Role of p38 Mitogen-Activated Protein Kinase Activation in Podocyte Injury and Proteinuria in Experimental Nephrotic Syndrome

Protease-Activated Receptor 1-Mediated Damage of Podocytes in Diabetic Nephropathy

There is clinical evidence that increased urinary serine proteases are associated with the disease severity in the setting of diabetic nephropathy (DN). Elevation of serine proteases may mediate [Ca2+]i dynamics in podocytes through the protease-activated receptors (PARs) pathway, including associated activation of nonspecific cation channels. Cultured human podocytes and freshly isolated glomeruli were used for fluorescence and immunohistochemistry stainings, calcium imaging, Western blot analysis, scanning ion conductance microscopy, and patch clamp analysis. Goto-Kakizaki, Wistar, type 2 DN (T2DN), and a novel PAR1 knockout on T2DN rat background rats were used to test the importance of PAR1-mediated signaling in DN settings. We found that PAR1 activation increases [Ca2+]i via TRPC6 channels. Both human cultured podocytes exposed to high glucose and podocytes from freshly isolated glomeruli of T2DN rats had increased PAR1-mediated [Ca2+]i compared with controls. Imaging experiments revealed that PAR1 activation plays a role in podocyte morphological changes. T2DN rats exhibited a significantly higher response to thrombin and urokinase. Moreover, the plasma concentration of thrombin in T2DN rats was significantly elevated compared with Wistar rats. T2DNPar1-/- rats were embryonically lethal. T2DNPar1+/- rats had a significant decrease in glomerular damage associated with DN lesions. Overall, these data provide evidence that, during the development of DN, elevated levels of serine proteases promote an excessive [Ca2+]i influx in podocytes through PAR1-TRPC6 signaling, ultimately leading to podocyte apoptosis, the development of albuminuria, and glomeruli damage.

ARTICLE HIGHLIGHTS

Increased urinary serine proteases are associated with diabetic nephropathy. During the development of diabetic nephropathy in type 2 diabetes, the elevation of serine proteases could overstimulate protease-activated receptor 1 (PAR1). PAR1 signaling is involved in the development of DN via TRPC6-mediated intracellular calcium signaling. This study provides fundamental knowledge that can be used to develop efficient therapeutic approaches targeting serine proteases or corresponding PAR pathways to prevent or slow the progression of diabetes-associated kidney diseases.

Dual deletion of guanylyl cyclase-A and p38 mitogen-activated protein kinase in podocytes with aldosterone administration causes glomerular intra-capillary thrombi

Natriuretic peptides exert not only blood-lowering but also kidney-protective effects through guanylyl cyclase-A (GC-A), a natriuretic peptide receptor. Signaling through GC-A has been shown to protect podocytes from aldosterone-induced glomerular injury, and a p38 mitogen-activated protein kinase (MAPK) inhibitor reduced glomerular injury in aldosterone-infused podocyte-specific GC-A knockout mice. To explore the role of p38 MAPK in podocytes, we constructed podocyte-specific p38 MAPK and GC-A double knockout mice (pod-double knockout mice). Unexpectedly, aldosterone-infused and high salt-fed (B-ALDO)-treated pod-double knockout mice resulted in elevated serum creatinine, massive albuminuria, macrophage infiltration, foot process effacement, nephrin and podocin reduction, and additionally, intra-capillary fibrin thrombi, indicating endothelial injury. Microarray analysis showed increased plasminogen activator inhibitor-1 (PAI-1) in glomeruli of B-ALDO-treated pod-double knockout mice. In B-ALDO-treated pod-double knockout mice, PAI-1 increased in podocytes, and treatment with PAI-1 neutralizing antibody ameliorated intra-capillary thrombus formation. In vitro, deletion of p38 MAPK by the CRISPR/Cas9 system and knockdown of GC-A in human cultured podocytes upregulated PAI-1 and transforming growth factor- β1 (TGF-β1). When p38 MAPK knockout podocytes, transfected with a small interfering RNA to suppress GC-A, were co-cultured with glomerular endothelial cells in a transwell system, the expression of TGF-β1 was increased in glomerular endothelial cells. PAI-1 inhibition ameliorated both podocyte and endothelial injury in the transwell system signifying elevated PAI-1 in podocytes is a factor disrupting normal podocyte-endothelial crosstalk. Thus, our results indicate that genetic dual deletion of p38 MAPK and GC-A in podocytes accelerates both podocyte and endothelial injuries, suggesting these two molecules play indispensable roles in podocyte function.

Mycophenolic acid directly protects podocytes by preserving the actin cytoskeleton and increasing cell survival

Mycophenolate Mofetil (MMF) has an established role as a therapeutic agent in childhood nephrotic syndrome. While other immunosuppressants have been shown to positively affect podocytes, direct effects of MMF on podocytes remain largely unknown. The present study examines the effects of MMF's active component Mycophenolic Acid (MPA) on the transcriptome of podocytes and investigates its biological significance. We performed transcriptomics in cultured murine podocytes exposed to MPA to generate hypotheses on podocyte-specific effects of MPA. Accordingly, we further analyzed biological MPA effects on actin cytoskeleton morphology after treatment with bovine serum albumin (BSA) by immunofluorescence staining, as well as on cell survival following exposure to TNF-α and cycloheximide by neutral red assay. MPA treatment significantly (adjusted p < 0.05) affected expression of 351 genes in podocytes. Gene Ontology term enrichment analysis particularly clustered terms related to actin and inflammation-related cell death. Indeed, quantification of the actin cytoskeleton of BSA treated podocytes revealed a significant increase of thickness and number of actin filaments after treatment with MPA. Further, MPA significantly reduced TNFα and cycloheximide induced cell death. MPA has a substantial effect on the transcriptome of podocytes in vitro, particularly including functional clusters related to non-immune cell dependent mechanisms. This may provide a molecular basis for direct beneficial effects of MPA on the structural integrity and survival of podocytes under pro-inflammatory conditions.

Kaempferol attenuates doxorubicin-induced renal tubular injury by inhibiting ROS/ASK1-mediated activation of the MAPK signaling pathway

BACKGROUND AND OBJECTIVE

Doxorubicin (DOX) is one of the most commonly used antineoplastic agents; however, its considerable nephrotoxicity restricts its clinical use. Kaempferol (KPF), a naturally-occurring flavonoid, possesses various biological benefits, including anti-tumor activity that has garnered increasing attention. This study aimed to evaluate the possible reno-protective role of KPF in DOX nephrotoxicity.

METHODS

Male BALB/c mice were injected with DOX via the tail vein to imitate renal damage. Their body and kidney were weighed after 2 weeks of KPF therapy, and urine, serum, and tissue samples were obtained to establish proteinuria, serum creatinine, and pathological alterations. The variations in SOD, GSH, CTA, MDA, and SOD2 expression in renal tissues were measured, and p-ASK1, p-p38, and P-JNK were evaluated by western blot. Cell viability was detected using MTT tests. Apoptosis was assessed by TUNEL, Hoechst 33342, PI staining, and western blot. Fluorescent ROS probes were used to assess oxidative cell damage.

RESULTS

KPF ameliorated DOX-induced renal injury, improved proteinuria and renal function, restored GSH content, SOD activity and CTA activity in kidneys, inhibited the overproduction of MDA, and suppressed DOX-induced activation of the MAPK signaling pathway. In NRK-52E cells, KPF significantly inhibited DOX-induced ROS overproduction, restrained the activation of MAPK signaling pathway, and alleviated DOX-induced cell morphological damage and loss of cell viability, While it did not affect the toxicity of DOX to 4T1 cells.

CONCLUSION

KPF provides a protective effect against DOX-induced nephrotoxicity while maintaining the cytotoxicity of DOX in breast cancer cells, thereby it may provide a viable solution to lessen renal toxicity in cancer patients receiving DOX.

Inhibition of p38 MAPK decreases hyperglycemia-induced nephrin endocytosis and attenuates albuminuria

Abstract

Chronic hyperglycemia, as in diabetes mellitus, may cause glomerular damage with microalbuminuria as an early sign. Noteworthy, even acute hyperglycemia can increase glomerular permeability before structural damage of the glomerular filter can be detected. Despite intensive research, specific antiproteinuric therapy is not available so far. Thus, a deeper understanding of the molecular mechanisms of albuminuria is desirable. P38 MAPK signaling is involved in the development of hyperglycemia-induced albuminuria. However, the mechanism of increased p38 MAPK activity leading to increased permeability and albuminuria remained unclear. Recently, we demonstrated that acute hyperglycemia triggers endocytosis of nephrin, the key molecule of the slit diaphragm, and induces albuminuria. Here, we identify p38 MAPK as a pivotal regulator of hyperglycemia-induced nephrin endocytosis. Activated p38 MAPK phosphorylates the nephrin c-terminus at serine 1146, facilitating the interaction of PKCα with nephrin. PKCα phosphorylates nephrin at threonine residues 1120 and 1125, mediating the binding of β-arrestin2 to nephrin. β-arrestin2 triggers endocytosis of nephrin by coupling it to the endocytic machinery, leading to increased glomerular permeability. Pharmacological inhibition of p38 MAPK preserves nephrin surface expression and significantly attenuates albuminuria.

Key messages

Acute hyperglycemia triggers endocytosis of nephrin.

Activated p38 MAPK phosphorylates the nephrin c-terminus at serine 1146, facilitating the interaction of PKCα with nephrin.

PKCα phosphorylates nephrin at threonine residues 1120 and 1125, mediating the binding of β-arrestin2 to nephrin.

β-arrestin2 triggers endocytosis of nephrin by coupling it to the endocytic machinery, leading to a leaky glomerular filter.

