Podocyte injury and repair mechanisms

Relationship between time to clinical remission and relapse in adults with steroid-sensitive minimal change disease: a retrospective cohort study

OBJECTIVE

Minimal change disease (MCD) is a common nephrotic syndrome that is usually steroid-sensitive and has high relapse rate. The aim of this study was to investigate the relationship between time to clinical remission and recurrence after the initial steroid therapy.

METHODS

Among 305 adult patients diagnosed with MCD via light and electron microscopy, sensitive to steroids, and hospitalized for nephrotic syndrome in the Department of Nephrology of the Affiliated Hospital of Guangdong Medical University in China, 88 were included in this retrospective cohort study. Cox regression analysis was performed with time to clinical remission and 24-hour urine protein quantification (24 hUTP), absolute basophil (BA) and basophil percentage (BA%) as independent variables. Independent variables with significant differences and the time to remission were used to construct a Cox regression model to exclude the influence of confounding factors. The receiver operating characteristic (ROC) curve was plotted according to the independent variable of time to clinical remission.

RESULTS

No significant differences were found between the relapse and non-relapse groups in terms of sex, age at onset, or prevalent hypertension. There were significant differences in time to clinical remission, 24 hUTP, BA and BA% between the relapse and non-relapse groups. The risk of recurrence was significantly higher in patients with clinical remission of 15-21, 22-28 and 29-56 days than in those who had clinical remission of 1-7 days. In addition, patients with clinical remission of >26.5 days had a significantly higher risk of recurrence than those in the other groups.

CONCLUSIONS

Overall, the time of clinical remission is a potential factor for predicting the recurrence of steroid-sensitive MCD in adults.

Protopanaxadiol synergizes with glucocorticoids to enhance the therapeutic effect in adriamycin-induced nephrotic syndrome

To date, glucocorticoids remain the mainstay of treatment of nephrotic syndrome (NS). However, serious side effects and development of drug-resistance following long-term use limit the application of glucocorticoids. Protopanaxadiol (PPD) possesses activity of dissociating transactivation from transrepression by glucocorticoid receptor (GR), which may serve as a potential selective GR modulator. However, steroid-like effects of PPD in vivo are unclear and not defined. How to translate PPD into clinical practice remains to be explored. The current study explored the renoprotection and potential mechanism of PPD and its combination with steroid hormones using adriamycin-induced NS rats. Adriamycin was given intravenously to rats to induce nephropathy. The determination of proteinuria, biochemical changes and inflammatory cytokines were performed, and pathological changes were examined by histopathological examination. Immunostaining and PCR were used to analyze the expression of interesting proteins and genes. The results showed that PPD, alone and in combination with prednisone, efficiently alleviate the symptoms of NS, attenuate nephropathy, improve adriamycin-induced podocyte injury by reducing desmin and increasing synaptopodin expression. In addition, the combined treatment reduced the expression of NF-κB protein and mRNA, as well as cytokine levels, and yet increased the expression of GR protein and mRNA. PPD modulated the transactivation of GR, manifested as repressing TAT, PEPCK and ANGPTL4 mRNA expressions mediated by GR. Meanwhile, PPD inhibited elevation of blood glucose and immune organ atrophy induced by prednisone. In summary, PPD increases the therapeutic effect of prednisone in NS while effectively prevents or decreases the appearance of side effects of glucocorticoids.

Blood pressure targets for hypertension in people with chronic renal disease

BACKGROUND

Chronic kidney disease (CKD) is an independent risk factor for cardiovascular disease, development of end-stage renal disease, and all-cause mortality. It affects around 10% of the population worldwide. The prevalence of hypertension in people with CKD ranges from 22% in stage 1 to 80% in stage 4. Elevated arterial blood pressure is one of the major independent risk factors for adverse cardiovascular events. Thereby, reducing blood pressure to below standard targets may be beneficial but could also increase the risk of adverse events. The optimal blood pressure target in people with hypertension and CKD remains unknown.

OBJECTIVES

Primary: to compare the effects of standard and lower-than-standard blood pressure targets for hypertension in people with chronic kidney disease on mortality and morbidity outcomes. Secondary: to assess the magnitude of reductions in systolic and diastolic blood pressure, the proportion of participants reaching blood pressure targets, and the number of drugs necessary to achieve the assigned target.

SEARCH METHODS

We used standard, extensive Cochrane search methods. We searched the Cochrane Hypertension Specialized Register, CENTRAL, MEDLINE, Embase, one other database, and two trial registers up to 8 February 2023. We also contacted authors of relevant papers regarding further published and unpublished work. We applied no language restrictions.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) in people with hypertension and CKD that provided at least twelve months' follow-up. Eligible interventions compared lower targets for systolic/diastolic blood pressure (130/80 mmHg or lower) to standard targets for blood pressure (140 to 160/90 to 100 mmHg or lower). Participants were adults with CKD and elevated blood pressure documented in a standard way on at least two occasions, or already receiving treatment for elevated blood pressure.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methods. Our critical outcomes were: total mortality, total serious adverse events, total cardiovascular events, cardiovascular mortality, and progression to end-stage renal disease. Important outcomes were: participant withdrawals due to adverse effects, and number of participants with a doubling of serum creatinine level or at least a 50% reduction in the glomerular filtration rate (GFR) at the end of the study. We used GRADE to assess the certainty of the evidence for the critical outcomes. This review received no funding.

MAIN RESULTS

We included six RCTs that contributed data for meta-analysis, involving 7348 participants overall (range 840 to 4733 people per study). The mean follow-up was 3.6 years (range 1.0 to 8.0 years). Three studies were publicly funded, two were privately funded, and one had both public and private funding. All RCTs provided individual participant data. None of the included studies blinded participants or clinicians because of the need to titrate antihypertensive drugs to reach a specific blood pressure target. However, an independent committee blinded to group allocation assessed clinical events in all studies. Critical outcomes. Compared with standard blood pressure targets, lower targets likely result in little to no difference in total mortality (risk ratio (RR) 0.90, 95% confidence interval (CI) 0.76 to 1.06; 6 studies, 7348 participants), total serious adverse events (RR 1.01, 95% CI 0.94 to 1.08; 6 studies, 7348 participants), and total cardiovascular events (RR 1.00, 95% CI 0.87 to 1.15; 5 studies, 6508 participants), all with moderate-certainty evidence. Compared with standard blood pressure targets, lower targets may result in little to no difference in cardiovascular mortality (RR 0.90, 95% CI 0.70 to 1.16; 6 studies, 7348 participants) and progression to end-stage renal disease (RR 0.94, 95% CI 0.80 to 1.11; 4 studies, 4788 participants), both with low-certainty evidence. Important outcomes. We found little to no differences in: participant withdrawals due to adverse effects; and the number of participants with a doubling of serum creatinine level, or at least a 50% reduction in GFR at the end of the study. Exploratory outcomes. Compared to the standard blood pressure target groups, participants in the lower target groups achieved lower systolic and diastolic blood pressure values after one year, and required a higher number of antihypertensive drugs at the end of the studies. A higher proportion of participants in the standard blood pressure target groups achieved the targets they were assigned than did participants in the intensive target groups.

AUTHORS' CONCLUSIONS

Compared to a standard blood pressure target, lower blood pressure targets probably result in little to no difference in total mortality, total serious adverse events, and total cardiovascular events, and may result in little to no difference in total cardiovascular mortality or in the progression to end-stage renal disease in people with hypertension and CKD. However, the evidence underpinning these conclusions has several limitations. All studies were open design, blood pressure measurement was performed at a medical office, and there was scant information about adverse events. Future research should include high-quality adverse event data, report results for people with different levels of proteinuria, and consider out-of-office blood pressure monitoring. Several studies are ongoing, and may provide new evidence for this topic in the near future.

