H/ACA Box Small Nucleolar RNA 7A Promotes the Self-Renewal of Human Umbilical Cord Mesenchymal Stem Cells.

Human umbilical cord blood derived mesenchymal stem cells (uMSC) are pluripotent cells that have been now considered as a promising candidate for various cell-based therapies. However, their limited in vitro proliferation ability and the gradual loss of pluripotency set barricades for further usages. Emerging evidence suggests that small nucleolar RNAs (snoRNA) are actively involved in cell proliferation especially in tumor cells, but their roles in stem cells are largely unknown. In this study, we demonstrated that H/ACA box small nucleolar RNA 7A (SNORA7A) is inversely correlated to the decreased proliferation rate during in vitro passaging of uMSC. Further investigations indicate that SNORA7A overexpression can promote uMSC proliferation and self-renewal. The inhibition of SNORA7A using antisense oligonucleotides significantly reduces the expression and the binding of SNORA7A to DKC1, core protein that essential to form small nucleolar ribonucleo-particles (snoRNP) complex and catalyze pseudouridines in 28S RNA. And the inhibition also significantly suppresses uMSC proliferation and self-renewal. Moreover, overexpression of SNORA7A transcripts with mutations of binding regions for snoRNP core proteins and 28S RNA did not induce proliferation and self-renewal. Besides, SNORA7A also suppresses both the osteogenic and adipogenic differentiation, strengthening its self-renewal maintaining roles in uMSC. Taken together, our study for the first time showed that H/ACA box snoRNAs are actively involved in MSC proliferation as well as pluripotency control, and we identify SNORA7A as one of the critical snoRNAs that regulate the proliferation and self-renewal of uMSC through snoRNP recruiting. Stem Cells 2017;35:222-235.

miR-26b-3p Regulates Human Umbilical Cord-Derived Mesenchymal Stem Cell Proliferation by Targeting Estrogen Receptor.

Human umbilical cord-derived mesenchymal stem cells (hUC-MSC) have been considered as promising candidates for cell-based regeneration medicine. However, the application was limited to its poor in vitro proliferation ability against the huge demand of cells. MicroRNA plays important roles in the regulation of cell proliferation, apoptosis, and differentiation. The objective of this study is to explore the roles of miRNAs in regulating the in vitro proliferation of hUC-MSC and unveil their possible mechanism. In this study, we found that miR-26b-3p was significantly upregulated during serial in vitro passage of hUC-MSC and was correlated with cellular senescence and cell cycle genes. The overexpression of miR-26b-3p greatly inhibited the proliferation of hUC-MSC in vitro, which is indicated by 5-ethynyl-2'-deoxyuridine (EdU) incorporation assay, cell cycle, and cell growth curve analyses. miR-26b-3p suppression partly rescued this phenotype by maintaining its proliferation ability in vitro. For mechanism studies, we predicted and validated that miR-26b-3p suppresses estrogen receptor 1 (ESR1) expression by directly binding to the coding sequence (CDS) region of its message RNA (mRNA), thus subsequently changing the expression of its downstream effector Cyclin D1. In conclusion, we found that miR-26b-3p played an important role in the regulation of hUC-MSC proliferation in vitro by targeting the ESR-CCND1 pathway.