Yes-associated protein (YAP) promotes cell survival by inhibiting proapoptotic dendrin signaling

Podocyte-targeted therapies - progress and future directions

Podocytes are the key target cells for injury across the spectrum of primary and secondary proteinuric kidney disorders, which account for up to 90% of cases of kidney failure worldwide. Seminal experimental and clinical studies have established a causative link between podocyte depletion and the magnitude of proteinuria in progressive glomerular disease. However, no substantial advances have been made in glomerular disease therapies, and the standard of care for podocytopathies relies on repurposed immunosuppressive drugs. The past two decades have seen a remarkable expansion in understanding of the mechanistic basis of podocyte injury, with prospects increasing for precision-based treatment approaches. Dozens of disease-causing genes with roles in the pathogenesis of clinical podocytopathies have been identified, as well as a number of putative glomerular permeability factors. These achievements, together with the identification of novel targets of podocyte injury, the development of potential approaches to harness the endogenous podocyte regenerative potential of progenitor cell populations, ongoing clinical trials of podocyte-specific pharmacological agents and the development of podocyte-directed drug delivery systems, contribute to an optimistic outlook for the future of glomerular disease therapy.

Engineered human iPS cell models reveal altered podocytogenesis and glomerular capillary wall in CHD-associated SMAD2 mutations

Early developmental programming involves extensive cell lineage diversification through shared molecular signaling networks. Clinical observations of congenital heart disease (CHD) patients carrying SMAD2 genetic variants revealed correlations with multi-organ impairments at the developmental and functional levels. For example, many CHD patients present with glomerulosclerosis, periglomerular fibrosis, and albuminuria. Still, it remains largely unknown whether SMAD2 variants associated with CHD can directly alter kidney cell fate, tissue patterning, and organ-level function. To address this question, we engineered human iPS cells (iPSCs) and organ-on-a-chip systems to uncover the role of pathogenic SMAD2 variants in kidney podocytogenesis. Our results show that abrogation of SMAD2 causes altered patterning of the mesoderm and intermediate mesoderm (IM) cell lineages, which give rise to nearly all kidney cell types. Upon further differentiation of IM cells, the mutant podocytes failed to develop arborizations and interdigitations. A reconstituted glomerulus-on-a-chip platform exhibited significant proteinuria as clinically observed in glomerulopathies. This study implicates CHD-associated SMAD2 mutations in kidney tissue malformation and provides opportunities for therapeutic discovery in the future.

Rehmapicrogenin attenuates lipopolysaccharide-induced podocyte injury and kidney dysfunctions by regulating nuclear factor E2-related factor 2/antioxidant response element signalling

BACKGROUND

Apoptosis and oxidative stress in kidneys are critical players in acute kidney injury (AKI). Rehmapicrogenin, a monomeric compound extracted from Rehmanniae radix, has been found to possess nitric oxide inhibitory and anti-inflammatory activities. Thus, this study aimed to investigate the roles and mechanisms of rehmapicrogenin in AKI.

METHODS

Lipopolysaccharide (LPS) was used to induce AKI-like conditions. Cell survival conditions were detected by cell counting kit-8 assays and flow cytometry. Several renal function markers including blood urea nitrogen, proteinuria, creatinine, and albumin were measured. Apoptosis and reactive oxygen species (ROS) production were examined by TUNEL and dihydroethidium staining, respectively. Haematoxylin-eosin staining and periodic acid-Schiff staining were conducted to assess histopathological changes. Gene expression was evaluated by western blotting, commercially available kits and immunofluorescence staining.

RESULTS

For in vitro analysis, rehmapicrogenin inhibited the LPS-induced podocyte apoptosis by activating the Nrf2/ARE pathway. For in vivo analysis, rehmapicrogenin improved renal functions in LPS-induced mice. Additionally, rehmapicrogenin suppressed LPS-induced podocyte apoptosis and oxidative stress in kidney tissues. Mechanistically, rehmapicrogenin activated the Nrf2/ARE pathway in LPS-induced mice.

CONCLUSION

Rehmapicrogenin relieves the podocyte injury and renal dysfunctions through activating the Nrf2/ARE pathway to inhibit apoptosis and oxidative stress.

Inhibition of transcriptional coactivator YAP Impairs the expression and function of transcription factor WT1 in diabetic podocyte injury

Podocyte injury and loss are hallmarks of diabetic nephropathy (DN). However, the molecular mechanisms underlying these phenomena remain poorly understood. YAP (Yes-associated protein) is an important transcriptional coactivator that binds with various other transcription factors, including the TEAD family members (nuclear effectors of the Hippo pathway), that regulate cell proliferation, differentiation, and apoptosis. The present study found an increase in YAP phosphorylation at S127 of YAP and a reduction of nuclear YAP localization in podocytes of diabetic mouse and human kidneys, suggesting dysregulation of YAP may play a role in diabetic podocyte injury. Tamoxifen-inducible podocyte-specific Yap gene knockout mice (YappodKO) exhibited accelerated and worsened diabetic kidney injury. YAP inactivation decreased transcription factor WT1 expression with subsequent reduction of Tead1 and other well-known targets of WT1 in diabetic podocytes. Thus, our study not only sheds light on the pathophysiological roles of the Hippo pathway in diabetic podocyte injury but may also lead to the development of new therapeutic strategies to prevent and/or treat DN by targeting the Hippo signaling pathway.

Combination therapy with DHA and BMSCs suppressed podocyte injury and attenuated renal fibrosis by modulating the TGF-β1/Smad pathway in MN mice

Artemisinin has immunomodulatory, anti-inflammatory, and antifibrotic effects. Some studies have demonstrated that artemisinins have a protective effect on the kidney. DHA is a derivative of artemisinin and has effects similar to those of artemisinin. Human bone marrow-derived mesenchymal stem cells (BMSCs) accelerate renal repair following acute injury. In the study, we investigated the effects of combination therapy with DHA and BMSCs on membranous nephropathy (MN) mice. The 24-h urinary protein, serum total cholesterol (TC) and triglyceride (TG) levels, and renal histopathology, were measured to evaluate kidney damage. Anti-PLA2R, IgG, and complement 3 (C3) were detected by ELISA. The expression levels of the podocyte injury-related proteins were analyzed by immunohistochemistry. The protein expression levels of α-SMA, ED-1, TGF-β1, p-Smad2, and p-Smad3 were detected by western blot to analyze renal fibrosis and its regulatory mechanism. Results showed that combination therapy with DHA and BMSCs significantly ameliorated kidney damage in MN model mice by decreasing the levels of 24 h urinary protein, TC and TG. This combination therapy also improved renal histology and reduced the expression of IgG and C3 in the glomerulus. In addition, this combination therapy decreased the expression of podocin and nephrin and relieved renal fibrosis by downregulating α-SMA and ED-1. Furthermore, this combination therapy suppressed TGF-β1 expression and Smad2/3 phosphorylation. This result (i.e., this combination therapy inhibited the TGF-β1/Smad pathway) was also supported in vitro. Taken together, combination therapy with DHA and BMSCs ameliorated podocyte injury and renal fibrosis in MN mice by downregulating the TGFβ1/Smad pathway.

The role of the FSGS disease gene product and nuclear pore protein NUP205 in regulating nuclear localization and activity of transcriptional regulators YAP and TAZ

Mutations in genes encoding nuclear pore proteins (NUPs) lead to the development of steroid-resistant nephrotic syndrome and focal segmental glomerulosclerosis (FSGS). However, the precise molecular mechanisms by which NUP dysfunction contributes to podocyte injury preceding FSGS remain unclear. The tightly regulated activity of Yes-associated protein (YAP) and WW-domain-containing transcription regulator 1 (TAZ), the transcriptional effectors of the Hippo pathway, is crucial for podocytes and the maintenance of the glomerular filter. In this study, we investigate the impact of NUPs on the regulation of YAP/TAZ nuclear import and activity in podocytes. In unbiased interactome studies using quantitative label-free mass spectrometry, we identify the FSGS disease gene products NUP107, NUP133, NUP205, and Exportin-5 (XPO5) as components of YAP and TAZ protein complexes in podocytes. Moreover, we demonstrate that NUP205 is essential for YAP/TAZ nuclear import. Consistently, both the nuclear interaction of YAP/TAZ with TEA domain transcription factor 1 and their transcriptional activity were dependent on NUP205 expression. Additionally, we elucidate a regulatory feedback mechanism whereby YAP activity is modulated in response to TAZ-mediated NUP205 expression. In conclusion, this study establishes a connection between the FSGS disease protein NUP205 and the activity of the transcriptional regulators and Hippo effectors YAP and TAZ and it proposes a potential pathological role of YAP/TAZ dysregulation in podocytes of patients with pathogenic NUP205 variants.

