Mesencephalic astrocyte-derived neurotrophic factor (MANF) has a unique mechanism to rescue apoptotic neurons

Mesencephalic astrocyte-derived neurotrophic factor prevents neuron loss via inhibiting ischemia-induced apoptosis

Mesencephalic astrocyte-derived neurotrophic factor (MANF) has been shown to be up-regulated under the focal cerebral ischemia and protected against ischemic injury in rats. However, the underlying mechanisms are unclear. The aim of this study was to verify the protection of MANF on the cerebral ischemic injury and further investigate the possible mechanisms. Rat focal ischemic model was established by middle cerebral artery occlusion (MCAO). The recombinant human MANF was therapeutically administrated to the ipsilateral ventricle at 2 h after MCAO. MANF decreased the number of the propidium iodide (PI)- and TUNEL-positive neural cells. Contrarily, MANF protected the NeuN-positive cells in hippocampus and cortex from death induced by ischemia. The more interesting results in this study were that MANF repressed the cleavage of caspase-3 triggered by focal cerebral ischemia. MANF also reduced the elevated levels of BIP/Grp78, phosphorylated IRE1, and splicing XBP1 induced by focal cerebral ischemia, but not affect CHOP expression. Meanwhile, focal cerebral ischemia elevated the levels of XBP1 mRNA, including unspliced XBP1 (XBP1u) and spliced XBP1 (XBP1s). However, MANF did not affect the expression of XBP1 mRNA, neither XBP1u nor XBP1s. These results suggest that MANF can prevent the neuron loss via inhibiting ischemia-induced apoptosis and regulating unfolded protein response-related genes.

MANF is indispensable for the proliferation and survival of pancreatic β cells

All forms of diabetes mellitus (DM) are characterized by the loss of functional pancreatic β cell mass, leading to insufficient insulin secretion. Thus, identification of novel approaches to protect and restore β cells is essential for the development of DM therapies. Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an endoplasmic reticulum (ER)-stress-inducible protein, but its physiological role in mammals has remained obscure. We generated MANF-deficient mice that strikingly develop severe diabetes due to progressive postnatal reduction of β cell mass, caused by decreased proliferation and increased apoptosis. Additionally, we show that lack of MANF in vivo in mouse leads to chronic unfolded protein response (UPR) activation in pancreatic islets. Importantly, MANF protein enhanced β cell proliferation in vitro and overexpression of MANF in the pancreas of diabetic mice enhanced β cell regeneration. We demonstrate that MANF specifically promotes β cell proliferation and survival, thereby constituting a therapeutic candidate for β cell protection and regeneration.

Age-dependent decrease in chaperone activity impairs MANF expression, leading to Purkinje cell degeneration in inducible SCA17 mice

Although protein-misfolding-mediated neurodegenerative diseases have been linked to aging, how aging contributes to selective neurodegeneration remains unclear. We established spinocerebellar ataxia 17 (SCA17) knockin mice that inducibly express one copy of mutant TATA box binding protein (TBP) at different ages by tamoxifen-mediated Cre recombination. We find that more mutant TBP accumulates in older mouse and that this accumulation correlates with age-related decreases in Hsc70 and chaperone activity. Consistently, older SCA17 mice experienced earlier neurological symptom onset and more severe Purkinje cell degeneration. Mutant TBP shows decreased association with XBP1s, resulting in the reduced transcription of mesencephalic astrocyte-derived neurotrophic factor (MANF), which is enriched in Purkinje cells. Expression of Hsc70 improves the TBP-XBP1s interaction and MANF transcription, and overexpression of MANF ameliorates mutant TBP-mediated Purkinje cell degeneration via protein kinase C (PKC)-dependent signaling. These findings suggest that the age-related decline in chaperone activity affects polyglutamine protein function that is important for the viability of specific types of neurons.

