Nonalcoholic fatty liver disease (
NAFLD) is an emerging global pandemic. Though significant progress has been made in unraveling the pathophysiology of the disease, the role of
protein phosphatase 2A (PP2A) and its subsequent inhibition by environmental and genetic factors in
NAFLD pathophysiology remains unclear. The present report tests the hypothesis that an exogenous PP2A inhibitor leads to hepatic
inflammation and fibrogenesis via an
NADPH oxidase 2 (NOX2)-dependent pathway in
NAFLD. Results showed that
microcystin (MC) administration, a potent PP2A inhibitor found in environmental exposure, led to an exacerbation of
NAFLD pathology with increased CD68 immunoreactivity, the release of proinflammatory
cytokines, and stellate cell activation, a process that was attenuated in mice that lacked the p47phox gene and miR21 knockout mice. Mechanistically,
leptin-primed immortalized Kupffer cells (a mimicked model for an
NAFLD condition) treated with
apocynin or nitrone spin trap 5,5 dimethyl-1-
pyrroline N-
oxide (DMPO) had significantly decreased CD68 and decreased miR21 and α-smooth muscle actin levels, suggesting the role of NOX2-dependent
reactive oxygen species in miR21-induced Kupffer cell activation and stellate cell pathology. Furthermore, NOX2-dependent
peroxynitrite generation was primarily responsible for cellular events observed following MC exposure since incubation with
phenylboronic acid attenuated miR21 levels, Kupffer cell activation, and inflammatory
cytokine release. Furthermore, blocking of the AKT pathway attenuated PP2A inhibitor-induced NOX2 activation and miR21 upregulation. Taken together, we show that PP2A may have protective roles, and its inhibition exacerbates
NAFLD pathology via activating NOX2-dependent
peroxynitrite generation, thus increasing miR21-induced pathology.NEW & NOTEWORTHY
Protein phosphatase 2A inhibition causes
nonalcoholic steatohepatitis (NASH) progression via
NADPH oxidase 2. In addition to a novel emchanism of action, we describe a new tool to describe NASH histopathology.