[Show abstract][Hide abstract] ABSTRACT: Blood filtration in the kidney glomerulus is essential for physiological homeostasis. The filtration apparatus of the kidney glomerulus is composed of three distinct components: the fenestrated endothelial cells, the glomerular basement membrane, and interdigitating foot processes of podocytes that form the slit diaphragm. Recent studies have demonstrated that podocytes play a crucial role in blood filtration and in the pathogenesis of proteinuria and glomerular sclerosis; however, the molecular mechanisms that organize the podocyte filtration barrier are not fully understood. In this study, we suggest that tight junction protein 1 (Tjp1 or ZO-1), which is encoded by Tjp1 gene, plays an essential role in establishing the podocyte filtration barrier. The podocyte-specific deletion of Tjp1 down-regulated the expression of podocyte membrane proteins, impaired the interdigitation of the foot processes and the formation of the slit diaphragm, resulting in glomerular dysfunction. We found the possibility that podocyte filtration barrier requires the integration of two independent units, the pre-existing epithelial junction components and the newly synthesized podocyte-specific components, at the final stage in glomerular morphogenesis, for which Tjp1 is indispensable. Together with previous findings that Tjp1 expression was decreased in glomerular diseases in human and animal models, our results indicate that the suppression of Tjp1 could directly aggravate glomerular disorders, highlights Tjp1 as a potential therapeutic target. Citation: Itoh M, Nakadate K, Horibata Y, Matsusaka T, Xu J, et al. (2014) The Structural and Functional Organization of the Podocyte Filtration Slits Is Regulated by Tjp1/ZO-1. PLoS ONE 9(9): e106621. doi:10.1371/journal.pone.0106621 Copyright: ß 2014 Itoh et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability: The authors confirm that all data underlying the findings are fully available without restriction. All relevant data are within the paper and its Supporting Information files. Funding: This work was supported by JSPS KAKENHI to M.I. (Grant Number 23590242). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist.
[Show abstract][Hide abstract] ABSTRACT: Metabolic acidosis, a common complication of CKD, causes mitochondrial stress by undefined mechanisms. Selective autophagy of impaired mitochondria, called mitophagy, contributes toward maintaining cellular homeostasis in various settings. We hypothesized that mitophagy is involved in proximal tubular cell adaptations to chronic metabolic acidosis. In transgenic mice expressing green fluorescent protein-tagged microtubule-associated protein 1 light chain 3 (GFP-LC3), NH4Cl loading increased the number of GFP puncta exclusively in the proximal tubule. In vitro, culture in acidic medium produced similar results in proximal tubular cell lines stably expressing GFP-LC3 and facilitated the degradation of SQSTM1/p62 in wild-type cells, indicating enhanced autophagic flux. Upon acid loading, proximal tubule-specific autophagy-deficient (Atg5-deficient) mice displayed significantly reduced ammonium production and severe metabolic acidosis compared with wild-type mice. In vitro and in vivo, acid loading caused Atg5-deficient proximal tubular cells to exhibit reduced mitochondrial respiratory chain activity, reduced mitochondrial membrane potential, and fragmented morphology with marked swelling in mitochondria. GFP-LC3-tagged autophagosomes colocalized with ubiquitinated mitochondria in proximal tubular cells cultured in acidic medium, suggesting that metabolic acidosis induces mitophagy. Furthermore, restoration of Atg5-intact nuclei in Atg5-deficient proximal tubular cells increased mitochondrial membrane potential and ammoniagenesis. In conclusion, metabolic acidosis induces autophagy in proximal tubular cells, which is indispensable for maintaining proper mitochondrial functions including ammoniagenesis, and thus for adapted urinary acid excretion. Our results provide a rationale for the beneficial effect of alkali supplementation in CKD, a condition in which autophagy may be reduced, and suggest a new therapeutic option for acidosis by modulating autophagy.
Journal of the American Society of Nephrology 04/2014; · 8.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: NFE2-related factor 2 (Nrf2) is a master regulatory transcription factor for antioxidant genes. Inhibition of its adaptor protein, Kelch-like ECH-associated protein 1 (Keap1), activates Nrf2. Podocyte injury triggers the progressive deterioration of glomerular damage toward glomerulosclerosis. We examined whether modulation of the Keap1-Nrf2 system has an impact on this process.
