Upregulation of nestin, vimentin, and desmin in rat podocytes in response to injury

The intermediate filament nestin is highly expressed in normal human podocytes and podocytes in glomerular disease

The intermediate protein nestin is expressed in proliferating embryonic tissues and adult tissues undergoing repair. Recently this protein been identified in rodent podocytes. Its role in this cell is unknown, since podocytes are believed to be terminally differentiated and nondividing. We report the first study of nestin in human kidney. Nestin expression in normal mature human glomeruli was confined to podocytes. In developing kidney, nestin was detected in metanephric blastema and in podocytic cells at all stages of glomerular development. Nestin co-localized with vimentin but not with actin or heavy chain myosin IIA, using a mouse podocyte cell line. Knockdown of nestin in a murine podocyte cell line failed to produce any obvious phenotypic change or alteration in vimentin distribution but was associated with increased cell cycling. A survey of glomerular diseases failed to identify any condition lacking nestin, indicating that the protein is critical for some aspect of podocyte function. Perhaps through an association with vimentin, nestin serves to bolster the mechanical strength of these cells that experience high tensile stress during glomerular filtration. Nestin was also expressed in podocytes that are reported to be 'dysregulated' (lacking podocyte markers). Thus, nestin has a potential as a reliable podocyte marker, even for podocytes that are not completely differentiated (for example, during development) or 'dedifferentiated' in glomerular disease.

A nest in renal fibrosis?

Sakairi and collaborators show that some tubular cells as well as some interstitial myofibroblasts express the intermediate filament protein nestin. These findings evoke questions about the origin and role of these nestin-positive cells in the development of tubulointerstitial fibrosis.

Actin filament organization of foot processes in vertebrate glomerular podocytes

We investigated the actin filament organization and immunolocalization of actin-binding proteins (alpha-actinin and cortactin) in the podocyte foot processes of eight vertebrate species (lamprey, carp, newt, frog, gecko, turtle, quail, and rat). Three types of actin cytoskeleton were found in these foot processes. (1) A cortical actin network with cortactin filling the space between the plasma membrane and the other actin cytoskeletons described below was found in all of the species examined here. The data indicated that the cortical actin network was the minimal essential actin cytoskeleton for the formation and maintenance of the foot processes in vertebrate podocytes. (2) An actin bundle with alpha-actinin existing along the longitudinal axis of foot process above the level of slit diaphragms was only observed in quail and rat. (3) An actin fascicle consisting of much fewer numbers of actin filaments than that of the actin bundle was observed in the species other than quail and rat, but at various frequencies. These findings suggest that the actin bundle is an additional actin cytoskeleton reflecting a functional state peculiar to quail and rat glomeruli. Considering the higher intraglomerular pressure and the extremely thin filtration barrier in birds and mammals, the foot processes probably mainly protect the thinner filtration barrier from the higher internal pressure occurring in quail and rat glomeruli. Therefore, we consider that the actin bundle plays a crucial role in the mechanical protection of the filtration barrier. Moreover, the actin fascicle may be a potential precursor of the actin bundle.

Expression of nestin in the podocytes of normal and diseased human kidneys

The complex cyto-architecture of the podocyte is critical for glomerular permselectivity. The present study characterizes the expression of nestin, an intermediate filament protein, in human kidneys. In normal kidneys, nestin was detected at the periphery of glomerular capillary loops. Colabeling showed nestin was expressed in WT1-positive cells. Within the podocyte, nestin immunoreactivity was present in the cell body and primary process. This was supported by immunoelectron microscopy. Nestin also colocalized with vimentin in the periphery of capillary loops but not in the mesangium. Nestin was not detected in other structures of the adult human kidney. To determine the potential role of nestin in proteinuria, nestin was examined in kidney biopsies from patients with or without proteinuria. These patients were diagnosed with IgA nephropathy with mild mesangial expansion but without proteinuria, IgA nephropathy with proteinuria, membranous nephropathy (MN), and focal segmental glomerular sclerosis (FSGS). The distribution of nestin in these biopsies was similar to that in the normal kidney. Semiquantitative analysis of immunostaining showed that glomerular nestin expression in IgA nephropathy without proteinuria was not different from normal kidney; however, nestin expression in kidneys of patients with IgA nephropathy and proteinuria, or MN and FSGS with proteinuria was significantly reduced compared with normal kidney ( P < 0.01). Reduced nestin mRNA expression in the patients with IgA nephropathy with proteinuria and FSGN was also observed by quantitative real-time PCR. These studies suggest that nestin may play an important role in maintaining normal podocyte function in the human kidney.

