A recent study has suggested that fibroblasts can be converted into mouse-induced neural stem cells (miNSCs) through the expression of defined factors. However, successful generation of human iNSCs (hiNSCs) has proven challenging to achieve. Here, using microRNA (miRNA) expression profile analyses, we showed that let-7 microRNA has critical roles for the formation of PAX6/NESTIN-positive colonies from human adult fibroblasts and the proliferation and self-renewal of hiNSCs. HMGA2, a let-7-targeting gene, enables induction of hiNSCs that displayed morphological/molecular features and in vitro/in vivo differentiation potential similar to H9-derived NSCs. Interestingly, HMGA2 facilitated the efficient conversion of senescent somatic cells or blood CD34+ cells into hiNSCs through an interaction with SOX2, whereas other combinations or SOX2 alone showed a limited conversion ability. Taken together, these findings suggest that HMGA2/let-7 facilitates direct reprogramming toward hiNSCs in minimal conditions and maintains hiNSC self-renewal, providing a strategy for the clinical treatment of neurological diseases.

MicroRNAs have been shown to effectively regulate gene expression at the translational level. Recently, we identified novel microRNAs that were upregulated in a mouse model of spinal cord injury. Among those, we have focused on microRNA 486, which directly represses NeuroD6 expression through a conserved sequence in its untranslated region. We correlated the overexpression of microRNA 486 in motor neurons with a poor outcome due to progressive neurodegeneration and a pathophysiology that is mediated by reactive oxygen species. The expression of microRNA 486 was induced by reactive oxygen species that were produced by inflammatory factors, and reactive oxygen species were accumulated in response to the knockdown of NeuroD6, which enhances the downregulation of glutathione peroxidase 3 and thioredoxin-like 1 after traumatic spinal cord injury. NeuroD6 directly bound to regulatory regions of thioredoxin-like 1 and glutathione peroxidase 3 in motor neurons and activated their expression, which promoted reactive oxygen species scavenging. Moreover, knocking down microRNA 486 induced the expression of NeuroD6, which effectively ameliorated the spinal cord injury and allowed the mice to recover motor function. The infusion of exogenic NeuroD6 in spinal cord injury lesions effectively blocked apoptosis by reactivating thioredoxin-like 1 and glutathione peroxidase 3, which was accompanied by a recovery of motor function. Collectively, these findings have identified a novel microRNA in spinal cord injury lesions called microRNA 486, demonstrating a new role for NeuroD6 in neuroprotection, and suggest a potential therapeutic target for spinal cord injuries.

Neuropathic pain is a well-known type of chronic pain caused by damage to the nervous system. Until recently, many researchers have primarily focused on identifying cellular or chemical sources of neuropathic pain or have approached neuropathic pain via the basis of biological study. We investigated whether both mmu-mir-23b (miR23b) and NADPH oxidase 4 (NOX4) antibody infusion can alleviate neuropathic pain by compensating for abnormally downregulated miR23b via reducing the expression of its target gene, NOX4, a reactive oxygen species (ROS) family member overexpressed in neuropathic pain. Ectopic miR23b expression effectively downregulated NOX4 and finally normalized glutamic acid decarboxylase 65/67 expression. Moreover, animals with neuropathic pain showed significantly improved paw withdrawal thresholds (PWTs) following miR23b infusion. Normalizing miR23b expression in tissue lesions, caused by neuropathic pain induction, reduced inflammatory mediators and increased several ROS scavengers. Moreover, γ-aminobutyric acid (GABA)ergic neurons coexpressed suboptimal levels of miR23b and elevated NOX4/ROS after pain induction at the cellular level. MiR23b finally protects GABAergic neurons against ROS/p38/c-Jun N-terminal kinase (JNK)-mediated apoptotic death. By evaluating the functional behavior of mice receiving pain/miR23b, normal/anti-miR23b, anti-miR23b/si-NOX4, pain/NOX4 antibody, pain/ascorbic acid, and pain/ascorbic acid/NOX4 antibody, the positive role of miR23b and the negative role of NOX4 in neuropathic pain were confirmed. Based on this study, we conclude that miR23b has a crucial role in the amelioration of neuropathic pain in injured spinal cord by inactivating its target gene, NOX4, and protection of GABAergic neurons from cell death. We finally suggest that infusion of miR23b and NOX4 antibody may provide attractive diagnostic and therapeutic resources for effective pain modulation in neuropathic pain.

MicroRNAs (miRNAs) compose a relatively new discipline in biomedical research, and many physiological processes in disease have been associated with changes in miRNA expression. Several studies report that miRNAs participate in biological processes such as the control of secondary injury in several disease models. Recently, we identified novel miRNAs that were abnormally up-regulated in a traumatic spinal cord injury (SCI). In the current study, we focused on miR20a, which causes continuing motor neuron degeneration when overexpressed in SCI lesions. Blocking miR20a in SCI animals led to neural cell survival and eventual neurogenesis with rescued expression of the key target gene, neurogenin 1 (Ngn1). Infusion of siNgn1 resulted in functional deficit in the hindlimbs caused by aggressive secondary injury and actively enhanced the inflammation involved in secondary injury progression. The events involving miR20a underlie motor neuron and myelin destruction and pathophysiology and ultimately block regeneration in injured spinal cords. Inhibition of miR20a expression effectively induced definitive motor neuron survival and neurogenesis, and SCI animals showed improved functional deficit. In this study, we showed that abnormal expression of miR20a induces secondary injury, which suggests that miR20a could be a potential target for therapeutic intervention following SCI.

Niemann Pick disease type C1 (NPC) is an autosomal recessive disease characterized by progressive neurological deterioration leading to premature death. In this study, we hypothesized that human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) have the multifunctional abilities to ameliorate NPC symptoms in the brain. To test this hypothesis, hUCB-MSCs were transplanted into the hippocampus of NPC mice in the early asymptomatic stage. This transplantation resulted in the recovery of motor function in the Rota Rod test and impaired cholesterol homeostasis leading to increased levels of cholesterol efflux-related genes such as LXRα, ABCA1, and ABCG5 while decreased levels of 3-hydroxy-3-methylglutaryl coenzyme A reductase were observed in NPC mice. In the cerebrum, hUCB-MSCs enhanced neuronal cell survival and proliferation, where they directly differentiated into electrically active MAP2-positive neurons as demonstrated by whole-cell patch clamping. In addition, we observed that hUCB-MSCs reduced Purkinje neuronal loss by suppression of inflammatory and apoptotic signaling in the cerebellum as shown by immunohistochemistry. We further investigated how hUCB-MSCs enhance cellular survival and inhibit apoptosis in NPC mice. Neuronal cell survival was associated with increased PI3K/AKT and JAK2/STAT3 signaling; moreover, hUCB-MSCs modulated the levels of GABA/glutamate transporters such as GAT1, EAAT2, EAAT3, and GAD6 in NPC mice as assessed by Western blot analysis. Taken together, our findings suggest that hUCB-MSCs might play multifunctional roles in neuronal cell survival and ameliorating motor deficits of NPC mice.