Composition of gut microbiota in obese and normal-weight Mexican school-age children and its association with metabolic traits

BACKGROUND

Childhood obesity is a serious public health problem in Mexico. Adult gut microbiota composition has been linked to obesity, but few studies have addressed the role of gut microbiota in childhood obesity.

OBJECTIVES

The aim of this study is to compare gut microbiota composition in obese and normal-weight children and to associate gut microbiota profiles with amino acid serum levels and obesity-related metabolic traits.

METHODS

Microbial taxa relative abundance was determined by 16S rRNA sequencing in 67 normal-weight and 71 obese children aged 6-12 years. Serum amino acid levels were measured by mass spectrometry. Associations between microbiota composition, metabolic parameters and amino acid serum levels were tested.

RESULTS

No significant differences in phyla abundances or Firmicutes/Bacteroidetes ratios were observed between normal-weight and obese children. However, Bacteroides eggerthii abundance was significantly higher in obese children and correlated positively with body fat percentage and negatively with insoluble fibre intake. Additionally, Bacteroides plebeius and unclassified Christensenellaceae abundances were significantly higher in normal-weight children. Abundance of both these species correlated negatively with phenylalanine serum levels, a metabolite also found to be associated with obesity in Mexican children.

CONCLUSIONS

The study identified bacterial species associated with obesity, metabolic complications and amino acid serum levels in Mexican children.

Trimethylamine N-oxide levels are associated with NASH in obese subjects with type 2 diabetes

AIMS

Trimethylamine N-oxide (TMAO), choline and betaine serum levels have been associated with metabolic diseases including type 2 diabetes (T2D) and non-alcoholic fatty liver disease (NAFLD). These associations could be mediated by insulin resistance. However, the relationships among these metabolites, insulin resistance and NAFLD have not been thoroughly investigated. Moreover, it has recently been suggested that TMAO could play a role in NAFLD by altering bile acid metabolism. We examined the association between circulating TMAO, choline and betaine levels and NAFLD in obese subjects.

METHODS

Serum TMAO, choline, betaine and bile acid levels were measured in 357 Mexican obese patients with different grades of NAFLD as determined by liver histology. Associations of NAFLD with TMAO, choline and betaine levels were tested. Moreover, association of TMAO levels with non-alcoholic steatohepatitis (NASH) was tested separately in patients with and without T2D.

RESULTS

TMAO and choline levels were significantly associated with NAFLD histologic features and NASH risk. While increased serum TMAO levels were significantly associated with NASH in patients with T2D, in non-T2D subjects this association lost significance after adjusting for sex, BMI and HOMA2-IR. Moreover, circulating secondary bile acids were associated both with increased TMAO levels and NASH.

CONCLUSIONS

In obese patients, circulating TMAO levels were associated with NASH mainly in the presence of T2D. Functional studies are required to evaluate the role of insulin resistance and T2D in this association, both highly prevalent in NASH patients.

TCF7L2 is associated with high serum triacylglycerol and differentially expressed in adipose tissue in families with familial combined hyperlipidaemia

AIMS/HYPOTHESIS

Common DNA variants of the transcription factor 7-like 2 gene (TCF7L2) are associated with type 2 diabetes. Familial combined hyperlipidaemia (FCHL) is characterised by hypertriacylglycerolaemia, hypercholesterolaemia, or both. Additionally, disturbances in glucose metabolism are commonly seen in FCHL. Therefore, we hypothesised that TCF7L2 may contribute to the genetic susceptibility for this common dyslipidaemia.

METHODS

We investigated the effect of the TCF7L2 variants, rs7903146 and rs12255372, on FCHL and its component traits triacylglycerol (TG), total cholesterol (TC) and apolipoprotein B (ApoB) in 759 individuals from 55 Mexican families. As a replication sample, 719 individuals from 60 Finnish FCHL families were analysed. We also used quantitative RT-PCR to evaluate the transcript levels of TCF7L2 in 47 subcutaneous fat biopsies from unrelated Mexican FCHL and normolipidaemic participants.

RESULTS

Significant evidence for association was observed for high TG for the T alleles of rs7903146 and rs12255372 (p = 0.005 and p = 0.01) in Mexican FCHL families. No evidence for association was observed for FCHL, TC, ApoB or glucose in Mexicans. When testing rs7903146 and rs12255372 for replication in Finnish FCHL families, these single nucleotide polymorphisms were associated with TG (p = 0.01 and p = 0.007). Furthermore, we observed statistically significant decreases in the mRNA levels (p = 0.0002) of TCF7L2 in FCHL- and TG-affected individuals. TCF7L2 expression was not altered by the SNP genotypes.

CONCLUSIONS/INTERPRETATION

These data show that rs7903146 and rs12255372 are significantly associated with high TG in FCHL families from two different populations. In addition, significantly decreased expression of TCF7L2 was observed in TG- and FCHL-affected individuals.