Nrf2 null-mutant (KO) and Keap1 hypomorphic knockdown (KD) mice were crossed with NEP25 mice, in which podocyte-specific injury can be induced by an immunotoxin.
Thiobarbituric acid reactive substances, 8-hydroxydeoxyguanosine and phosphorylated JNK were increased in the injured NEP25 kidney. Real-time PCR revealed that Keap1 KD upregulated Nrf2 target genes, including Gclc, Gclm, Gstp1, Gstp2 and Nqo1 in the glomerulus. However, podocyte injury did not upregulate these genes in Keap1 wild-type mice, nor did it further increase the expression of those genes in Keap1 KD mice. Three weeks after the induction of podocyte injury, glomerulosclerosis was considerably more attenuated in Keap1 KD mice than in control mice (median sclerosis index, 0.27 versus 3.03, on a 0-4 scale). Keap1 KD mice also showed considerably preserved nephrin staining (median index, 6.76 versus 0.91, on a 0-8 scale) and decreased glomeruli containing desmin-positive injured podocytes (median percentage, 24.5% versus 85.8%), along with a decrease in mRNAs for Fn1, Tgfb1, Col4a4 and Col1a2.
Thus, podocyte injury cannot effectively activate Nrf2, but Nrf2 activation by Keap1 knockdown attenuates glomerulosclerosis. These results indicate that the Nrf2-Keap1 system is a promising drug target for the treatment of chronic kidney diseases.
[Show abstract][Hide abstract] ABSTRACT: Podocyte injury is the first step in the progression of glomerulosclerosis. Previous studies have demonstrated the beneficial effect of bone morphogenetic protein 7 (Bmp7) in podocyte injury and the existence of native Bmp signaling in podocytes. Local activity of Bmp7 is controlled by cell-type specific Bmp antagonists, which inhibit the binding of Bmp7 to its receptors. Here we show that the product of Twisted gastrulation (Twsg1), a Bmp antagonist, is the central negative regulator of Bmp function in podocytes and that Twsg1 null mice are resistant to podocyte injury. Twsg1 was the most abundant Bmp antagonist in murine cultured podocytes. The administration of Bmp induced podocyte differentiation through Smad signaling, whereas the simultaneous administration of Twsg1 antagonized the effect. The administration of Bmp also inhibited podocyte proliferation, whereas simultaneous administration of Twsg1 antagonized the effect. Twsg1 was expressed in the glomerular parietal cells (PECs) and distal nephron of the healthy kidney, and additionally in damaged glomerular cells in a murine model of podocyte injury. Twsg1 null mice exhibited milder hypoalbuminemia and hyperlipidemia, and milder histological changes while maintaining the expression of podocyte markers during podocyte injury model. Taken together, our results show that Twsg1 plays a critical role in the modulation of protective action of Bmp7 on podocytes, and that inhibition of Twsg1 is a promising means of development of novel treatment for podocyte injury.
PLoS ONE 01/2014; 9(2):e89135. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: TSPAN8 encoding tetraspanin-8 was identified as a candidate gene for immunoglobulin A nephropathy (IgAN) by a genome-wide association study using microsatellites in the Japanese population. Tetraspanin-8 is a cell surface protein that contributes to the migration and invasion of epithelial cells.
[Show abstract][Hide abstract] ABSTRACT: Recent studies have reported that podocytes are postnatally generated from progenitor cells localized in Bowman's capsule or in the bone marrow. In the present study, we investigated whether or not podocyte regeneration is important in the repair of injured glomeruli after mild podocyte injury in mice.
Mild podocyte injury was induced in NEP25 mice (n = 8) by injecting an immunotoxin, LMB2 (0.625 ng/g body weight). Control mice, not injured by LMB2 injection (n = 7) was used as a comparison. Proliferating cells were labeled by continuous infusion of bromodeoxyuridine (BrdU). Podocytes, identified by nephrin, WT1 or podocin staining, that had incorporated BrdU were enumerated 4 weeks later.
