Here we report a new isolation method for mouse glomeruli. The method is fast and simple and allows for the isolation of virtually all glomeruli present in the adult mouse kidney with minimal contamination of nonglomerular cells. Mice were perfused through the heart with magnetic 4.5-m diameter Dynabeads. Kidneys were minced into small pieces, digested by collagenase, filtered, and collected using a magnet. The number of glomeruli retrieved from one adult mouse was 20,131 ؎ 4699 (mean ؎ SD, n ؍ 14) with a purity of 97.5 ؎ 1.7%. The isolated glomeruli retained intact morphology, as confirmed by light and electron microscopy, as well as intact mRNA integrity, as confirmed by Northern blot analysis. The method was applicable also to newborn mice, which allows for the isolation of immature developmental stage glomeruli. This method makes feasible transcript profiling and proteomic analysis of the developing, healthy and diseased mouse glomerulus. As the genome projects are near completion, 1,2 an important step in the functional analysis of genome data are the determination of transcriptomes corresponding to specific cellular functions and states of differentiation. Such analyses require methods allowing for the isolation of highly homogenous population of cells and/or microorgans from in vivo situations. One such microorgan is the kidney glomerulus. Glomeruli constitute ϳ10% of whole kidney tissues and are unique structures of microvasculature mainly made up of three highly specialized cell types; fenestrated endothelial cells, mesangial cells, and podocytes. These cell types together with the glomerular basement membrane form the permeable barrier across which blood is filtered to produce primary urine. During the past decade several gene products have been shown to play essential roles in glomerulus development, 3-5 function, and pathology. 6 However, our knowledge of the molecular mechanisms governing glomerulus morphogenesis and development of the specialized features of its individual cells is still very limited. An obvious difficulty in addressing these issues stems from the low abundance of the glomerulus cells and the inability of the glomerulus cell types to retain their differentiated features in cell culture. Podocytes, for example, make up less than 2% of kidney tissues. Although endothelial cells and pericytes exist outside the glomerulus, their phenotype within the glomerulus is quite distinct from related cells elsewhere. 7 We describe a new protocol for the isolation of glomeruli from mice. The protocol is fast and allows for the isolation of virtually all glomeruli present in a mouse kidney at 97% purity. The method thus allows for transcript profiling and proteomic analysis of the glomerulus using standard procedures.
Platelet-derived growth factor-B (PDGFB) is necessary for normal cardiovascular development, but the relative importance of different cellular sources of PDGFB has not been established. Using Cre-lox techniques, we show here that genetic ablation of Pdgfb in endothelial cells leads to impaired recruitment of pericytes to blood vessels. The endothelium-restricted Pdgfb knockout mutants also developed organ defects including cardiac, placental and renal abnormalities. These defects were similar to those observed in Pdgfb null mice. However, in marked contrast to the embryonic lethality of Pdgfb null mutants, the endothelium-specific mutants survived into adulthood with persistent pathological changes, including brain microhemorrhages, focal astrogliosis, and kidney glomerulus abnormalities. This spectrum of pathological changes is reminiscent of diabetic microangiopathy, suggesting that the endothelium-restricted Pdgfb knockouts may serve as models for some of the pathogenic events of vascular complications to diabetes.
To advance our understanding of development, function and diseases in the kidney glomerulus, we have established and large-scale sequenced cDNA libraries from mouse glomeruli at different stages of development, resulting in a catalogue of 6053 different genes. The glomerular cDNA clones were arrayed and hybridized against a series of labeled targets from isolated glomeruli, non-glomerular kidney tissue, FACS-sorted podocytes and brain capillaries, which identified over 300 glomerular cell-enriched transcripts, some of which were further sublocalized to podocytes, mesangial cells and juxtaglomerular cells by in situ hybridization. For the earliest podocyte marker identified, Foxc2, knockout mice were used to analyze the role of this protein during glomerular development. We show that Foxc2 controls the expression of a distinct set of podocyte genes involved in podocyte differentiation and glomerular basement membrane maturation. The primary podocyte defects also cause abnormal differentiation and organization of the glomerular vascular cells. We surmise that studies on the other novel glomerulus-enriched transcripts identified in this study will provide new insight into glomerular development and pathomechanisms of disease.
