striatum after NSD1015-treatment indicates how active TH-enzyme is. There were no significant differences in the concentrations of dopamine and metabolites during the baseline. MANF and CDNF increased the release of dopamine from the nerve terminals compared to GDNF and PBS one week after the surgery. Three weeks after the surgery there was still significant increase in the release of dopamine in MANF group compared to GDNF group. Also the dopamine-DOPAC-turnover was increased significantly in MANF group compared to GDNF and PBS groups one week after the surgery. DOPAC/HVA -ratio was significantly smaller in GDNF group than in other groups one week after the surgery. These findings suggest that MANF potentiates dopaminergic neurotransmission most drasticly. The effects of MANF seem to last longer time than the effects of other neurotrophic factors. CDNF seems to increase the release of dopamine from the nerve terminals as well. The potentiation of dopaminergic neurotransmission could be due to increased biosynthesis of dopamine or due to the potentiation of the function of nerve terminals. In the results of the TH-activity experiment there was a trend according to which L-DOPA is synthesized less after the neurotrophic factor treatment that after the PBS treatment. This suggests that neurotrophic factors might decrease the activity of TH-enzyme.