Increased proximal tubular cholesterol content: implications for cell injury and "acquired cytoresistance".
BACKGROUND
Acute renal failure (ARF) leads to secondary adaptive changes that serve to protect proximal tubules from subsequent ischemic or toxic damage [so-called "acquired cytoresistance" (CR)]. A characteristic of CR is increased plasma membrane resistance to attack. Therefore, this study sought to identify potential changes in plasma membrane lipid composition in CR tubules/renal cortex and, if present, to test whether they might mechanistically contribute to the CR state.


METHODS
Renal cortices/isolated tubules were obtained from CR mouse kidneys (18-hr postinduction of ischemia reperfusion, myoglobinuria, or ureteral obstruction). Their plasma membrane phospholipid/cholesterol profiles were compared with those observed in either control tissues or tissues obtained one to two hours post-renal damage (that is, prior to emergence of CR).


RESULTS
Either no changes or inconsistent changes in phospholipid profiles were observed in CR tissues. Conversely, CR (vs. control) tissues demonstrated a consistent 25 to 50% increase in membrane cholesterol content. To ascertain whether cholesterol impacts tubule susceptibility to injury, its levels were reduced in proximal tubule (HK-2) cells with either (a) mevastatin, (b) a cholesterol "stripping" agent, (c) cholesterol oxidase, or (d) cholesterol esterase. Then cell susceptibility to injury [adenosine 5'-triphosphate (ATP) depletion; Fe-mediated oxidant stress] was assessed. In each instance, cholesterol reductions dramatically sensitized to superimposed injury (for example, a 2 to 3 times increase in the % of lactate dehydrogenase release). When cholesterol levels were restored to normal in CR tubules (with a "stripping" agent), an increased tubule susceptibility to injury resulted. Because cholesterol decreases membrane fluidity, the impact of a membrane-fluidizing agent (A2C) on cell injury was assessed. A2C dramatically sensitized HK-2 cells to superimposed attack.


CONCLUSIONS
ARF leads to an up-regulation of proximal tubule cholesterol content. The latter may then contribute to acquired CR, possibly by stabilizing the plasma membrane via its antifluidizing effect.
Zager
R A
RA
The Fred Hutchinson Cancer Research Center, Seattle, Washington, USA. dzager@fhcrc.org
Burkhart
K M
KM
Johnson
A C
AC
Sacks
B M
BM
D058186:Acute Kidney Injury / Q000378:metabolism; D000818:Animals; D002784:Cholesterol / Q000032:analysis / Q000502:physiology*; D002789:Cholesterol Oxidase / Q000494:pharmacology; D003505:Cyclodextrins / Q000494:pharmacology; D019610:Cytoprotection; D007672:Kidney Cortex / Q000737:chemistry; D007687:Kidney Tubules, Proximal / Q000737:chemistry / Q000473:pathology*; D008148:Lovastatin / Q000031:analogs & derivatives / Q000494:pharmacology; D008297:Male; D008560:Membrane Fluidity; D051379:Mice; D010743:Phospholipids / Q000032:analysis; D002787:Sterol Esterase / Q000494:pharmacology; D047392:beta-Cyclodextrins
D003505:Cyclodextrins; D010743:Phospholipids; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin; C012258:mevastatin; D002784:Cholesterol; D008148:Lovastatin; D002789:Cholesterol Oxidase; D002787:Sterol Esterase