Overexpression of conserved dopamine neurotrophic factor (CDNF) in astrocytes alleviates endoplasmic reticulum stress-induced cell damage and inflammatory cytokine secretion

Delivery of CDNF by AAV-mediated gene transfer protects dopamine neurons and regulates ER stress and inflammation in an acute MPTP mouse model of Parkinson's disease

Cerebral dopamine neurotrophic factor (CDNF) and its close structural relative, mesencephalic astrocyte-derived neurotrophic factor (MANF), are proteins with neurotrophic properties. CDNF protects and restores the function of dopamine (DA) neurons in rodent and non-human primate (NHP) toxin models of Parkinson's disease (PD) and therefore shows promise as a drug candidate for disease-modifying treatment of PD. Moreover, CDNF was found to be safe and to have some therapeutic effects on PD patients in phase 1/2 clinical trials. However, the mechanism underlying the neurotrophic activity of CDNF is unknown. In this study, we delivered human CDNF (hCDNF) to the brain using an adeno-associated viral (AAV) vector and demonstrated the neurotrophic effect of AAV-hCDNF in an acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. AAV-hCDNF resulted in the expression of hCDNF in the striatum (STR) and substantia nigra (SN), and no toxic effects on the nigrostriatal pathway were observed. Intrastriatal injection of AAV-hCDNF reduced motor impairment and partially alleviated gait dysfunction in the acute MPTP mouse model. In addition, gene therapy with AAV-hCDNF had significant neuroprotective effects on the nigrostriatal pathway and decreased the levels of interleukin 1beta (IL-1β) and complement 3 (C3) in glial cells in the acute MPTP mouse model. Moreover, AAV-hCDNF reduced C/EBP homologous protein (CHOP) and glucose regulatory protein 78 (GRP78) expression in astroglia. These results suggest that the neuroprotective effects of CDNF may be mediated at least in part through the regulation of neuroinflammation and the UPR pathway in a mouse MPTP model of PD in vivo.

Adult aberrant astrocytes submitted to late passage cultivation lost differentiation markers and decreased their pro-inflammatory profile

In amyotrophic lateral sclerosis (ALS), astrocytes are considered key players in some non-cell non-neuronal autonomous mechanisms that underlie motor neuron death. However, it is unknown how much of these deleterious features were permanently acquired. To assess this point, we evaluated if the most remarkable features of neurotoxic aberrant glial phenotypes (AbAs) isolated from paralytic rats of the ALS model G93A Cu/Zn superoxide dismutase 1 (SOD1) could remain upon long lasting cultivation. Real time PCR, immunolabelling and zymography analysis showed that upon many passages, AbAs preserved the cell proliferation capacity, mitochondrial function and response to different compounds that inhibit some key astrocyte functions but decreased the expression of parameters associated to cell lineage, homeostasis and inflammation. As these results are contrary to the sustained inflammatory status observed along disease progression in SOD1G93A rats, we propose that the most AbAs remarkable features related to homeostasis and neurotoxicity were not permanently acquired and might depend on the signaling coming from the injuring microenvironment present in the degenerating spinal cord of terminal rats.

HER-096 is a CDNF-derived brain-penetrating peptidomimetic that protects dopaminergic neurons in a mouse synucleinopathy model of Parkinson's disease

Cerebral dopamine neurotrophic factor (CDNF) is an unconventional neurotropic factor that modulates unfolded protein response (UPR) pathway signaling and alleviates endoplasmic reticulum (ER) stress providing cytoprotective effects in different models of neurodegenerative disorders. Here, we developed a brain-penetrating peptidomimetic compound based on human CDNF. This compound called HER-096 shows similar potency and mechanism of action as CDNF, and promotes dopamine neuron survival, reduces α-synuclein aggregation and modulates UPR signaling in in vitro models. HER-096 is metabolically stable and able to penetrate to cerebrospinal (CSF) and brain interstitial fluids (ISF) after subcutaneous administration, with an extended CSF and brain ISF half-life compared to plasma. Subcutaneously administered HER-096 modulated UPR pathway activity, protected dopamine neurons, and reduced α-synuclein aggregates and neuroinflammation in substantia nigra of aged mice with synucleinopathy. Peptidomimetic HER-096 is a candidate for development of a disease-modifying therapy for Parkinson's disease with a patient-friendly route of administration.

Inhibition of Protein Aggregation and Endoplasmic Reticulum Stress as a Targeted Therapy for α-Synucleinopathy

α-synuclein (α-syn) is an intrinsically disordered protein abundant in the central nervous system. Physiologically, the protein regulates vesicle trafficking and neurotransmitter release in the presynaptic terminals. Pathologies related to misfolding and aggregation of α-syn are referred to as α-synucleinopathies, and they constitute a frequent cause of neurodegeneration. The most common α-synucleinopathy, Parkinson's disease (PD), is caused by abnormal accumulation of α-syn in the dopaminergic neurons of the midbrain. This results in protein overload, activation of endoplasmic reticulum (ER) stress, and, ultimately, neural cell apoptosis and neurodegeneration. To date, the available treatment options for PD are only symptomatic and rely on dopamine replacement therapy or palliative surgery. As the prevalence of PD has skyrocketed in recent years, there is a pending issue for development of new disease-modifying strategies. These include anti-aggregative agents that target α-syn directly (gene therapy, small molecules and immunization), indirectly (modulators of ER stress, oxidative stress and clearance pathways) or combine both actions (natural compounds). Herein, we provide an overview on the characteristic features of the structure and pathogenic mechanisms of α-syn that could be targeted with novel molecular-based therapies.

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.

The Unconventional Growth Factors Cerebral Dopamine Neurotrophic Factor and Mesencephalic Astrocyte-Derived Neurotrophic Factor Promote Post-ischemic Neurological Recovery, Perilesional Brain Remodeling, and Lesion-Remote Axonal Plasticity

Considerable efforts are currently made to develop strategies that boost endogenous recovery once a stroke has occurred. Owing to their restorative properties, neurotrophic factors are attractive candidates that capitalize on endogenous response mechanisms. Non-conventional growth factors cerebral dopamine neurotrophic factor (CDNF) and mesencephalic astrocyte-derived neurotrophic factor (MANF) promote neuronal survival and reduce neurological deficits in the acute phase of ischemic stroke in mice. Their effects on endogenous repair and recovery mechanisms in the stroke recovery phase were so far unknown. By intracerebroventricular delivery of CDNF or MANF starting 3 days post-stroke (1 µg/day for 28 days via miniosmotic pumps), we show that delayed CDNF and MANF administration promoted functional neurological recovery assessed by a battery of behavioral tests, increased long-term neuronal survival, reduced delayed brain atrophy, glial scar formation, and, in case of CDNF but not MANF, increased endogenous neurogenesis in the perilesional brain tissue. Besides, CDNF and MANF administration increased long-distance outgrowth of terminal axons emanating from the contralesional pyramidal tract, which crossed the midline to innervate ipsilesional facial nucleus. This plasticity promoting effect was accompanied by downregulation of the axonal growth inhibitor versican and the guidance molecules ephrin B1 and B2 in the previously ischemic hemisphere at 14 dpi, which represents a sensitive time-point for axonal growth. CDNF and MANF reduced the expression of the proinflammatory cytokines IL1β and TNFα in both hemispheres. The effects of non-conventional growth factors in the ischemic brain should further be examined since they might help to identify targets for restorative stroke therapy.

