Attenuation of renal injury by depleting cDC1 and by repurposing Flt3 inhibitor in anti-GBM disease.

Previous studies found cDC1s to be protective in early stage anti-GBM disease through Tregs, but pathogenic in late stage Adriamycin nephropathy through CD8+ T cells. Flt3 ligand is a growth factor essential for cDC1 development and Flt3 inhibitors are currently used for cancer treatment. We conducted this study to clarify the role and mechanisms of effects of cDC1s at different time points in anti-GBM disease. In addition, we aimed to utilize drug repurposing of Flt3 inhibitors to target cDC1s as a treatment of anti-GBM disease. We found that in human anti-GBM disease, the number of cDC1s increased significantly, proportionally more than cDC2s. The number of CD8+ T cells also increased significantly and their number correlated with cDC1 number. In XCR1-DTR mice, late (day 12-21) but not early (day 3-12) depletion of cDC1s attenuated kidney injury in mice with anti-GBM disease. cDC1s separated from kidneys of anti-GBM disease mice were found to have a pro-inflammatory phenotype (i.e. express high level of IL-6, IL-12 and IL-23) in late but not early stage. In the late depletion model, the number of CD8+ T cells was also reduced, but not Tregs. CD8+ T cells separated from kidneys of anti-GBM disease mice expressed high levels of cytotoxic molecules (granzyme B and perforin) and inflammatory cytokines (TNF-α and IFN-γ), and their expression reduced significantly after cDC1 depletion with diphtheria toxin. These findings were reproduced using a Flt3 inhibitor in wild type mice. Therefore, cDC1s are pathogenic in anti-GBM disease through activation of CD8+ T cells. Flt3 inhibition successfully attenuated kidney injury through depletion of cDC1s. Repurposing Flt3 inhibitors has potential as a novel therapeutic strategy for anti-GBM disease.

Interleukin-33 Exacerbates IgA Glomerulonephritis in Transgenic Mice Overexpressing B Cell Activating Factor.

BACKGROUND: The cytokine IL-33 is an activator of innate lymphoid cells 2 (ILC2s) in innate immunity and allergic inflammation. B cell activating factor (BAFF) plays a central role in B cell proliferation and differentiation, and high levels of this protein cause excess antibody production, including IgA. BAFF-transgenic mice overexpress BAFF and spontaneously develop glomerulonephritis that resembles human IgA nephropathy. METHODS: We administered IL-33 or PBS to wild-type and BAFF-transgenic mice. After treating Rag1-deficient mice with IL-33, with or without anti-CD90.2 to preferentially deplete ILC2s, we isolated splenocytes, which were adoptively transferred into BAFF-transgenic mice. RESULTS: BAFF-transgenic mice treated with IL-33 developed more severe kidney dysfunction and proteinuria, glomerular sclerosis, tubulointerstitial damage, and glomerular deposition of IgA and C3. Compared with wild-type mice, BAFF-transgenic mice exhibited increases of CD19+ B cells in spleen and kidney and ILC2s in kidney and intestine, which were further increased by administration of IL-33. Administering IL-33 to wild-type mice had no effect on kidney function or histology, nor did it alter the number of ILC2s in spleen, kidney, or intestine. To understand the role of ILC2s, splenocytes were transferred from IL-33-treated Rag1-deficient mice into BAFF-transgenic mice. Glomerulonephritis and IgA deposition were exacerbated by transfer of IL-33-stimulated Rag1-deficient splenocytes, but not by ILC2 (anti-CD90.2)-depleted splenocytes. Wild-type mice infused with IL-33-treated Rag1-deficient splenocytes showed no change in kidney function or ILC2 numbers or distribution. CONCLUSIONS: IL-33-expanded ILC2s exacerbated IgA glomerulonephritis in a mouse model. These findings indicate that IL-33 and ILC2s warrant evaluation as possible mediators of human IgA nephropathy.

Imbalance of circulating innate lymphoid cell subpopulations in patients with chronic kidney disease.

