LDL stimulates collagen mRNA synthesis in mesangial cells through induction of PKC and TGF-β expression.

Abnormal lipid accumulation in glomeruli could be implicated in the pathogenesis of glomerulosclerosis. Low-density lipoprotein (LDL) stimulates collagen mRNA expression in cultured human mesangial cells (HMC). To explore the possible molecular mechanisms by which LDL promotes collagen gene expression, we examined the effects of LDL on protein kinase C (PKC) activity and transforming growth factor-β (TGF-β) expression in relation to collagen gene regulation in HMC. LDL (200 μg/ml) induced an acute increase in PKC activity, particularly PKC-α and -δ, within 15 min, which decreased to control value at 2 h. LDL stimulated TGF-β1, and α1(I) and α1(IV) collagen mRNA expression within 30 min of incubation with HMC, and levels remained elevated until hour 4. LDL induced the secretion of TGF-β by HMC. This TGF-β was shown by CCL-64 mink lung cell assay to be, in part, bioactive. The stimulatory effects of LDL on collagen gene regulation in HMC were blocked by the inhibition of PKC using GF-109203X (GFX) or the downregulation of PKC using phorbol myristate acetate. Neutralizing antibody to TGF-β inhibited the increased collagen mRNA expression by HMC exposed to LDL. The downregulation or inhibition of PKC did not affect the stimulatory effect of LDL on TGF-β mRNA or protein expression. These results suggest that in HMC, LDL stimulates collagen mRNA expression through the rapid activation of PKC-α and -δ and transcriptional upregulation of TGF-β. Thus PKC and TGF-β may function as independent key signaling intermediaries in the pathway by which LDL upregulates collagen gene expression in HMC.