Nuclear exclusion of YAP exacerbates podocyte apoptosis and disease progression in Adriamycin-induced focal segmental glomerulosclerosis

Inhibition of YAP can down-regulate NLRP3 inflammasome and improve anti-tuberculosis drug-induced liver injury

Yes-associated protein (YAP) is a core effector molecule in the Hippo signalling pathway, but its role in antituberculosis drug-induced liver injury (ADLI) is unclear. We aimed to explore the regulatory effects of YAP on the NLRP3 inflammasome in ADLI and its potential hepatoprotective effects.An ADLI animal model was established. Various indicators of experimental animals were detected at 0, 7, 14, and 21 days. On day 7, HE staining observed liver tissue, and liver index, ALT, and AST levels confirmed the ADLI model. YAP's mRNA and protein levels were examined, YAP inhibitor effects were observed, and NLRP3 inflammasome, inflammation, and oxidative stress indicators were analysed.It was found that the mRNA and protein levels of YAP increased during ADLI and then decreased due to the action of YAP inhibitors. YAP caused an elevation in NLRP3 inflammasome indicators, as well as increased expression of inflammation and oxidative stress. After feeding with YAP inhibitors, these indicators were reduced.The results suggest that targeting YAP may be a novel therapeutic strategy for alleviating antituberculosis drug-induced liver injury.

Integrin Trafficking, Fibronectin Architecture, and Glomerular Injury upon Adiponectin Receptor 1 Depletion

Key Points

Glomerular expression of adiponectin receptor 1 (AdipoR1) was lower in people with type 2 diabetes and correlates with podocyte loss. AdipoR1 knockout induced glomerular injury and fibrosis in mice, predominantly in males. AdipoR1 knockdown podocytes showed impaired trafficking of active integrin β 1, fibronectin accumulation, impaired adhesion, and increased apoptosis.

Background

Deficiency of adiponectin and its downstream signaling may contribute to the pathogenesis of kidney injury in type 2 diabetes. Adiponectin activates intracellular signaling using adiponectin receptor 1 (AdipoR1) and adiponectin receptor 2, but the role of adiponectin receptor–mediated signaling in glomerular injury in type 2 diabetes remains unknown.

Methods

The expression of AdipoR1 in the kidneys of people with type 2 diabetes and the expression of podocyte proteins or injury markers in the kidneys of AdipoR1 knockout (AdipoR1-KO) mice and immortalized AdipoR1-deficient human podocytes were investigated by immunohistochemistry and immunoblotting. The functional role of AdipoR1 was studied in AdipoR1-deficient podocytes by performing assays for apoptosis, cytokine secretion, mechanical stress, adhesion, and endocytic trafficking.

Results

Glomerular AdipoR1 expression was lower in type 2 diabetes and associated kidney disease, correlating with higher body mass index and podocyte loss. Male AdipoR1-KO mice showed typical signs of early diabetic kidney disease, including albuminuria, glomerular structural abnormalities, and lower expression of central podocyte proteins; females were less affected. Podocyte apoptosis increased in female and male AdipoR1-KO mice, and excessive podocyte loss, potentially due to detachment, was detected in males. AdipoR1 deficiency impaired the yes-associated protein–mediated mechanoresponse and induced accumulation of the extracellular matrix (ECM) protein fibronectin in the glomeruli in vivo and podocytes in vitro . Functionally, AdipoR1 deficiency impaired endocytosis of the ECM receptor active integrin β 1, disturbed focal adhesion turnover, and remodulated podocyte-derived ECM, thereby reducing podocyte adhesion.

Conclusions

AdipoR1 deficiency in mice resulted in the development of kidney injury predominantly in males. Mechanistically, AdipoR1 loss in podocytes impaired endocytosis of active integrin β 1, which plausibly compromised focal adhesion dynamics, disturbed fibronectin matrix turnover, and hindered podocyte adhesion.