Glia-Neurotrophic Factor Relationships: Possible Role in Pathobiology of Neuroinflammation-Related Brain Disorders

Neurotrophic factors (NTFs) play an important role in maintaining homeostasis of the central nervous system (CNS) by regulating the survival, differentiation, maturation, and development of neurons and by participating in the regeneration of damaged tissues. Disturbances in the level and functioning of NTFs can lead to many diseases of the nervous system, including degenerative diseases, mental diseases, and neurodevelopmental disorders. Each CNS disease is characterized by a unique pathomechanism, however, the involvement of certain processes in its etiology is common, such as neuroinflammation, dysregulation of NTFs levels, or mitochondrial dysfunction. It has been shown that NTFs can control the activation of glial cells by directing them toward a neuroprotective and anti-inflammatory phenotype and activating signaling pathways responsible for neuronal survival. In this review, our goal is to outline the current state of knowledge about the processes affected by NTFs, the crosstalk between NTFs, mitochondria, and the nervous and immune systems, leading to the inhibition of neuroinflammation and oxidative stress, and thus the inhibition of the development and progression of CNS disorders.

Protective mechanisms by glial cell line-derived neurotrophic factor and cerebral dopamine neurotrophic factor against the α-synuclein accumulation in Parkinson's disease

Synucleinopathies constitute a disease family named after alpha-synuclein protein, which is a significant component of the intracellular inclusions called Lewy bodies. Accompanying the progressive neurodegeneration, Lewy bodies and neurites are the main histopathologies of synucleinopathies. The complicated role of alpha-synuclein in the disease pathology makes it an attractive therapeutic target for disease-modifying treatments. GDNF is one of the most potent neurotrophic factors for dopamine neurons, whereas CDNF is protective and neurorestorative with entirely different mechanisms of action. Both have been in the clinical trials for the most common synucleinopathy, Parkinson's disease. With the AAV-GDNF clinical trials ongoing and the CDNF trial being finalized, their effects on abnormal alpha-synuclein accumulation are of great interest. Previous animal studies with an alpha-synuclein overexpression model have shown that GDNF was ineffective against alpha-synuclein accumulation. However, a recent study with cell culture and animal models of alpha-synuclein fibril inoculation has demonstrated the opposite by revealing that the GDNF/RET signaling cascade is required for the protective effect of GDNF on alpha-synuclein aggregation. CDNF, an ER resident protein, was shown to bind alpha-synuclein directly. CDNF reduced the uptake of alpha-synuclein fibrils by the neurons and alleviated the behavioral deficits induced by fibrils injected into the mouse brain. Thus, GDNF and CDNF can modulate different symptoms and pathologies of Parkinson's disease, and perhaps, similarly for other synucleinopathies. Their unique mechanisms for preventing alpha-synuclein-related pathology should be studied more carefully to develop disease-modifying therapies.

ZC3H4 regulates infiltrating monocytes, attenuating pulmonary fibrosis through IL-10

Silicosis is a pulmonary fibrosis-associated disease caused by the inhalation of large amounts of free silicon dioxide (SiO₂) that mainly manifests as early inflammation and late pulmonary fibrosis. As macrophage precursors, monocytes accumulate in the lung during early inflammation, but their role in the development of silicosis is unclear. Single-cell sequencing (cell numbers = 25,002), Western blotting, quantitative real-time PCR, ELISA and cell functional experiments were used to explore the specific effects of monocytes on fibroblasts. The CRISPR/Cas9 system was used to specifically knock down ZC3H4, a novel member of the CCCH zinc finger protein family, and was combined with pharmacological methods to explore the mechanism by which ZC3H4 affects chemokine and cytokine secretion. The results indicated that (1) SiO₂ induced an infiltrating phenotype in monocytes; (2) infiltrating monocytes inhibited the activation, viability and migration of fibroblasts by regulating IL-10 but not IL-8; and (3) SiO₂ downregulated IL-10 via ZC3H4-induced autophagy. This study revealed that ZC3H4 regulated the secretion function of monocytes, which, in turn, inhibited fibroblast function in early inflammation through autophagy signaling, thereby reducing pulmonary fibrosis. These findings provide a new idea for the clinical treatment of silicosis.

Bromocriptine-QR Therapy Reduces Sympathetic Tone and Ameliorates a Pro-Oxidative/Pro-Inflammatory Phenotype in Peripheral Blood Mononuclear Cells and Plasma of Type 2 Diabetes Subjects

Bromocriptine-QR is a sympatholytic dopamine D2 agonist for the treatment of type 2 diabetes that has demonstrated rapid (within 1 year) substantial reductions in adverse cardiovascular events in this population by as yet incompletely delineated mechanisms. However, a chronic state of elevated sympathetic nervous system activity and central hypodopaminergic function has been demonstrated to potentiate an immune system pro-oxidative/pro-inflammatory condition and this immune phenotype is known to contribute significantly to the advancement of cardiovascular disease (CVD). Therefore, the possibility exists that bromocriptine-QR therapy may reduce adverse cardiovascular events in type 2 diabetes subjects via attenuation of this underlying chronic pro-oxidative/pro-inflammatory state. The present study was undertaken to assess the impact of bromocriptine-QR on a wide range of immune pro-oxidative/pro-inflammatory biochemical pathways and genes known to be operative in the genesis and progression of CVD. Inflammatory peripheral blood mononuclear cell biology is both a significant contributor to cardiovascular disease and also a marker of the body’s systemic pro-inflammatory status. Therefore, this study investigated the effects of 4-month circadian-timed (within 2 h of waking in the morning) bromocriptine-QR therapy (3.2 mg/day) in type 2 diabetes subjects whose glycemia was not optimally controlled on the glucagon-like peptide 1 receptor agonist on (i) gene expression status (via qPCR) of a wide array of mononuclear cell pro-oxidative/pro-inflammatory genes known to participate in the genesis and progression of CVD (OXR1, NRF2, NQO1, SOD1, SOD2, CAT, GSR, GPX1, GPX4, GCH1, HMOX1, BiP, EIF2α, ATF4, PERK, XBP1, ATF6, CHOP, GSK3β, NFkB, TXNIP, PIN1, BECN1, TLR2, TLR4, TLR10, MAPK8, NLRP3, CCR2, GCR, L-selectin, VCAM1, ICAM1) and (ii) humoral measures of sympathetic tone (norepinephrine and normetanephrine), whole-body oxidative stress (nitrotyrosine, TBARS), and pro-inflammatory factors (IL-1β, IL-6, IL-18, MCP-1, prolactin, C-reactive protein [CRP]). Relative to pre-treatment status, 4 months of bromocriptine-QR therapy resulted in significant reductions of mRNA levels in PBMC endoplasmic reticulum stress-unfolded protein response effectors [GRP78/BiP (34%), EIF2α (32%), ATF4 (29%), XBP1 (25%), PIN1 (14%), BECN1 (23%)], oxidative stress response proteins [OXR1 (31%), NRF2 (32%), NQO1 (39%), SOD1 (52%), CAT (26%), GPX1 (33%), GPX4 (31%), GCH1 (30%), HMOX1 (40%)], mRNA levels of TLR pro-inflammatory pathway proteins [TLR2 (46%), TLR4 (20%), GSK3β (19%), NFkB (33%), TXNIP (18%), NLRP3 (32%), CCR2 (24%), GCR (28%)], mRNA levels of pro-inflammatory cellular receptor proteins CCR2 and GCR by 24% and 28%, and adhesion molecule proteins L-selectin (35%) and VCAM1 (24%). Relative to baseline, bromocriptine-QR therapy also significantly reduced plasma levels of norepinephrine and normetanephrine by 33% and 22%, respectively, plasma pro-oxidative markers nitrotyrosine and TBARS by 13% and 10%, respectively, and pro-inflammatory factors IL-18, MCP1, IL-1β, prolactin, and CRP by 21%,13%, 12%, 42%, and 45%, respectively. These findings suggest a unique role for circadian-timed bromocriptine-QR sympatholytic dopamine agonist therapy in reducing systemic low-grade sterile inflammation to thereby reduce cardiovascular disease risk.

Neurotrophins as Therapeutic Agents for Parkinson’s Disease; New Chances From Focused Ultrasound?