Polygala fallax Hemsl. ameliorated high glucose-induced podocyte injury by modulating mitochondrial mPTP opening through the SIRT1/PGC-1α pathway

This study aimed to investigate the effects and molecular mechanism of PF on high glucose (HG)-induced podocyte injury. Results found that PF increased proliferation activity, decreased apoptosis, LDH, and caspase-3 levels, and increased nephrin and podocin expression in HG-induced cells. Similarly, PF improved HG-induced mitochondrial damage, decreased Ca2+ and ROS content, alleviated oxidative stress, inhibited mPTP opening, increased mitochondrial membrane potential, and decreased the expressions of Drp1, Bak, Bax, and Cytc in cytoplasm, increased the expressions of SIRT1, PGC-1α, HSP70, HK2, and Cytc in mitochondria of podocytes. The use of mPTP agonist/blocker and SIRT1 inhibitor confirmed that PF alleviates HG-induced podocyte injury by regulating mitochondrial mPTP opening through SIRT1/PGC-1α. In addition, PF affected HK2-VDAC1 protein binding to regulate mPTP opening via the SIRT1/PGC-1α pathway. In conclusion, PF-regulated HK2-VDAC1 protein binding affected mitochondrial mPTP opening and improved HG-induced podocyte injury through the SIRT1/PGC-1α pathway.

Brain-Derived Neurotrophic Factor-Loaded Low-Temperature-Sensitive liposomes as a drug delivery system for repairing podocyte damage

Podocytes, cells of the glomerular filtration barrier, play a crucial role in kidney diseases and are gaining attention as potential targets for new therapies. Brain-Derived Neurotrophic Factor (BDNF) has shown promising results in repairing podocyte damage, but its efficacy via parenteral administration is limited by a short half-life. Low temperature sensitive liposomes (LTSL) are a promising tool for targeted BDNF delivery, preserving its activity after encapsulation. This study aimed to improve LTSL design for efficient BDNF encapsulation and targeted release to podocytes, while maintaining stability and biological activity, and exploiting the conjugation of targeting peptides. While cyclic RGD (cRGD) was used for targeting endothelial cells in vitro, a homing peptide (HITSLLS) was conjugated for more specific uptake by glomerular endothelial cells in vivo. BDNF-loaded LTSL successfully repaired cytoskeleton damage in podocytes and reduced albumin permeability in a glomerular co-culture model. cRGD conjugation enhanced endothelial cell targeting and uptake, highlighting an improved therapeutic effect when BDNF release was induced by thermoresponsive liposomal degradation. In vivo, targeted LTSL showed evidence of accumulation in the kidneys, and their BDNF delivery decreased proteinuria and ameliorated kidney histology. These findings highlight the potential of BDNF-LTSL formulations in restoring podocyte function and treating glomerular diseases.

Tmem30a protects against podocyte injury through suppression of pyroptosis

Podocytopathies, such as focal segmental glomerulosclerosis (FSGS), are characterized by podocyte injury and can easily progress to end-stage kidney disease. However, the mechanisms underlying podocyte injury remain unclear. We observed podocyte injury along with pyroptosis in patients with FSGS. Bioinformatic analysis of public datasets revealed that transmembrane protein 30a (Tmem30a) might be associated with FSGS. The expression of Temem30a and the podocyte-related protein, nephrin, were significantly downregulated in patients with FSGS, adriamycin (ADR)-induced mice, and podocyte-specific Tmem30a lox P /loxP ; NPHS2-Cre mice, whereas the expression of NLR family pyrin domain containing 3 (NLRP3) and ASC, two pyroptosis-related proteins, were significantly upregulated. Meanwhile, the pyroptosis inhibitor MCC950 and disulfiram (DSF) increased Tmem30a and podocyte-related proteins expression, and inhibited pyroptosis-related proteins expression in ADR-induced mouse podocytes and Tmem30a knockdown (KD) mouse podocytes. Therefore, Tmem30a might protect against podocyte injury by inhibiting pyroptosis, suggesting a potential therapeutic target for podocytopathies.

Blockade of Notch1 Signaling Alleviated Podocyte Injury in Lupus Nephritis Via Inhibition of NLRP3 Inflammasome Activation

To explore the role of Notch1 pathway in the pathogenesis of podocyte injury, and to provide novel strategy for podocyte repair in lupus nephritis (LN). Bioinformatics analysis and immunofluorescence assay were applied to determine the expression and localization of Notch1 intracellular domain1 (NICD1) in kidneys of LN patients and MRL/lpr mice. The stable podocyte injury model in vitro was established by puromycin aminonucleoside (PAN) treatment. Expression of inflammasome activation related gene was detected by qPCR. The podocytes with PAN treatment were cultured with or without N-S-phenyl-glycine-t-butylester (DAPT), an inhibitor of Notch1 pathway. NICD1, Wilm'stumor1 (WT1), nucleotide-binding oligomerization domain-like receptors 3 (NLRP3), and absent in melanoma-like receptors 2 (AIM2) were detected by western blot. In vivo, MRL/lpr mice were administrated with DAPT or vehicle. The LN symptoms were assessed. The podocyte injury was evaluated, and the NLRP3 in podocytes of mice was detected. Notch1 pathway was overactivated in glomeruli of LN patients. NICD1 was colocalized with podocytes of LN patients and MRL/lpr mice. The inflammasome-related genes were significantly increased in podocytes with PAN treatment. NICD1 and NLRP3 were significantly decreased, while WT1 was significantly increased in injured podocytes treated with DAPT in vitro. In vivo, lupus-like symptoms were alleviated in DAPT treatment group. Notch1 pathway was inhibited in kidneys of mice treated with DAPT. The renal inflammation was reduced and the podocyte injury was mitigated in DAPT treatment group. The NLRP3 was decreased in podocytes of mice treated with DAPT. Notch1 pathway was overactivated in podocytes of LN patients and MRL/lpr mice. Blockade of Notch1 pathway reduced renal inflammation and alleviated podocyte injury via inhibition of NLRP3 inflammasome activation in LN.

Podocin, mTOR, and CHOP dysregulation contributes to nephrotoxicity induced of lipopolysaccharide/diclofenac combination in rats: Curcumin and silymarin could afford protective effect

AIM

Sepsis is a common cause of acute kidney injury (AKI). Lipopolysaccharides (LPS) are the main gram-negative bacterial cell wall component with a well-documented inflammatory impact. Diclofenac (DIC) is a non-steroidal anti-inflammatory drug with a potential nephrotoxic effect. Curcumin (CUR) and silymarin (SY) are natural products with a wide range of pharmacological activities, including antioxidant and anti-inflammatory ones. The objective of this study was to examine the protective impact of CUR and SY against kidney damage induced by LPS/DIC co-exposure.

MATERIALS AND METHODS

Four groups of rats were used; control; LPS/DIC, LPS/DIC + CUR, and LPS/DIC + SY group. LPS/DIC combination induced renal injury at an LPS dose much lower than a nephrotoxic one.

KEY FINDING

Nephrotoxicity was confirmed by histopathological examination and significant elevation of renal function markers. LPS/DIC induced oxidative stress in renal tissues, evidenced by decreasing reduced glutathione and superoxide dismutase, and increasing lipid peroxidation. Inflammatory response of LPS/DIC was associated with a significant increase of renal IL-1β and TNF-α. Treatment with either CUR or SY shifted measured parameters to the opposite side. Moreover, LPS/DIC exposure was associated with upregulation of mTOR and endoplasmic reticulum stress protein (CHOP) and downregulation of podocin These effects were accompanied by reduced gene expression of cystatin C and KIM-1. CUR and SY ameliorated LPS/DIC effect on the aforementioned genes and protein significantly.

SIGNIFICANCE

This study confirms the potential nephrotoxicity; mechanisms include upregulation of mTOR, CHOP, cystatin C, and KIM-1 and downregulation of podocin. Moreover, both CUR and SY are promising nephroprotective products against LPS/DIC co-exposure.

