In vivo mapping of hemodynamic responses mediated by tubuloglomerular feedback in hypertensive kidneys.

The kidney has a sophisticated vascular structure that performs the unique function of filtering blood and managing blood pressure. Tubuloglomerular feedback is an intra-nephron negative feedback mechanism stabilizing single-nephron blood flow, glomerular filtration rate, and tubular flow rate, which is exhibited as self-sustained oscillations in single-nephron blood flow. We report the application of multi-scale laser speckle imaging to monitor global blood flow changes across the kidney surface (low zoom) and local changes in individual microvessels (high zoom) in normotensive and spontaneously hypertensive rats in vivo. We reveal significant differences in the parameters of TGF-mediated hemodynamics and patterns of synchronization. Furthermore, systemic infusion of a glucagon-like-peptide-1 receptor agonist, a potential renoprotective agent, induces vasodilation in both groups but only alters the magnitude of the TGF in Sprague Dawleys, although the underlying mechanisms remain unclear.

Deficiency of IKKα in Macrophages Mitigates Fibrosis Progression in the Kidney after Renal Ischemia-Reperfusion Injury.

Aims. Acute kidney injury (AKI) can lead to chronic kidney disease (CKD), and macrophages play a key role in this process. The aim of this study was to discover the role of IκB kinase α (IKKα) in macrophages in the process of AKI-to-CKD transition. Main Methods. We crossed lyz2-Cre mice with IKKα-floxed mice to generate mice with IKKα ablation in macrophages (Mac IKKα-/-). A mouse renal ischemia/reperfusion injury (IRI) model was induced by clamping the renal artery for 45 minutes. Treated mice were evaluated for blood biochemistry, tissue histopathology, and fibrosis markers. Macrophages were isolated from the peritoneal cavity for coculturing with tubular epithelial cells (TECs) and flow cytometry analysis. Key Findings. We found that fibrosis and kidney function loss after IRI were significantly alleviated in Mac IKKα-/- mice compared with wild-type (WT) mice. The expression of fibrosis markers and the infiltration of M2 macrophages were decreased in the kidneys of Mac IKKα-/- mice after IRI. The in vitro experiment showed that the IRI TECs cocultured with IKKα-/- macrophages (KO MΦs) downregulated the fibrosis markers accompanied by a downregulation of Wnt/ß-catenin signaling. Significance. These data support the hypothesis that IKKα is involved in mediating macrophage polarization and increasing the expression of fibrosis-promoting inflammatory factors in macrophages. Therefore, knockdown of IKKα in macrophages may be a potential method that can be used to alleviate the AKI-to-CKD transition after IRI.

Renal ischemia/reperfusion injury in rats is probably due to the activation of the 5-HT degradation system in proximal renal tubular epithelial cells.

AIMS: To explore the relationship between renal ischemia/reperfusion injury (RIRI) and the activation of the renal 5-HT degradation system, including 5-HT2A receptor (5-HT2AR), 5-HT synthases and monoamine oxidase-A (MAO-A). MAIN METHODS: Rat RIRI was induced by removing the right kidney, causing ischemia of the left kidney for 45 min and reperfusion for different times. RIRI model (ischemia for 45 min and reperfusion for 24 h) was pretreated with 5-HT2AR antagonist sarpogrelate hydrochloride (SH) and the 5-HT synthase inhibitor carbidopa. In HK-2 cells, cellular damage was induced by hypoxia (24 h)/reoxygenation (12 h) (H/R) and treated with SH, carbidopa or the MAO-A inhibitor clorgyline. Hematoxylin-eosin, immunohistochemistry, TUNEL and fluorescent probe staining, RT-qPCR, western blotting, ELISA, etc. were used in the tests. KEY FINDINGS: The development of RIRI and the emergence of the RIRI peak were consistent with renal 5-HT degradation system activation. The highest expression regions of the 5-HT degradation system overlapped with those of the most severe lesions in the kidney, which were in proximal renal tubules. Rat RIRI and HK-2 cell damage, including oxidative stress, inflammation and apoptosis, could be almost abolished by synergistic inhibition of SH and carbidopa. Clorgyline also abolished the cellular damage induced by H/R. H/R-induced production of mitochondrial ROS in HK-2 cells was due to MAO-A-catalyzed 5-HT degradation, and 5-HT2AR was involved by mediating the expression of 5-HT synthases and MAO-A. SIGNIFICANCE: These findings revealed a close association between RIRI and activation of the renal 5-HT degradation system.