Magnetic Resonance–guided Focused Ultrasound (MRgFUS) represents an effective micro-lesioning approach to target pharmaco-resistant tremor, mostly in patients afflicted by essential tremor (ET) and/or Parkinson’s disease (PD). So far, experimental protocols are verifying the clinical extension to other facets of the movement disorder galaxy (i.e., internal pallidus for disabling dyskinesias). Aside from those neurosurgical options, one of the most intriguing opportunities of this technique relies on its capability to remedy the impermeability of blood–brain barrier (BBB). Temporary BBB opening through low-intensity focused ultrasound turned out to be safe and feasible in patients with PD, Alzheimer’s disease, and amyotrophic lateral sclerosis. As a mere consequence of the procedures, some groups described even reversible but significant mild cognitive amelioration, up to hippocampal neurogenesis partially associated to the increased of endogenous brain-derived neurotrophic factor (BDNF). A further development elevates MRgFUS to the status of therapeutic tool for drug delivery of putative neurorestorative therapies. Since 2012, FUS-assisted intravenous administration of BDNF or neurturin allowed hippocampal or striatal delivery. Experimental studies emphasized synergistic modalities. In a rodent model for Huntington’s disease, engineered liposomes can carry glial cell line–derived neurotrophic factor (GDNF) plasmid DNA (GDNFp) to form a GDNFp-liposome (GDNFp-LPs) complex through pulsed FUS exposures with microbubbles; in a subacute MPTP-PD model, the combination of intravenous administration of neurotrophic factors (either through protein or gene delivery) plus FUS did curb nigrostriatal degeneration. Here, we explore these arguments, focusing on the current, translational application of neurotrophins in neurodegenerative diseases.

The Specific Role of Reactive Astrocytes in Stroke

Astrocytes are essential in maintaining normal brain functions such as blood brain barrier (BBB) homeostasis and synapse formation as the most abundant cell type in the central nervous system (CNS). After the stroke, astrocytes are known as reactive astrocytes (RAs) because they are stimulated by various damage-associated molecular patterns (DAMPs) and cytokines, resulting in significant changes in their reactivity, gene expression, and functional characteristics. RAs perform multiple functions after stroke. The inflammatory response of RAs may aggravate neuro-inflammation and release toxic factors to exert neurological damage. However, RAs also reduce excitotoxicity and release neurotrophies to promote neuroprotection. Furthermore, RAs contribute to angiogenesis and axonal remodeling to promote neurological recovery. Therefore, RAs' biphasic roles and mechanisms make them an effective target for functional recovery after the stroke. In this review, we summarized the dynamic functional changes and internal molecular mechanisms of RAs, as well as their therapeutic potential and strategies, in order to comprehensively understand the role of RAs in the outcome of stroke disease and provide a new direction for the clinical treatment of stroke.

Endoplasmic Reticulum Stress-Associated Neuronal Death and Innate Immune Response in Neurological Diseases

Neuronal death and inflammatory response are two common pathological hallmarks of acute central nervous system injury and chronic degenerative disorders, both of which are closely related to cognitive and motor dysfunction associated with various neurological diseases. Neurological diseases are highly heterogeneous; however, they share a common pathogenesis, that is, the aberrant accumulation of misfolded/unfolded proteins within the endoplasmic reticulum (ER). Fortunately, the cell has intrinsic quality control mechanisms to maintain the proteostasis network, such as chaperone-mediated folding and ER-associated degradation. However, when these control mechanisms fail, misfolded/unfolded proteins accumulate in the ER lumen and contribute to ER stress. ER stress has been implicated in nearly all neurological diseases. ER stress initiates the unfolded protein response to restore proteostasis, and if the damage is irreversible, it elicits intracellular cascades of death and inflammation. With the growing appreciation of a functional association between ER stress and neurological diseases and with the improved understanding of the multiple underlying molecular mechanisms, pharmacological and genetic targeting of ER stress are beginning to emerge as therapeutic approaches for neurological diseases.

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.

Activation and Role of Astrocytes in Ischemic Stroke

Ischemic stroke refers to the disorder of blood supply of local brain tissue caused by various reasons. It has high morbidity and mortality worldwide. Astrocytes are the most abundant glial cells in the central nervous system (CNS). They are responsible for the homeostasis, nutrition, and protection of the CNS and play an essential role in many nervous system diseases’ physiological and pathological processes. After stroke injury, astrocytes are activated and play a protective role through the heterogeneous and gradual changes of their gene expression, morphology, proliferation, and function, that is, reactive astrocytes. However, the position of reactive astrocytes has always been a controversial topic. Many studies have shown that reactive astrocytes are a double-edged sword with both beneficial and harmful effects. It is worth noting that their different spatial and temporal expression determines astrocytes’ various functions. Here, we comprehensively review the different roles and mechanisms of astrocytes after ischemic stroke. In addition, the intracellular mechanism of astrocyte activation has also been involved. More importantly, due to the complex cascade reaction and action mechanism after ischemic stroke, the role of astrocytes is still difficult to define. Still, there is no doubt that astrocytes are one of the critical factors mediating the deterioration or improvement of ischemic stroke.

Cerebral dopamine neurotrophic factor transfection in dopamine neurons using neurotensin-polyplex nanoparticles reverses 6-hydroxydopamine-induced nigrostriatal neurodegeneration

Overexpression of neurotrophic factors in nigral dopamine neurons is a promising approach to reverse neurodegeneration of the nigrostriatal dopamine system, a hallmark in Parkinson's disease. The human cerebral dopamine neurotrophic factor (hCDNF) has recently emerged as a strong candidate for Parkinson's disease therapy. This study shows that hCDNF expression in dopamine neurons using the neurotensin-polyplex nanoparticle system reverses 6-hydroxydopamine-induced morphological, biochemical, and behavioral alterations. Three independent electron microscopy techniques showed that the neurotensin-polyplex nanoparticles containing the hCDNF gene, ranging in size from 20 to 150 nm, enabled the expression of a secretable hCDNF in vitro. Their injection in the substantia nigra compacta on day 21 after the 6-hydroxydopamine lesion resulted in detectable hCDNF in dopamine neurons, whose levels remained constant throughout the study in the substantia nigra compacta and striatum. Compared with the lesioned group, tyrosine hydroxylase-positive (TH⁺) nigral cell population and TH⁺ fiber density rose in the substantia nigra compacta and striatum after hCDNF transfection. An increase in βIII-tubulin and growth-associated protein 43 phospho-S41 (GAP43p) followed TH⁺ cell recovery, as well as dopamine and its catabolite levels. Partial reversal (80%) of drug-activated circling behavior and full recovery of spontaneous motor and non-motor behavior were achieved. Brain-derived neurotrophic factor recovery in dopamine neurons that also occurred suggests its participation in the neurotrophic effects. These findings support the potential of nanoparticle-mediated hCDNF gene delivery to develop a disease-modifying treatment against Parkinson's disease. The Institutional Animal Care and Use Committee of Centro de Investigación y de Estudios Avanzados approved our experimental procedures for animal use (authorization No. 162-15) on June 9, 2019.

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.

Recent insights on astrocyte mechanisms in CNS homeostasis, pathology, and repair

Astrocytes play essential roles in development, homeostasis, injury, and repair of the central nervous system (CNS). Their development is tightly regulated by distinct spatial and temporal cues during embryogenesis and into adulthood throughout the CNS. Astrocytes have several important responsibilities such as regulating blood flow and permeability of the blood-CNS barrier, glucose metabolism and storage, synapse formation and function, and axon myelination. In CNS pathologies, astrocytes also play critical parts in both injury and repair mechanisms. Upon injury, they undergo a robust phenotypic shift known as "reactive astrogliosis," which results in both constructive and deleterious outcomes. Astrocyte activation and migration at the site of injury provides an early defense mechanism to minimize the extent of injury by enveloping the lesion area. However, astrogliosis also contributes to the inhibitory microenvironment of CNS injury and potentiate secondary injury mechanisms, such as inflammation, oxidative stress, and glutamate excitotoxicity, which facilitate neurodegeneration in CNS pathologies. Intriguingly, reactive astrocytes are increasingly a focus in current therapeutic strategies as their activation can be modulated toward a neuroprotective and reparative phenotype. This review will discuss recent advancements in knowledge regarding the development and role of astrocytes in the healthy and pathological CNS. We will also review how astrocytes have been genetically modified to optimize their reparative potential after injury, and how they may be transdifferentiated into neurons and oligodendrocytes to promote repair after CNS injury and neurodegeneration.