Spatiotemporal expression of MANF in the developing rat brain

Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an evolutionarily conserved neurotrophic factor which exhibited neuroprotective properties. Recent studies suggested that MANF may play a role in the neural development of Drosophila and zebra fishes. In this study, we investigated the spatiotemporal expression of MANF in the brain of postnatal and adult rats. MANF expression appeared wide spread and mainly localized in neurons. In the cerebral cortex, neurons in layer IV and VI displayed particularly strong MANF immunoreactivity. In the hippocampus, intensive MANF expression was observed throughout the subfields of Cornu Amonis (CA1, CA2, and CA3) and the granular layer of the dentate gyrus (DG). In the substantia nigra, high MANF expression was shown in the substantia nigra pars compacta (SNpc). In the thalamus, the anterodorsal thalamic nucleus (ADTN) exhibited the highest MANF immunoreactivity. In the hypothalamus, intensive MANF immunoreactivity was shown in the supraoptic nucleus (SON) and tuberomammillary nucleus (TMN). In the cerebellum, MANF was localized in the external germinal layer (EGL), Purkinje cell layer (PCL), internal granule layer (IGL) and the deep cerebellar nuclei (DCN). We examined the developmental expression of MANF on postnatal day (PD) 3, 5, 7, 9, 15, 21, 30 and adulthood. In general, the levels of MANF were high in the early PDs (PD3 and PD5), and declined gradually as the brain matured; MANF expression in the adult brain was the lowest among all time points examined. However, in some structures, such as PCL, IGL, SON, TMN and locus coeruleus (LC), high expression of MANF sustained throughout the postnatal period and persisted into adulthood. Our results indicated that MANF was developmentally regulated and may play a role in the maturation of the central nervous system (CNS).

Characterization of the structural and functional determinants of MANF/CDNF in Drosophila in vivo model

Mammalian MANF and CDNF proteins are evolutionarily conserved neurotrophic factors that can protect and repair mammalian dopaminergic neurons in vivo. In Drosophila, the sole MANF protein (DmManf) is needed for the maintenance of dopaminergic neurites and dopamine levels. Although both secreted and intracellular roles for MANF and CDNF have been demonstrated, very little is known about the molecular mechanism of their action. Here, by using a transgenic rescue approach in the DmManf mutant background we show that only full-length MANF containing both the amino-terminal saposin-like and carboxy-terminal SAP-domains can rescue the larval lethality of the DmManf mutant. Independent N- or C-terminal domains of MANF, even when co-expressed together, fail to rescue. Deleting the signal peptide or mutating the CXXC motif in the C-terminal domain destroys the activity of full-length DmManf. Positively charged surface amino acids and the C-terminal endoplasmic reticulum retention signal are necessary for rescue of DmManf mutant lethality when DmManf is expressed in a restricted pattern. Furthermore, rescue experiments with non-ubiquitous expression reveals functional differences between the C-terminal domain of human MANF and CDNF. Finally, DmManf and its C-terminal domain rescue mammalian sympathetic neurons from toxin-induced apoptosis in vitro demonstrating functional similarity of the mammalian and fly proteins. Our study offers further insights into the functional conservation between invertebrate and mammalian MANF/CDNF proteins and reveals the importance of the C-terminal domain for MANF activity in vivo.

Reversal of dopamine neurons and locomotor ability degeneration in aged rats with smilagenin

The purpose of this paper is to study the effect of smilagenin (SMI) (PYM50028), a sapogenin compound originally identified from Chinese medicinal herb, on dopamine neurons and locomotor ability in aged rats. Experiments were carried out on young and aged Sprague-Dawley rats, which were daily administered with either SMI (18mg/kg/day) or vehicle (0.5% sodium carboxymethycellulose [CMCNa]). Open-field and rotarod performance tests revealed that behavioral ability was impaired in aged rats and was improved by oral administration of smilagenin. Immunohistochemical data showed that tyrosine hydroxylase (TH)-positive neuron numbers in the substantia nigra pars compacta (unbiased stereological counting) were altered with aging and were increased by smilagenin treatment. Likewise, the dopamine receptor density and the striatal dopamine transporter (DAT) density ((125)I-2β-carbomethoxy-3β-(4-iodophenyl)-N-(3-fluoropropyl) nortropane [(125)I-FP-CIT] autoradiography) were significantly lowered in aged rats as compared to young rats, and treatment with smilagenin significantly elevated the dopamine receptor and DAT density in aged rats. Furthermore, smilagenin enhances glial cell-derived neurotrophic factor (GDNF) release both in the striatum and midbrain. These results indicate a possible role of smilagenin in the treatment of age-related extrapyramidal disorders.

