Deletion of ARNT (Aryl Hydrocarbon Receptor Nuclear Translocator) in β-Cells Causes Islet Transplant Failure with Impaired β-Cell Function

Abstract

BackgroundReplacing β-cells by islet-transplantation can cure type 1 diabetes, but up to 70% of β-cells die within 10 days of transplantation. ARNT (Aryl hydrocarbon Receptor Nuclear Translocator) regulates β-cell function, and potentially survival. Lack of ARNT impairs the ability of β-cells to respond to physiological stress and potentiates the onset of diabetes, but the exact role of ARNT in graft outcome is unknown.AimTo investigate the effect of β-cell deletion of ARNT on graft outcomes.MethodsIslets were isolated from donor mice which had β-cell specific ARNT-deletion (β-ARNT) or littermate floxed controls. The islets were transplanted into diabetic SCID recipients in ratios of (a) 3 donors: 1 recipient, (b) 1 donor: 1 recipient or (c) ½ of the islets from 1 donor: 1 recipient. After 28 days, the kidney containing the graft was removed (nephrectomy) to exclude regeneration of the endogenous pancreas.ResultsIn the supra-physiological-mass model (3∶1), both groups achieved reasonable glycaemia, with slightly higher levels in β-ARNT-recipients. In adequate-mass model (1∶1), β-ARNT recipients had poor glucose control versus floxed-control recipients and versus the β-ARNT donors. In the low-β-cell-mass model (½:1) β-ARNT transplants completely failed, whereas controls had good outcomes. Unexpectedly, there was no difference in the graft insulin content or β-cell mass between groups indicating that the defect was not due to early altered β-cell survival.ConclusionOutcomes for islet transplants lacking β-cell ARNT were poor, unless markedly supra-physiological masses of islets were transplanted. In the 1∶1 transplant model, there was no difference in β-cell volume. This is surprising because transplants of islets lacking one of the ARNT-partners HIF-1α have increased apoptosis and decreased islet volume. ARNT also partners HIF-2α and AhR (aryl hydrocarbon receptor) to form active transcriptional complexes, and further work to understand the roles of HIF-2α and AhR in transplant outcomes is needed.

Muscle Arnt/Hif1β Is Dispensable in Myofiber Type Determination, Vascularization and Insulin Sensitivity

“…Selective deletion of ARNT in beta cell of the pancreas leads to glucose intolerance, impaired insulin secretion and deregulated islet gene expression [6,7]. Other studies using conditional knockout mice have additionally reported the critical role of pancreatic ARNT in beta cell transplant, and glucose tolerance during pregnancy [8,9]. ARNT expression is also repressed in diabetic livers.…”

β Cell Hypoxia-Inducible Factor-1α Is Required for the Prevention of Type 1 Diabetes

“…Mice that had random-fed BGLs of ≥ 20mmol/l (360mg/dl) on 2 separate occasions were considered diabetic. Intraperitoneal glucose tolerance tests (GTT, 2g/kg) were performed in mice fasted for 4 hours, as previously described ( Lalwani et al, 2014 ; Stokes et al, 2013 ; Scott et al, 2014 ).…”

“…Mouse islets were isolated and purified from uninfected and CV infected 8-week-old male FC and βHIF-1α mice as described previously ( Cheng et al, 2010 ; Gunton et al, 2005 ; Lalwani et al, 2014 ; Stokes et al, 2013 ). The pancreas was distended with 3mls of liberase containing solution, and incubated at 37°C for 16.5 minutes.…”

Bone muscle interactions and vitamin D

“…Osteocalcin which is produced by osteoblasts has recently come to a new light for its role in regulating beta-cell function [75]. Its classic use is as a marker of bone formation.…”

“…It is regulated by vitamin D and its gene contains a vitamin D response element (VDRE) indicating direct regulation by vitamin D [2]. It has potential effects in muscle, in which it alters mitochondrial function, insulin sensitivity [75], and possibly strength in women.…”