Upregulation of Mitochondrial Sirt3 and Alleviation of the Inflammatory Phenotype in Macrophages by Estrogen

Background: Aging and comorbidities like type 2 diabetes and obesity contribute to the development of chronic systemic inflammation, which impacts the development of heart failure and vascular disease. Increasing evidence suggests a role of pro-inflammatory M1 macrophages in chronic inflammation. A shift of metabolism from mitochondrial oxidation to glycolysis is essential for the activation of the pro-inflammatory M1 phenotype. Thus, reprogramming the macrophage metabolism may alleviate the pro-inflammatory phenotype and protect against cardiovascular diseases. In the present study, we hypothesized that the activation of estrogen receptors leads to the elevation of the mitochondrial deacetylase Sirt3, which supports mitochondrial function and mitigates the pro-inflammatory phenotype in macrophages.

Materials and methods: Experiments were performed using the mouse macrophage cell line RAW264.7, as well as primary male or female murine bone marrow macrophages (BMMs). Macrophages were treated for 24 h with estradiol (E2) or vehicle (dextrin). The effect of E2 on Sirt3 expression was investigated in pro-inflammatory M1, anti-inflammatory/immunoregulatory M2, and naïve M0 macrophages. Mitochondrial respiration was measured by Seahorse assay, and protein expression and acetylation were determined by western blotting.

Results: E2 treatment upregulated mitochondrial Sirt3, reduced mitochondrial protein acetylation, and increased basal mitochondrial respiration in naïve RAW264.7 macrophages. Similar effects on Sirt3 expression and mitochondrial protein acetylation were observed in primary female but not in male murine BMMs. Although E2 upregulated Sirt3 in naïve M0, pro-inflammatory M1, and anti-inflammatory/immunoregulatory M2 macrophages, it reduced superoxide dismutase 2 acetylation and suppressed mitochondrial reactive oxygen species formation only in pro-inflammatory M1 macrophages. E2 alleviated the pro-inflammatory phenotype in M1 RAW264.7 cells.

Conclusions: The study suggests that E2 treatment upregulates Sirt3 expression in macrophages. In primary BMMs, female-specific Sirt3 upregulation was observed. The Sirt3 upregulation was accompanied by mitochondrial protein deacetylation and the alleviation of the oxidative and pro-inflammatory phenotype in M1 macrophages. Thus, the E2-Sirt3 axis might be used in a therapeutic strategy to fight chronic systemic inflammation and prevent the development of inflammation-linked diseases.