Pharmacological inhibition of p38 MAPK preserves nephrin surface expression and significantly attenuates albuminuria under hyperglycemic conditions.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00109-022-02184-5.

Effect of Nephropathy Prescription I on the Expression of Angptl3 and Podocyte-Associated Protein in Mice with Adriamycin-Induced Nephropathy

Objective

This study aimed to investigate the effects of Nephropathy Prescription I on the expression of angptl3, nephrin, and podocin, in addition to its protective effects on podocytes in mice with adriamycin-induced nephropathy.

Methods

BALB/c mice were randomly divided into the control (C), adriamycin (Model or M), adriamycin + Nephropathy Prescription I (M + Z), adriamycin + prednisone acetate (M + S), and adriamycin + Nephropathy Prescription I + prednisone acetate groups (M + Z + S). All mice except those in the C group in the experimental groups were treated with a single tail vein injection of adriamycin. The urine albumin-creatinine ratio was measured before model establishment and on the 7th day, 14th day, 21st day, and 28th day of doxorubicin injection. All the mice were sacrificed on the 29th day. Blood samples were collected to observe biochemical indicators in the serum. The morphological structure and podocyte ultrastructure in the kidney were observed using light and electron microscopy, respectively. The expression of angptl3, nephrin, and podocin at the mRNA and protein levels was detected by real-time PCR and western blotting, respectively.

Results

Following modeling with adriamycin, albuminuria was observed in urine samples in the first week, and the urinary protein/creatinine ratio increased maximally in the fourth week in the M group (P < 0.05). In contrast, the urinary protein/creatinine ratio significantly decreased (P < 0.05) in the third week in the (M + Z) group compared to that in the M group. Similarly, this ratio decreased in the (M + S) and (M + Z + S) groups compared to that in the M group throughout the experiment. Compared with the C group, serum albumin content and the expression of nephrin and podocin decreased (P < 0.05), whereas blood lipid level and the expression of angptl3 increased (P < 0.05) in the M group. Glomerular foot process fusion was observed in this group using electron microscopy. In all the intervention groups, serum albumin content and the expression of nephrin and podocin increased (P < 0.05), whereas blood lipid level and the expression of angptl3 decreased (P < 0.05), with alleviated glomerular foot process injury observed particularly in the (M + Z + S) group.

Conclusion

The Nephropathy Prescription I can alleviate albuminuria, increase serum albumin levels, lower blood lipid levels, and reduce the fusion of foot processes of podocytes in mice with adriamycin-induced nephropathy. The protective effects of the Nephropathy Prescription I may function by reducing Angptl3 expression and increasing nephrin and podocin expression.

Osteocrin ameliorates adriamycin nephropathy via p38 mitogen-activated protein kinase inhibition

Natriuretic peptides exert multiple effects by binding to natriuretic peptide receptors (NPRs). Osteocrin (OSTN) binds with high affinity to NPR-C, a clearance receptor for natriuretic peptides, and inhibits degradation of natriuretic peptides and consequently enhances guanylyl cyclase-A (GC-A/NPR1) signaling. However, the roles of OSTN in the kidney have not been well clarified. Adriamycin (ADR) nephropathy in wild-type mice showed albuminuria, glomerular basement membrane changes, increased podocyte injuries, infiltration of macrophages, and p38 mitogen-activated protein kinase (MAPK) activation. All these phenotypes were improved in OSTN- transgenic (Tg) mice and NPR3 knockout (KO) mice, with no further improvement in OSTN-Tg/NPR3 KO double mutant mice, indicating that OSTN works through NPR3. On the contrary, OSTN KO mice increased urinary albumin levels, and pharmacological blockade of p38 MAPK in OSTN KO mice ameliorated ADR nephropathy. In vitro, combination treatment with ANP and OSTN, or FR167653, p38 MAPK inhibitor, reduced Ccl2 and Des mRNA expression in murine podocytes (MPC5). OSTN increased intracellular cyclic guanosine monophosphate (cGMP) in MPC5 through GC-A. We have elucidated that circulating OSTN improves ADR nephropathy by enhancing GC-A signaling and consequently suppressing p38 MAPK activation. These results suggest that OSTN could be a promising therapeutic agent for podocyte injury.

Inhibitory Potential of Murraya Koenigii (L.) and Ficus Carica L. Extracts Against Aldose Reductase (ALR), Advanced Glycation End Products (AGEs) Formation and Sorbitol Accumulation

Introduction: Murraya koenigii (L.) and Ficus carica L. are traditionally used plants with significant medicinal and nutritional values. Aim and Objective: The present study was focused on the evaluation of hydro-alcoholic and aqueous extracts of M. koenigii (L.) leaves [MKHA (M. koenigii (L.) hydro-alcoholic extract) and MKAQ (M. koenigii (L.) aqueous extract)] and dried fruits of F. carica L. [FCHA (F. carica L. hydro-alcoholic extract) and FCAQ (F. carica L. aqueous extract)] in the attenuation of markers of microvascular complications associated with diabetes mellitus which can be further used to investigate the pharmacological activity of these plants in treatment of diabetes and its complications. Material and Method: The attenuating effect of the extracts was evaluated by calculating the ALR1 enzyme inhibition in a kidney of Wistar rat, anti-glycation activity in bovine serum albumin (BSA) and erythrocyte sorbitol accumulation inhibition in heparinized human blood. Results: A significant inhibitory effect (IC50 6.47μg/ml,7.26μg/ml,8.93 μg/ml and 9.66μg/ml) was observed with different concentrations of extracts (MKHA, MKAQ, FCHA and FCAQ) respectively, against ALR enzyme. After the 4th week of incubation, the inhibition of AGEs formation by MKHA, MKAQ, FCHA and FCAQ (500μg/ml) was found to be 82.58%, 78.58%, 74.39% and 69.56% respectively. MKHA, MKAQ, FCHA and FCAQ were found to exhibit significant inhibition against the accumulation of sorbitol in RBCs with IC50 188.88 μg/ml, 247.74μg/ml, 291.94μg/ml and 345.34μg/ml, respectively. Conclusion: The administration of different concentrations of MKHA, MKAQ, FCHA and FCAQ significantly attenuated ALR, AGEs and sorbitol accumulation; hence, it can provide a basis for identification and development of new inhibitors of these biomarkers.

Ghrelin octanoylation by ghrelin O-acyltransferase: protein acylation impacting metabolic and neuroendocrine signalling

The acylated peptide hormone ghrelin impacts a wide range of physiological processes but is most well known for controlling hunger and metabolic regulation. Ghrelin requires a unique posttranslational modification, serine octanoylation, to bind and activate signalling through its cognate GHS-R1a receptor. Ghrelin acylation is catalysed by ghrelin O-acyltransferase (GOAT), a member of the membrane-bound O-acyltransferase (MBOAT) enzyme family. The ghrelin/GOAT/GHS-R1a system is defined by multiple unique aspects within both protein biochemistry and endocrinology. Ghrelin serves as the only substrate for GOAT within the human proteome and, among the multiple hormones involved in energy homeostasis and metabolism such as insulin and leptin, acts as the only known hormone in circulation that directly stimulates appetite and hunger signalling. Advances in GOAT enzymology, structural modelling and inhibitor development have revolutionized our understanding of this enzyme and offered new tools for investigating ghrelin signalling at the molecular and organismal levels. In this review, we briefly summarize the current state of knowledge regarding ghrelin signalling and ghrelin/GOAT enzymology, discuss the GOAT structural model in the context of recently reported MBOAT enzyme superfamily member structures, and highlight the growing complement of GOAT inhibitors that offer options for both ghrelin signalling studies and therapeutic applications.

Transforming growth factor-β1-induced podocyte injury is associated with increased microRNA-155 expression, enhanced inflammatory responses and MAPK pathway activation

MicroRNA-155 (miR-155) is associated with various diseases. However, the potential role of miR-155 in early glomerular disease (EGD) remains elusive. In the present study, the clinical significance of urinary miR-155 expression was explored in patients with EGD using receiver operating characteristic curve analysis. Conditionally immortalized mouse podocytes were cultured in vitro and treated with transforming growth factor-β1 (TGF-β1) at different concentrations and durations. The gene expression levels of mRNAs and miR-155 were detected using reverse transcription-quantitative PCR. Synaptopodin, CD2-associated protein (CD2AP), p38, and extracellular signal-regulated kinase (Erk) 1/2 expressions were detected using western blotting. Cell supernatants were collected for assaying tumor necrosis factor (TNF)-α and interleukin (IL)-6 concentrations using enzyme-linked immunosorbent assay. The Pearson correlation analysis was used to analyze the correlation between miR-155 levels and TNF-α or IL-6. It was found that miR-155 levels in urine have high sensitivity and specificity in the diagnosis of EGD. Time- and dose-dependent TGF-β1 treatments downregulated synaptopodin and CD2AP expression levels, and activated the p38 and Erk 1/2 pathway. However, these effects were attenuated by p38 and Erk 1/2 phosphorylation inhibitors. Additionally, TNF-α and IL-6 secretions were elevated, and their concentrations were positively correlated with the expression of miR-155 during podocyte injury. Thus, the present study indicated that miR-155 is a potential biomarker for the diagnosis of EGD, and its expression is associated with the release of pro-inflammatory cytokines and activation of mitogen-activated protein kinase (MAPK) pathway in TGF-β1-induced podocyte injury. The present study suggests that the TGF-β1/miR-155/MAPK axis is a novel target in the mechanism of EGD.

