Spatiotemporal expression of MANF in the developing rat brain

Navigating the Landscape of MANF Research: A Scientometric Journey with CiteSpace Analysis

This study employs bibliometric analysis through CiteSpace to comprehensively evaluate the status and trends of MANF (mesencephalic astrocyte-derived neurotrophic factor) research spanning 25 years (1997-2022). It aims to fill the gap in objective and comprehensive reviews of MANF research. MANF-related studies were extracted from the Web of Science database. MANF publications were quantitatively and qualitatively analyzed for various factors by CiteSpace, including publication volume, journals, countries/regions, institutions, and authors. Keywords and references were visually analyzed to unveil research evolution and hotspot. Analysis of 353 MANF-related articles revealed escalating annual publications, indicating growing recognition of MANF's importance. High-impact journals such as the International Journal of Molecular Sciences and Journal of Biological Chemistry underscored MANF's interdisciplinary significance. Collaborative networks highlighted China and the USA's pivotal roles, while influential figures and partnerships drove understanding of MANF's mechanisms. Co-word analysis of MANF-related keywords exposed key evolutionary hotspots, encompassing neurotrophic effects, cytoprotective roles, MANF-related diseases, and the CDNF/MANF family. This progression from basic understanding to clinical potential showcased MANF's versatility from cellular protection to therapy. Bibliometric analysis reveals MANF's diverse research trends and pathways, from basics to clinical applications, driving medical progress. This comprehensive assessment enriches understanding and empowers researchers for dynamic evolution, advancing innovation, and benefiting patients. Bibliometric analysis of MANF research. The graphical abstract depicts the bibliometric analysis of MANF research, highlighting its aims, methods, and key results.

Upregulation of mesencephalic astrocyte-derived neurotrophic factor (MANF) expression offers protection against alcohol neurotoxicity

Alcohol exposure has detrimental effects on both the developing and mature brain. Endoplasmic reticulum (ER) stress is one of the mechanisms that contributes to alcohol-induced neuronal damages. Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an ER stress-responsive protein and is neuroprotective in multiple neuronal injury and neurodegenerative disease models. MANF deficiency has been shown to exacerbate alcohol-induced ER stress and neurodegeneration. However, it is unknown whether MANF supplement is sufficient to protect against alcohol neurotoxicity. Alcohol alters MANF expression in the brain, but the mechanisms underlying alcohol modulation of MANF expression remain unclear. This study was designed to determine how alcohol alters MANF expression in neuronal cells and whether exogeneous MANF can alleviate alcohol neurotoxicity. We showed that alcohol increased MANF transcription and secretion without affecting MANF mRNA stability and protein degradation. ER stress was necessary for alcohol-induced MANF upregulation, as pharmacological inhibition of ER stress by 4-PBA diminished alcohol-induced MANF expression. In addition, the presence of ER stress response element II (ERSE-II) was required for alcohol-stimulated MANF transcription. Mutations or deletion of this sequence abolished alcohol-regulated transcriptional activity. We generated MANF knockout (KO) neuronal cells using CRISPR/Cas9. MANF KO cells exhibited increased unfolded protein response (UPR) and were more susceptible to alcohol-induced cell death. On the other hand, MANF upregulation by the addition of recombinant MANF protein or adenovirus gene transduction protected neuronal cells against alcohol-induced cell death. Further studies using early postnatal mouse pups demonstrated that enhanced MANF expression in the brain by intracerebroventricular (ICV) injection of MANF adeno-associated viruses ameliorated alcohol-induced cell death. Thus, alcohol increased MANF expression through inducing ER stress, which could be a protective response. Exogenous MANF was able to protect against alcohol-induced neurodegeneration.

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.

Mesencephalic Astrocyte-Derived Neurotrophic Factor (MANF): An Emerging Therapeutic Target for Neurodegenerative Disorders

Mesencephalic astrocyte-derived neurotrophic factor (MANF) is a member of the new family of neurotrophic factors (NTFs) with a unique structure and functions compared to other conventionally known NTFs. MANF is broadly expressed in developing and mature tissues, including the central nervous system and peripheral nervous system tissues. Growing research demonstrated that MANF protects neurons from endoplasmic reticulum (ER) stress-associated complications by restoring ER homeostasis and regulating unfolded protein response. This review discusses MANF signaling in neurodegenerative conditions with specific emphasis given to its overall effect and mechanisms of action in experimental models of Parkinson’s disease, Alzheimer’s disease, and stroke. Additional perspectives on its potential unexplored roles in other neurodegenerative conditions are also given.