Innate lymphoid cells (ILCs) are a newly identified heterogeneous family of innate immune cells. We conducted this study to investigate the frequency of circulating ILC subsets in various chronic kidney diseases (CKD). In DN, the proportion of total ILCs and certain ILC subgroups increased significantly. Positive correlations between proportion of total ILCs, ILC1s and body mass index, glycated hemoglobin were observed in DN. In LN, a significantly increased proportion of ILC1s was found in parallel with a reduced proportion of ILC2s. The proportions of total ILCs and ILC1s were correlated with WBC count and the level of C3. In all enrolled patients, the proportion of total ILCs and ILC1s was significantly correlated with the levels of ACR and GFR. In the present study, the proportion of circulating ILC subsets increased significantly in various types of CKD and correlated with clinico-pathological features, which suggests a possible role for ILCs in CKD.

Up-Regulation of DNA Damage Response Signaling in Autosomal Dominant Polycystic Kidney Disease.

DNA damage and alterations in DNA damage response (DDR) signaling could be one of the molecular mechanisms mediating focal kidney cyst formation in autosomal dominant polycystic kidney disease (ADPKD). The aim of this study was to test the hypothesis that markers of DNA damage and DDR signaling are increased in human and experimental ADPKD. In the human ADPKD transcriptome, the number of up-regulated DDR-related genes was increased by 16.6-fold compared with that in normal kidney, and by 2.5-fold in cystic compared with that in minimally cystic tissue (P < 0.0001). In end-stage human ADPKD tissue, γ-H2A histone family member X (H2AX), phosphorylated ataxia telangiectasia and radiation-sensitive mutant 3 (Rad3)-related (pATR), and phosphorylated ataxia telangiectasia mutated (pATM) localized to cystic kidney epithelial cells. In vitro, pATR and pATM were also constitutively increased in human ADPKD tubular cells (WT 9-7 and 9-12) compared with control (HK-2). In addition, extrinsic oxidative DNA damage by hydrogen peroxide augmented γ-H2AX and cell survival in human ADPKD cells, and exacerbated cyst growth in the three-dimensional Madin-Darby canine kidney cyst model. In contrast, DDR-related gene expression was only transiently increased on postnatal day 0 in Pkd1RC/RC mice, and not altered at later time points up to 12 months of age. In conclusion, DDR signaling is dysregulated in human ADPKD and during the early phases of murine ADPKD. The constitutive expression of the DDR pathway in ADPKD may promote survival of PKD1-mutated cells and contribute to kidney cyst growth.

Innate lymphoid cells in kidney diseases.

It is well known that innate immune cells, including dendritic cells, macrophages, and natural killer cells, contribute to pathogenesis and protection in various kidney diseases. The understanding of innate immunity has been advanced recently by the discovery of a new group of innate lymphoid cells (ILCs), including ILC1, ILC2, and ILC3. ILCs lack adaptive antigen receptors, yet can be triggered by various pathogens and rapidly provide an abundant source of immunomodulatory cytokines to exert immediate immune reactions and direct subsequent innate and adaptive immune responses. ILCs play critical roles in immunity, tissue homeostasis, and pathological inflammation. In this review, we highlight the biological function of ILC subpopulations in the normal kidney, and their important roles in acute and chronic kidney diseases, thus demonstrating the emerging importance of ILC-regulated immunity in this special organ and providing insights for future research directions and therapeutic interventions.

Targeted deletion of nicotinamide adenine dinucleotide phosphate oxidase 4 from proximal tubules is dispensable for diabetic kidney disease development.

