sPLA2-IB and PLA2R Mediate Aberrant Glucose Metabolism in Podocytes via Hyperactivation of the mTOR/HIF-1α Pathway

Secretory phospholipase A2 group IB (sPLA2-IB) and M-type phospholipase A2 receptor (PLA2R) are closely related to proteinuria and idiopathic membranous nephropathy (IMN). Podocytes are important components of the glomerular filtration barrier and glucose metabolism, including glycolysis and tricarboxylic acid (TCA) cycle, is crucial for maintaining podocyte physiological function. Aberrant energy metabolism has been reported in proteinuria diseases, including diabetic nephropathy. However, altering energy states in podocytes in IMN remain unknown. The study aimed to determine whether sPLA2-IB induces energy metabolism abnormalities in podocytes. Cultured podocytes were treated with sPLA2-IB. siRNAs were used to knockdown expression of HIF-1α and PLA2R. Adenosine triphosphate (ATP) levels, the oxygen consumption rate and lactate content were assessed. Key enzyme of glycolysis, PKM2 and LDHA, TCA cycle-related enzymes and mTOR/HIF-1α pathway, were analyzed by PCR and immunoblotting. MTT assay was used for cell viability and phalloidin for cytoskeleton staining. sPLA2-IB induced insufficient energy states in podocytes, by decreased ATP production, increased lactate accumulation and reduced oxygen consumption rates. Under sPLA2-IB stimulation, LDHA and PKM2 were increased, while TCA cycle-related enzymes (CS, FH and SDHD) were decreased, with upregulated mTOR and HIF-1α. Mechanically, HIF-1α knockdown mitigated sPLA2-IB -induced LDHA upregulation and downregulated TCA cycle-related enzymes. Rapamycin (inhibitor of mTOR) reversed decreased ATP levels and oxygen consumption. 3-MA (activator of mTOR) aggravated lactate production. PLA2R knockdown reversed PKM2 and LDHA upregulation, FH and SDHD downregulation, and increased mTOR and HIF-1α expression. PLA2R activation by sPLA2-IB caused abnormal energy states in podocytes. The underlying mechanism involved the activation of mTOR/HIF-1α pathway.