FIGURE 1.

Metabolism in Normal Renal TECs. In the proximal tubules of the kidney, long-chain fatty acids are absorbed via transport proteins such as CD36 and fatty acid binding protein (FABP). These fatty acids are catalyzed by acyl-CoA synthetase on the outer mitochondrial membrane to form acyl-CoA in conjunction with coenzyme A (CoA). Acyl-CoA is then shuttled through a channel into the mitochondrial intermembrane space where it encounters carnitine palmitoyltransferase 1 (CPT1) that is embedded in the membrane. Under the catalysis of CPT1, acyl-CoA is conjugated with carnitine to form acylcarnitine. This acylcarnitine is then transported across the mitochondrial inner membrane by carnitine-acylcarnitine translocase (CACT). Subsequently, acylcarnitine is converted back to acyl-CoA by carnitine acyltransferase 2 (CPT2), which is associated with the mitochondrial inner membrane. Acyl-CoA then undergoes a series of reactions including dehydrogenation, hydration, dehydrogenation, and thiolytic cleavage, constituting the β-oxidation process. This leads to the production of acetyl-CoA, while concomitantly generating FADH2 and NADH. The acetyl-CoA enters the TCA cycle, resulting in additional molecules of FADH2 and NADH. These electron carriers—FADH2 and NADH—from both the β-oxidation and the TCA cycle partake in the respiratory chain, transferring electrons to oxygen atoms; this electron transfer event is coupled with the phosphorylation of ADP to create ATP. Under conditions of oxygen deprivation, cells primarily generate energy through anaerobic glycolysis.CD36, cluster of differentiation 36; TEC, Tubular Epithelial Cell; CPT-1, carnitine O-palmitoyltransferase 1; CACT, carnitine-acylcarnitine translocase; CPT-2, carnitine O-palmitoyltransferase 2; TCA, tricarboxylic acid cycle; FADH2, reduced flavin adenine dinucleotide; NADH, reduced nicotinamide adenine dinucleotide; ATP, adenosine triphosphate; ADP, adenosine diphosphate.