Neuron-Astrocyte Interactions in Parkinson's Disease

Parkinson’s disease (PD) is the second most common neurodegenerative disease. PD patients exhibit motor symptoms such as akinesia/bradykinesia, tremor, rigidity, and postural instability due to a loss of nigrostriatal dopaminergic neurons. Although the pathogenesis in sporadic PD remains unknown, there is a consensus on the involvement of non-neuronal cells in the progression of PD pathology. Astrocytes are the most numerous glial cells in the central nervous system. Normally, astrocytes protect neurons by releasing neurotrophic factors, producing antioxidants, and disposing of neuronal waste products. However, in pathological situations, astrocytes are known to produce inflammatory cytokines. In addition, various studies have reported that astrocyte dysfunction also leads to neurodegeneration in PD. In this article, we summarize the interaction of astrocytes and dopaminergic neurons, review the pathogenic role of astrocytes in PD, and discuss therapeutic strategies for the prevention of dopaminergic neurodegeneration. This review highlights neuron-astrocyte interaction as a target for the development of disease-modifying drugs for PD in the future.

Congrong Shujing Granule-Induced GRP78 Expression Reduced Endoplasmic Reticulum Stress and Neuronal Apoptosis in the Midbrain in a Parkinson's Disease Rat Model

The main pathological changes inherent in Parkinson's disease (PD) are degeneration and loss of dopamine neurons in the midbrain and formation of Lewy bodies. Many studies have shown that the pathogenesis of PD is closely related to endoplasmic reticulum (ER) oxidative stress. This study combined various traditional Chinese medicines to prepare Congrong Shujing granules (CSGs). The optimal dose combination of the ingredients was identified by experimental intervention in SH-SY5Y cells in vitro. A PD rat model was established by intraperitoneal injection of rotenone sunflower oil emulsion. The suspension tests were performed on the 14th day after modeling and also on the 14th day after CSG intervention (5.88 g/kg, 11.76 g/kg, and 23.52 g/kg). We evaluated the changes in motor function and the expression of neuronal cell functional marker proteins, ER stress (ERS) marker proteins, and apoptosis-related pathway proteins of neuronal cells. Changes in cellular ultrastructure were observed by electron microscopy. Our results showed that CSG treatment lengthened the duration of PD rats' gripping to the wire. 78 kDa glucose-regulated protein (GRP78) expression in the substantia nigra was significantly upregulated in the middle- and high-dose CSG groups after 14 days of treatment compared with the model group. The expression of the key dopaminergic neuron functional enzyme tyrosine hydroxylase (TH) and cerebral dopamine neurotrophic factor (CDNF) was elevated. The expression of c-Jun N-terminal kinase (JNK) and phosphorylated c-Jun decreased, and cell apoptosis was significantly reduced. Compared with the model group, the treatment groups had fewer ER fragmentation and degranulation (ribosome shedding) and abundant ER and mitochondria suggesting that CSG reduced ER stress and neuronal apoptosis in the midbrain of a PD rat model by inducing the expression of molecular chaperone GRP78.

Protective Functions of Reactive Astrocytes Following Central Nervous System Insult

Astrocytes play important roles in numerous central nervous system disorders including autoimmune inflammatory, hypoxic, and degenerative diseases such as Multiple Sclerosis, ischemic stroke, and Alzheimer’s disease. Depending on the spatial and temporal context, activated astrocytes may contribute to the pathogenesis, progression, and recovery of disease. Recent progress in the dissection of transcriptional responses to varying forms of central nervous system insult has shed light on the mechanisms that govern the complexity of reactive astrocyte functions. While a large body of research focuses on the pathogenic effects of reactive astrocytes, little is known about how they limit inflammation and contribute to tissue regeneration. However, these protective astrocyte pathways might be of relevance for the understanding of the underlying pathology in disease and may lead to novel targeted approaches to treat autoimmune inflammatory and degenerative disorders of the central nervous system. In this review article, we have revisited the emerging concept of protective astrocyte functions and discuss their role in the recovery from inflammatory and ischemic disease as well as their role in degenerative disorders. Focusing on soluble astrocyte derived mediators, we aggregate the existing knowledge on astrocyte functions in the maintenance of homeostasis as well as their reparative and tissue-protective function after acute lesions and in neurodegenerative disorders. Finally, we give an outlook of how these mediators may guide future therapeutic strategies to tackle yet untreatable disorders of the central nervous system.

Trophic activities of endoplasmic reticulum proteins CDNF and MANF

Mesencephalic astrocyte-derived neurotrophic factor (MANF) and cerebral dopamine neurotrophic factor (CDNF) are endoplasmic reticulum (ER) luminal proteins that confer trophic activities in a wide range of tissues under diverse pathological conditions. Despite initially being classified as neurotrophic factors, neither protein structurally nor functionally resembles bona fide neurotrophic factors. Their highly homologous structures comprise a unique globular, saposin-like domain within the N-terminus joined by a flexible linker to a C-terminus containing a SAP-like domain, CXXC motif and an ER retention sequence. Neurotrophic factors exert effects by binding to cognate receptors in the plasma membrane; however, no cell surface receptors have been identified for MANF and CDNF. Both can act as unfolded protein response (UPR) genes that modulate the UPR and inflammatory processes. The trophic activity of MANF and CDNF extends beyond the central nervous system with MANF being crucial for the development of pancreatic β cells and both have trophic effects in a variety of diseases related to the liver, heart, skeletal tissue, kidney and peripheral nervous system. In this article, the unique features of MANF and CDNF, such as their structure and mechanisms of action related to ER stress and inflammation, will be reviewed. Recently identified interactions with lipids and membrane trafficking will also be described. Lastly, their function and therapeutic potential in different diseases including a recent clinical trial using CDNF to treat Parkinson's disease will be discussed. Collectively, this review will highlight MANF and CDNF as broad-acting trophic factors that regulate functions of the endoplasmic reticulum.

Ginsenoside Rg1-induced activation of astrocytes promotes functional recovery via the PI3K/Akt signaling pathway following spinal cord injury

AIMS

To determine whether ginsenoside Rg1 is involved in scratch wound healing through altered expression of related molecules in astrocytes and improved functional recovery after spinal cord injury (SCI).

MATERIALS AND METHODS

Astrocytes were isolated from rats, followed by Rg1 treatment. The wound healing test was performed to observe the scratch wound healing in different groups. The expression of nerve growth factor (NGF), glial cell line-derived neurotrophic factor (GDNF), basic fibroblast growth factor (bFGF), and components of the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) signaling pathway were detected by western blot. Reverse transcription-polymerase chain reaction (RT-PCR) was used to measure the altered expression of laminin (LN) and fibronectin (FN). A revised Allen's method for the SCI model was performed, followed by Rg1 treatment. Then, functional scoring was conducted to evaluate the functional recovery. Hematoxylin-eosin (HE) staining showed changes in the void area. Finally, western blot assessed the expression of glial fibrillary acidic protein (GFAP) and chondroitin sulfate proteoglycans (CSPGs).

KEY FINDINGS

Rg1 mediated scratch wound healing through inducing an increased release of LN, FN, NGF, GDNF, and bFGF in vitro. Additionally, Rg1 activated the PI3K/Akt signaling pathway and promoted the functional recovery of hindlimb movement in rats. Furthermore, Rg1 significantly reduced the void area and downregulated the expression of GFAP and CSPGs.

SIGNIFICANCE

Rg1 not only enhanced the scratch wound repair in vitro through the release of astroglial neurotrophic factors, adhesion factors, and inhibitory factors, but it also improved the functional recovery in vivo following SCI.