BACKGROUND: The nicotinamide adenine dinucleotide phosphate oxidase isoform 4 (Nox4) mediates reactive oxygen species (ROS) production and renal fibrosis in diabetic kidney disease (DKD) at the level of the podocyte. However, the mitochondrial localization of Nox4 and its role as a mitochondrial bioenergetic sensor has recently been reported. Whether Nox4 drives pathology in DKD within the proximal tubular compartment, which is densely packed with mitochondria, is not yet known. METHODS: We generated a proximal tubular-specific Nox4 knockout mouse model by breeding Nox4flox/flox mice with mice expressing Cre recombinase under the control of the sodium-glucose cotransporter-2 promoter. Subsets of Nox4ptKO mice and their Nox4flox/flox littermates were injected with streptozotocin (STZ) to induce diabetes. Mice were followed for 20 weeks and renal injury was assessed. RESULTS: Genetic ablation of proximal tubular Nox4 (Nox4ptKO) resulted in no change in renal function and histology. Nox4ptKO mice and Nox4flox/flox littermates injected with STZ exhibited the hallmarks of DKD, including hyperfiltration, albuminuria, renal fibrosis and glomerulosclerosis. Surprisingly, diabetes-induced renal injury was not improved in Nox4ptKO STZ mice compared with Nox4flox/flox STZ mice. Although diabetes conferred ROS overproduction and increased the mitochondrial oxygen consumption rate, proximal tubular deletion of Nox4 did not normalize oxidative stress or mitochondrial bioenergetics. CONCLUSIONS: Taken together, these results demonstrate that genetic deletion of Nox4 from the proximal tubules does not influence DKD development, indicating that Nox4 localization within this highly energetic compartment is dispensable for chronic kidney disease pathogenesis in the setting of diabetes.

The IDEAL trial in Australia and New Zealand: clinical and economic impact.

BACKGROUND: The impact of research findings on clinical practice usually remains uncertain and unmeasured. To address this problem, we examined the long-term clinical and economic impact of the Initiating Dialysis Early and Late (IDEAL) trial using data from the Australia and New Zealand Dialysis and Transplant Registry. METHODS: We performed a registry-based study including all incident adult dialysis patients in Australia and New Zealand from July 2000 to June 2018. A piecewise linear regression model was used to examine differences in mean estimated glomerular filtration rate (eGFR) at dialysis commencement for the years prior to (2000-2010) and following (2010-2018) publication of the IDEAL trial results. The return on investment (ROI) was calculated using the total cost of performing the IDEAL trial and the cost or savings accruing in Australia and New Zealand from changes in dialysis initiation practice. RESULTS: From July 2000 to June 2010, mean eGFR at dialysis commencement increased at a rate of 0.21 mL/min/1.73 m2/year [95% confidence interval (CI) 0.19-0.23]. After the IDEAL trial results were published, mean eGFR at dialysis commencement did not show any temporal change [-0.01 mL/min/1.73 m2/year (95% CI -0.03-0.01)]. The ROI of the IDEAL trial was AU$35.70/AU$1 spent, an estimated savings to the Australian and New Zealand health systems of up to AU$84 million/year. CONCLUSIONS: The previous trend to higher eGFR at dialysis commencement changed following publication of the IDEAL trial results to a steady eGFR that has continued for a decade, avoiding unnecessary dialysis treatments and accruing savings to the Australian and New Zealand health systems.

Ethics of kidney care in the era of COVID-19.

The coronavirus disease 2019 pandemic presents significant challenges for health systems globally, including substantive ethical dilemmas that may pose specific concerns in the context of care for people with kidney disease. Ethical concerns may arise as changes in policy and practice affect the ability of all health professionals to fulfill their ethical duties toward their patients in providing best practice care. In this article, we briefly describe such concerns and elaborate on issues of particular ethical complexity in kidney care: equitable access to dialysis during pandemic surges; balancing the risks and benefits of different kidney failure treatments, specifically with regard to suspending kidney transplantation programs and prioritizing home dialysis, and barriers to shared decision-making; and ensuring ethical practice when using unproven interventions. We present preliminary advice on how to approach these issues and recommend urgent efforts to develop resources that will support health professionals and patients in managing them.

Strategic plan for integrated care of patients with kidney failure.

There is a huge gap between the number of patients worldwide requiring versus those actually receiving safe, sustainable, and equitable care for kidney failure. To address this, the International Society of Nephrology coordinated the development of a Strategic Plan for Integrated Care of Patients with Kidney Failure. Implementation of the plan will require engagement of the whole kidney community over the next 5-10 years.

