Selenium-SelK-GPX4 axis protects nucleus pulposus cells against mechanical overloading-induced ferroptosis and attenuates senescence of intervertebral disc.

Intervertebral disc degeneration (IVDD) is one of the most prevalent spinal degenerative disorders and imposes places heavy medical and economic burdens on individuals and society. Mechanical overloading applied to the intervertebral disc (IVD) has been widely recognized as an important cause of IVDD. Mechanical overloading-induced chondrocyte ferroptosis was reported, but the potential association between ferroptosis and mechanical overloading remains to be illustrated in nucleus pulposus (NP) cells. In this study, we discovered that excessive mechanical loading induced ferroptosis and endoplasmic reticulum (ER) stress, which were detected by mitochondria and associated markers, by increasing the intracellular free Ca2+ level through the Piezo1 ion channel localized on the plasma membrane and ER membrane in NP cells. Besides, we proposed that intracellular free Ca2+ level elevation and the activation of ER stress are positive feedback processes that promote each other, consistent with the results that the level of ER stress in coccygeal discs of aged Piezo1-CKO mice were significantly lower than that of aged WT mice. Then, we confirmed that selenium supplementation decreased intracellular free Ca2+ level by mitigating ER stress through upregulating Selenoprotein K (SelK) expression. Besides, ferroptosis caused by the impaired production and function of Glutathione peroxidase 4 (GPX4) due to mechanical overloading-induced calcium overload could be improved by selenium supplementation through Se-GPX4 axis and Se-SelK axis in vivo and in vitro, eventually presenting the stabilization of the extracellular matrix (ECM). Our findings reveal the important role of ferroptosis in mechanical overloading-induced IVDD, and selenium supplementation promotes significance to attenuate ferroptosis and thus alleviates IVDD, which might provide insights into potential therapeutic interventions for IVDD.

The MT1 receptor as the target of ramelteon neuroprotection in ischemic stroke.

Stroke is the leading cause of death and disability worldwide. Novel and effective therapies for ischemic stroke are urgently needed. Here, we report that melatonin receptor 1A (MT1) agonist ramelteon is a neuroprotective drug candidate as demonstrated by comprehensive experimental models of ischemic stroke, including a middle cerebral artery occlusion (MCAO) mouse model of cerebral ischemia in vivo, organotypic hippocampal slice cultures ex vivo, and cultured neurons in vitro; the neuroprotective effects of ramelteon are diminished in MT1-knockout (KO) mice and MT1-KO cultured neurons. For the first time, we report that the MT1 receptor is significantly depleted in the brain of MCAO mice, and ramelteon treatment significantly recovers the brain MT1 losses in MCAO mice, which is further explained by the Connectivity Map L1000 bioinformatic analysis that shows gene-expression signatures of MCAO mice are negatively connected to melatonin receptor agonist like Ramelteon. We demonstrate that ramelteon improves the cerebral blood flow signals in ischemic stroke that is potentially mediated, at least, partly by mechanisms of activating endothelial nitric oxide synthase. Our results also show that the neuroprotection of ramelteon counteracts reactive oxygen species-induced oxidative stress and activates the nuclear factor erythroid 2-related factor 2/heme oxygenase-1 pathway. Ramelteon inhibits the mitochondrial and autophagic death pathways in MCAO mice and cultured neurons, consistent with gene set enrichment analysis from a bioinformatics perspective angle. Our data suggest that Ramelteon is a potential neuroprotective drug candidate, and MT1 is the neuroprotective target for ischemic stroke, which provides new insights into stroke therapy. MT1-KO mice and cultured neurons may provide animal and cellular models of accelerated ischemic damage and neuronal cell death.

N-Acetylserotonin Alleviates Retinal Autophagy via TrkB/AKT/Nrf2 Signaling Pathway in Retinal Ischemia-Reperfusion Injury Rats.

