The mevalonate pathway during acute tubular injury: selected determinants and consequences.
Renal injury evokes tubular cholesterol accumulation, mediated in part by increased HMG CoA reductase (HMGCR) levels. The present study was undertaken to define potential molecular determinants of these changes and to ascertain the relative importance of increased cholesterol production versus mevalonate pathway-driven protein prenylation, on the emergence of the so-called postrenal injury "cytoresistant state." Cultured proximal tubule (HK-2) cells were subjected to Fe or ATP depletion injury, followed 1 to 24 hours later by assessments of: 1) sterol transcription factor expression (SREBP)-1 and -2); 2) HMGCR mRNA levels; and 3) Ras/Rho prenylation. HMGCR mRNA and Ras/Rho prenylation were also assessed after in vivo ischemic and Fe-mediated renal damage. Using specific inhibitors, the relative importance of protein prenylation versus terminal cholesterol synthesis on HK-2 cell susceptibility to injury was also assessed. Acute injury induced HK-2 cell SREBP disruption and reductions in HMGCR mRNA. Renal cortical HMGCR mRNA also fell in response to either in vivo ischemic or Fe-mediated oxidant damage. At 24 hours after in vitro/in vivo injury, a time of cholesterol buildup, no increase in Ras/Rho prenylation was observed. Prenylation inhibitors did not sensitize HK-2 cells to injury. Conversely, squalene synthase (terminal cholesterol synthesis) blockade sensitized HK-2 cells to both Fe and ATP depletion attack. We concluded that: 1) acute tubular cell injury can destroy SREBPs and lower HMGCR mRNA. This suggests that posttranscriptional/translational events are responsible for HMGCR enzyme and cholesterol accumulation after renal damage. 2) Injury-induced cholesterol accumulation appears dissociated from increased protein prenylation. 3) Cholesterol accumulation, per se, seems to be the dominant mechanism by which the mevalonate pathway contributes to the postrenal injury cytoresistant state.
Zager
Richard A
RA
Department of Medicine, the University of Washington, and the Fred Hutchinson Cancer Research Center, Seattle, Washington 98109-1024, USA. dzager@fhcrc.org
Shah
Vallabh O
VO
Shah
Hemangini V
HV
Zager
Philip G
PG
Johnson
Ali C M
AC
Hanson
Sherry
S
D000255:Adenosine Triphosphate / Q000172:deficiency; D000818:Animals; D022762:CCAAT-Enhancer-Binding Proteins / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D006903:Hydroxymethylglutaryl CoA Reductases / Q000378:metabolism; D000090463:Iron Deficiencies; D007684:Kidney Tubules / Q000378:metabolism* / Q000473:pathology; D008297:Male; D008798:Mevalonic Acid / Q000378:metabolism*; D051379:Mice; D051780:Sterol Regulatory Element Binding Protein 1; D014157:Transcription Factors
D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; C497388:Srebf1 protein, mouse; D051780:Sterol Regulatory Element Binding Protein 1; D014157:Transcription Factors; D000255:Adenosine Triphosphate; D002784:Cholesterol; D006903:Hydroxymethylglutaryl CoA Reductases; D008798:Mevalonic Acid