Ubiquitin C-terminal hydrolase L1 is required for pancreatic beta cell survival and function in lipotoxic conditions

Abstract

Aims/hypothesis 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.

Signaling Molecules Involved in Lipid-Induced Pancreatic Beta-Cell Dysfunction

“…-/ -mice as well (Chu et al, 2012). These data suggest that UCHL1 has essential functional and antiapoptotic roles in beta cells under lipid stress, highlighting a novel understanding of the importance of UCHL1 and the ubiquitin proteasome system in the pathobiology of lipotoxicity and T2DM.…”

“…UCHL1 was identified in a proteomic screen as the most upregulated protein in MIN6 beta cells treated with palmitate (Chu et al, 2012). In this study, Chu et al used a genetic loss-of-function model to test the hypothesis that UCHL1 was required for normal beta-cell function and fate under lipotoxic conditions and it was found that a 4-week high-fat (HFa) diet caused glucose intolerance and impaired insulin secretion in UCHL1…”

Multi-parameter, single-cell, kinetic analysis reveals multiple modes of cell death in primary pancreatic beta-cells

“…Studies by our group and others have also focused on the role of ER and cytosolic Ca 2+ dynamics in bcell survival and function upon the initiation of the intrinsic apoptotic pathway (Dror et al, 2008;Gwiazda et al, 2009;Luciani et al, 2009;Varadi and Rutter, 2002). We have previously noted robust glucose-dependent differences between the mechanisms of b-cell death with respect to the involvement of notch signaling, netrin signaling, carboxypeptidase E, ATP-citrate lyase, Uchl1 and intracellular Ca 2+ release channels (IP3R, RyR) (Chu et al, 2012; (A,B) Mouse b-cells carrying a caspase-3 sensor were stained with Hoechst, PI and AlexaFluor647-conjugated annexin V. Cells were treated with the indicated treatments under 5 mM (A) and 20 mM glucose (B) and imaged for 60 hours at 37˚C and 5% CO 2. The absolute time for the onset of plasma membrane blebbing, nuclear condensation, caspase-3 activation, annexinV incorporation, PI incorporation and protein loss were determined (n515-63, mean6s.e.m., * P,0.05 compared with 5 mM glucose).…”

UCHL1 deficiency exacerbates human islet amyloid polypeptide toxicity in β-cells

“…S2), presumably as a consequence of hyperglycemia, 27 signals released from apoptotic cells 28 and/or suppression of the antiproliferative activity of UCHL1 in β-cells. 8 Therefore, the hypothesis that UCHL1 deficiency enhances vulnerability of hIAPP-expressing β-cells to ER stress and apoptosis is supported, confirming a key role of the ubiquitin/ proteasome pathway in defense of β-cells from misfolded proteins.…”

“…[7][8][9][10][11][12][13][14][15] Both of these protein degradation pathways are compromised in β-cells in T2DM. 9,15 We recently reported that polyubiquinated proteins accumulate in β-cells in T2DM, also noted in β-cells of rodents with high expression of amyloidogenic hIAPP but not soluble rodent-IAPP.…”