Lipoapoptosis in beta-cells of obese prediabetic fa/fa rats. Role of serine palmitoyltransferase overexpression.
We reported that the lipoapoptosis of beta-cells observed in fat-laden islets of obese fa/fa Zucker Diabetic Fatty (ZDF) rats results from overproduction of ceramide, an initiator of the apoptotic cascade and is induced by long-chain fatty acids (FA). Whereas the ceramide of cytokine-induced apoptosis may be derived from sphingomyelin hydrolysis, FA-induced ceramide overproduction seems to be derived from FA. We therefore semiquantified mRNA of serine palmitoyltransferase (SPT), which catalyzes the first step in ceramide synthesis. It was 2-3-fold higher in fa/fa islets than in +/+ controls. [3H]Ceramide formation from [3H]serine was 2.2-4. 5-fold higher in fa/fa islets. Triacsin-C, which blocks palmitoyl-CoA synthesis, and L-cycloserine, which blocks SPT activity, completely blocked [3H]ceramide formation from [3H]serine. Islets of fa/fa rats are unresponsive to the lipopenic action of leptin, which normally depletes fat and prevents FA up-regulation of SPT. To determine the role of leptin unresponsiveness in the SPT overexpression, we transferred wild type OB-Rb cDNA to their islets; now leptin completely blocked the exaggerated FA-induced increase of SPT mRNA while reducing the fat content. Beta-cell lipoapoptosis was partially prevented in vivo by treating prediabetic ZDF rats with L-cycloserine for 2 weeks. Ceramide content and DNA fragmentation both declined 40-50%. We conclude that lipoapoptosis of ZDF rats is mediated by enhanced ceramide synthesis from FA and that blockade by SPT inhibitors prevents lipoapoptosis.
Shimabukuro
M
M
Gifford Laboratories for Diabetes Research, Departments of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75235, USA.
Higa
M
M
Zhou
Y T
YT
Wang
M Y
MY
Newgard
C B
CB
Unger
R H
RH
D000217:Acyltransferases / Q000235:genetics; D000818:Animals; D017209:Apoptosis / Q000235:genetics*; D002518:Ceramides / Q000096:biosynthesis; D003921:Diabetes Mellitus, Experimental / Q000150:complications / Q000473:pathology; D005227:Fatty Acids / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D007515:Islets of Langerhans / Q000473:pathology*; D020738:Leptin; D050356:Lipid Metabolism; D008297:Male; D009765:Obesity / Q000150:complications / Q000473:pathology*; D011236:Prediabetic State / Q000473:pathology*; D011506:Proteins / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D011924:Rats, Zucker; D012694:Serine / Q000378:metabolism; D051102:Serine C-Palmitoyltransferase
D002518:Ceramides; D005227:Fatty Acids; D020738:Leptin; D011506:Proteins; D012333:RNA, Messenger; D012694:Serine; D000217:Acyltransferases; D051102:Serine C-Palmitoyltransferase