Microcystin Activates Renal NOX2 and Exacerbates Nonalcoholic Fatty Liver Disease-induced Ectopic Glomerulonephritis

Abstract

Clinical evidence show NAFLD results in cardiovascular, intestinal and renal complications. Previous reports from our laboratory exhibited NAFLD induced ectopic inflammatory manifestations in the kidney that gave rise to glomerular inflammation. Extending our studies, we hypothesized that existing inflammatory conditions in NAFLD could make the kidneys more susceptible to environmental toxins. Microcystin-LR, a crucial component of harmful algal blooms has been shown to be hepatotoxic. Our results showed that exposure of MC in NAFLD mice caused a significant increase in mesangial cell activation as evidenced by increased a-SMA in the extracellular matrix surrounding the glomeruli. The kidneys surrounding the glomeruli also had increased NOX2 activation as shown by increased co-localization of p47 Phox and its membrane component gp91. To show whether NOX2 activation was crucial to microcystin exposure and exacerbation of renal toxicity, experiments were designed in vitro with immortalized mesangial cells of mouse origin. The cells incubated with (a) apocynin and (b) nitrone spin trap DMPO showed significantly decreased a-SMA, miR21 levels and proinflammatory cytokine release in the supernatant. In parallel, mice lacking miR21, a proinflammatory miR, known to be activated by NOX2, when exposed to MC in NAFLD showed decreased mesangial cell activation. Mechanistically, phenyl boronic acid incubated cells that are exposed to MC showed significantly decreased mesangial cell activation showing that peroxynitrite might be the major reactive species involved in mediation the activation process, release of proinflammatory micro RNAs and cytokines that are crucial for renal toxicity. Thus, in conclusion, MC exposure causes NOX2 activation that leads to mesangial cell activation and toxicity via releases of peroxynitrite and miR21.