Gene therapy with AAV2-CDNF provides functional benefits in a rat model of Parkinson's disease

Cerebral dopamine neurotrophic factor (CDNF) protein has been shown to protect the nigrostriatal dopaminergic pathway when given as intrastriatal infusions in rat and mouse models of Parkinson's disease (PD). In this study, we assessed the neuroprotective effect of CDNF delivered with a recombinant adeno-associated viral (AAV) serotype 2 vector in a rat 6-hydroxydopamine (6-OHDA) model of PD. AAV2 vectors encoding CDNF, glial cell line-derived neurotrophic factor (GDNF), or green fluorescent protein were injected into the rat striatum. Protein expression analysis showed that our AAV2 vector efficiently delivered the neurotrophic factor genes into the brain and gave rise to a long-lasting expression of the proteins. Two weeks after AAV2 vector injection, 6-OHDA was injected into the rat striatum, creating a progressive degeneration of the nigrostriatal dopaminergic system. Treatment with AAV2-CDNF resulted in a marked decrease in amphetamine-induced ipsilateral rotations while it provided only partial protection of tyrosine hydroxylase (TH)-immunoreactive cells in the rat substantia nigra pars compacta and TH-reactive fibers in the striatum. Results from this study provide additional evidence that CDNF can be considered a potential treatment of Parkinson's disease.

Mesencephalic astrocyte-derived neurotrophic factor (MANF) secretion and cell surface binding are modulated by KDEL receptors

Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an endoplasmic reticulum (ER) stress-responsive protein with neuroprotective effects in animal models of neurodegeneration, but the underlying mechanism is not understood. We constructed a set of lentiviral vectors that contain or lack the highly conserved final four amino acids of MANF ("RTDL"), which resemble the canonical ER retention signal ("KDEL"), to study MANF regulation in neuroblastoma cells and rat primary cortical neurons. The RTDL sequence was required for both ER retention and secretory response to ER stress. Overexpression of KDEL receptor paralogs (KDELRs) differentially reduced MANF secretion but had no effect on MANF lacking RTDL. MANF binding to the plasma membrane also required the RTDL sequence and was inhibited with a peptide known to interact with KDELRs, suggesting MANF binds KDELRs at the surface. We detected surface localization of FLAG-tagged KDELRs, with levels increasing following ER stress. Our study provides new insight into the regulation of MANF trafficking and has implications for other secreted proteins containing a KDEL-like retention signal.

Upregulation of mesencephalic astrocyte-derived neurotrophic factor in glial cells is associated with ischemia-induced glial activation

Background

Mesencephalic astrocyte-derived neurotrophic factor (MANF), a 20 kDa secreted protein, was originally derived from a rat mesencephalic type-1 astrocyte cell line. MANF belongs to a novel evolutionally conserved family of neurotrophic factors along with conserved dopamine neurotrophic factor. In recent years, ever-increasing evidence has shown that both of them play a remarkable protective role against various injuries to neurons in vivo or in vitro. However, the characteristics of MANF expression in the different types of glial cells, especially in astrocytes, remain unclear.

Methods

The model of focal cerebral ischemia was induced by rat middle cerebral artery occlusion. Double-labeled immunofluorescent staining was used to identify the types of neural cells expressing MANF. Primarily cultured glial cells were used to detect the response of glial cells to endoplasmic reticulum stress stimulation. Propidium iodide staining was used to determine dead cells. Reverse transcription PCR and western blotting were used to detect the levels of mRNA and proteins.