Crocin improves the renal autophagy in rat experimental membranous nephropathy via regulating the SIRT1/Nrf2/HO-1 signaling pathway

Membranous nephropathy (MN) is a glomerular disease. Crocin is isolated from saffron and gardenia. Its antioxidant, anti-inflammatory, anti-hyperlipidemic, anti-atherosclerotic, anti-tumor, free-radical scavenging and neuroprotective activities have been well established. We investigated the biological functions of crocin and its related mechanisms in MN. We established an experimental passive Heymann nephritis (PHN) rat model induced by anti-Fx1A antiserum. The rats were divided into sham, sham + crocin, PHN, PHN + crocin, and PHN + enalapril groups. Blood samples and kidneys of rats were collected for estimation of biochemical parameters in serum and oxidative stress indicators in kidney tissues. Histopathological changes of renal tissues were evaluated by hematoxylin and eosin, periodic acid-Schiff (PAS) and Masson staining. The podocyte number was estimated by immunohistochemistry staining of Wilms tumor type 1 (WT1). The deposition of rat anti-rabbit IgG antibodies, complement C3 and C5b-9 was detected by immunofluorescence staining. Western blotting was performed to measure the levels of Sirtuin 1 (Sirt1), nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase 1 (HO-1) and apoptosis-related proteins. The total cholesterol, triglycerides, creatinine, blood urea nitrogen, urine volume and urine albumin of PMN rats were significantly reduced by crocin. Additionally, crocin attenuated the renal histopathological changes. Moreover, the oxidative stress damage and podocyte loss and immune injury were relieved by crocin in PHN rats. Mechanistically, crocin administration activated the Sirt1/Nrf2/HO-1 pathways. The results provide a scientific basis that crocin could alleviate MN by inhibiting immune injury and podocyte damage through activating the Sirt1/Nrf2/HO-1 pathways.

Inhibition of Importin- α -Mediated Nuclear Localization of Dendrin Attenuates Podocyte Loss and Glomerulosclerosis

SIGNIFICANCE STATEMENT

Nuclear translocation of dendrin is observed in injured podocytes, but the mechanism and its consequence are unknown. In nephropathy mouse models, dendrin ablation attenuates proteinuria, podocyte loss, and glomerulosclerosis. The nuclear translocation of dendrin promotes c-Jun N -terminal kinase phosphorylation in podocytes, altering focal adhesion and enhancing cell detachment-induced apoptosis. We identified mediation of dendrin nuclear translocation by nuclear localization signal 1 (NLS1) sequence and adaptor protein importin- α . Inhibition of importin- α prevents nuclear translocation of dendrin, decreases podocyte loss, and attenuates glomerulosclerosis in nephropathy models. Thus, inhibiting importin- α -mediated nuclear translocation of dendrin is a potential strategy to halt podocyte loss and glomerulosclerosis.

BACKGROUND

Nuclear translocation of dendrin is observed in the glomeruli in numerous human renal diseases, but the mechanism remains unknown. This study investigated that mechanism and its consequence in podocytes.

METHODS

The effect of dendrin deficiency was studied in adriamycin (ADR) nephropathy model and membrane-associated guanylate kinase inverted 2 ( MAGI2 ) podocyte-specific knockout ( MAGI2 podKO) mice. The mechanism and the effect of nuclear translocation of dendrin were studied in podocytes overexpressing full-length dendrin and nuclear localization signal 1-deleted dendrin. Ivermectin was used to inhibit importin- α .

RESULTS

Dendrin ablation reduced albuminuria, podocyte loss, and glomerulosclerosis in ADR-induced nephropathy and MAGI2 podKO mice. Dendrin deficiency also prolonged the lifespan of MAGI2 podKO mice. Nuclear dendrin promoted c-Jun N -terminal kinase phosphorylation that subsequently altered focal adhesion, reducing cell attachment and enhancing apoptosis in cultured podocytes. Classical bipartite nuclear localization signal sequence and importin- α mediate nuclear translocation of dendrin. The inhibition of importin- α / β reduced dendrin nuclear translocation and apoptosis in vitro as well as albuminuria, podocyte loss, and glomerulosclerosis in ADR-induced nephropathy and MAGI2 podKO mice. Importin- α 3 colocalized with nuclear dendrin in the glomeruli of FSGS and IgA nephropathy patients.

CONCLUSIONS

Nuclear translocation of dendrin promotes cell detachment-induced apoptosis in podocytes. Therefore, inhibiting importin- α -mediated dendrin nuclear translocation is a potential strategy to prevent podocyte loss and glomerulosclerosis.

TYRO3 agonist as therapy for glomerular disease

Podocyte injury and loss are key drivers of primary and secondary glomerular diseases, such as focal segmental glomerulosclerosis (FSGS) and diabetic kidney disease (DKD). We previously demonstrated the renoprotective role of protein S (PS) and its cognate tyrosine-protein kinase receptor, TYRO3, in models of FSGS and DKD and that their signaling exerts antiapoptotic and antiinflammatory effects to confer protection against podocyte loss. Among the 3 TAM receptors (TYRO3, AXL, and MER), only TYRO3 expression is largely restricted to podocytes, and glomerular TYRO3 mRNA expression negatively correlates with human glomerular disease progression. Therefore, we posited that the agonistic PS/TYRO3 signaling could serve as a potential therapeutic approach to attenuate glomerular disease progression. As PS function is not limited to TYRO3-mediated signal transduction but includes its anticoagulant activity, we focused on the development of TYRO3 agonists as an optimal therapeutic approach to glomerular disease. Among the small-molecule TYRO3 agonistic compounds screened, compound 10 (C-10) showed a selective activation of TYRO3 without any effects on AXL or MER. We also confirmed that C-10 directly binds to TYRO3, but not the other receptors. In vivo, C-10 attenuated proteinuria, glomerular injury, and podocyte loss in mouse models of Adriamycin-induced nephropathy and a db/db model of type 2 diabetes. Moreover, these renoprotective effects of C-10 were lost in Tyro3-knockout mice, indicating that C-10 is a selective agonist of TYRO3 activity that mitigates podocyte injury and glomerular disease. Therefore, C-10, a TYRO3 agonist, could be potentially developed as a new therapy for glomerular disease.

Adriamycin-Induced Podocyte Injury Disrupts the YAP-TEAD1 Axis and Downregulates Cyr61 and CTGF Expression

The most severe forms of kidney diseases are often associated with irreversible damage to the glomerular podocytes, the highly specialized epithelial cells that encase glomerular capillaries and regulate the removal of toxins and waste from the blood. Several studies revealed significant changes to podocyte cytoskeletal structure during disease onset, suggesting possible roles of cellular mechanosensing in podocyte responses to injury. Still, this topic remains underexplored partly due to the lack of appropriate in vitro models that closely recapitulate human podocyte biology. Here, we leveraged our previously established method for the derivation of mature podocytes from human induced pluripotent stem cells (hiPSCs) to help uncover the roles of yes-associated protein (YAP), a transcriptional coactivator and mechanosensor, in podocyte injury response. We found that while the total expression levels of YAP remain relatively unchanged during Adriamycin (ADR)-induced podocyte injury, the YAP target genes connective tissue growth factor (CTGF) and cysteine-rich angiogenic inducer 61 (Cyr61) are significantly downregulated. Intriguingly, TEAD1 is significantly downregulated in podocytes injured with ADR. By examining multiple independent modes of cellular injury, we found that CTGF and Cyr61 expression are downregulated only when podocytes were exposed to molecules known to disrupt the cell's mechanical integrity or cytoskeletal structure. To our knowledge, this is the first report that the YAP-TEAD1 signaling axis is disrupted when stem cell-derived human podocytes experience biomechanical injury. Together, these results could help improve the understanding of kidney disease mechanisms and highlight CTGF and Cyr61 as potential therapeutic targets or biomarkers for patient stratification.