MiR-138 plays an important role in diabetic nephropathy through SIRT1-p38-TTP regulatory axis

Diabetic nephropathy (DN) is the main cause of chronic kidney disease (CKD) and is one of the most common and serious complications of diabetes mellitus (DM). Sirtuin 1 (SIRT1) and tristetraprolin (TTP) are two important protective factors in DN; however, the regulatory relationship between SIRT1 and TTP, and the underneath mechanism are interesting but still unclear. Identifying the key factors that regulate SIRT1 or TTP may be of great value to the understanding and treatment of the DN. In this study, through systematic experimental methods, we found that the expression of miR-138 was significantly upregulated in DN clinical patient samples, and our experimental results suggested that miR-138 could bind the 3'-UTR of SIRT1 and inhibit its expression in both cultured podocytes and db/db mice kidney tissues. Furthermore, our in vitro and in vivo experiments also indicated miR-138 could target SIRT1 and affect TTP through p38 pathway. And downregulation of miR-138 attenuated podocyte injury and showed some extent of therapeutic effects in DN mice models. Our findings revealed that the regulatory axis of miR-138-SIRT1-p38-TTP might play a key role in DN. We believe that these findings may be of some value for deepening the understanding of DN and may serve as a reference for future treatment of this disease.

Green synthesized selenium doped zinc oxide nano-antibiotic: synthesis, characterization and evaluation of antimicrobial, nanotoxicity and teratogenicity potential

A facile, green synthesis of selenium doped zinc oxide nano-antibiotic (Se-ZnO-NAB) using the Curcuma longa extract is reported to combat the increased emergence of methicillin-resistant Staphylococcus aureus (MRSA). The developed Se-ZnO-NAB were characterized for their physicochemical parameters and extensively evaluated for their toxicological potential in an animal model. The prepared Se-ZnO-NABs were characterized via Fourier transformed infrared spectroscopy to get functional insight into their surface chemistry, scanning electron microscopy revealing the polyhedral morphology with a size range of 36 ± 16 nm, having -28.9 ± 6.42 mV zeta potential, and inductively coupled plasma optical emission spectrometry confirming the amount of Se and Zn to be 14.43 and 71.70 mg L-1 respectively. Moreover, the antibacterial activity against MRSA showed significantly low minimum inhibitory concentration at 6.2 μg mL-1 when compared against antibiotics. Also, total protein content and reactive oxygen species production in MRSA, under the stressed environment of Se-ZnO-NAB, significantly (p < 0.05) decreased compared to the negative control. Moreover, the results of acute oral toxicity in rats showed moderate variations in blood biochemistry and histopathology of vital organs. The teratogenicity and fetal evaluations also revealed some signs of toxicity along with changes in biochemical parameters. The overall outcomes suggest that Se-ZnO-NAB can be of significant importance for combating multi-drug resistance but must be used with extreme caution, particularly in pregnancy, as moderate toxicity was observed at a toxic dose of 2000 mg kg-1.

A novel podocyte protein, R3h domain containing-like, inhibits TGF-β-induced p38 MAPK and regulates the structure of podocytes and glomerular basement membrane

Not only in kidney glomerular physiological function but also glomerular pathology especially in diabetic condition, glomerular podocytes play pivotal roles. Therefore, it is important to increase our knowledge about the genes and proteins expressed in podocytes. Recently, we have identified a novel podocyte-expressed gene, R3h domain containing-like (R3hdml) and analyzed its function in vivo as well as in vitro. Transforming growth factor-β (TGF-β) signaling regulated the expression of R3hdml. And R3hdml inhibited p38 mitogen-activated protein kinase phosphorylation, which was induced by TGF-β, leading to the amelioration of podocyte apoptosis. Furthermore, a lack of R3hdml in mice significantly worsened glomerular function in streptozotocin (STZ)-induced diabetes, while overexpression of R3hdml ameliorated albuminuria in STZ-induced diabetes. Our results surmise that the functional analyses of R3hdml may lead to the development of novel therapeutic strategies for diabetic nephropathy in the future. KEY MESSAGES: • A novel podocyte expressed protein R3h domain containing-like was identified. • R3HDML inhibits podocyte apoptosis by inhibiting TGF-β-mediated p38 MAPK signaling. • Overexpression of R3HDML ameliorates albuminuria in STZ-induced diabetes mice. • R3HDML may prove to be a novel therapeutic strategy for diabetic nephropathy.

Urinary- and Plasma-Derived Exosomes Reveal a Distinct MicroRNA Signature Associated With Albuminuria in Hypertension

Urinary albumin excretion (UAE) is a marker of cardiovascular risk and renal damage in hypertension. MicroRNAs (miRNAs) packaged into exosomes function as paracrine effectors in cell communication and the kidney is not exempt. This study aimed to state an exosomal miRNA profile/signature associated to hypertension with increased UAE and the impact of profibrotic TGF-β1 (transforming growth factor β1) on exosomes miRNA release. Therefore, exosomes samples from patients with hypertension with/without UAE were isolated and characterized. Three individual and unique small RNA libraries from each subject were prepared (total plasma, urinary, and plasma-derived exosomes) for next-generation sequencing profiling. Differentially expressed miRNAs were over-represented in Kyoto Encyclopedia of Genes and Genomes pathways, and selected miRNAs were validated by real-time quantitative polymerase chain reaction in a confirmation cohort. Thus, a signature of 29 dysregulated circulating miRNAs was identified in UAE hypertensive subjects, regulating 21 pathways. Moreover, changes in the levels of 4 exosomes-miRNAs were validated in a confirmation cohort and found associated with albuminuria. In particular miR-26a, major regulator of TGF-β signaling, was found downregulated in both type of exosomes when compared with healthy controls and to hypertension normoalbuminurics (P<0.01). Similarly, decreased miR-26a levels were found in podocyte-derived exosomes after TGF-β stress. Our results revealed an exosomes miRNA signature associated to albuminuria in hypertension. In particular, exosomes miR-26a seemed to play a key role in the regulation of TGF-β, a relevant effector in podocyte damage. These findings support the use of exosomes miRNAs as biomarkers of cardiovascular risk progression and therapeutic tools in early kidney damage.

Therapeutic trials in adult FSGS: lessons learned and the road forward

Focal segmental glomerulosclerosis (FSGS) is not a specific disease entity but a lesion that primarily targets the podocyte. In a broad sense, the causes of the lesion can be divided into those triggered by a presumed circulating permeability factor, those that occur secondary to a process that might originate outside the kidneys, those caused by a genetic mutation in a podocyte or glomerular basement membrane protein, and those that arise through an as yet unidentifiable process, seemingly unrelated to a circulating permeability factor. A careful attempt to correctly stratify patients with FSGS based on their clinical presentation and pathological findings on kidney biopsy is essential for sound treatment decisions in individual patients. However, it is also essential for the rational design of therapeutic trials in FSGS. Greater recognition of the pathophysiology underlying podocyte stress and damage in FSGS will increase the likelihood that the cause of an FSGS lesion is properly identified and enable stratification of patients in future interventional trials. Such efforts will facilitate the identification of effective therapeutic agents.

MicroRNA-874-3p Aggravates Doxorubicin-Induced Renal Podocyte Injury via Targeting Methionine Sulfoxide Reductase B3

Clinical application of doxorubicin (Dox) is limited due to its serious side effects including nephrotoxicity, and kidney podocytes play important roles in renal diseases. MicroRNAs (miRNAs) are critical regulators associated with human diseases. The purpose of this study was to explore a novel target in adjusting Dox-induced renal podocyte injury. Through a double luciferase reporter gene experiment, it was found that miR-874-3p directly targeted methionine sulfoxide reductase B3 (MsrB3). During the tests of miR-874-3p inhibitor and MsrB3 siRNA in human podocytes or miR-874-3p antagomir in mice, we found that the expression levels of downstream oxidative stress and apoptosis-related proteins were regulated by miR-874-3p/MsrB3 signal to alleviate or aggravate renal podocyte injury. The data in the present work showed that miR-874-3p aggravated Dox-caused renal podocyte injury by promoting apoptosis and oxidative damage via inhibiting MsrB3. Therefore, miR-874-3p/MsrB3 should be considered as a new therapeutic target in controlling renal podocyte injury induced by Dox.

Puromycin aminonucleoside-induced podocyte injury is ameliorated by the Smad3 inhibitor SIS3

Smad3 signaling and transgelin expression are often activated during puromycin aminonucleoside (PAN)‐induced podocyte injury. Here, we investigated whether the Smad3 inhibitor SIS3 can ameliorate damage to injured podocytes. A model of PAN‐induced podocyte injury was constructed using the MPC5 cell line. The effects of SIS3 on the expression of the podocyte cytoskeletal proteins transgelin, p15^INK4B, phosphor‐smad3, phosphor‐JAK/stat3, the apoptotic marker cleaved caspase 3, and c‐myc were investigated using western blot. The distribution of F‐actin in PAN‐induced podocyte injury was observed under an immunofluorescence microscope. PAN‐induced podocyte injury altered the distribution of F‐actin and transgelin, and colocalization of these two proteins was observed. Transgelin expression and Smad3 phosphorylation were increased in the MPC5 cell line with prolonged PAN treatment. In addition, c‐myc expression, p15^INK4B, and JAK phosphorylation were all increased after treatment with PAN. Treatment with the Smad3 inhibitor SIS3 reversed these phenomena and protected against PAN‐induced podocyte injury. Moreover, stimulating podocytes directly with TGFβ‐1 also led to enhanced expression of transgelin or phosphor‐JAK/stat3, and this could be inhibited by SIS3. In conclusion, transgelin expression was induced through the Smad3 signaling pathway during PAN‐induced podocyte injury, and the resulting abnormal distribution of F‐actin and the enhanced expression of transgelin could be reversed by blockade of this pathway.

