ACAD8-mediated valine catabolism inhibits mTOR signaling to suppress lipid accumulation and progression of clear cell renal cell carcinoma

BACKGROUND: Clear cell renal cell carcinoma (ccRCC) poses a serious threat to human health. Abnormal lipid accumulation is a hallmark biological feature of this malignancy; however, its underlying mechanisms remain incompletely understood. Our study aimed to identify a novel lipid-related biomarker and to elucidate the mechanisms driving aberrant lipid accumulation in ccRCC. METHODS: Weighted Gene Co-expression Network Analysis (WGCNA) was performed to identify a hub module and key genes related to lipid metabolism. qRT-PCR, western blotting, and immunohistochemistry (IHC) were used to assess ACAD8 expression. CCK-8, 2D and 3D colony formation, EdU, Transwell, and wound-healing assays were employed to investigate the biological functions of ACAD8. Subcutaneous tumor xenografts in BALB/c nude mice were used to determine the biological function of ACAD8 and its downstream pathways in vivo. BODIPY and Oil Red O staining were used to assess lipid accumulation, and triglyceride and total cholesterol levels were quantified. Leucine, isoleucine, and valine levels were measured using assay kits to assess the effects of ACAD8 on branched-chain amino acid (BCAA) levels. Bioinformatic analysis was conducted to identify potential downstream targets of ACAD8 and valine. RESULTS: ACAD8 was identified as a novel lipid-related biomarker for ccRCC, with its reduced expression correlating with more advanced clinical stages and poorer prognosis. Functionally, restoring ACAD8 expression inhibited lipid accumulation and tumor progression. Mechanistically, ACAD8 facilitated valine degradation, and the subsequent decrease in valine levels led to suppressed mTOR activation, thereby inhibiting SREBP1 activation and the downstream expression of FASN and SCD. CONCLUSION: Overall, our research indicated that the loss of ACAD8 resulted in the accumulation of valine and mTOR signaling activation, which promoted SREBP1 activation and increased lipogenesis, leading to lipid accumulation and tumor progression. Our findings link BCAA metabolism with lipid accumulation and may inform future biomarker development and therapeutic strategies for ccRCC.