Cerebral dopamine neurotrophic factor is essential for enteric neuronal development, maintenance, and regulation of gastrointestinal transit

Characterizing enteric neurons in dopamine transporter (DAT)-Cre reporter mice reveals dopaminergic subtypes with dual-transmitter content

The enteric nervous system (ENS) comprises a complex network of neurons whereby a subset appears to be dopaminergic although the characteristics, roles, and implications in disease are less understood. Most investigations relating to enteric dopamine (DA) neurons rely on immunoreactivity to tyrosine hydroxylase (TH)-the rate-limiting enzyme in the production of DA. However, TH immunoreactivity is likely to provide an incomplete picture. This study herein provides a comprehensive characterization of DA neurons in the gut using a reporter mouse line, expressing a fluorescent protein (tdTomato) under control of the DA transporter (DAT) promoter. Our findings confirm a unique localization of DA neurons in the gut and unveil the discrete subtypes of DA neurons in this organ, which we characterized using both immunofluorescence and single-cell transcriptomics, as well as validated using in situ hybridization. We observed distinct subtypes of DAT-tdTomato neurons expressing co-transmitters and modulators across both plexuses; some of them likely co-releasing acetylcholine, while others were positive for a slew of canonical DAergic markers (TH, VMAT2 and GIRK2). Interestingly, we uncovered a seemingly novel population of DA neurons unique to the ENS which was ChAT/DAT-tdTomato-immunoreactive and expressed Grp, Calcb, and Sst. Given the clear heterogeneity of DAergic gut neurons, further investigation is warranted to define their functional signatures and decipher their implication in disease.

CDNF and ER stress: Pharmacology and therapeutic possibilities

Cerebral dopamine neurotrophic factor (CDNF) is an endogenous protein in humans and other vertebrates, and it has been shown to have protective and restorative effects on cells in various disease models. Although it is named as a neurotrophic factor, its actions are drastically different from classical neurotrophic factors such as neurotrophins or the glial cell line-derived neurotrophic family of proteins. Like all secreted proteins, CDNF has a signal sequence at the N-terminus, but unlike common growth factors it has a KDEL-receptor retrieval sequence at the C-terminus. Thus, CDNF is mainly located in the ER. In response to adverse effects, such as ER stress, the expression of CDNF is upregulated and can alleviate ER stress. Also different from other neurotrophic factors, CDNF reduces protein aggregation and inflammation in disease models. Although it is an ER luminal protein, it can surprisingly directly interact with alpha-synuclein, a protein involved in the pathogenesis of synucleinopathies e.g., Parkinson's disease. Pleiotropic CDNF has therapeutic potential and has been tested as a recombinant human protein and gene therapy. The neuroprotective and neurorestorative effects have been described in a number of preclinical studies of Parkinson's disease, stroke and amyotrophic lateral sclerosis. Currently, it was successfully evaluated for safety in a phase 1/2 clinical trial for Parkinson's disease. Collectively, based on recent findings on the mode of action and therapeutic potential of CDNF, its use as a drug could be expanded to other ER stress-related diseases.

Effect of Prolong-life-with-nine-turn-method (Yan Nian Jiu Zhuan) Qigong on fatigue and gastrointestinal function in patients with chronic fatigue syndrome: Study protocol for a randomized controlled trial

INTRODUCTION

Chronic fatigue syndrome (CFS) is a physical and mental disorder in which long-term fatigue is the main symptom. CFS patients are often accompanied by functional gastrointestinal diseases (FGIDs), which lead to decreased quality of life and increased fatigue. Prolong-life-with-nine-turn-method (PLWNT) is a kind of physical and mental exercise. Its operation includes adjusting the mind, breathing and cooperating with eight self-rubbing methods and one upper body rocking method. PLWNT was used to improve the digestive function in ancient China and to treat FGIDs such as functional dyspepsia and irritable bowel syndrome in modern times. Previous studies have shown that PLWNT can reduce fatigue in patients with CFS. But it is unclear whether the effect of PLWNT on CFS fatigue is related to gastrointestinal function. The aim of this study was to explore the relationship between PLWNT and fatigue and gastrointestinal function in patients with CFS.

METHODS

This study is a non-inferiority randomized controlled trial (RCT). The whole study period is 38 weeks, including 2 weeks of baseline evaluation, 12 weeks of intervention and 6 months of follow-up. Ninety-six CFS patients will be stratified random assigned to the intervention group (PLWNT) and the control group (cognitive behavior treatment) in the ratio of 1:1 through the random number table generated by SPSS. In the evaluation of results, Multidimensional Fatigue Inventory-20 (MFI-20), Gastrointestinal Symptom Rating Scale (GSRS), Bristol Stool Form Scale (BSFS), and Short Form 36 item health survey (SF-36) will be evaluated at week 0 (baseline), week 6 (midterm), week 12 (endpoint) and month 9 (follow up). The intestinal flora will be evaluated at week 0 (baseline) and week 12 (endpoint). The data results will be processed by statistical experts. The data analysis will be based on the intention to treat principle and per-protocol analysis. In the efficacy evaluation, repeated measurement analysis of variance will be used for data conforming to normal distribution or approximate normal distribution. The data which do not conform to the analysis of repeated measurement variance will be analyzed by the generalized estimation equation Linear discriminant analysis will be used to clarify the difference species of intestinal flora. The significance level sets as 5%. The safety of interventions will be evaluated after each treatment session.

