Association of insulin resistance with polymorphic variants of Clock and Bmal1 genes: A case-control study

A systematic review of variations in circadian rhythm genes and type 2 diabetes

BACKGROUND

Type 2 diabetes is a chronic disease that has severe individual and societal consequences, which is forecast to worsen in the future. A new field of investigation is variations in circadian rhythm genes, in conjunction with diet and sleep variables, associations with, and effects on, type 2 diabetes development.

OBJECTIVE

This systematic review aimed to analyse all current literature regarding circadian rhythm gene variations and type 2 diabetes, and explore their interplay with diet and sleep variables on type 2 diabetes outcomes. This review was registered with PROSPERO (CRD42021259682).

METHODOLOGY

Embase and Pubmed were searched on 6/8/2021/11/8/2021 for studies of all designs, including participants from both sexes, all ethnicities, ages, and geographic locations. Participants with risk alleles/genotypes were compared with the wildtype regarding type 2 diabetes outcomes. Studies risk of bias were scored according to the risk of bias in non-randomised studies - interventions/exposures criteria.

RESULTS

In total, 31 studies were found (association n  =  29/intervention n  =  2) including >600,000 participants from various ethnicities, sexes, and ages. Variations in the melatonin receptor 1B, brain and muscle arnt-like 1 and period circadian regulator (PER) genes were consistently associated with type 2 diabetes outcomes.

CONCLUSIONS

Individuals with variations in melatonin receptor 1B, brain and muscle arnt-like 1 and PER may be at higher risk of type 2 diabetes. Further research is needed regarding other circadian rhythm genes. More longitudinal studies and randomised trials are required before clinical recommendations can be made.

Circadian Gene Variants in Diseases

The circadian rhythm is a self-sustaining 24 h cycle that regulates physiological processes within the body, including cycles of alertness and sleepiness. Cells have their own intrinsic clock, which consists of several proteins that regulate the circadian rhythm of each individual cell. The core of the molecular clock in human cells consists of four main circadian proteins that work in pairs. The CLOCK-BMAL1 heterodimer and the PER-CRY heterodimer each regulate the other pair's expression, forming a negative feedback loop. Several other proteins are involved in regulating the expression of the main circadian genes, and can therefore also influence the circadian rhythm of cells. This review focuses on the existing knowledge regarding circadian gene variants in both the main and secondary circadian genes, and their association with various diseases, such as tumors, metabolic diseases, cardiovascular diseases, and sleep disorders.

Association of BMAL1 clock gene polymorphisms with fasting glucose in children

BACKGROUND

The brain and muscle Arnt-like protein-1 (BMAL1) gene is an important circadian clock gene and previous studies have found that certain polymorphisms are associated with type 2 diabetes in adults. However, it remains unknown if such polymorphisms can affect fasting glucose in children and if other factors modify the associations.

METHODS

A school-based cross-sectional study with 947 Chinese children was conducted. A multivariable linear regression model was used to analyze the association between BMAL1 gene polymorphisms and fasting glucose level.

RESULTS

After adjusting for age, sex, body mass index (BMI), physical activity, and unhealthy diet, GG genotype carriers of BMAL1 rs3789327 had higher fasting glucose than AA/GA genotype carriers (b = 0.101, SE = 0.050, P = 0.045). Adjusting for the same confounders, rs3816358 was shown to be significantly associated with fasting glucose (b = 0.060, SE = 0.028, P = 0.032). Furthermore, a significant interaction between rs3789327 and nutritional status on fasting glucose was identified (P_interaction = 0.009); rs3789327 was associated with fasting glucose in the overweight/obese subgroup (b = 0.353, SE = 0.126, P = 0.006), but not in non-overweight/non-obese children.

CONCLUSIONS

BMAL1 polymorphisms were significantly associated with the fasting glucose level in children. Additionally, the observed interaction between nutritional status and BMAL1 supports promoting an optimal BMI in children genetically predisposed to higher glucose level.

IMPACT

Polymorphisms in the essential circadian clock gene BMAL1 were associated with fasting blood glucose levels in children. Additionally, there was a significant interaction between nutritional status and BMAL1 affecting fasting glucose levels. BMAL1 rs3789327 was associated with fasting glucose only in overweight/obese children. This finding could bring novel insights into mechanisms by which nutritional status influences fasting glucose in children.

