ABSTRACT
BACKGROUND: There is evidence that one of the key type 2 diabetes (T2D) loci identified by GWAS exerts its influence early on in life through its impact on pediatric BMI. This locus on 10q23 harbors three genes, encoding hematopoietically expressed homeobox (HHEX), insulin-degrading enzyme (IDE) and kinesin family member 11 (KIF11), respectively. METHODS: We analyzed the impact of adipogeneis on the mRNA and protein expression levels of these genes in the human adipocyte Simpson-Golabi-Behmel syndrome (SGBS) cell line in order to investigate which could be the culprit gene(s) in this region of linkage disequilibrium. RESULTS: Following activation of differentiation with a PPARγ ligand, we observed ~20% decrease in IDE, ~40% decrease in HHEX and in excess of 80% decrease in KIF11 mRNA levels when comparing the adipocyte and pre-adipocyte states. We also observed decreases in KIF11 and IDE protein levels, but conversely we observed a dramatic increase in HHEX protein levels. Subsequent time course experiments revealed some marked changes in expression as early as three hours after activation of differentiation. CONCLUSION: Our data suggest that the expression of all three genes at this locus are impacted during SGBS adipogenesis and provides insights in to the possible mechanisms of how the genes at this 10q23 locus could influence both adipocyte differentiation and susceptibility to T2D through insulin resistance.
Subject(s)
Body Mass Index , Chromosomes, Human, Pair 10/genetics , Diabetes Mellitus, Type 2/genetics , Gene Expression Profiling , Adipocytes/drug effects , Adipocytes/metabolism , Adipogenesis/drug effects , Adipogenesis/genetics , Arrhythmias, Cardiac/genetics , Cell Line , Chromans/pharmacology , Genetic Diseases, X-Linked/genetics , Genetic Loci , Genetic Predisposition to Disease , Gigantism/genetics , Heart Defects, Congenital/genetics , Homeodomain Proteins/biosynthesis , Humans , Hypoglycemic Agents/pharmacology , Insulin Resistance/genetics , Insulysin/biosynthesis , Intellectual Disability/genetics , Kinesins/biosynthesis , Linkage Disequilibrium/genetics , Rosiglitazone , Thiazolidinediones/pharmacology , Transcription Factors/biosynthesis , TroglitazoneABSTRACT
OBJECTIVE: Congenital hyperinsulinemic hypoglycemia is a group of genetic disorders of insulin secretion most commonly associated with inactivating mutations of the ß-cell ATP-sensitive K(+) channel (K(ATP) channel) genes ABCC8 (SUR1) and KCNJ11 (Kir6.2). Recessive mutations of these genes cause hyperinsulinism that is unresponsive to treatment with diazoxide, a channel agonist. Dominant K(ATP) mutations have been associated with diazoxide-responsive disease. We hypothesized that some medically uncontrollable cases with only one K(ATP) mutation might have dominant, diazoxide-unresponsive disease. RESEARCH DESIGN AND METHODS: Mutations of the K(ATP) genes were identified by sequencing genomic DNA. Effects of mutations on K(ATP) channel function in vitro were studied by expression in COSm6 cells. RESULTS: In 15 families with diazoxide-unresponsive diffuse hyperinsulism, we found 17 patients with a monoallelic missense mutation of SUR1. Nine probands had de novo mutations, two had an affected sibling or parent, and four had an asymptomatic carrier parent. Of the 13 different mutations, 12 were novel. Expression of mutations revealed normal trafficking of channels but severely impaired responses to diazoxide or MgADP. Responses were significantly lower compared with nine SUR1 mutations associated with dominant, diazoxide-responsive hyperinsulinism. CONCLUSIONS: These results demonstrate that some dominant mutations of SUR1 can cause diazoxide-unresponsive hyperinsulinism. In vitro expression studies may be helpful in distinguishing such mutations from dominant mutations of SUR1 associated with diazoxide-responsive disease.