Regulatory innate lymphoid cells suppress innate immunity and reduce renal ischemia/reperfusion injury.

Innate lymphoid cells are a recently recognized group of immune cells with critical roles in tissue homeostasis and inflammation. Regulatory innate lymphoid cells are a newly identified subset of innate lymphoid cells, which play a suppressive role in the innate immune response, favoring the resolution of intestinal inflammation. However, the expression and role of regulatory innate lymphoid cells in kidney has not been reported. Here, we show that regulatory innate lymphoid cells are present in both human and mouse kidney, express similar surface markers and form a similar proportion of total kidney innate lymphoid cells. Regulatory innate lymphoid cells from kidney were expanded in vitro with a combination of IL-2, IL-7 and transforming growth factor-ß. These cells exhibited immunosuppressive effects on innate immune cells via secretion of IL-10 and transforming growth factor-ß. Moreover, treatment with IL-2/IL-2 antibody complexes (IL-2C) promoted expansion of regulatory innate lymphoid cells in vivo, and prevent renal ischemia/reperfusion injury in Rag-/- mice that lack adaptive immune cells including Tregs. Depletion of regulatory innate lymphoid cells with anti-CD25 antibody abolished the beneficial effects of IL-2C in the Rag-/- mice. Adoptive transfer of ex vivo expanded regulatory innate lymphoid cells improved renal function and attenuated histologic damage when given before or after induction of ischemia/reperfusion injury in association with reduction of neutrophil infiltration and induction of reparative M2 macrophages in kidney. Thus, our study shows that regulatory innate lymphoid cells suppress innate renal inflammation and ischemia/reperfusion injury.

M2 macrophages in kidney disease: biology, therapies, and perspectives.

Tissue macrophages are crucial players in homeostasis, inflammation, and immunity. They are characterized by heterogeneity and plasticity, due to which they display a continuum of phenotypes with M1/M2 presenting 2 extremes of this continuum. M2 macrophages are usually termed in the literature as anti-inflammatory and wound healing. Substantial progress has been made in elucidating the biology of M2 macrophages and their potential for clinical translation. In this review we discuss the current state of knowledge in M2 macrophage research with an emphasis on kidney disease. We explore their therapeutic potential and the challenges in using them as cellular therapies. Some new regulators that shape macrophage polarization and potential areas for future research are also examined.

Dialysis initiation, modality choice, access, and prescription: conclusions from a Kidney Disease: Improving Global Outcomes (KDIGO) Controversies Conference.

Globally, the number of patients undergoing maintenance dialysis is increasing, yet throughout the world there is significant variability in the practice of initiating dialysis. Factors such as availability of resources, reasons for starting dialysis, timing of dialysis initiation, patient education and preparedness, dialysis modality and access, as well as varied "country-specific" factors significantly affect patient experiences and outcomes. As the burden of end-stage kidney disease (ESKD) has increased globally, there has also been a growing recognition of the importance of patient involvement in determining the goals of care and decisions regarding treatment. In January 2018, KDIGO (Kidney Disease: Improving Global Outcomes) convened a Controversies Conference focused on dialysis initiation, including modality choice, access, and prescription. Here we present a summary of the conference discussions, including identified knowledge gaps, areas of controversy, and priorities for research. A major novel theme represented during the conference was the need to move away from a "one-size-fits-all" approach to dialysis and provide more individualized care that incorporates patient goals and preferences while still maintaining best practices for quality and safety. Identifying and including patient-centered goals that can be validated as quality indicators in the context of diverse health care systems to achieve equity of outcomes will require alignment of goals and incentives between patients, providers, regulators, and payers that will vary across health care jurisdictions.

Increasing access to integrated ESKD care as part of universal health coverage.