INTRODUCTION: The objective of this study was to investigate the impact of N-acetylserotonin (NAS) on the autophagy of retinal cells in rats with retinal ischemia-reperfusion injury (RIRI) and to explore the mechanisms by which NAS administration can alleviate RIRI through the tropomyosin-related kinase receptor B (TrkB)/protein kinase B (Akt)/nuclear factor erythroid-derived factor 2-related factor (Nrf2) signaling pathway. METHODS: Healthy adult male rats were randomly assigned to four groups: sham, RIRI, RIRI+NAS, and RIRI+NAS+ANA-12. The RIRI group was induced by elevating intraocular pressure, and changes in retinal structure and edema were assessed using H&E staining. The RIRI+NAS and RIRI+NAS+ANA-12 groups received intraperitoneal injections of NAS before and after modeling. The RIRI+NAS+ANA-12 group was also administered ANA-12, a TrkB antagonist. Immunohistochemical staining and Western blot analysis were used to evaluate phosphorylated TrkB (p-TrkB), phosphorylated Akt (p-Akt), Nrf2, sequestosome 1 (P62), and microtubule-associated protein 1 light chain 3 (LC3-II) levels in the retinas of each group. Electroretinogram was recorded to detect retinal function in each group of rats 24 h after modeling. RESULTS: The RIRI+NAS group had a thinner retina and more retinal ganglion cells (RGCs) than RIRI and RIRI+NAS+ANA-12 groups (p < 0.05). Immunohistochemical staining and Western blot results showed that p-TrkB, p-Akt, n-Nrf2, and P62 levels in the RIRI+NAS group were higher compared with those in RIRI and RIRI+NAS+ANA-12 groups (p < 0.05). Also, lower LC3-II levels were observed in the RIRI+NAS group compared with that in RIRI and RIRI+NAS+ANA-12 groups (p < 0.05). Electroretinogram recording results showed that 24 h after retinal ischemia-reperfusion, the magnitude of b-wave changes was attenuated in the RIRI+NAS group compared with the RIRI group (p < 0.05). CONCLUSION: The administration of NAS activates the TrkB/Akt/Nrf2 signaling pathway, reduces autophagy, alleviates retinal edema, promotes the survival of retinal ganglion cells (RGCs), and provides neuroprotection against retinal injury.

Molecular Toxicology and Pathophysiology of Comorbid Alcohol Use Disorder and Post-Traumatic Stress Disorder Associated with Traumatic Brain Injury.

The increasing comorbidity of alcohol use disorder (AUD) and post-traumatic stress disorder (PTSD) associated with traumatic brain injury (TBI) is a serious medical, economic, and social issue. However, the molecular toxicology and pathophysiological mechanisms of comorbid AUD and PTSD are not well understood and the identification of the comorbidity state markers is significantly challenging. This review summarizes the main characteristics of comorbidity between AUD and PTSD (AUD/PTSD) and highlights the significance of a comprehensive understanding of the molecular toxicology and pathophysiological mechanisms of AUD/PTSD, particularly following TBI, with a focus on the role of metabolomics, inflammation, neuroendocrine, signal transduction pathways, and genetic regulation. Instead of a separate disease state, a comprehensive examination of comorbid AUD and PTSD is emphasized by considering additive and synergistic interactions between the two diseases. Finally, we propose several hypotheses of molecular mechanisms for AUD/PTSD and discuss potential future research directions that may provide new insights and translational application opportunities.

Megalin mediates 25-hydroxyvitamin D3 actions in human mesenchymal stem cells.