CDNF Protein Therapy in 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.

Trophic Factors in Inflammation and Regeneration: The Role of MANF and CDNF

Regeneration is an important process in multicellular organisms, responsible for homeostatic renewal and repair of different organs after injury. Immune cell activation is observed at early stages of the regenerative response and its regulation is essential for regenerative success. Thus, immune regulators play central roles in optimizing regenerative responses. Neurotrophic factors (NTFs) are secreted molecules, defined by their ability to support neuronal cell types. However, emerging evidence suggests that they can also play important functions in the regulation of immune cell activation and tissue repair. Here we discuss the literature supporting a role of NTFs in the regulation of inflammation and regeneration. We will focus, in particular, in the emerging roles of mesencephalic astrocyte-derived neurotrophic factor (MANF) and cerebral dopamine neurotrophic factor (CDNF) in the regulation of immune cell function and in the central role that immune modulation plays in their biological activity in vivo. Finally, we will discuss the potential use of these factors to optimize regenerative success in vivo, both within and beyond the nervous system.

Neurotrophic factors hold promise for the future of Parkinson's disease treatment: is there a light at the end of the tunnel?

Parkinson's disease (PD) is the second most common neurodegenerative disorder and is characterized by a spectrum of clinicopathologic signs and a complex etiology. PD results from the degeneration of dopaminergic (DAergic) neurons in the substantia nigra. Current therapies for PD are only able to alleviate symptoms without stopping disease progression. In addition, the available therapeutic strategies do not have long-lasting effects. Furthermore, these therapies cause different ranges of adverse side effects. There is great interest in neurotrophic factors (NTFs) due to their ability to promote the survival of different neural cells. These factors are divided into four families: neurotrophins, neurokines, the glial cell line-derived NTF family of ligands, and the newly recognized cerebral DA NTF/mesencephalic astrocyte-derived NTF family. The protective and therapeutic effects of these factors on DAergic neurons make them suitable for the prevention of progressive cell loss in PD. Based on the above premise, we focus on the protective effects of NTFs, especially CDNF and MANF, on nigrostriatal DAergic neurons in PD.

Outside in: Unraveling the Role of Neuroinflammation in the Progression of Parkinson's Disease

Neuroinflammation is one of the most important processes involved in the pathogenesis of Parkinson's disease (PD). The current concept of neuroinflammation comprises an inflammation process, which occurs in the central nervous system due to molecules released from brain-resident and/or blood-derived immune cells. Furthermore, the evidence of the contribution of systemic delivered molecules to the disease pathogenesis, such as the gut microbiota composition, has been increasing during the last years. Under physiological conditions, microglia and astrocytes support the well-being and well-function of the brain through diverse functions, including neurotrophic factor secretion in both intact and injured brain. On the other hand, genes that cause PD are expressed in astrocytes and microglia, shifting their neuroprotective role to a pathogenic one, contributing to disease onset and progression. In addition, growth factors are a subset of molecules that promote cellular survival, differentiation and maturation, which are critical signaling factors promoting the communication between cells, including neurons and blood-derived immune cells. We summarize the potential targeting of astrocytes and microglia and the systemic contribution of the gut microbiota in neuroinflammation process archived in PD.

Mesencephalic Astrocyte-Derived Neurotrophic Factor (MANF) Elevates Stimulus-Evoked Release of Dopamine in Freely-Moving Rats

Neurotrophic factors (NTFs) hold potential as disease-modifying therapies for neurodegenerative disorders like Parkinson's disease. Glial cell line-derived neurotrophic factor (GDNF), cerebral dopamine neurotrophic factor (CDNF), and mesencephalic astrocyte-derived neurotrophic factor (MANF) have shown neuroprotective and restorative effects on nigral dopaminergic neurons in various animal models of Parkinson's disease. To date, however, their effects on brain neurochemistry have not been compared using in vivo microdialysis. We measured extracellular concentration of dopamine and activity of dopamine neurochemistry-regulating enzymes in the nigrostriatal system of rat brain. NTFs were unilaterally injected into the striatum of intact Wistar rats. Brain microdialysis experiments were performed 1 and 3 weeks later in freely-moving animals. One week after the treatment, we observed enhanced stimulus-evoked release of dopamine in the striatum of MANF-treated rats, but not in rats treated with GDNF or CDNF. MANF also increased dopamine turnover. Although GDNF did not affect the extracellular level of dopamine, we found significantly elevated tyrosine hydroxylase (TH) and catechol-O-methyltransferase (COMT) activity and decreased monoamine oxidase A (MAO-A) activity in striatal tissue samples 1 week after GDNF injection. The results show that GDNF, CDNF, and MANF have divergent effects on dopaminergic neurotransmission, as well as on dopamine synthetizing and metabolizing enzymes. Although the cellular mechanisms remain to be clarified, knowing the biological effects of exogenously administrated NTFs in intact brain is an important step towards developing novel neurotrophic treatments for degenerative brain diseases.

Mild Endoplasmic Reticulum Stress Protects Against Lipopolysaccharide-Induced Astrocytic Activation and Blood-Brain Barrier Hyperpermeability

Recent research has revealed that uncontrolled chronic neuroinflammation is closely associated with diverse neurodegenerative diseases, by impairing blood-brain barrier (BBB) function and astrocytic reaction. Endoplasmic reticulum (ER) stress is conventionally linked to the loss of neuronal structure and function and should be widely attenuated. This notion has been questioned by recent experimental studies, which have shown that non-harmful levels of ER stress had numerous beneficial roles against neurodegeneration, including neuroprotection and inhibition of cytokine production. Here, we investigated the mild ER stress-based regulation of LPS-induced inflammatory responses in astrocytes. Primary astrocytes were exposed to tunicamycin (TM), a compound that activates ER stress, with or without the ER-stress inhibitor sodium 4-phenylbutyrate (4-PBA) before LPS treatment. Astrocytic activation, proinflammatory factor production, and the extent of ER stress were assessed. In addition, the effect of mild ER stress on astrocytes and BBB function was determined in vivo. Male Sprague-Dawley rats received intracerebroventricular injections of TM with or without intraperitoneal 4-PBA before LPS administration. The levels of astrocytic activation and BBB permeability were measured after treatment. Our results showed that lower doses of TM resulted in a mild ER-stress response without inducing cytotoxicity and tissue toxicity. Non-toxic ER-stress preconditioning ameliorated LPS-induced overactivation and inflammatory responses in astrocytes. Moreover, pre-exposure to non-lethal doses of TM improved LPS-induced BBB impairment and cognitive ability dysfunction in rats. However, 4-PBA, reversed the protective effect of TM preconditioning in vitro and in vivo. We conclude that mild ER stress (“preconditioning”) can alleviate LPS-induced astrocytic activation and BBB disruption. Our findings provide a better understanding for the regulatory role of ER stress in neuroinflammation and indicate that mild ER stress might have therapeutic value for the treatment of neurodegenerative diseases.

Cerebral Dopamine Neurotrophic Factor (CDNF) Has Neuroprotective Effects against Cerebral Ischemia That May Occur through the Endoplasmic Reticulum Stress Pathway

Cerebral dopamine neurotrophic factor (CDNF), previously known as the conserved dopamine neurotrophic factor, belongs to the evolutionarily conserved CDNF/mesencephalic astrocyte-derived neurotrophic factor MANF family of neurotrophic factors that demonstrate neurotrophic activities in dopaminergic neurons. The function of CDNF during brain ischemia is still not known. MANF is identified as an endoplasmic reticulum (ER) stress protein; however, the role of CDNF in ER stress remains to be fully elucidated. Here, we test the neuroprotective effect of CDNF on middle cerebral artery occlusion (MCAO) rats and neurons and astrocytes treated with oxygen–glucose depletion (OGD). We also investigate the expression of CDNF in cerebral ischemia and in primary neurons treated with ER stress-inducing agents. Our results show that CDNF can significantly reduce infarct volume, reduce apoptotic cells and improve motor function in MCAO rats, while CDNF can increase the cell viability of neurons and astrocytes treated by OGD. The expression of CDNF was upregulated in the peri-infarct tissue at 2 h of ischemia/24 h reperfusion. ER stress inducer can induce CDNF expression in primary cultured neurons. Our data indicate that CDNF has neuroprotective effects on cerebral ischemia and the OGD cell model and the protective mechanism of CDNF may occur through ER stress pathways.