Semaphorin3A-Inhibitor Ameliorates Doxorubicin-Induced Podocyte Injury

Podocyte injury is an independent risk factor for the progression of renal diseases. Semaphorin3A (SEMA3A), expressed in podocytes and tubular cells in the mammalian adult kidneys, has been reported to regulate diverse biological functions and be associated with renal diseases. Here, we investigated pathological roles of SEMA3A signaling on podocyte injury using a doxorubicin (Dox)-induced mouse model and examined the therapeutic effect of SEMA3A-inhibitor (SEMA3A-I). We demonstrated that Dox caused massive albuminuria and podocyte apoptosis as well as an increase of SEMA3A expression in podocytes, all of which were ameliorated with SEMA3A-I treatment. In addition, c-Jun N-terminal kinase (JNK), known as a downstream of SEMA3A signaling, was activated in Dox-injected mouse podocytes while SEMA3A-I treatment partially blocked the activation. In vitro, SEMA3A-I protected against Dox-induced podocyte apoptosis and recombinant SEMA3A caused podocyte apoptosis with activation of JNK signaling. JNK inhibitor, SP600125, attenuated SEMA3A-induced podocyte apoptosis, indicating that the JNK pathway would be involved in SEMA3A-induced podocyte apoptosis. Furthermore, the analysis of human data revealed a positive correlation between levels of urinary SEMA3A and protein, suggesting that SEMA3A is associated with podocyte injury. In conclusion, SEMA3A has essential roles in podocyte injury and it would be the therapeutic target for protecting from podocyte injury.

Assessing the Impact of Losmapimod on Proteinuria in Idiopathic Focal Segmental Glomerulosclerosis

Introduction

Idiopathic focal segmental glomerulosclerosis (FSGS) is a leading cause of nephrotic syndrome and end-stage renal disease. In preclinical models and biopsies of human FSGS kidneys, p38 mitogen-activated protein kinase (MAPK) has demonstrated enhanced activity; and p38 MAPK inhibition has improved disease markers. This proof-of-concept trial aimed to assess efficacy, safety, tolerability, and pharmacokinetics of losmapimod, an oral p38 MAPK inhibitor, in humans with FSGS.

Methods

A single-arm, multicenter, open-label, Phase II trial (NCT02000440) was conducted in adults with FSGS; proteinuria ≥2.0 g/d; estimated glomerular filtration rate (eGFR) ≥45 ml/min per 1.73 m²; blood pressure <140/90 mm Hg. Collapsing and genetic forms of FSGS were excluded. The primary endpoint was number of patients with ≥50% proteinuria reduction and eGFR ≥70% of baseline after receiving losmapimod twice-daily for 16 to 24 weeks.

Results

Seventeen patients received ≥1 losmapimod dose. No patients achieved the primary endpoint; therefore, the study was terminated following a prespecified interim analysis. At week 24, proteinuria reductions between 20% and <50% were observed in 4 patients and proteinuria increases >20% in 3 patients. One patient achieved a proteinuria response (≥50% reduction) at week 2 but subsequently relapsed. Losmapimod pharmacokinetics were consistent with prior studies. No serious adverse events (AEs) were reported.

Conclusion

p38 MAPK inhibition with losmapimod did not result in ≥50% reduction of proteinuria in patients with FSGS. However, study population heterogeneity may have contributed to our negative findings and therefore this does not eliminate the potential to demonstrate benefit in a population more sensitive to p38 MAPK inhibition if identifiable in the future by precision-medicine methods.

Crocin protects against cardiotoxicity induced by doxorubicin through TLR-2/NF-κB signal pathway in vivo and vitro

Doxorubicin (DOX) is widely used to treat multiple of tumors, but its clinical trials are allied with some serious adverse events mainly cardiac functional abnormalities. So the objective of our investigation is to identify the cardioprotective action of crocin (CRO), a natural compound derived from saffron, against DOX-induced cardiotoxicity. CRO was injected intraperitoneally (i.p.) to rats for sixconsecutive days and DOX (i.p.) was administered on the fourth day. H9c2 cells were treated with DOX for 24 h after being pre-treated by CRO for 2 h. CROreduced tachycardiaand J-point elevation,decreased the levelsof serum creatine kinase, lactate dehydrogenase,glutamic-oxalacetic transaminase and glutamic-pyruvic transaminase.CRO exerted positive effect on DOX-induced ROS productionand changes of oxidative stress biomarkers. CRO significantlydecreased intracellular Ca²⁺ concentration andincreased mitochondria membrane potentialin H9c2 cells. CRO also resisted the DOX-induced high expressionof tumor necrosis factor-αand interleukin-6, inhibitedapoptosisand improved the abnormal expression levels of Bcl-2, Bax and Caspase-3 proteins.CRO obviously restrained DOX-mediatedhigh expression of toll-like receptor-2 (TLR-2) and nuclear factor kappa-B (NF-κB) in ventricular tissue. Inbrief,CRO distinctly restrained DOX-mediated cardiotoxicity by inhibiting oxidative stress, inflammation, apoptoticandredressingcardiomyocyte calcium dyshomeostasis and mitochondria damage.These cardioprotective effects may berelated closely with the TLR2/NF-κB pathway.

Human Th17 cells produce a soluble mediator that increases podocyte motility via signaling pathways that mimic PAR-1 activation

The specific pathogenesis of idiopathic nephrotic syndrome (NS) is poorly understood, and the role of immune mediators remains contentious. However, there is good evidence for the role of a circulating factor, and we recently postulated circulating proteases as candidate factors. Immunosuppressive therapy with glucocorticoids (GCs) and T cell inhibitors are widely used in the clinical treatment of NS. Given that T helper (CD4⁺) cells expressing IL-17A (so-called Th17 cells) have recently been reported to be resistant to GC treatment, and GC resistance remains a major challenge in the management of NS, we hypothesized that Th17 cells produce a circulating factor that is capable of signaling to the podocyte and inducing deleterious phenotypic changes. To test this, we generated human Th17 cells from healthy volunteers and added the supernatants from these T cell cultures to conditionally immortalized human podocytes in vitro. This demonstrated that podocytes treated with Th17 cell culture supernatant, as well as with patient disease plasma, showed significant stimulation of JNK and p38 MAPK pathways and an increase in motility, which was blocked using a JNK inhibitor. We have previously shown that nephrotic plasma elicits a podocyte response via protease-activated receptor-1 (PAR-1). Stimulation of PAR-1 in podocytes elicited the same signaling response as Th17 cell culture supernatant treatment. Equally, protease inhibitors with Th17 cell culture treatment blocked the signaling response. This was not replicated by the reagents added to Th17 cell cultures or by IL-17A. Hence, we conclude that an undefined soluble mediator produced by Th17 cells mimics the deleterious effect of PAR-1 activation in vitro. Given the association between pathogenic subsets of Th17 cells and GC resistance, these observations have potential therapeutic relevance for patients with NS.

Markers of renal fibrosis: How do they correlate with podocyte damage in glomerular diseases?

BACKGROUND

Renal fibrosis is the result of the interaction of cellular and molecular pathways, which is induced by sustained glomerular injury and involves the podocytes and multiple profibrotic factors. In this study, we investigated the correlation of the mRNA expression of podocyte proteins and profibrotic factors with renal fibrosis measured in renal biopsies of patients with primary and secondary glomerulopathies.

METHODS

Eighty-four adult patients with primary or secondary glomerular diseases and 12 controls were included. Demographic and clinical data were collected. Seventy-two percent of the renal biopsies were done less than one year from clinical disease manifestation. The quantification of the podocyte-associated mRNAs of alpha-actinin-4, podocin, and podocalyxin, as well as of the profibrotic factors TGF-β1, CTGF, and VEGF-A were quantified by real-time polymerase chain reaction. The percent positive area of renal fibrosis was measured by immunohistochemistry staining, using anti-CTGF and anti-HHF35 antibodies and unpolarized Sirius Red. Correlations between the expression of tissue mRNAs and the positive area of fibrosis for the measured markers were made by Spearman's rank correlation coefficient.

RESULTS

In relation to control biopsies, podocyte-specific proteins were downregulated in podocytopathies, in proliferative nephritis, in diabetic kidney disease (DRD), and in IgA nephropathy (IgAN). Messenger RNA of TGF-β1, CTGF, and VEGF-A was upregulated in patients with podocytopathies and in DRD but not in proliferative nephritis and IgAN. Tissue mRNA expression of TGF-β1, CTGF, and VEGF-A were strongly correlated with renal fibrosis, as measured by HHF35; however, the correlation, albeit significant, was moderate for Sirius Red and weak for CTGF. The percent positive area of renal fibrosis measured by Sirius Red was similar between podocytopathies and DRD and significantly higher in podocytopathies compared to IgAN or proliferative nephritis.

CONCLUSIONS

In patients with glomerular diseases, the mRNA of TGF-β1, CTGF, and VEGF-A correlated positively with the extent of renal fibrosis, and the positive area of fibrosis was larger in the podocytopathies and in DRD as measured by Sirius Red. The pathways connecting podocyte damage and activation of profibrotic factors to kidney tissue fibrosis need to be better investigated.