Manf Enhances the Pyroptosis Inhibition of Bone Marrow-derived Mesenchymal Stem Cells to Relieve Cerebral Infarction Injury

Cerebral infarction is a common disease characterized by high mortality, a narrow therapeutic window, and limited therapeutic options. Recently, cell therapy based on gene modification has brought a glimmer of hope to the treatment of cerebral infarction although the explicit underlying mechanism is beyond being well dissected. In the present study, we constructed an animal model of middle cerebral artery occlusion (MCAO), compared differentially expressed genes (DEGs) between the sham and MCAO groups by single-cell RNA sequencing (scRNA-seq) to explore the potential cell death-related pathways involved in cerebral infarction, and transfected Manf into BMSCs by lentivirus. Subsequently, we injected BMSCs (bone marrow-derived mesenchymal stem cells), Manf-modified BMSCs, or lentivirus encoding Manf into the brain. Their effects on MANF content, apoptosis, pyroptosis, infarct volume in the brain, and neurological function were evaluated after MCAO. We found that the DEGs upregulated in four major cell clusters after MCAO and were enriched with not only apoptosis, ferroptosis, and necroptosis but also with pyroptosis-related pathways. In addition, transfection of Manf into BMSCs significantly increased the expression and secretion of MANF in BMSCs; BMSCs, Manf-modified BMSCs, and Manf treatment all resulted in an increase in Manf content in the brain, a decrease in the expression of apoptosis- and pyroptosis-related molecules, a reduction in infarct volume, and an improvement in neurological function after MCAO. Moreover, Manf-modified BMSCs have the strongest therapeutic effect. Collectively, Manf-modified BMSCs ameliorate ischemic injury after cerebral infarction by repressing apoptosis- and pyroptosis-related molecules, which represents a new cell therapy strategy for cerebral infarction.

Feeding-induced hepatokines and crosstalk with multi-organ: A novel therapeutic target for Type 2 diabetes

Hyperglycemia, which can be caused by either an insulin deficit and/or insulin resistance, is the main symptom of Type 2 diabetes, a significant endocrine metabolic illness. Conventional medications, including insulin and oral antidiabetic medicines, can alleviate the signs of diabetes but cannot restore insulin release in a physiologically normal amount. The liver detects and reacts to shifts in the nutritional condition that occur under a wide variety of metabolic situations, making it an essential organ for maintaining energy homeostasis. It also performs a crucial function in glucolipid metabolism through the secretion of hepatokines. Emerging research shows that feeding induces hepatokines release, which regulates glucose and lipid metabolism. Notably, these feeding-induced hepatokines act on multiple organs to regulate glucolipotoxicity and thus influence the development of T2DM. In this review, we focus on describing how feeding-induced cross-talk between hepatokines, including Adropin, Manf, Leap2 and Pcsk9, and metabolic organs (e.g.brain, heart, pancreas, and adipose tissue) affects metabolic disorders, thus revealing a novel approach for both controlling and managing of Type 2 diabetes as a promising medication.

UPR Responsive Genes Manf and Xbp1 in Stroke

Stroke is a devastating medical condition with no treatment to hasten recovery. Its abrupt nature results in cataclysmic changes in the affected tissues. Resident cells fail to cope with the cellular stress resulting in massive cell death, which cannot be endogenously repaired. A potential strategy to improve stroke outcomes is to boost endogenous pro-survival pathways. The unfolded protein response (UPR), an evolutionarily conserved stress response, provides a promising opportunity to ameliorate the survival of stressed cells. Recent studies from us and others have pointed toward mesencephalic astrocyte-derived neurotrophic factor (MANF) being a UPR responsive gene with an active role in maintaining proteostasis. Its pro-survival effects have been demonstrated in several disease models such as diabetes, neurodegeneration, and stroke. MANF has an ER-signal peptide and an ER-retention signal; it is secreted by ER calcium depletion and exits cells upon cell death. Although its functions remain elusive, conducted experiments suggest that the endogenous MANF in the ER lumen and exogenously administered MANF protein have different mechanisms of action. Here, we will revisit recent and older bodies of literature aiming to delineate the expression profile of MANF. We will focus on its neuroprotective roles in regulating neurogenesis and inflammation upon post-stroke administration. At the same time, we will investigate commonalities and differences with another UPR responsive gene, X-box binding protein 1 (XBP1), which has recently been associated with MANF’s function. This will be the first systematic comparison of these two UPR responsive genes aiming at revealing previously uncovered associations between them. Overall, understanding the mode of action of these UPR responsive genes could provide novel approaches to promote cell survival.

Deficiency of mesencephalic astrocyte-derived neurotrophic factor affects neurogenesis in mouse brain

The mechanisms underlying the regulation of neurogenesis in the adult brain remain unclear. Mesencephalic astrocyte-derived neurotrophic factor (MANF) is a neurotrophic factor that has been implicated in various neuropathological processes and endoplasmic reticulum stress. However, the role of MANF in neurogenesis has not been investigated. Using a central nervous system (CNS)-specific Manf knock-out mouse model, we examined the role of MANF in mouse neurogenesis. We demonstrated that MANF deficiency increased BrdU labeling and Ki-67 positive cells in the subgranular zone and subventricular zone. MANF knock-out-induced upregulation of proliferative activity was accompanied by a decrease of cell cycle inhibitors (p15 and p27), an increase of G2/M marker (phospho-histone H3), as well as an increase of neural progenitor markers (Sox2 and NeuroD1) in the brain. In vitro studies using N2A neuroblastoma cells showed that the gain-of-function of MANF inhibited cell cycle progression, whereas the loss-of-function of MANF promoted cell cycle progression. Collectively, our findings indicate MANF deficiency affects cell proliferation and suggest a role of MANF in the neurogenesis of the adult brain.

