Progression of chronic kidney disease: too much cellular talk causes damage

Metabolic Reprogramming and Renal Fibrosis

There are several causes of chronic kidney disease, but all of these patients have renal fibrosis. Although many studies have examined the pathogenesis of renal fibrosis, there are still no effective treatments. A healthy and balanced metabolism is necessary for normal cell growth, proliferation, and function, but metabolic abnormalities can lead to pathological changes. Normal energy metabolism is particularly important for maintaining the structure and function of the kidneys because they consume large amounts of energy. We describe the metabolic reprogramming that occurs during renal fibrosis, which includes changes in fatty acid metabolism and glucose metabolism, and the relationship of these changes with renal fibrosis. We also describe the potential role of novel drugs that disrupt this metabolic reprogramming and the development of fibrosis, and current and future challenges in the treatment of fibrosis.

Quercetin alleviates chronic renal failure by targeting the PI3k/Akt pathway

Chronic renal failure (CRF) threatens human health greatly and attracts worldwide concerns of health professionals in the public health sector. In our preliminary study, we found that Compound capsule (Shengqing Jiangzhuo Capsule, SQJZJN) had a significant therapeutic effect on CRF. Quercetin is one of the main components of this Compound capsule. In this study, we investigated the effect of Quercetin monomer on CRF and the regulation of PI3k/Akt pathway. Network pharmacology analysis methods were employed to analyze the SQJZJN/Quercetin/PIK3R1 network relationships. In this study, a CRF rat model was prepared using the gavage adenine solution method and detected the indicators of Creatinine (Cr), Blood Urea Nitrogen (BUN), and Uric Acid (UA). After treating the rat model with Quercetin and PIK3R1-interfering lentivirus, respectively, we observed the changes on the histological morphology of the kidney and detected apoptosis using TUNEL staining. Gene and protein expression associated with renal function were detected using qPCR, WB and immunofluorescence. Quercetin was identified as the main ingredient of SQJZJN by the network pharmacological screening and Quercetin at 1.5 and 3 g/(kg.d) concentrations could effectively alleviate the CRF symptoms, reduce the levels of Cr, BUN, and UA, and markedly inhibit cell apoptosis demonstrated by the intragastric administration. Furthermore, the protein expression of p-PI3K, p-AKT, NLRP3, caspase1, AQP1, and AQP2 in all groups was detected by immunofluorescence and western blot assays, indicating that Quercetin could reduce the expression of NLRP3, caspase1, p-PI3k, and p-Akt, and increase the expression of AQP1 and AQP2 in the renal tissues of CRF rats. Being labeled with biotin and incubated with the total protein extracted from kidney tissues, Quercetin could bind to PIK3R1. Following the PIK3R1 interference lentivirus was injected into the CRF model rats by tail vein, the CRF symptoms were effectively alleviated in the PIK3R1 interference group, consistent with the effect of Quercetin. Taken together, Quercetin, a major component of SQJZJN, might minimize renal fibrosis and apoptosis in CRF rats by inhibiting the PI3k/Akt pathway through targeting PIK3R1. By regulating AQP1 and AQP2, both water retention and toxin accumulation were reduced.

The mTOR inhibitor everolimus attenuates tacrolimus-induced renal interstitial fibrosis in rats

AIMS

Tacrolimus-a widely used immunosuppressant to prevent allograft rejection after organ transplantation-is nephrotoxic, increasing the risk of kidney injury accompanied by kidney fibrosis. The mammalian target of rapamycin (mTOR) inhibitor, everolimus, is an immunosuppressant used together with tacrolimus. Although mTOR signaling inhibition has been demonstrated to exhibit antifibrotic effects, the efficacy of everolimus against tacrolimus-induced kidney fibrosis has not been explored. Therefore, we evaluated the protective effects of everolimus against tacrolimus-induced kidney fibrosis.

MAIN METHODS

To assess antifibrotic effect of everolimus against tacrolimus-induced kidney fibrosis, male Wistar rats were subcutaneously administered vehicle or tacrolimus (5 mg/kg per day) and/or everolimus (0.2 mg/kg per day) for 2 weeks after bilateral renal ischemia for 45 min. The antifibrotic effect of everolimus was also assessed using rat kidney fibroblast cell line (NRK-49F).

KEY FINDINGS

Tacrolimus administration increased predominant profibrotic cytokine transforming growth factor-β (TGF-β) and fibroblast activation marker α-smooth muscle actin (α-SMA) expression and promoted the infiltration of macrophages in the kidney cortex, resulting in renal interstitial fibrosis in rats. Tacrolimus increased serum creatinine, blood urea nitrogen, kidney injury molecule-1 (KIM-1), and kidney injuries, such as tubular dilation, vacuolization, and glomerular atrophy. Everolimus administration attenuated tacrolimus-induced kidney fibrosis and the associated abnormalities. Everolimus strongly suppressed TGF-β-induced kidney fibroblast activation and extracellular matrix protein expression by the mTOR signaling inhibition.

SIGNIFICANCE

We demonstrated that everolimus attenuates tacrolimus-induced renal interstitial fibrosis in rats. Owing to its protective effect against tacrolimus-induced kidney fibrosis, everolimus may be useful when used concomitantly with tacrolimus.

NSC828779 Alleviates Renal Tubulointerstitial Lesions Involving Interleukin-36 Signaling in Mice

Renal tubulointerstitial lesions (TILs), a common pathologic hallmark of chronic kidney disease that evolves to end-stage renal disease, is characterized by progressive inflammation and pronounced fibrosis of the kidney. However, current therapeutic approaches to treat these lesions remain largely ineffectual. Previously, we demonstrated that elevated IL-36α levels in human renal tissue and urine are implicated in impaired renal function, and IL-36 signaling enhances activation of NLRP3 inflammasome in a mouse model of TILs. Recently, we synthesized NSC828779, a salicylanilide derivative (protected by U.S. patents with US 8975255 B2 and US 9162993 B2), which inhibits activation of NF-κB signaling with high immunomodulatory potency and low IC50, and we hypothesized that it would be a potential drug candidate for renal TILs. The current study validated the therapeutic effects of NSC828779 on TILs using a mouse model of unilateral ureteral obstruction (UUO) and relevant cell models, including renal tubular epithelial cells under mechanically induced constant pressure. Treatment with NSC828779 improved renal lesions, as demonstrated by dramatically reduced severity of renal inflammation and fibrosis and decreased urinary cytokine levels in UUO mice. This small molecule specifically inhibits the IL-36α/NLRP3 inflammasome pathway. Based on these results, the beneficial outcome represents synergistic suppression of both the IL-36α-activated MAPK/NLRP3 inflammasome and STAT3- and Smad2/3-dependent fibrogenic signaling. NSC828779 appears justified as a new drug candidate to treat renal progressive inflammation and fibrosis.

Potential Therapeutic Effects of Natural Plant Compounds in Kidney Disease

Background: The blockade of the progression or onset of pathological events is essential for the homeostasis of an organism. Some common pathological mechanisms involving a wide range of diseases are the uncontrolled inflammatory reactions that promote fibrosis, oxidative reactions, and other alterations. Natural plant compounds (NPCs) are bioactive elements obtained from natural sources that can regulate physiological processes. Inflammation is recognized as an important factor in the development and evolution of chronic renal damage. Consequently, any compound able to modulate inflammation or inflammation-related processes can be thought of as a renal protective agent and/or a potential treatment tool for controlling renal damage. The objective of this research was to review the beneficial effects of bioactive natural compounds on kidney damage to reveal their efficacy as demonstrated in clinical studies. Methods: This systematic review is based on relevant studies focused on the impact of NPCs with therapeutic potential for kidney disease treatment in humans. Results: Clinical studies have evaluated NPCs as a different way to treat or prevent renal damage and appear to show some benefits in improving OS, inflammation, and antioxidant capacity, therefore making them promising therapeutic tools to reduce or prevent the onset and progression of KD pathogenesis. Conclusions: This review shows the promising clinical properties of NPC in KD therapy. However, more robust clinical trials are needed to establish their safety and therapeutic effects in the area of renal damage.

Possible Preventative/Rehabilitative Role of Gliflozins in OSA and T2DM. A Systematic Literature Review-Based Hypothesis

Obstructive sleep apnoea (OSA) is characterized by frequent apnoea episodes during sleep due to upper airway obstruction. The present review summarizes current knowledge on inter-relationships between OSA and type 2 diabetes mellitus (T2DM) and suggests the former as a possible target for sodium-glucose co-transporter-2 inhibitors (SGLT-2i). Based on pathophysiological mechanisms underlying OSA onset and renal SGLT-2 effects, we suggest that SGLT-2i indications might expand beyond current ones, including glucose, lipids, uric acid, blood pressure, and body weight control as well as chronic heart failure and kidney disease prevention.

