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Sphingomyelinase and membrane sphingomyelin content: determinants ofProximal tubule cell susceptibility to injury.
J Am Soc Nephrol 2000; 11(5):894-902JA

Abstract

Ceramides acutely accumulate in proximal tubules during injury. Pathogenic relevance of this change is suggested by observations that adding ceramide to tubular cells alters superimposed hypoxic and toxic attack. Ceramide accumulation during cell injury is thought to arise from sphingomyelinase (SMase)-mediated sphingomyelin (SM) hydrolysis +/- decreased catabolism. Thus, ceramide addition to cells cannot precisely simulate pathophysiologic events. Therefore, this study assessed direct effects of SMase activity on tubular cell viability under basal conditions and during superimposed attack. Cultured human proximal tubule (HK-2) cells were exposed to differing SMase doses. Its effects on cell phospholipids, ceramides, proliferation rates, and susceptibility to injury (ATP depletion, Fe-mediated oxidant stress) were assessed. Because SMase reduces cell SM content, the effect of exogenous SM on membrane injury (intact cells, isolated vesicles) was also tested. Finally, because SM decreases membrane fluidity, the impact of a fluidizing agent (A(2)C) on membrane injury (phospholipase A(2), lipid peroxidation) was addressed. SMase reduced HK-2 SM content by approximately 33%, but only modest ceramide increments resulted (suggesting high endogenous ceramidase activity). SMase, by itself, caused no cell death (lactate dehydrogenase release). However, it was mildly antiproliferative, and it dramatically predisposed to both ATP depletion- and Fe-mediated attack. SMase also predisposed isolated vesicles to damage, suggesting that its impact on intact cells reflects a direct membrane effect. Adding SM to intact cells (or vesicles) mitigated ATP depletion and Fe- and phospholipase A(2)-induced damage. In contrast, A(2)C rendered membranes more vulnerable to attack. SMase predisposes tubular cells to superimposed ATP depletion and oxidant injury. This may be explained by SM losses, and not simply cytotoxic ceramide gains, given that SM can directly decrease cell/membrane damage. The ability of SM to decrease membrane fluidity may explain, at least in part, its cytoprotective effect.

Authors+Show Affiliations

The Fred Hutchinson Cancer Research Center and the University of Washington, Seattle, Washington, USA. dzager@fhcrc.orgNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, U.S. Gov't, P.H.S.

Language

eng

PubMed ID

10770967

Citation

Zager, R A., et al. "Sphingomyelinase and Membrane Sphingomyelin Content: Determinants ofProximal Tubule Cell Susceptibility to Injury." Journal of the American Society of Nephrology : JASN, vol. 11, no. 5, 2000, pp. 894-902.
Zager RA, Burkhart KM, Johnson A. Sphingomyelinase and membrane sphingomyelin content: determinants ofProximal tubule cell susceptibility to injury. J Am Soc Nephrol. 2000;11(5):894-902.
Zager, R. A., Burkhart, K. M., & Johnson, A. (2000). Sphingomyelinase and membrane sphingomyelin content: determinants ofProximal tubule cell susceptibility to injury. Journal of the American Society of Nephrology : JASN, 11(5), pp. 894-902.
Zager RA, Burkhart KM, Johnson A. Sphingomyelinase and Membrane Sphingomyelin Content: Determinants ofProximal Tubule Cell Susceptibility to Injury. J Am Soc Nephrol. 2000;11(5):894-902. PubMed PMID: 10770967.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Sphingomyelinase and membrane sphingomyelin content: determinants ofProximal tubule cell susceptibility to injury. AU - Zager,R A, AU - Burkhart,K M, AU - Johnson,A, PY - 2000/4/20/pubmed PY - 2000/6/17/medline PY - 2000/4/20/entrez SP - 894 EP - 902 JF - Journal of the American Society of Nephrology : JASN JO - J. Am. Soc. Nephrol. VL - 11 IS - 5 N2 - Ceramides acutely accumulate in proximal tubules during injury. Pathogenic relevance of this change is suggested by observations that adding ceramide to tubular cells alters superimposed hypoxic and toxic attack. Ceramide accumulation during cell injury is thought to arise from sphingomyelinase (SMase)-mediated sphingomyelin (SM) hydrolysis +/- decreased catabolism. Thus, ceramide addition to cells cannot precisely simulate pathophysiologic events. Therefore, this study assessed direct effects of SMase activity on tubular cell viability under basal conditions and during superimposed attack. Cultured human proximal tubule (HK-2) cells were exposed to differing SMase doses. Its effects on cell phospholipids, ceramides, proliferation rates, and susceptibility to injury (ATP depletion, Fe-mediated oxidant stress) were assessed. Because SMase reduces cell SM content, the effect of exogenous SM on membrane injury (intact cells, isolated vesicles) was also tested. Finally, because SM decreases membrane fluidity, the impact of a fluidizing agent (A(2)C) on membrane injury (phospholipase A(2), lipid peroxidation) was addressed. SMase reduced HK-2 SM content by approximately 33%, but only modest ceramide increments resulted (suggesting high endogenous ceramidase activity). SMase, by itself, caused no cell death (lactate dehydrogenase release). However, it was mildly antiproliferative, and it dramatically predisposed to both ATP depletion- and Fe-mediated attack. SMase also predisposed isolated vesicles to damage, suggesting that its impact on intact cells reflects a direct membrane effect. Adding SM to intact cells (or vesicles) mitigated ATP depletion and Fe- and phospholipase A(2)-induced damage. In contrast, A(2)C rendered membranes more vulnerable to attack. SMase predisposes tubular cells to superimposed ATP depletion and oxidant injury. This may be explained by SM losses, and not simply cytotoxic ceramide gains, given that SM can directly decrease cell/membrane damage. The ability of SM to decrease membrane fluidity may explain, at least in part, its cytoprotective effect. SN - 1046-6673 UR - https://www.unboundmedicine.com/medline/citation/10770967/Sphingomyelinase_and_membrane_sphingomyelin_content:_determinants_ofProximal_tubule_cell_susceptibility_to_injury_ L2 - http://jasn.asnjournals.org/cgi/pmidlookup?view=long&pmid=10770967 DB - PRIME DP - Unbound Medicine ER -