Potential Role of MANF, an ER Stress Responsive Neurotrophic Factor, in Protecting Against Alcohol Neurotoxicity

Alcohol exposure during pregnancy is harmful to the fetus and causes a wide range of long-lasting physiological and neurocognitive impairments, collectively referred to as fetal alcohol spectrum disorders (FASD). The neurobehavioral deficits observed in FASD result from structural and functional damages in the brain, with neurodegeneration being the most destructive consequence. Currently, there are no therapies for FASD. It is exigent to delineate the underlying mechanisms of alcohol neurotoxicity and develop an effective strategy of treatment. ER stress, caused by the accumulation of unfolded/misfolded proteins in the ER, is the hallmark of many neurodegenerative diseases, including alcohol-induced neurodegeneration. Mesencephalic astrocyte-derived neurotrophic factor (MANF) is a newly discovered endoplasmic reticulum (ER) stress responsive neurotrophic factor that regulates diverse neuronal functions. This review summarizes the recent findings revealing the effects of MANF on the CNS and its protective role against neurodegeneration. Particularly, we focus the role of MANF on alcohol-induced ER stress and neurodegeneration and discuss the therapeutic potential of MANF in treating alcohol neurotoxicity such as FASD.

MANF: A Novel Endoplasmic Reticulum Stress Response Protein-The Role in Neurological and Metabolic Disorders

The mesencephalic astrocyte-derived neurotrophic factor (MANF), also named as arginine-rich protein (ARP) or arginine-rich mutated in early-stage tumors (ARMET), is a novel evolutionary conserved protein related to unfolded protein response. Growing evidence suggests that MANF critically involves in many ER stress-related diseases with a protective effect. Here, we review the function of MANF based on its structure in neurological and metabolic disorders and summarize its potential applications in disease diagnosis and therapies.

Increased MANF Expression in the Inferior Temporal Gyrus in Patients With Alzheimer Disease

Alzheimer disease (AD) is an aging-related disorder linked to endoplasmic reticulum (ER) stress. The main pathologic feature of AD is the presence of extracellular senile plaques and intraneuronal neurofibrillary tangles (NFTs) in the brain. In neurodegenerative diseases, the unfolded protein response (UPR) induced by ER stress ensures cell survival. Mesencephalic astrocyte-derived neurotrophic factor (MANF) protects against ER stress and has been implicated in the pathogenesis of AD. MANF is expressed in neurons of the brain and spinal cord. However, there have been no investigations on MANF expression in the brain of AD patients. This was addressed in the present study by immunohistochemistry, western blotting, and quantitative analyses of postmortem brain specimens. We examined the localization and expression levels of MANF in the inferior temporal gyrus of the cortex (ITGC) in AD patients (n = 5), preclinical (pre-)AD patients (n = 5), and age-matched non-dementia controls (n = 5) by double immunofluorescence labeling with antibodies against the neuron-specific nuclear protein neuronal nuclei (NeuN), ER chaperone protein 78-kDa glucose-regulated protein (GRP78), and MANF. The results showed that MANF was mainly expressed in neurons of the ITGC in all 3 groups; However, the number of MANF-positive neurons was significantly higher in pre-AD (Braak stage III/IV) and AD (Braak stage V/VI) patients than that in the control group. Thus, MANF is overexpressed in AD and pre-AD, suggesting that it can serve as a diagnostic marker for early stage disease.

MANF is neuroprotective against ethanol-induced neurodegeneration through ameliorating ER stress

Fetal alcohol spectrum disorders (FASD) are a spectrum of developmental disorders caused by prenatal alcohol exposure. Neuronal loss or neurodegeneration in the central nervous system (CNS) is one of the most devastating features in FASD. It is imperative to delineate the underlying mechanisms to facilitate the treatment of FASD. Endoplasmic reticulum (ER) stress is a hallmark and an underlying mechanism of many neurodegenerative diseases, including ethanol-induced neurodegeneration. Mesencephalic astrocyte-derived neurotrophic factor (MANF) responds to ER stress and has been identified as a protein upregulated in response to ethanol exposure during the brain development. To investigate the role of MANF in ethanol-induced neurodegeneration and its association with ER stress regulation, we established a CNS-specific Manf knockout mouse model and examined the effects of MANF deficiency on ethanol-induced neuronal apoptosis and ER stress using a third-trimester equivalent mouse model. We found MANF deficiency exacerbated ethanol-induced neuronal apoptosis and ER stress and that blocking ER stress abrogated the harmful effects of MANF deficiency on ethanol-induced neuronal apoptosis. Moreover, using an animal model of ER-stress-induced neurodegeneration, we demonstrated that MANF deficiency potentiated tunicamycin (TM)-induced ER stress and neurodegeneration. A whole transcriptome RNA sequencing also supported the functionality of MANF in ER stress modulation and revealed targets that may mediate the ER stress-buffering capacity of MANF. Collectively, these results suggest that MANF is a neurotrophic factor that can protect neurons against ethanol-induced neurodegeneration by ameliorating ER stress.