Nestin expression in the kidney with an obstructed ureter

Nestin is an intermediate filament protein originally identified in neuroepithelial stem cells. This cytoskeletal-associated protein is also expressed in some non-neuronal organs including renal tubular cells and glomerular endothelial cells during kidney development. Little is known, however, about nestin expression in the kidney during injury. In this study, we find nestin expression induced in renal tubular and interstitial myofibroblasts in the adult rat kidney following unilateral ureteral obstruction. The degree of nestin expression was well correlated with the degree of tubulointerstitial fibrosis. Immunohistochemical identification of specific nephron segments showed that nestin was primarily expressed by proximal tubules, partially by distal tubules and thick ascending limbs of Henle but not by collecting ducts. The nestin-positive tubular cells also expressed vimentin and heat-shock protein 47 (HSP47) suggesting these cells reverted to a mesenchymal phenotype. Not all vimentin- or HSP-expressing cells expressed nestin; however, suggesting that nestin is distinct from these conventional mesenchymal markers. Nestin expression was also found associated with phenotypical changes in cultured renal cells induced by hypoxia or transforming growth factor-beta. Nestin expression was located in hypoxic regions of the kidney with an obstructed ureter. Our results indicate that nestin could be a novel marker for tubulointerstitial injury.

Snail, a transcriptional regulator, represses nephrin expression in glomerular epithelial cells of nephrotic rats

Snail is a DNA-binding molecule that plays a pivotal role in regulating cell adhesion and epithelial to mesenchymal transition. Visceral epithelial cells (podocytes) in kidney glomeruli form a sophisticated cell-cell junction called a slit diaphragm that prevents the loss of plasma protein during ultrafiltration. Nephrin, located in the slit diaphragm and critical for maintaining the integrity of this structure, belongs to the class of cell adhesion molecules of the immunoglobulin super-family. As previously reported, the transcriptional activity of nephrin is a determinant of the integrity of the slit diaphragm in puromycin aminonucleoside (PAN) nephrosis rats. Here, we examined the role of Snail in nephrin expression. In accordance with the downregulation of nephrin in PAN nephrosis rats, Snail was upregulated in vivo and its DNA-binding activity was stimulated in injured podocytes while normal podocytes did not express Snail. An in vitro study demonstrated that Snail bound to E-box motifs in a specific segment of the rat nephrin gene repressed the transcription of nephrin and downregulated nephrin protein. We also found that the expression level of Snail in injured podocytes was regulated by GSK3, which is known to phosphorylate Snail and induce its proteolysis. Pharmacological in vitro and in vivo inhibition studies of GSK3 suggested that GSK3 activity decreased in injured podocytes and this change partially contributed to the decrease in nephrin and increase in Snail and proteinuria. Concordantly, we found that Wnt-2 was upregulated in injured podocytes and activated the Wnt canonical pathway. As the Wnt canonical pathway inactivates GSK3, it is likely that Wnt-2 accounts for the accumulation of Snail in injured podocytes. In conclusion, Snail is a key molecule, which perturbs the integrity of the slit diaphragm through transcriptional repression of nephrin under pathological conditions. Wnt-GSK3 pathway participates in this mechanism.

Normal distribution and medullary-to-cortical shift of Nestin-expressing cells in acute renal ischemia

Nestin, a marker of multi-lineage stem and progenitor cells, is a member of intermediate filament family, which is expressed in neuroepithelial stem cells, several embryonic cell types, including mesonephric mesenchyme, endothelial cells of developing blood vessels, and in the adult kidney. We used Nestin-green fluorescent protein (GFP) transgenic mice to characterize its expression in normal and post-ischemic kidneys. Nestin-GFP-expressing cells were detected in large clusters within the papilla, along the vasa rectae, and, less prominently, in the glomeruli and juxta-glomerular arterioles. In mice subjected to 30 min bilateral renal ischemia, glomerular, endothelial, and perivascular cells showed increased Nestin expression. In the post-ischemic period, there was an increase in fluorescence intensity with no significant changes in the total number of Nestin-GFP-expressing cells. Time-lapse fluorescence microscopy performed before and after ischemia ruled out the possibility of engraftment by the circulating Nestin-expressing cells, at least within the first 3 h post-ischemia. Incubation of non-perfused kidney sections resulted in a medullary-to-cortical migration of Nestin-GFP-positive cells with the rate of expansion of their front averaging 40 microm/30 min during the first 3 h and was detectable already after 30 min of incubation. Explant matrigel cultures of the kidney and aorta exhibited sprouting angiogenesis with cells co-expressing Nestin and endothelial marker, Tie-2. In conclusion, several lines of circumstantial evidence identify a sub-population of Nestin-expressing cells with the mural cells, which are recruited in the post-ischemic period to migrate from the medulla toward the renal cortex. These migrating Nestin-positive cells may be involved in the process of post-ischemic tissue regeneration.

