Ischemia induces early expression of a new transcription factor (6A3-5) in kidney vascular smooth muscle cells: studies in rat and human renal pathology

Nephroscreen™: a diagnostic test for predicting acute renal failure?

Acute renal failure is a frequent and often fatal complication of hospitalized patients. While the risk of acute renal failure among select patient groups is well recognized, physicians currently rely on diagnostic tests such as changes of serum creatinine and indirect assessment of the glomerular filtration rate to diagnose acute renal failure. Although these parameters capture the degree of kidney function lost, they are not warning signs of evolving kidney injury. While the clinical emergence of acute renal failure is sudden, the pathologic changes preceding loss of kidney function are not so sudden. Nephroscreen is a fast and easy-to-use urine enzyme-linked immunosorbent assay test designed to quantify specific pathologic events preceding death of renal proximal tubule cells. It detects acute kidney damage days before serum creatinine rises and may open new avenues to defining acute renal failure as well as treating acute renal failure patients earlier and more effectively.

SOX9 protein induces a chondrogenic phenotype of mesangial cells and contributes to advanced diabetic nephropathy

Diabetic nephropathy (DN) is the most important chronic kidney disease. We previously reported that Smad1 transcriptionally regulates the expression of extracellular matrix in DN. Phenotypic change in mesangial cells (MCs) is a key pathologic event in the progression of DN. The aim of this study is to investigate a novel mechanism underlying chondrogenic phenotypic change in MCs that results in the development of DN. MCs showed chondrogenic potential in a micromass culture, and BMP4 induced the expression of chondrocyte markers (SRY-related HMG Box 9 (SOX9) and type II collagen (COL2)). Advanced glycation end products induced the expression of chondrocyte marker proteins downstream from the BMP4-Smad1 signaling pathway in MCs. In addition, hypoxia also induced the expression of BMP4, hypoxia-inducible factor-1α (HIF-1α), and chondrocyte markers. Overexpression of SOX9 caused ectopic expression of proteoglycans and COL2 in MCs. Furthermore, forced expression of Smad1 induced chondrocyte markers as well. Dorsomorphin inhibited these inductions. Glomerular expressions of HIF-1α, BMP4, and chondrocyte markers were observed in diabetic nephropathy mice. These positive stainings were observed in mesangial sclerotic lesions. SOX9 was partially colocalized with HIF-1α and BMP4 in diabetic glomeruli. BMP4 knock-in transgenic mice showed not only similar pathological lesions to DN, but also the induction of chondrocyte markers in the sclerotic lesions. Here we demonstrate that HIF-1α and BMP4 induce SOX9 expression and subsequent chondrogenic phenotype change in DN. The results suggested that the transdifferentiation of MCs into chondrocyte-like cells in chronic hypoxic stress may result in irreversible structural change in DN.

Renal tubulointerstitial fibrosis: common but never simple

Regardless of etiology, all patients with chronic renal disease show a progressive decline in renal function with time. Fibrosis, so-called scarring, is a key cause of this pathophysiology. Fibrosis involves an excess accumulation of extracellular matrix (primarily composed of collagen) and usually results in loss of function when normal tissue is replaced with scar tissue. While recent major advances have led to a much better understanding of this process, many problems remain. We for instance know little about why some wounds heal and others scar and little about how many putative antifibrotic agents work. This review discusses recent advances in our understanding of the mechanisms of tubulointerstitial fibrosis, focusing on the regulation and role of the myofibroblast in this process, the role of recently recognized endogenous antifibrotic factors, controversy surrounding the effects of metalloproteinases, and the opportunities presented by new treatment strategies that abrogate and may even reverse fibrosis.

Hemoglobin is expressed by mesangial cells and reduces oxidant stress

Hemoglobin (Hb) serves as the main oxygen transporter in erythrocytes, but it is also expressed in nonhematopoietic organs, where it serves an unknown function. In this study, microarray and proteomic analyses demonstrated Hb expression in the kidney. Rat kidneys were perfused extensively with saline, and glomeruli were isolated by several techniques (sieving, manual dissection, and laser capture-microdissection). Reverse transcriptase-PCR revealed glomerular alpha- and beta-globin expression, and immunoblotting demonstrated expression of the protein. In situ hybridization studies showed expression of the globin subunits in the mesangium, and immunostaining confirmed this localization of Hb. Furthermore, globin mRNA expression was detected in primary cultures of rat mesangial cells but not in cultured glomerular endothelial or epithelial cells. For investigation of Hb function in mesangial cells, the SV40-MES13 murine mesangial cell line was transfected with a vector expressing alpha- and beta-globins; this overexpression reduced production of hydrogen peroxide-induced intracellular radical oxygen species and enhanced cell viability against oxidative stress. In summary, Hb is expressed by rat mesangial cells, and its potential functions may include antioxidative defense.

6A3-5/Osa2 is an early activated gene implicated in the control of vascular smooth muscle cell functions

Vascular smooth muscle cells (VSMC) growth plays a key role in the pathophysiology of vascular diseases. However, the molecular mechanisms controlling gene transcription in VSMC remain poorly understood. We previously identified, by differential display, a new gene (6A3-5) overexpressed in proliferating rat VSMC. In this study, we have cloned the full-length cDNA by screening a rat foetal brain cDNA library and investigated its functions. The 6A3-5 protein shows 4 putative conserved functional motifs: a DNA binding domain called ARID (AT-rich interaction domain), two recently described motifs (Osa Homology Domain), and a nuclear localization signal. The deduced protein sequence was observed to be 85% identical to the recently described human Osa2 gene. Immunolabelling, using an anti-6A3-5/Osa2 monoclonal antibody, showed a nuclear localization of the 6A3-5/Osa2 protein. In addition, PDGF upregulated 6A3-5/Osa2 expression at both the transcript and protein levels in a dose and time-dependent fashion. The pattern of upregulation by PDGF was reminiscent of the early responsive gene c-fos. The PDGF-induced upregulation of 6A3-5/Osa2 and proliferation of VSMC were significantly inhibited in a dose and sequence-dependent fashion by an antisense, but not by sense, scrambled or mismatched oligonucleotides directed against 6A3-5/Osa2. In VSMC of aortas derived from hypertensive (LH) rats, 6A3-5/Osa2 is overexpressed as compared to that in normotensive (LL) rats. The 6A3-5/Osa2-gene expression is downregulated by an ACE inhibitor and upregulated by exogenous AngiotensinII in LH rats. In summary, these results indicate that 6A3-5/Osa2 is an early activated gene that belongs to a new family of proteins involved in the control of VSMC growth.