The Role of HADHB in Mitochondrial Fatty Acid Metabolism During Initiation of Metastasis in ccRCC.

The initiation and progression of clear cell renal cell carcinoma (ccRCC) are closely linked to significant metabolic alterations. Specifically, lipid metabolism alterations and their association with the high invasiveness in ccRCC require further investigation. After conducting RNA-sequencing (RNA-seq), we discovered that Hydroxyacyl-CoA Dehydrogenase Trifunctional Multienzyme Complex Subunit Beta (HADHB) was significantly downregulated in the highly invasive ccRCC cell line. It was found that the expression of HADHB in ccRCC tumor tissues was lower than that in paracancer tissues, which is associated with poor patient prognosis. Subsequently, we confirmed that highly invasive ccRCC exhibited an increased lipid accumulation due to the suppression of mitochondrial fatty acid transport and enhanced conversion of fatty acids to triglycerides within cancer cells. Specifically, the downregulation of HADHB inhibited mitochondrial fatty acid β-oxidation (FAO) in cancer cells, leading to partial impairment of mitochondrial function and decreased ATP production. However, this trade-off involving the reduction of a high-yield ATP production conferred an advantage by reducing reactive oxygen species (ROS) generation within cancer cells, thereby protecting them from oxidative stress and enhancing their invasive potential. Furthermore, the downregulation of HADHB promoted epithelial-mesenchymal transition (EMT) and angiogenesis in cancer cells, accelerating the progression of ccRCC and endowing ccRCC cells with metastatic capabilities.