An evolutionary perspective on the role of mesencephalic astrocyte-derived neurotrophic factor (MANF): At the crossroads of poriferan innate immune and apoptotic pathways

The mesencephalic astrocyte-derived neurotrophic factor (MANF) belongs to a recently discovered family of neurotrophic factors. MANF can be secreted but is generally resident within the endoplasmic reticulum (ER) in neuronal and non-neuronal cells, where it is involved in the ER stress response with pro-survival effects. Here we report the discovery of the MANF homolog SDMANF in the sponge Suberites domuncula. The basal positioning of sponges (phylum Porifera) in the animal tree of life offers a unique vantage point on the early evolution of the metazoan-specific genetic toolkit and molecular pathways. Since sponges lack a conventional nervous system, SDMANF presents an enticing opportunity to investigate the evolutionary ancient role of these neurotrophic factors. SDMANF shares considerable sequence similarity with its metazoan homologs. It also comprises a putative protein binding domain with sequence similarities to the Bcl-2 family of apoptotic regulators. In Suberites, SDMANF is expressed in the vicinity of bacteriocytes, where it co-localizes with the toll-like receptor SDTLR. In transfected human cells, SDMANF was detected in both the organelle protein fraction and the cell culture medium. The intracellular SDMANF protein level was up-regulated in response to both a Golgi/ER transport inhibitor and bacterial lipopolysaccharides (LPS). Upon LPS challenge, transfected cells revealed a decreased caspase-3 activity and increased cell viability with no inducible Bax expression compared to the wild type. These results suggest a deep evolutionary original cytoprotective role of MANF, at the crossroads of innate immune and apoptotic pathways, of which a neurotrophic function might have arisen later in metazoan evolution.

In vivo screening reveals interactions between Drosophila Manf and genes involved in the mitochondria and the ubiquinone synthesis pathway

BACKGROUND

Mesencephalic Astrocyte-derived Neurotrophic Factor (MANF) and Cerebral Dopamine Neurotrophic Factor (CDNF) form an evolutionarily conserved family of neurotrophic factors. Orthologues for MANF/CDNF are the only neurotrophic factors as yet identified in invertebrates with conserved amino acid sequence. Previous studies indicate that mammalian MANF and CDNF support and protect brain dopaminergic system in non-cell-autonomous manner. However, MANF has also been shown to function intracellularly in the endoplasmic reticulum. To date, the knowledge on the interacting partners of MANF/CDNF and signaling pathways they activate is rudimentary. Here, we have employed the Drosophila genetics to screen for potential interaction partners of Drosophila Manf (DmManf) in vivo.

RESULTS

We first show that DmManf plays a role in the development of Drosophila wing. We exploited this function by using Drosophila UAS-RNAi lines and discovered novel genetic interactions of DmManf with genes known to function in the mitochondria. We also found evidence of an interaction between DmManf and the Drosophila homologue encoding Ku70, the closest structural homologue of SAP domain of mammalian MANF.

CONCLUSIONS

In addition to the previously known functions of MANF/CDNF protein family, DmManf also interacts with mitochondria-related genes. Our data supports the functional importance of these evolutionarily significant proteins and provides new insights for the future studies.

Circulating mesencephalic astrocyte-derived neurotrophic factor is increased in newly diagnosed prediabetic and diabetic patients, and is associated with insulin resistance

Evidence has shown that endoplasmic reticulum (ER) stress was involved in the progression to type 2 diabetes mellitus (T2DM) and development of insulin resistance. Mesencephalic astrocyte-derived neurotrophic factor (MANF) is a novel secreted protein upregulated by ER stress. This study aimed to assess serum level of MANF in normal glucose tolerance (NGT) participants and newly diagnosed prediabetic and T2DM patients. A total of 257 participants with NGT, newly diagnosed prediabetes or T2DM were recruited from Yinchao and Hangtian communities of Chengdu, Sichuan, China. Serum MANF level was quantified by enzyme-linked immunosorbent assay (ELISA). The mean age for the 257 participants (147 females) was 62±8 years (range 44-78): 71 with NGT, 115 with newly diagnosed prediabetes and 71 with T2DM. Mean serum MANF level was significantly higher with newly diagnosed prediabetes and T2DM than NGT (2.89±1.09 and 3.03±1.73 vs 2.13±1.37 ng/mL, both p<0.001). MANF level was not correlated with insulin sensitivity indexes (homeostasis model assessment for insulin resistance [HOMA-IR], Matsuda Index and quantitative insulin sensitivity check index [QUICKI]) for NGT and T2DM participants but was correlated with such indexes for prediabetes patients. We concluded that serum MANF level was higher in patients with newly diagnosed prediabetes and T2DM than in NGT controls. MANF appears to be associated with Matsuda Index, QUICKI and HOMA-IR in prediabetes patients.

Cerebral dopamine neurotrophic factor protects H9c2 cardiomyocytes from apoptosis

BACKGROUND

Cerebral dopamine neurotrophic factor (CDNF) has been studied in animal models of Parkinson's disease, where it was shown to repair and protect dopamine neurons. Alongside its neurotrophic activity, it can also localize in the endoplasmic reticulum (ER) acting as an ER stress response (ERSR) protein to maintain ER homeostasis. Since ER stress plays a major role in the development and progression of cardiovascular diseases, we investigated the role of CDNF in cardiomyocytes during ER stress.

MATERIAL AND METHODS

Initially, the expression of CDNF was tested by treating H9c2 cells with various concentrations of tunicamycin (TM) and performing reverse-transcriptase polymerase chain reaction and Western blotting. To evaluate the overexpression of CDNF in cardiomyocytes, H9c2 cells were transfected with pcDNA-CDNF and analyzed by Western blotting and indirect immunofluorescence microscopy. The effects of CDNF on cardiomyocytes during ER stress were analyzed with CCK-8 method and TUNEL staining using cells transfected with pcDNA-CDNF or pcDNA3.1. The percentage of TUNEL-positive cells was quantified as the apoptotic level.

RESULTS

Our results showed that CDNF protein expression can be induced by activation of ER stress in cultured cardiomyocytes. Moreover, overexpression of CDNF improved cell viability and protected cardiomyocytes from apoptosis induced by ER stress.

CONCLUSION

The findings presented here contribute toward identifying the physiological functions of CDNF in cardiovascular diseases.

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.

Evidence for an Additive Neurorestorative Effect of Simultaneously Administered CDNF and GDNF in Hemiparkinsonian Rats: Implications for Different Mechanism of Action

Parkinson's disease (PD) is a neurodegenerative disorder associated with a progressive loss of dopaminergic (DAergic) neurons of the substantia nigra (SN) and the accumulation of intracellular inclusions containing α-synuclein. Current therapies do not stop the progression of the disease, and the efficacy of these treatments wanes over time. Neurotrophic factors (NTFs) are naturally occurring proteins promoting the survival and differentiation of neurons and the maintenance of neuronal contacts. CDNF (cerebral dopamine NTF) and GDNF (glial cell line-derived NTF) are able to protect DAergic neurons against toxin-induced degeneration in experimental models of PD. Here, we report an additive neurorestorative effect of coadministration of CDNF and GDNF in the unilateral 6-hydroxydopamine (6-OHDA) lesion model of PD in rats. NTFs were given into the striatum four weeks after unilateral intrastriatal injection of 6-OHDA (20 µg). Amphetamine-induced (2.5 mg/kg, i.p.) rotational behavior was measured every two weeks. Number of tyrosine hydroxylase (TH)-positive cells from SN pars compacta (SNpc) and density of TH-positive fibers in the striatum were analyzed at 12 weeks after lesion. CDNF and GDNF alone restored the DAergic function, and one specific dose combination had an additive effect: CDNF (2.5µg) and GDNF (1µg) coadministration led to a stronger trophic effect relative to either of the single treatments alone. The additive effect may indicate different mechanism of action for the NTFs. Indeed, both NTFs activated the survival promoting PI3 kinase (PI3K)-Akt signaling pathway, but only CDNF decreased the expression level of tested endoplasmatic reticulum (ER) stress markers ATF6, glucose-regulated protein 78 (GRP78), and phosphorylation of eukaryotic initiation factor 2α subunit (eIF2α).