Osteoblast differentiation of human mesenchymal stem cells (hMSCs) is stimulated by 1α,25-dihydroxycholecalciferol [1α,25(OH)2D3] and 25-hydroxycholecalciferol [25(OH)D3]; the latter's effects require intracellular hydroxylation to 1α,25(OH)2D3. Thus, hMSCs are both a source of and target for 1α,25(OH)2D3. Megalin is a transmembrane receptor for serum d-binding protein (DBP) in kidney cells and is required for uptake of the 25(OH)D3-DBP complex. We tested the hypothesis that megalin is required for D actions in hMSCs with cells from surgically discarded marrow for RT-PCR, for effects of 25(OH)D3 and 1α,25(OH)2D3, for 1α,25(OH)2D3 biosynthesis, for osteoblastogenesis, and for small interfering RNA for megalin (si-Meg) and control (si-Ctr). In hMSCs with high constitutive megalin expression, both 1α,25(OH)2D3 and 25(OH)D3 stimulated osteoblastogenesis (P < 0.05), but only 1α,25(OH)2D3 did so in hMSCs with lower megalin (lo-Meg, P < 0.001) or in si-Meg cells (P < 0.05). In addition, 1α,25(OH)2D3 biosynthesis was significantly lower in lo-Meg (46%, P = 0.034) and in si-Meg (23%, P < 0.001) than each control. Leptin significantly stimulated megalin expression 2.1-fold in lo-Meg cells (P < 0.01). These studies show that megalin is expressed in hMSCs and is required for the biosynthesis of 1α,25(OH)2D3 and for the 25(OH)D3/DBP complex to stimulate vitamin D receptor targets and osteoblastogenesis.-Gao, Y., Zhou, S., Luu, S., Glowacki, J. Megalin mediates 25-hydroxyvitamin D3 actions in human mesenchymal stem cells.

Melatonin and Autophagy in Aging-Related Neurodegenerative Diseases.

With aging, the nervous system gradually undergoes degeneration. Increased oxidative stress, endoplasmic reticulum stress, mitochondrial dysfunction, and cell death are considered to be common pathophysiological mechanisms of various neurodegenerative diseases (NDDs) such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), organophosphate-induced delayed neuropathy (OPIDN), and amyotrophic lateral sclerosis (ALS). Autophagy is a cellular basic metabolic process that degrades the aggregated or misfolded proteins and abnormal organelles in cells. The abnormal regulation of neuronal autophagy is accompanied by the accumulation and deposition of irregular proteins, leading to changes in neuron homeostasis and neurodegeneration. Autophagy exhibits both a protective mechanism and a damage pathway related to programmed cell death. Because of its "double-edged sword", autophagy plays an important role in neurological damage and NDDs including AD, PD, HD, OPIDN, and ALS. Melatonin is a neuroendocrine hormone mainly synthesized in the pineal gland and exhibits a wide range of biological functions, such as sleep control, regulating circadian rhythm, immune enhancement, metabolism regulation, antioxidant, anti-aging, and anti-tumor effects. It can prevent cell death, reduce inflammation, block calcium channels, etc. In this review, we briefly discuss the neuroprotective role of melatonin against various NDDs via regulating autophagy, which could be a new field for future translational research and clinical studies to discover preventive or therapeutic agents for many NDDs.

Role of Alcohol Drinking in Alzheimer's Disease, Parkinson's Disease, and Amyotrophic Lateral Sclerosis.

Neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS), increase as the population ages around the world. Environmental factors also play an important role in most cases. Alcohol consumption exists extensively and it acts as one of the environmental factors that promotes these neurodegenerative diseases. The brain is a major target for the actions of alcohol, and heavy alcohol consumption has long been associated with brain damage. Chronic alcohol intake leads to elevated glutamate-induced excitotoxicity, oxidative stress and permanent neuronal damage associated with malnutrition. The relationship and contributing mechanisms of alcohol with these three diseases are different. Epidemiological studies have reported a reduction in the prevalence of Alzheimer's disease in individuals who drink low amounts of alcohol; low or moderate concentrations of ethanol protect against ß-amyloid (Aß) toxicity in hippocampal neurons; and excessive amounts of ethanol increase accumulation of Aß and Tau phosphorylation. Alcohol has been suggested to be either protective of, or not associated with, PD. However, experimental animal studies indicate that chronic heavy alcohol consumption may have dopamine neurotoxic effects through the induction of Cytochrome P450 2E1 (CYP2E1) and an increase in the amount of α-Synuclein (αSYN) relevant to PD. The findings on the association between alcohol consumption and ALS are inconsistent; a recent population-based study suggests that alcohol drinking seems to not influence the risk of developing ALS. Additional research is needed to clarify the potential etiological involvement of alcohol intake in causing or resulting in major neurodegenerative diseases, which will eventually lead to potential therapeutics against these alcoholic neurodegenerative diseases.

