Role of LOX-1 in Ang II-induced oxidative functional damage in renal tubular epithelial cells

The lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), plays an important role in angiotension II (Ang II)-induced hypertensive renal injury associated with pro-inflammatory responses, tubular functional damage and cellular apotosis. In this study, we report on the role of LOX-1 in Ang II-induced oxidative functional damage and underlying signaling in human renal proximal tubular epithelial cells (HRPTEpiCs). The exposure to Ang II enhanced the expression of the NADPH oxidases (the p22phox, p47phox and Nox4 subunits), LOX-1 and the adhesion molecule, ICAM-1. It also promoted monocytic U937 cell adherences to HRPTEpiCs, increased reactive oxygen species formation and stimulated apotosis, which was concomitant with an increase in the activation of p38 and p44/42 mitogen-activated protein kinases (MAPK). Furthermore, the Ang II treatment disturbed the balance of the Bcl-2 family proteins, destabilized mitochondrial membrane potential, and subsequently triggered the release of cytochrome c into the cytosol, causing the activation of caspase-3. The NADPH oxidase inhibitors and LOX-1 small interfering RNA markedly ameliorated these detrimental effects by reducing LOX-1 expression and MAPK activation. The p38 and p44/42MAPK inhibitors also inhibited the Ang II-induced functional damage without affecting LOX-1 expression in the HRPTEpiCs. These observations suggest that LOX-1 mediates Ang II-induced renal tubular epithelial dysfunction. In addition, MAPK pathway activation occurs downstream of the Ang II/reactive oxygen species/LOX-1 cascade.