Contribution of Chromosome 1q21-q23 to Familial Combined Hyperlipidemia in Mexican Families

Familial combined hyperlipidemia (FCHL) is the most common familial dyslipidemia, with a prevalence of 1-2% in the general population. A major locus for FCHL has been mapped to chromosome 1q21-q23 in Finnish, Chinese, German and US families. We studied seven extended Mexican families with 153 members, including 64 affected subjects. A total of 11 markers were genotyped, including D1S104 which has been linked to FCHL in other studies. Two point linkage analysis for the FCHL phenotype, and for the elevated triglyceride (TG) trait, allowing for heterogeneity, gave a maximum HLOD of 1.67 (alpha = 0.49) and 1.93 (alpha = 0.43) at D1S2768 (2.69 cM proximal to D1S104) respectively. Heterogeneity and non-parametric (NPL) multipoint analyses for the FCHL phenotype and the TG trait showed maximum HLODs of 1.27 (alpha = 0.46) and 1.64 (alpha = 0.38), and NPLs of 4.00 (P = 0.0001) and 3.68 (P = 0.0003) near D1S2768, respectively. In addition, analysis of four candidate genes putatively involved in the expression of FCHL showed no evidence of linkage for the LCAT gene or the APOA1/C3/A4/A5 gene cluster. However, we cannot exclude the participation of these genes, or the LIPC and LPL genes, as minor susceptibility loci in the expression of FCHL, or the TG or elevated total cholesterol (TC) traits in our families. In conclusion, our data confirm the involvement of a major susceptibility locus on chromosome 1q21-q23 in FCHL Mexican families, consistent with findings in other populations.

A genome-wide association study identifies novel gene associations with facial skin wrinkling and mole count in Latin Americans

BACKGROUND

Genome-wide association studies (GWASs) have identified genes influencing skin ageing and mole count in Europeans, but little is known about the relevance of these (or other genes) in non-Europeans.

OBJECTIVES

To conduct a GWAS for facial skin ageing and mole count in adults < 40 years old, of mixed European, Native American and African ancestry, recruited in Latin America.

METHODS

Skin ageing and mole count scores were obtained from facial photographs of over 6000 individuals. After quality control checks, three wrinkling traits and mole count were retained for genetic analyses. DNA samples were genotyped with Illumina's HumanOmniExpress chip. Association testing was performed on around 8 703 729 single-nucleotide polymorphisms (SNPs) across the autosomal genome.

RESULTS

Genome-wide significant association was observed at four genome regions: two were associated with wrinkling (in 1p13·3 and 21q21·2), one with mole count (in 1q32·3) and one with both wrinkling and mole count (in 5p13·2). Associated SNPs in 5p13·2 and in 1p13·3 are intronic within SLC45A2 and VAV3, respectively, while SNPs in 1q32·3 are near the SLC30A1 gene, and those in 21q21·2 occur in a gene desert. Analyses of SNPs in IRF4 and MC1R are consistent with a role of these genes in skin ageing.

CONCLUSIONS

We replicate the association of wrinkling with variants in SLC45A2, IRF4 and MC1R reported in Europeans. We identify VAV3 and SLC30A1 as two novel candidate genes impacting on wrinkling and mole count, respectively. We provide the first evidence that SLC45A2 influences mole count, in addition to variants in this gene affecting melanoma risk in Europeans.

Susceptibility background for type 2 diabetes in eleven Mexican Indigenous populations: HNF4A gene analysis

The genetic risk of developing type 2 diabetes (T2D) increases in parallel with the proportion of Native American ancestry. Mestizo Mexicans have a 70% Native Amerindian genetic background. The T130I polymorphism in the HNF4A gene has been associated with early-onset T2D in mestizo Mexicans. Thus, the aim of the present study was to evaluate the frequency and relationship of the T130I variant in the HNF4A gene with risk factors for developing T2D in eleven indigenous groups from Mexico. In two groups, all exons of the HNF4A gene were directly sequenced; in the remaining the T130I polymorphism was analyzed by restriction fragment length polymorphism. Ancestry informative markers were assessed to confirm the Amerindian component. An additional analysis of EHH was carried out. Interestingly, HNF4A gene screening revealed only the presence of the T130I polymorphism. The range frequency of the risk allele (T) in the indigenous groups was from 2.7 to 16%. Genotypic frequencies (T130I/I130I) were higher and significantly different from those of all of the populations included in the HapMap Project (P < 0.005). EHH scores suggest a positive selection for T130I polymorphism. Metabolic traits indicate a relationship between the T130I/I130I genotypes with high triglyceride concentrations in the indigenous groups (P < 0.005). These results strongly suggest that the high frequency of the T130I polymorphism and its biological relationship with dysfunction in lipid metabolism in Mexican indigenous groups is a risk factor for the developing of T2D in Mexicans.

HNF-1alpha G574S is a functional variant with decreased transactivation activity

AIM

To assess the functional consequence of the hepatocyte nuclear factor 1alpha gene (HNF-1alpha) G574S variant previously proposed as a diabetes susceptibility allele, in a group of Mexican Type 2 diabetic patients with end-stage renal disease (ESRD).

METHODS

The transcriptional activity of the HNF-1alpha G574S recombinant protein on the human insulin promoter was assessed by transfection assays in RINm5f and HepG2 cell lines.

RESULTS

Two unrelated Mexican diabetic patients with no known African ancestry were found to carry the G574S variant. This substitution was not found among unrelated healthy control subjects. Whereas the G574S HNF-1alpha transcription activation of the human insulin promoter was 40% lower than that of the wild-type protein in RINm5f beta cells, no difference was found in a hepatic cell line (HepG2).

CONCLUSIONS

G574S affects the transactivation potential of HNF-1alpha on the insulin promoter in pancreatic beta-cells. Although it has been difficult to prove its role in the development of diabetes in case-control association studies, this variant exhibits functional effects consistent with it being a potential diabetes susceptibility allele.