Protection of melatonin in experimental models of newborn hypoxic-ischemic brain injury through MT1 receptor.

The function of melatonin as a protective agent against newborn hypoxic-ischemic (H-I) brain injury is not yet well studied, and the mechanisms by which melatonin causes neuroprotection in neurological diseases are still evolving. This study was designed to investigate whether expression of MT1 receptors is reduced in newborn H-I brain injury and whether the protective action of melatonin is by alterations of the MT1 receptors. We demonstrated that there was significant reduction in MT1 receptors in ischemic brain of mouse pups in vivo following H-I brain injury and that melatonin offers neuroprotection through upregulation of MT1 receptors. The role of MT1 receptors was further supported by observation of increased mortality in MT1 knockout mice following H-I brain injury and the reversal of the inhibitory role of melatonin on mitochondrial cell death pathways by the melatonin receptor antagonist, luzindole. These data demonstrate that melatonin mediates its neuroprotective effect in mouse models of newborn H-I brain injury, at least in part, by the restoration of MT1 receptors, the inhibition of mitochondrial cell death pathways and the suppression of astrocytic and microglial activation.

Dehydroepiandrosterone Stimulation of Osteoblastogenesis in Human MSCs Requires IGF-I Signaling.

Dehydroepiandrosterone (DHEA) is an adrenal steroid that circulates in high concentrations in humans in its sulfated form, DHEAS. Clinical and epidemiological studies suggested that low DHEAS levels may be associated with low bone mass. Previously, we and others showed that the effects of DHEA on the skeleton may be conferred partly by their ability to inhibit skeletal catabolic agents, for example, bone resorptive cytokine IL-6. In this study, we tested the hypothesis that the anabolic effects of DHEA on osteoblastogenesis require IGF-I signaling pathways. Using both primary cultures and a cell line of human bone marrow-derived mesenchymal stem cells (hMSCs), we show that DHEA and other steroids stimulate osteoblastogenesis as shown by alkaline phosphatase activity and osteoblast gene induction. The stimulation by DHEA on both IGF-I gene expression and osteoblastogenesis in hMSCs requires IGF-I receptor, PI3K, p38 MAPK, or p42/44 MAPK signaling pathways. This study adds information to indicate that DHEA may be useful for treating bone diseases through its inhibition of skeletal catabolic IL-6 and stimulation of anabolic IGF-I-mediated mechanisms. J. Cell. Biochem. 117: 1769-1774, 2016. © 2015 Wiley Periodicals, Inc.

N-acetyl-serotonin offers neuroprotection through inhibiting mitochondrial death pathways and autophagic activation in experimental models of ischemic injury.