MiR-30 family prevents uPAR-ITGB3 signaling activation through calcineurin-NFATC pathway to protect podocytes

Urokinase plasminogen activator receptor (uPAR) is upregulated in podocytes of glomerular diseases and crucially mediates podocyte injury through integrin β3 (ITGB3). We previously showed that the miR-30 family maintains podocyte structure and function by inhibiting injurious calcineurin signaling through nuclear factor of activated T cells C (NFATC). Here, we tested whether the miR-30-calcineurin-NFATC and uPAR-ITGB3 pathways, two of the major pathways leading to podocyte injury, could interact. We found that podocyte-specific miR-30 knockdown in mice induced uPAR upregulation and ITGB3 activation, accompanied by proteinuria and podocyte injury. These effects of miR-30 knockdown were reduced using inhibitors of ITGB3, calcineurin, and NFATC, respectively, which are known to be antiproteinuric. These results indicate that miR-30 deficiency leads to calcineurin-NFATC signaling activation, which in turn activates the uPAR-ITGB3 pathway. In cultured podocytes, miR-30 knockdown also activated uPAR-ITGB3 signaling, leading to Rho GTPase activation, synaptopodin downregulation and podocyte injury. To explore uPAR-ITGB3 signaling regulation by miR-30 in podocytopathy development, we treated mice with lipopolysaccharide (LPS) and found that miR-30 was downregulated in podocytes, accompanied by uPAR upregulation and ITGB3 activation. We obtained the same results in cultured podocytes treated with LPS. Podocyte-specific transgenic miR-30 abolished uPAR-ITGB3 signaling and ameliorated podocyte injury and proteinuria in mice. Taken together, these experiments show that uPAR-ITGB3 signaling is negatively regulated by miR-30 through calcineurin-NFATC pathway, a novel mechanism underlying podocyte injury in glomerular diseases. Our study has elucidated the relationship among the crucial players governing podocyte pathophysiology and the antiproteinuric actions of drugs commonly used for podocytopathies.

Diabetes-Induced DUSP4 Reduction Promotes Podocyte Dysfunction and Progression of Diabetic Nephropathy

Diabetic nephropathy (DN) remains the leading cause of end-stage renal disease. Hyperglycemia-induced podocyte dysfunction is a major contributor of renal function impairment in DN. Previous studies showed that activation of mitogen-activated protein kinase (MAPK) in diabetes promotes podocyte dysfunction and cell death. Dual specificity phosphatases (DUSPs) are a family of phosphatases mainly responsible for MAPK inhibition. In this study, we demonstrated that diabetes and high glucose exposure decreased DUSP4 expression in cultured podocytes and glomeruli. Diabetes-induced DUSP4 reduction enhanced p38 and c-Jun N-terminal kinase (JNK) activity and podocyte dysfunction. The overexpression of DUSP4 prevented the activation of p38, JNK, caspase 3/7 activity, and NADPH oxidase 4 expression induced by high glucose level exposure. Deletion of DUSP4 exacerbated albuminuria and increased mesangial expansion and glomerular fibrosis in diabetic mice. These morphological changes were associated with profound podocyte foot process effacement, cell death, and sustained p38 and JNK activation. Moreover, inhibition of protein kinase C-δ prevented DUSP4 expression decline and p38/JNK activation in the podocytes and renal cortex of diabetic mice. Analysis of DUSP4 expression in the renal cortex of patients with diabetes revealed that decreased DUSP4 mRNA expression correlated with reduced estimated glomerular filtration rate (<60 mL/min/1.73 m²). Thus, this study demonstrates that preserving DUSP4 expression could protect against podocyte dysfunction and preserve glomerular function in DN.

Pharmacological levels of hydrogen sulfide inhibit oxidative cell injury through regulating the redox state of thioredoxin

Hydrogen sulfide (H₂S) is a gaseous mediator with multifaceted biological activities. It has anti-inflammatory and anti-oxidative effects. Currently, the mechanisms are not fully understood. Given that Trx/ASK1/P38 signaling pathway mediates many oxidative cell responses, we tested whether and how H₂S affected this pathway. Exposure of podocytes to Adriamycin (ADR), an antitumor drug, led to a P38-mediated oxidative cell injury, as evidenced by the increased protein carbonylation, oxidative activation of P38, and prevention of the cell death by antioxidants, NADPH oxidase inhibitor and P38 inhibitor. In the presence of H₂S donor NaHS, however, the podocyte injury was largely prevented. NaHS also significantly prevented cell death elicited by H₂O₂, menadione, and thioredoxin (Trx) inhibitors. These effects of H₂S were also associated with a potent inhibition of P38. Further analysis revealed that H₂S did not affect the protein level of TXNIP and Trx, two pivotal regulators of ASK1/P38 activation, but it promoted the dissociation of Trx from TXNIP. Moreover, it disrupted the H₂O₂-initiated polymerization of Trx and converted Trx from the oxidized to the reduced form. In HepG2 cells, inhibition of H₂S-producing enzyme cystathionine γ-lyase (CSE) increased Trx oxidation, promoted Trx binding to TXNIP and exaggerated cell injury caused by Trx inhibition. Collectively, our results indicate that H₂S exerted its antioxidative effects through the regulation of the redox state of Trx and interference with Trx/ASK1/P38 signaling pathway. Given the importance of the pathway in the mediation of multiple oxidative cell responses, our study thus provides novel mechanistic insight into the action of H₂S.

Effect of Baoshenfang Formula on Podocyte Injury via Inhibiting the NOX-4/ROS/p38 Pathway in Diabetic Nephropathy

Diabetic nephropathy (DN) is a serious kidney-related complication of type 1 and type 2 diabetes. The Chinese herbal formula Baoshenfang (BSF) shows therapeutic potential in attenuating oxidative stress and apoptosis in podocytes in DN. This study evaluated the effects of BSF on podocyte injury in vivo and in vitro and explored the possible involvement of the nicotinamide adenine dinucleotide phosphate-oxidase-4/reactive oxygen species- (NOX-4/ROS-) activated p38 pathway. In the identified compounds by mass spectrometry, some active constituents of BSF were reported to show antioxidative activity. In addition, we found that BSF significantly decreased 24-hour urinary protein, serum creatinine, and blood urea nitrogen in DN patients. BSF treatment increased the nephrin expression, alleviated oxidative cellular damage, and inhibited Bcl-2 family-associated podocyte apoptosis in high-glucose cultured podocytes and/or in diabetic rats. More importantly, BSF also decreased phospho-p38, while high glucose-mediated apoptosis was blocked by p38 mitogen-activated protein kinase inhibitor in cultured podocytes, indicating that the antiapoptotic effect of BSF is p38 pathway-dependent. High glucose-induced upexpression of NOX-4 was normalized by BSF, and NOX-4 siRNAs inhibited the phosphorylation of p38, suggesting that the activated p38 pathway is at least partially mediated by NOX-4. In conclusion, BSF can decrease proteinuria and protect podocytes from injury in DN, in part through inhibiting the NOX-4/ROS/p38 pathway.

Differential toxicities of triptolide to immortalized podocytes and the podocytes in vivo

Triptolide (TP) has an anti-proteinuric effect and is used for the treatment of podocytopathies. TP has also been shown to act directly on immortalized podocytes in culture to protect them from injury. In the present study, we examined the effect of TP on healthy podocytes both in vitro and in vivo to better understand the action of TP on podocytes. We found that treatment of TP at 10 ng/ml, a concentration that is routinely used for podocyte protection, was sufficient to activate pro-apoptotic signaling of MAPK p38, p53 and BAX and induced apoptosis in cultured podocytes; and higher concentrations of TP exacerbated the p38, p53 and BAX activations and apoptosis. Moreover, TP severely downregulated the genes that are essential for podocyte structure and function. Interestingly, in contrast with other agents TP-induced podocyte injury was not prevented by glucocorticoids. In vivo, high-dose TP treatment for prolonged time did not cause podocyte injury, essential genes downregulation, and proteinuria in mice. TP was also not toxic to the podocytes with isolated glomeruli ex vivo. In summary, TP is toxic to immortalized podocytes in culture but not to the podocytes in animals or isolated glomeruli ex vivo. Our study suggests that immortalized podocytes might have genetically evolved to become sensitive to TP toxicity and thus caution should be taken in interpreting data from immortalized podocytes. Nevertheless, in vivo TP could be as safe as glucocorticoids in treating podocytopathies. Finally, TP may be used as a unique in vitro model for studying steroid-resistant podocytopathies.

The long noncoding RNA LOC105374325 causes podocyte injury in individuals with focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a common kidney disease that results in nephrotic syndrome. FSGS arises from dysfunction and apoptosis of podocytes in the glomerulus of the kidney, leading to podocytopathy. The molecular mechanisms underlying podocyte apoptosis remain incompletely understood. Using an array of gene expression profiling, PCR, and in situ hybridization assay, we found here that the levels of the long noncoding RNA LOC105374325 were elevated in the renal podocytes of individuals with FSGS. We also observed that the microRNAs miR-34c and miR-196a/b down-regulated the expression of the apoptosis regulators BCL2-associated X, apoptosis regulator (Bax), and BCL2 antagonist/killer 1 (Bak) in podocytes. Competitive binding between LOC105374325 and miR-34c or miR-196a/b increased Bax and Bak levels and caused podocyte apoptosis. Of note, the mitogen-activated protein kinase P38 and the transcription factor CCAAT enhancer-binding protein β (C/EBPβ) up-regulated LOC105374325 expression. P38 inhibition or C/EBPβ silencing decreased LOC105374325 levels and inhibited apoptosis in adriamycin-treated podocytes. LOC105374325 overexpression decreased miR-34c and miR-196a/b levels, increased Bax and Bak levels, and induced proteinuria and focal segmental lesions in mice. In conclusion, activation of the P38/C/EBPβ pathway stimulates the expression of LOC105374325, which, in turn, increases Bax and Bak levels and causes apoptosis by competitively binding to miR-34c and miR-196a/b in the podocytes of individuals with FSGS.