The role of dendrin in IgA nephropathy

BACKGROUND

Immunoglobulin A nephropathy (IgAN) and its systemic variant IgA vasculitis (IgAV) damage the glomeruli, resulting in proteinuria, hematuria and kidney impairment. Dendrin is a podocyte-specific protein suggested to be involved in the pathogenesis of IgAN. Upon cell injury, dendrin translocates from the slit diaphragm to the nucleus, where it is suggested to induce apoptosis and cytoskeletal changes, resulting in proteinuria and accelerated disease progression in mice. Here we investigated gene and protein expression of dendrin in relation to clinical and histopathological findings to further elucidate its role in IgAN/IgAV.

METHODS

Glomerular gene expression was measured using microarray on 30 IgAN/IgAV patients, 5 patients with membranous nephropathy (MN) and 20 deceased kidney donors. Dendrin was spatially evaluated on kidney tissue sections by immunofluorescence (IF) staining (IgAN patients, n = 4; nephrectomized kidneys, n = 3) and semi-quantified by immunogold electron microscopy (IgAN/IgAV patients, n = 21; MN, n = 5; living kidney donors, n = 6). Histopathological grading was performed according to the Oxford and Banff classifications. Clinical data were collected at the time of biopsy and follow-up.

RESULTS

Dendrin mRNA levels were higher (P = .01) in IgAN patients compared with MN patients and controls and most prominently in patients with preserved kidney function and fewer chronic histopathological changes. Whereas IF staining did not differ between groups, immunoelectron microscopy revealed that a higher relative nuclear dendrin concentration in IgAN patients was associated with a slower annual progression rate and milder histopathological changes.

CONCLUSION

Dendrin messenger RNA levels and relative nuclear protein concentrations are increased and associated with a more benign phenotype and progression in IgAN/IgAV patients.

TAZ is important for maintenance of the integrity of podocytes

The podocyte is an important component of the glomerular filtration barrier, and maintenance of the integrity of its highly specified structure and function is critical for normal kidney function. Yes-associated protein (YAP)/transcriptional coactivator with PDZ-binding motif (TAZ) are two crucial effectors of the Hippo signaling pathway, and recent studies have shown that podocyte-specific YAP deletion causes podocyte apoptosis and the development of focal segmental glomerulosclerosis followed by progressive renal failure. In the present study, we investigated a potential role of the YAP paralog TAZ in podocytes. TAZ was found to be constitutively active in podocytes, and mice with podocyte-specific deletion of TAZ (TazpodKO) developed proteinuria starting at 4 wk of age and had increased podocyte apoptosis. Using primary cultured podocytes or immortalized mouse podocytes from Tazflox/flox mice, we found that TAZ is a transcriptional activator for TEAD-dependent expression of synaptopodin, zonula occludens-1, and zonula occludens-2. This is the first study to determine that TAZ plays an important role in the maintenance of the structure and function of podocytes.NEW & NOTEWORTHY Podocytes play an important role in maintaining the integrity of the structure and function of the kidney. We observed that mice with selective deletion of transcriptional coactivator with PDZ-binding motif (TAZ) in podocytes developed proteinuria. TAZ is constitutively active and critical for expression of synaptopodin, zonula occludens-1, and zonula occludens-2 in podocytes. The findings of this study implicate TAZ as an important mediator of podocyte structural integrity and provide further insights into the role of Hippo-Yes-associated protein/TAZ in podocyte biology.

Hippo/YAP signaling pathway protects against neomycin-induced hair cell damage in the mouse cochlea

The Hippo/Yes-associated protein (YAP) signaling pathway has been shown to be able to maintain organ size and homeostasis by regulating cell proliferation, differentiation, and apoptosis. The abuse of aminoglycosides is one of the main causes of sensorineural hearing loss (SSNHL). However, the role of the Hippo/YAP signaling pathway in cochlear hair cell (HC) damage protection in the auditory field is still unclear. In this study, we used the YAP agonist XMU-MP-1 (XMU) and the inhibitor Verteporfin (VP) to regulate the Hippo/YAP signaling pathway in vitro. We showed that YAP overexpression reduced neomycin-induced HC loss, while downregulated YAP expression increased HC vulnerability after neomycin exposure in vitro. We next found that activation of YAP expression inhibited C-Abl-mediated cell apoptosis, which led to reduced HC loss. Many previous studies have reported that the level of reactive oxygen species (ROS) is significantly increased in cochlear HCs after neomycin exposure. In our study, we also found that YAP overexpression significantly decreased ROS accumulation, while downregulation of YAP expression increased ROS accumulation. In summary, our results demonstrate that the Hippo/YAP signaling pathway plays an important role in reducing HC injury and maintaining auditory function after aminoglycoside exposure. YAP overexpression could protect against neomycin-induced HC loss by inhibiting C-Abl-mediated cell apoptosis and decreasing ROS accumulation, suggesting that YAP could be a novel therapeutic target for aminoglycosides-induced sensorineural hearing loss in the clinic.

Near complete deletion of KMT2D in a college student

Pathogenic variants in KMT2D are typically associated with Kabuki syndrome (KS), a rare multisystem disorder. KS is characterized by facial dysmorphisms, intellectual disability, skeletal and dermatoglyphic differences, and poor growth. Seventy percent of individuals with clinically diagnosed KS have a confirmed pathogenic variant in KMT2D or less commonly KDM6A. The majority of mutations found in KMT2D are de novo nonsense or frameshift, with deletions and duplications rarely reported in the literature. Here, we present the case of near complete deletion of KMT2D in a college student with normal intelligence discovered via exome sequencing and EpiSign methylation testing. This case provides evidence that large deletions in KMT2D are compatible with normal intelligence and presents EpiSign as a method for discovering molecular causes of KS not identified by traditional molecular testing.

Riluzole-induced apoptosis in osteosarcoma is mediated through Yes-associated protein upon phosphorylation by c-Abl Kinase

Our lab has previously demonstrated Riluzole to be an effective drug in inhibiting proliferation and inducing apoptosis in both human and mouse osteosarcoma. Yes-associated protein is a transcription co-activator, known to be involved in cell proliferation or apoptosis depending on its protein partner. In the present study we investigated the role of YAP in apoptosis in osteosarcoma, we hypothesized that YAP may be activated by Riluzole to induce apoptosis in osteosarcoma. By knocking down the expression of YAP, we have demonstrated that Riluzole failed to induce apoptosis in YAP deficient osteosarcoma cells. Riluzole caused translocation of YAP from the cytoplasm to the nucleus, indicating YAP’s role in apoptosis. Both Riluzole-induced phosphorylation of YAP at tyrosine 357 and Riluzole-induced apoptosis were blocked by inhibitors of c-Abl kinase. In addition, knockdown of c-Abl kinase prevented Riluzole-induced apoptosis in LM7 cells. We further demonstrated that Riluzole promoted interaction between YAP and p73, while c-Abl kinase inhibitors abolished the interaction. Subsequently, we demonstrated that Riluzole enhanced activity of the Bax promoter in a luciferase reporter assay and enhanced YAP/p73 binding on endogenous Bax promoter in a ChIP assay. Our data supports a novel mechanism in which Riluzole activates c-Abl kinase to regulate pro-apoptotic activity of YAP in osteosarcoma.

Proteome and Phosphoproteome Analyses Reveal the Kinase Regulatory Network Involved in Glycogen Synthesis Kinase 3β

Diabetic nephropathy is the most common chronic kidney disease in the world and the main cause of end-stage renal disease (ESRD). The structural integrity of podocytes is fundamental to the normal function of the glomerulus, and the role of glycogen synthase kinase 3β (GSK-3β) in podocytes is complicated. A thorough understanding of GSK-3β is crucial to understand the mechanism of diabetic nephropathy. To analyze the roles of GSK-3β in podocytes, GSK-3β knockdown lentivirus by clustered regularly interspaced short palindromic repeats (CRISPR)–CRISPR-associated protein (Cas)9 was applied to establish stable cell lines. Mass spectrometry was utilized to search for differentially expressed proteins. Consequently, we found 34 proteins with higher levels and 115 proteins with lower levels in GSk-3β knockdown cells than in control cells and identified 581 phosphosites with higher phosphorylation levels and 288 phosphosites with lower phosphorylation levels. We performed functional enrichment analysis of these proteins and phosphorylated proteins based on public databases. Enrichment analysis revealed that GSK-3β participates in the spliceosome, Hippo signaling pathway, actin binding, structural molecule activity, and other pathways. Then, we used motif analysis of phosphate sites to determine 89 conserved motifs based on 1,068 phosphoserine (pS) sites and 15 conserved motifs in view of 104 phosphothreonine (pT) sites. Additionally, protein–protein interaction network analysis was carried out using the STRING database. Cytoscape’s add-on Molecular Complex Detection (MCODE) was used to analyze key and core protein groups. In quantitative differential protein analysis, four MCODEs were obtained, and 22 MCODEs were obtained in the analysis of the phosphoproteome of differentially expressed proteins. Finally, we analyzed the kinase regulatory network in podocytes after GSK-3β knockdown and identified 299 protein kinases and 3,460 significantly changed phosphorylation modification sites on 1,574 proteins. These results will be valuable for further research on GSK-3β.