N-acetylserotonin (NAS) is an immediate precursor of melatonin, which we have reported is neuroprotective against ischemic injury. Here we test whether NAS is a potential neuroprotective agent in experimental models of ischemic injury. We demonstrate that NAS inhibits cell death induced by oxygen-glucose deprivation or H2O2 in primary cerebrocortical neurons and primary hippocampal neurons in vitro, and organotypic hippocampal slice cultures ex vivo and reduces hypoxia/ischemia injury in the middle cerebral artery occlusion mouse model of cerebral ischemia in vivo. We find that NAS is neuroprotective by inhibiting the mitochondrial cell death pathway and the autophagic cell death pathway. The neuroprotective effects of NAS may result from the influence of mitochondrial permeability transition pore opening, mitochondrial fragmentation, and inhibition of the subsequent release of apoptogenic factors cytochrome c, Smac, and apoptosis-inducing factor from mitochondria to cytoplasm, and activation of caspase-3, -9, as well as the suppression of the activation of autophagy under stress conditions by increasing LC3-II and Beclin-1 levels and decreasing p62 level. However, NAS, unlike melatonin, does not provide neuroprotection through the activation of melatonin receptor 1A. We demonstrate that NAS reaches the brain subsequent to intraperitoneal injection using liquid chromatography/mass spectrometry analysis. Given that it occurs naturally and has low toxicity, NAS, like melatonin, has potential as a novel therapy for ischemic injury.

N-acetyl-l-tryptophan, but not N-acetyl-d-tryptophan, rescues neuronal cell death in models of amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by progressive motor neuron loss. Evidence suggests that mitochondrial dysfunction, apoptosis, oxidative stress, inflammation, glutamate excitotoxicity, and proteasomal dysfunction are all responsible for ALS pathogenesis. N-acetyl-tryptophan has been identified as an inhibitor of mitochondrial cytochrome c release and therefore is a potential neuroprotective agent. By quantifying cell death, we demonstrate that N-acetyl-l-tryptophan (L-NAT) and N-acetyl-DL-tryptophan are neuroprotective in NSC-34 motor neuron-like cells and/or primary motor neurons, while their isomer N-acetyl-d-tryptophan has no protective effect. These findings are consistent with energy minimization and molecular modeling analysis, confirming that L-NAT generates the most stable complex with the neurokinin-1 receptor (NK-1R). L-NAT inhibits the secretion of Substance P and IL-1ß (Enzyme-Linked Immunosorbent Assay and/or dot blots) and mitochondrial dysfunction by effectively inhibiting the release of cytochrome c/Smac/AIF from mitochondria into the cytoplasm and activation of apoptotic pathways, including the activation of caspase-1, -9, and -3, as well as proteasomal dysfunction through restoring chymotrypsin-like, trypsin-like, and caspase-like proteasome activity. These data provide insight into the molecular mechanisms by which L-NAT offers neuroprotection in models of ALS and suggest its potential as a novel therapeutic strategy for ALS. We demonstrate that L-NAT (N-acetyl-l-tryptophan), but not D-NAT, rescues NSC-34 cells and primary motor neurons from cell death. L-NAT inhibits the secretion of Substance P and IL-1ß, and caspase-1 activation, the release of cytochrome c/Smac/AIF, and the activation of caspase -9, and -3, as well as proteasomal dysfunction. The data suggest the potential of L-NAT as a novel therapeutic strategy for amyotrophic lateral sclerosis (ALS). AIF, apoptosis-inducing factor.

Effect of age on regulation of human osteoclast differentiation.

Human skeletal aging is characterized as a gradual loss of bone mass due to an excess of bone resorption not balanced by new bone formation. Using human marrow cells, we tested the hypothesis that there is an age-dependent increase in osteoclastogenesis due to intrinsic changes in regulatory factors [macrophage-colony stimulating factor (M-CSF), receptor activator of NF-κB ligand (RANKL), and osteoprotegerin (OPG)] and their receptors [c-fms and RANK]. In bone marrow cells (BMCs), c-fms (r = 0.61, P = 0.006) and RANK expression (r = 0.59, P = 0.008) were increased with age (27-82 years, n = 19). In vitro generation of osteoclasts was increased with age (r = 0.89, P = 0.007). In enriched marrow stromal cells (MSCs), constitutive expression of RANKL was increased with age (r = 0.41, P = 0.049) and expression of OPG was inversely correlated with age (r = -0.43, P = 0.039). Accordingly, there was an age-related increase in RANKL/OPG (r = 0.56, P = 0.005). These data indicate an age-related increase in human osteoclastogenesis that is associated with an intrinsic increase in expression of c-fms and RANK in osteoclast progenitors, and, in the supporting MSCs, an increase in pro-osteoclastogenic RANKL expression and a decrease in anti-osteoclastogenic OPG. These findings support the hypothesis that human marrow cells and their products can contribute to skeletal aging by increasing the generation of bone-resorbing osteoclasts. These findings help to explain underlying molecular mechanisms of progressive bone loss with advancing age in humans.