Mesencephalic Astrocyte-Derived Neurotrophic Factor (MANF) Regulates Neurite Outgrowth Through the Activation of Akt/mTOR and Erk/mTOR Signaling Pathways

Neurite outgrowth is essential for brain development and the recovery of brain injury and neurodegenerative diseases. In this study, we examined the role of the neurotrophic factor MANF in regulating neurite outgrowth. We generated MANF knockout (KO) neuro2a (N2a) cell lines using clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 and demonstrated that MANF KO N2a cells failed to grow neurites in response to RA stimulation. Using MANF siRNA, this finding was confirmed in human SH-SY5Y neuronal cell line. Nevertheless, MANF overexpression by adenovirus transduction or addition of MANF into culture media facilitated the growth of longer neurites in RA-treated N2a cells. MANF deficiency resulted in inhibition of Akt, Erk, mTOR, and P70S6, and impaired protein synthesis. MANF overexpression on the other hand facilitated the growth of longer neurites by activating Akt, Erk, mTOR, and P70S6. Pharmacological blockade of Akt, Erk or mTOR eliminated the promoting effect of MANF on neurite outgrowth. These findings suggest that MANF positively regulated neurite outgrowth by activating Akt/mTOR and Erk/mTOR signaling pathways.

Cerebral dopamine neurotrophic factor-deficiency leads to degeneration of enteric neurons and altered brain dopamine neuronal function in mice

Cerebral dopamine neurotrophic factor (CDNF) is neuroprotective for nigrostriatal dopamine neurons and restores dopaminergic function in animal models of Parkinson’s disease (PD). To understand the role of CDNF in mammals, we generated CDNF knockout mice (Cdnf^−/−), which are viable, fertile, and have a normal life-span. Surprisingly, an age-dependent loss of enteric neurons occurs selectively in the submucosal but not in the myenteric plexus. This neuronal loss is a consequence not of increased apoptosis but of neurodegeneration and autophagy. Quantitatively, the neurodegeneration and autophagy found in the submucosal plexus in duodenum, ileum and colon of the Cdnf^−/− mouse are much greater than in those of Cdnf^+/+ mice. The selective vulnerability of submucosal neurons to the absence of CDNF is reminiscent of the tendency of pathological abnormalities to occur in the submucosal plexus in biopsies of patients with PD. In contrast, the number of substantia nigra dopamine neurons and dopamine and its metabolite concentrations in the striatum are unaltered in Cdnf^−/− mice; however, there is an age-dependent deficit in the function of the dopamine system in Cdnf^−/− male mice analyzed. This is observed as D-amphetamine-induced hyperactivity, aberrant dopamine transporter function, and as increased D-amphetamine-induced dopamine release demonstrating that dopaminergic axon terminal function in the striatum of the Cdnf^−/− mouse brain is altered. The deficiencies of Cdnf^−/− mice, therefore, are reminiscent of those seen in early stages of Parkinson’s disease.

Increased Serum Levels of Mesencephalic Astrocyte-Derived Neurotrophic Factor in Subjects With Parkinson's Disease

Background

Mesencephalic astrocyte-derived neurotrophic factor (MANF) and cerebral dopamine neurotrophic factor (CDNF) promote the survival of midbrain dopamine neurons in animal models of Parkinson’s disease (PD). However, little is known about endogenous concentrations of MANF and CDNF in human PD patients, and their relation to PD pathogenesis. Our main objective was to study whether circulating concentrations of MANF and CDNF differ between PD patients and controls, and if they correlate with clinical parameters. Levels of circulating CDNF were studied for the first time.

Methods

MANF and CDNF levels were measured from serum samples of 34 PD patients and 35 controls using validated in-lab-designed enzyme-linked immunosorbent assay (ELISAs). MANF and CDNF mRNA levels in whole blood samples of 60 PD patients and 30 controls were measured by quantitative real time polymerase chain reaction (qRT-PCR). MANF concentrations in different blood cell types were measured by ELISA.

Results

Circulating MANF concentrations were significantly higher in PD patients compared to controls (P < 0.001) and were positively correlated with Beck Depression Inventory (BDI) depression rating. MANF protein was present in blood cells, however, MANF mRNA levels in the blood did not differ between PD patients and controls (P = 0.44). The mean concentration of serum CDNF was 33 pg/ml in the controls. CDNF levels were not altered in PD patients (P = 0.25).

Conclusion

MANF but not CDNF level was increased in the blood of PD patients. It would be interesting to examine the blood level of MANF from early stage PD patients in future studies to test whether MANF can be used as a clinical marker of PD.