Protease-Activated Receptor 1 Contributes to Microcirculation Failure and Tubular Damage in Renal Ischemia-Reperfusion Injury in Mice.

Ischemia-reperfusion- (IR-) induced kidney injury is difficult to avoid during renal transplantation and robot-assisted partial nephrectomy. Renal IR injury is characterized by tubular damage, microcirculation failure, and inflammation, which coordinately augment renal injury; however, no specific treatment is available for these conditions. Protease-activated receptor-1 (PAR-1) and its ligand, thrombin, are involved in coagulation and were shown to be associated with epithelial cell injury. Here, we hypothesized that PAR-1 exaggerated renal IR-induced tubular cell damage and microcirculation failure and that pharmacological inhibition of PAR-1 by Q94 could prevent these injuries. Renal warm IR increased the expression of PAR-1 in the renal tubules. Q94 attenuated renal IR-induced changes and histopathological damage. Microcirculation failure analyzed by congestion in the histopathology and blood cell flow examined by intravital multiphoton microscopy were suppressed by Q94 treatment. Q94 also dramatically increased tubular cell proliferation despite the lower renal damage. Thrombin suppressed cell proliferation and induced apoptosis in the tubules; these effects were prevented by Q94 treatment. Taken together, PAR-1 was associated with renal IR injury. Inhibition of PAR-1 ameliorated injury possibly by improving renal microcirculation and tubular cell survival/proliferation.

A distinctive distribution of hypoxia-inducible factor-1α in cultured renal tubular cells with hypoperfusion simulated by coverslip placement.

Chronic hypoxia in the renal tubulointerstitium plays a key role in the progression of chronic kidney disease (CKD). It is therefore important to investigate tubular hypoxia and the activity of hypoxia-inducible factor (HIF)-1α in response to hypoxia. Rarefaction of the peritubular capillary causes hypoperfusion in CKD; however, the effect of hypoperfusion on HIFs has rarely been investigated. We induced hypoperfusion caused by coverslip placement in human kidney-2 cells, and observed an oxygen gradient under the coverslip. Immunocytochemistry of HIF-1α showed a doughnut-shaped formation on the edge of a pimonidazole-positive area, which we named the "HIF-ring". The oxygen tension of the HIF-ring was estimated to be between approximately 4 mmHg and 20 mmHg. This result was not compatible with those of past research showing HIF-1α accumulation in the anoxic range with homogeneous oxygen tension. We further observed the presence of a pH gradient under a coverslip, as well as a shift of the HIF ring due to changes in the pH of the culture medium, suggesting that the HIF ring was formed by suppression of HIF-1α related to low pH. This research demonstrated that HIF-1α activation mimics the physiological state in cultured cells with hypoperfusion.

Peritubular Capillary Rarefaction: An Underappreciated Regulator of CKD Progression.

Peritubular capillary (PTC) rarefaction is commonly detected in chronic kidney disease (CKD) such as hypertensive nephrosclerosis and diabetic nephropathy. Moreover, PTC rarefaction prominently correlates with impaired kidney function and predicts the future development of end-stage renal disease in patients with CKD. However, it is still underappreciated that PTC rarefaction is a pivotal regulator of CKD progression, primarily because the molecular mechanisms of PTC rarefaction have not been well-elucidated. In addition to the established mechanisms (reduced proangiogenic factors and increased anti-angiogenic factors), recent studies discovered significant contribution of the following elements to PTC loss: (1) prompt susceptibility of PTC to injury, (2) impaired proliferation of PTC, (3) apoptosis/senescence of PTC, and (4) pericyte detachment from PTC. Mainly based on the recent and novel findings in basic research and clinical study, this review describes the roles of the above-mentioned elements in PTC loss and focuses on the major factors regulating PTC angiogenesis, the assessment of PTC rarefaction and its surrogate markers, and an overview of the possible therapeutic agents to mitigate PTC rarefaction during CKD progression. PTC rarefaction is not only a prominent histological characteristic of CKD but also a central driving force of CKD progression.

Calcium dobesilate mediates renal interstitial fibrosis and delay renal peritubular capillary loss through Sirt1/p53 signaling pathway.