Dickkopf 3-a novel biomarker of the 'kidney injury continuum'

Chronic kidney disease (CKD) is a global public health problem accompanied by substantial comorbidities and reduced life expectancy. In this respect, progressive CKD leading to uraemia can be seen as a systemic disease with a critical impact on virtually all organ systems. Therefore, it is of particular importance to identify patients with ongoing CKD progression, which is challenging, because the individual course of CKD is difficult to predict. Patterns of progression in CKD patients include linear and non-linear trajectories of GFR loss, but kidney function can also remain stable for years. Moreover, a substantial GFR decline may occur in the absence of higher-grade albuminuria (non-proteinuric CKD), rendering the measurement of albuminuria less reliable for progression prediction in such individuals. In the present review, we focus on the recently identified glycoprotein Dickkopf-3 (DKK3) as a stress-induced, renal tubular epithelial cell-derived, pro-fibrotic molecule. In experimental CKD models, DKK3 promoted renal tubulointerstitial fibrosis through modulation of the canonical Wnt/β-catenin signalling pathway. In clinical studies, increased urinary DKK3 levels identified patients at high risk for short-term CKD progression, regardless of the cause of kidney disease, baseline kidney function and albuminuria. Moreover, increased urinary DKK3 levels are associated with a high risk for acute kidney injury and the subsequent loss of kidney function after cardiac surgery. These findings highlight DKK3 as a mediator of renal tubular cell damage in kidney injury and short-term progression of kidney disease, with potential therapeutic implications.

Remdesivir Inhibits Tubulointerstitial Fibrosis in Obstructed Kidneys

Aim: Kidney impairment is observed in patients with COVID-19. The effect of anti-COVID-19 agent remdesivir on kidneys is currently unknown. We aimed to determine the effect of remdesivir on renal fibrosis and its downstream mechanisms. Methods: Remdesivir and its active nucleoside metabolite GS-441524 were used to treat TGF-β stimulated renal fibroblasts (NRK-49F) and human renal epithelial (HK2) cells. Vehicle or remdesivir were given by intraperitoneal injection or renal injection through the left ureter in unilateral ureteral obstruction (UUO) mice. Serum and kidneys were harvested. The concentrations of remdesivir and GS-441524 were measured using LC-MS/MS. Renal and liver function were assessed. Renal fibrosis was evaluated by Masson's trichrome staining and Western blotting. Results: Remdesivir and GS-441524 inhibited the expression of fibrotic markers (fibronectin and aSMA) in NRK-49F and HK2 cells. Intraperitoneal injection or renal injection of remdesivir attenuated renal fibrosis in UUO kidneys. Renal and liver function were unchanged in remdesivir treated UUO mice. Two remdesivir metabolites were detected after injection. Phosphorylation of Smad3 that was enhanced in cell and animal models for renal fibrosis was attenuated by remdesivir. In addition, the expression of Smad7, an anti-fibrotic factor, was increased after remdesivir treatment in vitro and in vivo. Moreover, knockdown of Smad7 blocked the antifibrotic effect of GS and RDV on renal cells. Conclusion: Remdesivir inhibits renal fibrosis in obstructed kidneys.

The Genomic Response to TGF-β1 Dictates Failed Repair and Progression of Fibrotic Disease in the Obstructed Kidney

Tubulointerstitial fibrosis is a common and diagnostic hallmark of a spectrum of chronic renal disorders. While the etiology varies as to the causative nature of the underlying pathology, persistent TGF-β1 signaling drives the relentless progression of renal fibrotic disease. TGF-β1 orchestrates the multifaceted program of kidney fibrogenesis involving proximal tubular dysfunction, failed epithelial recovery or re-differentiation, capillary collapse and subsequent interstitial fibrosis eventually leading to chronic and ultimately end-stage disease. An increasing complement of non-canonical elements function as co-factors in TGF-β1 signaling. p53 is a particularly prominent transcriptional co-regulator of several TGF-β1 fibrotic-response genes by complexing with TGF-β1 receptor-activated SMADs. This cooperative p53/TGF-β1 genomic cluster includes genes involved in cellular proliferative control, survival, apoptosis, senescence, and ECM remodeling. While the molecular basis for this co-dependency remains to be determined, a subset of TGF-β1-regulated genes possess both p53- and SMAD-binding motifs. Increases in p53 expression and phosphorylation, moreover, are evident in various forms of renal injury as well as kidney allograft rejection. Targeted reduction of p53 levels by pharmacologic and genetic approaches attenuates expression of the involved genes and mitigates the fibrotic response confirming a key role for p53 in renal disorders. This review focuses on mechanisms underlying TGF-β1-induced renal fibrosis largely in the context of ureteral obstruction, which mimics the pathophysiology of pediatric unilateral ureteropelvic junction obstruction, and the role of p53 as a transcriptional regulator within the TGF-β1 repertoire of fibrosis-promoting genes.

Analysis of genes associated with proinflammatory and profibrotic pathways upregulated in ischemia-induced chronic kidney disease in cats

OBJECTIVE

To use RNA sequencing (RNAseq) to characterize renal transcriptional activities of genes associated with proinflammatory and profibrotic pathways in ischemia-induced chronic kidney disease (CKD) in cats.

SAMPLES

Banked renal tissues from 6 cats with experimentally induced CKD (renal ischemia [RI] group) and 9 healthy cats (control group).

PROCEDURES

Transcriptome analysis with RNAseq, followed by gene ontology and cluster analyses, were performed on banked tissue samples of the right kidneys (control kidneys) from cats in the control group and of both kidneys from cats in the RI group, in which unilateral (right) RI had been induced 6 months before the cats were euthanized and the ischemic kidneys (IKs) and contralateral nonischemic kidneys (CNIKs) were harvested. Results for the IKs, CNIKs, and control kidneys were compared to identify potential differentially expressed genes and overrepresented proinflammatory and profibrotic pathways.

RESULTS

Genes from the gene ontology pathways of collagen binding (eg, transforming growth factor-β1), metalloendopeptidase activity (eg, metalloproteinase [MMP]-7, MMP-9, MMP-11, MMP-13, MMP-16, MMP-23B, and MMP-28), chemokine activity, and T-cell migration were overrepresented as upregulated in tissue samples of the IKs versus control kidneys. Genes associated with the extracellular matrix (eg, TIMP-1, fibulin-1, secreted phosphoprotein-1, matrix Gla protein, and connective tissue growth factor) were upregulated in tissue samples from both the IKs and CNIKs, compared with tissues from the control kidneys.

CONCLUSIONS AND CLINICAL RELEVANCE

Unilateral ischemic injury differentially altered gene expression in both kidneys, compared with control kidneys. Fibulin-1, secreted phosphoprotein-1, and matrix Gla protein may be candidate biomarkers of active kidney injury in cats.

Precision medicine in diabetic nephropathy and chronic kidney disease

Progressive chronic kidney disease (CKD) in individuals with type 2 diabetes mellitus is a global public health problem accompanied by substantial comorbidities and reduced life expectancy. In this respect, CKD leading to uremia can be seen as a systemic disease with a critical impact on virtually all organ systems. Thus it is of particular importance to identify patients with incipient CKD and ongoing CKD progression, but the individual course of CKD is challenging to predict. Patterns of progression in persons with CKD include linear and nonlinear trajectories of glomerular filtration rate (GFR) loss. Kidney function can also remain stable for years, especially in the elderly. In particular, one-fifth of individuals show a substantial GFR decline in the absence of high albuminuria (nonproteinuric CKD), rendering albuminuria less suitable for predicting the progression in such individuals.

IFN-I Mediates Lupus Nephritis From the Beginning to Renal Fibrosis

Lupus nephritis (LN) is a common complication of systemic lupus erythematosus (SLE) and a major risk factor for morbidity and mortality. The abundant cell-free nucleic (DNA/RNA) in SLE patients, especially dsDNA, is a key substance in the pathogenesis of SLE and LN. The deposition of DNA/RNA-immune complexes (DNA/RNA-ICs) in the glomerulus causes a series of inflammatory reactions that lead to resident renal cell disturbance and eventually renal fibrosis. Cell-free DNA/RNA is the most effective inducer of type I interferons (IFN-I). Resident renal cells (rather than infiltrating immune cells) are the main source of IFN-I in the kidney. IFN-I in turn damages resident renal cells. Not only are resident renal cells victims, but also participants in this immunity war. However, the mechanism for generation of IFN-I in resident renal cells and the pathological mechanism of IFN-I promoting renal fibrosis have not been fully elucidated. This paper reviews the latest epidemiology of LN and its development process, discusses the mechanism for generation of IFN-I in resident renal cells and the role of IFN-I in the pathogenesis of LN, and may open a new perspective for the treatment of LN.

