A novel HDAC6 inhibitor, CKD-504, is effective in treating preclinical models of huntington's disease.

Huntington's disease (HD) is a neurodegenerative disorder, of which pathogenesis is caused by a polyglutamine expansion in the amino-terminus of huntingtin gene that resulted in the aggregation of mutant HTT proteins. HD is characterized by progressive motor dysfunction, cognitive impairment and neuropsychiatric disturbances. Histone deacetylase 6 (HDAC6), a microtubule-associated deacetylase, has been shown to induce transport- and release-defect phenotypes in HD models, whilst treatment with HDAC6 inhibitors ameliorates the phenotypic effects of HD by increasing the levels of α-tubulin acetylation, as well as decreasing the accumulation of mutant huntingtin (mHTT) aggregates, suggesting HDAC6 inhibitor as a HD therapeutics. In this study, we employed in vitro neural stem cell (NSC) model and in vivo YAC128 transgenic (TG) mouse model of HD to test the effect of a novel HDAC6 selective inhibitor, CKD-504, developed by Chong Kun Dang (CKD Pharmaceutical Corp., Korea). We found that treatment of CKD-504 increased tubulin acetylation, microtubule stabilization, axonal transport, and the decrease of mutant huntingtin protein in vitro. From in vivo study, we observed CKD-504 improved the pathology of Huntington's disease: alleviated behavioral deficits, increased axonal transport and number of neurons, restored synaptic function in corticostriatal (CS) circuit, reduced mHTT accumulation, inflammation and tau hyperphosphorylation in YAC128 TG mouse model. These novel results highlight CKD-504 as a potential therapeutic strategy in HD. [BMB Reports 2023; 56(3): 178-183].

Neural Transplants From Human Induced Pluripotent Stem Cells Rescue the Pathology and Behavioral Defects in a Rodent Model of Huntington's Disease.

Huntington's disease (HD) is a devastating, autosomal-dominant inheritance disorder with the progressive loss of medium spiny neurons (MSNs) and corticostriatal connections in the brain. Cell replacement therapy has been proposed as a potential therapeutic strategy to treat HD. Among various types of stem cells, human-induced pluripotent stem cells (iPSCs) have received special attention to develop disease modeling and cell therapy for HD. In the present study, the therapeutic effects of neural precursor cells (NPCs) derived from a human iPSC line (1231A3-NPCs) were investigated in the quinolinic acid (QA)-lesioned rat model of HD. 1231A3-NPCs were transplanted into the ipsilateral striatum 1 week after QA lesioning, and the transplanted animals showed significant behavioral improvements for up to 12 weeks based on the staircase, rotarod, stepping, apomorphine-induced rotation, and cylinder tests. Transplanted 1231A3-NPCs also partially replaced the lost neurons, enhanced endogenous neurogenesis, reduced inflammatory responses, and reconstituted the damaged neuronal connections. Taken together, these results strongly indicate that NPCs derived from iPSCs can potentially be useful to treat HD in the future.

Neural stem cells derived from the developing forebrain of YAC128 mice exhibit pathological features of Huntington's disease.

OBJECTIVES: Huntington's disease (HD) is a devastating neurodegenerative disease caused by polyglutamine (polyQ) expansion in the huntingtin (HTT) gene. Mutant huntingtin (mHTT) is the main cause of HD and is associated with impaired mitochondrial dynamics, ubiquitin-proteasome system and autophagy, as well as tauopathy. In this study, we aimed to establish a new neural stem cell line for HD studies. MATERIALS AND METHODS: YAC128 mice are a yeast artificial chromosome (YAC)-based transgenic mouse model of HD. These mice express a full-length human mutant HTT gene with 128 CAG repeats and exhibit various pathophysiological features of HD. In this study, we isolated a new neural stem cell line from the forebrains of YAC128 mouse embryos (E12.5) and analysed its characteristics using cellular and biochemical methods. RESULTS: Compared to wild-type (WT) NSCs, the YAC128 NSC line exhibited greater proliferation and migration capacity. In addition to mHTT expression, increased intracellular Ca2+ levels and dysfunctional mitochondrial membrane potential were observed in the YAC128 NSCs. YAC128 NSCs had defects in mitochondrial dynamics, including a deficit in mitochondrial axonal transport and unbalanced fusion and fission processes. YAC128 NSCs also displayed decreased voltage response variability and Na+ current amplitude. Additionally, the ubiquitin-proteasome and autophagy systems were impaired in the YAC128 NSCs. CONCLUSIONS: We have established a new neural stem line from YAC128 transgenic mice, which may serve as a useful resource for studying HD pathogenesis and drug screening.

