Mouse HSF1 Disruption Perturbs Redox State and Increases Mitochondrial Oxidative Stress in Kidney

Increased synthesis of heat shock proteins (Hsps), mainly regulated by heat shock factor 1 (Hsf1), protects the heart against oxidative stress under pathophysiological conditions such as ischemia/reperfusion. To investigate whether Hsps might exert a similar protective effect under physiological conditions in the kidney, we first evaluated the HSF1-dependent expression of several Hsps, including Hsp25, alphaB-crystallin (alphaBC), Hsp70, and Hsp90. Unlike either alphaBC or Hsp70, protein expression of Hsp25 and Hsp90 was decreased 26% and 50%, respectively, in Hsf1 knockout compared with the wild-type mice. The effects of Hsp down-regulation on renal cellular redox status are presently unknown. Indeed, HSF1 deficiency caused a 37% decrease in renal cellular GSH/GSSG ratio, a marker of redox status, and a 40% increase in the rate of mitochondrial superoxide generation in Hsf1 knockout compared with wild-type mice. HSF1 disruption also increased mitochondrial permeability transition pore opening and induced greater mitochondrial membrane potential change (48% increase versus wild type). Thus, the present study demonstrates that Hsf1-dependent transcription of selective Hsps is required for normal renal homeostasis, which protects renal cells against oxidative stress under physiological conditions. The source of mitochondrial superoxide generation is discussed.