Genetic Background and Clinicopathologic Features of Adult-onset Nephronophthisis

Introduction

Recently, nephronophthisis (NPH) has been considered a monogenic cause of end-stage renal disease (ESRD) in adults. However, adult-onset NPH is difficult to accurately diagnose and has not been reported in a cohort study. In this study, we assessed the genetic background and clinicopathologic features of adult NPH.

Methods

We investigated 18 sporadic adult patients who were suspected as having NPH by renal biopsy. We analyzed 69 genes that cause hereditary cystic kidney disease and compared clinicopathologic findings between patients with and without pathogenic mutations in NPH-causing genes.

Results

Seven of 18 patients had pathogenic NPH-causing mutations in NPHP1, NPHP3, NPHP4, or CEP164. Compared with patients without pathogenic mutations, those with pathogenic mutations were significantly younger but did not significantly differ in the classic NPH pathologic findings, such as tubular cysts. On the other hand, the number of tubules with thick tubular basement membrane (TBM) duplication, which was defined as >10-μm thickness, was significantly higher in patients with genetically proven adult NPH than in those without pathogenic mutations. α-Smooth muscle actin (α-SMA)-positive myofibroblasts were detected inside thick TBM duplication.

Conclusions

In adult patients with NPH, thick TBM duplication was the specific finding. Our analysis also suggested that older patients tended to have no pathogenic mutations, even when they were suspected to have NPH by renal biopsy. These findings could be the novel clinical clue for the diagnosis of NPH in adult patients.

Proximal tubule LPA1 and LPA2 receptors use divergent signaling pathways to additively increase profibrotic cytokine secretion

Lysophosphatidic acid (LPA) increases platelet-derived growth factor-B (PDGFB) and connective tissue growth factor (CTGF) production and secretion by proximal tubule (PT) cells through LPA2 receptor-Gqα-αvβ6-integrin-mediated activation of transforming growth factor-β1 (TGFB1). LPA2, β6-integrin, PDGFB, and CTGF increase in kidneys after ischemia-reperfusion injury (IRI), coinciding with fibrosis. The TGFB1 receptor antagonist SD-208 prevents increases of β6-integrin, TGFB1-SMAD signaling, and PDGFB/CTGF expression after IRI and ameliorates fibrosis (Geng H, Lan R, Singha PK, Gilchrist A, Weinreb PH, Violette SM, Weinberg JM, Saikumar P, Venkatachalam MA. Am J Pathol 181: 1236-1249, 2012; Geng H, Lan R, Wang G, Siddiqi AR, Naski MC, Brooks AI, Barnes JL, Saikumar P, Weinberg JM, Venkatachalam MA. Am J Pathol 174: 1291-1308, 2009). We report now that LPA1 receptor signaling through epidermal growth factor receptor (EGFR)-ERK1/2-activator protein-1 cooperates with LPA2-dependent TGFB1 signaling to additively increase PDGFB/CTGF production and secretion by PT cells. Conversely, inhibition of both pathways results in greater suppression of PDGFB/CTGF production and secretion and promotes greater PT cellular differentiation than inhibiting one pathway alone. Antagonism of the LPA-generating enzyme autotaxin suppressed signaling through both pathways. After IRI, kidneys showed not only more LPA2, nuclear SMAD2/3, and PDGFB/CTGF but also increased LPA1 and autotaxin proteins, together with enhanced EGFR/ERK1/2 activation. Remarkably, the TGFB1 receptor antagonist SD-208 prevented all of these abnormalities excepting increased LPA2. SD-208 inhibits only one arm of LPA signaling: LPA2-Gqα-αvβ6-integrin-dependent production of active TGFB1 and its receptor-bound downstream effects. Consequently, far-reaching protection by SD-208 against IRI-induced signaling alterations and tubule-interstitial pathology is not fully explained by our data. TGFB1-dependent feedforward modulation of LPA1 signaling is one possibility. SD-208 effects may also involve mitigation of injury caused by IRI-induced TGFB1 signaling in endothelial cells and monocytes. Our results have translational implications for using TGFB1 receptor antagonists, LPA1 and LPA2 inhibitors concurrently, and autotaxin inhibitors in acute kidney injury to prevent the development of chronic kidney disease.

Kidney Allograft Fibrosis: Diagnostic and Therapeutic Strategies

Interstitial fibrosis with tubule atrophy (IF/TA) is the response to virtually any sustained kidney injury and correlates inversely with kidney function and allograft survival. IF/TA is driven by various pathways that include hypoxia, renin-angiotensin-aldosterone system, transforming growth factor (TGF)-β signaling, cellular rejection, inflammation and others. In this review we will focus on key pathways in the progress of renal fibrosis, diagnosis and therapy of allograft fibrosis. This review discusses the role and origin of myofibroblasts as matrix producing cells and therapeutic targets in renal fibrosis with a particular focus on renal allografts. We summarize current trends to use multi-omic approaches to identify new biomarkers for IF/TA detection and to predict allograft survival. Furthermore, we review current imaging strategies that might help to identify and follow-up IF/TA complementary or as alternative to invasive biopsies. We further discuss current clinical trials and therapeutic strategies to treat kidney fibrosis.Supplemental Visual Abstract; http://links.lww.com/TP/C141.

Nicotinamide Supplementation Attenuates Renal Interstitial Fibrosis via Boosting the Activity of Sirtuins

Background

Progressive tubulointerstitial fibrosis (TIF) is the final common pathway leading to ESRD. There is an urgent need to develop effective approaches slowing the progression of TIF. Previous studies showed that systemic supplementation of nicotinamide (NAM) increases renal NAD⁺ and reverses ischemic-reperfusion induced acute renal injury. However, the role and mechanism of NAM in TIF has been unclear.

Methods

In vivo, we injected NAM (0.25 mg/g) 3 days before unilateral ureter obstruction (UUO) till day 7 post-operation. In vitro, mouse primary proximal tubular epithelial cells (PTCs), rat renal NRK-49F cells, and human renal proximal tubular epithelial cell (HK-2) were pretreated with the indicated concentration of NAM 1 h before incubation with transform growth factor-β1 (TGF-β1) or aristolochic acid (AA) for 24 or 48 h. To evaluate the role of sirtuins (SIRTs), PTCs were pretreated with EX527 or resveratrol 30 min before incubation with NAM and TGF-β1.

Results

In the present study, we demonstrated that NAM supplementation prevented UUO-induced TIF, and AA-induced renal injury. NAM also decreased the expression of pro-fibrotic proteins and pro-inflammatory cytokines (IL-6 and TNF-α) and attenuated interstitial inflammation. In vitro experiment showed that, NAM inhibited AA-induced G2/M arrest of HK-2 cells by downregulating the expression of cyclin G1, a target gene of p53. In addition, NAM inhibited TGF-β1-induced fibroblast proliferation and activation shown as downregulated expression of collagen I, fibronectin, PCNA, cyclin D1, IL-6, and TNF-α. NAM decreased the acetylation of Smad3 and p53. EX527, an inhibitor of SIRT1, reversed the effect of NAM on TGF-β1-induced matrix protein production. However, resveratrol, a SIRT1 activator, did not further boost the protective effect of NAM on reducing matrix protein production.

Conclusions

Taken together, these data indicate that NAM supplementation could inhibit TIF at least partially by boosting the activity of sirtuins.

Association between Uremic Toxin Concentrations and Bone Mineral Density after Kidney Transplantation

Although uremic osteoporosis is a component of mineral and bone disorder in chronic kidney disease, uremic toxin (UT) concentrations in patients with end-stage kidney disease and bone mineral density (BMD) changes after kidney transplantation have not previously been described. We hypothesized that elevated UT concentrations at the time of transplantation could have a negative impact on bone during the early post-transplantation period. Hence, we sought to determine whether concentrations of UTs (trimethylamine-N-oxide, indoxylsulfate, p-cresylsulfate, p-cresylglucuronide, indole-3-acetic acid, hippuric acid, and 3-carboxy-4-methyl-5-propyl-furanpropionic acid) upon transplantation are predictive markers for (i) osteoporosis one month after transplantation, and (ii) a BMD decrease and the occurrence of fractures 12 and 24 months after kidney transplantation. Between 2012 and 2018, 310 kidney transplant recipients were included, and dual-energy X-ray absorptiometry was performed 1, 12, and 24 months after transplantation. The UT concentrations upon transplantation were determined by reverse-phase high-performance liquid chromatography. Indoxylsulfate concentrations upon transplantation were positively correlated with BMD one month after transplantation for the femoral neck but were not associated with osteoporosis status upon transplantation. Concentrations of the other UTs upon transplantation were not associated with osteoporosis or BMD one month after transplantation. None of the UT concentrations were associated with BMD changes and the occurrence of osteoporotic fractures 12 and 24 months after transplantation. Hence, UT concentrations at the time of kidney transplantation were not predictive markers of osteoporosis or fractures.