Human-to-mouse prion-like propagation of mutant huntingtin protein.

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder of the central nervous system (CNS) that is defined by a CAG expansion in exon 1 of the huntingtin gene leading to the production of mutant huntingtin (mHtt). To date, the disease pathophysiology has been thought to be primarily driven by cell-autonomous mechanisms, but, here, we demonstrate that fibroblasts derived from HD patients carrying either 72, 143 and 180 CAG repeats as well as induced pluripotent stem cells (iPSCs) also characterized by 143 CAG repeats can transmit protein aggregates to genetically unrelated and healthy host tissue following implantation into the cerebral ventricles of neonatal mice in a non-cell-autonomous fashion. Transmitted mHtt aggregates gave rise to both motor and cognitive impairments, loss of striatal medium spiny neurons, increased inflammation and gliosis in associated brain regions, thereby recapitulating the behavioural and pathological phenotypes which characterizes HD. In addition, both in vitro work using co-cultures of mouse neural stem cells with 143 CAG fibroblasts and the SH-SY5Y human neuroblastoma cell line as well as in vivo experiments conducted in newborn wild-type mice suggest that exosomes can cargo mHtt between cells triggering the manifestation of HD-related behaviour and pathology. This is the first evidence of human-to-mouse prion-like propagation of mHtt in the mammalian brain; a finding which will help unravel the molecular bases of HD pathology as well as to lead to the development of a whole new range of therapies for neurodegenerative diseases of the CNS.

Ghrelin stimulates proliferation, migration and differentiation of neural progenitors from the subventricular zone in the adult mice.

Ghrelin has been shown to regulate neurogenesis in the hippocampus. The aim of this study was to investigate the possible influence of ghrelin on cell proliferation and neuroblast formation in the subventricular zone (SVZ) and rostral migratory system (RMS) and generation of interneurons in the olfactory bulb (OB). We found that ghrelin receptors were expressed in the SVZ-RMS-OB system. Ghrelin knockout (GKO) mice have fewer proliferating neural progenitor cells and neuroblasts in the SVZ, while ghrelin administration attenuated these changes. We also found that not only the number of BrdU-labeled cells but also the fraction of migratory neuroblasts in the RMS was decreased in the GKO mice compared with controls. Treatment of GKO mice with ghrelin restored these numbers to the wild-type control values. Far fewer BrdU/NeuN double-labeled cells were found in the OB of GKO mice than in wild-type mice 4 weeks after labeling, which were increased by ghrelin replacement. GKO mice showed less numbers of BrdU/calbindin, BrdU/calretinin and BrdU/tyrosine hydroxylase double-labeled cells in the periglomerular layer of the OB. However, these numbers were increased to wild-type values after ghrelin administration. Finally, in the GH-deficient spontaneous dwarf rats, ghrelin increased the number of progenitor cells and neuroblasts in the SVZ, without significant effect on the differentiation in the OB. These findings suggest that ghrelin is involved in the regulation of proliferation of progenitor cells in the SVZ, the number of migratory neuroblasts in the SVZ, and the differentiation of interneurons in the OB.

Ghrelin-induced hippocampal neurogenesis and enhancement of cognitive function are mediated independently of GH/IGF-1 axis: lessons from the spontaneous dwarf rats.