Calcium dobesilate (Cad), a protective agent, protects against microvascular damage, and diseases such as diabetic retinopathy and diabetic nephropathy. However, these vascular protective effects have not been demonstrated in chronic kidney disease (CKD). In this study, we aimed to determine the ability of Cad to protect against renal interstitial fibrosis induced by unilateral ureteral obstruction (UUO) and identify the underlying therapeutic mechanisms of Cad during hypoxia/serum deprivation (H/SD) in human umbilical vein endothelial cells (HUVECs). A total of 36 male mice were randomly assigned into 3 groups (12 mice in each group): the Sham-operated group (Sham), the saline solution-treated UUO mice group (UUO), and the Cad administration (intragastrically) group (Cad). The mice in Cad group were administered Cad (100 mg/kg) daily by oral gavage and slaughtered on the 7th and 14th days post-surgery. Six mice from each group were sacrificed by sodium pentobarbital injection on the 7th and 14th day after surgery. Tissue hypoxia, cell apoptosis and fibrotic lesions were detected by Immunostaining and Western blot. Peritubular capillaries (PTCs) injury was measured by a novel technique of fluorescent microangiography (FMA). Endothelial cell-to-mesenchymal transition (EndMT) were identified by immunofluorescence and Western blot. HUVECs proliferation was measured via Cell Counting Kit­8 assays and Edu staining. Sirt1 and its downstream gene in Cad regulation of endothelial were detected. Hematoxylin-eosin (HE), Masson-trichrome stains and Histological findings showed that Cad administration markedly reduced hypoxia and renal interstitial fibrosis at each time point in UUO. Meanwhile, Cad protect against EndMT process of PTCs by increasing CD31 expression and decreasing α-smooth muscle actin and fibronectin expression. in vitro studies showed that there was a proliferative response of the HUVECs incubated with Cad (10 µM) in H/SD. Sirt1 was suppressed after small interfering RNA (siRNA) was transfected in HUVECs. Mechanistically, Cad enhanced Sirt1 signaling, which was accompanied by increased levels of p53 acetylation (ac-p53). Meanwhile, protein expression of Bcl-2, and VE-cadherin were downregulated, Bax, and α-SMA were upregulated. In summary, the therapeutic effect of Cad in obstructive nephropathy were likely through suppressing EndMT progression and promoting anti-apoptotic effects after via activating the Sirt1/p53 signaling pathway.

Simultaneous Three-Dimensional Vascular and Tubular Imaging of Whole Mouse Kidneys With X-ray µCT.

Concurrent three-dimensional imaging of the renal vascular and tubular systems on the whole-kidney scale with capillary level resolution is labor-intensive and technically difficult. Approaches based on vascular corrosion casting and X-ray micro computed tomography (µCT), for example, suffer from vascular filling artifacts and necessitate imaging with an additional modality to acquire tubules. In this work, we report on a new sample preparation, image acquisition, and quantification protocol for simultaneous vascular and tubular µCT imaging of whole, uncorroded mouse kidneys. The protocol consists of vascular perfusion with the water-soluble, aldehyde-fixable, polymeric X-ray contrast agent XlinCA, followed by laboratory-source µCT imaging and structural analysis using the freely available Fiji/ImageJ software. We achieved consistent filling of the entire capillary bed and staining of the tubules in the cortex and outer medulla. After imaging at isotropic voxel sizes of 3.3 and 4.4 µm, we segmented vascular and tubular systems and quantified luminal volumes, surface areas, diffusion distances, and vessel path lengths. This protocol permits the analysis of vascular and tubular parameters with higher reliability than vascular corrosion casting, less labor than serial sectioning and leaves tissue intact for subsequent histological examination with light and electron microscopy.

Interleukin-24 is a novel diagnostic biomarker for the severity of acute kidney injury.

There is a clinical need for sensitive acute kidney injury (AKI) biomarkers that enable early therapeutic interventions and prediction of disease prognosis. In this study, we monitored interleukin (IL)-24 expressed in kidneys with severe AKI that progresses to atrophic kidney in a mouse model of ischemia-reperfusion injury (IRI). Therefore, we evaluated IL-24 as a potential biomarker not only for early diagnosis of AKI, but also for predicting progression to chronic kidney disease (CKD). Serum IL-24 was detected earlier than the elevation of serum creatinine levels and urinary IL-24 was detected as early as neutrophil gelatinase associated lipocalin (NGAL) in severe AKI (60 min of IRI). In addition, serum and urine IL-24 levels tended to increase in relation to ischemia duration. In such kidneys, vascular smooth muscle cells expressed IL-24 in response to the injury in the renal tubular epithelial cell and its target was the renal tubular epithelial cell itself. IL-24 may play a pivotal role in the communication between tubular epithelial cells and vascular smooth muscle cells and, in conclusion, IL-24 can be used as a sensitive biomarker for AKI.

