Abstract 4141726: Ceramides produced by gut bacteria <i>Bacteroides thetaiotaomicron</i> causally induce aortic perivascular adipose tissue-endothelial cell senescence in aged host

Introduction: Specific ceramides play a crucial role in cellular senescence by upregulating the SASP in the vasculature, leading to atherosclerosis in the aging population. Gut microbiota is emerging as a regulator of circulating ceramides in the host. However, it remains unknown what/how gut bacteria causally regulate ceramide-induced perivascular adipose tissue (PVAT) and endothelial cell (EC) senescence in aging. Methods: To address the knowledge gap in gut-derived ceramides and their regulation of (peri)vascular aging, we performed high-throughput multi-omics (fecal shotgun metagenomics and plasma LC-MS/MS lipidomics) coupled with bacterial colonization, senescence, and cell-cell interaction studies. Results: Our metagenomic and plasma lipidomic studies on human (TwinsUK Aging Cohort, n=900; Aging Heart Zurich Cohort, n&gt;800) and mouse (&gt;24 vs. 3 months, n=6) aging cohorts pinpointed a higher abundance of Bacteroides thetaiotaomicron (B. theta) harboring the serine palmitoyltransferase ( SPT ) gene, synthesizing deleterious ceramides C18:1/16:0 and C18:1/18:0 in old hosts. Importantly, plasma levels of the ceramides were positively associated with major adverse cardiovascular events (MACE) in atherosclerotic CVD patients within the Aging Heart Zurich Cohort (n=105). In vivo colonization of young mice with B. theta (4-weeks) confirmed a marked increase in circulating Cer 18:1/16:0 and 18:1/18:0, accompanied by higher signals of the SASP component IL6 and the proliferative arrest marker p16 INK4a in aortic PVAT and ECs. These mice also exhibited reduced vasorelaxation responses and angiogenic incompetence. As a proof of concept, our PVAT-EC co-culture studies demonstrated that addition of the ceramides induces senescence and dysfunction in PVAT by upregulating Notch1 signaling. This upregulation increases IL1β and its downstream IL6, leading to the downregulation of adipocyte function markers UCP1 and adiponectin. The released IL6 also induced a senescence phenotype in ECs, evidenced by increased SA-β-gal activity, DNA damage response (↑ γ-H2A.X), telomere attrition (↓ hTERT), and proliferative arrest (↑ p16 INK4a &amp;p19 INK4d ). Conclusion: This research identifies B. theta as a causal contributor to deleterious ceramides in the host circulation, leading to (peri)vascular senescence and dysfunction in aging. Targeting B. theta offers a novel microbiome-based approach to decelerate (peri)vascular senescence and extend healthspan, with potential clinical applications.