Results

We found that MANF was predominantly expressed in neurons in both normal and ischemic cortex. Despite its name, MANF was poorly expressed in glial cells, including astrocytes, in normal brain tissue. However, the expression of MANF was upregulated in the glial cells under focal cerebral ischemia, including the astrocytes. This expression was also induced by several endoplasmic reticulum stress inducers and nutrient deprivation in cultured primary glial cells. The most interesting phenomenon observed in this study was the pattern of MANF expression in the microglia. The expression of MANF was closely associated with the morphology and state of microglia, accompanied by the upregulation of BIP/Grp78.

Conclusions

These results indicate that MANF expression was upregulated in the activated glial cells, which may contribute to the mechanism of ischemia-induced neural injury.

MANF regulates dopaminergic neuron development in larval zebrafish

Mesencephalic astrocyte derived neurotrophic factor (MANF) is recognized as a dopaminergic neurotrophic factor, which can protect dopaminergic neurons from neurotoxic damage. However, little is known about the function of MANF during the vertebrate development. Here, we report that MANF expression is widespread during embryonic development and in adult organs analyzed by qPCR and in situ hybridization in zebrafish. Knockdown of MANF expression with antisense splice-blocking morpholino oligonucleotides resulted in no apparent abnormal phenotype. Nevertheless, the dopamine level of MANF morphants was lower than that of the wild type larvae, the expression levels of the two tyrosine hydroxylase gene transcripts were decreased and a decrease in neuron number in certain groups of th1 and th2 cells in the diencephalon region in MANF morphants was observed. These defects were rescued by injection of exogenous manf mRNA. Strikingly, manf mRNA could partly restore the decrease of th1 positive cells in Nr4a2-deficient larvae. These results suggest that MANF is involved in the regulation of the development of dopaminergic system in zebrafish.

Zonisamide up-regulated the mRNAs encoding astrocytic anti-oxidative and neurotrophic factors

Zonisamide has been proven as an effective drug for the recovery of degenerating dopaminergic neurons in the animal models of Parkinson's disease. However, several lines of evidence have questioned the neuroprotective capacity of zonisamide in animal models of Parkinson's disease. Although it suppresses dopaminergic neurodegeneration in animal models, the cellular and molecular mechanisms underlying the effectiveness of zonisamide are not fully understood. The current study demonstrates the effects of zonisamide on astrocyte cultures and two 6-hydroxydopamine-induced models of Parkinson's disease. Using primary astrocyte cultures, we showed that zonisamide up-regulated the expression of mRNA encoding mesencephalic astrocyte-derived neurotrophic factor, vascular endothelial growth factor, proliferating cell nuclear antigen, metallothionein-2, copper/zinc superoxide dismutase, and manganese superoxide dismutase. Similar responses to zonisamide were found in substantia nigra where the rats were pre-treated with 6-hydroxydopamine. Notably, pharmacological inhibition of 6-hydroxydopamine-induced toxicity by zonisamide pre-treatment was also confirmed using rat mesencephalic organotypic slice cultures of substantia nigra. In addition to this, zonisamide post-treatment also attenuated the nigral tyrosine hydroxylase-positive neuronal loss induced by 6-hydroxydopamine. Taken together, these studies demonstrate that zonisamide protected dopamine neurons in two Parkinson's disease models through a novel mechanism, namely increasing the expression of some important astrocyte-mediated neurotrophic and anti-oxidative factors.

Gene expression analysis of Drosophilaa Manf mutants reveals perturbations in membrane traffic and major metabolic changes

BACKGROUND

MANF and CDNF are evolutionarily conserved neurotrophic factors that specifically support dopaminergic neurons. To date, the receptors and signalling pathways of this novel MANF/CDNF family have remained unknown. Independent studies have showed upregulation of MANF by unfolded protein response (UPR). To enlighten the role of MANF in multicellular organism development we carried out a microarray-based analysis of the transcriptional changes induced by the loss and overexpression of Drosophila Manf.

