Regulation Of Mesenchymal Stem Cell Differentiation By Phosphatase SHP1

Mesenchymal stem cells?MSCs?are multiple stem cells exist in various tissues.They are the common precursor of osteoblasts and adipocytes.The differentiation of these cells into these two cell types is tightly regulated.Improper fate decision of the differentiation is believed to be involved in the manifestation of various disorders,such as obesity,osteoporosis,and osteopetrosis.However,the detail mechanisms controlling the balance between osteogenesis and adipogenesis are still elusive.Src Homology 2?SH2?domain-containing phosphatase-1?SHP1?is a member of the protein–tyrosine phosphatase?PTP?family and is predominantly expressed in hematopoietic cells.The SHP1 molecule consists of two SH2 domains and one N-terminal domain.The SH2 domains bind to target subsrate proteins,and the N-terminal domain is a central catalytic domain that dephosphorylates thesubstrate molecules.The function of SHP1 is traditionally considered to regulate processes including cell growth,proliferation and differentiation of hematopoietic cells.However,its role on commitment of stem cells and some progenitor cells is unveiled recently.Here,we reported that viable motheaten?me^v/me^v?mice possessing SHP1 with defective phosphatase activity spontaneously developed osteoporosis.In supporting a role of SHP1 in bone metabolism,it was found that SHP1 expression was dramatically increased during osteogenic differentiation of wild-type MSCs.Coversely,MSCs from me^v/me^v mice exhibited a significantly reduced osteogenic potency and a robust increase in adipogenic potency,whereas specific knockdown of SHP1in wild type MSCs by shRNA inhibited osteogenic differentiation and promoted adipogenic differentiation.Consistent with these results,overexpression SHP1 in MSCs was found to promote osteogenic differentiation and inhibit adipogenic differentiation.Importantly,when hydroxyapatite-tricalcium?HA-TCP?material coated with MSCs was transplanted into nude mice,there was less bone formation of SHP1-deficient MSCs as compared with that of wild-type MSCs.To clarify the mechanism of SHP1-regulated MSC differentiation,the expression level of osteoblast-and adipocyte-specific transcriptional factors were detected.We found that the levels of Runt-related transcription factor 2?Runx2?,osteopontin?OPN?,Osteocalcin?OCN?and collagen 1??Col1??were significantly lower in me^v/me^v MSCs during their osteogenesis process,while the levels of CCAAT/enhancer-binding proteins??C/EBP??,Fatty acid binding protein 4?FABP4?and Adiponectin were dramatically higher in me^v/me^v MSCs during adipogenesis.Consistent with these results,in undifferentiated me^v/me^v MSCs the protein level of Runx2 was decreased,while the protein levels of C/EBP?and Peroxisome proliferator activated receptor??PPAR??were increased.The Wnt/?-catenin and BMP signaling pathways were shown to regulate the expression of various transcription factors critical for the differentiation of MSCs.We found that SHP1 had positively regulatory role on the Wnt/?-catenin signalling process although the BMP signals were unaffected.Specifically,SHP1 was found to bind GSK3?,and suppress its kinase activity by dephosphorylation of pY216,which led to the accumulation and translocation into nucleus of?-catenin.Deficiency of SHP1 in MSCs promotes degradation of?-catenin due to an increased phosphorylation of?-catenin by GSK3?.To definitely address the physiological role of SHP1 in MSCs,we generated SHP1^fl/flDermo1-cre mice by crossing SHP1^fl/fl mice with Dermo1-cre mice and we found that Dermo1-cre was expressed in mesenchymal lineadge cells.The length of the teeth of these mice is shorter and the volume of tibia is also smaller.On the other hand,the ratio of fat to body weight and the weight of gonadal adipose tissue increased in SHP1^fl/flDermo1-cre mice.Taking together,our study revealed a novel role of SHP1 in controlling tissue homeostasis by modulating MSC differentiation via regulating the Wnt/?-catenin signalling pathway.