LYSOPHOSPHATIDIC ACID ACTIVATES BMP2 GENE PROMOTER THROUGH A RHOA-PHOSPHORYLATED P65 SERINE 536 PATHWAY IN AORTIC VALVE INTERSTITIAL CELLS: IMPLICATION FOR CALCIFIC AORTIC VALVE DISEASE

Abstract

Calcific aortic valve disease (CAVD) is the most common heart valve disorder. There is so far no medical treatment for CAVD that could prevent its progression. Recently, we demonstrated that lysophosphatidic acid (LPA) is produced by autotaxine enzyme (ATX) in mineralized aortic valves. However, no clear evidence has been given regarding the mechanism of action by which the LPA acts on mineralization and the inflammatory process within the aortic valve. By using different approaches in vitro we have investigated the effect of LPA on the osteogenic phenotype and its role as pro-mineralizing. We have also documented the NF-κB signaling pathway by analysis of promoter activity and of transcripts targets measurement by q - PCR. In cell culture we found that the expression of osteogenic genes (BMP2, RUNX2, BGLAP, and COL1A1), alkaline phosphatase (ALP) activity and VICs mineralization were increased by several-fold after treatment of cells with LPA. Also, we have shown that LPA-induced osteogenic response relied on RhoA pathway downstream of the LPA receptor-1 (LPAR1). In this regard, we found that RhoA is a regulator of the NF-κB pathway and promotes BMP2 expression. In addition, by using promoter luciferase assay we documented that NF-κB-p65 phosphorylation on Ser536 (phospho-Ser-536 p65) activates BMP2 promoter following treatment with LPA. We next showed by using chromatin immunoprecipitation assays (ChIP) that the binding of phospho-Ser-536 p65 to BMP2 promoter is not reversed by IκBα overexpression, an inhibitor of NF-κB pathway. Together, these results suggest that LPA induced VICs mineralization by a phospho-Ser-536 p65 pathway, which defines a mechanism of activation that does not respond to the negative feedback of IκBα. Hence, we documented a novel mechanism whereby LPAR1 and RhoA modulate the NF-κB pathway and its downstream target BMP-2, which is a strong promoter of VICs mineralization.