A total of 742 corpuscles were inspected in serial sections stained for BrdU and nephrin; 19% showed sclerosis. BrdU(+) cells were observed in both the glomeruli and Bowman's capsules, averaging 2.5 ± 3.1 in non-sclerotic corpuscles and 7.0 ± 5.8 in sclerotic corpuscles. Only one BrdU(+) cell was also positive for nephrin. Another cell, localized at a position consistent with its potential identification as a podocyte, was nephrin negative but had incorporated BrdU. WT1 staining similarly revealed that only two nuclei were doubly positive for BrdU and WT1. Additional 1676 corpuscles were inspected by double staining for BrdU and podocin; none were doubly positive.
Podocytes are not replenished by proliferation of endogenous progenitor cells in mice with glomerular injury.
[Show abstract][Hide abstract] ABSTRACT: Intrarenal angiotensin II is increased in kidney diseases independently of plasma angiotensin II and is thought to promote progressive deterioration of renal architecture. Here we investigated the mechanism of enhanced renal angiotensin II generation in kidney glomerular diseases. For this, kidney- or liver-specific angiotensinogen gene (Agt) knockout was superimposed on the mouse model of inducible podocyte injury (NEP25). Seven days after induction of podocyte injury, renal angiotensin II was increased ninefold in NEP25 mice with intact Agt, accompanied by increases in urinary albumin and angiotensinogen excretion, renal angiotensinogen protein, and its mRNA. Kidney Agt knockout attenuated renal Agt mRNA but not renal angiotensin II, renal, or urinary angiotensinogen protein. In contrast, liver Agt knockout markedly reduced renal angiotensin II to 18.7% of that of control NEP25 mice, renal and urinary angiotensinogen protein, but not renal Agt mRNA. Renal angiotensin II had no relationship with renal Agt mRNA, or with renal renin mRNA, which was elevated in liver Agt knockouts. Kidney and liver dual Agt knockout mice showed phenotypes comparable to those of liver Agt knockout mice. Thus, increased renal angiotensin II generation upon severe podocyte injury is attributed to increased filtered angiotensinogen of liver origin resulting from loss of macromolecular barrier function of the glomerular capillary wall that occurs upon severe podocyte injury.Kidney International advance online publication, 27 November 2013; doi:10.1038/ki.2013.453.
Kidney International 11/2013; · 8.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Focal segmental glomerulosclerosis (FSGS) is a podocyte disease. Among the various histologies of FSGS, active epithelial changes - hyperplasia as typically seen in the collapsing variant - indicates disease progression. Using a podocyte-specific injury model of FSGS carrying a genetic podocyte tag combined with double immunostaining by different sets of podocytes and parietal epithelial cell (PEC) markers (Nestin/Pax8, WT1/Claudin1, and Podocalyxin/Pax2), we investigated the direction of epithelial phenotypic transition and its role in FSGS. FSGS mice showed progressive proteinuria and renal dysfunction often accompanied by epithelial hyperplasia, wherein X-gal-positive podocyte-tagged cells were markedly decreased. The average numbers of double-positive cells in all sets of markers were significantly increased in the FSGS mice compared to the controls. In addition, the average numbers of double-positive cells for X-gal/Pax8, Nestin/Pax8 and Podocalyxin/Pax2 staining in the FSGS mice were comparable, whereas those of WT1/Claudin1 were significantly increased. When we divided glomeruli from FSGS mice into those with FSGS lesions and those without, double-positive cells tended to be more closely associated with glomeruli without FSGS lesions compared to those with FSGS lesions. Moreover, the majority of double-positive cells appeared to be isolated and very rarely associated with FSGS lesions (1/1,997 glomeruli). This study is the first to show the incidence and localization of epithelial cells with phenotypically changing in FSGS using a genetic tag. The results suggest that the major direction of epithelial phenotypic transition in cellular FSGS is from podocytes to PECs, and that these cells were less participated in the active lesions of FSGS.