DISCUSSION

This trial will provide evidence to PLWNT exerting positive effects on fatigue and gastrointestinal function of CFS. It will further explore whether the improvement of PLWNT on CFS fatigue is related to gastrointestinal function.

TRIAL REGISTRATION

The trial was registered at Chinese Clinical Trial Registry http://www.chictr.org.cn/showproj.aspx?proj=151456 (Registration No.: ChiCTR2200056530). Date: 2022-02-07.

CDNF and MANF in the brain dopamine system and their potential as treatment for Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disease characterized by gradual loss of midbrain dopamine neurons, leading to impaired motor function. Preclinical studies have indicated cerebral dopamine neurotrophic factor (CDNF) and mesencephalic astrocyte-derived neurotrophic factor (MANF) to be potential therapeutic molecules for the treatment of PD. CDNF was proven to be safe and well tolerated when tested in Phase I-II clinical trials in PD patients. Neuroprotective and neurorestorative effects of CDNF and MANF were demonstrated in animal models of PD, where they promoted the survival of dopamine neurons and improved motor function. However, biological roles of endogenous CDNF and MANF proteins in the midbrain dopamine system have been less clear. In addition to extracellular trophic activities, CDNF/MANF proteins function intracellularly in the endoplasmic reticulum (ER), where they modulate protein homeostasis and protect cells against ER stress by regulating the unfolded protein response (UPR). Here, our aim is to give an overview of the biology of endogenous CDNF and MANF in the brain dopamine system. We will discuss recent studies on CDNF and MANF knockout animal models, and effects of CDNF and MANF in preclinical models of PD. To elucidate possible roles of CDNF and MANF in human biology, we will review CDNF and MANF tissue expression patterns and regulation of CDNF/MANF levels in human diseases. Finally, we will discuss novel findings related to the molecular mechanism of CDNF and MANF action in ER stress, UPR, and inflammation, all of which are mechanisms potentially involved in the pathophysiology of PD.

Intraputamenal Cerebral Dopamine Neurotrophic Factor in Parkinson's Disease: A Randomized, Double-Blind, Multicenter Phase 1 Trial

BACKGROUND

Cerebral dopamine neurotrophic factor (CDNF) is an unconventional neurotrophic factor that protects dopamine neurons and improves motor function in animal models of Parkinson's disease (PD).

OBJECTIVE

The primary objectives of this study were to assess the safety and tolerability of both CDNF and the drug delivery system (DDS) in patients with PD of moderate severity.

METHODS

We assessed the safety and tolerability of monthly intraputamenal CDNF infusions in patients with PD using an investigational DDS, a bone-anchored transcutaneous port connected to four catheters. This phase 1 trial was divided into a placebo-controlled, double-blind, 6-month main study followed by an active-treatment 6-month extension. Eligible patients, aged 35 to 75 years, had moderate idiopathic PD for 5 to 15 years and Hoehn and Yahr score ≤ 3 (off state). Seventeen patients were randomized to placebo (n = 6), 0.4 mg CDNF (n = 6), or 1.2 mg CDNF (n = 5). The primary endpoints were safety and tolerability of CDNF and DDS and catheter implantation accuracy. Secondary endpoints were measures of PD symptoms, including Unified Parkinson's Disease Rating Scale, and DDS patency and port stability. Exploratory endpoints included motor symptom assessment (PKG, Global Kinetics Pty Ltd, Melbourne, Australia) and positron emission tomography using dopamine transporter radioligand [18 F]FE-PE2I.

RESULTS

Drug-related adverse events were mild to moderate with no difference between placebo and treatment groups. No severe adverse events were associated with the drug, and device delivery accuracy met specification. The severe adverse events recorded were associated with the infusion procedure and did not reoccur after procedural modification. There were no significant changes between placebo and CDNF treatment groups in secondary endpoints between baseline and the end of the main and extension studies.