Mesencephalic Astrocyte-Derived Neurotrophic Factor (MANF) Is Highly Expressed in Mouse Tissues With Metabolic Function

Mesencephalic astrocyte-derived neurotrophic factor (MANF) and cerebral dopamine neurotrophic factor (CDNF) form a family of atypical growth factors discovered for their neuroprotective properties in the central nervous system (CNS) in animal models of neurodegenerative diseases. Although their mechanism of protective action still remains unclear, it has been suggested that both MANF and CDNF promote cell survival through regulating the unfolded protein response (UPR), thereby relieving endoplasmic reticulum (ER) stress. Recent studies identified MANF for its emerging roles in metabolic function, inflammation and pancreatic β-cells. We have found that MANF deletion from the pancreas and β-cells leads to postnatal depletion of β-cells and diabetes. Moreover, global MANF-deficiency in mice results in severe diabetes-independent growth retardation. As the expression pattern of MANF in mouse tissues has not been extensively studied, we set out to thoroughly investigate MANF expression in embryonic and adult mice using immunohistochemistry, histochemical X-gal staining, enzyme-linked immunosorbent assay (ELISA), and quantitative reverse transcription PCR (RT-qPCR). We found that MANF is highly expressed in brain neurons regulating energy homeostasis and appetite, as well as in hypothalamic nuclei producing hormones and neuropeptides important for different body functions. Strong expression of MANF was also observed in peripheral mouse tissues and cells with high secretory and metabolic function. These include pituitary gland and interestingly we found that the anterior pituitary gland is smaller in MANF-deficient mice compared to wild-type mice. Consequently, we found reduction in the number of growth hormone- and prolactin-producing cells. This combined with increased expression of UPR genes, reduced number of proliferating cells in the anterior pituitary and dysregulated expression of pituitary hormones might contribute to the severe growth defect seen in the MANF knockout mice. Moreover, in this study we compared MANF and CDNF levels in mouse tissues. Unlike MANF, CDNF protein levels are generally lower in mouse tissues, and the highest levels of CDNF was observed in the tissues with high-energy demands and oxidative roles, including heart, muscle, testis, and brown adipose tissue.

MANF: A New Player in the Control of Energy Homeostasis, and Beyond

All human behaviors, including the control of energy homeostasis, are ultimately mediated by neuronal activities in the brain. Neurotrophic factors represent a protein family that plays important roles in regulating neuronal development, function, and survival. It has been well established that canonical neurotrophic factors, such as brain-derived neurotrophic factor (BDNF) and ciliary neurotrophic factor (CNTF), play important roles in the central regulation of energy homeostasis. Recently, a class of non-canonical neurotrophic factors, represented by mesencephalic astrocyte-derived neurotrophic factor (MANF), has been discovered. MANF is structurally and functionally distinct from those canonical neurotrophic factors, hence raising the issue of MANF being non-canonical. Nonetheless, emerging evidence suggests that MANF is critically involved in many neuronal activities. Here, we review our current understanding about the functions of MANF in the brain, with a primary focus on the control of energy homeostasis.

Activator protein‑1 is a novel regulator of mesencephalic astrocyte‑derived neurotrophic factor transcription

Mesencephalic astrocyte‑derived neurotrophic factor (MANF) is an endoplasmic reticulum stress‑inducible protein, which has been suggested to be upregulated in inflammatory diseases; however, how inflammation regulates its transcription remains unclear. Activator protein‑1 (AP‑1), which is a transcription factor complex composed of c‑Fos and c‑Jun, is activated during the inflammatory process. The present study aimed to investigate whether the AP‑1 complex regulates MANF transcription. The results of a luciferase reporter assay revealed that one of three putative AP‑1 binding sites in the MANF promoter region is essential for enhancement of MANF transcription. Mechanistically, AP‑1 was revealed to directly bind to the promoter region of the MANF gene by chromatin immunoprecipitation assay. Furthermore, MANF was strongly expressed in the liver tissues of patients with hepatitis B virus (HBV) infection, compared with in normal liver tissues from patients with hepatic hemangioma. Furthermore, c‑Fos and c‑Jun were also upregulated in the nuclei of hepatocytes from patients with HBV infection. In mice treated with carbon tetrachloride, the expression patterns of MANF, c‑Fos and c‑Jun were similar to those in patients with HBV. These results suggested that the AP‑1 complex may be a novel regulator of MANF transcription, which may be involved in liver inflammation and fibrosis.