Reelin through the years: From brain development to inflammation

Reelin was originally identified as a regulator of neuronal migration and synaptic function, but its non-neuronal functions have received far less attention. Reelin participates in organ development and physiological functions in various tissues, but it is also dysregulated in some diseases. In the cardiovascular system, Reelin is abundant in the blood, where it contributes to platelet adhesion and coagulation, as well as vascular adhesion and permeability of leukocytes. It is a pro-inflammatory and pro-thrombotic factor with important implications for autoinflammatory and autoimmune diseases such as multiple sclerosis, Alzheimer's disease, arthritis, atherosclerosis, or cancer. Mechanistically, Reelin is a large secreted glycoprotein that binds to several membrane receptors, including ApoER2, VLDLR, integrins, and ephrins. Reelin signaling depends on the cell type but mostly involves phosphorylation of NF-κB, PI3K, AKT, or JAK/STAT. This review focuses on non-neuronal functions and the therapeutic potential of Reelin, while highlighting secretion, signaling, and functional similarities between cell types.

Danggui Shaoyaosan attenuates doxorubicin induced Nephrotic Syndrome through regulating on PI3K/Akt Pathway

The study aimed to explore the role and the underlying mechanism of Danggui Shaoyaosan (DSS) in nephrotic syndrome (NS). NS rat model was induced by doxorubicin injection twice. After DSS treatment, inflammation and oxidative stress index were detected via ELISA. Western blot was used for the protein detection. Go and KEGG analysis was applied to evaluate target gene and signaling of DSS. MCP-5 cell was applied for the cell rescue experiments and mechanism exploration. The 24 h urine protein levels of NS rats increased significantly, which was reduced by DSS treatment in a concentration-dependent manner. After DSS treatment, levels of BUN, SCr, TG and TC were also decreased, and serum ALB and TP levels were increased in rats. GO and KEGG pathway enrichment identified PI3K-Akt to be the candidate signaling of DSS in the treatment of NS, which was activated in NS rats. The recuse experiments in MCP-5 demonstrated that IGF-1, the agonist of PI3K/AKT, abolished the beneficial role of DSS in podocyte cell viability, apoptosis, inflammation and oxidative stress. In conclusion, DSS exerts a protective role against the development of NS. The mechanism is related to the improvement of podocyte injury and the inhibition of PI3K/Akt pathway-related proteins.

Deciphering the pharmacological mechanisms of Rostellularia procumbens (L) Nees. Extract alleviates adriamycin-induced nephropathy in vivo and in vitro

BACKGROUND

Rostellularia procumbens (L) Nees. is an effective traditional Chinese herbal medicine for the treatment of patients with chronic glomerulonephritis (CGN) in the clinic. However, the underlying molecular mechanisms need further elucidation.

PURPOSE

This study aims to investigate the renoprotective mechanisms of n-butanol extract from Rostellularia procumbens (L) Nees. (J-NE) in vivo and in vitro.

METHODS

The components of J-NE were analyzed by UPLC-MS/MS. In vivo, the nephropathy model was induced in mice by tail vein injection with adriamycin (10 mg·kg^-1), and mice were treated with vehicle or J-NE or benazepril by daily gavage. In vitro, MPC5 cells exposed to adriamycin (0.3 μg/ml) were treated with J-NE. The effects of J-NE inhibit podocyte apoptosis and protect against adriamycin-induced nephropathy were determined by Network pharmacology, RNA-seq, qPCR, ELISA, immunoblotting, flow cytometry, and TUNEL assay, according to the experimental protocols.

RESULT

The results showed that treatment significantly improved ADR-induced renal pathological changes, and the therapeutic mechanism of J-NE was related to the inhibition of podocyte apoptosis. Further molecular mechanism studies found that J-NE inhibited inflammation, increase the proteins expression levels of Nephrin and Podocin, reduce TRPC6 and Desmin expression levels and calcium ion levels in podocytes, and decrease the proteins expression levels of PI3K, p-PI3K, Akt and p-Akt to attenuated apoptosis. Furthermore, 38 compounds of J-NE were identified.

CONCLUSION

J-NE exerted the renoprotective effects by inhibiting podocyte apoptosis, which provides effective evidence for the treatment of J-NE targeting renal injury in CGN.

In situ assessment of Mindin as a biomarker of podocyte lesions in diabetic nephropathy

Diabetic nephropathy (DN) is the leading cause of chronic kidney disease and end-stage renal failure worldwide. Several mechanisms are involved in the pathogenesis of this disease, which culminate in morphological changes such as podocyte injury. Despite the complex diagnosis and pathogenesis, limited attempts have been made to establish new biomarkers for DN. The higher concentration of Mindin protein in the urine of patients with type 2 diabetes mellitus suggests that it plays a role in DN. Therefore, this study investigated whether in situ protein expression of Mindin can be considered a potential DN biomarker. Fifty renal biopsies from patients diagnosed with DN, 57 with nondiabetic glomerular diseases, including 17 with focal segmental glomerulosclerosis (FSGS), 14 with minimal lesion disease (MLD) and 27 with immunoglobulin A nephropathy (IgAN), and 23 adult kidney samples from autopsies (control group) were evaluated for Mindin expression by immunohistochemistry. Podocyte density was inferred by Wilms' tumor 1 (WT1) immunostaining, while foot process effacement was assessed by transmission electron microscopy. Receiver operative characteristic (ROC) analysis was performed to determine the biomarker sensitivity/specificity. Low podocyte density and increased Mindin expression were observed in all cases of DN, regardless of their class. In the DN group, Mindin expression was significantly higher than that in the FSGS, MCD, IgAN and control groups. Higher Mindin expression was significantly positively correlated with foot process effacement only in class III DN cases. Furthermore, Mindin protein presented high specificity in the biopsies of patients with DN (p < 0.0001). Our data suggest that Mindin may play a role in DN pathogenesis and is a promising biomarker of podocyte lesions.

Epigenetic Modulation of Gremlin-1/NOTCH Pathway in Experimental Crescentic Immune-Mediated Glomerulonephritis

Crescentic glomerulonephritis is a devastating autoimmune disease that without early and properly treatment may rapidly progress to end-stage renal disease and death. Current immunosuppressive treatment provides limited efficacy and an important burden of adverse events. Epigenetic drugs are a source of novel therapeutic tools. Among them, bromodomain and extraterminal domain (BET) inhibitors (iBETs) block the interaction between bromodomains and acetylated proteins, including histones and transcription factors. iBETs have demonstrated protective effects on malignancy, inflammatory disorders and experimental kidney disease. Recently, Gremlin-1 was proposed as a urinary biomarker of disease progression in human anti-neutrophil cytoplasmic antibody (ANCA)-associated crescentic glomerulonephritis. We have now evaluated whether iBETs could regulate Gremlin-1 in experimental anti-glomerular basement membrane nephritis induced by nephrotoxic serum (NTS) in mice, a model resembling human crescentic glomerulonephritis. In NTS-injected mice, the iBET JQ1 inhibited renal Gremlin-1 overexpression and diminished glomerular damage, restoring podocyte numbers. Chromatin immunoprecipitation assay demonstrated BRD4 enrichment of the Grem-1 gene promoter in injured kidneys, consistent with Gremlin-1 epigenetic regulation. Moreover, JQ1 blocked BRD4 binding and inhibited Grem-1 gene transcription. The beneficial effect of iBETs was also mediated by modulation of NOTCH pathway. JQ1 inhibited the gene expression of the NOTCH effectors Hes-1 and Hey-1 in NTS-injured kidneys. Our results further support the role for epigenetic drugs, such as iBETs, in the treatment of rapidly progressive crescentic glomerulonephritis.

Predicting lupus membranous nephritis using reduced picolinic acid to tryptophan ratio as a urinary biomarker

The current gold standard for classifying lupus nephritis (LN) progression is a renal biopsy, which is an invasive procedure. Undergoing a series of biopsies for monitoring disease progression and treatments is unlikely suitable for patients with LN. Thus, there is an urgent need for non-invasive alternative biomarkers that can facilitate LN class diagnosis. Such biomarkers will be very useful in guiding intervention strategies to mitigate or treat patients with LN. Urine samples were collected from two independent cohorts. Patients with LN were classified into proliferative (class III/IV) and membranous (class V) by kidney histopathology. Metabolomics was performed to identify potential metabolites, which could be specific for the classification of membranous LN. The ratio of picolinic acid (Pic) to tryptophan (Trp) ([Pic/Trp] ratio) was found to be a promising candidate for LN diagnostic and membranous classification. It has high potential as an alternative biomarker for the non-invasive diagnosis of LN.