Integrin β3 overexpression contributes to podocyte injury through inhibiting RhoA/YAP signaling pathway

Axis formed by integrin β3 (ITGβ3)-Ras homolog gene family, member A (RhoA), and Yes-associated protein (YAP) plays an important role in atherosclerosis. In addition, ITGβ3 overexpression was noted in high-glucose (HG) exposure podocytes. However, the ITGβ3–RhoA–YAP axis on HG-induced podocyte injury remains unclear. This study aimed to investigate whether ITGβ3 regulates podocyte injury by regulating the RhoA–YAP axis. The function and potential mechanism of ITGβ3 were observed through in vitro wound-healing assays, flow cytometry, reverse transcription-quantitative polymerase chain reaction (RT-qPCR), and western blot assay. Results showed that HG treatment increased the ability of wound closure and apoptosis; however, in spite of HG treatment, ITGβ3 inhibition mitigated the ability of wound closure and apoptosis in podocytes. By contrast, overexpression of ITGβ3 increased the wound closure and apoptosis abilities of podocytes. Under HG treatment, ITGβ3 knockdown is associated with upregulation of RhoA, total YAP1, and nucleus YAP1, whereas ITGβ3 overexpression has opposite effect. In addition, RhoA overexpression in podocytes reverses the effect of ITGβ3 overexpression on the wound closure and apoptosis abilities of podocytes, rescue the expression of YAP in ITGβ3 overexpression podocytes. Taken together, ITGβ3 overexpression promotes podocytes injury by inhibiting RhoA-YAP axis. This will provide a new clue for preventing podocyte from damage.

Old Mice Have Less Transcriptional Activation But Similar Periosteal Cell Proliferation Compared to Young-Adult Mice in Response to in vivo Mechanical Loading

Mechanical loading is a potent strategy to induce bone formation, but with aging, the bone formation response to the same mechanical stimulus diminishes. Our main objectives were to (i) discover the potential transcriptional differences and (ii) compare the periosteal cell proliferation between tibias of young-adult and old mice in response to strain-matched mechanical loading. First, to discover potential age-related transcriptional differences, we performed RNA sequencing (RNA-seq) to compare the loading responses between tibias of young-adult (5-month) and old (22-month) C57BL/6N female mice following 1, 3, or 5 days of axial loading (loaded versus non-loaded). Compared to young-adult mice, old mice had less transcriptional activation following loading at each time point, as measured by the number of differentially expressed genes (DEGs) and the fold-changes of the DEGs. Old mice engaged fewer pathways and gene ontology (GO) processes, showing less activation of processes related to proliferation and differentiation. In tibias of young-adult mice, we observed prominent Wnt signaling, extracellular matrix (ECM), and neuronal responses, which were diminished with aging. Additionally, we identified several targets that may be effective in restoring the mechanoresponsiveness of aged bone, including nerve growth factor (NGF), Notum, prostaglandin signaling, Nell-1, and the AP-1 family. Second, to directly test the extent to which periosteal cell proliferation was diminished in old mice, we used bromodeoxyuridine (BrdU) in a separate cohort of mice to label cells that divided during the 5-day loading interval. Young-adult and old mice had an average of 15.5 and 16.7 BrdU+ surface cells/mm, respectively, suggesting that impaired proliferation in the first 5 days of loading does not explain the diminished bone formation response with aging. We conclude that old mice have diminished transcriptional activation following mechanical loading, but periosteal proliferation in the first 5 days of loading does not differ between tibias of young-adult and old mice. © 2020 American Society for Bone and Mineral Research.

YAP/TAZ affects the development of pulmonary fibrosis by regulating multiple signaling pathways

YAP and TAZ are important co-activators of various biological processes in human body. YAP/TAZ plays a vital role in the development of pulmonary fibrosis. Dysregulation of the YAP/TAZ signaling pathway is one of the most important causes of pulmonary fibrosis. Therefore, considering its crucial role, summary of the signal mechanism of YAP/TAZ is of certain guiding significance for the research of YAP/TAZ as a therapeutic target. The present review provided a detailed introduction to various YAP/TAZ-related signaling pathways and clarified the specific role of YAP/TAZ in these pathways. In the meantime, we summarized and evaluated possible applications of YAP/TAZ in the treatment of pulmonary fibrosis. Overall, our study is of guiding significance for future research on the functional mechanism of YAP/TAZ underlying lung diseases as well as for identification of novel therapeutic targets specific to pulmonary fibrosis.

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.

RASSF1A, puppeteer of cellular homeostasis, fights tumorigenesis, and metastasis-an updated review

The Ras association domain family protein1 isoform A (RASSF1A) is a well-known tumor-suppressor protein frequently inactivated in various human cancers. Consistent with its function as a molecular scaffold protein, referred to in many studies, RASSF1A prevents initiation of tumorigenesis, growth, and dissemination through different biological functions, including cell cycle arrest, migration/metastasis inhibition, microtubular stabilization, and apoptosis promotion. As a regulator of key cancer pathways, namely Ras/Rho GTPases and Hippo signaling without ignoring strong interaction with microtubules, RASSF1A is indeed one of the guardians of cell homeostasis. To date, as we approach the two decade anniversary of RASSF1A's discovery, this review will summarize our current knowledge on the RASSF1A key interactions as a tumor suppressor and discuss their impact on cell fate during carcinogenesis. This could facilitate a deeper understanding of tumor development and provide us with new strategies in cancer treatment by targeting the RASSF1A pathway.

Safety Considerations in the Development of Hippo Pathway Inhibitors in Cancers

The Hippo pathway is a critical regulator of cell and organ growth and has emerged as a target for therapeutic intervention in cancers. Its signaling is thought to play an important role in various physiological processes including homeostasis and tissue regeneration. To date there has been limited information about potential pharmacology-related (on-target) safety liabilities of Hippo pathway inhibitors in the context of cancer indications. Herein, we review data from human genetic disorders and genetically engineered rodent models to gain insight into safety liabilities that may emerge from the inhibition of Hippo pathway. Germline systemic deletion of murine Hippo pathway effectors (Yap, Taz, and Teads) resulted in embryonic lethality or developmental phenotypes. Mouse models with tissue-specific deletion (or mutant overexpression) of the key effectors in Hippo pathways have indicated that, at least in some tissues, Hippo signaling may be dispensable for physiological homeostasis; and appears to be critical for regeneration upon tissue damage, indicating that patients with underlying comorbidities and/or insults caused by therapeutic agents and/or comedications may have a higher risk. Caution should be taken in interpreting phenotypes from tissue-specific transgenic animal models since some tissue-specific promoters are turned on during development. In addition, therapeutic agents may result in systemic effects not well-predicted by animal models with tissue-specific gene deletion. Therefore, the development of models that allows for systemic deletion of Yap and/or Taz in adult animals will be key in evaluating the potential safety liabilities of Hippo pathway modulation. In this review, we focus on potential challenges and strategies for targeting the Hippo pathway in cancers.

Effects of Spaceflight and Simulated Microgravity on YAP1 Expression in Cardiovascular Progenitors: Implications for Cell-Based Repair

Spaceflight alters many processes of the human body including cardiac function and cardiac progenitor cell behavior. The mechanism behind these changes remains largely unknown; however, simulated microgravity devices are making it easier for researchers to study the effects of microgravity. To study the changes that take place in cardiac progenitor cells in microgravity environments, adult cardiac progenitor cells were cultured aboard the International Space Station (ISS) as well as on a clinostat and examined for changes in Hippo signaling, a pathway known to regulate cardiac development. Cells cultured under microgravity conditions, spaceflight-induced or simulated, displayed upregulation of downstream genes involved in the Hippo pathway such as YAP1 and SOD2. YAP1 is known to play a role in cardiac regeneration which led us to investigate YAP1 expression in a sheep model of cardiovascular repair. Additionally, to mimic the effects of microgravity, drug treatment was used to induce Hippo related genes as well as a regulator of the Hippo pathway, miRNA-302a. These studies provide insight into the changes that occur in space and how the effects of these changes relate to cardiac regeneration studies.