Emerging Roles for Mesencephalic Astrocyte-Derived Neurotrophic Factor (MANF) in Pancreatic Beta Cells and Diabetes

Mesencephalic astrocyte-derived neurotrophic factor (MANF) was originally identified as a secreted trophic factor for dopamine neurons in vitro. It protects and restores damaged cells in rodent models of Parkinson's disease, brain and heart ischemia, spinocerebellar ataxia and retina in vivo. However, its exact mechanism of action is not known. MANF is widely expressed in most human and mouse organs with high levels in secretory tissues. Intracellularly, MANF localizes to the endoplasmic reticulum (ER) and ER stress increases it's expression in cells and tissues. Furthermore, increased MANF levels has been detected in the sera of young children with newly diagnosed Type 1 (T1D) diabetes and Type 2 (T2D) diabetic patients. ER stress is caused by the accumulation of misfolded and aggregated proteins in the ER. It activates a cellular defense mechanism, the unfolded protein response (UPR), a signaling cascade trying to restore ER homeostasis. However, if prolonged, unresolved ER stress leads to apoptosis. Unresolved ER stress contributes to the progressive death of pancreatic insulin-producing beta cells in both T1D and T2D. Diabetes mellitus is characterized by hyperglycemia, caused by the inability of the beta cells to maintain sufficient levels of circulating insulin. The current medications, insulin and antidiabetic drugs, alleviate diabetic symptoms but cannot reconstitute physiological insulin secretion which increases the risk of devastating vascular complications of the disease. Thus, one of the main strategies in improving current diabetes therapy is to define and validate novel approaches to protect beta cells from stress as well as activate their regeneration. Embryonic deletion of the Manf gene in mice led to gradual postnatal development of insulin-deficient diabetes caused by reduced beta cell proliferation and increased beta cell death due to increased and sustained ER stress. In vitro, recombinant MANF partly protected mouse and human beta cells from ER stress-induced beta cell death and potentiated mouse and human beta cell proliferation. Importantly, in vivo overexpression of MANF in the pancreas of T1D mice led to increased beta cell proliferation and decreased beta cell death, suggesting that MANF could be a new therapeutic candidate for beta cell protection and regeneration in diabetes.

Mesencephalic astrocyte-derived neurotrophic factor affords neuroprotection to early brain injury induced by subarachnoid hemorrhage via activating Akt-dependent prosurvival pathway and defending blood-brain barrier integrity

This study aimed to explore the neuroprotective effect of mesencephalic astrocyte-derived neurotrophic factor (MANF) protein on early brain injury caused by subarachnoid hemorrhage (SAH) and the relevant mechanisms in experimental rats, expecting to understand whether MANF was a potential therapeutic target for SAH treatment. A perforation model of SAH was introduced into the study. Recombinant human MANF (rh-MANF) and protein kinase B (Akt) inhibitor (MK2206) were used to explore the effect and the mechanisms. Multiple approaches for systemic assessment were employed in the research, including the Garcia test, the SAH grade, Evans blue (EB) dye leakage, brain-water content (BWC), the rotarod test, and the Morris water-navigation task, as were biotechniques, such as immunohistochemistry, Western blot, transmission electron microscopy, and flow cytometry. MANF was mainly expressed in rat neurons, and its expression increased significantly at 3 h after SAH induction and peaked at 24 h. Stereotactic injection of rh-MANF into the cerebroventricle significantly increased the level of MANF, p-Akt, p-mouse double minute 2 homolog (p-MDM2), and B-cell lymphoma 2 (Bcl-2) in brain tissue, whereas it down-regulated the expression of P53, Bcl-2-associated X protein (Bax), and cleaved caspase-3, which indicated that neuronal apoptosis was remarkably suppressed. Expression of matrix metallopeptidase 9 (MMP-9) was also suppressed by the rh-MANF injection. Furthermore, neurologic deficits, EB dye leakage, and BWC were reduced, and long-lasting neuroprotection was noted with rh-MANF administration. The antiapoptotic and blood-brain barrier (BBB) protective effect could be offset by administering MK2206. MANF could alleviate neuronal apoptosis by activating Akt-dependent prosurvival pathway and abate BBB damage via MMP-9 suppression. MANF showed not only transient but also long-lasting neuroprotective properties. The rh-MANF as a potential drug for treating SAH might be of clinical use.-Li, T., Xu, W., Gao, L., Guan, G., Zhang, Z., He, P., Xu, H., Fan, L., Yan, F., Chen, G. Mesencephalic astrocyte-derived neurotrophic factor affords neuroprotection to early brain injury induced by subarachnoid hemorrhage via activating Akt-dependent prosurvival pathway and defending blood-brain barrier integrity.

MANF attenuates neuronal apoptosis and promotes behavioral recovery via Akt/MDM-2/p53 pathway after traumatic spinal cord injury in rats