Individual uromodulin serum concentration is independent of glomerular filtration rate in healthy kidney donors

OBJECTIVES

The mucoprotein uromodulin is considered to correlate with glomerular filtration rates (GFR) in patients with chronic kidney disease (CKD). Here we investigated how serum uromodulin is associated with measured GFR using inulin-clearance and GFR estimated by CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation in healthy subjects.

METHODS

We assessed possible correlations between uromodulin serum concentrations, inulin-GFR and CKD-EPI-GFR in a well characterized study cohort of 112 healthy living kidney donors with two kidneys before and 64 with one kidney after kidney donation. A subgroup of 32 individuals, which presented data before and after nephrectomy, was assessed separately.

RESULTS

All 112 healthy living kidney donors with two kidneys revealed individual serum uromodulin concentrations between 60.1 and 450.5 µg/L. Sixty-four healthy kidney donors after nephrectomy had significantly lower median (interquartile range) serum uromodulin concentrations (124 [101-166] vs. 185 [152-238] µg/L), inulin-GFR (67.3 [60.6-74.6] vs. 93.5 [82.1-104.4] mL/min/1.73 m²), and CKD-EPI-GFR (61.2 [53.1-69.7] vs. 88.6 [80.0-97.1] mL/min/1.73 m²) as compared to the 112 donors before donation (p<0.001). The subgroup of 32 subjects, which presented data before and after nephrectomy, showed almost the same pattern of kidney function. No statistically relevant associations were found between serum uromodulin and inulin-GFR or CKD-EPI-GFR regarding this healthy population.

CONCLUSIONS

These novel findings indicate that - in contrast to patients with CKD - serum uromodulin concentrations are not correlated with measured and estimated GFR in healthy individuals.

Compound K inhibits priming and mitochondria-associated activating signals of NLRP3 inflammasome in renal tubulointerstitial lesions

BACKGROUND

Renal tubulointerstitial lesions (TILs), a key pathological hallmark for chronic kidney disease to progress to end-stage renal disease, feature renal tubular atrophy, interstitial mononuclear leukocyte infiltration and fibrosis in the kidney. Our study tested the renoprotective and therapeutic effects of compound K (CK), as described in our US patent (US7932057B2), on renal TILs using a mouse unilateral ureteral obstruction (UUO) model.

METHODS

Renal pathology was performed and renal draining lymph nodes were subjected to flow cytometry analysis. Mechanism-based experiments included the analysis of mitochondrial dysfunction, a model of tubular epithelial cells (TECs) under mechanically induced constant pressure (MICP) and tandem mass tags (TMT)-based proteomics analysis.

RESULTS

Administration of CK ameliorated renal TILs by reducing urine levels of proinflammatory cytokines, and preventing mononuclear leukocyte infiltration and fibrosis in the kidney. The beneficial effects clearly correlated with its inhibition of: (i) NF-κB-associated priming and the mitochondria-associated activating signals of the NLRP3 inflammasome; (ii) STAT3 signalling, which in part prevents NLRP3 inflammasome activation; and (iii) the TGF-β-dependent Smad2/Smad3 fibrotic pathway, in renal tissues, renal TECs under MICP and/or activated macrophages, the latter as a major inflammatory player contributing to renal TILs. Meanwhile, TMT-based proteomics analysis revealed downregulated renal NLRP3 inflammasome activation-associated signalling pathways in CK-treated UUO mice.

CONCLUSIONS

The present study, for the first time, presents the potent renoprotective and therapeutic effects of CK on renal TILs by targeting the NLRP3 inflammasome and STAT3 signalling.

Extracellular vesicles produced by bone marrow mesenchymal stem cells attenuate renal fibrosis, in part by inhibiting the RhoA/ROCK pathway, in a UUO rat model

Background

Extracellular vesicles produced by bone marrow mesenchymal stem cells (BMSC-EVs) can play important roles in the repair of injured tissues. Though numerous studies have reported the effect of EVs on renal fibrosis, the underlying mechanisms remain unclear. We hypothesized that BMSC-EVs containing milk fat globule–epidermal growth factor–factor 8 (MFG-E8) could attenuate renal fibrosis by inhibiting the RhoA/ROCK pathway.

Methods

We investigated whether BMSC-EVs have anti-fibrotic effects in a rat model of renal fibrosis, in which rats were subjected to unilateral ureteral obstruction (UUO), as well as in cultured HK2 cells. Extracellular vesicles from BMSCs were collected and co-cultured with HK2 cells during transforming growth factor-β1 (TGF-β1) treatment. HK2 cells co-cultured with TGF-β1 were also treated with the ROCK inhibitor, Y-27632.

Results

Compared with the Sham group, UUO rats displayed fibrotic abnormalities, accompanied by an increased expression of α-smooth muscle actin and Fibronectin and reduced expression of E-cadherin. These molecular and pathological changes suggested increased inflammation in damaged kidneys. Oxidative stress, as evidenced by an increased level of MDA and decreased levels of SOD1 and Catalase, was also observed in UUO kidneys. Additionally, activation of cleaved caspase-3 and PARP1 and increased apoptosis in the proximal tubules confirmed tubular cell apoptosis in the UUO group. All of these phenotypes exhibited by UUO rats were suppressed by treatment with BMSC-EVs. However, the protective effect of BMSC-EVs was completely abolished by the inhibition of MFG-E8. Consistent with the in vivo results, treatment with BMSC-EVs reduced inflammation, oxidative stress, apoptosis, and fibrosis in HK-2 cells stimulated with TGF-β1 in vitro. Interestingly, treatment with Y-27632 protected HK-2 cells against inflammation and fibrosis, although oxidative stress and apoptosis were unchanged.

Conclusions

Our results show that BMSC-EVs containing MFG-E8 attenuate renal fibrosis in a rat model of renal fibrosis, partly through RhoA/ROCK pathway inhibition.

Drp1-regulated PARK2-dependent mitophagy protects against renal fibrosis in unilateral ureteral obstruction

Mitophagy is a principle mechanism to degrade damaged mitochondria through PARK2-dependent or PARK2-independent pathway. Mitophagy has been identified to play an important role in acute kidney disease, whereas its role in renal fibrosis remains ill-defined. We sought to investigate the involvement and regulation of mitophagy in renal tubular epithelial cell(RTEC) injury and renal fibrosis after unilateral ureteral obstruction(UUO). Mitochondrial damageand mitochondrial reactive oxygen species (ROS) production was increased in kidney after obstruction of the left ureter. Mitophagy was increased in kidneys following UUO and HK-2 cells under hypoxia exposure, assessed by electron microscopy of mitophagosome, colocalization of MitotrackerRed-stained mitochondria and LC3 staining. The upregulation of PINK1, PARK2, and LC3 II in mitochondrial fraction was observed in the obstructed kidney and hypoxia-exposed HK-2 cells. Pink1 or Park2 gene deletion markedly increased mtROS production, mitochondrial damage, TGFβ1 expression in RTEC, and renal fibrosis in UUO. Mitochondrial recruitment of Drp1 was also induced after UUO. The Drp1 inhibitor, Mdivi-1, decreased mitochondrial PINK1, PARK2 and LC3II level, increased mtROS production both in vivo and in vitro, activated TGFβ1-Smad2/3 signaling in HK-2 cells under hypoxia and worsened renal fibrosis following UUO. The upregulation of TGFβ1 signaling in hypoxia-treated HK-2 cells due to PINK1 or PARK2 silencing, or worsened renal fibrosis after UUO due to Pink1-or Park2-KO mice was rescued by mitoTEMPO, a mitochondria-targeted antioxidant. The findings of this study suggest that Drp1-regulated PARK2-dependent mitophagy plays a critical role in hypoxia-induced renal tubular epithelial cell injury and renal fibrosis in UUO.