Molecular Mechanisms of Hypertensive Nephropathy: Renoprotective Effect of Losartan through Hsp70

Hypertensive nephrosclerosis is the second most common cause of end-stage renal disease after diabetes. For years, hypertensive kidney disease has been focused on the afferent arterioles and glomeruli damage and the involvement of the renin angiotensin system (RAS). Nonetheless, in recent years, novel evidence has demonstrated that persistent high blood pressure injures tubular cells, leading to epithelial–mesenchymal transition (EMT) and tubulointerstitial fibrosis. Injury primarily determined at the glomerular level by hypertension causes changes in post-glomerular peritubular capillaries that in turn induce endothelial damage and hypoxia. Microvasculature dysfunction, by inducing hypoxic environment, triggers inflammation, EMT with epithelial cells dedifferentiation and fibrosis. Hypertensive kidney disease also includes podocyte effacement and loss, leading to disruption of the filtration barrier. This review highlights the molecular mechanisms and histologic aspects involved in the pathophysiology of hypertensive kidney disease incorporating knowledge about EMT and tubulointerstitial fibrosis. The role of the Hsp70 chaperone on the angiotensin II–induced EMT after angiotensin II type 1 receptor (AT₁R) blockage, as a possible molecular target for therapeutic strategy against hypertensive renal damage is discussed.

Renal Cell-Targeted Drug Delivery Strategy for Acute Kidney Injury and Chronic Kidney Disease: A Mini-Review

Kidney diseases, including acute kidney injury (AKI) and chronic kidney disease (CKD), have become a global public health concern associated with high morbidity, mortality, and healthcare costs. However, at present, very few effective and specific drug therapies are available, owing to the poor therapeutic efficacy and systemic side effects. Kidney-targeted drug delivery, as a potential strategy for solving these problems, has received great attention in the fields of AKI and CKD in recent years. Here, we review the literature on renal targeted, more specifically, renal cell-targeted formulations of AKI and CKD that offered biodistribution data. First, we provide a broad overview of the unique structural characteristics and injured cells of acute and chronic injured kidneys. We then separately summarize literature examples of renal targeted formulations according to the difference of target cells and elaborate on the appropriate formulation design criteria for AKI and CKD. Finally, we propose a hypothetic strategy to improve the renal accumulation of glomerular cell-targeted formulation by escaping the uptake of the reticuloendothelial system and provide some perspectives for future studies.

CCL24 Protects Renal Function by Controlling Inflammation in Podocytes

Diabetic nephropathy (DN) is one of the most lethal complications of diabetes mellitus with chronic inflammation. We have examined the role of the inflammatory chemokine CCL24 in DN. We observed that serum levels of CCL24 were significantly elevated in patients with DN. Not only that, the expression of CCL24 was significantly increased in the kidneys of DN mice. The kidney of DN mice showed increased renal fibrosis and inflammation. We characterized an in vitro podocyte cell model with high glucose. Western blot analysis showed that expression of CCL24 was significantly increased under high-glucose conditions. Stimulation with high glucose (35 mmol/L) resulted in an increase in CCL24 expression in the first 48 hours but changed little after 72 hours. Moreover, with glucose stimulation, the level of podocyte fibrosis gradually increased, the expression of the proinflammatory cytokine IL-1β was upregulated, and the expression of the glucose transporter GLUT4, involved in the insulin signal regulation pathway, also increased. It is suggested that CCL24 is involved in the pathogenesis of DN. In order to study the specific role of CCL24 in this process, we used the CRISPR-Cas9 technique to knock out CCL24 expression in podocytes. Compared with the control group, the podocyte inflammatory response induced by high glucose after CCL24 knockout was significantly increased. These results suggest that CCL24 plays a role in the development of early DN by exerting an anti-inflammatory effect, at least, in podocytes.

PTPN14 deficiency alleviates podocyte injury through suppressing inflammation and fibrosis by targeting TRIP6 in diabetic nephropathy

Diabetic nephropathy (DN) is a common complication of diabetes, and a leading cause of end-stage renal disease. However, the pathogenesis that contributes to DKD is still not fully understood. Protein tyrosine phosphatase non-receptor type 14 (PTPN14), a non receptor tyrosine phosphatase, has numerous cellular events, such as inflammation and cell death. But its potential on DKD has not been investigated yet. In this study, we found that PTPN14 expression was markedly up-regulated in kidney samples of DKD patients, which were confirmed in diabetic mice and were clearly localized in glomeruli. The diabetic mouse model was established using streptozotocin (STZ) in wild type (WT) or PTPN knockout (KO) mice. After, STZ challenge, STZ mice displayed improved kidney functions. The results also showed that STZ-induced histological changes and podocyte injury in renal tissues, which were effectively alleviated by PTPN14 deletion. Moreover, PTPN14 deficiency significantly mitigated inflammatory response and fibrosis in glomeruli of STZ-challenged mice through restraining the activation of nuclear factor-κB (NF-κB) and transforming growth factor (TGF)-β1 signaling pathways, respectively. The inhibitory effects of PTPN14 suppression on inflammation and fibrosis were confirmed in high glucose (HG)-incubated podocytes. We further found that thyroid receptor interactor protein 6 (TRIP6) expression was dramatically up-regulated in glomeruli of STZ-challenged mice, and was abolished by PTPN14 deletion, which was confirmed in HG-treated podocytes with PTPN14 knockdown. Intriguingly, our in vitro studies showed that PTPN14 directly interacted with TRIP6. Of note, over-expressing TRIP6 markedly abrogated the effects of PTPN14 silence to restrict inflammatory response and fibrosis in HG-incubated podocytes. Taken together, our findings demonstrated that targeting PTPN14 may provide feasible therapies for DKD treatment.

The Protective Effect of Shen Qi Wan on Adenine-Induced Podocyte Injury

Podocytes are a special type of differentiated epithelial cells that maintain the glomerular filtration barrier in the kidney. Injury or damages in podocytes can cause kidney-related disorders, like CKD. The injury or dysfunction of podocytes can occur by different metabolic disorders. Due to the severity and complexity of podocyte injuries, this state is considered as a serious health issue worldwide. Here, we examined and addressed the efficacy of an alternative Chinese medicine, Shen Qi Wan (SQW), on podocyte-related kidney injury. We evaluated the role and mechanism of action of SQW in podocyte injury. We observed that SQW significantly reduced 24-hour urinary protein and blood urea nitrogen levels and alleviated the pathological damage caused by adenine. Moreover, SQW significantly decreased the expression of nephrin and increased the expression of WT1 and AQP1 in the kidney of mice treated with adenine. We observed that SQW did not effectively reduce the high level of proteinuria in AQP1^−/− mice indicating the prominent role of AQP1 in the SQW-ameliorating pathway. Transmission electron microscopy (TEM) images indicated the food processes effacement in AQP1^−/− mice were not lessened by SQW. In conclusion, podocyte injury could alter the pathological nature of the kidney, and SQW administration relieves the nature of pathogenesis by activating AQP1.

Association between Renal Podocalyxin Expression and Renal Dysfunction in Patients with Diabetic Nephropathy: A Single-Center, Retrospective Case-Control Study

This retrospective study investigated whether podocalyxin expression in renal biopsies and urine of patients with diabetic nephropathy (DN) is associated with renal function. This retrospective study included 32 patients with nephropathy, secondary to type 2 diabetes treated at the First Hospital of Lanzhou University (January 2010 to January 2015). Compared with the control group, the DN group had a significantly lower renal expression of podocalyxin and higher urinary podocalyxin/creatinine ratio. Patients with DN were divided into the high and low expression groups according to podocalyxin expression in renal tissues. Patients in the low expression group had longer diabetes duration, lower plasma albumin and eGFR, higher glycated hemoglobin (HbA1c), 24 h urinary protein, serum creatinine, and urinary podocalyxin/creatinine ratio, and more severe glomerular, tubulointerstitial, and renal interstitial inflammation than patients in the high expression group (all P < 0.01). The renal survival rate was significantly lower in the low expression group than in the high expression group (P < 0.01). Single-factor Cox regression analysis showed that reduced podocalyxin expression and increased urinary podocalyxin excretion were associated with poor renal outcome. Measuring podocalyxin levels in renal tissues and urine could help evaluate the progression of DN.