N-acetylserotonin alleviates retinal ischemia-reperfusion injury via HMGB1/RAGE/NF-κB pathway in rats.

AIM: To observe the effects of N-acetylserotonin (NAS) administration on retinal ischemia-reperfusion (RIR) injury in rats and explore the underlying mechanisms involving the high mobility group box 1 (HMGB1)/receptor for advanced glycation end-products (RAGE)/nuclear factor-kappa B (NF-κB) signaling pathway. METHODS: A rat model of RIR was developed by increasing the pressure of the anterior chamber of the eye. Eighty male Sprague Dawley were randomly divided into five groups: sham group (n=8), RIR group (n=28), RIR+NAS group (n=28), RIR+FPS-ZM1 group (n=8) and RIR+NAS+ FPS-ZM1 group (n=8). The therapeutic effects of NAS were examined by hematoxylin-eosin (H&E) staining, and retinal ganglion cells (RGCs) counting. The expression of interleukin 1 beta (IL-1ß), HMGB1, RAGE, and nod-like receptor 3 (NLRP3) proteins and the phosphorylation of nuclear factor-kappa B (p-NF-κB) were analyzed by immunohistochemistry staining and Western blot analysis. The expression of HMGB1 protein was also detected by enzyme-linked immunosorbent assay (ELISA). RESULTS: H&E staining results showed that NAS significantly reduced retinal edema and increased the number of RGCs in RIR rats. With NAS therapy, the HMGB1 and RAGE expression decreased significantly, and the activation of the NF-κB/NLRP3 pathway was antagonized along with the inhibition of p-NF-κB and NLRP3 protein expression. Additionally, NAS exhibited an anti-inflammatory effect by reducing IL-1ß expression. The inhibitory of RAGE binding to HMGB1 by RAGE inhibitor FPS-ZM1 led to a significant decrease of p-NF-κB and NLRP3 expression, so as to the IL-1ß expression and retinal edema, accompanied by an increase of RGCs in RIR rats. CONCLUSION: NAS may exhibit a neuroprotective effect against RIR via the HMGB1/RAGE/NF-κB signaling pathway, which may be a useful therapeutic target for retinal disease.

Inhibition of miR-199b-5p reduces pathological alterations in osteoarthritis by potentially targeting Fzd6 and Gcnt2.

Osteoarthritis (OA) is a degenerative disease with a high prevalence in the elderly population, but our understanding of its mechanisms remains incomplete. Analysis of serum exosomal small RNA sequencing data from clinical patients and gene expression data from OA patient serum and cartilage obtained from the GEO database revealed a common dysregulated miRNA, miR-199b-5p. In vitro cell experiments demonstrated that miR-199b-5p inhibits chondrocyte vitality and promotes extracellular matrix degradation. Conversely, inhibition of miR-199b-5p under inflammatory conditions exhibited protective effects against damage. Local viral injection of miR-199b-5p into mice induced a decrease in pain threshold and OA-like changes. In an OA model, inhibition of miR-199b-5p alleviated the pathological progression of OA. Furthermore, bioinformatics analysis and experimental validation identified Gcnt2 and Fzd6 as potential target genes of MiR-199b-5p. Thus, these results indicated that MiR-199b-5p/Gcnt2 and Fzd6 axis might be a novel therapeutic target for the treatment of OA.

Burden evaluation and prediction of osteoarthritis and site-specific osteoarthritis coupled with attributable risk factors in China from 1990 to 2030.