The global nephrology community recognizes the need for a cohesive strategy to address the growing problem of end-stage kidney disease (ESKD). In March 2018, the International Society of Nephrology hosted a summit on integrated ESKD care, including 92 individuals from around the globe with diverse expertise and professional backgrounds. The attendees were from 41 countries, including 16 participants from 11 low- and lower-middle-income countries. The purpose was to develop a strategic plan to improve worldwide access to integrated ESKD care, by identifying and prioritizing key activities across 8 themes: (i) estimates of ESKD burden and treatment coverage, (ii) advocacy, (iii) education and training/workforce, (iv) financing/funding models, (v) ethics, (vi) dialysis, (vii) transplantation, and (viii) conservative care. Action plans with prioritized lists of goals, activities, and key deliverables, and an overarching performance framework were developed for each theme. Examples of these key deliverables include improved data availability, integration of core registry measures and analysis to inform development of health care policy; a framework for advocacy; improved and continued stakeholder engagement; improved workforce training; equitable, efficient, and cost-effective funding models; greater understanding and greater application of ethical principles in practice and policy; definition and application of standards for safe and sustainable dialysis treatment and a set of measurable quality parameters; and integration of dialysis, transplantation, and comprehensive conservative care as ESKD treatment options within the context of overall health priorities. Intended users of the action plans include clinicians, patients and their families, scientists, industry partners, government decision makers, and advocacy organizations. Implementation of this integrated and comprehensive plan is intended to improve quality and access to care and thereby reduce serious health-related suffering of adults and children affected by ESKD worldwide.

Flt3 inhibition alleviates chronic kidney disease by suppressing CD103+ dendritic cell-mediated T cell activation.

BACKGROUND: Chronic kidney disease (CKD) is a global public health problem, which lacks effective treatment. Previously, we have shown that CD103+ dendritic cells (DCs) are pathogenic in adriamycin nephropathy (AN), a model of human focal segmental glomerulosclerosis (FSGS). Fms-like tyrosine kinase 3 (Flt3) is a receptor that is expressed with high specificity on tissue resident CD103+ DCs. METHODS: To test the effect on CD103+ DCs and kidney injury of inhibition of Flt3, we used a selective Flt3 inhibitor (AC220) to treat mice with AN. RESULTS: Human CD141+ DCs, homologous to murine CD103+ DCs, were significantly increased in patients with FSGS. The number of kidney CD103+ DCs, but not CD103- DCs or plasmacytoid DCs, was significantly decreased in AN mice after AC220 administration. Treatment with AC220 significantly improved kidney function and reduced kidney injury and fibrosis in AN mice. AC220-treated AN mice had decreased levels of inflammatory cytokines and chemokines, tumor necrosis factor-α, interleukin (IL)-1ß, IL-6, CCL2 and CCL5 and reduced kidney infiltration of CD4 T cells and CD8 T cells. The protective effect of AC220 was associated with its suppression of CD103+ DCs-mediated CD8 T cell proliferation and activation in AN mice. CONCLUSION: Flt3 inhibitor AC220 effectively reduced kidney injury in AN mice, suggesting that this inhibitor might be a useful pharmaceutical agent to treat CKD.

Potentiating Tissue-Resident Type 2 Innate Lymphoid Cells by IL-33 to Prevent Renal Ischemia-Reperfusion Injury.

The IL-33-type 2 innate lymphoid cell (ILC2) axis has an important role in tissue homeostasis, inflammation, and wound healing. However, the relative importance of this innate immune pathway for immunotherapy against inflammation and tissue damage remains unclear. Here, we show that treatment with recombinant mouse IL-33 prevented renal structural and functional injury and reduced mortality in mice subjected to ischemia-reperfusion injury (IRI). Compared with control-treated IRI mice, IL-33-treated IRI mice had increased levels of IL-4 and IL-13 in serum and kidney and more ILC2, regulatory T cells (Tregs), and anti-inflammatory (M2) macrophages. Depletion of ILC2, but not Tregs, substantially abolished the protective effect of IL-33 on renal IRI. Adoptive transfer of ex vivo-expanded ILC2 prevented renal injury in mice subjected to IRI. This protective effect associated with induction of M2 macrophages in kidney and required ILC2 production of amphiregulin. Treatment of mice with IL-33 or ILC2 after IRI was also renoprotective. Furthermore, in a humanized mouse model of renal IRI, treatment with human IL-33 or transfer of ex vivo-expanded human ILC2 ameliorated renal IRI. This study has uncovered a major protective role of the IL-33-ILC2 axis in renal IRI that could be potentiated as a therapeutic strategy.

