title: Accumulation of ceramide in slow-twitch muscle contributes to the development of insulin resistance in the obese JCR:LA-cp rat.
abstract: What is the central question of this study? The aim was to determine whether the accumulation of ceramide contributes to skeletal muscle insulin resistance in the JCR obese rat. What is the main finding and its importance? Our main new finding is that ceramides accumulate only in slow-twitch skeletal muscle in the JCR obese rat and that reducing ceramide content in this muscle type by inhibition of serine palmitoyl transferase-1 halts the progression of insulin resistance in this rat model predisposed to early development of type 2 diabetes. Our findings highlight the importance of assessing insulin signalling/sensitivity and lipid intermediate accumulation in different muscle fibre types. It has been postulated that insulin resistance results from the accumulation of cytosolic lipid metabolites (i.e. diacylglycerol/ceramide) that impede insulin signalling and impair glucose homeostasis. De novo ceramide synthesis is catalysed by serine palmitoyl transferase-1. Our aim was to determine whether de novo ceramide synthesis plays a role during development of insulin resistance in the JCR:LA-cp obese rat. Ten-week-old JCR:LA-cp obese rats were supplemented with either vehicle or the serine palmitoyl transferase-1 inhibitor l-cycloserine (360 mg l(-1) ) in their drinking water for a 2 week period, and glycaemia was assessed by meal tolerance testing. Treatment of JCR:LA-cp obese rats with l-cycloserine improved their plasma glucose and insulin levels during a meal tolerance test. Examination of muscle lipid metabolites and protein phosphorylation patterns revealed differential signatures in slow-twitch (soleus) versus fast-twitch muscle (gastrocnemius), in that ceramide levels were increased in soleus but not gastrocnemius muscles of JCR:LA-cp obese rats. Likewise, improved glycaemia in l-cycloserine-treated JCR:LA-cp obese rats was associated with enhanced Akt and pyruvate dehydrogenase signalling in soleus but not gastrocnemius muscles, probably as a result of l-cycloserine reducing elevated ceramides in this muscle type. Potential mechanisms of ceramide-mediated insulin resistance involve activation of atypical protein kinase Cζ/λ and protein phosphatase 2A; however, neither of these was altered in muscles of JCR:LA-cp obese rats. Our results suggest a key role for ceramide in the development of insulin resistance in the JCR:LA-cp obese rat, while supporting serine palmitoyl transferase-1 inhibition as a novel target for treatment of obesity-associated insulin resistance.
authors: Cardiovascular Translational Science Institute, University of Alberta, Edmonton, Alberta, Canada.|Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Alberta, Canada.
authors: Natasha
authors: N
authors: Fillmore
authors: Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Alberta, Canada.
authors: Wendy
authors: W
authors: Keung
authors: Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Alberta, Canada.|Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada.
authors: Sandra E
authors: SE
authors: Kelly
authors: Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Alberta, Canada.|Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada.
authors: Spencer D
authors: SD
authors: Proctor
authors: Cardiovascular Translational Science Institute, University of Alberta, Edmonton, Alberta, Canada.|Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Alberta, Canada.|Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada.
authors: Gary D
authors: GD
authors: Lopaschuk
authors: Cardiovascular Translational Science Institute, University of Alberta, Edmonton, Alberta, Canada.|Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada.|Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Alberta, Canada.
authors: John R
authors: JR
authors: Ussher
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000097:blood; D001786:Blood Glucose / Q000378:metabolism; D002518:Ceramides / Q000378:metabolism*; D003523:Cycloserine / Q000494:pharmacology; D004195:Disease Models, Animal; D004734:Energy Metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007328:Insulin / Q000097:blood; D007333:Insulin Resistance; D007527:Isoenzymes / Q000378:metabolism; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism; D018657:Muscle Fibers, Slow-Twitch / Q000187:drug effects / Q000378:metabolism*; D009765:Obesity / Q000097:blood / Q000378:metabolism* / Q000503:physiopathology; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D054648:Protein Phosphatase 2 / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011768:Pyruvate Dehydrogenase Complex / Q000378:metabolism; D051381:Rats; D051102:Serine C-Palmitoyltransferase / Q000037:antagonists & inhibitors / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D000099293:Protein Kinase C-lambda
chemical_list: D015415:Biomarkers; D001786:Blood Glucose; D002518:Ceramides; D003523:Cycloserine; D004791:Enzyme Inhibitors; D007328:Insulin; D007527:Isoenzymes; D011493:Protein Kinase C; D054648:Protein Phosphatase 2; D051057:Proto-Oncogene Proteins c-akt; D011768:Pyruvate Dehydrogenase Complex; D051102:Serine C-Palmitoyltransferase; D000099293:Protein Kinase C-lambda