Protein phosphatase 2A (PP2A) inhibition in NAFLD leads to an underlying intestinal fibrotic pathology that is NOX2 dependent

Increased oxidative stress exacerbates the condition of Non-Alcoholic Fatty Liver Disease (NAFLD) which is a global pandemic, leading to its progression to the state of chronic inflammation and fibrosis (NASH). Protein phosphatase 2A (PP2A) is an enzyme that plays an important role in fibrosis, but its role in controlling the production of reactive oxygen species is unclear. Our studies show that the environmental toxin microcystin, an inhibitor of PP2A, specifically inhibits the enzyme and generates higher oxidative stress. The above process activated TGF-β fibrotic signaling pathway in the intestines that was mediated by NOX2. Results using mouse NAFLD models and transformed rat intestinal epithelial cells showed that inhibiting PP2A by administration of microcystin led to increased NOX2 activation, increased SMAD2/3-SMAD4 co-localization and increased alpha smooth muscle actin immuno-reactivity. This process was greatly attenuated in p47 phox knockout mice signifying an important role of NOX2. Mechanistically, rat intestinal epithelial cells were treated with apocynin, DMPO and phenylboronic acid which showed significantly decreased NOX2 activation, SMAD co-localization and α-SMA immuno-reactivity. A significant decrease of NOX2 and TGF-β signaling in NOX4 inhibitor treated samples indicated that there might be a possibility of dependency of NOX isoforms on each other. This study gives us hope to explore novel therapeutic strategies by increasing PP2A in situ by administration of PP2A agonists for the treatment of NASH.