The Association between Circadian Clock Gene Polymorphisms and Metabolic Syndrome: A Systematic Review and Meta-Analysis

Metabolic syndrome (MetS) is a combination of cardiovascular risk factors associated with type 2 diabetes, obesity, and cardiovascular diseases. The circadian clock gene polymorphisms are very likely to participate in metabolic syndrome genesis and development. However, research findings of the association between circadian rhythm gene polymorphisms and MetS and its comorbidities are not consistent. In this study, a review of the association of circadian clock gene polymorphisms with overall MetS risk was performed. In addition, a meta-analysis was performed to clarify the association between circadian clock gene polymorphisms and MetS susceptibility based on available data. The PubMed and Scopus databases were searched for studies reporting the association between circadian rhythm gene polymorphisms (ARNTL, BMAL1, CLOCK, CRY, PER, NPAS2, REV-ERBα, REV-ERBβ, and RORα) and MetS, and its comorbidities diabetes, obesity, and hypertension. Thirteen independent studies were analyzed with 17,381 subjects in total. The results revealed that the BMAL1 rs7950226 polymorphism was associated with an increased risk of MetS in the overall population. In contrast, the CLOCK rs1801260 and rs6850524 polymorphisms were not associated with MetS. This study suggests that some circadian rhythm gene polymorphisms might be associated with MetS in different populations and potentially used as predictive biomarkers for MetS.

Downregulation of Arntl mRNA Expression in Women with Hypertension: A Case-Control Study

BACKGROUND

Previous studies have reported that disturbance of endogenous circadian rhythms enhances the chance of hypertension and suggested that circadian clock genes could have a crucial function in the onset of the disease. This case-control study was aimed to investigate the association of the mRNA expression of aryl hydrocarbon receptor nuclear translocator like (Arntl), clock circadian regulator (Clock), and period circadian regulators 1 and 2 (Per1 and Per2) with hypertension and blood pressure levels.

METHODS

A total of 172 subjects were recruited in this study, including 86 hypertension and 86 nonhypertension controls. The mRNA expression levels in peripheral blood mononuclear cells were determined by real-time quantitative polymerase chain reaction. The differences in Arntl, Clock, Per1, and Per2 mRNA expression were compared between the 2 groups, and the relationship between mRNA expression and cardiometabolic risk profiles was also assessed.

RESULTS

We found that the mRNA expression of Arntl was downregulated in the hypertension cases compared with controls in women (1.10 [0.66, 1.71] vs. 1.30 [0.99, 2.06], p = 0.031). There was a significant negative correlation between the Arntl mRNA expression and SBP (r = -0.301, p = 0.004) and DBP (r = -0.222, p = 0.034) in women. In men, a negative correlation between the Per1 mRNA expression and SBP (r = -0.247, p = 0.026) was found.

CONCLUSIONS

The Arntl mRNA expression may play an important role in progression of hypertension in women.

The Association of Cardiovascular Disease with the T3111C Polymorphism in the CLOCK Gene

Background and Objectives: Cardiovascular diseases (CVDs) are among the leading causes of death worldwide, although CVD mortality has decreased in developed countries. Numerous pathophysiological processes lead to the development of CVDs. The circadian rhythm coordinates many physiological processes, and its disruption can lead to many pathophysiological changes. One of the significant circadian rhythm genes is the CLOCK gene, whose polymorphisms are associated with CVD risk factors. Research findings of the association between CLOCK gene polymorphism and CVDs and its comorbidities are not consistent. This meta-analysis was conducted to quantify the associations between T3111C polymorphism and the risk of CVDs. Materials and Methods: The PubMed and Scopus databases were searched for studies reporting onthe association between T3111C (rs1801260) in the circadian CLOCK gene and cardiovascular disease and its comorbidities such as obesity, hypertension, insulin resistance, and coronary artery disease. A fixed-effect model was used to calculate the pooled odds ratio and 95% confidence interval by comprehensive meta-analysis software. Results: Five independent studies, including case-control, cross-sectional, and cohort research methods, were analyzed with 3123 subjects in total. The meta-analysis revealed a significant association between T3111C polymorphism and cardiovascular disease (OR = 1.32, 95% CI: 1.16–1.50, p < 0.001) with significant heterogeneity (I2 = 91.1%, p < 0.001) and no publication bias. The subgroup analysis on comorbidity related to CVDs revealed that hypertension was associated with T3111C polymorphism (OR = 2.02, 95% CI: 1.60–2.54, p < 0.001). Conclusions: Our meta-analysis based on available studies using a fixed model shows that T3111C polymorphism in the CLOCK gene is associated with CVD susceptibility.