Small molecule-driven SIRT3-autophagy mediated NLRP3 inflammasome inhibition ameliorates inflammatory crosstalk between macrophages and adipocytes

Background and purpose: IL-1β, mainly produced by macrophages via the NLRP3 inflammasome, mediates the inflammatory crosstalk between macrophages and adipocytes. In our previous study, AEDC [(16S,20S,24R)-12β-acetoxy-16,23-epoxy-24,25-dihydroxy-3β-(β-D-xylopyranosyloxy)-9,19-cyclolanost-22(23)-ene], a cycloartane triterpenoid isolated from Actaea vaginata (Ranunculaceae), was found to possess anti-inflammatory effect on LPS-treated RAW264.7 macrophages. The current study was designed to investigate whether AEDC modulates macrophage-adipocyte crosstalk to alleviate adipose tissue inflammation.

Experimental approach: The anti-inflammatory effect of AEDC was evaluated on LPS plus ATP-induced THP-1 macrophages and C57BL/6J mice. The expression of autophagy-related and NLRP3 inflammasome complex proteins were analyzed by Western blots, immunofluorescence staining and co-immunoprecipitation. The pro-inflammatory cytokines levels were determined by ELISA kits. The adipose tissue inflammation was evaluated by histological analysis and immunohistochemical staining.

Key results: AEDC (5 and 10 μM) activated autophagy, which in turn suppressed the NLRP3 inflammasome activation and IL-1β secretion in THP-1 macrophages. AEDC increased the expression of SIRT3 deacetylase and enhanced its deacetylating activity to reverse mitochondrial dysfunction and activate AMP-activated protein kinase, which together induced autophagy. Moreover, AEDC (10 μM) attenuated macrophage-conditioned medium-induced inflammatory responses in adipocytes, and blocked THP-1 macrophages migration towards 3T3-L1 adipocytes. In inflammation mice, AEDC (5 and 20 mg·Kg^-1 ) treatment reduced the levels of pro-inflammatory cytokines in serum and epididymal adipose tissue, and reduced macrophage infiltration to alleviate adipose tissue inflammation.

Conclusion and implications: In summary, AEDC attenuated the inflammatory crosstalk between macrophages and adipocytes through SIRT3-autopahgy mediated NLRP3 inflammasome inhibition, which might be a candidate for the treatment of adipose tissue inflammation-related metabolic disorders.

Keywords: Cycloartane triterpenoid; IL-1β; NLRP3 inflammasome; adipocytes; adipose tissue inflammation; autophagy; macrophages.