Zhen-wu-tang ameliorates membranous nephropathy rats through inhibiting NF-κB pathway and NLRP3 inflammasome

BACKGROUND

Zhen-wu-tang (ZWT), a traditional herbal formula, has been widely used for the treatment of kidney diseases in clinics, but the underlying molecular mechanisms have not been fully understood.

PURPOSE

Inflammation mediated podocyte injury has been reported to constitute a crucial part in the pathogenesis of membranous nephropathy (MN). The current study was designed to evaluate the effect of ZWT on MN related to nuclear factor-κB (NF-κB) pathway and NLRP3 inflammasome.

METHODS

The main components of ZWT were identified by 3D-ultra performance liquid chromatography (3D-UPLC) assay. A MN rat model induced by cationic-bovine serum albumin (C-BSA) and podocytes stimulated by TNF-α were used in this study. The 24 h urine protein, serum total cholesterol (TC) and triglyceride (TG), as well as kidney histology were measured to evaluate kidney damage. The expressions of IgG and complement 3 (C3), and the co-localization of NLRP3 and ASC were detected by immunofluorescence. The expressions of podocyte injury related protein desmin, podocin were measured by immunohistochemistry and western blot. Cell vitality of cultured podocytes was detected by MTT assay, as apoptosis assay was measured via flow cytometry. The protein expressions of p-p65, p-IκBα, NLRP3, Caspase-1, IL-1β were detected by western blot.

RESULTS

Our results showed that ZWT significantly ameliorated kidney damage in MN model rats by decreasing the levels of 24 h urine protein, TC and TG. ZWT also improved renal histology and reduced the expressions of IgG and C3 in glomerulus. In addition, ZWT lessened the expressions of desmin, but increased podocin expression in vivo and vitro. ZWT protected cultured podocytes by maintaining cell vitality and inhibiting apoptosis. Moreover, we found that ZWT suppressed the expressions of NLRP3, Caspase-1, IL-1β and the co-localization of NLRP3 and ASC. Furthermore, the inhibition of NLRP3 inflammasome under ZWT treatment were accompanied by down-regulation of NF-κB pathway, as the p-p65 and p-IκBα protein expression were reduced.

CONCLUSIONS

Our present study indicates that the inhibition of NF-κB pathway and NLRP3 inflammasome might be the potential mechanisms for the therapeutic effects of ZWT against MN.

Butyrate promotes the adaptation of intestinal smooth muscle cells through the yes-associated protein (YAP) pathway in a rat model of short bowel syndrome

Our previous study demonstrated that the proliferation of human intestinal smooth muscle (ISM) cells was stimulated by butyrate through the yes-associated protein (YAP) pathway in vitro, suggesting a valuable approach for intestinal adaption of short bowel syndrome (SBS). This study was conducted to confirm these findings in vivo. Three-week-old Sprague-Dawley rats were randomly divided into the following groups: Sham group (bowel transection and reanastomosis), SB W group (80% small bowel resection/water ad libitum), and SB Bu group (80% small bowel resection/50 mM sodium butyrate ad libitum). Morphological changes were determined by hematoxylin and eosin staining; the proliferation rate of ISM cells was examined by Ki67 staining, and apoptosis was determined in the TUNEL assay. Changes in the expression of YAP and its downstream genes were evaluated by quantitative-polymerase chain reaction and western blotting. Fourteen days post-operation, a significant increase in ISM thickness was observed in the SB Bu group compared to the SB W group, accompanied by enhanced proliferation of ISM cells and suppression of apoptosis. Notably, YAP expression was also significantly increased in the SB Bu group, with a 6.5-fold increase in the proportion of YAP-positive ISM cells, 2.2-fold increase in YAP mRNA expression, and 3.4-fold increase in protein expression. In conclusion, our results suggest that butyrate promotes ISM adaption through YAP in vivo, which may be a potential therapeutic approach for SBS patients.

Expression of DENDRIN in several glomerular diseases and correlation to pathological parameters and renal failure - preliminary study

Background

In glomerular injury dendrin translocates from the slit diaphragm to the podocyte nucleus, inducing apoptosis. We analyzed dendrin expression in IgA glomerulonephritis and Henoch Schönlein purpura (IgAN/HSP) versus in podocytopathies minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS), and compared it to pathohistological findings and renal function at the time of biopsy and the last follow-up.

Methods

Twenty males and 13 females with median of age 35 years (min-max: 3–76) who underwent percutaneous renal biopsy and had diagnosis of glomerular disease (GD) were included in this retrospective study. Fifteen patients had IgAN/HSP and eighteen podocytopathy. Control group consisted of ten patients who underwent nephrectomy due to renal cancer. Dendrin expression pattern (membranous, dual, nuclear or negative), number of dendrin positive nuclei and proportion of dendrin negative glomeruli were analyzed.

Results

In GD and the control group significant differences in number of dendrin positive nuclei and proportion of dendrin negative glomeruli were found (P = 0.004 and P = 0.003, respectively). Number of dendrin positive nuclei was higher in podocytopathies than in IgAN/HSP, 3.90 versus 1.67 (P = 0.028). Proportion of dendrin negative glomeruli correlated to higher rates of interstitial fibrosis (P = 0.038), tubular atrophy (P = 0.011) and globally sclerotic glomeruli (P = 0.008). Dual and nuclear dendrin expression pattern were connected with lower rate of interstitial fibrosis and tubular atrophy than negative dendrin expression pattern (P = 0.024 and P = 0.017, respectively). Proportion of dendrin negative glomeruli correlated with lower creatinine clearance (CC) at the time of biopsy and the last follow-up (P = 0.010 and P < 0.001, respectively). Dendrin expression pattern correlated to CC at the last follow-up (P = 0.009), being lower in patients with negative than nuclear or dual dendrin expression (P = 0.034 and P = 0.004, respectively).

Conclusion

In this pilot study the number of dendrin positive nuclei was higher in podocytopathies than in inflammatory GD. Negative dendrin expression pattern correlated to chronic tubulointerstitial changes and lower CC, which needs to be confirmed in a larger series.

Leonurine ameliorates adriamycin-induced podocyte injury via suppression of oxidative stress

Leonurine, a major bioactive component from Herba Leonuri, shows therapeutic potential in several diseases, including diabetes, cardiovascular disease, bovine mastitis and depression. In kidney, it was reported that leonurine was performing a protective effect in both acute kidney injury and renal fibrosis mice models. The aim of this study is to investigate the effect of leonurine in podocyte injury. In the mice model of adriamycin (ADR) -induced nephropathy, the application of leonurine significantly prevented early kidney damage, macrophage infiltration and proteinuria. Meanwhile, leonurine suppressed ADR-induced podocyte injury and reactive oxygen species (ROS) production. Consistent to in vivo results, leonurine prevented ADR-induced podocyte injury and ROS production in cultured human podocytes. All these results suggested that leonurine might suppress ADR-induced podocyte injury via inhibiting oxidative stress. Leonurine might be a novel therapeutic drug for prevention of glomerular diseases.

Proteinuric Kidney Diseases: A Podocyte's Slit Diaphragm and Cytoskeleton Approach

Proteinuric kidney diseases are a group of disorders with diverse pathological mechanisms associated with significant losses of protein in the urine. The glomerular filtration barrier (GFB), comprised of the three important layers, the fenestrated glomerular endothelium, the glomerular basement membrane (GBM), and the podocyte, dictates that disruption of any one of these structures should lead to proteinuric disease. Podocytes, in particular, have long been considered as the final gatekeeper of the GFB. This specialized visceral epithelial cell contains a complex framework of cytoskeletons forming foot processes and mediate important cell signaling to maintain podocyte health. In this review, we will focus on slit diaphragm proteins such as nephrin, podocin, TRPC6/5, as well as cytoskeletal proteins Rho/small GTPases and synaptopodin and their respective roles in participating in the pathogenesis of proteinuric kidney diseases. Furthermore, we will summarize the potential therapeutic options targeting the podocyte to treat this group of kidney diseases.

