Studies of renal injury IV: The GLUT1 gene protects renal cells from cyclosporine A toxicity

Abstract

Renal cells activate the GLUT1 gene when exposed to stress. This response promotes glucose influx and glycolysis, which protects cells and preserves viability. We tested the hypothesis that cytotoxicity from cyclosporine A (CsA), a valuable but nephrotoxic immunosuppressor, also activated the GLUT1 gene. Methods and Results. GLUT1 nuclear transcription was increased in LLCPK1 cells injured with CsA, 10-5 mol/L or more for 24 hours, with increases of GLUT1 mRNA and protein levels, resulting in greater glucose consumption and glycolysis. The integrated stress response to CsA toxicity was cytoprotective, as blockade of glucose influx and glycolysis with 10-4 mol/L phloretin magnified CsA toxicity. Remarkably, whereas phloretin reduced GLUT1 transcription, it still increased GLUT1 protein and mRNA levels, and even amplified their responses to CsA. Interestingly, intracellular pH was preserved despite of greater lactic acid production in the face of Na+/H+ exchange inhibition from CsA toxicity. However, further inhibition of Na+/H+ exchange with amiloride greatly magnified CsA toxicity and GLUT1 gene transcription. Activation of the GLUT1 gene during renal cell injury is mediated by at least two redundant systems. CsA stimulates GLUT1 gene transcription when membrane transport delivers glucose to the cell. However, when glucose delivery is compromised, GLUT1 gene expression is still supported by alternative mechanisms that remain operational even after cellular energy metabolism is compromised further by inhibition of glucose and glycolytic fluxes.