Microcystin Exposure Exacerbates Nonalcoholic Fatty Liver Disease (Nafld) Via Nox2 Dependent Activation Of Mir21-Induced Inflammatory Pathways

Non-alcoholic fatty liver disease is an emerging global pandemic with 15% of the cases progressing to steatohepatitis or cirrhosis and eventually to hepatocellular carcinoma. Though significant progress has been made in unravelling the pathophysiology of the disease, the effect of environmental and genetic factors in an underlying NAFLD pathophysiology remains unclear. The present report tests the hypothesis that microcystin (MC), a principal component of harmful algal blooms activates Kupffer cells and hepatic stellate cells, crucial mediators in hepatic fibrogenesis via NOX2 dependent pathway in an underlying condition of NAFLD. Mice that had mild steatosis and showed signs of NAFLD were exposed to microcystin via an intraperitoneal route. Results showed that MC exposure led to exacerbation of NAFLD pathology with increased CD68 immunoreactivity, release of proinflammatory cytokines and stellate cell activation, a process that was attenuated in miR21 knockout mice and mice that lacked the p47 phox gene. Mechanistically, immortalized Kupffer cells treated with apocynin or nitrone spin trap DMPO had significantly decreased CD68, decreased miR21 and α-SMA levels signifying the role of NOX2-dedendent reactive oxygen species in miR21-induced Kupffer cell activation and stellate cell pathology. Further, NOX2 dependent peroxynitrite generation was primarily responsible for cellular events observed following MC exposure since incubation with phenyl boronic acid attenuated miR21 levels, Kuppfer cell activation and inflammatory cytokine release. Taken together, we show that MC exposure exacerbates NAFLD pathology via NOX2 dependent peroxynitrite generation by increasing miR21 levels.