We recently have reported that ghrelin modulates adult hippocampal neurogenesis. However, there is a possibility that the action of ghrelin on hippocampal neurogenesis could be, in part, due to the ability of ghrelin to stimulate the GH/insulin-like growth factor (IGF)-1 axis, where both GH and IGF-1 infusions are known to increase hippocampal neurogenesis. To explore this possibility, we assessed the impact of ghrelin on progenitor cell proliferation and differentiation in the dentate gyrus (DG) of spontaneous dwarf rats (SDRs), a dwarf strain with a mutation of the GH gene resulting in total loss of GH. Double immunohistochemical staining revealed that Ki-67-positive progenitor cells and doublecortin (DCX)-positive neuroblasts in the DG of the SDRs expressed ghrelin receptors. We found that ghrelin treatment in the SDRs significantly increased the number of proliferating cell nuclear antigen- and BrdU-labeled cells in the DG. The number of DCX-labeled cells in the DG of ghrelin-treated SDRs was also significantly increased compared with the vehicle-treated controls. To test whether ghrelin has a direct effect on cognitive performance independently of somatotropic axis, hippocampus-dependent learning and memory were assessed using the Y-maze and novel object recognition (NOR) test in the SDRs. Ghrelin treatment for 4 weeks by subcutaneous osmotic pump significantly increased alternation rates in the Y-maze and exploration time for novel object in the NOR test compared to vehicle-treated controls. Our results indicate that ghrelin-induced adult hippocampal neurogenesis and enhancement of cognitive function are mediated independently of somatotropic axis.

Multiple signaling pathways mediate ghrelin-induced proliferation of hippocampal neural stem cells.

Ghrelin, an endogenous ligand for the GH secretagogue receptor (GHS-R) receptor 1a (GHS-R1a), has been implicated in several physiologic processes involving the hippocampus. The aim of this study was to investigate the molecular mechanisms of ghrelin-stimulated neurogenesis using cultured adult rat hippocampal neural stem cells (NSCs). The expression of GHS-R1a was detected in hippocampal NSCs, as assessed by western blot analysis and immunocytochemistry. Ghrelin treatment increased the proliferation of cultured hippocampal NSCs assessed by BrdU incorporation. The exposure of cells to the receptor-specific antagonist d-Lys-3-GHRP-6 abolished the proliferative effect of ghrelin. By contrast, ghrelin showed no significant effect on cell differentiation. The expression of GHS-R1a was significantly increased by ghrelin treatment. The analysis of signaling pathways showed that ghrelin caused rapid activation of ERK1/2 and Akt, which were blocked by the GHS-R1a antagonist. In addition, ghrelin stimulated the phosphorylation of Akt downstream effectors, such as glycogen synthase kinase (GSK)-3ß, mammalian target of rapamycin (mTOR), and p70(S6K). The activation of STAT3 was also caused by ghrelin treatment. Furthermore, pretreatment of cells with specific inhibitors of MEK/ERK1/2, phosphatidylinositol-3-kinase (PI3K)/Akt, mTOR, and Jak2/STAT3 attenuated ghrelin-induced cell proliferation. Taken together, our results support a role for ghrelin in adult hippocampal neurogenesis and suggest the involvement of the ERK1/2, PI3K/Akt, and STAT3 signaling pathways in the mediation of the actions of ghrelin on neurogenesis. Our data also suggest that PI3K/Akt-mediated inactivation of GSK-3ß and activation of mTOR/p70(S6K) contribute to the proliferative effect of ghrelin.

Ghrelin directly stimulates adult hippocampal neurogenesis: implications for learning and memory.

Adult hippocampal neurogenesis is important in mediating hippocampal-dependent learning and memory. Exogenous ghrelin is known to stimulate progenitor cell proliferation in the dentate gyrus of adult hippocampus. The aim of this study was to investigate the role of endogenous ghrelin in regulating the in vivo proliferation and differentiation of the newly generating cells in the adult hippocampus using ghrelin knockout (GKO) mice. Targeted deletion of ghrelin gene resulted in reduced numbers of progenitor cells in the subgranular zone (SGZ) of the hippocampus, while ghrelin treatment restored progenitor cell numbers to those of wild-type controls. We also found that not only the number of bromodeoxyuridine (BrdU)-positive cells but also the fraction of immature neurons and newly generated neurons were decreased in the GKO mice, which were increased by ghrelin replacement. Additionally, in the GKO mice, we observed impairment of memory performance in Y-maze task and novel object recognition test. However, these functional deficiencies were attenuated by ghrelin administration. These results suggest that ghrelin directly induces proliferation and differentiation of adult neural progenitor cells in the SGZ. Our data suggest ghrelin may be a plausible therapeutic potential to enhance learning and memory processes.