CONCLUSIONS

Intraputamenally administered CDNF was safe and well tolerated, and possible signs of biological response to the drug were observed in individual patients. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

CDNF Interacts with ER Chaperones and Requires UPR Sensors to Promote Neuronal Survival

Cerebral dopamine neurotrophic factor (CDNF) is a neurotrophic factor that has beneficial effects on dopamine neurons in both in vitro and in vivo models of Parkinson's disease (PD). CDNF was recently tested in phase I-II clinical trials for the treatment of PD, but the mechanisms underlying its neuroprotective properties are still poorly understood, although studies have suggested its role in the regulation of endoplasmic reticulum (ER) homeostasis and the unfolded protein response (UPR). The aim of this study was to investigate the mechanism of action of CDNF through analyzing the involvement of UPR signaling in its anti-apoptotic function. We used tunicamycin to induce ER stress in mice in vivo and used cultured primary neurons and found that CDNF expression is regulated by ER stress in vivo and that the involvement of UPR pathways is important for the neuroprotective function of CDNF. Moreover, we used AP-MS and BiFC to perform the first interactome screening for CDNF and report novel binding partners of CDNF. These findings allowed us to hypothesize that CDNF protects neurons from ER-stress-inducing agents by modulating UPR signaling towards cell survival outcomes.

Similarities and differences between nigral and enteric dopaminergic neurons unravel distinctive involvement in Parkinson's disease

In addition to the well-known degeneration of midbrain dopaminergic neurons, enteric neurons can also be affected in neurodegenerative disorders such as Parkinson's disease (PD). Dopaminergic neurons have recently been identified in the enteric nervous system (ENS). While ENS dopaminergic neurons have been shown to degenerate in genetic mouse models of PD, analyses of their survival in enteric biopsies of PD patients have provided inconsistent results to date. In this context, this review seeks to highlight the distinctive and shared factors and properties that control the evolution of these two sets of dopaminergic neurons from neuronal precursors to aging neurons. Although their cellular sources and developmental times of origin differ, midbrain and ENS dopaminergic neurons express many transcription factors in common and their respective environments express similar neurotrophic molecules. For example, Foxa2 and Sox6 are expressed by both populations to promote the specification, differentiation, and long-term maintenance of the dopaminergic phenotype. Both populations exhibit sustained patterns of excitability that drive intrinsic vulnerability over time. In disorders such as PD, colon biopsies have revealed aggregation of alpha-synuclein in the submucosal plexus where dopaminergic neurons reside and lack blood barrier protection. Thus, these enteric neurons may be more susceptible to neurotoxic insults and aggregation of α-synuclein that spreads from gut to midbrain. Under sustained stress, inefficient autophagy leads to neurodegeneration, GI motility dysfunction, and PD symptoms. Recent findings suggest that novel neurotrophic factors such as CDNF have the potential to be used as neuroprotective agents to prevent and treat ENS symptoms of PD.

CDNF and MANF regulate ER stress in a tissue-specific manner

Cerebral dopamine neurotrophic factor (CDNF) and mesencephalic astrocyte-derived neurotrophic factor (MANF) display cytoprotective effects in animal models of neurodegenerative diseases. These endoplasmic reticulum (ER)-resident proteins belong to the same protein family and function as ER stress regulators. The relationship between CDNF and MANF function, as well as their capability for functional compensation, is unknown. We aimed to investigate these questions by generating mice lacking both CDNF and MANF. Results showed that CDNF-deficient Manf^−/− mice presented the same phenotypes of growth defect and diabetes as Manf^−/− mice. In the muscle, CDNF deficiency resulted in increased activation of unfolded protein response (UPR), which was aggravated when MANF was ablated. In the brain, the combined loss of CDNF and MANF did not exacerbate UPR activation caused by the loss of MANF alone. Consequently, CDNF and MANF deficiency in the brain did not cause degeneration of dopamine neurons. In conclusion, CDNF and MANF present functional redundancy in the muscle, but not in the other tissues examined here. Thus, they regulate the UPR in a tissue-specific manner.

Maternal Separation Induced Visceral Hypersensitivity Evaluated via Novel and Small Size Distention Balloon in Post-weaning Mice

Early life stress (ELS) disposes to functional gastrointestinal diseases in adult, such as irritable bowel syndrome (IBS). Maternal separation (MS) is a well-known animal model of IBS and has been shown to induce visceral hypersensitivity in adult rats and mice. However, to the best of our knowledge, it has not been reported whether MS induces visceral hypersensitivity in young mice, such as the post-weaning mice. Moreover, the method for evaluation of visceral sensitivity also has not been described. Accordingly, the present study aims to evaluate the visceral sensitivity caused by MS in post-weaning mice and develop a novel and small size distention balloon for assessment of visceral sensitivity of such mice. Male pups of C57BL/6 mice were randomly divided into two groups, MS (n = 12) and non-separation (NS) (n = 10). MS pups were separated from the dams through postnatal days (PND) 2 to 14, while NS pups were undisturbed. After, all pups stayed with respective dams and were weaned at PND 22. Visceral sensitivity was evaluated by colorectal distention (CRD) with a novel and small size distention balloon at PND 25. The threshold of abdominal withdrawal reflex (AWR) scores were significantly lower in MS than NS. In addition, AWR scores at different pressures of CRD were significantly higher in MS than NS. The results demonstrate that MS induced visceral hypersensitivity in post-weaning mice. The designed small size distention balloon for evaluation of visceral sensitivity is of significance to further study the pathophysiology of IBS from early life to adulthood.