OBJECTIVE: This study aimed to estimate and predict the burden of osteoarthritis (OA) and site-specific OA (hip, knee, hand, and others) from 1990 to 2030 and their attributable risk factors in China. METHOD: Data were obtained from the Global Burden of Diseases 2019. The burden was estimated by analyzing the trends of prevalence, incidence, and disability-adjusted life years (DALY). Population attributable risk (PAR) was calculated to assess the impact of high body mass index (BMI). The prediction from 2020 to 2030 was implemented by Bayesian age-period-cohort analysis. RESULTS: In China, prevalent cases, DALY, and incident cases of OA increased to 132.81 million, 4.72 million, and 10.68 million, respectively. Age-standardized rates (ASRs) of prevalence, DALYs, and incidence increased for OA and site-specific OA, especially for hip OA. Site-specific OA showed different susceptible peaking ages, and the burden for those over 50 years old became serious. Female preference existed in the trends for knee OA but not in those for hip, hand, and other OA. PARs of high BMI continued to increase, impacting knee OA more than hip OA and showing female preference. In the next decade, incident cases for OA and site-specific OA will continue to increase, despite that the ASR of OA incidence will decrease. CONCLUSIONS: OA and site-specific OA remain huge public health challenges in China. The burden of OA and site-specific OA is increasing, especially among people over 50 years old. Health education, exercise, and removing modifiable risk factors contribute to alleviate the growing burden. Key Points • In China, the burden of osteoarthritis and site-specific osteoarthritis (hip, knee, hand, and others) as well as the Risk Factor (high body mass index) increased greatly from 1990 to 2019. • It is estimated that incident cases for OA and site-specific OA will continue to increase, despite that the ASR of OA incidence will decrease.

Tryptophan Metabolism in Alzheimer's Disease with the Involvement of Microglia and Astrocyte Crosstalk and Gut-Brain Axis.

Alzheimer's disease (AD) is an age-dependent neurodegenerative disease characterized by extracellular Amyloid Aß peptide (Aß) deposition and intracellular Tau protein aggregation. Glia, especially microglia and astrocytes are core participants during the progression of AD and these cells are the mediators of Aß clearance and degradation. The microbiota-gut-brain axis (MGBA) is a complex interactive network between the gut and brain involved in neurodegeneration. MGBA affects the function of glia in the central nervous system (CNS), and microbial metabolites regulate the communication between astrocytes and microglia; however, whether such communication is part of AD pathophysiology remains unknown. One of the potential links in bilateral gut-brain communication is tryptophan (Trp) metabolism. The microbiota-originated Trp and its metabolites enter the CNS to control microglial activation, and the activated microglia subsequently affect astrocyte functions. The present review highlights the role of MGBA in AD pathology, especially the roles of Trp per se and its metabolism as a part of the gut microbiota and brain communications. We (i) discuss the roles of Trp derivatives in microglia-astrocyte crosstalk from a bioinformatics perspective, (ii) describe the role of glia polarization in the microglia-astrocyte crosstalk and AD pathology, and (iii) summarize the potential of Trp metabolism as a therapeutic target. Finally, we review the role of Trp in AD from the perspective of the gut-brain axis and microglia, as well as astrocyte crosstalk, to inspire the discovery of novel AD therapeutics.

Suppression of homeobox transcription factor VentX promotes expansion of human hematopoietic stem/multipotent progenitor cells.

