Investigation of insulin promoter factor 1 gene C18R and R197H variants association with type 2 diabetes mellitus in Bangladeshi population

Abstract

Diabetes Mellitus (DM) is a common metabolic disorder, resulting from defects in insulin secretion, insulin action, or both. But the molecular mechanism behind the basic defects of DM is not yet fully understood. Defect in insulin secretion is the key factor in Type 2 Diabetes Mellitus (T2DM). The β- cell specific transcription factor, Insulin Promoter Factor -1 (IPF1) gene, is essential to pancreatic development and the maintenance of β-cell mass. Existing scientific evidence have explored the role of IPF1 gene in the development of MODY & T2DM but contradictions also exist in different population. Therefore, in this study, we aimed to investigate whether the polymorphisms of the IPF1 gene’s C18R (T/C) and R197H (G/A) variants interplays the pathogenesis of T2DM in the Bangladeshi population. A total number of 445 subjects were recruited in this study to screen genetic variants in the coding region. Among the subjects, 245 were healthy controls and 200 were T2DM patients. Genomic DNA was extracted from whole blood using the QIAGEN Genomic DNA Extraction Kit. Polymorphism of C18R (T/C) & R197H (G/A) variants of the IPF1 gene, were investigated using the PCR-RFLP method. Among the study population BMI, WHR and serum glucose level were significantly higher in the diabetic group compared to the non-diabetic group. Of the total, 200 T2DM subjects only 1 C18R (T/C) Single Nucleotide Polymorphism (SNP) was found and in case of R197H (G/A) variant this number was 7, which shows 0.5% mutation found in C18R (T/C) and 3.5% in R197H (G/A) variant of IPF1 gene, in the T2DM subjects. In the computational study, IPF1 gene shows both of the mutation C18R and R197H belong to the transactivation domain and DNA binding conserved homeodomain, respectively. Several studies had shown, Arginine (Arg) mutation to Cysteine (Cis) residue or vice versa close to the NH2-terminal and IPF-1's first proline-rich domains has less serious or less functionality impacts. Secondary structure prediction and 3D modeling of IPF1 showed the R197H mutation located within the DNA binding domain but not belong to the residues those have DNA bases contact. Mutating Argine (Arg) to Histidine (His) residue in the 3D model showed there were no clashes/and contacts with the neighboring residues. Since it might accommodate properly within this area and could be the reason behind the negligible binding free energy change due to mutation. Very little frequency of C18R and R197H mutations were found from the molecular analysis and the computational study also showed, both of these variants are not much influencing, this might be due to they do not contribute to make significant changes in IPF1 protein structure and functionality. From our study, it can be suggested that C18R and R197H mutations of the IPF1 gene, cannot be consider as an influencing factor to develop T2DM in Bangladeshi population.