Cell cycle disorders in podocytes: an emerging and increasingly recognized phenomenon

Proteinuria is observed in various kidney diseases and is frequently associated with a compromised glomerular filtration barrier. Podocytes, as a crucial component of this barrier, play an essential role in preserving the kidney's normal filtration function. Podocytes are terminally differentiated cells that typically do not proliferate. However, certain harmful stimuli can trigger podocytes to re-enter the cell cycle. Due to its unique cytoskeletal structure, podocytes are unable to maintain the structure of the foot process and complete cell division at the same time, eventually form binucleated or multinucleated podocytes. Studies have found that podocytes re-entering the cell cycle are more susceptible to injury, and are prone to detachment from the basement membrane or apoptosis, which are accompanied by the widening of foot processes. This eventually leads to podocyte mitotic catastrophe and the development of proteinuria. Podocyte cell cycle disorders have previously been found mainly in focal segmental glomerulosclerosis and IgA nephropathy. In recent years, this phenomenon has been frequently identified in diabetic kidney disease and lupus nephritis. An expanding body of research has begun to investigate the mechanisms underlying podocyte cell cycle disorders, including cell cycle re-entry, cell cycle arrest, and mitotic catastrophe. This review consolidates the existing literature on podocyte cell cycle disorders in renal diseases and summarizes the molecules that trigger podocyte re-entry into the cell cycle, thereby providing new drug targets for mitigating podocyte damage. This is essential for alleviating podocyte injury, reducing proteinuria, and delaying the progression of kidney diseases.

CRB2 depletion induces YAP signaling and disrupts mechanosensing in podocytes

Focal segmental glomerulosclerosis (FSGS) is a histologic lesion caused by a variety of injurious stimuli that lead to dysfunction/loss of glomerular visceral epithelial cells (i.e., podocytes). Pathogenic mutations in crumbs homolog-2 (CRB2), encoding the type 1 transmembrane protein crumbs homolog-2, have been shown to cause early-onset corticosteroid-resistant nephrotic syndrome (SRNS)/FSGS. Here, we identified a two-generation Indian kindred (DUK40595) with biopsy-proven SRNS/FSGS caused by a compound heterozygous mutation in CRB2 comprised of the previously described truncating mutation p.Gly1036_Alafs*43 and a rare 9-bp deletion mutation p.Leu1074_Asp1076del. Because compound heterozygous mutations involving the truncating p.Gly1036_Alafs*43 variant have been associated with reduced CRB2 expression in podocytes and autosomal recessive SRNS/FSGS, we sought to define the pathogenic effects of CRB2 deficiency in podocytes. We show that CRB2 knockdown induces yes-associated protein (YAP) activity and target gene expression in podocytes. It upregulates YAP-mediated mechanosignaling and increases the density of focal adhesion and F-actin. Using elastic resonator interference stress microscopy (ERISM), we demonstrate that CRB2 knockdown also enhances podocyte contractility in a substrate stiffness-dependent manner. The knockdown effect decreases with increasing substrate stiffness, indicating impaired mechanosensing in CRB2 knockdown cells at low substrate stiffness. Although the mechanical activation of CRB2 knockdown cells is associated with increased YAP activity, the enhanced cell contractility is not significantly reduced by the selective YAP inhibitors K-975 and verteporfin, suggesting that multiple pathways may be involved in mechanosignaling downstream of CRB2. Taken together, these studies provide the first evidence that CRB2 deficiency may impair podocyte mechanotransduction via disruption of YAP signaling in podocytes.NEW & NOTEWORTHY We identified a rare compound heterozygous CRB2 mutation as the cause of familial SRNS/FSGS in a two-generation East Asian kindred. Modeling the effect of the mutation, we show that CRB2 knockdown in podocytes induces YAP transcriptional activity and upregulates YAP-mediated mechanosignaling. Using elastic resonator interference stress microscopy (ERISM), we demonstrate that CRB2 knockdown enhances podocyte contractility in a substrate stiffness-dependent manner. The knockdown effect decreases with increasing substrate stiffness, indicating impaired mechanosensing in CRB2-deficient podocytes.