RESULTS

The most dramatic change of expression was observed with genes coding membrane transport proteins and genes related to metabolism. When evaluating in parallel the ultrastructural data and transcriptome changes of maternal/zygotic and only zygotic Manf mutants, the endoplasmic reticulum (ER) stress and membrane traffic alterations were evident. In Drosophila Manf mutants the expression of several genes involved in Parkinson's disease (PD) was altered as well.

CONCLUSIONS

We conclude that besides a neurotrophic factor, Manf is an important cellular survival factor needed to overcome the UPR especially in tissues with high secretory function. In the absence of Manf, the expression of genes involved in membrane transport, particularly exocytosis and endosomal recycling pathway was altered. In neurodegenerative diseases, such as PD, correct protein folding and proteasome function as well as neurotransmitter synthesis and uptake are crucial for the survival of neurons. The degeneration of dopaminergic neurons is the hallmark for PD and our work provides a clue on the mechanisms by which the novel neurotrophic factor MANF protects these neurons.

Intracellular trafficking and secretion of mouse mesencephalic astrocyte-derived neurotrophic factor

Recently, mesencephalic astrocyte-derived neurotrophic factor (MANF) has been reported to prevent cell death under some pathophysiological conditions. MANF, also referred to as arginine rich, mutated in early stage of tumors (Armet), was identified as an endoplasmic reticulum (ER) stress-inducible factor. Using RT-PCR, we found two variants of MANF mRNA: wild type, which contains exon 1 (wt-MANF), and one lacking exon 1, which is presumably not secreted (ΔΝ-MANF) in Neuro2a cells. The latter has a putative translational start site upstream of the second exon in the mouse MANF gene. Comparing the expression of wt-MANF with that of ΔΝ-MANF, we found that the amount of intracellular ΔΝ-MANF was much lower than that of wt-MANF. Furthermore, ΔΝ-MANF was not detected in the culture medium after its transient transfection into Neuro2a cells. Deletion of several α-helices of mouse MANF decreased its intracellular stability and secretion. Secretion of wt-MANF was almost completely inhibited by either treatment with brefeldin A (BFA), which disrupts the Golgi apparatus structure, or overexpression of a dominant negative Sar1 (Sar1[H79G]), which is reported to impair COPII-mediated transport from the ER to the Golgi apparatus. In addition, the enforced expression of glucose-regulated protein 78 kDa (GRP78) attenuated the secretion of wt-MANF and led to its intracellular accumulation. MANF lacking the four C-terminal amino acids (ΔC-MANF) accumulated at low levels in the cells, but its intracellular level was increased by GRP78 overexpression. The amount of ΔC-MANF in the culture medium was partially down-regulated after co-transfection of GRP78. Substitution of the amino acids RTDL at the C-terminus of mouse MANF with KDEL, the canonical ER localization signal in GRP78, markedly decreased MANF secretion and its secretion was further attenuated by GRP78 overexpression. Taken together, our data show that the secretion of MANF is regulated via COPII-mediated transport and that its C-terminus could be responsible for its retention in the ER through GRP78. The alternate isotype, ΔΝ-MANF, may be less stable in cells than wt-MANF and may not be secreted extracellularly.

The preclinical discovery of amyotrophic lateral sclerosis drugs

INTRODUCTION

Amyotrophic lateral sclerosis (ALS), also referred to as Lou Gehrig's disease, is characterized by the progressive loss of cells in the brain and spinal cord that leads to debilitation and death in 3 - 5 years. Only one therapeutic drug, riluzole, has been approved for ALS and this drug improves survival by 2 - 3 months. The need for new therapeutics that can postpone or slow the progression of the motor deficits and prolong survival is still a strong unmet medical need.

