Identification of an HNF1A p.Gly292fs Frameshift Mutation Presenting as Diabetes During Pregnancy in a Maltese Family

Lysine 117 Residue Is Essential for the Function of the Hepatocyte Nuclear Factor 1α

Hepatocyte nuclear factor 1α (HNF1α) plays essential roles in controlling development and metabolism; its mutations are clearly linked to the occurrence of maturity-onset diabetes of the young (MODY3) in humans. Lysine 117 (K117) to glutamic acid (E117) mutation in the HNF1α gene has been clinically associated with MODY3, but no functional data on this variant are available. Here, we addressed the role of lysine 117 in HNF1α function using a knock-in animal model and site-directed mutagenesis. HNF1α K117E homozygous mice exhibited dwarfism, hepatic dysfunction, renal Fanconi syndrome, and progressive wasting syndrome. These phenotypes were very similar to those of mice with complete HNF1α deficiency, suggesting that K117 is critical to HNF1α functions. K117E homozygotes developed diabetes in the early postnatal period. The relative deficiency of serum insulin levels and the normal response to insulin treatment in homozygous mice were markedly similar to those in the MODY3 disorder in humans. Moreover, K117E heterozygous mutant causes age-dependent glucose intolerance, which is similar to the pathogenesis of MODY3 as well. K117 mutants significantly reduced the overall transactivation and DNA binding capacity of HNF1α by disrupting dimerization. Collectively, our findings reveal a previously unappreciated role of POU domain of HNF1α in homodimerization and provide important clues for identifying the molecular basis of HNF1α-related diseases such as MODY3.

ARTICLE HIGHLIGHTS

HNF1α K117E homozygous mice exhibited dwarfism, hepatic dysfunction, renal Fanconi syndrome, and progressive wasting syndrome. K117E homozygotes developed diabetes in the early postnatal period. K117E heterozygous mutant causes age-dependent glucose intolerance, which is similar to the pathogenesis of maturity-onset diabetes of the young. K117 mutants significantly reduced the overall transactivation and DNA binding capacity of HNF1α by disrupting dimerization.

Maturity-Onset Diabetes of the Young: Mutations, Physiological Consequences, and Treatment Options

Maturity-Onset Diabetes of the Young (MODY) is a rare form of diabetes which affects between 1% and 5% of diagnosed diabetes cases. Clinical characterizations of MODY include onset of diabetes at an early age (before the age of 30), autosomal dominant inheritance pattern, impaired glucose-induced secretion of insulin, and hyperglycemia. Presently, 14 MODY subtypes have been identified. Within these subtypes are several mutations which contribute to the different MODY phenotypes. Despite the identification of these 14 subtypes, MODY is often misdiagnosed as type 1 or type 2 diabetes mellitus due to an overlap in clinical features, high cost and limited availability of genetic testing, and unfamiliarity with MODY outside of the medical profession. The primary aim of this review is to investigate the genetic characterization of the MODY subtypes. Additionally, this review will elucidate the link between the genetics, function, and clinical manifestations of MODY in each of the 14 subtypes. In providing this knowledge, we hope to assist in the accurate diagnosis of MODY patients and, subsequently, in ensuring they receive appropriate treatment.

Human iPSCs-Derived Endothelial Cells with Mutation in HNF1A as a Model of Maturity-Onset Diabetes of the Young

Patients with HNF1A-maturity-onset diabetes of the young (MODY) often develop endothelial dysfunction and related microvascular complications, like retinopathy. As the clinical phenotype of HNF1A-MODY diabetes varies considerably, we used human induced pluripotent stem cells (hiPSCs) from two healthy individuals (control) to generate isogenic lines with mutation in HNF1A gene. Subsequently, control hiPSCs and their respective HNF1A clones were differentiated toward endothelial cells (hiPSC-ECs) and different markers/functions were compared. Human iPSC-ECs from all cell lines showed similar expression of CD31 and Tie-2. VE-cadherin expression was lower in HNF1A-mutated isogenic lines, but only in clones derived from one control hiPSCs. In the other isogenic set and cells derived from HNF1A-MODY patients, no difference in VE-cadherin expression was observed, suggesting the impact of the genetic background on this endothelial marker. All tested hiPSC-ECs showed an expected angiogenic response regardless of the mutation introduced. Isogenic hiPSC-ECs responded similarly to stimulation with pro-inflammatory cytokine TNF-α with the increase in ICAM-1 and permeability, however, HNF1A mutated hiPSC-ECs showed higher permeability in comparison to the control cells. Summarizing, both mono- and biallelic mutations of HNF1A in hiPSC-ECs lead to increased permeability in response to TNF-α in normal glycemic conditions, which may have relevance to HNF1A-MODY microvascular complications.