The role of the TSC-22 (-396) A/G variant in the development of diabetic nephropathy

Overexpression of TSC-22 (transforming growth factor- β-stimulated clone-22) causes marked obesity, splenic abnormality and B cell lymphoma in transgenic mice

In this study, we generated transgenic (Tg) mice, which overexpressed transforming growth factor (TGF)-β stimulated clone-22 (TSC-22), and investigate the functional role of TSC-22 on their development and pathogenesis. We obtained 13 Tg-founders (two mice from C57BL6/J and 11 mice from BDF1). Three of 13 Tg-founders were sterile, and the remaining Tg-founders also could generate only a limited number of the F1 generation. We obtained 32 Tg-F1 mice. Most of the Tg-mice showed marked obesity. Histopathological examination could be performed on 31 Tg-mice; seventeen mice died by some disease in their entire life and 14 mice were killed for examination. Most of the Tg-mice examined showed splenic abnormality, in which marked increase of the megakaryocytes, unclearness of the margin of the red pulp and the white pulp, and the enlargement of the white pulp was observed. B cell lymphoma was developed in 10 (71%) of 14 disease-died F1 mice. These results indicate that constitutive over-expression of TSC-22 might disturb the normal embryogenesis and the normal lipid metabolism, and induce the oncogenic differentiation of hematopoietic cells.

Post-transcriptional up-regulation of Tsc-22 by Ybx1, a target of miR-216a, mediates TGF-{beta}-induced collagen expression in kidney cells

Increased accumulation of extracellular matrix proteins and hypertrophy induced by transforming growth factor-β1 (TGF-β) in renal mesangial cells (MC) are hallmark features of diabetic nephropathy. Although the post-transcriptional regulation of key genes has been implicated in these events, details are not fully understood. Here we show that TGF-β increased microRNA-216a (miR-216a) levels in mouse MC, with parallel down-regulation of Ybx1, a miR-216a target and RNA-binding protein. TGF-β also enhanced protein levels of Tsc-22 (TGF-β-stimulated clone 22) and collagen type I α-2 (Col1a2) expression in MC through far upstream enhancer E-boxes by interaction of Tsc-22 with an E-box regulator, Tfe3. Ybx1 colocalized with processing bodies in MC and formed a ribonucleoprotein complex with Tsc-22 mRNA, and this complex formation was reduced by TGF-β, miR-216a mimics, or Ybx1 shRNA to increase Tsc-22 protein levels but enhanced by miR-216a inhibitor oligonucleotides. Chromatin immunoprecipitation (ChIP) assays revealed that TGF-β could increase the occupancies of Tsc-22 and Tfe3 on enhancer E-boxes of Col1a2. Co-immunoprecipitation assays revealed that TGF-β promoted the interaction of Tsc-22 with Tfe3. These results demonstrate that post-transcriptional regulation of Tsc-22 mediated through Ybx1, a miR-216a target, plays a key role in TGF-β-induced Col1a2 in MC related to the pathogenesis of diabetic nephropathy.

TGF-β1 and TSC-22 Gene Polymorphisms and Susceptibility to Microvascular Complications in Type 2 Diabetes

BACKGROUND/AIM

There is a strong evidence for the involvement of genetic factors in diabetic microvascular complications. The aim of our study was to investigate the role of molecular variants of the TGF-beta1 (transforming growth factor beta 1) and the TSC-22 (transforming growth factor beta stimulated clone 22) genes in diabetic nephropathy and diabetic retinopathy in type 2 diabetes.

METHODS

A case-control study was conducted in 503 patients and 400 healthy subjects. DNA samples were genotyped by polymerase chain reaction and restriction fragment length polymorphism methods.

RESULTS

Among the patients, 245 had diabetic nephropathy, 195 had retinopathy, and 168 were free from complications. All subjects were genotyped for T869C and C -509T polymorphisms of the TGF-beta1 gene and for -396 polymorphism of the TSC-22 gene. A significantly increased frequency of the CC genotype of the T869C polymorphism was observed in patients with nephropathy and retinopathy (33 and 48%, respectively, vs. 19 and 15%, respectively, in controls and patients free from complications). The frequency of the C allele was also higher (0.58 for nephropathy and 0.64 for retinopathy vs. 0.42 in controls). The G allele of the TSC-22 polymorphism was associated with an increased risk of diabetic nephropathy (frequency 0.15 vs. 0.07 and 0.06, respectively, in patients free from complications and controls). An interaction was observed between the G allele of the TSC-22 polymorphism and the C-allele of the TGF-beta polymorphism.

CONCLUSIONS

Our data suggest the association of TGF-beta T869C gene polymorphism with an increased risk of nephropathy and retinopathy in type 2 diabetes patients. It interacts with the TSC-22 gene involved in the TGF-beta signaling pathway, promoting the development of diabetic nephropathy.

Concordance of functional in vitro data and epidemiological associations in complex disease genetics

PURPOSE

We aimed to assess whether epidemiological evidence on genetic associations for complex diseases concord with in vitro functional data.

METHODS

We examined 36 studies on bi-allelic markers and 23 studies on haplotypes where investigators had addressed both epidemiological associations and the functional effect of the same gene variants in luciferase reporter systems in vitro.

RESULTS

There was no correlation between epidemiological odds ratios and luciferase activity ratios (-0.09, P = 0.60). Luciferase activity ratios could not tell whether a probed epidemiologic association would be significant or not (area under receiver operating characteristics curve, 0.52). Luciferase results usually were qualitatively similar across cell lines and experimental conditions, with some exceptions. A luciferase activity ratio of 1.44 adequately separated statistically significant from non-significant functional differences (area under receiver operating characteristics curve, 0.95). Binary and continuous disease outcomes usually gave concordant results; other in vitro methods, in particular EMSA, agreed with luciferase results. Selective reporting and use of different variants and contrasts between functional and epidemiological analyses were common in these studies.

CONCLUSIONS

In vitro biological data and epidemiology provide independent lines of evidence on complex diseases. We provide suggestions for improving the design and reporting of studies addressing both in vitro and epidemiological effects.

Assessment of 115 candidate genes for diabetic nephropathy by transmission/disequilibrium test

Several lines of evidence, including familial aggregation, suggest that allelic variation contributes to risk of diabetic nephropathy. To assess the evidence for specific susceptibility genes, we used the transmission/disequilibrium test (TDT) to analyze 115 candidate genes for linkage and association with diabetic nephropathy. A comprehensive survey of this sort has not been undertaken before. Single nucleotide polymorphisms and simple tandem repeat polymorphisms located within 10 kb of the candidate genes were genotyped in a total of 72 type 1 diabetic families of European descent. All families had at least one offspring with diabetes and end-stage renal disease or proteinuria. As a consequence of the large number of statistical tests and modest P values, findings for some genes may be false-positives. Furthermore, the small sample size resulted in limited power, so the effects of some tested genes may not be detectable, even if they contribute to susceptibility. Nevertheless, nominally significant TDT results (P < 0.05) were obtained with polymorphisms in 20 genes, including 12 that have not been studied previously: aquaporin 1; B-cell leukemia/lymphoma 2 (bcl-2) proto-oncogene; catalase; glutathione peroxidase 1; IGF1; laminin alpha 4; laminin, gamma 1; SMAD, mothers against DPP homolog 3; transforming growth factor, beta receptor II; transforming growth factor, beta receptor III; tissue inhibitor of metalloproteinase 3; and upstream transcription factor 1. In addition, our results provide modest support for a number of candidate genes previously studied by others.