[Show abstract][Hide abstract] ABSTRACT: Obesity is an independent risk factor for renal dysfunction in patients with CKDs, including diabetic nephropathy, but the mechanism underlying this connection remains unclear. Autophagy is an intracellular degradation system that maintains intracellular homeostasis by removing damaged proteins and organelles, and autophagy insufficiency is associated with the pathogenesis of obesity-related diseases. We therefore examined the role of autophagy in obesity-mediated exacerbation of proteinuria-induced proximal tubular epithelial cell damage in mice and in human renal biopsy specimens. In nonobese mice, overt proteinuria, induced by intraperitoneal free fatty acid-albumin overload, led to mild tubular damage and apoptosis, and activated autophagy in proximal tubules reabsorbing urinary albumin. In contrast, diet-induced obesity suppressed proteinuria-induced autophagy and exacerbated proteinuria-induced tubular cell damage. Proximal tubule-specific autophagy-deficient mice, resulting from an Atg5 gene deletion, subjected to intraperitoneal free fatty acid-albumin overload developed severe proteinuria-induced tubular damage, suggesting that proteinuria-induced autophagy is renoprotective. Mammalian target of rapamycin (mTOR), a potent suppressor of autophagy, was activated in proximal tubules of obese mice, and treatment with an mTOR inhibitor ameliorated obesity-mediated autophagy insufficiency. Furthermore, both mTOR hyperactivation and autophagy suppression were observed in tubular cells of specimens obtained from obese patients with proteinuria. Thus, in addition to enhancing the understanding of obesity-related cell vulnerability in the kidneys, these results suggest that restoring the renoprotective action of autophagy in proximal tubules may improve renal outcomes in obese patients.
Journal of the American Society of Nephrology 10/2013; · 8.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Chronic metabolic stress is related to diseases, whereas autophagy supplies nutrients by recycling the degradative products. Cyclosporin A (CsA), a frequently used immunosuppressant, induces metabolic stress via effects on mitochondrial respiration, and thereby, its chronic usage is often limited. Here we show that autophagy plays a protective role against CsA-induced metabolic stress in kidney proximal tubule epithelial cells. Autophagy-deficiency leads to decreased mitochondrial membrane potential, which coincides with metabolic abnormalities as characterized by decreased levels of amino acids, increased tricarboxylic acid (TCA) ratio (the levels of intermediates of the latter part of the TCA cycle, over levels of intermediates in the earlier part), and decreased products of oxidative phosphorylation (ATP). In addition to the altered profile of amino acids, CsA decreased the hyperpolarization of mitochondria with the disturbance of mitochondrial energy metabolism in autophagy-competent cells, i.e., increased TCA ratio and worsening of the NAD(+)/NADH ratio, coupled with decreased energy status, which suggests that adaptation to CsA employs autophagy to supply electron donors from amino acids via intermediates of the latter part of the TCA cycle. The TCA ratio of autophagy-deficient cells was further worsened with decreased levels of amino acids in response to CsA, and, as a result, the deficiency of autophagy failed to adapt to the CsA-induced metabolic stress. Deterioration of the TCA ratio further worsened energy status. The CsA-induced metabolic stress also activated regulatory genes of metabolism and apoptotic signals, whose expressions were accelerated in autophagy-deficient cells. These data provide new perspectives on autophagy in conditions of chronic metabolic stress in disease.
[Show abstract][Hide abstract] ABSTRACT: Background: Mice carrying the null-mutated Foxc1 gene frequently develop an anomalous double collecting system. These mice provide an ideal opportunity to specify the role of ectopic budding in the development of congenital anomalies of the kidney and urinary tract. Methods: Tissue specimens were collected from Foxc1(ch/ch) mutants at several embryonic stages and at birth. The upper and lower pole kidneys were qualitatively and quantitatively examined by histology, in situ hybridization and immunohistochemistry. Results: Upper pole kidneys of newborn Foxc1(ch/ch) mice were significantly more hypoplastic and contained significantly fewer glomeruli than their lower pole counterparts. On embryonic day 14.5, the stage immediately before the formation of the first urine, the upper pole kidney was already smaller than the lower pole kidney. Neither histology nor immunostaining for kidney markers showed dysplastic regions in either kidney of newborn Foxc1(ch/ch) mice. Of note, expression of Foxc1 was restricted to maturing podocytes and was not detectable in any intermediate structure of nephron development in the nephrogenic zone. Conclusion: Ectopic budding alone results only in kidney hypoplasia but not dysplasia. The development of dysplasticity in the maturing kidney involves gene(s) that function beyond the initial budding stage within the metanephros.
