RESUMEN
BACKGROUND AND AIM: Several lines of evidence indicate that glucose homeostasis may be under the control of Akt2 and it can therefore be seen as a candidate gene for human insulin resistance (IR) and related phenotypes. The aim of our study was the identification of Akt2 common allelic variants that might modulate susceptibility to IR and related metabolic abnormalities. METHODS AND RESULTS: The Akt2 gene (exons, 5' and 3' regulatory regions) was re-sequenced in samples of 50 blood donors from the Gargano region. Two single nucleotide polymorphisms (SNPs) in 5' (rs11669332 and rs969531) and two in 3' (rs2304186 and C1658T) regulatory regions were exploited in an association study using 661 healthy unrelated Caucasian individuals from the same region. Individuals being homozygous for the T allele of rs11669332 (an Akt2 promoter) showed lower systolic blood pressure (p=0.04), total/HDL cholesterol ratio (p=0.02) and the metabolic syndrome score (p=0.04), while carriers of the A allele of rs969531 (in 5'-UTR) showed higher systolic blood pressure (p=0.027). The association between phenotypic traits and possible haplotypes was tested as well. However, no haplotype affecting the risk of metabolic abnormalities was found. CONCLUSIONS: Two variants in 5' regulatory region of Akt2 gene are associated and may modulate susceptibility to IR and related metabolic abnormalities.
Asunto(s)
Variación Genética , Resistencia a la Insulina/genética , Síndrome Metabólico/genética , Polimorfismo de Nucleótido Simple , Proteínas Proto-Oncogénicas c-akt/genética , Regiones no Traducidas 3'/genética , Regiones no Traducidas 5'/genética , Adulto , Alelos , Exones , Femenino , Predisposición Genética a la Enfermedad , Haplotipos , Humanos , Desequilibrio de Ligamiento , Masculino , Datos de Secuencia MolecularRESUMEN
Insulin resistance, which is pathogenic for type 2 diabetes (T2D), is under the control of largely unknown genetic determinants. LAR, a protein-tyrosine phosphatase which inhibits insulin signalling, is overexpressed in animal and human models of insulin resistance. We studied the entire sequence of the LAR gene by SSCP analysis and automatic DNA sequencing, with the aim of verifying whether its sequence variants might be associated with insulin resistance. In the 276 bp sequence upstream of the transcriptional start site (i.e. a region we have identified as having basal promoter activity) a -127 bp T-->A SNP (5% frequency) was associated with lower body mass index (BMI) ( P=0.03), waist circumference ( P=0.01), blood pressure ( P=0.01) and urinary albumin/creatinine ratio ( P=0.04) in 589 non-diabetic unrelated individuals from the Gargano region (central east coast of Italy). To quantify the risk for a high body weight conferred by the -127 T-->A SNP, the whole cohort was divided into tertiles according to the individual BMI. The risk of belonging to the heavier tertile, as compared to the leaner one, was reduced by approximately 60%. In a population from East Sicily ( n=307), T/A genotype carriers ( n=13) showed lower triglyceride levels ( P=0.04) and higher insulin sensitivity as indicated by lower plasma glucose ( P=0.03) and serum insulin ( P=0.006) during oral glucose tolerance testing (OGTT). Promoter activity, studied by cDNA transfection experiments, was similar for the A and T alleles. In conclusion, a genetic variant of the LAR gene promoter is consistently associated with features of insulin resistance in two different Caucasian populations. Although the biological relevance of this variant has yet to be determined, this finding underlines the potential importance of the LAR gene in dysregulation of insulin sensitivity and related disorders.
Asunto(s)
Resistencia a la Insulina/genética , Proteínas del Tejido Nervioso/genética , Obesidad/genética , Polimorfismo de Nucleótido Simple , Regiones Promotoras Genéticas/genética , Proteínas Tirosina Fosfatasas/genética , Receptores de Superficie Celular/genética , Adulto , Alelos , Índice de Masa Corporal , Diabetes Mellitus Tipo 2/genética , Femenino , Humanos , Masculino , Persona de Mediana Edad , Obesidad/patología , Polimorfismo Conformacional Retorcido-Simple , Proteínas Tirosina Fosfatasas Clase 2 Similares a ReceptoresRESUMEN
Ectonucleotide pyrophosphatase phosphodiesterase 1 (ENPP1) inhibits insulin-receptor (IR) signaling and, when over-expressed, induces insulin resistance in vitro and in vivo. Understanding the regulation of ENPP1 expression may, thus, unravel new molecular mechanisms of insulin resistance. Recent data point to a pivotal role of the ENPP1 3'UTR, in modulating ENPP1 mRNA stability and expression. We sought to identify trans-acting proteins binding the ENPP1-3'UTR and to investigate their role on ENPP1 expression and on IR signaling. By RNA electrophoresis mobility shift analysis and tandem mass spectrometry, we demonstrated the binding of heat shock protein 70 (HSP70) to ENPP1-3'UTR. Through this binding, HSP70 stabilizes ENPP1 mRNA and increases ENPP1 transcript and protein levels. This positive modulation of ENPP1 expression is paralleled by a reduced insulin-induced IR and IRS-1 phosphorylation. Taken together these data suggest that HSP70, by affecting ENPP1 expression, may be a novel mediator of altered insulin signaling.