The aim of this study was to investigate the potential effect and mechanism of action of MANF in attenuating neuronal apoptosis following t-SCI. A clip compressive model was used to induce a crush injury of the spinal cord in a total of 230 rats. The Basso, Beattie, and Bresnahan (BBB) score, spinal cord water content, and blood spinal cord barrier (BSCB) permeability were evaluated. The expression levels of MANF and its downstream proteins were examined by western blotting. Immunofluorescence staining of MANF, NeuN, GFAP, Iba-1, cleaved caspase-3, and TUNEL staining were also performed. Cells were counted in six randomly selected fields in the gray matter regions of the sections from two spinal cord sites (2 mm rostral and caudal to the epicenter of the injury) per sample. A cell-based mechanical injury model was also conducted using SH-SY5Y cells. Cell apoptosis and viability were assessed by flow cytometry, an MTT assay, and trypan blue staining. Subcellular structures were observed by transmission electron microscopy. MANF was mainly expressed in neurons. The expression levels of MANF, and its downstream target, p-Akt, were gradually increased and after t-SCI. Treatment with MANF increased Bcl-2 and decreased Bax and CC-3 levels; these effects were reversed on treatment with MK2206. The BBB score, spinal cord water content, and BSCB destruction were also ameliorated by MANF treatment. MANF decreases neuronal apoptosis and improves neurological function through Akt/MDM-2/p53 pathway after t-SCI. Therefore, MANF might be a potential treatment for patients with t-SCI.© 2018 BioFactors, 2018.

Photoreceptor Protection by Mesencephalic Astrocyte-Derived Neurotrophic Factor (MANF)

Retinal degenerations are a major cause of vision impairment and blindness. Neuroprotective therapy is a promising therapeutic strategy for retinal degenerative diseases. We investigated a novel neurotrophic factor mesencephalic astrocyte-derived neurotrophic factor (MANF) in the retina. MANF is expressed at a high level during postnatal development and the expression declines to a lower level as the retina matures. Müller cells are the major cells expressing MANF. It is also found in the retinal ganglion cells, in the inner nuclear layer (INL) neurons, and in retinal pigment epithelial (RPE) cells. Intravitreal injection of recombinant human (rh)MANF significantly protected rod and cone photoreceptors in rats carrying the rhodopsin S334ter mutation, and preserved electroretinograms (ERGs) in the rd10 (Pde6b^rd10/rd10 ) mice. These results indicate that MANF is a native protein in the retina and is a potent neurotrophic factor for photoreceptor protection.

MANF Is Essential for Neurite Extension and Neuronal Migration in the Developing Cortex

Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an endoplasmic reticulum (ER) resident protein with neuroprotective effects. Previous studies have shown that MANF expression is altered in the developing rodent cortex in a spatiotemporal manner. However, the role of MANF in mammalian neurogenesis is not known. The aim of this study was to determine the role of MANF in neural stem cell (NSC) proliferation, differentiation, and cerebral cortex development. We found that MANF is highly expressed in neural lineage cells, including NSCs in the developing brain. We discovered that MANF-deficient NSCs in culture are viable and show no defect in proliferation. However, MANF-deficient cells have deficits in neurite extension upon neuronal differentiation. In vivo, MANF removal leads to slower neuronal migration and impaired neurite outgrowth. In vitro, mechanistic studies indicate that impaired neurite growth is preceded by reduced de novo protein synthesis and constitutively activated unfolded protein response (UPR) pathways. This study is the first to demonstrate that MANF is a novel and critical regulator of neurite growth and neuronal migration in mammalian cortical development.

MANF regulates hypothalamic control of food intake and body weight

The hypothalamus has a vital role in controlling food intake and energy homeostasis; its activity is modulated by neuropeptides and endocrine factors. Mesencephalic astrocyte-derived neurotrophic factor (MANF) is a neurotrophic factor that is also localized in the endoplasmic reticulum (ER) in neurons. Here we show that MANF is highly enriched in distinct nuclei of the mouse hypothalamus, and that MANF expression in the hypothalamus is upregulated in response to fasting. Increasing or decreasing hypothalamic MANF protein levels causes hyperphagia or hypophagia, respectively. Moreover, MANF triggers hypothalamic insulin resistance by enhancing the ER localization and activity of PIP4k2b, a kinase known to regulate insulin signaling. Our findings indicate that MANF influences food intake and body weight by modulating hypothalamic insulin signaling.MANF is a neurotrophic factor that is secreted but also mediates the unfolded protein response acting intracellularly. Here, the authors show that MANF expression in the brain is influenced by nutritional cues, and hypothalamic MANF influences food intake and systemic energy homeostasis.

Cerebral Dopamine Neurotrophic Factor: A Potential Therapeutic Agent for Parkinson's Disease

The application of neurotrophic factors (NTFs) is a promising therapeutic strategy for neurodegenerative disorders such as Parkinson's disease (PD). Many NTFs have been reported to enhance the survival, regeneration, and differentiation of neurons and to induce synaptic plasticity. However, because of their potential side-effects and low efficacy after clinical administration, more potent treatments for neurodegenerative disorders are being sought. Cerebral dopamine neurotrophic factor (CDNF), a newly-identified NTF homologous to mesencephalic astrocyte-derived NTF, is structurally and functionally different from other NTFs, providing new hope especially for PD patients. In various animal models of PD, CDNF is efficient in protecting and repairing dopaminergic neurons, and it inhibits endoplasmic reticulum stress, neuroinflammation, and apoptosis. Recent progress in all facets of CDNF research has enabled researchers to better understand its beneficial effects in the treatment of PD.