[Show abstract][Hide abstract] ABSTRACT: Collapsing focal segmental glomerulosclerosis (cFSGS) is a progressive kidney disease characterized by glomerular collapse with epithelial hyperplasia. Here we used a transgenic mouse model of cFSGS with immunotoxin-induced podocyte-specific injury to determine the role for Notch signaling in its pathogenesis. The mice exhibited progressive loss of podocytes and severe proteinuria concomitant with histological features of cFSGS. Hyperplastic epithelium was negative for genetic podocyte tags, but positive for the parietal epithelial cell marker claudin-1, and expressed Notch1, Jagged1, and Hes1 mRNA and protein. Enhanced Notch mRNA expression induced by transforming growth factor-β1 in cultured parietal epithelial cells was associated with mesenchymal markers (α-smooth muscle actin, vimentin, and Snail1). Notch inhibition in vitro suppressed these phenotypic transcripts and Notch-dependent cell migration. Moreover, Notch inhibition in vivo significantly decreased parietal epithelial cell lesions but worsened proteinuria and histopathology in our cFSGS model. Thus, aberrant Notch1-mediated parietal epithelial cell migration with phenotypic changes appears to underlie the pathogenesis of cFSGS. Parietal epithelial cell hyperplasia may also represent an adaptive response to compensate for a disrupted filtration barrier with progressive podocyte loss.Kidney International advance online publication, 27 February 2013; doi:10.1038/ki.2013.48.
Kidney International 02/2013; · 8.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Angiotensin II content in the kidney is much higher than in the plasma, and it increases more in kidney diseases through an uncertain mechanism. Because the kidney abundantly expresses angiotensinogen mRNA, transcriptional dysregulation of angiotensinogen within the kidney is one potential cause of increased renal angiotensin II in the setting of disease. Here, we observed that kidney-specific angiotensinogen knockout mice had levels of renal angiotensinogen protein and angiotensin II that were similar to those levels of control mice. In contrast, liver-specific knockout of angiotensinogen nearly abolished plasma and renal angiotensinogen protein and renal tissue angiotensin II. Immunohistochemical analysis in mosaic proximal tubules of megalin knockout mice revealed that angiotensinogen protein was incorporated selectively in megalin-intact cells of the proximal tubule, indicating that the proximal tubule reabsorbs filtered angiotensinogen through megalin. Disruption of the filtration barrier in a transgenic mouse model of podocyte-selective injury increased renal angiotensin II content and markedly increased both tubular and urinary angiotensinogen protein without an increase in renal renin activity, supporting the dependency of renal angiotensin II generation on filtered angiotensinogen. Taken together, these data suggest that liver-derived angiotensinogen is the primary source of renal angiotensinogen protein and angiotensin II. Furthermore, an abnormal increase in the permeability of the glomerular capillary wall to angiotensinogen, which characterizes proteinuric kidney diseases, enhances the synthesis of renal angiotensin II.
Journal of the American Society of Nephrology 04/2012; 23(7):1181-9. · 8.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Angiotensin I-converting enzyme inhibitors and angiotensin receptor blockers protect podocytes more effectively than other anti-hypertensive drugs. Transgenic rats overexpressing angiotensin II Type 1 (AT1) receptor selectively in podocytes have been shown to develop glomerulosclerosis. The prevailing hypothesis is that angiotensin II has a capacity of directly acting on the AT1 receptor of podocytes to induce injury. We therefore investigated the mechanism of reno-protective effect of AT1 receptor in a mouse model of HIV-1 nephropathy.
We generated transgenic mice carrying the HIV-1 gene (control/HIV-1) or both HIV-1 gene and podocyte-selectively nullified AT1 gene (AT1KO/HIV-1). In these mice, we measured urinary protein or albumin excretion and performed histological analysis.
At 8 months of age, AT1KO/HIV-1 (n = 13) and control/HIV-1 (n = 15) mice were statistically indistinguishable with respect to urinary albumin/creatinine ratio (median 2.5 versus 9.1 mg/mg), glomerulosclerosis (median 0.63 versus 0.45 on 0-4 scale) and downregulation of nephrin (median 6.90 versus 7.02 on 0-8 scale). In contrast to the observed lack of effect of podocyte-specific AT1KO, systemic AT1 inhibition with AT1 blocker (ARB) significantly attenuated proteinuria and glomerulosclerosis in HIV-1 mice.
These results indicate that the protective effect of ARB is mediated through its receptors on cells other than podocytes, such as efferent arteriolar smooth muscle cells.
