Distinct function of miR-17-92 cluster in the dorsal and ventral adult hippocampal neurogenesis

Neural extracellular vesicle-derived miR-17 in blood as a potential biomarker of subthreshold depression

Subthreshold depression (StD) is a depressive state that does not fulfil the criteria for major depressive disorder (MDD); however, StD has a risk for progression to MDD, and early intervention is therefore needed. Recently, a method for extracting neural extracellular vesicles (NEVs) excreted from neural cells of the brain from blood has been established, and microRNAs (miRNAs) encapsulated in NEVs are attracting interest because of their potential correlation to the pathogenesis of psychiatric disorders. However, miRNAs closely related to StD are still unknown. Therefore, to try to identify miRNAs closely related to the degree of StD, we examined the correlations between expression levels of some candidate miRNAs in NEVs and Patient Health Questionnaire-9 (PHQ-9) scores in subjects. Total RNAs in NEVs were extracted from serum of young adult males who had PHQ-9 scores of less than 10 (n = 9). Expression levels of eight miRNAs that were previously reported to be depression-associated miRNAs (let-7a-5p, miR-17-5p, miR-26b-5p, miR-34a-5p, miR-132-3p, miR-182-5p, miR-212-3p, and miR-1202) were measured using real-time PCR. Two of the eight miRNAs (miR-17-5p and miR-26b-5p) were stably detected. The relative expression levels of miR-17-5p showed a significant positive correlation with PHQ-9 scores (r = 0.85, p < 0.01), while those of miR-26b-5p showed no significance. Although a larger-scale analysis is needed due to the small number of subjects, these findings suggest that miR-17-5p in NEVs is a potential biomarker for StD.

The unique plasticity of hippocampal adult-born neurons: Contributing to a heterogeneous dentate

The dentate gyrus (DG) of the hippocampus is evolutionarily conserved as one of the few sites of adult neurogenesis in mammals. Although there is clear evidence that neurogenesis is necessary for healthy hippocampal function, whether adult-born neurons are simply integrated into existing hippocampal networks to serve a similar purpose to that of developmentally born neurons or whether they represent a discrete cell population with unique functions remains less clear. In this review, we consider evidence for discrete cellular, synaptic, and structural features of adult-born DG neurons, suggesting that neurogenesis contributes to the formation of a heterogeneous DG. We therefore propose that hippocampal neurogenesis creates a specialized neuronal subpopulation that may play a key role in hippocampal functions like episodic memory. We note critical gaps in this extensive body of work, including a general failure to include female animals in relevant research and a need for more precise consideration of intrahippocampal neuroanatomy.

Extracellular Vesicles Derived from Neural Progenitor Cells--a Preclinical Evaluation for Stroke Treatment in Mice

Stem cells such as mesenchymal stem cells (MSCs) enhance neurological recovery in preclinical stroke models by secreting extracellular vesicles (EVs). Since previous reports have focused on the application of MSC-EVs only, the role of the most suitable host cell for EV enrichment and preclinical stroke treatment remains elusive. The present study aimed to evaluate the therapeutic potential of EVs derived from neural progenitor cells (NPCs) following experimental stroke. Using the PEG technique, EVs were enriched and characterized by electron microscopy, proteomics, rt-PCR, nanosight tracking analysis, and Western blotting. Different dosages of NPC-EVs displaying a characteristic profile in size, shape, cargo protein, and non-coding RNA contents were incubated in the presence of cerebral organoids exposed to oxygen-glucose deprivation (OGD), significantly reducing cell injury when compared with control organoids. Systemic administration of NPC-EVs in male C57BL6 mice following experimental ischemia enhanced neurological recovery and neuroregeneration for as long as 3 months. Interestingly, the therapeutic impact of such NPC-EVs was found to be not inferior to MSC-EVs. Flow cytometric analyses of blood and brain samples 7 days post-stroke demonstrated increased blood concentrations of B and T lymphocytes after NPC-EV delivery, without affecting cerebral cell counts. Likewise, a biodistribution analysis after systemic delivery of NPC-EVs revealed the majority of NPC-EVs to be found in extracranial organs such as the liver and the lung. This proof-of-concept study supports the idea of EVs being a general concept of stem cell–induced neuroprotection under stroke conditions, where EVs contribute to reverting the peripheral post-stroke immunosuppression.

MicroRNAs miR-25, let-7 and miR-124 regulate the neurogenic potential of Müller glia in mice

Müller glial cells (MG) generate retinal progenitor (RPC)-like cells after injury in non-mammalian species, although this does not occur in the mammalian retina. Studies have profiled gene expression in these cells to define genes that may be relevant to their differences in neurogenic potential. However, less is known about differences in micro-RNA (miRNA) expression. In this study, we compared miRNAs from RPCs and MG to identify miRNAs more highly expressed in RPCs, and others more highly expressed in MG. To determine whether these miRNAs are relevant to the difference in neurogenic potential between these two cell types, we tested them in dissociated cultures of MG using either mimics or antagomiRs to increase or reduce expression, respectively. Among the miRNAs tested, miR-25 and miR-124 overexpression, or let-7 antagonism, induced Ascl1 expression and conversion of ∼40% of mature MG into a neuronal/RPC phenotype. Our results suggest that the differences in miRNA expression between MG and RPCs contribute to their difference in neurogenic potential, and that manipulations in miRNAs provide a new tool with which to reprogram MG for retinal regeneration.