Background: Recent studies indicate mitochondrial dysfunction is a dominant pathway in diabetic kidney disease (DKD), however underlying mechanisms are unclear. Here we examined if Crabtree effect by glucose is a cause of mitochondrial dysfunction in kidney.
Methods: Lactate was measured by by YSI biochemistry analyzer. TCA cycle metabolites were measured by gas chromatography mass spectroscopy in urine samples of type 1 and type 2 DKD mouse models. Changes in oxygen consumption (OCR) and extracellular acidification i(ECAR) were analyzed on a Seahorse extracellular flux analyzer. Immunohistochemical analysis was performed on FFPE-embedded mouse kidney sections. Western blot analysis was performed on kidney cortical sections and HK2 cells.
Results: Significantly increased urine and plasma lactate along with a decrease in several TCA cycle metabolites were observed in both type 1 and type 2 diabetic mice. Mitochondrial functional analysis in different kidney cells showed a profound respiratory inhibition and stimulation of lactate by glucose in proximal tubules, but not in mesangial cells and podocytes. Pyruvate at above physiological concentration reversed the glucose-induced inhibition of OCR. Western blotting of kidney cortical tissue sections showed a significant increase in phospho PDH in diabetic kidney tissues and in HK2 cells treated with high glucose. In normal conditions, phospho PDH was predominantly on distal tubules, however in diabetic conditions a significant increase in phospho PDH was noted in proximal tubule cells. Dichloroacetate, an inhibitor of PDK completely reversed the glucose induced respiratory inhibition in proximal tubule epithelial cells.
Conclusions: Mitochondrial dysfunction in proximal tubule epithelial cells may potentially be due to high-glucose induced PDH phosphorylation resulting in limited pyruvate oxidation into mitochondria and enhanced lactate production.
M. Darshi: None. J.J. Kim: None. V. Drel: None. A.N. Murphy: Advisory Panel; Self; Cytokinetics Inc. Consultant; Self; Agilent Technologies.
JDRF; U.S. Department of Veterans Affairs