[Show abstract][Hide abstract] ABSTRACT: Autophagy is a highly conserved bulk protein degradation pathway involved in cellular homeostasis. Although emerging evidence indicates involvement of autophagy in various conditions, efforts to clarify the role of autophagy in renal tubules are beginning to be elucidated. In the present study, we examined the hypothesis that autophagy guards against acute kidney injury (AKI) by modulating several deteriorative pathways that lead to tubular cell death using a cisplatin-induced model of AKI. Cisplatin treatment of GFP-LC3 (green fluorescent protein-microtubule-associated protein 1 light chain 3) transgenic mice induced autophagy in kidney proximal tubules in a time-dependent manner. Proximal tubule-specific autophagy-deficient mice exhibited more severe cisplatin-induced AKI than did control mice, as assessed via kidney function and morphologic findings. In addition, cisplatin induced more severe DNA damage and p53 activation, concomitant with an increase in apoptotic cell number, and a massive accumulation of protein aggregates in autophagy-deficient proximal tubules. Cisplatin treatment significantly increased reactive oxygen species-producing damaged mitochondria in immortalized autophagy-deficient proximal tubular cells when compared with autophagy-retrieved control cells. In conclusion, autophagy guards kidney proximal tubules against AKI, possibly by alleviating DNA damage and reactive oxygen species production and by eliminating toxic protein aggregates. Enhancing autophagy may provide a novel therapeutic option to minimize AKI.
American Journal Of Pathology 02/2012; 180(2):517-25. · 4.60 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Loss of podocytes promotes glomerulosclerosis, but whether this results from a continued primary insult or a secondary mechanism triggered by the initial loss of podocytes is unknown. We generated chimeric mice in which only a subpopulation of podocytes expressed hCD25, which is the receptor for the immunotoxin LMB2. In addition, genetic labeling of hCD25-negative cells with human placental alkaline phosphatase allowed the study of these two distinct podocyte populations. Administration of LMB2 did not cause podocyte injury in hCD25-negative control mice. In contrast, LMB2 severely damaged or sloughed off the subpopulation of hCD25-positive podocytes within the chimeric glomeruli. Moreover, hCD25-negative podocytes, which were immune to the initial toxin injury, developed injury as early as 4 d after LMB2 injection, evidenced by foot process effacement, upregulation of desmin, and downregulation of nephrin, podocin, and podocalyxin. Furthermore, the magnitude of secondary injury correlated with the magnitude of primary injury, supporting the concept of an amplified cascade of podocyte injury. In conclusion, podocyte damage can propagate injury by triggering secondary damage of "remnant" intact podocytes, even when the primary insult is short-lived. This transmission of podocyte injury may form a vicious cycle leading to accelerated podocyte deterioration and glomerulosclerosis.
Journal of the American Society of Nephrology 06/2011; 22(7):1275-85. · 8.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Autophagy is a bulk protein degradation system that likely plays an important role in normal proximal tubule function and recovery from acute ischemic kidney injury. Using conditional Atg5 gene deletion to eliminate autophagy in the proximal tubule, we determined whether autophagy prevents accumulation of damaged proteins and organelles with aging and ischemic renal injury. Autophagy-deficient cells accumulated deformed mitochondria and cytoplasmic inclusions, leading to cellular hypertrophy and eventual degeneration not observed in wildtype controls. In autophagy-deficient mice, I/R injury increased proximal tubule cell apoptosis with accumulation of p62 and ubiquitin positive cytoplasmic inclusions. Compared with control animals, autophagy-deficient mice exhibited significantly greater elevations in serum urea nitrogen and creatinine. These data suggest that autophagy maintains proximal tubule cell homeostasis and protects against ischemic injury. Enhancing autophagy may provide a novel therapeutic approach to minimize acute kidney injury and slow CKD progression.