Fibrinogen links podocyte injury with Toll-like receptor 4 and is associated with disease activity in FSGS patients

AIM

Fibrinogen (Fg) is reported to participate in inflammation through Toll-like receptor 4 (TLR4). However, it remains unknown whether Fg might induce podocyte damage through TLR4 and be related to disease activity in patients with focal segmental glomerulosclerosis (FSGS).

METHODS

We observed Fg-induced alterations in actin and apoptosis in cultured human podocytes transfected with or without TLR4 siRNA. Expression of TLR4, phospho-p38 MAPK and phospho-NF-κB p65 was evaluated by quantitative reverse transcription polymerase chain reaction (qRT-PCR) or western blotting, and we analysed urinary Fg levels in adriamycin-treated mice and double immunofluorescence staining for TLR4, Fg and podocin. Urinary Fg changes were also analyzed in FSGS patients under prednisone treatment.

RESULTS

First, Fg dose-dependently induced actin damage and apoptosis in cultured human podocytes, with an Fg-induced increase in TLR4 expression, and TLR4 siRNA transfection prevented these effects. TLR4 knockdown inhibited activation of p38 MAPK and NF-κB p65 in podocytes. Elevated urinary Fg levels were positively correlated with albuminuria in adriamycin-treated mice, in which Fg and TLR4 colocalized and exhibited increased expression in podocytes. Additionally, elevated urinary Fg levels were positively correlated with 24-h proteinuria and foot process width in FSGS patients. Urinary Fg levels were significantly decreased in patients with complete remission but not in those without remission.

CONCLUSIONS

Fg induced podocytes injury via the TLR4-p38 MAPK-NF-κB p65 pathway. In FSGS patients, urinary Fg levels reflect therapeutic response to prednisone and disease activity.

Plectin protects podocytes from adriamycin-induced apoptosis and F-actin cytoskeletal disruption through the integrin α6β4/FAK/p38 MAPK pathway

Podocyte injury is an early pathological change characteristic of various glomerular diseases, and apoptosis and F‐actin cytoskeletal disruption are typical features of podocyte injury. In this study, we found that adriamycin (ADR) treatment resulted in typical podocyte injury and repressed plectin expression. Restoring plectin expression protected against ADR‐induced podocyte injury whereas siRNA‐mediated plectin silencing produced similar effects as ADR‐induced podocyte injury, suggesting that plectin plays a key role in preventing podocyte injury. Further analysis showed that plectin repression induced significant integrin α6β4, focal adhesion kinase (FAK) and p38 MAPK phosphorylation. Mutating Y1494, a key tyrosine residue in the integrin β4 subunit, blocked FAK and p38 phosphorylation, thereby alleviating podocyte injury. Inhibitor studies demonstrated that FAK Y397 phosphorylation promoted p38 activation, resulting in podocyte apoptosis and F‐actin cytoskeletal disruption. In vivo studies showed that administration of ADR to rats resulted in significantly increased 24‐hour urine protein levels along with decreased plectin expression and activated integrin α6β4, FAK, and p38. Taken together, these findings indicated that plectin protects podocytes from ADR‐induced apoptosis and F‐actin cytoskeletal disruption by inhibiting integrin α6β4/FAK/p38 pathway activation and that plectin may be a therapeutic target for podocyte injury‐related glomerular diseases.

ASK1 inhibitor treatment suppresses p38/JNK signalling with reduced kidney inflammation and fibrosis in rat crescentic glomerulonephritis

Activation of p38 mitogen‐activated protein kinase (MAPK) and c‐Jun amino terminal kinase (JNK) is prominent in human crescentic glomerulonephritis. p38 and JNK inhibitors suppress crescentic disease in animal models; however, the upstream mechanisms inducing activation of these kinases in crescentic glomerulonephritis are unknown. We investigated the hypothesis that apoptosis signal‐regulating kinase 1 (ASK1/MAP3K5) promote p38/JNK activation and renal injury in models of nephrotoxic serum nephritis (NTN); acute glomerular injury in SD rats, and crescentic disease in WKY rats. Treatment with the selective ASK1 inhibitor, GS‐444217 or vehicle began 1 hour before nephrotoxic serum injection and continued until animals were killed on day 1 (SD rats) or 14 (WKY rats). NTN resulted in phosphorylation (activation) of p38 and c‐Jun in both models which was substantially reduced by ASK1 inhibitor treatment. In SD rats, GS‐444217 prevented proteinuria and glomerular thrombosis with suppression of macrophage activation on day 1 NTN. In WKY rats, GS‐444217 reduced crescent formation, prevented renal impairment and reduced proteinuria on day 14 NTN. Macrophage activation, T‐cell infiltration and renal fibrosis were also reduced by GS‐444217. In conclusion, GS‐444217 treatment inhibited p38/JNK activation and development of renal injury in rat NTN. ASK1 inhibitors may have therapeutic potential in rapidly progressive glomerulonephritis.

A case of lipoprotein glomerulopathy with a rare apolipoprotein E isoform combined with neurofibromatosis type I

Lipoprotein glomerulopathy (LPG) is a rare inherited disease characterized by histopathological features of lipoprotein thrombi in dilated glomerular capillaries and type III like hyperlipoproteinemia with heterozygous mutation of the apolipoprotein (apo) E gene. We herein present the case of a 50-year-old woman with LPG complicated by neurofibromatosis type 1 (NF1). To the best of our knowledge, this is the first report of a case of LPG complicated by NF1. On the other hand, she had not only a heterozygous apoE-Sendai mutation, which is one of the most frequent apoE variants in LPG patients, but also a rare isoform of ApoE5 (Glu3Lys). Although apoE mutation has been recognized as having a principal role in the pathogenesis of LPG, some other factors are assumed to be present in the pathogenesis of LPG, because many asymptomatic carriers of apoE variants are recognized. The coexistence of NF1 or apoE5 (Glu3Lys) allele might play a role as an additional factor in the development of LPG.

Pharmacological and genetic inhibition of downstream targets of p38 MAPK in experimental nephrotic syndrome

Nie X, Chanley MA, Pengal R, Thomas DB, Agrawal S, Smoyer WE. Pharmacological and genetic inhibition of downstream targets of p38 MAPK in experimental nephrotic syndrome. Am J Physiol Renal Physiol 314: F602-F613, 2018. First published November 29, 2017; doi: 10.1152/ajprenal.00207.2017 .-The p38 MAPK pathway plays a crucial role in various glomerulopathies, with activation being associated with disease and inhibition being associated with disease amelioration. We hypothesized that the downstream targets of p38 MAPK, MAPK-activated protein kinase 2 and/or 3 (MK2 and/or MK3), play an important role in mediating injury in experimental nephrotic syndrome via their actions on their downstream substrates heat shock protein B1 (HSPB1) and cyclooxygenase-2 (COX-2). To test this hypothesis, the effects of both pharmacological and genetic inhibition of MK2 and MK3 were examined in mouse adriamycin (ADR) and rat puromycin aminonucleoside (PAN) nephropathy models. MK2^-/-, MK3^-/-, and MK2^-/-MK3^-/- mice were generated in the Sv129 background and subjected to ADR-induced nephropathy. MK2 and MK3 protein expression was completely abrogated in the respective knockout genotypes, and massive proteinuria and renal histopathological changes developed after ADR treatment. Furthermore, renal cortical HSPB1 was induced in all four genotypes by day 21, but HSPB1 was activated only in the wild-type and MK3^-/- mice. Expression of the stress proteins HSPB8 and glucose-regulated protein 78 (GRP78) remained unaltered across all genotypes. Finally, while MK2 and/or MK3-knockout downregulated the proinflammatory enzyme COX-2, ADR significantly induced renal cortical COX-2 only in MK2^-/- mice. Additionally, pharmacological MK2 inhibition with PF-318 during PAN-induced nephropathy did not result in significant proteinuria reduction in rats. Together, these data suggest that while the inhibition of MK2 and/or MK3 regulates the renal stress response, our currently available approaches are not yet able to safely and effectively reduce proteinuria in experimental nephrotic syndrome and that other p38MAPK downstream targets should also be considered to improve the future treatment of glomerular disease.

Peroxisome proliferator activating receptor-γ and the podocyte

Over the past two decades it has become clear that the glomerular podocyte is a key cell in preventing albuminuria, kidney failure and cardiovascular morbidity. Understanding the key pathways that protect the podocyte in times of glomerular stress, which can also be therapeutically manipulated, are highly attractive. In the following review we assess the evidence that the peroxisome proliferator activating receptor (PPAR) agonists are beneficial for podocyte and kidney function with a focus on PPAR-γ. We explain our current understanding of the mechanisms of action of these agonists and the evidence they are beneficial in diabetic and non-diabetic kidney disease. We also outline why these drugs have not been widely used for kidney disease in the past but they may be in the future.

High-content screening assay-based discovery of paullones as novel podocyte-protective agents

Podocyte dysfunction and loss is an early event and a hallmark of proteinuric kidney diseases. A podocyte's normal function is maintained via its unique cellular architecture that relies on an intracellular network of filaments, including filamentous actin (F-actin) and microtubules, that provides mechanical support. Damage to this filamentous network leads to changes in cellular morphology and results in podocyte injury, dysfunction, and death. Conversely, stabilization of this network protects podocytes and ameliorates proteinuria. This suggests that stabilization of podocyte architecture via its filamentous network could be a key therapeutic strategy for proteinuric kidney diseases. However, development of podocyte-directed therapeutics, especially those that target the cell's filamentous network, is still lacking, partly because of unavailability of appropriate cellular assays for use in a drug discovery environment. Here, we describe a new high-content screening-based methodology and its implementation on podocytes to identify paullone derivatives as a novel group of podocyte-protective compounds. We find that three compounds, i.e., kenpaullone, 1-azakenpaullone, and alsterpaullone, dose dependently protect podocytes from puromycin aminonucleoside (PAN)-mediated injury in vitro by reducing PAN-induced changes in both the filamentous actin and microtubules, with alsterpaullone providing maximal protection. Mechanistic studies further show that alsterpaullone suppressed PAN-induced activation of signaling downstream of GSK3β and p38 mitogen-activated protein kinase. In vivo it reduced ADR-induced glomerular injury in a zebrafish model. Together, these results identify paullone derivatives as novel podocyte-protective agents for future therapeutic development.