Role of Renal Hypoxia in the Progression From Acute Kidney Injury to Chronic Kidney Disease.

Over the past 20 years, there has been an increased appreciation of the long-term sequelae of acute kidney injury (AKI) and the potential development of chronic kidney disease (CKD). Several pathophysiologic features have been proposed to mediate AKI to CKD progression including maladaptive alterations in tubular, interstitial, inflammatory, and vascular cells. These alterations likely interact to culminate in the progression to CKD. In this article we focus primarily on evidence of vascular rarefaction secondary to AKI, and the potential mechanisms by which rarefaction occurs in relation to other alterations in tubular and interstitial compartments. We further focus on the potential that rarefaction contributes to renal hypoxia. Consideration of the role of hypoxia in AKI to CKD transition focuses on experimental evidence of persistent renal hypoxia after AKI and experimental maneuvers to evaluate the influence of hypoxia, per se, in progressive disease. Finally, consideration of methods to evaluate hypoxia in patients is provided with the suggestion that noninvasive measurement of renal hypoxia may provide insight into progression in post-AKI patients.

Renal tubular injury exacerbated by vasohibin-1 deficiency in a murine cisplatin-induced acute kidney injury model.

Acute kidney injury (AKI) is frequently encountered in clinical practice, particularly secondarily to cardiovascular surgery and administration of nephrotoxic agents, and is increasingly recognized for initiating a transition to chronic kidney disease. Clarifying the pathogenesis of AKI could facilitate the development of novel preventive strategies, because the occurrence of hospital-acquired AKI is often anticipated. Vasohibin-1 (VASH1) was initially identified as an antiangiogenic factor derived from endothelial cells. VASH1 expression in endothelial cells has subsequently been reported to enhance cellular stress tolerance. Considering the importance of maintaining peritubular capillaries in preventing the progression of AKI, the present study aimed to examine whether VASH1 deletion is involved in the pathogenesis of cisplatin-induced AKI. For this, we injected male C57BL/6J wild-type (WT) and VASH1 heterozygous knockout (VASH1+/-) mice intraperitoneally with either 20 mg/kg cisplatin or vehicle solution. Seventy-two hours after cisplatin injection, increased serum creatinine concentrations and renal tubular injury accompanied by apoptosis and oxidative stress were more prominent in VASH1+/- mice than in WT mice. Cisplatin-induced peritubular capillary loss was also accelerated by VASH1 deficiency. Moreover, the increased expression of ICAM-1 in the peritubular capillaries of cisplatin-treated VASH1+/- mice was associated with a more marked infiltration of macrophages into the kidney. Taken together, VASH1 expression could have protective effects on cisplatin-induced AKI probably by maintaining the number and function of peritubular capillaries.

The protective effect of glutaredoxin 1/DJ-1/HSP70 signaling in renal tubular epithelial cells injury induced by ischemia.

AIMS: Gluaredoxin1 (GRX1) is an important protein of the cellular antioxidant defense system, but its role in renal epithelial cell injury caused by ischemia remains unclear. In this study, we aimed to gain insight into the role of GRX1 in HK-2 cells with oxygen glucose deprivation (OGD) injury, which served as an in vitro cell model of renal epithelial cell ischemic injury. We investigated the underlying regulation of GRX1, DJ-1, and HSP70 as well as the role of the GRX1/DJ-1/HSP70 signaling pathway in this model. MATERIALS AND METHODS: The protein and mRNA expressions were measured by Western blot and qRT-PCR assays, respectively. GRX1 was overexpressed by transfection of pcDNA.3.1-GRX1 and DJ-1 was inhibited by transfection with DJ-1 siRNA. Cell apoptosis, caspase-3 activity, lactate dehydrogenase (LDH) leakage, or superoxide dismutase (SOD) content was tested by the related detection kit. Reactive oxygen species (ROS) level was detected via carboxy-H2DCF-DA. KEY FINDINGS: We found that GRX1 was distinctly down-regulated in HK-2 cells after incubation under the OGD condition. GRX1 overexpression markedly constrained cell apoptosis, caspase-3 activity, LDH leakage, and the ROS level, while SOD content was elevated. GRX1 up-regulation increased DJ-1 and HSP70 protein expression, while DJ-1 inhibition significantly offset the effect of GRX1 overexpression on HSP70, indicating that GRX1 could regulate HSP70 via control of DJ-1. Moreover, we observed that HSP70 inhibition removed the constraints imposed by GRX1 overexpression on ROS level, LDH leakage, and caspase-3 activity. SIGNIFICANCE: Overall, this study showed that GRX1 minimizes cell injury and apoptosis in HK-2 cells under OGD conditions via regulation of DJ-1 and HSP70 expression.