Redirecting TGF-ß Signaling through the ß-Catenin/Foxo Complex Prevents Kidney Fibrosis.

TGF-ß is a key profibrotic factor, but targeting TGF-ß to prevent fibrosis also abolishes its protective anti-inflammatory effects. Here, we investigated the hypothesis that we can redirect TGF-ß signaling by preventing downstream profibrotic interaction of ß-catenin with T cell factor (TCF), thereby enhancing the interaction of ß-catenin with Foxo, a transcription factor that controls differentiation of TGF-ß induced regulatory T cells (iTregs), and thus, enhance anti-inflammatory effects of TGF-ß In iTregs derived from EL4 T cells treated with recombinant human TGF-ß1 (rhTGF-ß1) in vitro, inhibition of ß-catenin/TCF transcription with ICG-001 increased Foxp3 expression, interaction of ß-catenin and Foxo1, binding of Foxo1 to the Foxp3 promoter, and Foxo transcriptional activity. Moreover, the level of ß-catenin expression positively correlated with the level of Foxo1 binding to the Foxp3 promoter and Foxo transcriptional activity. T cell fate mapping in Foxp3gfp Ly5.1/5.2 mice revealed that coadministration of rhTGF-ß1 and ICG-001 further enhanced the expansion of iTregs and natural Tregs observed with rhTGF-ß1 treatment alone. Coadministration of rhTGF-ß1 with ICG-001 also increased the number of Tregs and reduced inflammation and fibrosis in the kidney fibrosis models of unilateral ureteric obstruction and ischemia-reperfusion injury. Notably, ICG-001 prevented the fibrosis in distant organs (lung and liver) caused by rhTGF-ß1. Together, our results show that diversion of ß-catenin from TCF- to Foxo-mediated transcription inhibits the ß-catenin/TCF-mediated profibrotic effects of TGF-ß while enhancing the ß-catenin/Foxo-mediated anti-inflammatory effects. Targeting ß-catenin/Foxo may be a novel therapeutic strategy in the treatment of fibrotic diseases that lead to organ failure.

Therapeutic potential of regulatory macrophages generated from peritoneal dialysate in adriamycin nephropathy.

Cell therapy using macrophages requires large amounts of cells, which are difficult to collect from patients. Patients undergoing peritoneal dialysis (PD) discard huge numbers of peritoneal macrophages in dialysate daily. Macrophages can be modulated to become regulatory macrophages, which have shown great promise as a therapeutic strategy in experimental kidney disease and human kidney transplantation. This study aimed to examine the potential of using peritoneal macrophages (PMs) from peritoneal dialysate to treat kidney disease. Monocytes/macrophages accounted for >40% of total peritoneal leukocytes in both patients and mice undergoing PD. PMs from patients and mice undergoing PD were more mature than peripheral monocytes/macrophages, as shown by low expression of C-C motif chemokine receptor 2 (CCR2) and morphological changes during in vitro culture. PMs from patients and mice undergoing PD displayed normal macrophage function and could be modulated into a regulatory (M2) phenotype. In vivo, adoptive transfer of peritoneal M2 macrophages derived from PD mice effectively protected against kidney injury in mice with adriamycin nephropathy (AN). Importantly, the transfused peritoneal M2 macrophages maintained their M2 phenotype in kidney of AN mice. In conclusion, PMs derived from patients and mice undergoing PD exhibited conventional macrophage features. Peritoneal M2 macrophages derived from PD mice are able to reduce kidney injury in AN, suggesting that peritoneal macrophages from patients undergoing PD may have the potential for clinical therapeutic application.

α3 Integrin of Cell-Cell Contact Mediates Kidney Fibrosis by Integrin-Linked Kinase in Proximal Tubular E-Cadherin Deficient Mice.