Losartan protects against intermittent hypoxia-induced peritubular capillary loss by modulating the renal renin-angiotensin system and angiogenesis factors

Obstructive sleep apnea is characterized by chronic intermittent hypoxia (CIH), which is a risk factor for renal peritubular capillary (PTC) loss, and angiotensin II receptor blockers can alleviate PTC loss. However, the mechanism by which losartan (an angiotensin II receptor blocker) reduces CIH-induced PTC loss and attenuates kidney damage is still unknown. Thus, in this study, we examined the protective effects of losartan against CIH-induced PTC loss and explored the underlying mechanisms in rat CIH model. The immunohistochemical staining of CD34 and morphological examination showed that CIH reduced PTC density and damaged tubular epithelial cells. Immunohistochemistry, enzyme-linked immunosorbent assay (ELISA), real-time quantitative PCR, and western blot analysis results revealed that CIH increased the expression of hypoxia inducible factor-1α (HIF-1α), angiotensin II (Ang II), angiotensin II type 1 receptor (AT1R), pro-angiogenesis factor vascular endothelial growth factor (VEGF), and anti-angiogenesis factor thrombospondin-1 (TSP-1) in the renal cortex of rats. CIH may up-regulate VEGF expression and simultaneously increase TSP-1 production. By histopathological, immunohistochemistry, ELISA, RT-qPCR, and western blot analysis, we found that the expressions of renal renin-angiotensin system (RAS), HIF-1α, VEGF, and TSP-1 were decreased, and PTC loss and tubular epithelial cell injury were attenuated with losartan treatment. Losartan ameliorated CIH-induced PTC loss by modulating renal RAS to improve the crosstalk between endothelial cells and tubular epithelial cells and subsequently regulate the balance of angiogenesis factors. Our study provided novel insights into the mechanisms of CIH-induced kidney damage and indicated that losartan could be a potential therapeutic agent for renal protection by alleviating CIH-induced PTC loss.

Tubular injury triggers podocyte dysfunction by β-catenin-driven release of MMP-7

Proteinuric chronic kidney disease (CKD) remains a major health problem worldwide. While it is well established that the progression of primary glomerular disease induces tubulointerstitial lesions, how tubular injury triggers glomerular damage is poorly understood. We hypothesized that injured tubules secrete mediators that adversely affect glomerular health. To test this, we used conditional knockout mice with tubule-specific ablation of β-catenin (Ksp-β-cat-/-) and subjected them to chronic angiotensin II (Ang II) infusion or Adriamycin. Compared with control mice, Ksp-β-cat-/- mice were dramatically protected from proteinuria and glomerular damage. MMP-7, a downstream target of β-catenin, was upregulated in treated control mice, but this induction was blunted in the Ksp-β-cat-/- littermates. Incubation of isolated glomeruli with MMP-7 ex vivo led to nephrin depletion and impaired glomerular permeability. Furthermore, MMP-7 specifically and directly degraded nephrin in cultured glomeruli or cell-free systems, and this effect was dependent on its proteolytic activity. In vivo, expression or infusion of exogenous MMP-7 caused proteinuria, and genetic ablation of MMP-7 protected mice from Ang II-induced proteinuria and glomerular injury. Collectively, these results demonstrate that β-catenin-driven MMP-7 release from renal tubules promotes glomerular injury via direct degradation of the key slit diaphragm protein nephrin.

Refining the Mouse Subtotal Nephrectomy in Male 129S2/SV Mice for Consistent Modeling of Progressive Kidney Disease With Renal Inflammation and Cardiac Dysfunction

Chronic kidney disease (CKD) is prevalent worldwide and is associated with significant co-morbidities including cardiovascular disease (CVD). Traditionally, the subtotal nephrectomy (remnant kidney) experimental model has been performed in rats to model progressive renal disease. The model experimentally mimics CKD by reducing nephron number, resulting in renal insufficiency. Presently, there is a lack of translation of pre-clinical findings into successful clinical results. The pre-clinical nephrology field would benefit from reproducible progressive renal disease models in mice in order to avail of more widely available transgenics and experimental tools to dissect mechanisms of disease. Here we evaluate if a simplified single step subtotal nephrectomy (STNx) model performed in the 129S2/SV mouse can recapitulate the renal and cardiac changes observed in patients with CKD in a reproducible and robust way. The single step STNx surgery was well-tolerated and resulted in clinically relevant outcomes including hypertension, increased urinary albumin:creatinine ratio, and significantly increased serum creatinine, phosphate and urea. STNx mice developed significant left ventricular hypertrophy without reduced ejection fraction or cardiac fibrosis. Analysis of intra-renal inflammation revealed persistent recruitment of Ly6C^hi monocytes transitioning to pro-fibrotic inflammatory macrophages in STNx kidneys. Unlike 129S2/SV mice, C57BL/6 mice exhibited renal fibrosis without proteinuria, renal dysfunction, or cardiac pathology. Therefore, the 129S2/SV genetic background is susceptible to induction of progressive proteinuric renal disease and cardiac hypertrophy using our refined, single-step flank STNx method. This reproducible model could be used to study the systemic pathophysiological changes induced by CKD in the kidney and the heart, intra-renal inflammation and for testing new therapies for CKD.

Inactivation of Tsc2 in Abcg2 lineage-derived cells drives the appearance of polycystic lesions and fibrosis in the adult kidney

Tuberous sclerosis complex 2 (TSC2), or tuberin, is a pivotal regulator of the mechanistic target of rapamycin signaling pathway that controls cell survival, proliferation, growth, and migration. Loss of Tsc2 function manifests in organ-specific consequences, the mechanisms of which remain incompletely understood. Recent single cell analysis of the kidney has identified ATP-binding cassette G2 (Abcg2) expression in renal proximal tubules of adult mice as well as a in a novel cell population. The impact in adult kidney of Tsc2 knockdown in the Abcg2-expressing lineage has not been evaluated. We engineered an inducible system in which expression of truncated Tsc2, lacking exons 36-37 with an intact 3' region and polycystin 1, is driven by Abcg2. Here, we demonstrate that selective expression of Tsc2fl36-37 in the Abcg2pos lineage drives recombination in proximal tubule epithelial and rare perivascular mesenchymal cells, which results in progressive proximal tubule injury, impaired kidney function, formation of cystic lesions, and fibrosis in adult mice. These data illustrate the critical importance of Tsc2 function in the Abcg2-expressing proximal tubule epithelium and mesenchyme during the development of cystic lesions and remodeling of kidney parenchyma.

Thrombospondin 1 and Its Diverse Roles as a Regulator of Extracellular Matrix in Fibrotic Disease

Thrombospondin 1 (TSP1) is a matricellular extracellular matrix protein that has diverse roles in regulating cellular processes important for the pathogenesis of fibrotic diseases. We will present evidence for the importance of TSP1 control of latent transforming growth factor beta activation in renal fibrosis with an emphasis on diabetic nephropathy. Other functions of TSP1 that affect renal fibrosis, including regulation of inflammation and capillary density, will be addressed. Emerging roles for TSP1 N-terminal domain regulation of collagen matrix assembly, direct effects of TSP1-collagen binding, and intracellular functions of TSP1 in mediating endoplasmic reticulum stress responses in extracellular matrix remodeling and fibrosis, which could potentially affect renal fibrogenesis, will also be discussed. Finally, we will address possible strategies for targeting TSP1 functions to treat fibrotic renal disease.

Epithelial-fibroblast cross talk aggravates the impact of the nephrotoxin ochratoxin A

BACKGROUND

Chronic nephropathies result from different pathogenic agents, including nutritional factors triggering vicious pathophysiological cycles. Ochratoxin A (OTA) is a globally occurring nephrotoxic mycotoxin detectable in a variety of foodstuff and suspected to cause tubulointerstitial damage. The underlying mechanisms are not sufficiently understood, compromising risk assessment. Because crosstalk of proximal tubule cells with fibroblasts is crucial for tubulointerstitial damage, we investigated the effects of OTA in co-culture of these two cell types.

METHODS

Rat renal proximal tubule cells (NRK-52E) and renal fibroblasts (NRK-49F) were exposed to nanomolar OTA concentrations under mono- and/or co-culture conditions for up to 48 h. We determined the impact on inflammation-, EMT- and fibrosis-associated proteins as well as microRNAs by western blot or qPCR, respectively. Alterations in cell morphology were quantitatively assessed. The roles of miRs, COX-2 and ERK1/2 in OTA-induced effects were investigated by specific inhibition.

FINDINGS

Only under co-culture condition, OTA caused an increase of vimentin, fibronectin and miR-21 and a decrease of collagen III, E-cadherin, COX-2 and WISP1 mRNA abundance in NRK-52E cells. In NRK-49F cells, OTA induced an increase of N-cadherin, COX-2, WISP1 in co-culture only. The OTA-induced increase of fibronectin in NRK-52E cells was prevented by simultaneous inhibition of miR-21 and -200a, COX-2 or ERK1/2. The OTA-induced increase of COX-2 in NRK-49F cells was prevented by inhibition of miR-21 and -200a or ERK1/2.

INTERPRETATION

Our results show that the complete nephropathic potential of nanomolar OTA, leading to EMT, is unveiled when cellular crosstalk is possible. In monoculture, the nephropathic potential is underestimated.

