PTGIS inhibited osteogenic and promoted angiogenic differentiation of bone marrow mesenchymal stem cells via endoplasmic reticulum stress mediated PI3K/AKT signaling.

Mesenchymal stem cells (MSCs) play a key role in ectopic mineralization. Effective treatment requires both inhibiting pathological calcification and promoting vessel growth. While prostacyclin synthase (PTGIS) is critical for vascular health, its role in regulating osteogenic and angiogenic differentiation in MSCs remains unclear. Following PTGIS modulation in bone marrow mesenchymal stem cells (BMSCs), osteogenesis was assessed by alkaline phosphatase (ALP) activity, Alizarin Red staining (ARS), and hydroxyapatite/tricalcium phosphate (HA/TCP) particles implantation. Angiogenesis was evaluated via a co-culture system of BMSCs and human umbilical vein endothelial cells (HUVECs). Mechanistic studies involved Ca²⁺ dynamics, western blotting, and pharmacological inhibition. Knockdown of PTGIS enhanced ALP activity, mineralization, the expression of the osteogenic marker DMP1/BSP, and bone-like tissue formation both in vitro and in vivo. Conversely, PTGIS knockdown reduced tubule formation in vitro and impaired blood vessel formation, and the expression of the angiogenic marker CD31 in vivo. Mechanistically, the overexpression of PTGIS promoted Ca²⁺ efflux, endoplasmic reticulum (ER) dilation and vacuolization, increased the levels of the ER stress markers BIP/GRP75, and elevated PI3K/AKT phosphorylation. The inhibition of either ER stress or AKT activity restored osteogenic capacity by enhancing ALP activity and mineralization, and suppressed angiogenic capacity by inhibiting tubule formation in BMSCs. PTGIS inhibited osteogenic and promoted angiogenic differentiation of BMSCs through ER stress mediated PI3K/AKT signaling pathway. This PTGIS-dependent regulatory pathway offers new insight into MSC fate determination and represents a potential therapeutic strategy for treating ectopic mineralization disorders.