Journal of the American Society of Nephrology 05/2011; 22(5):902-13. · 8.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Our previous studies using puromycin aminonucleoside (PAN) established that podocyte damage leads to glomerular growth arrest during development and glomerulosclerosis later in life. This study examined the potential benefit of maintaining podocyte-derived VEGF in podocyte defense and survival after PAN injury using conditional transgenic podocytes and mice, in which human VEGF-A (hVEGF) transgene expression is controlled by tetracycline responsive element (TRE) promoter and reverse tetracycline transactivator (rtTA) in podocytes. In vitro experiments used primary cultured podocytes harvested from mice carrying podocin-rtTA and TRE-hVEGF transgenes, in which hVEGF can be induced selectively. Induction of VEGF in PAN-exposed podocytes resulted in preservation of intrinsic VEGF, α-actinin-4 and synaptopodin, antiapoptotic marker Bcl-xL/Bax, as well as attenuation in apoptotic marker cleaved/total caspase-3. In vivo, compared with genotype controls, PAN-sensitive neonatal mice with physiologically relevant levels of podocyte-derived VEGF showed significantly larger glomeruli. Furthermore, PAN-induced up-regulation of desmin, down-regulation of synaptopodin and nephrin, and disruption of glomerular morphology were significantly attenuated in VEGF-induced transgenic mice. Our data indicate that podocyte-derived VEGF provides self-preservation functions, which can rescue the cell after injury and preempt subsequent deterioration of the glomerulus in developing mice.
Pediatric Research 03/2011; 70(1):83-9. · 2.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Urine outflow obstruction activates a variety of profibrotic factors, including the intrarenal renin-angiotensin system. However, the obstruction also nullifies the transmural hydraulic pressure difference across the glomerular capillary wall, an established inducer of glomerulosclerosis. In the present study, we investigated whether, and by what mechanism, urine outflow obstruction affects the process of progressive glomerulosclerosis. For this purpose, we tested the effect of unilateral ureteral obstruction (UUO) of 7 days duration in two distinct mouse models of glomerulosclerosis. In the human immunodeficiency virus (HIV) nephropathy model, where HIV-1 genes are selectively expressed in podocytes and develop progressive podocyte damage and glomerulosclerosis, UUO protected against sclerosis with preservation of podocytes morphologically and immunohistochemically. In contrast, the nonobstructed contralateral kidneys of these mice, as well as sham-operated HIV-1 mouse kidneys, developed severe podocyte injury and glomerulosclerosis. The protection against glomerulosclerosis imparted by ureteral obstruction was also documented in the NEP25 model of podocyte injury, in which a single injection of immunotoxin, LMB2, triggers selective podocyte injury followed by glomerulosclerosis, both of which were protected by UUO. Notably, intervention with an angiotensin II type 1 receptor antagonist provided only a partial protective effect in each of the models. These results demonstrate that urine outflow obstruction protects the glomerulus from progressive sclerosis. The results further reveal that this protection occurs at a very early stage of the pathologic process, namely, damage of podocytes.
[Show abstract][Hide abstract] ABSTRACT: In the present study, we tested the hypothesis that the renoprotective effect of an angiotensin receptor blocker depends on the angiotensin II type 1 (AT(1)) receptor on podocytes. For this purpose, we generated podocyte-specific knockout mice for the AT(1) gene (Agtr1a) and crossed with NEP25, in which selective podocyte injury can be induced by immunotoxin, anti-Tac(Fv)-PE38. Four weeks after the addition of anti-Tac(Fv)-PE38, urinary albumin:creatinine ratio was not attenuated in Agtr1a knockout/NEP25 mice (n=18) compared with that in control NEP25 mice (n=13; 8.08+/-2.41 in knockout versus 4.84+/-0.73 in control). Both strains of mice showed similar degrees of sclerosis (0.66+/-0.17 versus 0.82+/-0.27 on a 0 to 4 scale) and downregulation of nephrin (5.78+/-0.45 versus 5.65+/-0.58 on a 0 to 8 scale). In contrast, AT(1) antagonist or an angiotensin I-converting enzyme inhibitor, but not hydralazine, remarkably attenuated proteinuria and sclerosis in NEP25 mice. Moreover, continuous angiotensin II infusion induced microalbuminuria similarly in both Agtr1a knockout and wild-type mice. Thus, angiotensin inhibition can protect podocytes and prevent the development of glomerulosclerosis independent of podocyte AT(1). Possible mechanisms include inhibitory effects on AT(1) of other cells or through mechanisms independent of AT(1). Our study further demonstrates that measures that directly affect only nonpodocyte cells can have beneficial effects even when sclerosis is triggered by podocyte-specific injury.