Neurotrophic factors in Alzheimer's and Parkinson's diseases: implications for pathogenesis and therapy

Neurotrophic factors comprise essential secreted proteins that have several functions in neural and non-neural tissues, mediating the development, survival and maintenance of peripheral and central nervous system. Therefore, neurotrophic factor issue has been extensively investigated into the context of neurodegenerative diseases. Alzheimer's disease and Parkinson's disease show changes in the regulation of specific neurotrophic factors and their receptors, which appear to be critical for neuronal degeneration. Indeed, neurotrophic factors prevent cell death in degenerative processes and can enhance the growth and function of affected neurons in these disorders. Based on recent reports, this review discusses the main findings related to the neurotrophic factor support – mainly brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor – in the survival, proliferation and maturation of affected neurons in Alzheimer's disease and Parkinson's disease as well as their putative application as new therapeutic approach for these diseases management.

Mesencephalic astrocyte-derived neurotrophic factor attenuates inflammatory responses in lipopolysaccharide-induced neural stem cells by regulating NF-κB and phosphorylation of p38-MAPKs pathways

Mesencephalic astrocyte-derived neurotrophic factor (MANF), a new evolutionary conserved neurotrophic factor (NTF), has been reported to protect midbrain dopaminergic neurons of neurodegenerative diseases such as Parkinson's disease (PD) model. Neural stem cells (NSCs) can play a role as the therapeutic tool in neurodegenerative diseases, but the inflammatory responses of central nervous system (CNS) appear to harm this function. Although studies have previously demonstrated the protective effect of MANF on neurons of CNS, it is lacking in making great efforts on the function of MANF on NSCs. The aim of this study was to investigate the antiinflammatory responses and signaling mechanisms of MANF on lipopolysaccharide (LPS)-induced NSCs. In the results, MANF decreased the proinflammatory cytokines of IL-1β, TNF-α, and IFN-γ induced by LPS by regulating NF-κB and phosphorylation of p38-mitogen-activated protein kinases (MAPKs) pathways, neither p-JNK nor p-ERK signaling. These findings suggest that MANF can facilitate to protect the inflammatory responses of NSCs, and provide beneficial function for the application of NSCs in the therapy.

Therapeutic potential of the endoplasmic reticulum located and secreted CDNF/MANF family of neurotrophic factors in Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder where dopamine (DA) neurons in the substantia nigra degenerate and die. Since no cure for PD exists, there is a need for disease-modifying drugs. Glial cell line-derived neurotrophic factor (GDNF) and related neurturin (NRTN) can protect and repair DA neurons in neurotoxin animal models of PD. However, GDNF was unable to rescue DA neurons in an α-synuclein model of PD, and both factors have shown modest effects in phase two clinical trials. Neurotrophic factors (NTFs), cerebral DA NTF (CDNF) and mesencephalic astrocyte-derived NTF (MANF) form a novel family of evolutionarily conserved, endoplasmic reticulum (ER) located and secreted NTFs. CDNF and MANF have a unique structure and an unparalleled dual mode of action that differs from other known NTFs. Both protect cells from ER stress, and regulate the unfolded protein response via interacting with chaperons, and CDNF dissolves intracellular α-synuclein aggregates. By binding to putative plasma membrane receptors, they promote the survival of DA neurons similarly to conventional NTFs. In animal models of PD, CDNF protects and repairs DA neurons, regulates ER stress, and improves motor function more efficiently than other NTFs.

Analysis of the conserved neurotrophic factor MANF in the Drosophila adult brain

Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an evolutionarily conserved neurotrophic factor that supports and protects dopaminergic neurons. The Drosophila MANF (DmMANF) null mutant animals die during early development, and DmMANF is required for the maintenance of dopamine positive neurites. The aim of this study was to investigate the role of DmMANF during later developmental stages. Here we report that DmMANF expression in the adult brain is much wider than in the embryonic and larval stages. It is expressed in both glia and neurons including dopaminergic neurons. Clonal analysis showed that DmMANF is not required cell-autonomously for the differentiation of either glia or dopaminergic neurons. In addition, DmMANF overexpression resulted in no apparent abnormal dopaminergic phenotype while DmMANF silencing in glia resulted in prolonged larval stage.

Mesencephalic astrocyte-derived neurotrophic factor and cerebral dopamine neurotrophic factor: New endoplasmic reticulum stress response proteins

Mesencephalic astrocyte-derived neurotrophic factor (MANF) and cerebral dopamine neurotrophic factor (CDNF) are a novel evolutionary conserved neurotrophic factor (NTF) family. There are two distinct domains in MANF and CDNF 3-dimentional structure, N-terminal saposin-like domain and C-terminal SAP-domain, which suggest their unique mode of action. Although identified for their neurotrophic activity, recent studies have shown MANF and CDNF can protect cells during endoplasmic reticulum (ER) stress. This review summarizes the unique structure and related potential protective role for cells during ER stress of MANF and CDNF.