Hsp90 inhibition aggravates adriamycin-induced podocyte injury through intrinsic apoptosis pathway

Podocyte injury leads to impaired filtration barrier function of the kidney that underlies the pathophysiology of idiopathic nephrotic syndrome (INS), the most common NS occurring in children. The heat shock protein 90 (Hsp90) is involved in the regulation of apoptosis in a variety of cell types, however, little is known about its role in podocytes and whether it associated with NS. Here, we show that Hsp90 is upregulated in glomeruli podocytes from mice with adriamycin (ADR)-induced nephropathy, and that it is also upregulated in an immortalized podocyte cell line treated with ADR in vitro, together suggesting an association of Hsp90 upregulation in podocytes with NS pathogenesis. Functionally, Hsp90 inhibition with PU-H71 aggravates ADR-induced podocyte apoptosis and worsens the impairment of filtration barrier function. Mechanistically, Hsp90 inhibition with PU-H71 enhances the activation of intrinsic apoptotic pathway, and moreover, blockade of podocyte apoptosis with zVAD-fmk (aVAD), a pan-caspase inhibitor, abrogates effects of Hsp90 inhibition on filtration barrier function of ADR-treated podocytes, thus demonstrating that Hsp90 inhibition aggravates ADR-induced podocyte injury through intrinsic apoptosis pathway. In sum, this study reveals a detrimental role of Hsp90 inhibition in podocyte injury, which may offer it as a potential therapeutic target in NS therapy.

Identifying Synergistic Mechanisms of Multiple Ingredients in Shuangbai Tablets against Proteinuria by Virtual Screening and a Network Pharmacology Approach

Shuangbai Tablets (SBT), a traditional herbal mixture, has shown substantial clinical efficacy. However, a systematic mechanism of its active ingredients and pharmacological mechanisms of action against proteinuria continues being lacking. A network pharmacology approach was effectual in discovering the relationship of multiple ingredients and targets of the herbal mixture. This study aimed to identify key targets, major active ingredients, and pathways of SBT against proteinuria by network pharmacology approach combined with thin layer chromatography (TLC). Human phenotype (HP) disease analysis, gene ontology (GO) analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis, and molecular docking were used in this study. To this end, a total of 48 candidate targets of 118 active ingredients of SBT were identified. Network analysis showed PTGS2, ESR1, and NOS2 to be the three key targets, and beta-sitosterol, quercetin, and berberine were the three major active ingredients; among them one of the major active ingredients, quercetin, was discriminated by TLC. These results of the functional enrichment analysis indicated that the most relevant disease including these 48 candidate proteins is proteinuria, SBT treated proteinuria by sympathetically regulating multiple biological pathways, such as the HIF-1, RAS, AGE-RAGE, and VEGF signaling pathways. Additionally, molecular docking validation suggested that major active ingredients of SBT were capable of binding to HIF-1A and VEGFA of the main pathways. Consequently, key targets, major active ingredients, and pathways based on data analysis of SBT against proteinuria were systematically identified confirming its utility and providing a new drug against proteinuria.

Protective effect of umbilical cord mesenchymal stem cells combined with resveratrol against renal podocyte damage in NOD mice

BACKGROUND

The role of chronic inflammation initiated by persistent hyperglycemia in podocyte injury has attracted increasing attention. The advanced glycation end products (RAGE) receptor- nuclear factor-kappa B (NF-кB) signaling pathway is involved in the occurrence of inflammation. We speculate that treatment with human umbilical cord mesenchymal stem cells (hUCMSCs) combined with resveratrol can block this signaling pathway and protect podocyte function.

METHODS

Non obesity diabetes(NOD) mice were randomly divided into 5 groups: NOD-T1DM, Res, hUCMSCs, hUCMSCs + Res and insulin (INS)groups. Mice without diabetes were classified as NOD control group(NOD group). Blood glucose(BG), blood urea nitrogen(BUN), serum creatinine(SCr), 24-h urine albumin excretion rate (UAER) were measured. The expression of nephrin, WT1 and RAGE, MCP-1 in renal tissues were detected by Western blot, expression of NF-кB protein(P65) was determined by immunohistochemistry.

RESULTS

The combined treatment of hUCMSCs and Resveratrol can reduce BG, BUN, SCr, 24-h UAER, and the expression of the inflammatory factors MCP-1, RAGE and NF-кB; increase the number of podocytes and the expression of the podocyte-related proteins nephrin and WT1 in type 1 diabetes mellitus, and improve renal pathological structure.

CONCLUSIONS

Combining of hUCMSCs and resveratrol can better protect renal podocyte function, and the effects on the reduction of blood glucose and renal injury are better than those obtained by insulin treatment. This indicated that the combination of Res and hUCMSCs may be a novel therapeutic method for the treatment of DN.

Role of Podocyte Injury in Glomerulosclerosis

Finding new therapeutic targets of glomerulosclerosis treatment is an ongoing quest. Due to a living environment of various stresses and pathological stimuli, podocytes are prone to injuries; moreover, as a cell without proliferative potential, loss of podocytes is vital in the pathogenesis of glomerulosclerosis. Thus, sufficient understanding of factors and underlying mechanisms of podocyte injury facilitates the advancement of treating and prevention of glomerulosclerosis. The clinical symptom of podocyte injury is proteinuria, sometimes with loss of kidney functions progressing to glomerulosclerosis. Injury-induced changes in podocyte physiology and function are actually not a simple passive process, but a complex interaction of proteins that comprise the anatomical structure of podocytes at molecular levels. This chapter lists several aspects of podocyte injuries along with potential mechanisms, including glucose and lipid metabolism disorder, hypertension, RAS activation, micro-inflammation, immune disorder, and other factors. These aspects are not technically separated items, but intertwined with each other in the pathogenesis of podocyte injuries.

LncRNA CCAT1 functions as apoptosis inhibitor in podocytes via autophagy inhibition

Podocyte apoptosis importantly contributes to various kidney diseases. Long noncoding RNAs Colon cancer‐associated transcript‐1 (CCAT‐1) has been demonstrated for a critical role in cell proliferation. In the present study, the relationship between CCAT1 and popdocyte impairment, and the underlying mechanism was investigated. Podocytes were isolated from mice and then treated with tumor necrosis factor‐α to simulate podocyte injury. After developed CCAT1 overexpression or knockdown, cell viabilities were determined with the CCK‐8 assay, apoptosis was examined with Flow cytometry, the autophagy was observed by Western blot. Furthermore, phosphorylated PI3K and Akt expressions were examined. We found that after CCAT1 overexpression, the cell viability was significantly increased, apoptosis was significantly decreased, and autophagy was significantly inhibited, which was indicated by induced P62, LC3B‐I and decreased LC3B‐II. In addition, CCAT1 overexpression induced the levels of phosphorylated PI3K and Akt. With Rap treatment, these effects by CCAT1 were reversed. Furthermore, the results contrary to the effects by CCAT1 overexpression were presented after CCAT1 knockdown, and this was inhibited by 3‐MA. Taken together, our results suggested that CCAT1 induction critically participated in apoptosis inhibition in podocytes through autophagy inhibition via increasing PI3K/Akt signaling. This might act as a promising therapeutic intervention for renal diseases associated with podocyte apoptosis.

