Fibronectin enhances spinal cord astrocyte proliferation by elevating P2Y1 receptor expression.

After spinal cord injury (SCI), the formation of glial scar is a complex process that is attributed primarily to astrocytic proliferation, but the mechanism of astrocytes proliferation is still unclear. Fibronectin is a large extracellular glycoprotein that helps organize the matrix protein, and its main membrane receptor is the α5 β1 integrin subunit. In this study, fibronectin stimulated spinal cord astrocytic proliferation from two directions: fibronectin increased astrocytic proliferation via α5 β1 integrin receptor, and fibronectin upregulated the expression of P2Y1 receptor, and adenosine triphosphate (ATP) could enhance the astrocytic proliferation and induce more release of arachidonic acid and prostaglandin E2 via P2Y1. The upregulation of P2Y1 by fibronectin required [Ca2+]i and the activation of integrin link kinase (ILK) and Akt. We found that [Ca2+]i stimulated by fibronectin was α5 β1 integrin receptor dependent and that the phosphorylation of Akt or extracellular signal-regulated protein kinase (ERK1/2) induced by fibronectin mediated the activation of cAMP response element-binding protein (CREB) and signal transducer and activator of transcription 3 (Stat3). Our research suggests that the release of fibronectin and ATP could stimulate the spinal cord astrocytic proliferation after SCI, and the expression of P2Y1 increased by fibronectin would provide more sites for ATP, which could aggravate the proliferation and inflammation of spinal cord astrocytes.