Matrix metalloproteinase-7 protects against acute kidney injury by priming renal tubules for survival and regeneration.

Matrix metalloproteinase-7 (MMP-7) is a secreted endopeptidase that degrades a broad range of substrates. Recent studies have identified MMP-7 as an early biomarker to predict severe acute kidney injury (AKI) and poor outcomes after cardiac surgery; however, the role of MMP-7 in the pathogenesis of AKI is unknown. In this study, we investigated the expression of MMP-7 and the impact of MMP-7 deficiency in several models of AKI. MMP-7 was induced in renal tubules following ischemia/ reperfusion injury or cisplatin administration, and in folic acid-induced AKI. MMP-7 knockout mice experienced higher mortality, elevated serum creatinine, and more severe histologic lesions after ischemic or toxic insults. Tubular apoptosis and interstitial inflammation were more prominent in MMP-7 knockout kidneys. These histologic changes were accompanied by increased expression of FasL and other components of the extrinsic apoptotic pathway, as well as increased expression of pro-inflammatory chemokines. In a rescue experiment, exogenous MMP-7 ameliorated kidney injury in MMP-7 knockout mice after ischemia/reperfusion. In vitro, MMP-7 protected tubular epithelial cells against apoptosis by directly degrading FasL. In isolated tubules ex vivo, MMP-7 promoted cell proliferation by degrading E-cadherin and thereby liberating ß-catenin, priming renal tubules for regeneration. Taken together, these results suggest that induction of MMP-7 is protective in AKI by degrading FasL and mobilizing ß-catenin, thereby priming kidney tubules for survival and regeneration.

ß-hydroxybutyrate attenuates renal ischemia-reperfusion injury through its anti-pyroptotic effects.

Ketone bodies including ß-hydroxybutyrate (ß-OHB) have been shown to protect against ischemic tissue injury when present at low concentrations. We evaluated the impact of ß-OHB on renal ischemia/reperfusion injury (IRI). Mice were treated with a continuous infusion of ß-OHB using an osmotic mini-pump before and after IRI. We also tested the effects of increasing endogenous serum ß-OHB levels by fasting. Renal IRI was attenuated by ß-OHB treatment compared to saline control, with similar results in the fasting condition. ß-OHB treatment reduced the number of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-positive cells and increased expression of forkhead transcription factor O3 (FOXO3), an upstream regulator of pyroptosis. Although ß-OHB treatment did not impact markers of apoptosis, it decreased the expression of caspase-1 and proinflammatory cytokines, indicating that ß-OHB blocked pyroptosis. In a human proximal tubular cell line exposed to hypoxia and reoxygenation, ß-OHB reduced cell death in a FOXO3-dependent fashion. Histone acetylation was decreased in kidneys exposed to IRI and in proximal tubular cells exposed to hypoxia and reoxygenation, and this effect was ameliorated by ß-OHB through the inactivation of histone deacetylases. In vitro, ß-OHB treatment restored histone acetylation at the FOXO3 promoter. Consistent with epigenetic molecular effects, the renoprotective effects of ß-OHB were still observed when the continuous infusion was stopped at the time of IRI. Thus, ß-OHB attenuates renal IRI through anti-pyroptotic effects, likely mediated by an epigenetic effect on FOXO3 expression.

Biglycan evokes autophagy in macrophages via a novel CD44/Toll-like receptor 4 signaling axis in ischemia/reperfusion injury.