The motor protein Myo1c regulates transforming growth factor-β-signaling and fibrosis in podocytes

Transforming growth factor-β (TGF-β) is known to play a critical role in the pathogenesis of many progressive podocyte diseases. However, the molecular mechanisms regulating TGF-β signaling in podocytes remain unclear. Using a podocyte-specific myosin (Myo)1c knockout, we demonstrate whether Myo1c is critical for TGF-β-signaling in podocyte disease pathogenesis. Specifically, podocyte-specific Myo1c knockout mice were resistant to fibrotic injury induced by Adriamycin or nephrotoxic serum. Further, loss of Myo1c also protected from injury in the TGF-β-dependent unilateral ureteral obstruction mouse model of renal interstitial fibrosis. Mechanistic analyses showed that loss of Myo1c significantly blunted TGF-β signaling through downregulation of canonical and non-canonical TGF-β pathways. Interestingly, nuclear rather than the cytoplasmic Myo1c was found to play a central role in controlling TGF-β signaling through transcriptional regulation. Differential expression analysis of nuclear Myo1c-associated gene promoters showed that nuclear Myo1c targeted the TGF-β responsive gene growth differentiation factor (GDF)-15 and directly bound to the GDF-15 promoter. Importantly, GDF15 was found to be involved in podocyte pathogenesis, where GDF15 was upregulated in glomeruli of patients with focal segmental glomerulosclerosis. Thus, Myo1c-mediated regulation of TGF-β-responsive genes is central to the pathogenesis of podocyte injury. Hence, inhibiting this process may have clinical application in treating podocytopathies.

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

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

Septin 7 mediates high glucose-induced podocyte apoptosis

Podocyte depletion is a central pathological mechanism of diabetic nephropathy (DN). Hyperglycemia induced podocyte apoptosis, resulting in podocyte depletion. However, the crucial mechanism of hyperglycemia-induced podocyte apoptosis remains poorly understood. In this study, we evaluated the expression of septin 7, a GTP-binding protein, in glomerular podocytes of patients and mice with DN, and investigated the pro-apoptotic effect of septin 7 on high glucose (HG) induced podocyte apoptosis in vitro. We found septin 7 expression was markedly increased not only in glomerular podocytes of patients and db/db mice with DN but also in cultured podocytes with HG stimulation. Knocking down septin 7 with siRNA could attenuate HG induced podocytes apoptosis and excessive intracellular Ca²⁺ concentration. This study revealed septin7 may potentially play a proapoptotic role in podocyte under diabetic conditions and may provide a potential target for preventing podocyte apoptosis in DN.

Genistein and Myd88 Activate Autophagy in High Glucose-Induced Renal Podocytes In Vitro

BACKGROUND Renal podocyte damage plays a crucial role in the development of diabetic nephropathy. Genistein is derived from a leguminous plant, and MyD88 and TRIF are adaptor molecules in the Toll-like receptor (TLR) signaling pathway, which may play a role in autophagy. In this study, we utilized an in vitro high glucose (HG)-treated podocyte model to investigate the effects and underlying mechanisms of Genistein and MyD88 or TRIF siRNA induced autophagy and renal protection. MATERIAL AND METHODS An immortalized mouse podocyte cell line was treated with HG, Genistein, chloroquine, and/or transfected with specific Myd88 and TRIF siRNAs. The formation of autophagosomes and related autophagic vacuoles were monitored by transmission electron microscopy. The expression of autophagy-related factors and podocyte structure and functional markers, including LC3, p62, p-mTOR, synaptopodin, and nephrin, were measured by Western blot, and LC3 and p-mTOR expression were also assessed by immunofluorescence. RESULTS We showed that HG transiently (after 6-h exposure) induced expression of the autophagy activation marker LC3-II in podocytes. Genistein treatment induced autophagy in both normal and HG-treated podocytes through inactivating mTOR signaling. Moreover, Genistein protected podocytes against chloroquine in HG-cultured conditions in vitro by maintaining the level of autophagy-related proteins. In addition, MyD88 siRNA downregulated expression of autophagy-related proteins, whereas Genistein treatment reversed these effects. CONCLUSIONS This study demonstrated that Genistein-induced autophagy could be a potential treatment strategy for glomerular diseases.

Myeloid-Derived Suppressor Cells Induce Podocyte Injury Through Increasing Reactive Oxygen Species in Lupus Nephritis

The expansion of myeloid-derived suppressor cells (MDSCs) has been documented in murine models and patients with lupus nephritis (LN), but the exact role of MDSCs in this process remains largely unknown. In this study, we investigated whether MDSCs are involved in the process of podocyte injury in the development of LN. In toll-like receptor-7 (TLR-7) agonist imiquimod-induced lupus mice, we found the severe podocyte injury in glomeruli of lupus mice and significant expansion of MDSCs in spleens and kidneys of lupus mice. The function of TLR-7 activated MDSCs was enhanced including the increased generation of reactive oxygen species (ROS) in vivo and in vitro. Moreover, the ROS production of MDSCs induced podocyte injury through activating the p-38MAPK and NF-kB signaling. Furthermore, we verified that podocyte injury was indeed correlated with expansion of MDSCs and their ROS secretion in LN of pristane-induced lupus mice. These findings first indicate that the podocyte injury in LN was associated with the increased MDSCs in kidney and MDSCs may be a promising therapeutic target of LN in the future.

Protein Kinase A/CREB Signaling Prevents Adriamycin-Induced Podocyte Apoptosis via Upregulation of Mitochondrial Respiratory Chain Complexes

Previous work showed that the activation of protein kinase A (PKA) signaling promoted mitochondrial fusion and prevented podocyte apoptosis. The cAMP response element binding protein (CREB) is the main downstream transcription factor of PKA signaling. Here we show that the PKA agonist 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate-cyclic AMP (pCPT-cAMP) prevented the production of adriamycin (ADR)-induced reactive oxygen species and apoptosis in podocytes, which were inhibited by CREB RNA interference (RNAi). The activation of PKA enhanced mitochondrial function and prevented the ADR-induced decrease of mitochondrial respiratory chain complex I subunits, NADH-ubiquinone oxidoreductase complex (ND) 1/3/4 genes, and protein expression. Inhibition of CREB expression alleviated pCPT-cAMP-induced ND3, but not the recovery of ND1/4 protein, in ADR-treated podocytes. In addition, CREB RNAi blocked the pCPT-cAMP-induced increase in ATP and the expression of peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC1-α). The chromatin immunoprecipitation assay showed enrichment of CREB on PGC1-α and ND3 promoters, suggesting that these promoters are CREB targets. In vivo, both an endogenous cAMP activator (isoproterenol) and pCPT-cAMP decreased the albumin/creatinine ratio in mice with ADR nephropathy, reduced glomerular oxidative stress, and retained Wilm's tumor suppressor gene 1 (WT-1)-positive cells in glomeruli. We conclude that the upregulation of mitochondrial respiratory chain proteins played a partial role in the protection of PKA/CREB signaling.

Translational Aspects of Sphingolipid Metabolism in Renal Disorders

Sphingolipids, long thought to be passive components of biological membranes with merely a structural role, have proved throughout the past decade to be major players in the pathogenesis of many human diseases. The study and characterization of several genetic disorders like Fabry’s and Tay Sachs, where sphingolipid metabolism is disrupted, leading to a systemic array of clinical symptoms, have indeed helped elucidate and appreciate the importance of sphingolipids and their metabolites as active signaling molecules. In addition to being involved in dynamic cellular processes like apoptosis, senescence and differentiation, sphingolipids are implicated in critical physiological functions such as immune responses and pathophysiological conditions like inflammation and insulin resistance. Interestingly, the kidneys are among the most sensitive organ systems to sphingolipid alterations, rendering these molecules and the enzymes involved in their metabolism, promising therapeutic targets for numerous nephropathic complications that stand behind podocyte injury and renal failure.

