Human adipose microRNA-221 is upregulated in obesity and affects fat metabolism downstream of leptin and TNF-α

AIMS/HYPOTHESIS

MicroRNAs (miRNAs) are short endogenous RNAs that regulate multiple biological processes including adipogenesis and fat metabolism. We sought to identify miRNAs that correlate with BMI and to elucidate their upstream regulation and downstream targets.

METHODS

Microarray-based expression profiling of 233 miRNAs was performed on subcutaneous abdominal adipose tissue biopsies from 29 non-diabetic Pima Indian participants. Correlation of the expression levels of eight miRNAs with BMI was assessed by quantitative reverse transcription (QRT) PCR in adipose samples from 80 non-diabetic Pima Indians with a BMI of 21.6-54.0 kg/m(2). The upstream regulation of one of these miRNAs, miR-221, was tested by treating cultured human pre-adipocytes with leptin, TNF-α and insulin. Predicted targets of miR-221 were validated using QRT-PCR, immunoblots and luciferase assays. The downstream effects of miR-221 overexpression were assayed by proteomic analysis.

RESULTS

Expression levels of miR-221 were positively correlated with BMI (particularly in women) and fasting insulin concentrations, while the levels of miR-193a-3p and miR-193b-5p were negatively correlated with BMI; other miRNAs did not show significant associations in the 80 samples. miR-221 was downregulated by leptin and TNF-α treatment in cultured human pre-adipocytes. Conversely, miR-221 overexpression upregulated several proteins involved in fat metabolism, mimicking peroxisome proliferator-activated receptor (PPAR) activation. Furthermore, miR-221 directly downregulated the adiponectin receptor 1 (ADIPOR1) and the transcription factor v-ets erythroblastosis virus E26 oncogene homolog 1 (ETS1). Adiponectin signalling is known to promote insulin sensitivity, and ETS1 is crucial for angiogenesis.

CONCLUSIONS/INTERPRETATION

Our data suggest that miR-221 may contribute to the development of the insulin resistance that typically accompanies obesity, by affecting PPAR signalling pathways and by directly downregulating ADIPOR1 and ETS1.

Protein tyrosine phosphatase 1B is not a major susceptibility gene for type 2 diabetes mellitus or obesity among Pima Indians

AIM/HYPOTHESIS

Single-nucleotide polymorphisms (SNPs) in the protein tyrosine phosphatase 1B gene (PTPN1) have been reported to be associated with type 2 diabetes in white subjects, and insulin sensitivity and fasting glucose levels in Hispanic Americans. In this study, we determined whether SNPs in PTPN1 also have a role in type 2 diabetes susceptibility in Pima Indians, a population with the world's highest reported prevalence and incidence rates of this disease.

MATERIALS AND METHODS

Thirty-one SNPs across a 161-kb region encompassing PTPN1 were genotyped in 1,037 Pima Indians for association studies with type 2 diabetes and obesity.

RESULTS

Twenty-five of the SNPs had allele frequencies >0.05, and these SNPs fell into two linkage disequilibrium blocks (D' > 0.9). Block 1 contains six SNPs that span a 61-kb region upstream of PTPN1, while block 2 contains 19 SNPs that cover the entire PTPN1 gene. None of the SNPs, analysed individually or as haplotypes, was associated with either type 2 diabetes or obesity. However, three SNPs located in block 1 were nominally associated (p values ranging from 0.01 to 0.05) with insulin sensitivity as measured by the hyperinsulinaemic-euglycaemic clamp technique.

CONCLUSIONS/INTERPRETATION

Based on our association results, we conclude that SNPs within PTPN1 are unlikely to have a major role in the aetiology of type 2 diabetes or obesity in Pima Indians.

Mutations in the genes for hepatocyte nuclear factor (HNF)-1alpha, -4alpha, -1beta, and -3beta; the dimerization cofactor of HNF-1; and insulin promoter factor 1 are not common causes of early-onset type 2 diabetes in Pima Indians

OBJECTIVE

Maturity-onset diabetes of the young (MODY) is a genetically heterogeneous subtype of type 2 diabetes characterized by an early age at onset and autosomal dominant inheritance. MODY can result from heterozygous mutations in at least five genes. The purpose of this study was to determine whether alterations in known MODY genes and two MODY candidate genes contribute to the development of early-onset type 2 diabetes in Pima Indians.

RESEARCH DESIGN AND METHODS

The coding regions of the known MODY genes hepatocyte nuclear factor (HNF)-1alpha, HNF-4alpha, HNF-1beta, and insulin promoter factor 1 and the coding regions of two MODY candidate genes, HNF-3beta and the dimerization cofactor of HNF-1, were sequenced in genomic DNA from Pima Indians. The primary "affected" study population consisted of 46 Pima Indians whose age at onset of type 2 diabetes was < or =20 years. DNA sequence variants identified in the affected group were then analyzed in a group of 80 "unaffected" Pima Indians who were at least 40 years old and had normal glucose tolerance.

RESULTS

A total of 11 polymorphisms were detected in these genes. However, none of the polymorphisms differed in frequency among Pima Indians with an early age at onset of diabetes compared with older Pima Indians with normal glucose tolerance.

CONCLUSIONS

Mutations in these known MODY or MODY candidate genes are not a common cause of early-onset diabetes in Pima Indians.

Identification of bacteriophage K20 binding regions of OmpF and lipopolysaccharide in Escherichia coli K-12

Two classes of phage K20 resistant Escherichia coli K-12 mutants were obtained. One class of mutants possessed alterations within the ompF gene while the rfa gene cluster, which is responsible for lipopolysaccharide (LPS) synthesis, was affected in the second class of mutants. The OmpF mutants contained substitutions affecting residues localized within the surface-exposed loops 5, 6 or 7. A single deletion mutation resulted in the removal of eight residues of loop 5. These alterations prevented the binding of K20 to cell surface without affecting OmpF's channel activity. One LPS mutant characterized in detail contained an unusual aberration within the rfa gene cluster caused by an IS5 element. Its insertion mediated a deletion encompassing the rfaBIJ genes. Genetic complementation analysis revealed that the rfaB gene, whose product catalyzes the addition of a galactose residue to the first glucose molecule of the LPS core, is necessary to synthesize LPS able to serve as a co-receptor for phage K20.