Moduladores genéticos do ritmo circadiano em humanos : associação de polimorfismos em genes das via aferente do Núcleo Supraquiasmático (NSQ) com preferência diurna e hábitos de sono

Abstract

Regulation of Circadian rhythms is under control of a pacemaker called Suprachiasmatic Nucleus (SCN), which are synchronized by environmental factors. The SCNs receive external information from three different mean pathways: retinal hypothalamic tract, geniculo-hypothalamic tract and raphe nucleus projections; other pathways, such as melatonergic system, are included. Different transporters and receptors, including 5-HTT MT2, 5-HT1A, NPY2 and NMDA, mediate these signal transduction pathways. Diurnal preference is a phenotypic expression of endogenous circadian rhythms. Most association studies involving diurnal preference have focused on polymorphism in circadian genes, and low attention was given to genetic alterations in non-circadian genes. The aim of this study was to investigate potential genetic modulators of the circadian rhythms, associating polymorphisms in non-circadian genes with diurnal preference. Undergraduate students answered the Morning-Evening Questionnaire (MEQ) and the Munich Cronotype Questionnaire for determination of diurnal preference, sleep habits and social jetlag. For genetic association analysis, the extreme morning and evening, with the same number of intermediate (56 for each group), were selected. The polymorphisms were genotyped using normal PCR and Real Time PCR. An association between the rs4753426 alleles and diurnal preference was found, with the C allele more frequent in morning (62%) than evening types (47%) (n= 112). An interaction effect for 5-HTTLPR*rs2020933*rs6295 was observed in diurnal preference, with the mean MEQ scores higher in genotype combination S/S; A/A; C/G (M= 62,50 and DP= 15,47) (morning) compared to other combinations S/S; A/T; C/G (M= 22,0 and DP= 2,82) and S/S; A/A; G/G (M= 27,33 and DP= 5,92; F (2, 24) = 11,16, p < 0,001, ω2= 0,42) (n= 111). In addition, an interaction effect among the alleles from rs2234759, rs4753426 and rs6295 polymorphisms was found, with the mean MEQ scores higher in allelic combinations C-A-C (M= 53,60 and DP= ±17,32) and C-G-C (M= 62,43 and DP= ±11,35) compared to combinations C-A-G (M= 45,66 and DP= ±18,65) e T-A-C (M= 44,66 and DP= ±14,68); t(152)= 2,70, p= 0,008, d= 0,66 e t(53)= 3,68, p= 0,001, d= 0,97) (n= 168). In relationship to sleep habits, the interaction effect 5-HTTLPR(genotype)*diurnal preference in bedtime on weekdays was significantly different in evening types with L/S genotypes (M= 00:40 and DP= 1:18 hours) compared to L/L genotypes (M = 2:13 and DP = 1:23 hours) and S/S (M = 2:20 and DP = 1:20; F(4,158)= 3,90, p= 0,005, ω²= 0,02) (n =167). Additionally, in the interaction effect „diurnal preference*rs2020933(allele)‟, the midpoint of sleep on weekdays showed differences between the A allele (M= 4:27 and DP= 1:18) and T allele (M= 5:55 e DP= 1:47; t(110)= -3,68, p < 0,001, d= 0,96) (n=168) in evening types. According to rs2234759 polymorphism, a difference was observed for A allele (M= 6:30 e DP= 1:30) and G allele (M= 6:58 e DP = 1:24; t(334)= -2,27, p= 0,024, d= 0,25) (n= 168) regarding to sleep duration on weekdays. No genotypic/allelic correlation was found for social jetlag. Thus, these results demonstrated that genetic alterations in non-circadian genes can participate in circadian rhythm modulation, via NSQ afferent pathways. This can contribute to variability on circadian phenotypes, mainly by interaction among different polymorphisms in the signing molecules genes.