Ubiquitin C-terminal hydrolase L1 is required for pancreatic beta cell survival and function in lipotoxic conditions.
OBJECTIVE
Ubiquitin C-terminal hydrolase L1 (UCHL1) is associated with neurodegenerative diseases and has been suggested to have roles in pancreatic beta cells. Our proteomic analysis revealed that UCHL1 was the most increased protein in MIN6 cells exposed to palmitate. The present study used a genetic loss-of-function model to test the hypothesis that UCHL1 is required for normal beta cell function and fate under lipotoxic conditions.


METHODS
Human islets, mouse islets and MIN6 cells were used to analyse UCHL1 protein levels and regulation of UCHL1 by palmitate. The levels of free mono-ubiquitin and poly-ubiquitinated proteins were assessed. Gracile axonal dystrophy (GAD) mutant mice lacking UCHL1 were fed a normal or lipotoxic high-fat diet. Glucose tolerance, insulin tolerance and insulin secretion were assessed in vivo. Beta cell death and proliferation were assessed by TUNEL and proliferating cell nuclear antigen (PCNA) staining. Insulin secretion, calcium signalling, endoplasmic reticulum (ER) stress, apoptosis and SNARE protein levels were assessed in vitro.


RESULTS
UCHL1 protein, which was highly specific to beta cells, was increased by palmitate at basal glucose, but not in the context of hyperglycaemia associated with frank diabetes. Although islet development and function were initially normal in Uchl1                            (-/-) mice, a 4-week high-fat diet caused glucose intolerance and impaired insulin secretion. Uchl1                            (-/-) mice had increased ER stress and beta cell apoptosis. The levels of SNARE proteins were dysregulated in Uchl1                            (-/-) islets. Palmitate-stimulated vesicle-associated membrane protein 2 (VAMP2) ubiquitination was modulated by a chemical UCHL1 inhibitor.


CONCLUSIONS
Together, these data suggest that UCHL1 has essential functional and anti-apoptotic roles in beta cells under stress conditions associated with lipotoxicity.
Laboratory of Molecular Signaling in Diabetes, Diabetes Research Group, Department of Cellular and Physiological Sciences, University of British Columbia, 5358 Life Sciences Building, 2350 Health Sciences Mall, Vancouver, BC, Canada V6T 1Z3.
K Y
KY
Chu
H
H
Li
K
K
Wada
J D
JD
Johnson
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D059865:Endoplasmic Reticulum Stress; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism; D008297:Male; D051379:Mice; D008818:Mice, Neurologic Mutants; D019150:Neuroaxonal Dystrophies / Q000378:metabolism / Q000473:pathology; D019308:Palmitic Acid / Q000009:adverse effects*; D012333:RNA, Messenger / Q000378:metabolism; D050600:SNARE Proteins / Q000378:metabolism; D043222:Ubiquitin Thiolesterase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination / Q000187:drug effects; D015854:Up-Regulation / Q000187:drug effects; D050988:Vesicle-Associated Membrane Protein 2 / Q000378:metabolism
D004791:Enzyme Inhibitors; D007328:Insulin; D007527:Isoenzymes; D012333:RNA, Messenger; D050600:SNARE Proteins; C482860:UCHL1 protein, human; D050988:Vesicle-Associated Membrane Protein 2; D019308:Palmitic Acid; D043222:Ubiquitin Thiolesterase; C496976:Uchl1 protein, mouse