Loss of E-cadherin marks a defect in epithelial integrity and polarity during tissue injury and fibrosis. Whether loss of E-cadherin plays a causal role in fibrosis is uncertain. α3ß1 Integrin has been identified to complex with E-cadherin in cell-cell adhesion, but little is known about the details of their cross talk. Herein, E-cadherin gene (Cdh1) was selectively deleted from proximal tubules of murine kidney by Sglt2Cre. Ablation of E-cadherin up-regulated α3ß1 integrin at cell-cell adhesion. E-cadherin-deficient proximal tubular epithelial cell displayed enhanced transforming growth factor-ß1-induced α-smooth muscle actin (α-SMA) and vimentin expression, which was suppressed by siRNA silencing of α3 integrin, but not ß1 integrin. Up-regulation of transforming growth factor-ß1-induced α-SMA was mediated by an α3 integrin-dependent increase in integrin-linked kinase (ILK). Src phosphorylation of ß-catenin and consequent p-ß-catenin-Y654/p-Smad2 transcriptional complex underlies the transcriptional up-regulation of ILK. Kidney fibrosis after unilateral ureteric obstruction or ischemia reperfusion was increased in proximal tubule E-cadherin-deficient mice in comparison to that of E-cadherin intact control mice. The exacerbation of fibrosis was explained by the α3 integrin-dependent increase of ILK, ß-catenin nuclear translocation, and α-SMA/proximal tubular-specific Cre double positive staining in proximal tubular epithelial cell. These studies delineate a nonconventional integrin/ILK signaling by α3 integrin-dependent Src/p-ß-catenin-Y654/p-Smad2-mediated up-regulation of ILK through which loss of E-cadherin leads to kidney fibrosis.

Matrix metalloproteinase 9-dependent Notch signaling contributes to kidney fibrosis through peritubular endothelial-mesenchymal transition.

BACKGROUND: Endothelial cells are known to contribute to kidney fibrosis via endothelial-mesenchymal transition (EndoMT). Matrix metalloproteinase 9 (MMP-9) is known to be profibrotic. However, whether MMP-9 contributes to kidney fibrosis via EndoMT is unknown. METHODS: Primary mouse renal peritubular endothelial cells (MRPECs) were isolated and treated by recombinant human transforming growth factor beta 1 (rhTGF-ß1) with or without MMP-9 inhibitor or by recombinant human MMP-9 (rhMMP-9) alone. Kidney fibrosis was induced by unilateral ureteral obstruction (UUO) in MMP-9 knockout (KO) and wide-type (WT) control mice. The effects of MMP-9 on EndoMT of MRPECs and kidney fibrosis were examined. RESULTS: We showed that MRPECs underwent EndoMT after rhTGF-ß1 treatment or in UUO kidney as evidenced by decreased expression of endothelial markers, vascular endothelial cadherin (VE-cadherin) and CD31, and increased levels of mesenchymal markers, α-smooth muscle actin (α-SMA) and vimentin. The expression of fibrosis markers was also up-regulated significantly after rhTGF-ß1 treatment in MRPECs. The EndoMT and fibrosis markers were significantly less in rhTGF-ß1-treated MMP-9 KO MRPECs, whereas MMP-9 alone was sufficient to induce EndoMT in MRPECs. UUO kidney of MMP-9 KO mice showed significantly less interstitial fibrosis and EndoMT in MRPECs. Notch signaling shown by Notch intracellular domain (NICD) was increased, while Notch-1 was decreased in rhTGF-ß1-treated MRPECs of MMP-9 WT but not MMP-9 KO mice. Inhibition of MMP-9 or Notch signaling prevented rhTGF-ß1- or rhMMP-9-induced α-SMA and NICD upregulation in MRPECs. UUO kidney of MMP-9 KO mice had less staining of Notch signaling transcription factor Hey-1 in VE-cadherin-positive MRPECs than WT controls. CONCLUSIONS: Our results demonstrate that MMP-9-dependent Notch signaling plays an important role in kidney fibrosis through EndoMT of MRPECs.