Biglycan, a small leucine-rich proteoglycan, acts as a danger signal and is classically thought to promote macrophage recruitment via Toll-like receptors (TLR) 2 and 4. We have recently shown that biglycan signaling through TLR 2/4 and the CD14 co-receptor regulates inflammation, suggesting that TLR co-receptors may determine whether biglycan-TLR signaling is pro- or anti-inflammatory. Here, we sought to identify other co-receptors and characterize their impact on biglycan-TLR signaling. We found a marked increase in the number of autophagic macrophages in mice stably overexpressing soluble biglycan. In vitro, stimulation of murine macrophages with biglycan triggered autophagosome formation and enhanced the flux of autophagy markers. Soluble biglycan also promoted autophagy in human peripheral blood macrophages. Using macrophages from mice lacking TLR2 and/or TLR4, CD14, or CD44, we demonstrated that the pro-autophagy signal required TLR4 interaction with CD44, a receptor involved in adhesion, migration, lymphocyte activation, and angiogenesis. In vivo, transient overexpression of circulating biglycan at the onset of renal ischemia/reperfusion injury (IRI) enhanced M1 macrophage recruitment into the kidneys of Cd44+/+ and Cd44-/- mice but not Cd14-/- mice. The biglycan-CD44 interaction increased M1 autophagy and the number of renal M2 macrophages and reduced tubular damage following IRI. Thus, CD44 is a novel signaling co-receptor for biglycan, an interaction that is required for TLR4-CD44-dependent pro-autophagic activity in macrophages. Interfering with the interaction between biglycan and specific TLR co-receptors could represent a promising therapeutic intervention to curtail kidney inflammation and damage.

Caspase-3 Is a Pivotal Regulator of Microvascular Rarefaction and Renal Fibrosis after Ischemia-Reperfusion Injury.

Background Ischemia-reperfusion injury (IRI) is a major risk factor for chronic renal failure. Here, we characterize the different modes of programmed cell death in the tubular and microvascular compartments during the various stages of IRI-induced AKI, and their relative importance to renal fibrogenesis.Methods We performed unilateral renal artery clamping for 30 minutes and contralateral nephrectomy in wild-type mice (C57BL/6) or caspase-3-/- mice.Results Compared with their wild-type counterparts, caspase-3-/- mice in the early stage of AKI had high urine cystatin C levels, tubular injury scores, and serum creatinine levels. Electron microscopy revealed evidence of tubular epithelial cell necrosis in caspase-3-/- mice, and immunohistochemistry showed upregulation of the necroptosis marker receptor-interacting serine/threonine-protein kinase 3 (RIPK3) in renal cortical sections. Western blot analysis further demonstrated enhanced levels of phosphorylated RIPK3 in the kidneys of caspase-3-/- mice. In contrast, caspase-3-/- mice had less microvascular congestion and activation in the early and extension phases of AKI. In the long term (3 weeks after IRI), caspase-3-/- mice had reduced microvascular rarefaction and renal fibrosis, as well as decreased expression of α-smooth muscle actin and reduced collagen deposition within peritubular capillaries. Moreover, caspase-3-/- mice exhibited signs of reduced tubular ischemia, including lower tubular expression of hypoxia-inducible factor-1α and improved tubular injury scores.Conclusions These results establish the pivotal importance of caspase-3 in regulating microvascular endothelial cell apoptosis and renal fibrosis after IRI. These findings also demonstrate the predominant role of microvascular over tubular injury as a driver of progressive renal damage and fibrosis after IRI.

Hyperuricemia and Progression of Chronic Kidney Disease: Role of Phenotype Transition of Renal Tubular and Endothelial Cells.

BACKGROUND: Although the clinical implication of hyperuricemia in chronic kidney disease has been an issue of active debate, recent data suggested a causative role of uric acid (UA) in the development of renal disease. Afferent arteriopathy, an induction of oxidative stress and an activation of local inflammation, have been regarded as the mechanisms of UA-induced renal disease, which contribute to glomerular hypertrophy and interstitial fibrosis via endothelial dysfunction. However, there have been rare studies on the direct effect of UA on phenotype transition of renal cells such as epithelial-to-mesenchymal transition (EMT) or endothelial-to-mesenchymal transition (EndoMT). SUMMARY: We have reported that UA-induced EMT of cultured renal tubular cells, which was blocked by the organic anion transport inhibitor, probenecid. UA increased the expression of snail and slug, the transcriptional repressors of E-cadherin, which resulted in a downregulation of E-cadherin production. UA also increased the degradation of E-cadherin via ubiquitination. UA also induced EndoMT with an increase in ROS generation and glycocalyx shedding of cultured vascular endothelial cells. Treatment with antioxidants ameliorated UA-induced EndoMT. In the kidney of hyperuricemic rats, there was an evidence of EMT before the development of significant tubulointerstitial fibrosis, as shown by decreased E-cadherin expression and an increased α-smooth muscle actin (α-SMA) in renal tubular cells. Allopurinol significantly inhibited UA-induced EMT with an amelioration of renal fibrosis. In addition, endothelial staining in peritubular capillaries (PTC) was substantially decreased with de-novo expression of α-SMA in endothelial cells of PTC. Key Messages: UA per se induced a phenotypic transition of epithelial and endothelial cells via an induction of oxidative stress and glycocalyx shedding, which could be one of the mechanisms of UA-induced kidney disease.