Nuclear YAP localization as a key regulator of podocyte function

Podocytes are crucial for the establishment of the blood-urine filtration barrier in the glomeruli of the kidney. These cells are mainly affected during glomerulopathies causing proteinuria and kidney function impairment. Ongoing podocyte injury leads to podocyte loss, finally followed by end-stage kidney disease. Podocytes display a predominant nuclear localization of YAP (Yes-associated protein), one effector protein of the Hippo pathway, which regulates the balance between proliferation, differentiation, and apoptosis in cells. Nuclear active YAP seems to be critical for podocyte survival in vivo and in vitro. We can show here that different treatments leading to sequestration of YAP into the cytoplasm in podocytes, like decreased rigidity of the substrate, incubation with dasatinib, or overexpression of Hippo pathway members result in the induction of apoptosis. A RNA sequencing analysis of large tumor suppressor kinase 2 (LATS2) overexpressing podocytes confirmed a significant upregulation of apoptotic genes. The downregulation of Hippo pathway components suggests a feedback mechanism in podocytes. Noteworthy was the regulation of genes involved in cell–cell junction, the composition of the extracellular space, and cell migration. This suggests an influence of Hippo pathway activity on podocyte integrity. As focal segmental glomerulopathy (FSGS) goes along with an activation of the Hippo pathway in podocytes, a comparison of our data with two independent studies of transcriptional regulation in human FSGS glomeruli obtained from the Nephroseq database was performed. This comparison affirmed a multitude of consistent transcriptional changes concerning the regulation of genes influencing apoptosis and the Hippo signaling pathway as well as cell junction formation and cell migration. The link between Hippo pathway activation in podocytes and the regulation of junction and migration processes in vivo might be a fundamental mechanism of glomerular sclerosis and loss of renal function.

MAGI-2 and scaffold proteins in glomerulopathy

In many cells and tissues, including the glomerular filtration barrier, scaffold proteins are critical in optimizing signal transduction by enhancing structural stability and functionality of their ligands. Recently, mutations in scaffold protein membrane-associated guanylate kinase inverted 2 (MAGI-2) encoding gene were identified among the etiology of steroid-resistant nephrotic syndrome. MAGI-2 interacts with core proteins of multiple pathways, such as transforming growth factor-β signaling, planar cell polarity pathway, and Wnt/β-catenin signaling in podocyte and slit diaphragm. Through the interaction with its ligand, MAGI-2 modulates the regulation of apoptosis, cytoskeletal reorganization, and glomerular development. This review aims to summarize recent findings on the role of MAGI-2 and some other scaffold proteins, such as nephrin and synaptopodin, in the underlying mechanisms of glomerulopathy.

Hippo-yap signaling in ocular development and disease

The Hippo-Yes associated protein (Yap) pathway plays an important role in organ size control by regulating cell proliferation, apoptosis, and stem cell renewal. Hippo-Yap signaling also functions at the level of cellular development in a variety of organs through its effects on cell cycle control, cell survival, cell polarity, and cell fate. Because of its important roles in normal development and homeostasis, abnormal regulation of this pathway has been shown to lead to pathological outcomes such as tissue overgrowth, tumor formation, and abnormal organogenesis, including ocular-specific disorders. In this review, we summarize how normal and perturbed control of Yap signaling is implicated in ocular development and disease Developmental Dynamics 247:794-806, 2018. © 2018 Wiley Periodicals, Inc.

Protecting Podocytes: A Key Target for Therapy of Focal Segmental Glomerulosclerosis

BACKGROUND

Focal segmental glomerulosclerosis (FSGS) is a histologic pattern of injury demonstrated by renal biopsy that can arise from a diverse range of causes and mechanisms. It has an estimated incidence of 7 per 1 million and is the most common primary glomerular disorder leading to end-stage renal disease in the United States. This review focuses on damage to the podocyte and the consequences of this injury in patients with FSGS, the genetics of FSGS, and approaches to treatment with a focus on the effects on podocytes.

SUMMARY

The podocyte is central to the glomerular filtration barrier and is particularly vulnerable because of its highly differentiated post-mitotic phenotype. The progressive structural changes involved in the pathology of FSGS include podocyte foot process effacement, death of podocytes and exposure of the glomerular basement membrane, filtration of nonspecific plasma proteins, expansion of capillaries, misdirected filtration at points of synechiae, and mesangial matrix proliferation. Although damage to and death of podocytes can result from single-gene disorders, evidence also suggests a role for soluble factors, such as soluble urokinase-type plasminogen activator receptor, cardiotrophin-like cytokine-1, and anti-CD40 antibodies, that promote FSGS recurrence post transplant. Several classes of medications, including corticosteroids, calcineurin inhibitors, endothelin receptor antagonists, adrenocorticotropic hormone, and rituximab, have been shown to be effective for the treatment of FSGS and have been demonstrated to have significant protective effects on podocytes. Key Messages: Greater understanding of podocyte biology is essential to the identification of new treatment targets and medications for the management of patients with FSGS.

The Hippo pathway regulator KIBRA promotes podocyte injury by inhibiting YAP signaling and disrupting actin cytoskeletal dynamics

Kidney podocytes represent a key constituent of the glomerular filtration barrier. Identifying the molecular mechanisms of podocyte injury and survival is important for better understanding and management of kidney diseases. KIBRA (kidney brain protein), an upstream regulator of the Hippo signaling pathway encoded by the Wwc1 gene, shares the pro-injury properties of its putative binding partner dendrin and antagonizes the pro-survival signaling of the downstream Hippo pathway effector YAP (Yes-associated protein) in Drosophila and MCF10A cells. We recently identified YAP as an essential component of the glomerular filtration barrier that promotes podocyte survival by inhibiting dendrin pro-apoptotic function. Despite these recent advances, the signaling pathways that mediate podocyte injury remain poorly understood. Here we tested the hypothesis that, similar to its role in other model systems, KIBRA promotes podocyte injury. We found increased expression of KIBRA and phosphorylated YAP protein in glomeruli of patients with biopsy-proven focal segmental glomerulosclerosis (FSGS). KIBRA/WWc1 overexpression in murine podocytes promoted LATS kinase phosphorylation, leading to subsequent YAP Ser-127 phosphorylation, YAP cytoplasmic sequestration, and reduction in YAP target gene expression. Functionally, KIBRA overexpression induced significant morphological changes in podocytes, including disruption of the actin cytoskeletal architecture and reduction of focal adhesion size and number, all of which were rescued by subsequent YAP overexpression. Conversely, constitutive KIBRA knockout mice displayed reduced phosphorylated YAP and increased YAP expression at baseline. These mice were protected from acute podocyte foot process effacement following protamine sulfate perfusion. KIBRA knockdown podocytes were also protected against protamine-induced injury. These findings suggest an important role for KIBRA in the pathogenesis of podocyte injury and the progression of proteinuric kidney disease.

Cytoresistance after acute kidney injury is limited to the recovery period of proximal tubule integrity and possibly involves Hippo-YAP signaling

Rat proximal tubule (PT) cells that have recovered from severe acute kidney injury induced by uranyl acetate (UA) develop cytoresistance to subsequent UA treatments. We reported that enhanced G1 arrest might contribute to cytoresistance. Herein, we examined these mechanisms by investigating Yes-associated protein (YAP), a regulator of cell number, and survivin, a downstream mediator of YAP that inhibits apoptosis. Rats pretreated with saline (vehicle group) or UA (AKI group) were injected with UA 2 weeks, 2 months, or 6 months after treatment. Cytoresistance, evaluated by serum creatinine, was observed at 2 weeks, was attenuated at 2 months, and was lost at 6 months in the AKI group. Based on immunohistochemistry, overexpressed YAP/survivin in PT cells and an increased number of PT cells was found before the second insult at 2 weeks, regressed gradually, and returned to a normal value by 6 months in the AKI group. Cell cycle status, assessed by flow cytometry, was equivalent in all groups before the second insult. However, early G1 phase (cyclin D1-) and p27+ PT cells increased in the AKI group compared to those in the vehicle group until 2 months, but were comparable to those in the vehicle group at 6 months. p21+ PT cells increased at 2 weeks, but normalized by 2 months. Thus, PT cells that have recovered from AKI transiently overexpress YAP/survivin, probably inhibiting apoptosis and resulting in acquired cytoresistance. This effect occurs until PT remodeling is complete, subceullular PT integrity is restored, and cell numbers are normalized.