Proline-dependent and basophilic kinases phosphorylate human TRPC6 at serine 14 to control channel activity through increased membrane expression

Signaling via the transient receptor potential (TRP) ion channel C6 plays a pivotal role in hereditary and sporadic glomerular kidney disease. Several studies have identified gain-of-function mutations of TRPC6 and report induced expression and enhanced channel activity of TRPC6 in association with glomerular diseases. Interfering with TRPC6 activity may open novel therapeutic pathways. TRPC6 channel activity is controlled by protein expression and stability as well as intracellular trafficking. Identification of regulatory phosphorylation sites in TRPC6 and corresponding protein kinases is essential to understand the regulation of TRPC6 activity and may result in future therapeutic strategies. In this study, an unbiased phosphoproteomic screen of human TRPC6 identified several novel serine phosphorylation sites. The phosphorylation site at serine 14 of TRPC6 is embedded in a basophilic kinase motif that is highly conserved across species. We confirmed serine 14 as a target of MAPKs and proline-directed kinases like cyclin-dependent kinase 5 (Cdk5) in cell-based as well as in vitro kinase assays and quantitative phosphoproteomic analysis of TRPC6. Phosphorylation of TRPC6 at serine 14 enhances channel conductance by boosting membrane expression of TRPC6, whereas protein stability and multimerization of TRPC6 are not altered, making serine 14 phosphorylation a potential drug target to interfere with TRPC6 channel activity.-Hagmann, H., Mangold, N., Rinschen, M. M., Koenig, T., Kunzelmann, K., Schermer, B., Benzing, T., Brinkkoetter, P. T. Proline-dependent and basophilic kinases phosphorylate human TRPC6 at serine 14 to control channel activity through increased membrane expression.

C-X-C Chemokine Receptor Type 4 Plays a Crucial Role in Mediating Oxidative Stress-Induced Podocyte Injury

AIMS

Oxidative stress plays a role in mediating podocyte injury and proteinuria. However, the underlying mechanism remains poorly understood. In this study, we investigated the potential role of C-X-C chemokine receptor type 4 (CXCR4), the receptor for stromal cell-derived factor 1α (SDF-1α), in mediating oxidative stress-induced podocyte injury.

RESULTS

In mouse model of adriamycin nephropathy (ADR), CXCR4 expression was significantly induced in podocytes as early as 3 days. This was accompanied by an increased upregulation of oxidative stress in podocyte, as demonstrated by malondialdehyde assay, nitrotyrosine staining and secretion of 8-hydroxy-2'-deoxyguanosine in urine, and induction of NOX2 and NOX4, major subunits of NADPH oxidase. CXCR4 was also induced in human kidney biopsies with proteinuric kidney diseases and colocalized with advanced oxidation protein products (AOPPs), an established oxidative stress trigger. Using cultured podocytes and mouse model, we found that AOPPs induced significant loss of podocyte marker Wilms tumor 1 (WT1), nephrin, and podocalyxin, accompanied by upregulation of desmin both in vitro and in vivo. Furthermore, AOPPs worsened proteinuria and aggravated glomerulosclerosis in ADR. These effects were associated with marked activation of SDF-1α/CXCR4 axis in podocytes. Administration of AMD3100, a specific inhibitor of CXCR4, reduced proteinuria and ameliorated podocyte dysfunction and renal fibrosis triggered by AOPPs in mice. In glomerular miniorgan culture, AOPPs also induced CXCR4 expression and downregulated nephrin and WT1. Innovation and Conclusion: These results suggest that chemokine receptor CXCR4 plays a crucial role in mediating oxidative stress-induced podocyte injury, proteinuria, and renal fibrosis. CXCR4 could be a new target for mitigating podocyte injury, proteinuria, and glomerular sclerosis in proteinuric chronic kidney disease. Antioxid. Redox Signal. 27, 345-362.

Rediscovering Beta-2 Microglobulin As a Biomarker across the Spectrum of Kidney Diseases

There is currently an unmet need for better biomarkers across the spectrum of renal diseases. In this paper, we revisit the role of beta-2 microglobulin (β₂M) as a biomarker in patients with chronic kidney disease and end-stage renal disease. Prior to reviewing the numerous clinical studies in the area, we describe the basic biology of β₂M, focusing in particular on its role in maintaining the serum albumin levels and reclaiming the albumin in tubular fluid through the actions of the neonatal Fc receptor. Disorders of abnormal β₂M function arise as a result of altered binding of β₂M to its protein cofactors and the clinical manifestations are exemplified by rare human genetic conditions and mice knockouts. We highlight the utility of β₂M as a predictor of renal function and clinical outcomes in recent large database studies against predictions made by recently developed whole body population kinetic models. Furthermore, we discuss recent animal data suggesting that contrary to textbook dogma urinary β₂M may be a marker for glomerular rather than tubular pathology. We review the existing literature about β₂M as a biomarker in patients receiving renal replacement therapy, with particular emphasis on large outcome trials. We note emerging proteomic data suggesting that β₂M is a promising marker of chronic allograft nephropathy. Finally, we present data about the role of β₂M as a biomarker in a number of non-renal diseases. The goal of this comprehensive review is to direct attention to the multifaceted role of β₂M as a biomarker, and its exciting biology in order to propose the next steps required to bring this recently rediscovered biomarker into the twenty-first century.

Rac1 activation in podocytes induces the spectrum of nephrotic syndrome

Hyper-activation of Rac1, a small GTPase, in glomerular podocytes has been implicated in the pathogenesis of familial proteinuric kidney diseases. However, the role of Rac1 in acquired nephrotic syndrome is unknown. To gain direct insights into this, we generated a transgenic mouse model expressing a doxycycline-inducible constitutively active form of Rac1 (CA-Rac1) in podocytes. Regardless of the copy number, proteinuria occurred rapidly within five days, and the histology resembled minimal change disease. The degree and severity of proteinuria were dependent on the transgene copy number. Upon doxycycline withdrawal, proteinuria resolved completely (one copy) or nearly completely (two copy). After one month of doxycycline treatment, two-copy mice developed glomerulosclerosis that resembled focal segmental glomerulosclerosis (FSGS) with urinary shedding of transgene-expressing podocytes. p38 MAPK was activated in podocytes upon CA-Rac1 induction while a p38 inhibitor attenuated proteinuria, podocyte loss, and glomerulosclerosis. Mechanistically, activation of Rac1 in cultured mouse podocytes reduced adhesiveness to laminin and induced redistribution of β1 integrin, and both were partially reversed by the p38 inhibitor. Activation of Rac1 in podocytes was also seen in kidney biopsies from patients with minimal change disease and idiopathic FSGS by immunofluorescence while sera from the same patients activated Rac1 in cultured human podocytes. Thus, activation of Rac1 in podocytes causes a spectrum of disease ranging from minimal change disease to FSGS, due to podocyte detachment from the glomerular basement membrane that is partially dependent on p38 MAPK.

Natriuretic peptide receptor guanylyl cyclase-A pathway counteracts glomerular injury evoked by aldosterone through p38 mitogen-activated protein kinase inhibition

Guanylyl cyclase-A (GC-A) signaling, a natriuretic peptide receptor, exerts renoprotective effects by stimulating natriuresis and reducing blood pressure. Previously we demonstrated massive albuminuria with hypertension in uninephrectomized, aldosterone-infused, and high salt-fed (ALDO) systemic GC-A KO mice with enhanced phosphorylation of p38 mitogen-activated protein kinase (MAPK) in podocytes. In the present study, we examined the interaction between p38 MAPK and GC-A signaling. The administration of FR167653, p38 MAPK inhibitor, reduced systolic blood pressure (SBP), urinary albumin excretion, segmental sclerosis, podocyte injury, and apoptosis. To further investigate the local action of natriuretic peptide and p38 MAPK in podocytes, we generated podocyte-specific (pod) GC-A conditional KO (cKO) mice. ALDO pod GC-A cKO mice demonstrated increased urinary albumin excretion with marked mesangial expansion, podocyte injury and apoptosis, but without blood pressure elevation. FR167653 also suppressed urinary albumin excretion without reducing SBP. Finally, we revealed that atrial natriuretic peptide increased phosphorylation of MAPK phosphatase-1 (MKP-1) concomitant with inhibited phosphorylation of p38 MAPK in response to MAPK kinase 3 activation, thereby resulting in decreased mRNA expression of the apoptosis-related gene, Bax, and Bax/Bcl2 ratio in cultured podocytes. These results indicate that natriuretic peptide exerts a renoprotective effect via inhibiting phosphorylation of p38 MAPK in podocytes.