Recombinant AAV8-mediated intrastriatal gene delivery of CDNF protects rats against methamphetamine neurotoxicity

Methamphetamine (METH) exerts significant neurotoxicity in experimental animals and humans when taken at high doses or abused chronically. Long-term abusers have decreased dopamine levels, and they are more likely to develop Parkinson's disease (PD). To date, few medications are available to treat the METH-induced damage of neurons. Glial cell line-derived neurotrophic factor (GDNF) has been previously shown to reduce the dopamine-depleting effects of neurotoxic doses of METH. However, the effect of cerebral dopamine neurotrophic factor (CDNF), which has been reported to be more specific and efficient than GDNF in protecting dopaminergic neurons against 6-OHDA toxicity, in attenuating METH neurotoxicity has not been determined. Thus, the present study aimed to evaluate the neuroprotective effect of CDNF against METH-induced damage to the dopaminergic system in vitro and in vivo. In vitro, CDNF protein increased the survival rate and reduced the tyrosine hydroxylase (TH) loss of METH-treated PC12 cells. In vivo, METH was administered to rats following human CDNF overexpression mediated by the recombinant adeno-associated virus. Results demonstrated that CDNF overexpression in the brain could attenuate the METH-induced dopamine and TH loss in the striatum but could not lower METH-induced hyperthermia.

Key subdomains in the C-terminal of cerebral dopamine neurotrophic factor regulate the protein secretion

Cerebral dopamine neurotrophic factor (CDNF) is a novel evolutionary conserved neurotrophic factor (NTF) which can protect and repairs dopamine neurons in animal models of Parkinson's disease. The crystal structure of CDNF is dominated by eight α-helices and the 3-dimensional structure of CDNF consists of an N-terminal saposin-like domain and a C-terminal SAP-domain. In particular, the C-terminal domain contains two critical motifs, a CXXC motif and a putative ER retention signal sequences (KTEL) at the C-terminus, which indicate that CDNF may be involved in endoplasmic reticulum (ER) stress. In this study, we found that disrupting helix-7 in the C-terminal could significantly increase CDNF secretion. Moreover, we identified the 149aa-154aa is the key amino acids in helix-7. In all, these findings suggest that helix-7 in the C-terminal is important for CDNF secretion, which maybe potential affect CDNF function in ER stress.

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.

Transient transfection of human CDNF gene reduces the 6-hydroxydopamine-induced neuroinflammation in the rat substantia nigra

BACKGROUND

The anti-inflammatory effect of the cerebral dopamine neurotrophic factor (CDNF) was shown recently in primary glial cell cultures, yet such effect remains unknown both in vivo and in 6-hydroxydopamine (6-OHDA) models of Parkinson's disease (PD). We addressed this issue by performing an intranigral transfection of the human CDNF (hCDNF) gene in the critical period of inflammation after a single intrastriatal 6-OHDA injection in the rat.

METHODS

At day 15 after lesion, the plasmids p3xNBRE-hCDNF or p3xNBRE-EGFP, coding for enhanced green florescent protein (EGFP), were transfected into the rat substantia nigra (SN) using neurotensin (NTS)-polyplex. At day 15 post-transfection, we measured nitrite and lipoperoxide levels in the SN. We used ELISA to quantify the levels of TNF-α, IL-1β, IL-6, endogenous rat CDNF (rCDNF) and hCDNF. We also used qRT-PCR to measure rCDNF and hCDNF transcripts, and immunofluorescence assays to evaluate iNOS, CDNF and glial cells (microglia, astrocytes and Neuron/Glial type 2 (NG2) cells). Intact SNs were additional controls.

RESULTS

In the SN, 6-OHDA triggered nitrosative stress, increased inflammatory cytokines levels, and activated the multipotent progenitor NG2 cells, which convert into astrocytes to produce rCDNF. In comparison with the hemiparkinsonian rats that were transfected with the EGFP gene or without transfection, 6-OHDA treatment and p3xNBRE-hCDNF transfection increased the conversion of NG2 cells into astrocytes resulting in 4-fold increase in the rCDNF protein levels. The overexpressed CDNF reduced nitrosative stress, glial markers and IL-6 levels in the SN, but not TNF-α and IL-1β levels.

CONCLUSION

Our results show the anti-inflammatory effect of CDNF in a 6-OHDA rat of Parkinson's disease. Our results also suggest the possible participation of TNF-α, IL-1β and IL-6 in rCDNF production by astrocytes, supporting their anti-inflammatory role.

Transplantation of Cerebral Dopamine Neurotrophic Factor Transducted BMSCs in Contusion Spinal Cord Injury of Rats: Promotion of Nerve Regeneration by Alleviating Neuroinflammation

Traumatic spinal cord injury (SCI) causes neuron death and axonal damage resulting in functional motor and sensory loss, showing limited regeneration because of adverse microenvironment such as neuroinflammation and glial scarring. Currently, there is no effective therapy to treat SCI in clinical practice. Bone marrow-derived mesenchymal stem cells (BMSCs) are candidates for cell therapies but its effect is limited by neuroinflammation and adverse microenvironment in the injured spinal cord. In this study, we developed transgenic BMSCs overexpressing cerebral dopamine neurotrophic factor (CDNF), a secretory neurotrophic factor that showed potent effects on neuron protection, anti-inflammation, and sciatic nerve regeneration in previous studies. Our results showed that the transplantation of CDNF-BMSCs suppressed neuroinflammation and decreased the production of proinflammatory cytokines after SCI, resulting in the promotion of locomotor function and nerve regeneration of the injured spinal cord. This study presents a novel promising strategy for the treatment of spinal cord injury.

Conserved dopamine neurotrophic factor-transduced mesenchymal stem cells promote axon regeneration and functional recovery of injured sciatic nerve

Peripheral nerve injury (PNI) is a common disease that often results in axonal degeneration and the loss of neurons, ultimately leading to limited nerve regeneration and severe functional impairment. Currently, there are no effective treatments for PNI. In the present study, we transduced conserved dopamine neurotrophic factor (CDNF) into mesenchymal stem cells (MSCs) in collagen tubes to investigate their regenerative effects on rat peripheral nerves in an in vivo transection model. Scanning electron microscopy of the collagen tubes demonstrated their ability to be resorbed in vivo. We observed notable overexpression of the CDNF protein in the distal sciatic nerve after application of CDNF-MSCs. Quantitative analysis of neurofilament 200 (NF200) and S100 immunohistochemistry showed significant enhancement of axonal and Schwann cell regeneration in the group receiving CDNF-MSCs (CDNF-MSCs group) compared with the control groups. Myelination thickness, axon diameter and the axon-to fiber diameter ratio (G-ratio) were significantly higher in the CDNF-MSCs group at 8 and 12 weeks after nerve transection surgery. After surgery, the sciatic functional index, target muscle weight, wet weight ratio of gastrocnemius muscle and horseradish peroxidase (HRP) tracing demonstrated functional recovery. Light and electron microscopy confirmed successful regeneration of the sciatic nerve. The greater numbers of HRP-labeled neuron cell bodies and increased sciatic nerve index values (SFI) in the CDNF-MSCs group suggest that CDNF exerts neuroprotective effects in vivo. We also observed higher target muscle weights and a significant improvement in muscle atrophism in the CDNF-MSCs group. Collectively, these findings indicate that CDNF gene therapy delivered by MSCs is capable of promoting nerve regeneration and functional recovery, likely because of the significant neuroprotective and neurotrophic effects of CDNF and the superior environment offered by MSCs and collagen tubes.

