S. H. Xu1,2, Y. Li1,2, C. Zhang1,2, H. Vasquez1,2, K. Rebello1,2, J. S. Coselli1,2,3, D. Milewicz3,4, S. LeMaire1,2,3, Y. Shen1,2,3 1Baylor College Of Medicine, Department Of Cardiothoracic Surgery, Houston, TX, USA 2Baylor College Of Medicine, Texas Heart Institute, Houston, TX, USA 3Baylor College Of Medicine, Cardiovascular Research Institute, Houston, TX, USA 4University Of Texas Health Science Center At Houston, McGovern Medical School, Department Of Medical Genetics, Houston, TX, USA
Introduction: Ascending thoracic aortic aneurysms (ATAA) and their progression to acute dissection (ATAD) are associated with high mortality. Our recent single-cell RNA sequencing (scRNA-seq) analysis revealed a shift from a compensatory to a decompensatory phenotype in smooth muscle cells (SMCs) in human aortic tissue as ATAA progresses to ATAD. Because the tricarboxylic acid (TCA) cycle plays a critical role in mitochondrial function and cellular metabolism, we hypothesized that TCA cycle activity is elevated in SMCs of human ATAA tissues and reduced in ATAD tissues compared to non-diseased controls.
Methods: We performed scRNA-seq analysis of ascending aortic tissue from 9 patients with ATAA without dissection, 9 patients with ATAD (dissected and non-dissected areas collected separately), and 8 organ donor control subjects (Fig 1A). Within the SMC clusters analyzed, we identified differentially expressed TCA-related genes between control, ATAA, and ATAD patients. Single-cell flux estimation analysis (scFEA) was performed to estimate metabolic flux variation in TCA cycle activity in SMCs.
Results: We observed an upregulation of TCA cycle enzyme coding genes (e.g., SDHB, FH, MDH2) in SMCs of ATAA compared to controls and downregulation of these genes in SMCs of ATAD compared to controls. Upon analyzing metabolic pathways (e.g., fatty acid β-oxidation and pyruvate metabolism) that contribute acetyl coenzyme A (acetyl-CoA) to the TCA cycle, we found similar mRNA abundance from β-oxidation-related genes (e.g., ACADL, HADH, ECH1) in ATAA and controls, but significantly downregulated expression in ATAD compared to controls (p<0.001). scFEA analysis confirmed significantly lower fatty acid oxidation activity in ATAD compared to controls (p<0.001). While expression of PDHA1 (pyruvate dehydrogenase E1 subunit alpha 1, which catalyzes the conversion of pyruvate to acetyl-CoA) was similar across groups, the expression of lactate dehydrogenase coding gene LDHA, which converts pyruvate to lactate, was significantly increased in ATAD compared to ATAA (p<0.001) and controls (p<0.001). Through scFEA analysis, we observed significantly higher levels of pyruvate to lactate conversion in ATAD when compared to ATAA (p<0.001) and controls (p<0.001).
Conclusion: Our data suggest TCA cycle activity increased in ATAA and decreased in ATAD. This shift may play a role in the transition from mitochondrial compensation to mitochondrial failure as it relates to the progression from normal aorta to ATAA to ATAD. Increased β-oxidation and lactate fermentation in ATAD may indicate disruption of acetyl-CoA supply from fatty acid oxidation and shift toward anaerobic glycolysis as a result of impaired TCA cycle in SMCs of ATAD.
