Antilipolytic effect of calcimimetics depends on the allelic variant of calcium-sensing receptor gene polymorphism rs1042636 (Arg990Gly)

Exploring Adaptive Phenotypes for the Human Calcium-Sensing Receptor Polymorphism R990G

Rainforest hunter-gatherers from Southeast Asia are characterized by specific morphological features including a particularly dark skin color (D), short stature (S), woolly hair (W), and the presence of steatopygia (S)-fat accumulation localized in the hips (DSWS phenotype). Based on previous evidence in the Andamanese population, we first characterized signatures of adaptive natural selection around the calcium-sensing receptor gene in Southeast Asian rainforest groups presenting the DSWS phenotype and identified the R990G substitution (rs1042636) as a putative adaptive variant for experimental follow-up. Although the calcium-sensing receptor has a critical role in calcium homeostasis by directly regulating the parathyroid hormone secretion, it is expressed in different tissues and has been described to be involved in many biological functions. Previous works have also characterized the R990G substitution as an activating polymorphism of the calcium-sensing receptor associated with hypocalcemia. Therefore, we generated a knock-in mouse for this substitution and investigated organismal phenotypes that could have become adaptive in rainforest hunter-gatherers from Southeast Asia. Interestingly, we found that mouse homozygous for the derived allele show not only lower serum calcium concentration but also greater body weight and fat accumulation, probably because of enhanced preadipocyte differentiation and lipolysis impairment resulting from the calcium-sensing receptor activation mediated by R990G. We speculate that such differential features in humans could have facilitated the survival of hunter-gatherer groups during periods of nutritional stress in the challenging conditions of the Southeast Asian tropical rainforests.

Calcium-sensing receptor gene (CASR) polymorphisms and CASR transcript level concerning dyslipidemia in hemodialysis patients: a cross-sectional study

BACKGROUND

There is scarce data on CASR associations with dyslipidemia. We investigated in hemodialysis (HD) patients whether CASR single nucleotide polymorphisms (SNPs) rs7652589 and rs1801725 have associations with dyslipidemia and show epistatic interactions with SNPs of the energy homeostasis-associated gene (ENHO), retinoid X receptor α gene (RXRA), and liver X receptor α gene (LXRA).

METHODS

The study included 1208 HD subjects. For diagnosis of dyslipidemia, both K/DOQI criteria and atherogenic index ≥3.8 were used. CASR rs1801725 was genotyped by TaqMan SNP Genotyping Assay, other SNPs - by high-resolution melting curve analysis or polymerase chain reaction-restriction fragment length polymorphism, as appropriate. Relative transcript levels of CASR, ENHO, RXRA, and LXRA were measured in peripheral blood mononuclear cells. The occurrence of dyslipidemic phenotypes concerning tested polymorphisms was compared using models of inheritance. Haplotypes were estimated using the Haploview 4.2 software. Epistatic interactions between tested SNPs were analyzed using the logistic regression and epistasis option in the PLINK software.

RESULTS

Rs7652589 indicated a greater probability of atherogenic dyslipidemia in the dominant inheritance model (OR 1.4, 95%CI 1.0-2.0, P = 0.026), principally because of increased triglyceride (TG) levels. The rs1801725 variant allele was associated with a decreased probability of dyslipidemia characterized by non-HDL-cholesterol ≥130 mg/dL and TG ≥200 mg/dL (OR 0.6, 0.4-0.9, P = 0.012). There were no epistatic interactions between CASR and RXRA, LXRA, and ENHO regarding dyslipidemia. Both rs7652589 and rs1801725 SNPs were not in linkage disequilibrium (D' = 0.091, r² = 0.003 for the entire HD group) and their haplotypes did not correlate with dyslipidemia. Relative CASR transcript was lower at a borderline significance level in patients harboring the rs1801725 variant allele compared with homozygotes of the major allele (0.20, 0.06-7.80 vs. 0.43, 0.04-5.06, P = 0.058). CASR transcript correlated positively with RXRA transcript (adjusted P = 0.001), LXRA transcript (adjusted P = 0.0009), ENHO transcript (borderline significance, adjusted P = 0.055), dry body weight (adjusted P = 0.035), and renal replacement therapy duration (adjusted P = 0.013).

CONCLUSIONS

CASR polymorphisms (rs7652589, rs1801725) are associated with dyslipidemia in HD patients. CASR correlates with RXRA, LXRA, and ENHO at the transcript level. Further investigations may elucidate whether other CASR SNPs contribute to associations shown in this study.

Functional Study of Haplotypes in UGT1A1 Promoter to Find a Novel Genetic Variant Leading to Reduced Gene Expression

BACKGROUND

Uridine diphosphate glucuronyltransferase 1 family, A1 (UGT1A1) encodes for an enzyme that is a part of glucuronidation pathway, and a number of studies have shown that the promoter polymorphisms of UGT1A1 are associated with various diseases and drug response. In this study, we examined a possible association between UGT1A1 promoter haplotypes and the gene expression level.

METHODS

To identify promoter haplotype structure population, we directly sequenced the promoter region of UGT1A1 in 192 healthy Korean to identify 10 UGT1A1 promoter single-nucleotide polymorphisms (SNPs). Then, we genotyped the 10 SNPs in additional 192 non-Korean samples comprised of Chinese, Japanese, European American, and African American, and constructed haplotype structures. Furthermore, we conducted luciferase assay for the promoter SNP haplotypes to examine a possible expression change.

RESULTS

rs3755319C-rs2003569A-rs887829C-rs8175347(TA)6 (6.60 ± 0.15) and rs3755319A-rs2003569 G-rs887829C-rs8175347(TA)7 (2.79 ± 0.97) led to significantly lower gene expression when compared with rs3755319C-rs2003569 G-rs887829T-rs8175347(TA)6 (8.28 ± 0.60).

CONCLUSIONS

Our result suggests that the haplotypes in UGT1A1 promoter region can affect the expression level of the gene and drug metabolism associated with UGT1A1. Furthermore, in addition to rs8175347, rs3755319 was found to induce lower gene expression of UGT1A1.

Engendering biased signalling from the calcium-sensing receptor for the pharmacotherapy of diverse disorders

The human calcium-sensing receptor (CaSR) is widely expressed in the body, where its activity is regulated by multiple orthosteric and endogenous allosteric ligands. Each ligand stabilizes a unique subset of conformational states, which enables the CaSR to couple to distinct intracellular signalling pathways depending on the extracellular milieu in which it is bathed. Differential signalling arising from distinct receptor conformations favoured by each ligand is referred to as biased signalling. The outcome of CaSR activation also depends on the cell type in which it is expressed. Thus, the same ligand may activate diverse pathways in distinct cell types. Given that the CaSR is implicated in numerous physiological and pathophysiological processes, it is an ideal target for biased ligands that could be rationally designed to selectively regulate desired signalling pathways in preferred cell types.