Transcriptional Regulators YAP and TAZ Have Distinct Abilities to Compensate for One Another in Podocytes

Key Points

Background

Kidney function depends on the filtration of enormous volumes of plasma, exposing the filtration barrier to mechanical forces. Podocytes must adapt to these forces for the lifetime of an organism as they cannot self-renew. The molecular mechanisms of podocyte adaptation to mechanical stress remain unclear. YAP and TAZ are key mechanotransducers that relay mechanical stimuli to control transcription.

Methods

We made use of podocyte-specific knockout mouse models for Yap (YAPpKO), Taz (TAZpKO), or both (YAPpKO/TAZpKO) and analyzed single-nucleus RNA sequencing data of isolated glomeruli to delineate the distinct and shared roles of YAP and TAZ in podocyte homeostasis.

Results

Here, we found that YAP and TAZ have only partially overlapping functions and compensatory potential in podocytes in vivo. YAPpKO mice displayed podocyte damage and progressive kidney failure. By contrast, TAZpKO animals did not develop any overt disease, while the combined deletion of Yap and Taz caused a neonatal lethal phenotype. Single-nucleus RNA sequencing analysis revealed that in both YAPpKO and TAZpKO mice, a subpopulation of podocytes showed a similar stress response driven by activator protein 1, revealing a protective compensatory mechanism. However, TAZ failed to compensate sufficiently for the loss of YAP, resulting in dysregulation of Rho-GTPases and subsequently the actin cytoskeleton in diseased YAPpKO. Furthermore, we observed loss of ERBB4 expression exclusively in YAPpKO, underscoring the role of ERBB4 signaling as additional layer of YAP-specific regulation in maintaining podocyte survival.

Conclusions

In summary, we identified common and distinct roles for the two transcriptional regulators in podocyte homeostasis. YAP and TAZ can compensate for the loss of the other in podocytes to preserve viability. Still, although YAP can entirely compensate for the loss of TAZ securing podocyte health, TAZ fails to maintain all the YAP-specific functions leading to podocyte injury.

Apoptosis in kidney tissue of senior and geriatric cats with chronic kidney disease

Apoptosis, an important pathological event associated with kidney disease progression, is expected to be a therapeutic target in chronic kidney disease (CKD). However, its role in naturally occurring CKD in aged cats remains unclear. Therefore, here, we investigated kidney tissues from aged cats (≥10 years) with or without azotemic CKD to evaluate apoptotic events using a terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL) assay. The positive TUNEL signals of the renal cells were quantified and statistically analyzed for correlation with the severity of plasma creatinine (pCre) concentration, renal lesions (glomerulosclerosis, interstitial cell infiltration, peritubular capillaries, and interstitial fibrosis), and oxidative damage of the kidney tissue. Oxidative damage was evaluated using immunohistochemistry for 8-hydroxy-2'-deoxyguanosine (OHdG) and 4-hydroxynonenal (HNE). In the TUNEL assay, regardless of azotemia, positive nuclear signals were observed in the tubular epithelial and intraluminal cells, interstitial infiltrating cells, and glomerular cells. Quantitative TUNEL scores showed no significant differences between the azotemic and non-azotemic groups in any compartment of the kidney tissues. In the azotemic group, TUNEL scores did not correlate with pCre or renal lesion severity. However, the scores showed a significant positive correlation with the scores of 8-OHdG and 4-HNE. These findings suggest that apoptosis associated with oxidative damage in renal tissue is an initial pathological event that leads to CKD, rather than a change following CKD progression, in aged cats. Inhibiting apoptosis by antioxidant treatment may be a key strategy to prevent the development of CKD.

Podocyte YAP ablation decreases podocyte adhesion and exacerbates FSGS progression through α3β1 integrin

