A molecular morphometric approach to diabetic kidney disease can link structure to function and outcome.

Diabetic kidney disease is the leading cause of kidney failure. However, studies of molecular mechanisms of early kidney damage are lacking. Here we examined for possible linkage between transcriptional regulation and quantitative structural damage in early diabetic kidney disease in Pima Indians with type 2 diabetes. Tissue obtained from protocol kidney biopsies underwent genome-wide compartment-specific gene expression profiling and quantitative morphometric analysis. The ultrastructural lesion most strongly associated with transcriptional regulation was cortical interstitial fractional volume (VvInt), an index of tubule-interstitial damage. Transcriptional co-expression network analysis identified 1843 transcripts that correlated significantly with VvInt. These transcripts were enriched for pathways associated with mitochondrial dysfunction, inflammation, migratory mechanisms, and tubular metabolic functions. Pathway network analysis identified IL-1ß as a key upstream regulator of the inflammatory response and five transcription factors cooperating with p53 to regulate metabolic functions. VvInt-associated transcripts showed significant correlation with the urine albumin to creatinine ratio and measured glomerular filtration rate 10 years after biopsy, establishing a link between the early molecular events and long-term disease progression. Thus, molecular mechanisms active early in diabetic kidney disease were revealed by correlating intrarenal transcripts with quantitative morphometry and long-term outcomes. This provides a starting point for identification of urgently needed therapeutic targets and non-invasive biomarkers of early diabetic kidney disease.

Perspectives on systems biology applications in diabetic kidney disease.

Diabetic kidney disease (DKD) is a microvascular complication of type 1 and 2 diabetes with a devastating impact on individuals with the disease, their families, and society as a whole. DKD is the single most frequent cause of incident chronic kidney disease cases and accounts for over 40% of the population with end-stage renal disease. Contributing factors for the high prevalence are the increase in obesity and subsequent diabetes combined with an improved long-term survival with diabetes. Environment and genetic variations contribute to DKD susceptibility and progressive loss of kidney function. How the molecular mechanisms of genetic and environmental exposures interact during DKD initiation and progression is the focus of ongoing research efforts. The development of standardized, unbiased high-throughput profiling technologies of human DKD samples opens new avenues in capturing the multiple layers of DKD pathobiology. These techniques routinely interrogate analytes on a genome-wide scale generating comprehensive DKD-associated fingerprints. Linking the molecular fingerprints to deep clinical phenotypes may ultimately elucidate the intricate molecular interplay in a disease stage and subtype-specific manner. This insight will form the basis for accurate prognosis and facilitate targeted therapeutic interventions. In this review, we present ongoing efforts from large-scale data integration translating "-omics" research efforts into improved and individualized health care in DKD.

Hic-5 as a regulator of endothelial cell morphology and connective tissue growth factor gene expression.

The functional role of the LIM-domain protein Hic-5 was investigated in microvascular endothelial cells using a siRNA approach. Knock down of Hic-5 reduced endothelial cell spreading and impaired structural organization of the cells on basement membrane extracts. Furthermore, Hic-5 was involved in the regulation of the multifunctional protein connective tissue growth factor (CTGF, CCN2). Upon Hic-5 down-regulation, induction of CTGF by lysophosphatidic acid or colchicine was reduced. Inhibition of CTGF expression was even more pronounced in cells treated with transforming growth factor beta and inhibitors of histone deacetylases. Treatment of endothelial cells with Hic-5 siRNA reduced CTGF promoter activity. Mutation analyses of the promoter revealed transcription factors binding to the basic control element as part of the proposed Hic-5-modulated transcription complex. Further analyses showed down-regulation of Hic-5 protein upon overnight treatment with inhibitors of histone deacetylases. These data suggest that the reduced expression of Hic-5 may contribute to the anti-angiogenic effects of histone deacetylase inhibitors.

Differential regulation of connective tissue growth factor in renal cells by histone deacetylase inhibitors.

Regulation of the profibrotic and angiogenesis modulating cytokine connective tissue growth factor (CTGF) occurs primarily at the transcriptional level. Therefore, we hypothesized that histone deacetylating enzymes (HDAC), which modulate the accessibility of transcriptionally active promoter regions, might play a role in the regulation of CTGF gene expression. We analyzed microvascular endothelial cells, which showed immunoreactivity for acetylated histone in kidney sections, and compared them with renal tubular epithelial cells. Treatment of cultured endothelial cells with different HDAC inhibitors up-regulated CTGF mRNA and protein. Pre-treatment with HDAC inhibitors facilitated induction of CTGF by transforming growth factor-beta (TGF-beta) or lysophosphatidic acid. Transcription factors of the FoxO family were involved in the up-regulation of CTGF as shown at protein level and by reporter gene analyses. In tubular epithelial cells, up-regulation of CTGF was only observed when these cells were cultured as subconfluent cells. Dense cells, which are more likely to resemble tubular cells in vivo, showed no up-regulation upon treatment with HDAC inhibitors and were protected against CTGF induction by TGF-beta. Taken together, our data indicate that the effect of HDAC inhibitors on CTGF expression is largely cell dependent in non-tumour cells. Different cell type-specific transcription factors seem to determine whether CTGF expression is reduced or increased in cells exposed to HDAC inhibitors.