Cerebral dopamine neurotrophic factor protects and repairs dopamine neurons by novel mechanism

Midbrain dopamine neurons deteriorate in Parkinson's disease (PD) that is a progressive neurodegenerative movement disorder. No cure is available that would stop the dopaminergic decline or restore function of injured neurons in PD. Neurotrophic factors (NTFs), e.g., glial cell line-derived neurotrophic factor (GDNF) are small, secreted proteins that promote neuron survival during mammalian development and regulate adult neuronal plasticity, and they are studied as potential therapeutic agents for the treatment of neurodegenerative diseases. However, results from clinical trials of GDNF and related NTF neurturin (NRTN) in PD have been modest so far. In this review, we focus on cerebral dopamine neurotrophic factor (CDNF), an unconventional neurotrophic protein. CDNF delivered to the brain parenchyma protects and restores dopamine neurons in animal models of PD. In a recent Phase I-II clinical trial CDNF was found safe and well tolerated. CDNF deletion in mice led to age-dependent functional changes in the brain dopaminergic system and loss of enteric neurons resulting in slower gastrointestinal motility. These defects in Cdnf^-/- mice intriguingly resemble deficiencies observed in early stage PD. Different from classical NTFs, CDNF can function both as an extracellular trophic factor and as an intracellular, endoplasmic reticulum (ER) luminal protein that protects neurons and other cell types against ER stress. Similarly to the homologous mesencephalic astrocyte-derived neurotrophic factor (MANF), CDNF is able to regulate ER stress-induced unfolded protein response (UPR) signaling and promote protein homeostasis in the ER. Since ER stress is thought to be one of the pathophysiological mechanisms contributing to the dopaminergic degeneration in PD, CDNF, and its small-molecule derivatives that are under development may provide useful tools for experimental medicine and future therapies for the treatment of PD and other neurodegenerative protein-misfolding diseases.

High cellulose diet promotes intestinal motility through regulating intestinal immune homeostasis and serotonin biosynthesis

It is widely accepted dietary fiber intimately linked to inflammatory and nervous diseases, which often been described with altered gastrointestinal (GI) motility. However, how dose dietary fiber modulate inflammation and crosstalk influence GI function has not been explained in detail. We found fiber-free diet reduced intestinal motility, accompanied by upregulated proinflammatory immunocytes and inflammatory cytokines in colon of mice. We also discovered high-cellulose diet increased synthesis of serotonin and expression of neurotrophic factors, both of that have been reported involved in promoting intestinal motility. In addition, metabolomics analysis showed increased tryptophan metabolites in high-cellulose diet mice, which happened to be required for serotonin biosynthesis. Further analysis revealed high-cellulose diet changed the composition of gut microbiota, in particular by altering the ratio of Firmicutes to Bacteroidetes, consequently, concentration of short-chain fatty acids (SCFAs), especially acetate. Orally administration of acetate confirmed its modulating to serotonin synthesis, neurotrophic factors expression and immunocyte differentiation through regulating histone deacetylase (HDAC3) activity in colon. Together, our results demonstrated high-cellulose diet promote intestinal motility through regulating intestinal homeostasis and enteric nervous system by increasing acetate production and HDAC3 inhibition. Thus, rich cellulose diet or acetate supplement can be considered as dietary advice to improve clinically intestinal motility insufficiency.

Cerebral Dopamine Neurotrophic Factor (CDNF): Structure, Functions, and Therapeutic Potential

The cerebral dopamine neurotrophic factor (CDNF) together with the mesencephalic astrocyte-derived neurotrophic factor (MANF) form a unique family of neurotrophic factors (NTFs) structurally and functionally different from other proteins with neurotrophic activity. CDNF has no receptors on the cell membrane, is localized mainly in the cavity of endoplasmic reticulum (ER), and its primary function is to regulate ER stress. In addition, CDNF is able to suppress inflammation and apoptosis. Due to its functions, CDNF has demonstrated outstanding protective and restorative properties in various models of neuropathology associated with ER stress, including Parkinson's disease (PD). That is why CDNF already passed clinical trials in patients with PD. However, despite the name, CDNF functions extend far beyond the dopamine system in the brain. In particular, there are data on participation of CDNF in the maturation and maintenance of other neurotransmitter systems, regulation of the processes of neuroplasticity and non-motor behavior. In the present review, we discuss the features of CDNF structure and functions, its protective and regenerative properties.