Plantago asiatica L. Ameliorates Puromycin Aminonucleoside-Induced Nephrotic Syndrome by Suppressing Inflammation and Apoptosis

Objective: Nephrotic syndrome, a kidney disease with a variety of causes, is mainly characterized by heavy proteinuria, hypoproteinemia, and ascites. This study was designed to evaluate the underlying mechanism of action of Plantago asiatica L. (PAL) in treating nephrotic syndrome induced by puromycin aminonucleoside. Methods: PAL has been used in Asia as a traditional medicine and dietary health supplement. Sprague-Dawley (SD) rats were intravenously injected with puromycin aminonucleoside (75 mg/kg/day), then treated with either Losartan (30 mg/kg/day) or PAL (200 mg/kg/day) by oral gavage for seven days. Results: PAL significantly decreased ascites, proteinuria level, and plasma lipid parameters. In addition, treatment with PAL attenuated histological damage and hypoalbuminemia. Treatment with PAL also restored podocin expression and reduced inflammation markers such as intracellular adhesion molecules (ICAM-1), monocyte chemotactic protein-1 (MCP-1), tumor necrosis factor alpha (TNF-α) and high-mobility group box-1 (HMGB1). Lower expression levels of the apoptosis markers Bax, caspase-3 and capase-9 were documented in SD rats receiving PAL. PAL also significantly decreased the phosphorylation levels of MAPKs such as ERK, JNK and p38. Conclusion: As a multifunctional agent, PAL has a renoprotective effect in nephrotic syndrome rat models. The anti-inflammatory and anti-apoptotic properties, along with reductions in hyperlipidemia and ascites, represent important therapeutic effects. These results indicate that Plantago asiatica is likely to be a promising agent in the treatment of nephrotic syndrome.

Nicotine Induces Podocyte Apoptosis through Increasing Oxidative Stress

Background

Cigarette smoking plays an important role in the progression of chronic kidney disease (CKD). Nicotine, one of the major components of cigarette smoking, has been demonstrated to increase proliferation of renal mesangial cells. In this study, we examined the effect of nicotine on podocyte injury.

Methods

To determine the expression of nicotinic acetylcholine receptors (nAChR subunits) in podocytes, cDNAs and cell lysate of cultured human podocytes were used for the expression of nAChR mRNAs and proteins, respectively; and mouse renal cortical sections were subjected to immunofluorescant staining. We also studied the effect of nicotine on podocyte nephrin expression, reactive oxygen species (ROS) generation (via DCFDA loading followed by fluorometric analysis), proliferation, and apoptosis (morphologic assays). We evaluated the effect of nicotine on podocyte downstream signaling including phosphorylation of ERK1/2, JNK, and p38 and established causal relationships by using respective inhibitors. We used nAChR antagonists to confirm the role of nicotine on podocyte injury.

Results

Human podocytes displayed robust mRNA and protein expression of nAChR in vitro studies. In vivo studies, mice renal cortical sections revealed co-localization of nAChRs along with synaptopodin. In vitro studies, nephrin expression in podocyte was decreased by nicotine. Nicotine stimulated podocyte ROS generation; nonetheless, antioxidants such as N-acetyl cysteine (NAC) and TEMPOL (superoxide dismutase mimetic agent) inhibited this effect of nicotine. Nicotine did not modulate proliferation but promoted apoptosis in podocytes. Nicotine enhanced podocyte phosphorylation of ERK1/2, JNK, and p38, and their specific inhibitors attenuated nicotine-induced apoptosis. nAChR antagonists significantly suppressed the effects of nicotine on podocyte.

Conclusions

Nicotine induces podocyte apoptosis through ROS generation and associated downstream MAPKs signaling. The present study provides insight into molecular mechanisms involved in smoking associated progression of chronic kidney disease.

SIRT4 overexpression protects against diabetic nephropathy by inhibiting podocyte apoptosis

Diabetic nephropathy is a diabetic complication associated with capillary damage and increased mortality. Sirtuin 4 (SIRT4) plays an important role in mitochondrial function and the pathogenesis of metabolic diseases, including aging kidneys. The aim of the present study was to investigate the association between SIRT4 and diabetic nephropathy in a glucose-induced mouse podocyte model. A CCK-8 assay showed that glucose simulation significantly inhibited podocyte proliferation in a time- and concentration-dependent manner. Reverse transcription-quantitative polymerase chain reaction and western blot analysis showed that the mRNA and protein levels of SIRT4 were notably decreased in a concentration-dependent manner in glucose-simulated podocytes. However, SIRT4 overexpression increased proliferation and suppressed apoptosis, which was accompanied by increases in mitochondrial membrane potential and reduced production of reactive oxygen species (ROS). Notably, SIRT4 overexpression downregulated the expression of apoptosis-related proteins NOX1, Bax and phosphorylated p38 and upregulated the expression of Bcl-2 in glucose-simulated podocytes. In addition, SIRT4 overexpression significantly attenuated the inflammatory response, indicated by reductions in the levels of TNF-α, IL-1β and IL-6. These results demonstrate for the first time that the overexpression of SIRT4 prevents glucose-induced podocyte apoptosis and ROS production and suggest that podocyte apoptosis represents an early pathological mechanism leading to diabetic nephropathy.

Effect of Tongxinluo on Podocyte Apoptosis via Inhibition of Oxidative Stress and P38 Pathway in Diabetic Rats

Diabetic nephropathy (DN) has been the leading cause of end-stage renal disease (ESRD). Podocyte apoptosis is a main mechanism of progression of DN. It has been demonstrated that activated P38 and caspase-3 induced by oxidative stress mainly account for increased podocyte apoptosis and proteinuria in DN. Meanwhile, Tongxinluo (TXL) can ameliorate renal structure disruption and dysfunction in DN patients in our clinical practice. However, the effect of TXL on podocyte apoptosis and P38 pathway remains unclear. To explore the effect of TXL on podocyte apoptosis and its molecular mechanism in DN, our in vivo and in vitro studies were performed. TXL attenuated oxidative stress in podocyte in DN in our in vivo and in vitro studies. Moreover, TXL inhibited the activation of P38 and caspase-3. Bcl-2 and Bax expression was partially restored by TXL treatment in our in vivo and in vitro studies. More importantly, TXL decreased podocyte apoptosis in diabetic rats and high glucose cultured podocyte. In conclusion, TXL protects podocyte from apoptosis in DN, partially through its antioxidant effect and inhibiting of the activation of P38 and caspase-3.

Calcineurin inhibitors cyclosporin A and tacrolimus protect against podocyte injury induced by puromycin aminonucleoside in rodent models

Podocyte injury and the appearance of proteinuria are features of minimal-change disease (MCD). Cyclosporin A (CsA) and tacrolimus (FK506) has been reported to reduce proteinuria in patients with nephrotic syndrome, but mechanisms remain unknown. We, therefore, investigated the protective mechanisms of CsA and FK506 on proteinuria in a rat model of MCD induced by puromycin aminonucleoside (PAN) and in vitro cultured mouse podocytes. Our results showed that CsA and FK506 treatment decreased proteinuria via a mechanism associated to a reduction in the foot-process fusion and desmin, and a recovery of synaptopodin and podocin. In PAN-treated mouse podocytes, pre-incubation with CsA and FK506 restored the distribution of the actin cytoskeleton, increased the expression of synaptopodin and podocin, improved podocyte viability, and reduced the migrating activities of podocytes. Treatment with CsA and FK506 also inhibited PAN-induced podocytes apoptosis, which was associated with the induction of Bcl-xL and inhibition of Bax, cleaved caspase 3, and cleaved PARP expression. Further studies revealed that CsA and FK506 inhibited PAN-induced p38 and JNK signaling, thereby protecting podocytes from PAN-induced injury. In conclusion, CsA and FK506 inhibit proteinuria by protecting against PAN-induced podocyte injury, which may be associated with inhibition of the MAPK signaling pathway.

ASK1: a new therapeutic target for kidney disease

Stress-induced activation of p38 MAPK and JNK signaling is a feature of both acute and chronic kidney disease and is associated with disease progression. Inhibitors of p38 MAPK or JNK activation provide protection against inflammation and fibrosis in animal models of kidney disease; however, clinical trials of p38 MAPK and JNK inhibitors in other diseases (rheumatoid arthritis and pulmonary fibrosis) have been disappointing. Apoptosis signal-regulating kinase 1 (ASK1) acts as an upstream regulator for the activation of p38 MAPK and JNK in kidney disease. Mice lacking the Ask1 gene are healthy with normal homeostatic functions and are protected from acute kidney injury induced by ischemia-reperfusion and from renal interstitial fibrosis induced by ureteric obstruction. Recent studies have shown that a selective ASK1 inhibitor substantially reduced renal p38 MAPK activation and halted the progression of nephropathy in diabetic mice, and this has led to a current clinical trial of an ASK1 inhibitor in patients with stage 3 or 4 diabetic kidney disease. This review explores the rationale for targeting ASK1 in kidney disease and the therapeutic potential of ASK1 inhibitors based on current experimental evidence.

Drug discovery in focal and segmental glomerulosclerosis

Despite the high medical burden experienced by patients with focal segmental glomerulosclerosis, the etiology of the condition remains largely unknown. Focal segmental glomerulosclerosis is highly heterogeneous in clinical and morphologic manifestations. While this presents challenges for the development of new treatments, research investments over the last 2 decades have yielded a surfeit of potential avenues for therapeutic intervention. The development of many of those ideas and concepts into new therapies, however, has been very disappointing. Here, we describe some of the factors that have potentially contributed to the poor translational performance from this research investment, including the confidence we ascribe to a target, the conduct of experimental studies, and the availability of selective reagents to test hypotheses. We will discuss the significance of genetic and systems traits as well as other methods for reducing bias. We will analyze the limitations of a successful drug development. We will use specific examples hoping that these will guide a consensus for investment and drive greater translational quality. We hope that this substrate will serve to exemplify the tremendous opportunity for intervention as well as facilitate greater collaborative effort between industry, academia, and private foundations in promoting appropriate validation of these targets. Only then will we have achieved our goal for curative therapies for this devastating disease.