Excessive scar formation caused by myofibroblast aggregations is of great clinical importance during skin wound healing. Studies have shown that mesenchymal stem cells (MSCs) can promote skin regeneration, but whether MSCs contribute to scar formation remains undefined. We found that umbilical cord-derived MSCs (uMSCs) reduced scar formation and myofibroblast accumulation in a skin-defect mouse model. We found that these functions were mainly dependent on uMSC-derived exosomes (uMSC-Exos) and especially exosomal microRNAs. Through high-throughput RNA sequencing and functional analysis, we demonstrated that a group of uMSC-Exos enriched in specific microRNAs (miR-21, -23a, -125b, and -145) played key roles in suppressing myofibroblast formation by inhibiting the transforming growth factor-b2/SMAD2 pathway. Finally, using the strategy we established to block miRNAs inside the exosomes, we showed that these specific exosomal miRNAs were essential for the myofibroblast-suppressing and anti-scarring functions of uMSCs both in vitro and in vivo. Our study revealed a novel role of exosomal miRNAs in uMSC-mediated therapy, suggesting that the clinical application of uMSC-derived exosomes might represent a strategy to prevent scar formation during wound healing. STEM CELLS TRANSLATIONAL MEDICINE 2016;5:1425-1439 SIGNIFICANCEExosomes have been identified as a new type of major paracrine factor released by umbilical cordderived mesenchymal stem cells (uMSCs). They have been reported to be an important mediator of cell-to-cell communication. However, it is still unclear precisely which molecule or group of molecules carried within MSC-derived exosomes can mediate myofibroblast functions, especially in the process of wound repair. The present study explored the functional roles of uMSC-exosomal microRNAs in the process of myofibroblast formation, which can cause excessive scarring. This is an unreported function of uMSC exosomes. Also, for the first time, the uMSC-exosomal microRNAs were examined by high-throughput sequencing, with a group of specific microRNAs (miR-21, miR-23a, miR-125b, and miR-145) found to play key roles in suppressing myofibroblast formation by inhibiting excess a-smooth muscle actin and collagen deposition associated with activity of the transforming growth factor-b/SMAD2 signaling pathway.

Long non-coding RNAs (lncRNAs) are known players in the regulatory circuitry of the self-renewal in human embryonic stem cells (hESCs). However, most hESC-specific lncRNAs remain uncharacterized. Here we demonstrate that growth-arrest-specific transcript 5 (GAS5), a known tumour suppressor and growth arrest-related lncRNA, is highly expressed and directly regulated by pluripotency factors OCT4 and SOX2 in hESCs. Phenotypic analysis shows that GAS5 knockdown significantly impairs hESC self-renewal, but its overexpression significantly promotes hESC self-renewal. Using RNA sequencing and functional analysis, we demonstrate that GAS5 maintains NODAL signalling by protecting NODAL expression from miRNA-mediated degradation. Therefore, we propose that the above pluripotency factors, GAS5 and NODAL form a feed-forward signalling loop that maintains hESC self-renewal. As this regulatory function of GAS5 is stem cell specific, our findings also indicate that the functions of lncRNAs may vary in different cell types due to competing endogenous mechanisms.

