Mitochondrial DNA from hepatocytes induces upregulation of interleukin-33 expression of macrophages in nonalcoholic steatohepatitis

Objective In the present study, we propose that lipotoxicity induces the release of mitochondrial DNA (mtDNA) from hepatocytes, which in turn upregulates IL-33 expression in macrophages. Methods The mtDNA levels of plasma were determined in methionine- and mholine-deficient diet (MCD)-fed mice and NASH patients. Cultured hepatocytes were pre-incubated with Mito-TEMPO or rapamycin and were then stimulated with palmitic acid. The mtDNA levels in the cytosol were measured. The mtDNA from hepatocytes of mice was added to bone marrow-derived macrophages (BMDMs) in the presence of IRS (TLR9 antagonist). The expression of IL-33 in BMDMs was measured. Results Levels of mtDNA were higher in NASH patients and MCD-fed mice. Treatment of hepatocytes with palmitic acid in vitro induced mtDNA release into cytosol, which was attenuated by mito-TEMPO or rapamycin, and aggravated by inhibition of autophagy. Treatment of BMDMs with mtDNA enhanced IL-33 expression, which was attenuated by knockdown of TLR9. Treatment of BMDMs with mtDNA enhanced lipopolysaccharide (LPS)-induced production of IL-1β and TNF-α, which was attenuated by pretreatment with soluble ST2. Conclusion mtDNA released from injured hepatocytes under lipid overload induced the upregulation of IL-33 expression in macrophages via TLR9, and enhanced LPS-induced inflammatory cytokine production.