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Abstract
Fatty acid oxidation is the major energy pathway used by the kidney, although glycolysis becomes more important in the low oxygen environment of the medulla. Fatty acid oxidation appears to be reduced in renal fibrosis, and drugs that reverse this improve fibrosis. Expression of glycolytic genes is more variable, but some studies have shown that inhibiting glycolysis reduces renal fibrosis. To address the role of glycolysis in renal fibrosis, we have used a genetic approach. The crucial control point in the rate of glycolysis is 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase. Phosphorylation of the kidney isoform, PFKFB2, on residues Ser468 and Ser485 stimulates glycolysis and is the most important mechanism regulating glycolysis. We generated transgenic mice with inactivating mutations of Ser468 and Ser485 in PFKFB2 (PFKFB2 KI mice). These mutations were associated with a reduced ability to increase glycolysis in primary cultures of renal tubular cells from PFKFB2 KI mice compared to WT cells. This was associated in PFKFB2 KI mice with increased renal fibrosis, which was more severe in the unilaternal ureteric obstruction (UUO) model compared with the folic acid nephropathy (FAN) model. These studies show that phosphorylation of PFKFB2 is important in limiting renal fibrosis after injury, indicating that the ability to regulate and maintain adequate glycolysis in the kidney is crucial for renal homeostasis. The changes were most marked in the UUO model, probably reflecting a greater effect on distal renal tubules and the greater importance of glycolysis in the distal nephron.
Highlights
Fatty acid oxidation is the major energy pathway used by the kidney, glycolysis becomes more important in the low oxygen environment of the medulla
To determine whether inactivating mutation of the S er[468] and Ser[485] sites in PFKFB2 affected the ability of cells to increase glycolysis in response to stimuli, primary cultures of renal tubular epithelial cells were isolated from PFKFB2 KI mice (PFKFB2 KI TEC) and Wild type (WT) mice (WT TEC)
Expression of the proteins that determine the rate of glycolysis, namely hexokinase, phosphofructokinase 1 (PFK1) and pyruvate kinase (PKM2) was unchanged in the PFKFB2 KI TEC compared to WT (Fig. 2A–F)
Summary
Fatty acid oxidation is the major energy pathway used by the kidney, glycolysis becomes more important in the low oxygen environment of the medulla. This was associated in PFKFB2 KI mice with increased renal fibrosis, which was more severe in the unilaternal ureteric obstruction (UUO) model compared with the folic acid nephropathy (FAN) model These studies show that phosphorylation of PFKFB2 is important in limiting renal fibrosis after injury, indicating that the ability to regulate and maintain adequate glycolysis in the kidney is crucial for renal homeostasis. Recent evidence indicates that the development of renal fibrosis is accompanied by a reduction in fatty acid oxidation by tubular epithelial cells[1,2,3] Drugs that reverse this process reduce fibrosis in experimental models[1, 4].
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