Cell Biology – Immunology – Pathology
Kidney International (1999) 56, 1788–1797; doi:10.1046/j.1523-1755.1999.00745.x
Increased proximal tubular cholesterol content: Implications for cell injury and "acquired cytoresistance"
Richard A Zager, Kristin M Burkhart, Ali C M Johnson and Benjamin M Sacks
The Fred Hutchinson Cancer Research Center, and the University of Washington, Seattle, Washington, USA
Correspondence: Richard A. Zager, M.D., Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Room D2-190, Seattle, Washington 98019, USA. E-mail: dzager@fhcrc.org
Received 15 April 1999; Revised 9 June 1999; Accepted 16 June 1999.
Abstract
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.
Keywords:
acute renal failure, oxidant stress, ATP depletion, mevastatin, fluidity, phospholipids
