ROR alpha Induces KLF4-Mediated M2 Polarization in the Liver Macrophagesthat Protect against Nonalcoholic Steatohepatitis

The regulation of M1/M2 polarization in liver macrophages is closely associated with the progression of nonalcoholic steatohepatitis (NASH); however, the mechanism involved in this process remains unclear. Here, we describe the orphan nuclear receptor retinoic-acid-related orphan receptor alpha (ROR alpha) as a key regulator of M1/M2 polarization in hepatic residential Kupffer cells (KCs) and infiltrated monocyte-derived macrophages. ROR alpha enhanced M2 polarization in KCs by inducing the kruppel-like factor 4. M2 polarization was defective in KCs and bone-marrow-derived macrophages of the myeloid-specific ROR alpha null mice, and these mice were susceptible to HFD-induced NASH. We found that IL-10 played an important role in connecting the function of M2 KCs to lipid accumulation and apoptosis in hepatocytes. Importantly, M2 polarization was controlled by a ROR alpha activator, JC1-40, which improved symptoms of NASH. Our results suggest that the M2-promoting effects of ROR alpha in liver macrophages may provide better therapeutic strategies against NASH.