Up-regulation of skeletal muscle LIM protein 1 gene by 25-hydroxycholesterol may mediate morphological changes of rat aortic smooth muscle cells

Changes in the expression level of the skeletal muscle LIM protein 1 (SLIM1) in cultured A10 cells were monitored in response to 25-hydroxycholesterol (25-HC), an oxidized form of cholesterol present in the oxidized low-density lipoproteins. The level of SLIM1 mRNA was elevated in a time- and concentration-dependent manner by treatment of 25-HC. Expressions of smooth muscle (SM) α-actin and calponin-1 (CNN-1), early markers for SMC differentiation, were also increased by the 25-HC treatments. Expressions of all three genes (SLIM1, SM α-actin and CNN-1) were simultaneously elevated in the cells treated with 9-cis retinoic acid (RA). On the other hand, the SLIM1 expression induced by the 25-HC or 9-cis RA (as well as SM α-actin and CNN-1) was decreased by the treatment of 15d-PGJ2. Since the 25-HC, 9-cis RA and 15d-PGJ2 were ligands for the LXR, RXRα and PPARγ respectively, there might be a functional positive cross-talk between LXR and RXRα pathways and a negative cross-talk between PPARγ and LXR and/or RXRα pathways in the regulation of SLIM1 expression. The cells stably transfected with the expressional vector for SLIM1 also showed an elevation in the levels of SM α-actin and CNN-1. In addition, an over-production of SLIM1 in the cells resulted in a change in the cell-shape into a spindle-like form, which is identical to that observed after a prolonged treatment of the cells with cholesterol.