RESEARCH IN CONTEXT

Chronic nephropathies are a severe health burden and the result of different pathogenic mechanisms, including nutritional factors that trigger vicious pathophysiological cycles. Ochratoxin A (OTA) is a ubiquitous, globally occurring nephrotoxic mycotoxin detectable in a variety of foodstuff and suspected to cause tubulointerstitial damage. Because underlying pathomechanisms are unclear, risk assessment is problematic. Crosstalk of proximal tubule cells (the main target of OTA) with fibroblasts is crucial for the development of tubulointerstitial damage. We show that during co-culture of proximal tubule cells and fibroblasts, OTA-induced effects (e.g. epithelial-mesenchymal transition (EMT)) change significantly as compared to monoculture. Our results show that the complete nephropathic potential of OTA is unveiled when cellular crosstalk is possible. In monoculture, the nephropathic potential of OTA is underestimated.

Health Benefits of Resveratrol in Kidney Disease: Evidence from In Vitro and In Vivo Studies

Different diseases and disorders that affect the kidneys include, but are not limited to, glomerulonephritis, diabetic nephropathy, polycystic kidney disease, kidney stones, renal fibrosis, sepsis, and renal cell carcinoma. Kidney disease tends to develop over many years, making it difficult to identify until much later when kidney function is severely impaired and undergoing kidney failure. Although conservative care, symptom management, medication, dialysis, transplantation, and aggressive renal cancer therapy are some of the current strategies/approaches to kidney disease treatment, new preventative targeted therapies are needed. Epidemiological studies have suggested that a diet rich in fruits and vegetables is associated with health benefits including protection against kidney disease and renal cancer. Resveratrol, a polyphenol found in grapes and berries, has been reported to have antioxidant, anti-inflammatory, antidiabetic, hepatoprotective, neuroprotective, and anti-cancer properties. The current review summarizes the existing in vitro and in vivo animal and human studies examining the nephroprotective effects of resveratrol.

Pathological Characteristics of Periodontal Disease in Patients with Chronic Kidney Disease and Kidney Transplantation

Chronic kidney disease (CKD) is recognized as an irreversible reduction of functional nephrons and leads to an increased risk of various pathological conditions, including cardiovascular disease and neurological disorders, such as coronary artery calcification, hypertension, and stroke. In addition, CKD patients have impaired immunity against bacteria and viruses. Conversely, kidney transplantation (KT) is performed for patients with end-stage renal disease as a renal replacement therapy. Although kidney function is almost normalized by KT, immunosuppressive therapy is essential to maintain kidney allograft function and to prevent rejection. However, these patients are more susceptible to infection due to the immunosuppressive therapy required to maintain kidney allograft function. Thus, both CKD and KT present disadvantages in terms of suppression of immune function. Periodontal disease is defined as a chronic infection and inflammation of oral and periodontal tissues. Periodontal disease is characterized by the destruction of connective tissues of the periodontium and alveolar bone, which may lead to not only local symptoms but also systemic diseases, such as cardiovascular diseases, diabetes, liver disease, chronic obstructive pulmonary disease, and several types of cancer. In addition, the prevalence and severity of periodontal disease are significantly associated with mortality. Many researchers pay special attention to the pathological roles and clinical impact of periodontal disease in patients with CKD or KT. In this review, we provide information regarding important modulators of periodontal disease to better understand the relationship between periodontal disease and CKD and/or KT. Furthermore; we evaluate the impact of periodontal disease on various pathological conditions in patients with CKD and KT. Moreover, pathogens of periodontal disease common to CKD and KT are also discussed. Finally, we examine the importance of periodontal care in these patients. Thus, this review provides a comprehensive overview of the pathological roles and clinical significance of periodontal disease in patients with CKD and KT.

Telbivudine antagonizes TLR4 to inhibit the epithelial-to-mesenchymal transition in human proximal tubular epithelial cells in vitro

The antiviral drug Telbivudine (LdT) has an extrahepatic pharmaceutical effect that improves renal inflammation and tubulointerstitial fibrosis. However, the exact mechanism of action requires further investigation. Toll-like receptor 4 (TLR4) is involved in several physiological processes, including inflammation, fibrosis, innate immunity, and hepatitis B virus-associated glomerulonephritis. The epithelial-to-mesenchymal transition (EMT) is the characteristic pathological change in tubulointerstitial fibrosis. In this study, we used transforming growth factor-β (TGF-β) to stimulate human proximal tubular epithelial (HK-2) cells to investigate the effects of LdT in EMT. In addition, we treated HK-2 cells with a TLR4 agonist, lipopolysaccharide, to determine the effect of LdT on TLR4. The results indicated that LdT inhibited the expression of TLR4 and its downstream proteins. It also decreased the release of inflammatory factors, downregulated the TGF-β/Smad signaling pathway, and reversed the EMT changes seen in HK-2 cells. In conclusion, LdT antagonized TLR4 to inhibit EMT in proximal tubular epithelial cells.

Immunoglobulin light chains generate proinflammatory and profibrotic kidney injury

Because of the less-than-robust response to therapy and impact on choice of optimal chemotherapy and prognosis, chronic kidney disease has drawn attention in the treatment of multiple myeloma, a malignant hematologic disorder that can produce significant amounts of monoclonal immunoglobulin free light chains (FLCs). These low-molecular-weight proteins are relatively freely filtered through the glomerulus and are reabsorbed by the proximal tubule. The present study demonstrated that during the process of metabolism of immunoglobulin FLCs, ROS activated the STAT1 pathway in proximal tubule epithelium. STAT1 activation served as the seminal signaling molecule that produced the proinflammatory molecule IL-1β, as well as the profibrotic agent TGF-β by this portion of the nephron. These effects occurred in vivo and were produced specifically by the generation of hydrogen peroxide by the VL domain of the light chain. To the extent that the experiments reflect the human condition, these studies offer insights into the pathogenesis of progressive kidney failure in the setting of lymphoproliferative disorders, such as multiple myeloma, that feature increased circulating levels of monoclonal immunoglobulin fragments that require metabolism by the kidney.

Nephropathy induced by renal microembolism: a characterization of biochemical and histopathological changes in rats

The aim of this study was to investigate some biochemical parameters of renal function and the vascular, glomerular, tubular, and interstitial manifestations in the progression of nephropathy induced by renal microembolism. Renal microembolism was induced by the arterial injection of polymethacrylate microspheres in the remnant kidney of nephrectomized rats. Animals 110-120 days old were randomly divided into three groups: the control group (C; normal), the nephrectomized group (S; nephrectomized that did not undergo renal microembolism), and the model group (M, nephrectomized animals that underwent renal arterial microembolism). The animals were evaluated 30, 60, and 90 days after the induction of a renal microembolism. Blood and urine samples were collected to determine serum creatinine (Cr) and urea (Ur) concentrations and urine total protein (Pt) concentrations. The kidneys were weighed and processed for histopathological analysis using hematoxylin and eosin (HE), periodic acid-Schiff (PAS), Mallory-Azan, and Picro-Sirius staining. The samples were also subjected to immunohistochemistry with a proliferating cell nuclear antigen (PCNA) and a vascular endothelial growth factor receptor (VEGFR). The data demonstrated evidence of the occurrence of vascular, glomerular, tubular, and interstitial abnormalities in the renal tissue, and changes in the biochemical parameters of renal function (serum Cr and Ur and of 24-h urine Pt) in this experimental model of nephropathy induced by renal microembolism, which may indicate the development of chronic kidney disease (CKD). Additionally, the findings indicate that this is a good reproducibility model that may be useful for studying the pathogenesis of CKD that is caused by atheroembolism and possible treatment alternatives.

Advanced Oxidation Protein Products Aggravate Tubulointerstitial Fibrosis Through Protein Kinase C-Dependent Mitochondrial Injury in Early Diabetic Nephropathy

AIMS

Diabetic nephropathy (DN) is the most common microvascular complications and the principal cause of mortality and morbidity rates in patients with diabetes. The expression of advanced oxidation protein products (AOPPs) has been found in vacuolated renal tubules in DN and correlated with patients' decreased renal function. The accumulation of AOPPs is regarded as an initiating factor in podocyte injuries via the protein kinase C (PKC) signaling, which plays a critical role in triggering oxidative stress and mitochondrial injuries in diseases including DN. Whether AOPPs could induce mitochondrial injuries and fibrosis in renal tubules remains largely unknown. Herein, we tested the hypothesis that the accumulation of AOPPs in diabetes incurs mitochondrial dysfunction and oxidative stress, causing renal tubulointerstitial fibrosis (TIF) via PKC signaling pathway.

RESULTS

In vivo, intrarenal AOPPs accumulation correlated with oxidative stress, renal fibrosis, proteinuria, and declined renal function in DN patients and diabetic rats. AOPPs-induced mitochondrial injuries, apoptosis, and TIF were significantly mitigated by PKCη inhibition in diabetic rats. In vitro, high glucose (HG) stimulated AOPP expression and augmented PKC-mediated oxidative stress and fibrosis in HK-2 cells. Furthermore, we provide mechanistic evidence that inhibition of PKCη isoform alleviated mitochondrial injuries and function, attenuated apoptosis, and renal fibrosis in HG-cultured AOPPs-induced HK-2 cells. Innovation and Conclusion: We propose a novel mechanism that AOPPs-induced mitochondrial dysfunction and oxidative stress cause TIF in DN via activation of the PKCη isoform.