Insulin-like growth factor-1 inhibits 6-hydroxydopamine-mediated endoplasmic reticulum stress-induced apoptosis via regulation of heme oxygenase-1 and Nrf2 expression in PC12 cells.

Endoplasmic reticulum (ER) stress and oxidative stress appear to play a critical role in the progression of Parkinson's disease (PD). Insulin-like growth factor (IGF)-1, a 70-amino acid polypeptide trophic factor, acts as a potent neurotrophic, neurogenic, and neuroprotective/anti-apoptotic factor. In this study, we investigated the protective mechanisms of IGF-1 in rat pheochromocytoma PC12 cells exposed to the PD-related neurotoxin 6-hydroxydopamine (6-OHDA). The transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) coordinates expression of genes required for free radical scavenging, detoxification of xenobiotics, and maintenance of redox potential. Exposure of cells to 6-OHDA resulted in an increase in ER-stress-induced apoptotic cell death, which was significantly reduced by treatment of cells with IGF-1. IGF-1 treatment significantly increased BiP and C/EBP homologous protein expression in 6-OHDA-treated cultures. IGF-1 protected cells from 6-OHDA-induced insult by inhibiting intracellular reactive oxygen species generation. Compared with vehicle-treated controls, the expression of Nrf2 and heme oxygenase-1 (HO-1) was increased in 6-OHDA-treated cells. IGF-1 significantly up-regulated HO-1 in cells exposed to 6-OHDA. These results suggest that IGF-1 augment cellular anti-oxidant defense mechanism, at least in part, through the up-regulation of HO-1 expression.

Ghrelin protects spinal cord motoneurons against chronic glutamate excitotoxicity by inhibiting microglial activation.

Glutamate excitotoxicity is emerging as a contributor to degeneration of spinal cord motoneurons in amyotrophic lateral sclerosis (ALS). Recently, we have reported that ghrelin protects motoneurons against chronic glutamate excitotoxicity through the activation of extracellular signal-regulated kinase 1/2 and phosphatidylinositol-3-kinase/Akt/glycogen synthase kinase-3ß pathways. Previous studies suggest that activated microglia actively participate in the pathogenesis of ALS motoneuron degeneration. However, it is still unknown whether ghrelin exerts its protective effect on motoneurons via inhibition of microglial activation. In this study, we investigate organotypic spinal cord cultures (OSCCs) exposed to threohydroxyaspartate (THA), as a model of excitotoxic motoneuron degeneration, to determine if ghrelin prevents microglial activation. Exposure of OSCCs to THA for 3 weeks produced typical motoneuron death, and treatment of ghrelin significantly attenuated THA-induced motoneuron loss, as previously reported. Ghrelin prevented THA-induced microglial activation in the spinal cord and the expression of pro-inflammatory cytokines tumor necrosis factor-α and interleukin-1ß. Our data indicate that ghrelin may act as a survival factor for motoneurons by functioning as a microglia-deactivating factor and suggest that ghrelin may have therapeutic potential for the treatment of ALS and other neurodegenerative disorders where inflammatory responses play a critical role.

Ghrelin protects spinal cord motoneurons against chronic glutamate-induced excitotoxicity via ERK1/2 and phosphatidylinositol-3-kinase/Akt/glycogen synthase kinase-3ß pathways.