Nestin expression in adult and developing human kidney

Nestin is considered a marker of neurogenic and myogenic precursor cells. Its arrangement is regulated by cyclin-dependent kinase 5 (CDK5), which is expressed in murine podocytes. We investigated nestin expression in human adult and fetal kidney as well as CDK5 presence in adult human podocytes. Confocal microscopy demonstrated that adult glomeruli display nestin immunoreactivity in vimentin-expressing cells with the podocyte morphology and not in cells bearing the endothelial marker CD31. Glomerular nestin-positive cells were CDK5 immunoreactive as well. Western blotting of the intermediate filament-enriched cytoskeletal fraction and coimmunoprecipitation of nestin with anti-CDK5 antibodies confirmed these results. Nestin was also detected in developing glomeruli within immature podocytes and a few other cells. Confocal microscopy of experiments conducted with antibodies against nestin and endothelial markers demonstrated that endothelial cells belonging to capillaries invading the lower cleft of S-shaped bodies and the immature glomeruli were nestin immunoreactive. Similar experiments carried out with antibodies raised against nestin and alpha-smooth muscle actin showed that the first mesangial cells that populate the developing glomeruli expressed nestin. In conclusion, nestin is expressed in the human kidney from the first steps of glomerulogenesis within podocytes, mesangial, and endothelial cells. This expression, restricted to podocytes in mature glomeruli, appears associated with CDK5.

Intermediate filament protein nestin is expressed in developing kidney and heart and might be regulated by the Wilms' tumor suppressor Wt1

Nestin is an intermediate filament protein originally described in neural stem cells and a variety of progenitor cells. More recently, nestin was detected in rat kidney podocytes. We show here that nestin is expressed in a developmentally regulated pattern in the kidney. Nestin was detected by immunohistochemistry in the condensing mesenchyme surrounding the ureter, in developing glomeruli, in podocytes of the adult kidney, and in a podocyte cell line. Nestin shared a striking overlap in expression with the Wilms' tumor suppressor Wt1. Nestin was significantly upregulated in a cell line with inducible Wt1 expression upon induction of Wt1. Cotransfection experiments in human embryonic kidney cells (HEK293) revealed stimulation of a nestin intron 2 enhancer element up to six-fold by the Wt1(-KTS) splice variant. Nestin expression was significantly reduced in an inducible mouse model of glomerular disease. This model is based on podocyte-specific overexpression of Pax2 and associated with a loss of Wt1 expression. Furthermore, also in the developing heart, nestin was found in an overlapping pattern with Wt1 in the epicardium and the forming coronary vessels. Strikingly, in the hearts of Wt1 knockout mice, nestin was barely detectable compared with the hearts of wild-type embryos. Our results show that nestin is expressed at different stages of kidney and cardiac development and suggest that its expression in these organs might be regulated by the Wilms' tumor suppressor Wt1.

Differential expression of the intermediate filament protein nestin during renal development and its localization in adult podocytes

Nestin, an intermediate filament protein, is widely used as stem cell marker. Nestin has been shown to interact with other cytoskeleton proteins, suggesting a role in regulating cellular cytoskeletal structure. These studies examined renal nestin localization and developmental expression in mice. In developing kidney, anti-nestin antibody revealed strong immunoreactivity in vascular cleft of the S-shaped body and vascular tuft of capillary loop-stage glomerulus. The nestin-positive structures also were labeled by endothelial cell markers FLK1 and CD31 in immature glomeruli. Nestin was not detected in epithelial cells of immature glomeruli. In contrast, in mature glomerular, nestin immunoreactivity was observed only outside laminin-positive glomerular basement membrane, and co-localized with nephrin, consistent with podocyte nestin expression. In adult kidney, podocytes were the only cells that exhibited persistent nestin expression. Nestin was not detected in ureteric bud and its derivatives throughout renal development. Cell lineage studies, using a nestin promoter-driven Cre mouse and a ROSA26 reporter mouse, showed a strong beta-galactosidase activity in intermediate mesoderm in an embryonic day 10 embryo and all of the structures except those that were derived from ureteric bud in embryonic kidney through adult kidney. These studies show that nestin is expressed in progenitors of glomerular endothelial cells and renal progenitors that are derived from metanephric mesenchyme. In the adult kidney, nestin expression is restricted to differentiated podocytes, suggesting that nestin could play an important role in maintaining the structural integrity of the podocytes.