Reduced asymmetric dimethylarginine accumulation through inhibition of the type I protein arginine methyltransferases promotes renal fibrosis in obstructed kidneys

The role of asymmetric dimethylarginine (ADMA) in chronic kidney disease (CKD) is unclear. Through inhibition of type I protein arginine methyltransferases (PRMTs), a novel strategy, we aimed to determine the effect of ADMA on renal fibrosis and explore its underlying working mechanisms. After sham or unilateral ureter ligation (UUO) operation, 20-25 g male c57 mice were treated with vehicle or PT1001B, an inhibitor of type I PRMTs, for 13 d. Moreover, human kidney 2 (HK2) and normal rat kidney 49F (NRK-49F) cells were treated with various concentrations of PT1001B or ADMA in the presence of 2.5 ng/ml TGF-β. We found that treatment with PT1001B increased the deposition of extracellular matrix proteins, the expression of α smooth muscle actin, and connective tissue growth factor in UUO-induced fibrotic kidneys, which is correlated with reduced expression of PRMT1, reduced the production of ADMA, and increased expression of uromodulin. In TGF-β-stimulated HK2 and NRK-49F cells, PT1001B dose-dependently inhibited ADMA production, increased NO concentrations, and enhanced the expression of profibrotic proteins. Exogenous addition of ADMA inhibited the expression of profibrotic proteins dose-dependently and attenuated the profibrotic effect of PT1001B. Moreover, ADMA reduced the NO concentration in PT1001B-treated HK2 cells. Finally, we conclude that ADMA has an antifibrotic effect in obstructed kidneys, and future application of type I PRMT inhibitor should be done cautiously for patients with CKD.-Wu, M., Lin, P., Li, L., Chen, D., Yang, X., Xu, L., Zhou, B., Wang, C., Zhang, Y., Luo, C., Ye, C. Reduced asymmetric dimethylarginine accumulation through inhibition of the type I protein arginine methyltransferases promotes renal fibrosis in obstructed kidneys.

Peroxidasin and eosinophil peroxidase, but not myeloperoxidase, contribute to renal fibrosis in the murine unilateral ureteral obstruction model

Renal fibrosis is the pathological hallmark of chronic kidney disease (CKD) and manifests as glomerulosclerosis and tubulointerstitial fibrosis. Reactive oxygen species contribute significantly to renal inflammation and fibrosis, but most research has focused on superoxide and hydrogen peroxide (H2O2). The animal heme peroxidases myeloperoxidase (MPO), eosinophil peroxidase (EPX), and peroxidasin (PXDN) uniquely metabolize H2O2 into highly reactive and destructive hypohalous acids, such as hypobromous and hypochlorous acid. However, the role of these peroxidases and their downstream hypohalous acids in the pathogenesis of renal fibrosis is unclear. Our study defines the contribution of MPO, EPX, and PXDN to renal inflammation and tubulointerstitial fibrosis in the murine unilateral ureteral obstruction (UUO) model. Using a nonspecific inhibitor of animal heme peroxidases and peroxidase-specific knockout mice, we find that loss of EPX or PXDN, but not MPO, reduces renal fibrosis. Furthermore, we demonstrate that eosinophils, the source of EPX, accumulate in the renal interstitium after UUO. These findings point to EPX and PXDN as potential therapeutic targets for renal fibrosis and CKD and suggest that eosinophils modulate the response to renal injury.

Autophagy attenuates tubulointerstital fibrosis through regulating transforming growth factor-β and NLRP3 inflammasome signaling pathway

Renal fibrosis is the final common pathway of various renal injuries and it leads to chronic kidney disease. Autophagy is a cellular process of degradation of damaged cytoplasmic components and regulates cell death and proliferation. Cellular response during unilateral ureteral obstruction (UUO) is tubular segment specific. Thus the role of autophagy on renal tubulointerstitial fibrosis (TIF) after UUO may be different according to segment of nephron. The role of autophagy during UUO remains unclear especially in distal tubules. In this study, we investigated the role of autophagy in distal tubules on renal TIF using conditional knockout mice in which Atg7 was genetically ablated specifically in distal tubular epithelial cell (TEC). In green fluorescent protein (GFP)-LC3 transgenic mice, GFP-LC3 puncta was highly expressed in distal tubular cells of the obstructed kidneys after UUO. Genetic deletion of Atg7 specifically in distal TEC increased renal tubulointerstial fibrosis and epithelial-mesenchymal transition-like phenotype change after UUO through Smad4-dependent transforming growth factor (TGF)-β pathway. Distal tubule-specific autophagy-deficient mice increased the accumulation of damaged mitochondria and SQSTM1/p62-positive aggregates in the obstructed kidney and resulted in increased expression of NLRP3 inflammasome, interleukin (IL) 1-β and caspase-1. Distal TEC-specific Atg7 deletion enhanced apoptosis of TECs after UUO. In summary, our data showed that autophagy in distal TEC plays a protective role in development of renal tubulointerstial fibrosis through regulating the expression of TGF-β an IL1-β after UUO.

Inflammatory Mediators and Renal Fibrosis

Renal inflammation is the initial, healthy response to renal injury. However, prolonged inflammation promotes the fibrosis process, which leads to chronic pathology and eventually end-stage kidney disease. There are two major sources of inflammatory cells: first, bone marrow-derived leukocytes that include neutrophils, macrophages, fibrocytes and mast cells, and second, locally activated kidney cells such as mesangial cells, podocytes, tubular epithelial cells, endothelial cells and fibroblasts. These activated cells produce many profibrotic cytokines and growth factors that cause accumulation and activation of myofibroblasts, and enhance the production of the extracellular matrix. In particular, activated macrophages are key mediators that drive acute inflammation into chronic kidney disease. They produce large amounts of profibrotic factors and modify the microenvironment via a paracrine effect, and they also transdifferentiate to myofibroblasts directly, although the origin of myofibroblasts in the fibrosing kidney remains controversial. Collectively, understanding inflammatory cell functions and mechanisms during renal fibrosis is paramount to improving diagnosis and treatment of chronic kidney disease.

How Tubular Epithelial Cell Injury Contributes to Renal Fibrosis

The renal tubules are the major component of the kidney and are vulnerable to a variety of injuries including ischemia, proteinuria, toxins, and metabolic disorders. It has long been believed that tubules are the victim of injury. In this review, we shift this concept to renal tubules as a driving force in the progression of kidney disease. In response to injury, tubular epithelial cells (TECs) can synthesize and secrete varieties of bioactive molecules that drive interstitial inflammation and fibrosis. Innate immune-sensing receptors on the TECs also aggravate immune responses. Necroinflammation, an auto-amplification loop between tubular cell death and interstitial inflammation, leads to the exacerbation of renal injury. Furthermore, TECs also play an active role in progressive renal injury via mechanisms associated with the conversion into collagen-producing fibroblast phenotype, cell cycle arrest at both G1/S and G2/M checkpoints, and metabolic disorder. Thus, a better understanding the mechanisms by which tubular injury drives AKI and CKD is necessary for the development of therapeutics to halt the progression of CKD.

How Acute Kidney Injury Contributes to Renal Fibrosis

Acute kidney injury (AKI) is a widespread clinical syndrome directly associated with patient short-term and long-term morbidity and mortality. During the last decade, the incidence rate of AKI has been increasing, the repeated and severe episodes of AKI have been recognized as a major risk factor chronic kidney diseases (CKD) and end-stage kidney disease (ESRD) leading to global disease burden. Proposed pathological processes and risk factors that add to the transition of AKI to CKD and ESRD include severity and frequency of kidney injury, older age, gender, genetics and chronic health conditions like diabetes, hypertension, and obesity. Therefore, there is a great interest in learning about the mechanism of AKI leading to renal fibrosis, the ultimate renal lesions of CKD. Over the last several years, a significant attention has been given to the field of renal fibrosis with impressive progression in knowing the mechanism of renal fibrosis to detailed cellular characterization and molecular pathways implicated in tubulointerstitial fibrosis. Research and clinical trial are underway for emerging biomarkers detecting early kidney injury, predicting kidney disease progression and developing strategies to efficiently treat AKI and to minimize AKI progression to CKD and ESRD. Specific interventions to prevent renal fibrosis are still experimental. Potential therapeutic advances based on those molecular mechanisms will hopefully offer promising insights into the development of new therapeutic interventions for patients in the near future.

