Distinct Effects of <i>Bacteroidota</i> -derived Glycine Lipids L654 and L1256 on Vascular Function and Skeletal Muscle Mitochondrial Capacity

Introduction: The gut microbiome plays a crucial role in maintaining health through the production of bioactive molecules. However, some bacterial products, such as lipopolysaccharide can negatively affect the endothelial layer of arteries, triggering inflammatory signaling. Emerging evidence has identified glycine lipids produced by members of Bacteroidota, including Lipid 654 (L654) and Lipid 1256 (L1256), as modifiers to disease development. While L654 has been shown to protect against atherosclerotic plaque accumulation, the physiological impact of L1256, particularly in vascular and skeletal muscle function, remains unclear. Given the strong interconnection between vascular function and skeletal muscle health, this study aimed to investigate the effects of L654 and L1256 on endothelial function and mitochondrial respiratory function in skeletal muscle. Methods: Forty-five male, 8-week-old Ldlr -/- mice were randomly assigned to one of four experimental groups: a vehicle-injected chow diet-fed group (LFD, n=12), a vehicle-injected high-fat diet-fed group (HFD, n=10), a bacterial L654-injected HFD-fed group (L654, n=11), and a bacterial L1256-injected HFD-fed group (L1256, n=12). Mice were fed a high-fat diet for 8 weeks and received intraperitoneal injection three times per week for 8 weeks at a dose of 1 μg per injection. Following the intervention, femoral arteries were analyzed via pressure myography to evaluate vasodilatory responses to endothelium-dependent (flow-induced shear stress and acetylcholine [ACh]) stimuli. Mitochondrial respiratory function was assessed in permeabilized soleus muscle using high-resolution respirometry, Oroboros O2k system. One-way ANOVAs and LSD post-hoc tests were used to determine statistical differences between groups, with significance set at p &lt; 0.05. Results: There was no significant difference in body weight across the groups. Endothelium-dependent vasodilation, induced by either flow or ACh, showed no significant differences across conditions. Mitochondrial function analysis revealed no significant differences in the respiratory control ratio (RCR), LEAK, or complex I activity. However, maximum mitochondrial respiratory capacity was significantly higher in the L1256 compared to both the HFD and L654 groups, while the L654 group exhibited lower values compared to LFD (LFD: 118.5 ± 36.4, HFD: 103.9 ± 33.1, L654: 87.3 ± 24.1, L1256: 134.3 ± 35.3 pmol·s -1 ·mg -1 , p &lt; 0.05). Conclusion: Although previous studies suggest L654 may have protective vascular effects through the reduction of atherosclerotic plaque accumulation, our findings indicate no significant effects on endothelial vasodilatory function. However, L1256 enhanced maximum mitochondrial respiratory capacity in skeletal muscle, highlighting distinct physiological roles of these glycine lipids derived from Bacteroidota. Further research is warranted to elucidate the underlying mechanisms and potential implications for metabolic health. UConn CAHNR Pilot Study grant This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.