Connecting tubule glomerular feedback mediates tubuloglomerular feedback resetting after unilateral nephrectomy.

Unilaterally nephrectomized rats (UNx) have higher glomerular capillary pressure (PGC) that can cause significant glomerular injury in the remnant kidney. PGC is controlled by the ratio of afferent (Af-Art) and efferent arteriole resistance. Af-Art resistance in turn is regulated by two intrinsic feedback mechanisms: 1) tubuloglomerular feedback (TGF) that causes Af-Art constriction in response to increased NaCl in the macula densa; and 2) connecting tubule glomerular feedback (CTGF) that causes Af-Art dilatation in response to an increase in NaCl transport in the connecting tubule via the epithelial sodium channel (ENaC). Resetting of TGF post-UNx can allow systemic pressure to be transmitted to the glomerulus and cause renal damage, but the mechanism behind this resetting is unclear. Since CTGF is an Af-Art dilatory mechanism, we hypothesized that CTGF is increased after UNx and contributes to TGF resetting. To test this hypothesis, we performed UNx in Sprague-Dawley (8) rats. Twenty-four hours after surgery, we performed micropuncture of individual nephrons and measured stop-flow pressure (PSF). PSF is an indirect measurement of PGC. Maximal TGF response at 40 nl/min was 8.9 ± 1.24 mmHg in sham-UNx rats and 1.39 ± 1.02 mmHg in UNx rats, indicating TGF resetting after UNx. When CTGF was inhibited with the ENaC blocker benzamil (1 µM/l), the TGF response was 12.29 ± 2.01 mmHg in UNx rats and 13.03 ± 1.25 mmHg in sham-UNx rats, indicating restoration of the TGF responses in UNx. We conclude that enhanced CTGF contributes to TGF resetting after UNx.

Tubulointerstitial fibrosis can sensitize the kidney to subsequent glomerular injury.

Chronic glomerular injury is associated with eventual development of tubulointerstitial fibrosis. Here we aimed to assess whether, and how, mild chronic tubulointerstitial injury affects glomeruli. For this, we generated mice expressing different toxin receptors, one on their proximal tubular epithelial cells (diphtheria toxin receptor [DTR]) and the other only on podocytes (human CD25 [IL-2R] driven by the nephrin promoter [Nep25]), allowing serial induction of tubule-specific and glomerular (podocyte)-specific injury, respectively. Six weeks after diphtheria toxin injection, mild interstitial fibrosis was found in Nep25+/DTR+, but not in Nep25+/DTR- mice. However, atubular glomeruli and neuronal nitric oxide synthase, a mediator of tubuloglomerular feedback, were higher in Nep25+/DTR+ than in DTR- mice and these atubular glomeruli had less podocyte density as assessed by WT-1 biomarker expression. Peritubular capillary density, hypoxia-inducible factor-1 and -2, and cyclooxygenase 2 expression were similar at week six in the two groups. At week seven, all mice were given the immunotoxin LMB-2, which binds to CD25 to induce podocyte injury. Ten days later, proteinuria, podocyte injury, and glomerulosclerosis were more severe in Nep25+/DTR+ than Nep25+/DTR- mice with more severe sclerosis in the tubule-connected glomeruli. This supports the concept that even mild preexisting tubulointerstitial injury sensitizes glomeruli to subsequent podocyte-specific injury. Thus, increased atubular glomeruli and abnormal tubuloglomerular feedback significantly contribute to the crosstalk between the tubulointerstitium and glomeruli.