Mechanisms that regulate proliferation and expansion of human hematopoietic stem/multipotent progenitor cells (HSC/MPPs) are targets of intensive investigations. Several cell intrinsic factors and signaling pathways have been implicated in the proliferation and differentiation of human HSC/MPPs. Nevertheless, expansion of human HSC/MPPs for clinical application remains a critical challenge. VentX is a human homeobox transcription factor that was recently identified as an anti-proliferation and pro-differentiation factor in human hematopoietic cells. Here, we report that VentX expression is up-regulated during ontogenesis of human hematopoietic cells. Strikingly, suppression of VentX expression led to significant expansion of HSC/MPPs ex vivo and a 20-fold increase in engraftment potential in the NOD/SCID/IL2Rγ2(null) mouse model. VentX suppression helped preserve the HSC/MPP pools and promote clonogenicity of hematopoietic progenitor cells. Mechanistically, we show that VentX regulates critical cell cycle regulators and Wnt downstream genes previously implicated in HSC/MPP proliferation and expansion.

Induced Pluripotent Stem Cells and Their Applications in Amyotrophic Lateral Sclerosis.

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease that results in the loss of motor function in the central nervous system (CNS) and ultimately death. The mechanisms underlying ALS pathogenesis have not yet been fully elucidated, and ALS cannot be treated effectively. Most studies have applied animal or single-gene intervention cell lines as ALS disease models, but they cannot accurately reflect the pathological characteristics of ALS. Induced pluripotent stem cells (iPSCs) can be reprogrammed from somatic cells, possessing the ability to self-renew and differentiate into a variety of cells. iPSCs can be obtained from ALS patients with different genotypes and phenotypes, and the genetic background of the donor cells remains unchanged during reprogramming. iPSCs can differentiate into neurons and glial cells related to ALS. Therefore, iPSCs provide an excellent method to evaluate the impact of diseases on ALS patients. Moreover, patient-derived iPSCs are obtained from their own somatic cells, avoiding ethical concerns and posing only a low risk of immune rejection. The iPSC technology creates new hope for ALS treatment. Here, we review recent studies on iPSCs and their applications in disease modeling, drug screening and cell therapy in ALS, with a particular focus on the potential for ALS treatment.

The melatonin MT1 receptor axis modulates mutant Huntingtin-mediated toxicity.

Melatonin mediates neuroprotection in several experimental models of neurodegeneration. It is not yet known, however, whether melatonin provides neuroprotection in genetic models of Huntington's disease (HD). We report that melatonin delays disease onset and mortality in a transgenic mouse model of HD. Moreover, mutant huntingtin (htt)-mediated toxicity in cells, mice, and humans is associated with loss of the type 1 melatonin receptor (MT1). We observe high levels of MT1 receptor in mitochondria from the brains of wild-type mice but much less in brains from HD mice. Moreover, we demonstrate that melatonin inhibits mutant htt-induced caspase activation and preserves MT1 receptor expression. This observation is critical, because melatonin-mediated protection is dependent on the presence and activation of the MT1 receptor. In summary, we delineate a pathologic process whereby mutant htt-induced loss of the mitochondrial MT1 receptor enhances neuronal vulnerability and potentially accelerates the neurodegenerative process.

Inhibition of adipocytogenesis by canonical WNT signaling in human mesenchymal stem cells.

The WNT signaling pathway plays important roles in the self-renewal and differentiation of mesenchymal stem cells (MSCs). Little is known about WNT signaling in adipocyte differentiation of human MSCs. In this study, we tested the hypothesis that canonical and non-canonical WNTs differentially regulate in vitro adipocytogenesis in human MSCs. The expression of adipocyte gene PPARγ2, lipoprotein lipase, and adipsin increased during adipocytogenesis of hMSCs. Simultaneously, the expression of canonical WNT2, 10B, 13, and 14 decreased, whereas non-canonical WNT4 and 11 increased, and WNT5A was unchanged. A small molecule WNT mimetic, SB-216763, increased accumulation of ß-catenin protein, inhibited induction of WNT4 and 11 and inhibited adipocytogenesis. In contrast, knockdown of ß-catenin with siRNA resulted in spontaneous adipocytogenesis. These findings support the view that canonical WNT signaling inhibits and non-canonical WNT signaling promotes adipocytogenesis in adult human marrow-derived mesenchymal stem cells.