Project description:The molecular control of feeding after fasting is essential for maintaining energy homeostasis, and overfeeding usually leads to obesity. RNA interference has been clinically successful in managing diseases, and the identification of a feeding-regulated microRNA (miRNA), which remains a challenge, could be a strategy for combating obesity. By performing a comprehensive genome-wide microRNA screening in the arcuate nucleus of the hypothalamus (ARC) of fasted mice and ad libitum mice, we found a significant increase in miR-7a-5p levels after fasting. miR-7a-5p was highly expressed in the ARC, and inhibition of miR-7a-5p specifically in AgRP neurons reduced food intake and body weight gain. miR-7a-5p inhibited S6K1 gene expression by binding to its 3’-UTR. Furthermore, the reduction of food intake by anti-miR-7a-5p was partially reversed by the downregulated mechanistic target of rapamycin complex 1 (mTOR1)/ribosomal S6 kinase 1 (S6K1) signaling in the AgRP neurons. Importantly, intracerebroventricular administration of the miR-7a-5p inhibitor could reduce food intake and body weight. Collectively, our findings suggest miR-7a-5p as an orexigenic factor in AgRP neurons and a potential novel target for obesity treatment.
Project description:It is proposed that the impaired sympathoadrenal response to hypoglycemia induced by recurrent insulin-induced hypoglycemia (RH) is an adaptive phenomenon induced by specific changes in microRNA expression in the ventromedial hypothalamus (VMH). To test this hypothesis, genome-wide microRNAomic profiling of the VMH by RNA-sequencing was performed in control and RH treated rats. Differential expression analysis identified microRNA-7a-5p and microRNA-665 as potential mediators of this phenomenon. To further test this hypothesis, experiments were conducted consisting of targeted lentiviral-mediated overexpression of microRNA-7a-5p and downregulation of microRNA-665 in the VMH. Hyperinsulinemic hypoglycemic clamp experiments demonstrated that targeted overexpression of microRNA-7a-5p (but not downregulation of microRNA-665) in the VMH of RH rats restored the epinephrine response to hypoglycemia. This restored response to hypoglycemia was associated with a restoration of GABAA receptor gene expression. Finally, a direct interaction of microRNA-7a-5p with 3’-UTR of GABAA receptor α1-subunit (Gabra1) gene was demonstrated in a luciferase assay. These findings indicate that 1) the impaired sympathoadrenal response induced by RH is associated with changes in VMH microRNA expression, and 2) microRNA-7a-5p, possibly via direct downregulation of GABA receptor gene expression, may serve as a mediator of the altered sympathoadrenal response to hypoglycemia.
Project description:Surface expression of C-X-C chemokine receptor type 4 (CXCR4) in acute myeloid leukemia (AML) has been reported to be an independent prognostic factor for disease relapse and survival. We previously reported that targeting the stromal-derived factor 1α (SDF-1α)/CXCR4 axis could overcome resistance of AML cells to chemotherapy both in vitro and in vivo. To further explore the mechanism of targeting CXCR4, in the current study we focused on the regulation of microRNA. Microarray analysis revealed that the hsa-let-7a microRNA was down-regulated in OCI-AML3 cells by SDF-1α treatment and increased after CXCR4 inhibition. To further investigate the role of hsa-let-7a in leukemia biology, we overexpressed it in AML cell lines, which resulted in decreased Bcl-xL protein expression and consequently enhanced cell sensitivity to the chemotherapeutic agent cytarabine, both in vitro and in vivo. We also identified the transcription factor Yin Yang 1 (YY1) as a mediator that links the SDF-1α/CXCR4 axis with hsa-let-7a. Western blotting and immunocytochemistry demonstrated a correlation between YY1 and CXCR4 activation. ChIP assay confirmed the binding of YY1 to pri-let-7a DNA fragments. In primary AML samples (n=50), high CXCR4 surface expression was associated with low hsa-let-7a levels (r2=0.53). Improved effects of cytarabine treatment associated with greatly extended survival of human AML carrying mice was observed in primary human AML overexpressing hsa-let-7a. On the basis of these results, we propose that CXCR4 regulation of hsa-let-7a microRNA through YY1 and transcriptional silencing of the Bcl-xL protein together identifies a novel mechanism by which CXCR4 functions to induce chemoresistance in AML cells.