PB0673 - Short-chain fatty acids butyrate modulate macrophage function via HDAC-AhR crosstalk in immune thrombocytopenia

Background: immune thrombocytopenia (ITP) is an autoimmune disorder in which macrophages play a critical role. Short-chain fatty acids (SCFAs) butyrate are gut-microbiota-derived metabolites and have immunomodulatory effects on macrophages.

Aims: To further investigate the effect and underlying mechanism of butyrate on macrophages in ITP patients.

Methods: Plasma SCFAs were detected by gas chromatography and mass spectrometry. Human monocyte derived macrophages were induced with M-CSF, and treated with or without butyrate. The levels of TNF-α and IL-6 in supernatants were assayed by ELISA. The antigen presenting and phagocytic function of macrophages were evaluated by FCM. Acetylation levels was analyzed by chromatin immunoprecipitation (ChIP). The aryl hydrocarbon receptor (AhR) was knocked down by siRNA and overexpressed by lentivirus, and the function of macrophage and histone deacetylase (HDAC) activity were investigated. The AhR/HDAC interaction was analyzed by coimmunoprecipitation (Co-IP) experiment.

Results: We identified that there was a significant reduction of butyrate in plasma of ITP patients compared with HCs. Butyrate modulated macrophage showed decreased secretion of TNF-α and IL-6 compared with unmodulated ones. Butyrate modulated macrophage dramatically suppressed CD4+ T-cell proliferation and exhibited decreased phagocytic capability. Similar to trichostatin A (TSA), butyrate increased histone acetylation. ChIP experiments revealed that treatment of macrophages with butyrate or TSA led to an increase of histone 3 lysine 27 (H3k27) and histone 4 lysine 8 (H4K8) acetylation levels at the promoter regions of IL-6 and TNF-α. However, the suppression of IL-6 and TNF-α secretion, and H3K27 and H4K8 acetylation levels of macrophages after AhR siRNA transfection was significantly attenuated compared with that by mock-transfected macrophages. We then confirmed the physical interaction of AhR and HDAC by Co-IP.

Conclusion(s): Our results showed that butyrate regulates macrophage function through inhibition of HDAC and activation of AhR, demonstrating that butyrate supplementation may serve as a viable therapy for ITP.