SPARC promotes the development of erythroid progenitors

Secreted protein acidic and rich in cysteine (SPARC) is a well-recognized regulator that affects cell proliferation, differentiation, and survival. Here, we investigated the impact of SPARC on erythropoiesis. Erythropoiesis in bone marrow (BM) from SPARC−/− mice was analyzed by flow cytometry and colony-forming assays. The mechanisms that affected erythropoiesis were investigated by BM transplantation experiments. CD34+ cells from umbilical cord blood were isolated by MiniMACS, and the effect of SPARC on human erythropoiesis was assessed by colony-formation assay and erythroid differentiation culture. The hemoglobin level in peripheral blood (PB) was lower in SPARC−/− mice. Neither red blood cell count in PB nor the percentage of Ter119+ erythrocytes in BM showed significant difference between SPARC−/− and WT mice. However, the ability of SPARC−/− bone marrow cells (BMCs) to form erythroid burst-forming units (BFU-E), as well as spleen colony-forming units (CFU-S8), was significantly decreased. The addition of exogenous SPARC could promote the formation of BFU-E from SPARC−/− BMCs in vitro. And the impaired ability of SPARC−/− BMCs to form BFU-E could be restored by transplanted into WT BM microenvironment, whereas the BFU-E formation of WT BMCs was impaired after transplanted into SPARC−/− recipients. Furthermore, exogenous SPARC promoted umbilical cord blood CD34+ cells to form erythroid colonies and the hemoglobinization of erythroid, but did not affect the expression levels of glycophorin A and CD71. In conclusion, our results indicate that SPARC promotes the development of erythroid progenitors, but does not affect terminal erythroid differentiation.