Glomerulosclerosis Induced by Deficiency of Membrane-Associated Guanylate Kinase Inverted 2 in Kidney Podocytes

Membrane-associated guanylate kinase inverted 2 (MAGI-2) is a component of the slit diaphragm (SD) of glomerular podocytes. Here, we investigated the podocyte-specific function of MAGI-2 using newly generated podocyte-specific MAGI-2-knockout (MAGI-2-KO) mice. Compared with podocytes from wild-type mice, podocytes from MAGI-2-KO mice exhibited SD disruption, morphologic abnormalities of foot processes, and podocyte apoptosis leading to podocyte loss. These pathologic changes manifested as massive albuminuria by 8 weeks of age and glomerulosclerosis and significantly higher plasma creatinine levels at 12 weeks of age; all MAGI-2-KO mice died by 20 weeks of age. Loss of MAGI-2 in podocytes associated with decreased expression and nuclear translocation of dendrin, which is also a component of the SD complex. Dendrin translocates from the SD to the nucleus of injured podocytes, promoting apoptosis. Our coimmunoprecipitation and in vitro reconstitution studies showed that dendrin is phosphorylated by Fyn and dephosphorylated by PTP1B, and that Fyn-induced phosphorylation prevents Nedd4-2-mediated ubiquitination of dendrin. Under physiologic conditions in vivo, phosphorylated dendrin localized at the SDs; in the absence of MAGI-2, dephosphorylated dendrin accumulated in the nucleus. Furthermore, induction of experimental GN in rats led to the downregulation of MAGI-2 expression and the nuclear accumulation of dendrin in podocytes. In summary, MAGI-2 and Fyn protect dendrin from Nedd4-2-mediated ubiquitination and from nuclear translocation, thereby maintaining the physiologic homeostasis of podocytes, and the lack of MAGI-2 in podocytes results in FSGS.

YAP modulates TGF-β1-induced simultaneous apoptosis and EMT through upregulation of the EGF receptor

YAP is a transcriptional co-regulator that plays important roles in various patho-physiological processes, including the survival and death of cells. However, the effect of YAP on apoptosis and EMT, simultaneously mediated by TGF-β1, is not known. In this study, we demonstrate that YAP can modulate cell fate of apoptosis versus EMT by acting as a surviving factor. Overexpression of YAP in mouse mammary epithelial (NMuMG) cells suppressed TGF-β1-induced apoptosis, which shifted the cellular response predominantly toward EMT. In contrast, knockdown of YAP induced spontaneous apoptosis and enhanced TGF-β1-induced apoptosis, leading to a sharp decrease in the proportion of surviving cells that underwent EMT. These data suggest that YAP is an essential factor for modulating cellular responses to TGF-β1. Further investigation showed that YAP could regulate the expression level and activation of EGFR. Knockdown or inhibition of EGFR abolished the suppressive effect of YAP on apoptosis, whereas activation of EGFR by EGF significantly reduced apoptosis caused by the knockdown of YAP. The results indicate that EGFR and its activation are critical for YAP-mediated suppression of TGF-β1-induced apoptosis. This study provides a new understanding of the regulatory mechanism underlying the determination of cell fate in response to TGF-β1-mediated simultaneous apoptosis and EMT.

YAP-mediated mechanotransduction determines the podocyte's response to damage

Podocytes are terminally differentiated cells of the kidney filtration barrier. They are subjected to physiological filtration pressure and considerable mechanical strain, which can be further increased in various kidney diseases. When injury causes cytoskeletal reorganization and morphological alterations of these cells, the filtration barrier may become compromised and allow proteins to leak into the urine (a condition called proteinuria). Using time-resolved proteomics, we showed that podocyte injury stimulated the activity of the transcriptional coactivator YAP and the expression of YAP target genes in a rat model of glomerular disease before the development of proteinuria. Although the activities of YAP and its ortholog TAZ are activated by mechanical stress in most cell types, injury reduced YAP and TAZ activity in cultured human and mouse podocyte cell lines grown on stiff substrates. Culturing these cells on soft matrix or inhibiting stress fiber formation recapitulated the damage-induced YAP up-regulation observed in vivo, indicating a mechanotransduction-dependent mechanism of YAP activation in podocytes. YAP overexpression in cultured podocytes increased the abundance of extracellular matrix-related proteins that can contribute to fibrosis. YAP activity was increased in mouse models of diabetic nephropathy, and the YAP target CTGF was highly expressed in renal biopsies from glomerular disease patients. Although overexpression of human YAP in mice induced mild proteinuria, pharmacological inhibition of the interaction between YAP and its partner TEAD in rats ameliorated glomerular disease and reduced damage-induced mechanosignaling in the glomeruli. Thus, perturbation of YAP-dependent mechanosignaling is a potential therapeutic target for treating some glomerular diseases.

Hippo vs. Crab: tissue-specific functions of the mammalian Hippo pathway

The Hippo signaling pathway is a vital suppressor of tumorigenesis that is often inactivated in human cancers. In normal cells, the Hippo pathway is triggered by external forces such as cell crowding, or changes to the extracellular matrix or cell polarity. Once activated, Hippo signaling down-regulates transcription supported by the paralogous cofactors YAP1 and TAZ. The Hippo pathway's functions in normal and cancer biology have been dissected by studies of mutant mice with null or conditional tissue-specific mutations of Hippo signaling elements. In this review, we attempt to systematically summarize results that have been gleaned from detailed in vivo characterizations of these mutants. Our goal is to describe the physiological roles of Hippo signaling in several normal organ systems, as well as to emphasize how disruption of the Hippo pathway, and particularly hyperactivation of YAP1/TAZ, can be oncogenic.

Flow signaling and atherosclerosis

Atherosclerosis rarely develops in the region of arteries exposed to undisturbed flow (u-flow, unidirectional flow). Instead, atherogenesis occurs in the area exposed to disturbed flow (d-flow, multidirectional flow). Based on these general pathohistological observations, u-flow is considered to be athero-protective, while d-flow is atherogenic. The fact that u-flow and d-flow induce such clearly different biological responses in the wall of large arteries indicates that these two types of flow activate each distinct intracellular signaling cascade in vascular endothelial cells (ECs), which are directly exposed to blood flow. The ability of ECs to differentially respond to the two types of flow provides an opportunity to identify molecular events that lead to endothelial dysfunction and atherosclerosis. In this review, we will focus on various molecular events, which are differentially regulated by these two flow types. We will discuss how various kinases, ER stress, inflammasome, SUMOylation, and DNA methylation play roles in the differential flow response, endothelial dysfunction, and atherosclerosis. We will also discuss the interplay among the molecular events and how they coordinately regulate flow-dependent signaling and cellular responses. It is hoped that clear understanding of the way how the two flow types beget each unique phenotype in ECs will lead us to possible points of intervention against endothelial dysfunction and cardiovascular diseases.

Podocyte-actin dynamics in health and disease

Genetic studies of hereditary forms of nephrotic syndrome have identified several proteins that are involved in regulating the permselective properties of the glomerular filtration system. Further extensive research has elucidated the complex molecular basis of the glomerular filtration barrier and clearly established the pivotal role of podocytes in the pathophysiology of glomerular diseases. Podocyte architecture is centred on focal adhesions and slit diaphragms - multiprotein signalling hubs that regulate cell morphology and function. A highly interconnected actin cytoskeleton enables podocytes to adapt in order to accommodate environmental changes and maintain an intact glomerular filtration barrier. Actin-based endocytosis has now emerged as a regulator of podocyte integrity, providing an impetus for understanding the precise mechanisms that underlie the steady-state control of focal adhesion and slit diaphragm components. This Review outlines the role of actin dynamics and endocytosis in podocyte biology, and discusses how molecular heterogeneity in glomerular disorders could be exploited to deliver more rational therapeutic interventions, paving the way for targeted medicine in nephrology.

RhoA deficiency disrupts podocyte cytoskeleton and induces podocyte apoptosis by inhibiting YAP/dendrin signal

Background

Podocyte apoptosis is a major mechanism that leads to proteinuria in many kidney diseases. However, the concert mechanisms that cause podocyte apoptosis in these kidney diseases are not fully understood. RhoA is one of Rho GTPases that has been well studied and plays a key role in regulating cytoskeletal architecture. Previous study showed that insufficient RhoA could result in rat aortic smooth muscle cell apoptosis. However, whether RhoA is involved in podocyte apoptosis remains unknown.

Methods

Culture podocytes were treated with LPS, ADR or siRNA for 48 h before harvest. Subcellular immunoblotting, qRT-PCR, immunofluorescence and flow cytometry were used to exam the expression and function of RhoA or YAP in podocytes.