Excitotoxic degeneration of spinal cord motoneurons has been proposed as a pathogenic mechanism in amyotrophic lateral sclerosis (ALS). Recently, we have reported that ghrelin, an endogenous ligand for growth hormone secretagogue receptor (GHS-R) 1a, functions as a neuroprotective factor in various animal models of neurodegenerative diseases. In this study, the potential neuroprotective effects of ghrelin against chronic glutamate-induced cell death were studied by exposing organotypic spinal cord cultures (OSCC) to threohydroxyaspartate (THA), as a model of excitotoxic motoneuron degeneration. Ghrelin receptor was expressed on spinal cord motoneurons. Exposure of OSCC to THA for 3 weeks resulted in a significant loss of motoneurons. However, THA-induced loss of motoneurons was significantly reduced by treatment of ghrelin. Exposure of OSCC to the receptor-specific antagonist D-Lys-3-GHRP-6 abolished the protective effect of ghrelin against THA. Treatment of spinal cord cultures with ghrelin caused rapid phosphorylation of extracellular signal-regulated kinase 1/2, Akt, and glycogen synthase kinase-3ß (GSK-3ß). The effect of ghrelin on motoneuron survival was blocked by the MEK inhibitor PD98059 and the phosphatidylinositol-3-kinase (PI3K) inhibitor LY294002. Taken together, these findings indicate that ghrelin has neuroprotective effects against chronic glutamate toxicity by activating the MAPK and PI3K/Akt signaling pathways and suggest that administration of ghrelin may have the potential therapeutic value for the prevention of motoneuron degeneration in human ALS. Our data also suggest that PI3K/Akt-mediated inactivation of GSK-3ß in motoneurons contributes to the protective effect of ghrelin.

Hippocampus-dependent spatial learning and memory are impaired in growth hormone-deficient spontaneous dwarf rats.

Growth hormone (GH)/insulin-like growth factor-I deficiencies are known to cause alterations in brain development resulting in impairment of cognitive function. In order to investigate the behavioral phenotype of GH-deficient spontaneous dwarf rats (SDRs), we examined the behavior of the SDRs in the Morris water maze and Y-maze tasks. The SDRs showed severe deficits in spatial learning and memory compared to normal rats. The possibility that the cognitive impairment is associated with alteration of neurotransmitter systems was examined histologically following completion of the behavioral tests, using choline acetyltransferase (ChAT), vesicular glutamate transporter 1 (VGlut1) and glutamic acid decarboxylase (GAD6) immunohistochemistry as markers. In the SDRs the number of ChAT-stained basal forebrain cholinergic neurons was decreased. ChAT staining was also decreased in the hippocampus, one of the target areas of basal forebrain cholinergic neurons. Next, we examined the number of glutamatergic and GABAergic boutons in the hippocampal molecular layer and found a significant reduction in the density of VGlut1+ boutons and an increase in GAD6+ profiles, leading to a significantly reduced ratio in glutamatergic/GABAergic synapses. Finally, the number of newly generated cells in the subgranular zone of the hippocampus was significantly lower than in normal rats. Taken together, our data suggest that GH is an important regulator of hippocampus-dependent spatial learning and memory. The behavioral deficits in the SDRs may be explained by altered basal forebrain cholinergic innervation, imbalance in hippocampal glutamatergic/GABAergic synapses, and decreased neurogenesis in the hippocampus.

Ghrelin attenuates kainic acid-induced neuronal cell death in the mouse hippocampus.

Ghrelin is an endogenous ligand for GH secretagogue receptor type 1a (GHSR1a), and is produced and released mainly from the stomach. It has been recently demonstrated that ghrelin can function as a neuroprotective factor by inhibiting apoptotic pathways. Kainic acid (KA), an excitatory amino acid l-glutamate analog, causes neuronal death in the hippocampus; previous studies suggest that activated microglia and astrocytes actively participate in the pathogenesis of KA-induced hippocampal neurodegeneration. However, it is unclear whether ghrelin has neuroprotective effect in KA-induced hippocampal neurodegeneration. I.p. injection of KA produced typical neuronal cell death in the CA1 and CA3 pyramidal layers of the hippocampus, and the systemic administration of ghrelin significantly attenuated KA-induced neuronal cell death in these regions through the activation of GHSR1a. Ghrelin prevents KA-induced activation of microglia and astrocytes, and the expression of proinflammatory mediators tumor necrosis factor alpha, interleukin-1beta, and cyclooxygenase-2. The inhibitory effect of ghrelin on the activation of microglia and astrocytes appears to be associated with the inhibition of matrix metalloproteinase-3 expression in damaged hippocampal neurons. Our data suggest that ghrelin has a therapeutic potential for suppressing KA-induced pathogenesis in the brain.