Normal blood microvessels are lined by pericytes, which contribute to microvessel development and stability through mechanisms that are poorly understood. Pericyte deficiency has been implicated in the pathogenesis of microvascular abnormalities associated with diabetes and tumors. However, the unambiguous identification of pericytes is still a problem because of cellular heterogeneity and few available molecular markers. Here we describe an approach to identify pericyte markers based on transcription profiling of pericyte-deficient brain microvessels isolated from platelet-derived growth factor (PDGF-B)-/- and PDGF beta receptor (PDGFRbeta)-/- mouse mutants. The approach was validated by the identification of known pericyte markers among the most down-regulated genes in PDGF-B-/- and PDGFRbeta-/- microvessels. Of candidates for novel pericyte markers, we selected ATP-sensitive potassium-channel Kir6.1 (also known as Kcnj8) and sulfonylurea receptor 2, (SUR2, also known as Abcc9), both part of the same channel complex, as well as delta homologue 1 (DLK1) for in situ hybridization, which demonstrated their specific expression in brain pericytes of mouse embryos. We also show that Kir6.1 is highly expressed in pericytes in brain but undetectable in pericytes in skin and heart. The three new brain pericyte markers are signaling molecules implicated in ion transport and intercellular signaling, potentially opening new windows on pericyte function in brain microvessels.
The prorenin receptor is an accessory subunit of the vacuolar H ϩ -ATPase, suggesting that it has fundamental functions beyond activation of the local renin-angiotensin system. Podocytes express the prorenin receptor, but its function in these cells is unknown. Here, podocyte-specific, conditional, prorenin receptor-knockout mice died of kidney failure and severe proteinuria within 4 weeks of birth. The podocytes of these mice exhibited foot process effacement with reduced and altered localization of the slit-diaphragm proteins nephrin and podocin. Furthermore, the podocytes contained numerous autophagic vacuoles, confirmed by enhanced accumulation of microtubule-associated protein 1 light chain 3-positive intracellular vesicles. Ablation of the prorenin receptor selectively suppressed expression of the V 0 c-subunit of the vacuolar H ϩ -ATPase in podocytes, resulting in deacidification of intracellular vesicles. In conclusion, the prorenin receptor is important for the maintenance of normal podocyte structure and function.
The 26-year-old diagnostic criteria for WS were revised on the basis of the results of a nationwide epidemiological study. The proposed revised criteria will facilitate simpler, faster and more robust diagnosis of WS in the Japanese population.
Members of the mitogen activated protein (MAP) kinase family, extracellular signal-regulated kinase, stress-activated protein kinase-1/c-Jun NH 2 -terminal kinase, and p38, are central elements that transduce the signal generated by growth factors, cytokines, and stressing agents. It is well known that the platelet-derived growth factor (PDGF) activates extracellular signal-regulated kinase, which leads to cellular mitogenic response. On the other hand, the role of the other MAP kinases in mediating the cellular function of PDGF remains unclear. In the present study, we have investigated the functional role of the other MAP kinases in PDGF-mediated cellular responses. We show that ligand stimulation of PDGF receptors leads to the activation of p38 but not stress-activated protein kinase-1/c-Jun NH 2 -terminal kinase. Experiments using a specific inhibitor of p38, SB203580, show that the activation of p38 is required for PDGF-induced cell motility responses such as cell migration and actin reorganization but not required for PDGF-stimulated DNA synthesis. Analyses of tyrosine residue-mutated PDGF receptors show that Src homology 2 domain-containing proteins including Src family kinases, phosphatidylinositol 3-kinase, the GTPaseactivating protein of Ras, the Src homology 2 domaincontaining phosphatase SHP-2, phospholipase C-␥, and Crk do not play a major role in mediating the PDGFinduced activation of p38. Finally, the expression of dominant-negative Ras but not dominant-negative Rac inhibited p38 activation by PDGF, suggesting that Ras is a potent mediator in the p38 activation pathway downstream of PDGF receptors. Taken together, our present study proposes the existence of a Ras-dependent pathway for the activation of p38, which is important for cell motility responses elicited by PDGF stimulation.
Diabetic nephropathy is the major cause of end-stage renal failure throughout the world in both developed and developing countries. Diabetes affects all cell types of the kidney, including endothelial cells, tubulointerstitial cells, podocytes and mesangial cells. During the past decade, the importance of podocyte injury in the formation and progression of diabetic nephropathy has been established and emphasized. However, recent findings provide additional perspectives on pathogenesis of diabetic nephropathy. Glomerular endothelial damage is already present in the normoalbuminuric stage of the disease when podocyte injury starts. Genetic targeting of mice that cause endothelial injury leads to accelerated diabetic nephropathy. Tubulointerstitial damage, previously considered to be a secondary effect of glomerular protein leakage, was shown to have a primary significance in the progression of diabetic nephropathy. Emerging evidence suggests that the glomerular filtration barrier and tubulointerstitial compartment is a composite, dynamic entity where any injury of one cell type spreads to other cell types, and leads to the dysfunction of the whole apparatus. Accumulation of novel knowledge would provide a better understanding of the pathogenesis of diabetic nephropathy, and might lead to a development of a new therapeutic strategy for the disease.
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