Results

We found that the expression of RhoA and its activity were significantly decreased in LPS or ADR-injured podocytes, accompanying loss of stress fibers and increased cell apoptosis. Knocking down RhoA or its downstream effector mDia expression by siRNA also caused loss of stress fibers and podocyte apoptosis. Moreover, our results further demonstrated that RhoA deficiency could reduce the mRNA and protein expression of YAP, which had been regarded as an anti-apoptosis protein in podocyte. Silenced dendrin expression significantly abolished RhoA, mDia or YAP deficiency-induced podocyte apoptosis.

Conclusion

RhoA deficiency could disrupt podocyte cytoskeleton and induce podocyte apoptosis by inhibiting YAP/dendrin signal. RhoA/mDia/YAP/dendrin signal pathway may potentially play an important role in regulating podocyte apoptosis. Maintaining necessary RhoA would be one potent way to prevent proteinuria kidney diseases.

Hippo signaling in the kidney: the good and the bad

The Hippo signaling pathway is an evolutionarily conserved kinase cascade, playing multiple roles in embryonic development that controls organ size, cell proliferation, and apoptosis. At the center of this network lie the Hippo kinase target and downstream pathway effector Yes-associated protein (YAP) and its paralog TAZ. In its phosphorylated form, cytoplasmic YAP is sequestered in an inactive state. When it is dephosphorylated, YAP, a potent oncogene, is activated and relocates to the nucleus to interact with a number of transcription factors and signaling regulators that promote cell growth, differentiation, and survival. The identification of YAP activation in human cancers has made it an attractive target for chemotherapeutic drug development. Little is known to date about the function of the Hippo pathway in the kidney, but that is rapidly changing. Recent studies have shed light on the role of Hippo-YAP signaling in glomerular and lower urinary tract embryonic development, maintenance of podocyte homeostasis, the integrity of the glomerular filtration barrier, regulation of renal tubular cyst growth, renal epithelial injury in diabetes, and renal fibrogenesis. This review summarizes the current knowledge of the Hippo-YAP signaling axis in the kidney under normal and disease conditions.

Nephrin Suppresses Hippo Signaling through the Adaptor Proteins Nck and WTIP

Podocytes are key components of the kidney blood filtration barrier, and their ability to withstand hemodynamic strain is proposed to be closely tied to their unique and flexible cytoarchitecture. However, the mechanisms that control such mechanotransduction are poorly understood. We have previously established that tyrosine phosphorylation of the transmembrane protein nephrin promotes recruitment of the Nck1/2 cytoskeletal adaptor proteins and downstream actin remodeling. We now reveal that Nck integrates nephrin with the Hippo kinase cascade through association with the adaptor protein WTIP. Using mutational analysis, we show that Nck sequesters WTIP and its binding partner Lats1 to phosphorylated nephrin, resulting in decreased phospho-activation of Lats1. We further demonstrate that, coincident with nephrin dephosphorylation in a transient model of podocyte injury in mice, Lats1 is rapidly activated, and this precedes significant down-regulation of the transcription regulator Yap. Moreover, we show reduced levels of Yap protein in mice with chronic disruption of nephrin phospho-signaling. Together, these findings support the existence of a dynamic molecular link between nephrin signaling and the canonical Hippo pathway in podocytes, which may facilitate the conversion of mechanical cues to biochemical signals promoting podocyte viability.

Cdc42 deficiency induces podocyte apoptosis by inhibiting the Nwasp/stress fibers/YAP pathway

Podocyte apoptosis is a major mechanism that leads to proteinuria in many chronic kidney diseases. However, the concert mechanisms that cause podocyte apoptosis in these kidney diseases are not fully understood. The Rho family of small GTPases has been shown to be required in maintaining podocyte structure and function. Recent studies have indicated that podocyte-specific deletion of Cdc42 in vivo, but not of RhoA or Rac1, leads to congenital nephrotic syndrome and glomerulosclerosis. However, the underlying cellular events in podocyte controlled by Cdc42 remain unclear. Here, we assessed the cellular mechanisms by which Cdc42 regulates podocyte apoptosis. We found that the expression of Cdc42 and its activity were significantly decreased in high glucose-, lipopolysaccharide- or adriamycin-injured podocytes. Reduced Cdc42 expression in vitro and in vivo by small interfering RNA and selective Cdc42 inhibitor ML-141, respectively, caused podocyte apoptosis and proteinuria. Our results further demonstrated that insufficient Cdc42 or Nwasp, its downstream effector, could decrease the mRNA and protein expression of YAP, which had been regarded as an anti-apoptosis protein in podocyte. Moreover, our data indicated that the loss of stress fibers caused by Cdc42/Nwasp deficiency also decreased Yes-associated protein (YAP) mRNA and protein expression, and induced podocyte apoptosis. Podocyte apoptosis induced by Cdc42/Nwasp/stress fiber deficiency was significantly inhibited by overexpressing-active YAP. Thus, the Cdc42/Nwasp/stress fibers/YAP signal pathway may potentially play an important role in regulating podocyte apoptosis. Maintaining necessary Cdc42 would be one potent way to prevent proteinuria kidney diseases.

Podocytes

Podocytes are highly specialized cells of the kidney glomerulus that wrap around capillaries and that neighbor cells of the Bowman’s capsule. When it comes to glomerular filtration, podocytes play an active role in preventing plasma proteins from entering the urinary ultrafiltrate by providing a barrier comprising filtration slits between foot processes, which in aggregate represent a dynamic network of cellular extensions. Foot processes interdigitate with foot processes from adjacent podocytes and form a network of narrow and rather uniform gaps. The fenestrated endothelial cells retain blood cells but permit passage of small solutes and an overlying basement membrane less permeable to macromolecules, in particular to albumin. The cytoskeletal dynamics and structural plasticity of podocytes as well as the signaling between each of these distinct layers are essential for an efficient glomerular filtration and thus for proper renal function. The genetic or acquired impairment of podocytes may lead to foot process effacement (podocyte fusion or retraction), a morphological hallmark of proteinuric renal diseases. Here, we briefly discuss aspects of a contemporary view of podocytes in glomerular filtration, the patterns of structural changes in podocytes associated with common glomerular diseases, and the current state of basic and clinical research.

Relationship of and cross-talk between physical and biologic properties of the glomerulus

PURPOSE OF REVIEW

Cells and tissues must respond to physical stresses. Cells exist in an elastic environment determined by their matrix, matrix contacts, cell-cell contacts, and cytoskeletal structure. We discuss the determinants of the elastic environment of cells and its potential roles in glomerular disease.

RECENT FINDINGS

Control of the mechanical environment is sufficient to induce and maintain the differentiated state of cells including myofibroblasts. New experimental techniques permit precise measurement of the elastic characteristics of normal and diseased tissues and cells, and analysis of cell behavior and cytoskeletal structure in response to mechanical and elastic stimuli. Glomeruli become soft early in the course of several disease models, yet late stages are characterized by increased stiffness and fibrosis with loss of organ function. Work in hepatic fibrosis, arterial disease, and oncology demonstrate that increased collagen crosslinking by lysyl oxidase, an early step in the diseases, can result in a sufficient increase in tissue stiffness to alter cell behavior, leading to disease progression.

SUMMARY

The elastic environment of cells and tissues provides essential signals in development, differentiation, and disease. Identifying the mechanisms that determine the mechanical environment of glomerular cells will complement other approaches to reduce pathologic fibrosis and loss of tissue function.

Dendrin ablation prolongs life span by delaying kidney failure

Podocyte loss is central to the progression of proteinuric kidney diseases leading to end-stage kidney disease (ESKD), requiring renal replacement therapy, such as dialysis. Despite modern tools and techniques, the 5-year mortality of some patients requiring dialysis remains at about 70% to 80%. Thus, there is a great unmet need for podocyte-specific treatments aimed at preventing podocyte loss and the ensuing development of ESKD. Here, we show that ablation of the podocyte death-promoting protein dendrin delays the onset of ESKD, thereby expanding the life span of mice lacking the adapter protein CD2AP. Ablation of dendrin delays onset and severity of proteinuria and podocyte loss. In addition, dendrin ablation ameliorates mesangial volume expansion and up-regulation of mesangial fibronectin expression, which is mediated by a podocyte-secreted factor. In conclusion, onset of ESKD and death can be markedly delayed by blocking the function of dendrin.