The stem cell factor (SCF)/Kit system has served as a classic model in deciphering molecular signaling events in the hematopoietic compartment, and Kit expression is a most critical marker for hematopoietic stem cells (HSCs) and progenitors. However, it remains to be elucidated how Kit expression is regulated in HSCs. Herein we report that a cytoplasmic tyrosine phosphatase Shp2, acting down- IntroductionThe quiescence and entry into cycling of hematopoietic stem cells (HSCs) are tightly controlled and maintained in postnatal hematopoiesis by cytokines/growth factors and other signals in the microenvironment. 1,2 Stem cell factor, SCF (also known as Kit ligand, mast cell factor, or Steel factor) is encoded by the mouse Steel locus, and its receptor Kit (also called c-Kit) is encoded by the mouse White locus. 3,4 The biologic significance of Kit in hematopoiesis was first revealed in the white spotting (W) mutant mice. 5 Several W mutations with different levels of Kit kinase deficiency were found to correlate with the phenotype severity. 6 W 37 mutation in the conserved tyrosine kinase domain leads to complete loss of the kinase activity, and W 37 -homozygous mutant mice are embryonic lethal because of severe macrocytic anemia. A similar phenotype was found in the mouse strain with mutations at the Steel locus. Recently Waskow et al 7 investigated mild W mutants, identifying a pivotal role of Kit in development of multiple hematopoietic lineages. Kit is highly expressed in HSCs and is currently used as a phenotypic marker for HSCs. 8 Studies in the viable primary W mutant mice or in mice after transplantation indicate the importance of Kit signaling in maintaining adult HSC quiescence and survival. [9][10][11] Despite the wealth of knowledge on SCF/Kit signaling, it is poorly understood how Kit expression is regulated in HSCs and progenitors.Shp2, a tyrosine phosphatase with 2 Src-homology 2 (SH2) domains, is highly expressed in hematopoietic cells and has been shown to physically associate with ligand-activated Kit and other cell surface receptors. 12 Germline-dominant active mutations in PTPN11/Shp2 are found in approximately 50% of Noonan syndrome patients, who have a high risk of juvenile myelomonocytic leukemia. 13,14 Somatic gain-of-function mutations in PTPN11 have also been detected in nonsyndromic juvenile myelomonocytic leukemia, pediatric acute myeloid leukemia, B-cell precursor acute lymphoblastic leukemia, and myelodysplastic syndromes. [15][16][17] The expression of activated Shp2 leads to lethal myeloproliferative disease in transgenic or knockin mouse models. [18][19][20] Thus, PTPN11 has been proposed as the first proto-oncogene that encodes a tyrosine phosphatase. 21 However, the physiologic function of Shp2 in normal hematopoiesis in adults remains to be elucidated.Here we report a functional requirement for Shp2 in adult HSC maintenance and functions. Notably, we observed a prominent ablation of the Kit-positive stem/progenitor cell subpopulations in Shp2 ⌬/⌬ BM. Further analyses suggest tha...

Summary Bile acid (BA) biosynthesis is tightly controlled by intrahepatic negative feedback signaling elicited by BA binding to farnesoid X receptor (FXR), and also by enterohepatic communication involving ileal BA reabsorption and FGF15/19 secretion. However, how these pathways are coordinated is poorly understood. We show here that non-receptor tyrosine phosphatase Shp2 is a critical player that couples and regulates the intrahepatic and enterohepatic signals for repression of BA synthesis. Ablating Shp2 in hepatocytes suppressed signal relay from FGFR4, receptor for FGF15/19, and attenuated BA activation of FXR signaling, resulting in elevation of systemic BA levels and chronic hepatobiliary disorders in mice. Acting immediately downstream of FGFR4, Shp2 associates with FRS2α and promotes the receptor activation and signal relay to several pathways. These results elucidate a molecular mechanism for the control of BA homeostasis by Shp2 through orchestration of multiple signals in hepatocytes.

The molecular mechanism underlying adipogenesis and the physiological functions of adipose tissue are not fully understood. We describe here a unique mouse model of severe lipodystrophy. Ablation of Ptpn11/Shp2 in adipocytes, mediated by aP2-Cre, led to premature death, lack of white fat, low blood pressure, compensatory erythrocytosis, and hepatic steatosis in Shp2 fat−/− mice. Fat transplantation partially rescued the lifespan and blood pressure in Shp2 fat−/− mice, and administration of leptin also restored partially the blood pressure of mutant animals with endogenous leptin deficiency. Consistently, homozygous deletion of Shp2 inhibited adipocyte differentiation from embryonic stem (ES) cells. Biochemical analyses suggest a Shp2-TAO2-p38-p300-PPARγ pathway in adipogenesis, in which Shp2 suppresses p38 activation, leading to stabilization of p300 and enhanced PPARγ expression. Inhibition of p38 restored adipocyte differentiation from Shp2 −/− ES cells, and p38signaling is also suppressed in obese patients and obese animals. These results illustrate an essential role of adipose tissue in mammalian survival and physiology and also suggest a common signaling mechanism involved in adipogenesis and obesity development.transduction | preadipocyte | dephosphorylation | substrate trapping