Glomerular filtration drug injury: In vitro evaluation of functional and morphological podocyte perturbations

The kidney is an organ that plays a major role in the excretion of numerous compounds such as drugs and chemicals. However, a great number of pharmacological molecules are nephrotoxic, affecting the efficiency of the treatment and increasing morbidity or mortality. Focusing on glomerular filtration, we propose in this study a simple and reproducible in vitro human model that is able to bring to light a functional podocyte injury, correlated with morphologic/phenotypic changes after drug exposure. This model was used for the evaluation of paracellular permeability of FITC-dextran molecules as well as FITC-BSA after different treatments. Puromycin aminonucleoside and adriamycin, compounds known to induce proteinuria in vivo and that serve here as positive nephrotoxic drug controls, were able to induce an important increase in fluorescent probe passage through the cell monolayer. Different molecules were then evaluated for their potential effect on podocyte filtration. Our results demonstrated that a drug effect could be time dependent, stable or scalable and relatively specific. Immunofluorescence studies indicated that these functional perturbations were due to cytoskeletal perturbations, monolayer disassembly or could be correlated with a decrease in nephrin expression and/or ZO-1 relocation. Taken together, our results demonstrated that this in vitro human model represents an interesting tool for the screening of the renal toxicity of drugs.

Inducible ATF3-NFAT axis aggravates podocyte injury

Abstract

Podocyte injury and loss contribute to proteinuria, glomerulosclerosis, and eventually kidney failure. Activating transcription factor 3 (ATF3) is a stress inducible transcription factor that is transiently expressed following stimulation. However, we show for the first time an induction of ATF3 in podocytes from patients with chronic kidney disease, including minimal change disease, focal segmental glomerulosclerosis, and diabetic nephropathy. The role of ATF3 induction in podocytes under chronic conditions is currently unknown. Compared with the control (C57 or BKS), ATF3 expression was elevated in animal model of proteinuria (LPS-treated C57 mice) and the model of diabetic nephropathy (db/db mice). Similarly, ATF3 was increased in high glucose (HG)-treated, lipopolysaccharide (LPS)-treated, or Ionomycin-treated podocytes in vitro. Overexpression of ATF3 increased podocyte apoptosis and decreased expression of podocin, the cell marker of podocyte; in contrast, ATF3–small interfering RNA knockdown reduced podocyte apoptosis and increased podocin expression. The translocation of ATF3 to the nucleus was increased upon stimulation. ATF3 directly modulates the regulation of NFATc1 gene promoter activity and alters the expression of Wnt6 and Fzd9, direct target genes of NFATc1 signaling. The ATF3 binding site of NFATc1 gene promoter is located at the region 671–775 base pairs upstream of the transcription start site. These results indicate a novel inducible axis of ATF3–NFAT in podocyte injury and loss.

Key messages

• The stress factor ATF3 is induced in podocytes from proteinuric patients, including diabetes.

• ATF3 increased podocyte apoptosis and injury.

• ATF3 directly modulates the regulation of NFATc1 gene promoter activity.

Paeoniflorin ameliorates Adriamycin-induced nephrotic syndrome through the PPARγ/ANGPTL4 pathway in vivo and vitro

Paeoniflorin (PF), an effective composition that is extracted from Radix Paeoniae Alba, plays a role in protecting against various kidney diseases. However, the mechanism of PF on nephrotic syndrome (NS) remains unclear. The aim of this study was to investigate the protective role of PF on Adriamycin (ADR)-induced NS in vivo and vitro as well as its potential mechanism. In animal study, PF significantly decreased the levels of 24-h urine protein, blood urea nitrogen, serum creatinine, total cholesterol and triglycerides in NS rats, but increased the total protein and albumin levels. Hematoxylin-eosin (HE) staining revealed that the kidney lesion was resolved upon PF treatment. After treatment with PF, the morphology and number of podocytes in renal tissue were restored to normal. PF increased expression of synaptopodin and decreased expression of desmin, demonstrating a protective effect in podocyte injury. Further studies revealed that PF upregulated Peroxisome proliferator-activated receptor gamma (PPARγ) and restrained Angiopointin-like 4 (ANGPTL4) in kidney tissue. In vitro study, PF reduced Caspase3 and Bax and increased Bcl-2, indicating that the apoptosis rate of podocytes induced by ADR was reduced by PF. Furthermore, PF ameliorated podocyte injury by upregulating synaptopodin and reducing desmin. In accordance with animal study, PF downregulated ANGPTL4 by activating PPARγ. However, the therapeutic effects of PF were reversed by GW9662 (PPARγ inhibitor), likely by suppressing ANGPTL4 degradation. In general, these results demonstrate that PF has a good therapeutic effect on NS by activating PPARγ and subsequently inhibiting ANGPTL4.

Hypertensive nephropathy. Moving from classic to emerging pathogenetic mechanisms

Hypertensive kidney disease classically entails nephroangiosclerosis and hyalinosis with glomerular damage. However, in recent years, several evidences showed that high blood pressure also injures tubular cells, inducing epithelial-to-mesenchymal transition and tubulointerstitial fibrosis. Recently investigated mechanisms are also podocyte effacement and loss, which lead to denudation of the glomerular basement membrane and focal adhesion of the tufts to the Bowman's capsule, with reduced filtration and scars. Starting from the classic concept of nephroangiosclerosis, this review examines the recently emerged knowledge of new biochemical and molecular mechanisms underlying the kidney damage in hypertension and discusses how viable podocytes or podocyte-deriving proteins are promising tools for early diagnosis of renal remodelling in hypertension.

Apelin involved in progression of diabetic nephropathy by inhibiting autophagy in podocytes

Podocyte autophagy dysfunction has been reported to be responsible for the progression of diabetic nephropathy (DN), however, the factors contributed to autophagy dysfunction in type 2 diabetes are not fully understood. Among promoting factors in DN, an adipokine, apelin, had been showed to trigger podocyte dysfunction. Therefore, it is hypothesized that apelin, which is increased in plasma in type 2 diabetes, lead to podocyte apoptosis through inhibiting podocyte autophagy, which resulted in podocyte dysfunction followed by DN. KkAy mice (diabetic mice) and cultured podocytes (MPC5 cells and native podocytes) were treated with high glucose (HG) and apelin or its antagonist F13A. Renal function, podocyte autophagy, podocyte apoptosis and corresponding cell signaling pathways in podocytes were detected. The results showed that apelin aggravated the renal dysfunction and foot process injuries in kkAy mice, which is positively correlated to podocyte apoptosis and negatively correlated to podocyte autophagy. Apelin induced podocyte apoptosis and inhibited podocyte autophagy in both normal glucose and HG conditions while F13A reversed these effects. Investigations by western blot found that apelin inhibits podocyte autophagy through ERK-, Akt- and mTOR-dependent pathways. In conclusion, increased apelin concentration in plasma inhibited podocyte autophagy, which would lead to podocyte apoptosis and renal dysfunction in diabetes. These effects would contribute to the progression of DN.

c‑Maf inducing protein inhibits cofilin‑1 activity and alters podocyte cytoskeleton organization

The glomerular visceral epithelial cells, also termed podocytes, are key in maintaining the normal renal filtration barrier. Although it has been demonstrated that stimulation of c‑Maf inducing protein (CMIP) expression is involved in podocyte damage, the molecular events during this process remain unclear. In the current study, CMIP‑induced proximal signaling was investigated by focusing on its effect on cofilin‑1 activity in puromycin aminonucleoside (PA)‑damaged podocytes. An obvious elevation of CMIP expression and phosphorylated (p) cofilin‑1 levels was detected in cultured podocytes treated with PA and in glomeruli isolated from PA‑induced nephropathy rats. Stable knockdown of CMIP prevented upregulation of p‑cofilin‑1 and reorganization of actin cytoskeleton in PA‑treated podocytes. The activity of the Src family kinase Fyn was reduced, whereas small GTPase Ras homolog gene family, member A (RhoA) activity was increased in PA‑treated podocytes. Stimulation of CMIP expression inhibited Fyn activation and decreased the expression level of p‑p190RhoGAP, a negative regulator of RhoA activity. The level of p‑LIM domain kinase 1 (LIMK1), a downstream effector of RhoA, increased significantly in PA‑treated podocytes. Notably, the applications of RhoA inhibitor or knockdown of LIMK prevented increase of the p‑cofilin‑1 level in PA‑treated podocytes. Thus, the current data provided evidence that the CMIP/Fyn/RhoA/cofilin‑1 signaling pathway may be associated with actin disorganization and podocyte foot process spreading following podocyte injury.