AREAS COVERED

Although there are a number of drugs currently in clinical trials for ALS, this review provides an overview of the most promising biological targets and preclinical strategies that are currently being developed and deployed. The list of targets for ALS was compiled from a variety of websites including individual companies that have ALS programs and include those from the author's experience.

EXPERT OPINION

Progress is being made in the identification of possible new therapeutics for ALS with recent efforts in understanding the genetic causes of the disease, susceptibility factors and the development of additional preclinical animal models. However, many challenges remain in the identification of new ALS therapeutics including: the use of relevant biomarkers, the need for an earlier diagnosis of the disease and additional animal models. Multiple strategies need to be tested in the clinic in order to determine what will be effective in patients.

CDNF protects the nigrostriatal dopamine system and promotes recovery after MPTP treatment in mice

Cerebral dopamine neurotrophic factor (CDNF) is a recently discovered protein, which belongs to the evolutionarily conserved CDNF/MANF family of neurotrophic factors. The degeneration of dopamine neurons following 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment is well characterized, and efficacy in this model is considered a standard criterion for development of parkinsonian therapies. MPTP is a neurotoxin, which produces parkinsonian symptoms in humans and in C57/Bl6 mice. To date, there are no reports about the effects of CDNF on dopamine neuron survival or function in the MPTP rodent model, a critical gap. Therefore, we studied whether CDNF has neuroprotective and neurorestorative properties for the nigrostriatal dopamine system after MPTP injections in C57/Bl6 mice. We found that bilateral striatal CDNF injections, given 20 h before MPTP, improved horizontal and vertical motor behavior. CDNF pretreatment increased tyrosine hydroxylase (TH) immunoreactivity in the striatum and in the substantia nigra pars reticulata (SNpr), as well as the number of TH-positive cells in substantia nigra pars compacta (SNpc). Posttreatment with CDNF, given 1 week after MPTP injections, increased horizontal and vertical motor behavior of mice, as well as dopamine fiber densities in the striatum and the number of TH-positive cells in SNpc. CDNF did not alter any of the analyzed dopaminergic biomarkers or locomotor behavior in MPTP-untreated animals. We conclude that striatal CDNF administration is both neuroprotective and neurorestorative for the TH-positive cells in the nigrostriatal dopamine system in the MPTP model, which supports the development of CDNF-based treatment for Parkinson's disease.

Chronic infusion of CDNF prevents 6-OHDA-induced deficits in a rat model of Parkinson's disease

Cerebral dopamine neurotrophic factor (CDNF) and mesencephalic astrocyte-derived neurotrophic factor (MANF) constitute a novel, evolutionarily conserved family of neurotrophic factors (NTF) expressed in vertebrates and invertebrates. The effects of two-week infusions of CDNF, MANF and glial cell line-derived neurotrophic factor (GDNF) were studied in a rat 6-hydroxydopamine (6-OHDA) hemiparkinsonian model. Degeneration of nigrostriatal dopamine nerve tract after toxin injection was assessed by measuring amphetamine-induced rotational behavior, and at the end of the experiment by quantifying tyrosine hydroxylase (TH)-positive neurons in the substantia nigra pars compacta (SNpc) and TH-positive fibers in the striatum. The diffusion of the NTFs into the brain tissue following chronic infusion was also studied. Finally, we examined the transportation of intrastriatally injected (125)I-CDNF within the brain. The amphetamine-induced rotational behavior was gradually normalized in rats treated with CDNF for two weeks following the intrastriatal 6-OHDA injection. CDNF was also able to inhibit 6-OHDA-induced loss of TH-immunoreactive cells of the SNpc and TH-positive fibers in the striatum. MANF and GDNF had no statistically significant effect in any of the above measures. The volume of distribution for MANF in the striatum was significantly larger than that of GDNF after 3-day infusions. Both (125)I-CDNF and (125)I-GDNF were retrogradely transported from the striatum to the SN. No behavioral signs of toxicity were observed during treatment with the three NTFs. These results imply that CDNF may have potential as a neuroprotective or even neurorestorative therapy of PD.