Endoplasmic reticulum stress as a novel neuronal mediator in Alzheimer's disease

Alzheimer's disease (AD) is one of the most common types of progressive dementias. The typical neuropathological changes in AD include extracellular senile plaques, intracellular neurofibrillary tangles, and loss of neurons. The pathogenetic mechanism of this disease is not comprehensively understood yet. Recently, endoplasmic reticulum stress (ER stress) has been considered as a potential event involved in AD development. Some AD-related factors, such as misfolded protein and Ca(2+) depletion, could disrupt the homeostasis of ER lumen. In AD, the aggregated amyloid-beta peptide (Abeta) could induce ER stress in an assembly dependent way. The presenilin has been identified as a Ca(2+) channel. Mutations of presenilin could change the balance of Ca(2+) in ER lumen and thus disrupts the ER homeostasis. Furthermore, the ER stress could lead to cellular disorders like inflammation. Through activating the expression of inflammatory factors, ER stress triggers inflammatory response in AD pathology. Herein, we reviewed the recent progress of ER stress-induced unfolded protein response (UPR) and the roles of ER stress in AD pathological process.

Mechanisms of anti-inflammatory property of conserved dopamine neurotrophic factor: inhibition of JNK signaling in lipopolysaccharide-induced microglia

Microglia are important resident immune cells in the central nervous system (CNS) and involved in the neuroinflammation caused by CNS disorders, including brain trauma, ischemia, stroke, infections, inflammation, and neurodegenerative diseases. Our study explores the hypothesis that conserved dopamine neurotrophic factor (CDNF), a secretory neurotrophic factor, may provide a novel therapy for associated with neuroinflammation related to the microglia. We observed that CDNF was upregulated in rat primary microglia treated with 1 μg/mL lipopolysaccharide, an inflammatory inducer, for 24 h. Thus, we hypothesize that CDNF may play a role, mediator or inhibitor, in regulating the inflammation in microglial cells induced by LPS. Finally, our data showed that CDNF significantly attenuated the production of proinflammatory cytokines (PGE2 and IL-1β) and remarkably alleviated the cytotoxicity (percentage of lactate dehydrogenase released) in the LPS-induced microglia by suppressing the phosphorylation of JNK, but not the P38 or ERK pathways. These results demonstrate the anti-inflammatory property of CDNF by inhibition of JNK signaling in LPS-induced microglia, suggesting that CDNF may be a potential novel agent for the treatment of neuroinflammation in the CNS disorders.

Construction of bicistronic lentiviral vectors for tracking the expression of CDNF in transduced cells

CDNF is a recently described evolutionary conserved neurotrophic factor reported to be of relevance for the treatment of Parkinson's disease. Treatment with recombinant CDNF showed neurorestorative and neuroprotective effects on dopaminergic neurons in Parkinsonian animal models. Similar results are obtained using adeno-associated viral (AAV) vectors for CDNF expression in these animal models; however, the extent of the transduced brain tissue is difficult to assess due to the lack of reporter genes in the vectors used. Here, we describe two bicistronic lentiviral plasmids based on the Δ1D/2A and IRES elements for the expression of EGFP and rat CDNF, in order to track the transduced cells expressing CDNF with EGFP fluorescence. Transfected heterologous cells or transduced neurons with these vectors are easily identified by EGFP fluorescence and CDNF expression results in its recruitment to the endoplasmic reticulum (ER) by both bicistronic vectors. CDNF immunostaining is also observed in the Golgi apparatus when expressed in heterologous cells or hippocampal neuronal cultures; however, colocalization with a dense core secretory vesicle marker was scarce. Additionally, we showed that the expression of CDNF inhibited dendrite formation in hypothalamic neurons, suggesting that CDNF expressed by these bicistronic lentiviral vectors is functional and could have a role in neuronal morphology. The bicistronic lentiviral plasmids developed here could be of use to study the effect of rat CDNF at the cellular level or to better delineate the perikarya of neurons transduced with lentiviral vectors in animal models of Parkinson's disease.

Epidermal growth factor receptor inhibitor ameliorates excessive astrogliosis and improves the regeneration microenvironment and functional recovery in adult rats following spinal cord injury

BACKGROUND

Astrogliosis is a common phenomenon after spinal cord injury (SCI). Although this process exerts positive effects on axonal regeneration, excessive astrogliosis imparts negative effects on neuronal repair and recovery. Epidermal growth factor receptor (EGFR) pathway is critical to the regulation of reactive astrogliosis, and therefore is a potential target of therapeutics to better control the response. In this report, we aim to investigate whether blocking EGFR signaling using an EGFR tyrosine kinase specific inhibitor can attenuate reactive astrogliosis and promote functional recovery after a traumatic SCI.

METHOD

The astrocyte scratch injury model in vitro and the weight-drop SCI model in vivo were used as model systems. PD168393 was used to inhibit EGFR signaling activation. Astrocytic activation and phosphorylated EGFR (pEGFR) were observed after immunofluorescence staining and Western blot analysis. The rate of proliferation was determined by immunofluorescence detection of BrdU-incorporating cells located next to the wound. The levels of TNF-α, iNOS, COX-2 and IL-1β in the culture medium under different conditions were assayed by ELISA. Western blot was performed to semi-quantify the expression of EGFR/pEGFR, glial fibrillary acid protein (GFAP) and chondroitin sulfate proteoglycans (CSPGs). Myelin was stained by Luxol Fast Blue Staining. Cresyl violet eosin staining was performed to analyze the lesion cavity volume and neuronal survival following injury. Finally, functional scoring and residual urine recording were performed to show the rats' recovery.

RESULTS

EGFR phosphorylation was found to parallel astrocyte activation, and EGFR inhibitor PD168393 potently inhibited scratch-induced reactive astrogliosis and proinflammatory cytokine/mediator secretion of reactive astrocytes in vitro. Moreover, local administration of PD168393 in the injured area suppressed CSPGs production and glial scar formation, and resulted in reduced demyelination and neuronal loss, which correlated with remarkable hindlimb motor function and bladder improvement in SCI rats.

CONCLUSIONS

The specific EGFR inhibitor PD168393 can ameliorate excessive reactive astrogliosis and facilitate a more favorable environment for axonal regeneration after SCI. As such, EGFR inhibitor may be a promising therapeutic intervention in CNS injury.

Protective effect of tomatine against hydrogen peroxide-induced neurotoxicity in neuroblastoma (SH-SY5Y) cells

OBJECTIVES

Reactive oxygen species can induce cell apoptosis, and oxidative stress has been implicated in a variety of neurodegenerative disorders. Tomatine, which is a naturally occurring steroidal glycoalkaloid isolated from Solanum cathayanum, has shown potent anti-oxidant properties.

METHODS

In this study, we used the SH-SY5Y cell line as an in vitro model and investigated the protective effect of tomatine against hydrogen peroxide (H2 O2 )-induced neurotoxicity in SH-SY5Y cells.

KEY FINDINGS

Tomatine might inhibit the release of cellular lactate dehydrogenase, increase anti-oxidant enzyme activity and glutathione content, reverse the downregulated protein expression of the brain-derived neurotrophic factor (BDNF), inhibit expression of Bax and activations of caspase-3 and caspase-9 in H2 O2 -induced SH-SY5Y cells.

CONCLUSIONS

Tomatine exerted beneficially neuroprotective effect on H2 O2 -induced SH-SY5Y cells, mainly enhancing intracellular anti-oxidant enzyme activity and BDNF expression, inhibiting H2 O2 -induced oxidative stress as well as expression of Bax and activations of caspase-3 and caspase-9, alleviating H2 O2 -induced SH-SY5Y cell injury and cell death.