Date Published: February 14, 2019
Publisher: Public Library of Science
Author(s): Maha Daghestani, Rituraj Purohit, Mazin Daghestani, Mamoon Daghistani, Arjumand Warsy, Rasheed Ahmad.
The Gln233Arg (A>G; rs1137101) polymorphism of the leptin receptor gene (LEPR) has been investigated extensively and is reported to be associated with different metabolic states. In this investigation, we aimed to study the frequency of Gln233Arg genotypes and alleles in a group of Saudi women stratified by their body mass index (BMI), to correlate the LEPR genotypes with variations in anthropometric, lipid and hormonal parameters and to investigate conformational and structural variations in the mutant LEPR using molecular dynamic (MD) investigations. The study group included 122 Saudi women (normal weight = 60; obese = 62) attending the clinics for a routine checkup. Anthropometric data: height, weight, waist and hip circumference were recorded and fasting serum sample was used to estimate glucose, lipids, ghrelin, leptin and insulin. BMI, W/H ratio, and HOMA-IR values were calculated. Whole blood sample was used to extract DNA; exon 6 of the LEPR gene was amplified by PCR and sequencing was conducted on an ABI 3100 Avant Genetic Analyser. Molecular Dynamic Simulation studies were carried out using different softwares. The results showed the presence of all three genotypes of Gln233Arg in Saudi women, but the frequencies were significantly different when compared to reports from some populations. No differences were seen in the genotype and allele frequencies between the normal weight and obese women. Stratification by the genotypes showed significantly higher BMI, waist and hip circumference, leptin, insulin, fasting glucose and HOMA-IR and lower ghrelin levels in obese women carrying the GG genotype. Even in the normal weight group, individuals with GG genotype had higher BMI, waist and hip circumference and significantly lower ghrelin levels. The MD studies showed a significant effect of the Gln/Arg substitution on the conformation, flexibility, root-mean-square fluctuation (RMSF), radius of gyration (Rg) values, solvent-accessible surface area (SASA) and number of inter- and intra-molecular H-bonds. The results suggest that the structural changes brought about by the mutation, influence the signaling pathways by some unknown mechanism, which may be contributing to the abnormalities seen in the individuals carrying the G allele of rs1137101.
The adipose-specific hormone leptin (LEP; 164160), regulates energy expenditure, satiety, and adipose tissue mass through hypothalamic effect, by binding to the leptin receptor (LEPR, OB-R; CD295), which is a single transmembrane–domain receptor belonging to the cytochrome family receptors [1–6]. It also plays essential roles by stimulating immune and barrier cells and hence promotes the activation, proliferation, cell death resistance and wound repair . It exerts its action on the target cells by binding with high affinity, to the cytokine receptor homology-2 (CRH2) domain, of the LEPR. This binding induces clustering of the activated receptor complexes, Janus Kinase 2 (JAK2), which catalyzes the phosphorylation of intracellular tyrosine residues. The phosphorylation leads to the recruitment of several transcription factors, one of which is Signal Transducer and Activator of Transcription 3 (STAT3). The STAT3 becomes activated and dimerizes, and is translocated to the nuclear region, where it initiates a transcriptional program for several genes [8–10].
The local Ethics Committee at the Umm Al Qura University, Makkah Al Mukaramah, Saudi Arabia, approved this study (IRB No. 235). The study was conducted on 124 Saudi women (normal weight and obese) attending the Clinics at health centers in Makkah, Saudi Arabia, for a routine check-up. Informed consent was obtained from each female who volunteered to take part in the study and signed an informed consent.
The study group included 122 women of Saudi origin [normal weight: BMI ≤25 = 60; obese: BMI >30 kg/m2 = 62).
In this study, we have attempted to relate a substitution in LEPR with alterations in the structure of the receptor and their association with anthropometric, biochemical and hormonal variations in a group of normal weight and obese Saudi women. This polymorphism, an A to G transition in the gene, results in the substitution of a neutral amino acid, glutamine, by a basic amino acid, arginine at position 223 (Gln223Arg). We identified all three genotypes AA, AG and GG in the Saudi females and the frequencies of the A and G alleles were compared with those reported for other populations in NCBI databases . The wild-type A occurs at the highest frequency in the Saudis (0.798) and the results are closer to the frequencies reported for the British (0.610), Puerto Ricans (0.610) and Colombians (0.596), followed by the Punjabi in Pakistan (0.573), Luhya in Kenya (0.520), Toscani in Italy (0.561), Europeans (0.531) and Americans (0.563). The East Asian including Chinese (0.131) and Japanese (0.154) have the lowest frequency of ‘A’ allele. These wide variations in allele frequencies in different populations may be due to multiple contributing environmental and genetic factors.