Jian-Pi-Yi-Shen Formula ameliorates chronic kidney disease: involvement of mitochondrial quality control network

BACKGROUND

Jian-Pi-Yi-Shen Formula (JPYSF), a Chinese herbal decoction with the efficacies of 'fortify the spleen and tonify the kidney' and 'activate blood and resolve stasis', is effective for the treatment of chronic kidney disease in clinic. However, the underlying mechanism remains unclear. The aim of this study was to investigate the therapeutic effects and possible mechanisms of JPYSF on retarding chronic kidney disease progression in 5/6 nephrectomized (5/6 Nx) rats.

METHODS

Perindopril (4 mg/kg/d) and JPYSF (2.72 g/kg/d) were administrated by gavage to 5/6 Nx rats daily for 6 weeks. The therapeutic effects of JPYSF were evaluated by renal function, pathological injury, and fibrosis. The protein levels associated with mitochondrial quality control network were measured by Western blot and immunofluorescence analysis.

RESULTS

5/6 Nx rats showed obvious decline in renal function as evidenced by increased serum creatinine, blood urea nitrogen, and urinary protein excretion, and significant injury in kidney structure as evidenced by glomerular hypertrophy, tubular atrophy, and interstitial fibrosis. Administration of JPYSF for 6 weeks could improve renal function and ameliorate kidney structure injury in 5/6 Nx rats. Furthermore, the remnant kidneys of 5/6 Nx rats showed unbalanced mitochondrial quality control network manifested as decreased mitochondrial biogenesis, fusion, and mitophagy, and increased mitochondrial fission. Treatment of JPYSF could restore aforesaid aspects of mitochondrial quality control network.

CONCLUSIONS

These results indicate that JPYSF can notably ameliorate 5/6 Nx-induced chronic kidney disease, which may be related with modulation of mitochondrial quality control network.

Renal tubular epithelial cells: the neglected mediator of tubulointerstitial fibrosis after injury

Renal fibrosis, especially tubulointerstitial fibrosis, is the inevitable outcome of all progressive chronic kidney diseases (CKDs) and exerts a great health burden worldwide. For a long time, interests in renal fibrosis have been concentrated on fibroblasts and myofibroblasts. However, in recent years, growing numbers of studies have focused on the role of tubular epithelial cells (TECs). TECs, rather than a victim or bystander, are probably a neglected mediator in renal fibrosis, responding to a variety of injuries. The maladaptive repair mechanisms of TECs may be the key point in this process. In this review, we will focus on the role of TECs in tubulointerstitial fibrosis. We will follow the fate of a tubular cell and depict the intracellular changes after injury. We will then discuss how the repair mechanism of tubular cells becomes maladaptive, and we will finally discuss the intercellular crosstalk in the interstitium that ultimately proceeds tubulointerstitial fibrosis.

Mechanism of Fibrosis in HNF1B-Related Autosomal Dominant Tubulointerstitial Kidney Disease

BACKGROUND

Mutation of HNF1B, the gene encoding transcription factor HNF-1β, is one cause of autosomal dominant tubulointerstitial kidney disease, a syndrome characterized by tubular cysts, renal fibrosis, and progressive decline in renal function. HNF-1β has also been implicated in epithelial-mesenchymal transition (EMT) pathways, and sustained EMT is associated with tissue fibrosis. The mechanism whereby mutated HNF1B leads to tubulointerstitial fibrosis is not known.

METHODS

To explore the mechanism of fibrosis, we created HNF-1β-deficient mIMCD3 renal epithelial cells, used RNA-sequencing analysis to reveal differentially expressed genes in wild-type and HNF-1β-deficient mIMCD3 cells, and performed cell lineage analysis in HNF-1β mutant mice.

RESULTS

The HNF-1β-deficient cells exhibited properties characteristic of mesenchymal cells such as fibroblasts, including spindle-shaped morphology, loss of contact inhibition, and increased cell migration. These cells also showed upregulation of fibrosis and EMT pathways, including upregulation of Twist2, Snail1, Snail2, and Zeb2, which are key EMT transcription factors. Mechanistically, HNF-1β directly represses Twist2, and ablation of Twist2 partially rescued the fibroblastic phenotype of HNF-1β mutant cells. Kidneys from HNF-1β mutant mice showed increased expression of Twist2 and its downstream target Snai2. Cell lineage analysis indicated that HNF-1β mutant epithelial cells do not transdifferentiate into kidney myofibroblasts. Rather, HNF-1β mutant epithelial cells secrete high levels of TGF-β ligands that activate downstream Smad transcription factors in renal interstitial cells.

CONCLUSIONS

Ablation of HNF-1β in renal epithelial cells leads to the activation of a Twist2-dependent transcriptional network that induces EMT and aberrant TGF-β signaling, resulting in renal fibrosis through a cell-nonautonomous mechanism.

Renal fibrosis: Primacy of the proximal tubule

Tubulointerstitial fibrosis (TIF) is the hallmark of chronic kidney disease and best predictor of renal survival. Many different cell types contribute to TIF progression including tubular epithelial cells, myofibroblasts, endothelia, and inflammatory cells. Previously, most of the attention has centered on myofibroblasts given their central importance in extracellular matrix production. However, emerging data focuses on how the response of the proximal tubule, a specialized epithelial segment vulnerable to injury, plays a central role in TIF progression. Several proximal tubular responses such as de-differentiation, cell cycle changes, autophagy, and metabolic changes may be adaptive initially, but can lead to maladaptive responses that promote TIF both through autocrine and paracrine effects. This review discusses the current paradigm of TIF progression and the increasingly important role of the proximal tubule in promoting TIF both in tubulointerstitial and glomerular injuries. A better understanding and appreciation of the role of the proximal tubule in TIF has important implications for therapeutic strategies to halt chronic kidney disease progression.

A blockade of PI3Kγ signaling effectively mitigates angiotensin II-induced renal injury and fibrosis in a mouse model

Chronic kidney disease (CKD) poses a formidable challenge for public healthcare worldwide as vast majority of patients with CKD are also at risk of accelerated cardiovascular disease and death. Renal fibrosis is the common manifestation of CKD that usually leads to end-stage renal disease although the molecular events leading to chronic renal fibrosis and eventually chronic renal failure remain to be fully understood. Nonetheless, emerging evidence suggests that an aberrant activation of PI3Kγ signaling may play an important role in regulating profibrotic phenotypes. Here, we investigate whether a blockade of PI3Kγ signaling exerts any beneficial effect on alleviating kidney injury and renal fibrosis. Using a mouse model of angiotensin II (Ang II)-induced renal damage, we demonstrate that PI3Kγ inhibitor AS605240 effectively mitigates Ang II-induced increases in serum creatinine and blood urea nitrogen, renal interstitial collagen deposition, the accumulation of ECM proteins and the expression of α-Sma and fibrosis-related genes in vivo. Mechanistically, we reveal that AS605240 effectively inhibits Ang II-induced cell proliferation and phosphorylation of Akt in fibroblast cells. Furthermore, we demonstrate that Ang II-upregulated expression of IL-6, Tnf-α, IL-1β and Tgf-β1 is significantly attenuated in the mice treated with AS605240. Taken together, our results demonstrate that PI3Kγ may function as a critical mediator of Ang II-induced renal injury and fibrosis. It is thus conceivable that targeted inhibition of PI3Kγ signaling may constitute a novel therapeutic approach to the clinical management of renal fibrosis, renal hypertension and/or CKD.

Cellular and molecular mechanisms of kidney fibrosis

Renal fibrosis is the final pathological process common to any ongoing, chronic kidney injury or maladaptive repair. It is considered as the underlying pathological process of chronic kidney disease (CKD), which affects more than 10% of world population and for which treatment options are limited. Renal fibrosis is defined by excessive deposition of extracellular matrix, which disrupts and replaces the functional parenchyma that leads to organ failure. Kidney's histological structure can be divided into three main compartments, all of which can be affected by fibrosis, specifically termed glomerulosclerosis in glomeruli, interstitial fibrosis in tubulointerstitium and arteriosclerosis and perivascular fibrosis in vasculature. In this review, we summarized the different appearance, cellular origin and major emerging processes and mediators of fibrosis in each compartment. We also depicted and discussed the challenges in translation of anti-fibrotic treatment to clinical practice and discuss possible solutions and future directions.

Advances in early biomarkers of diabetic nephropathy

Diabetic nephropathy is the main cause of chronic kidney disease, and represents the most common and serious complication of diabetes. The exact pathogenesis is complex and not elucidated. Several factors and mechanisms contribute to the development and outcome of diabetic nephropathy. An early diagnosis and intervention may slow down disease progression. A variety of biological markers associated with diabetic nephropathy were found in recent years, which was important for predicting the occurrence and development of the disease. Therefore, this article provides an overview of early biomarkers that are associated with diabetic nephropathy.