Podocyte Activation of NLRP3 Inflammasomes Contributes to the Development of Proteinuria in Lupus Nephritis

OBJECTIVE

Development of proteinuria in lupus nephritis (LN) is associated with podocyte dysfunction. The NLRP3 inflammasome has been implicated in the pathogenesis of LN. The purpose of this study was to investigate whether NLRP3 inflammasome activation is involved in the development of podocyte injury in LN.

METHODS

A fluorescence-labeled caspase 1 inhibitor probe was used to detect the activation of NLRP3 inflammasomes in podocytes derived from lupus-prone NZM2328 mice and from renal biopsy tissues obtained from patients with LN. MCC950, a selective inhibitor of NLRP3, was used to treat NZM2328 mice. Proteinuria, podocyte ultrastructure, and renal pathology were evaluated. In vitro, sera from diseased NZM2328 mice were used to stimulate a podocyte cell line, and the cells were analyzed by flow cytometry.

RESULTS

NLRP3 inflammasomes were activated in podocytes from lupus-prone mice and from patients with LN. Inhibition of NLRP3 with MCC950 ameliorated proteinuria, renal histologic lesions, and podocyte foot process effacement in lupus-prone mice. In vitro, sera from diseased NZM2328 mice activated NLRP3 inflammasomes in the podocyte cell line through the production of reactive oxygen species.

CONCLUSION

NLRP3 inflammasomes were activated in podocytes from lupus-prone mice and from LN patients. Activation of NLRP3 is involved in the pathogenesis of podocyte injuries and the development of proteinuria in LN.

Dab1 Contributes to Angiotensin II-Induced Apoptosis via p38 Signaling Pathway in Podocytes

Numerous studies have found that angiotensin II (Ang II) participates in podocyte apoptosis and exacerbates progression of end-stage kidney disease (ESKD). However, its underlying mechanism remains largely unexplored. As a homolog of Drosophila disabled (Dab) protein, Dab1 plays a vital role in cytoskeleton, neuronal migration, and proliferation. In the present study, our data revealed that Ang II-infused rats developed hypertension, proteinuria, and podocyte injury accompanied by Dab1 phosphorylation and increased reelin expression in kidney. Moreover, Ang II induced podocyte apoptosis in vitro. Dab1 phosphorylation and reelin expression in podocytes were increased after exposure to Ang II. Conversely, Dab1 small interfering RNA (siRNA) exerted protective effects on Ang II-induced podocyte apoptosis, resulting in decreased p38 phosphorylation and reelin expression. These results indicated that Dab1 mediated Ang II-induced podocyte apoptosis via p38 signaling pathway.

Ultrasmall polymeric nanocarriers for drug delivery to podocytes in kidney glomerulus

We explored the use of new drug-loaded nanocarriers and their targeted delivery to the kidney glomerulus and in particular to podocytes, in order to overcome the failure of current therapeutic regimens in patients with proteinuric (i.e. abnormal amount of proteins in the urine) diseases. Podocytes are glomerular cells which are mainly responsible for glomerular filtration and are primarily or secondarily involved in chronic kidney diseases. Therefore, the possibility to utilise a podocyte-targeted drug delivery could represent a major breakthrough in kidney disease research, particularly in terms of dosage reduction and elimination of systemic side effects of current therapies. Four-arm star-shaped polymers, with/without a hydrophobic poly-ε-caprolactone core and a brush-like polyethylene glycol (PEG) hydrophilic shell, were synthesised by controlled/living polymerisation (ROP and ATRP) to allow the formation of stable ultrasmall colloidal nanomaterials of tuneable size (5-30nm), which are able to cross the glomerular filtration barrier (GFB). The effects of these nanomaterials on glomerular cells were evaluated in vitro. Nanomaterial accumulation and permeability in the kidney glomerulus were also assessed in mice under physiological and pathological conditions. Drug (dexamethasone) encapsulation was performed in order to test loading capacity, release kinetics, and podocyte repairing effects. The marked efficacy of these drug-loaded nanocarriers in repairing damaged podocytes may pave the way for developing a cell-targeted administration of new and traditional drugs, increasing efficacy and limiting side effects.

Polymer Nanoparticle Engineering for Podocyte Repair: From in Vitro Models to New Nanotherapeutics in Kidney Diseases

Specific therapeutic targeting of kidney podocytes, the highly differentiated ramified glomerular cells involved in the onset and/or progression of proteinuric diseases, could become the optimal strategy for preventing chronic kidney disease. With this aim, we developed a library of engineered polymeric nanoparticles (NPs) of tuneable size and surface properties and evaluated their interaction with podocytes. NP cytotoxicity, uptake, and cytoskeletal effects on podocytes were first assessed. On the basis of these data, nanodelivery of dexamethasone loaded into selected biocompatible NPs was successful in repairing damaged podocytes. Finally, a three-dimensional in vitro system of co-culture of endothelial cells and podocytes was exploited as a new tool for mimicking the mechanisms of NP interaction with glomerular cells and the repair of the kidney filtration barrier.

Podocyte injury: the role of proteinuria, urinary plasminogen, and oxidative stress

Podocytes are the key target for injury in proteinuric glomerular diseases that result in podocyte loss, progressive focal segmental glomerular sclerosis (FSGS), and renal failure. Current evidence suggests that the initiation of podocyte injury and associated proteinuria can be separated from factors that drive and maintain these pathogenic processes leading to FSGS. In nephrotic urine aberrant glomerular filtration of plasminogen (Plg) is activated to the biologically active serine protease plasmin by urokinase-type plasminogen activator (uPA). In vivo inhibition of uPA mitigates Plg activation and development of FSGS in several proteinuric models of renal disease including 5/6 nephrectomy. Here, we show that Plg is markedly increased in the urine in two murine models of proteinuric kidney disease associated with podocyte injury: Tg26 HIV-associated nephropathy and the Cd2ap^-/- model of FSGS. We show that human podocytes express uPA and three Plg receptors: uPAR, tPA, and Plg-RKT. We demonstrate that Plg treatment of podocytes specifically upregulates NADPH oxidase isoforms NOX2/NOX4 and increases production of mitochondrial-dependent superoxide anion (O₂^-) that promotes endothelin-1 synthesis. Plg via O₂^- also promotes expression of the B scavenger receptor CD36 and subsequent increased intracellular cholesterol uptake resulting in podocyte apoptosis. Taken together, our findings suggest that following disruption of the glomerular filtration barrier at the onset of proteinuric disease, podocytes are exposed to Plg resulting in further injury mediated by oxidative stress. We suggest that chronic exposure to Plg could serve as a "second hit" in glomerular disease and that Plg is potentially an attractive target for therapeutic intervention.

Loss of Kynurenine 3-Mono-oxygenase Causes Proteinuria

Changes in metabolite levels of the kynurenine pathway have been observed in patients with CKD, suggesting involvement of this pathway in disease pathogenesis. Our recent genetic analysis in the mouse identified the kynurenine 3-mono-oxygenase (KMO) gene (Kmo) as a candidate gene associated with albuminuria. This study investigated this association in more detail. We compared KMO abundance in the glomeruli of mice and humans under normal and diabetic conditions, observing a decrease in glomerular KMO expression with diabetes. Knockdown of kmo expression in zebrafish and genetic deletion of Kmo in mice each led to a proteinuria phenotype. We observed pronounced podocyte foot process effacement on long stretches of the filtration barrier in the zebrafish knockdown model and mild podocyte foot process effacement in the mouse model, whereas all other structures within the kidney remained unremarkable. These data establish the candidacy of KMO as a causal factor for changes in the kidney leading to proteinuria and indicate a functional role for KMO and metabolites of the tryptophan pathway in podocytes.