Background and aims: Kidney disease is a common complication of diabetes and also an indicator of increased risk of cardiovascular disease and mortality. During early onset of disease, glomerular specific podocyte dysfunction has been characterized by both dedifferentiation and death. Furthermore, progression of the disease and the sustained hyperglycaemic environment presents with proximal tubule functional metabolic alterations followed by cell death. To this end we aimed to study the metabolic profiles of both cell types to characterize respiratory capacities, not only at rest but also under duress induced by hyperglycaemic insult.
Methods: Human immortalized podocyte and proximal tube cells (PTC) were studied to define respiratory abilities in both normo and hyperglycaemic conditions. Using the Seahorse XF24 analyser real-time outputs were determined including basal respiratory capability, ATP generation and maximal respiration. Furthermore markers of cell injury were analysed by using real-time QPCR and western blot analysis.
Results: PTCs presented a maximal respiratory capacity which was significantly greater than that of podocyte cells under normoglycaemic conditions. Under hyperglycaemic conditions maximal respiratory capacity of each cell type was altered. Real-time QPCR highlighted altered expression of markers in cell specific response to the hyperglycaemic environment. Furthermore, protein expression of kidney injury marker Kidney Injury Molecule 1(KIM-1) along with reduced expression of type IV collagen denote PTC dysfunction, with podocyte dysfunction highlighted in loss of nephrin protein expression.
Conclusion: Metabolic analyses of both cell types highlight respiratory sensitivity to alterations in the glycaemic environment. This effect was underlined by altered gene expression of factors presenting cell specific dysfunction. Furthermore loss of protein expression of podocyte marker nephrin as well as PTC KIM-1 expression highlights cellular dysfunction. In summation, the diminished capability for respiratory capacity presented in podocytes, in comparison with proximal tubules, may go some way to elucidation of the preliminary events during diabetic kidney disease.