Abstract Body (Do not enter title and authors here): Background: Ketone body β-hydroxybutyrate (BHB), a lipid metabolic intermediate, is known as protective functions in cardiovascular diseases. We had reported that BHB attenuated chronic kidney disease through anti-inflammation. Abdominal aortic aneurysm (AAA) is a devastating cardiovascular disease without effective medication treatment. It is unclear whether BHB attenuates AAA formation and the potential molecular mechanism.
Methods: Exogenous supplementation of BHB, and systemic HMGCS2(the key enzyme for the synthesis of BHB) knockout mice were employed to observe the effect of BHB on AAA with angiotensin II (Ang II)-induced in ApoE knockout/CaPO4-induced in C57BL/6J mice. Ultrasonography, histology and immunohistochemistry, Gelatine zymography were used to evaluate the formation of AAA. Bioinformatics analysis, small interfering RNA, pathway inhibitor, DNA pulldown and CUT&RUN were used to explore the potential mechanisms.
Results: Clinically, we found that AAA patients showed low expression of BHB in serum and in aortic tissue compared with healthy human subject. Exogenous supplementation of BHB exhibited a reduced maximal diameter of AAA, alleviated vascular elastin degradation, and decreased the gathering of extracellular matrix proteins (MMPs) in Ang II-induced ApoE knockout mice and CaPO4-induced C57BL/6J mice through decreasing the expression of inflammasome and MMPs in both macrophage and vascular smooth muscle cells (VSMCs). Conversely, HMGCS2 knockout mice significantly increased maximal diameter and deteriorated elastic fiber degradation of abdominal aorta. Furthermore, BHB attenuated Ang II+LPS-stimulated inflammasome and LPS-stimulated MMPs expression through PI3/AKT dependent mechanism, while the suppressive effects of BHB were reversed by LY294002 (PI3-kinase inhibitor). The top 10 most differentially upregulated mRNAs were identified by transcriptomics on the aorta, of these, Cytidine triphosphate synthase 1(CTPS1) was closely related to PI3K/AKT signaling pathway. We found that BHB significantly increased the expression of CTPS1, which CTPS1 siRNA could diminished the inhibition of BHB on inflammasome and MMPs in vivo and in vitro. Finally, we found that BHB regulated CTPS1 expression by enhancing local β-hydroxybutyrylation of H3K9 at the promoter of CTPS1 gene.
Conclusion: BHB attenuated AAA formation via BHB-mediated epigenetic modification of CTPS1 expression which activated PI3K/AKT signaling pathway in macrophages and VSMCs.