Severe proteinuria in focal segmental glomerulosclerosis (FSGS) is closely associated with decreased adhesion, and subsequent loss, of podocytes. Yes-associated protein (YAP) is a key transcriptional coactivator that plays a significant role in maintaining cellular homeostasis. However, its role in podocyte adhesion and its specific mechanism in FSGS progression remain unclear. In this study, an adriamycin (ADR)-induced FSGS model was established using podocyte-specific Yap knockout (KO) mice and control mice. These mice were further treated with Pyrintegrin, an agonist of α3β1 integrin, or a vehicle. Additionally, an ADR-induced FSGS model was constructed using podocyte-specific Itga3 KO mice, which were subsequently treated with 1-oleoyl lysophosphatidic acid (LPA), a YAP activator, or a vehicle. Our findings demonstrated that YAP was positively correlated with podocyte adhesion. Podocyte-specific Yap KO mice exhibited reduced levels of α3β1 integrin and podocyte adhesion. Yap KO aggravated the ADR-induced reduction in α3β1 integrin and podocyte adhesion, resulting in significantly increased segmental or global glomerulosclerosis and proteinuria. Notably, treatment with a β1 integrin agonist partially ameliorated the decrease of podocyte adhesion and the worsening FSGS progression caused by Yap KO. Mechanistically, YAP was found to transcriptionally regulate α3- and β1 integrin via transcriptional enhanced associate domain 3 (TEAD3), with TEAD3 binding to the promoter region of Itga3. Furthermore, Itga3 KO or knockdown abolished the beneficial effects of YAP activation on podocyte adhesion and FSGS progression. In conclusion, our results demonstrate that YAP regulates podocyte adhesion and FSGS progression through its transcriptional regulation of α3β1 integrin via TEAD3. This suggests that the YAP-TEAD3-α3β1 integrin axis may serve as a promising therapeutic target for FSGS. © 2024 The Pathological Society of Great Britain and Ireland.

Novel Pathogenic Mutation of P209L in TRPC6 Gene Causes Adult Focal Segmental Glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a leading kidney disease, clinically associated with proteinuria and progressive renal failure. The occurrence of this disease is partly related to gene mutations. We describe a single affected family member who presented with FSGS. We used high-throughput sequencing, sanger sequencing to identify the pathogenic mutations, and a systems genetics analysis in the BXD mice was conducted to explore the genetic regulatory mechanisms of pathogenic genes in the development of FSGS. We identified high urinary protein (++++) and creatinine levels (149 μmol/L) in a 29-year-old male diagnosed with a 5-year history of grade 2 hypertension. Histopathology of the kidney biopsy showed stromal hyperplasia at the glomerular segmental sclerosis and endothelial cell vacuolation degeneration. Whole-exome sequencing followed by Sanger sequencing revealed a heterozygous missense mutation (c.643C > T) in exon 2 of TRPC6, leading to the substitution of arginine with tryptophan at position 215 (p.Arg215Trp). Systems genetics analysis of the 53 BXD mice kidney transcriptomes identified Pygm as the upstream regulator of Trpc6. Those two genes are jointly involved in the regulation of FSGS mainly via Wnt and Hippo signaling pathways. We present a novel variant in the TRPC6 gene that causes FSGS. Moreover, our data suggested TRPC6 works with PYGM, as well as Wnt and Hippo signaling pathways to regulate renal function, which could guide future clinical prevention and targeted treatment for FSGS outcomes.

YAP1 preserves tubular mitochondrial quality control to mitigate diabetic kidney disease

Renal tubule cells act as a primary site of injury in diabetic kidney disease (DKD), with dysfunctional mitochondrial quality control (MQC) closely associated with progressive kidney dysfunction in this context. Our investigation delves into the observed inactivation of yes-associated protein 1 (YAP1) and consequential dysregulation of MQC within renal tubule cells among DKD subjects through bioinformatic analysis of transcriptomics data from the Gene Expression Omnibus (GEO) dataset. Receiver operating characteristic curve analysis unequivocally underscores the robust diagnostic accuracy of YAP1 and MQC-related genes for DKD. Furthermore, we observed YAP1 inactivation, accompanied by perturbed MQC, within cultured tubule cells exposed to high glucose (HG) and palmitic acid (PA). This pattern was also evident in the tubulointerstitial compartment of kidney sections from biopsy-approved DKD patients. Additionally, renal tubule cell-specific Yap1 deletion exacerbated kidney injury in diabetic mice. Mechanistically, Yap1 deletion disrupted MQC, leading to mitochondrial aberrations in mitobiogenesis and mitophagy within tubule cells, ultimately culminating in histologic tubular injury. Notably, Yap1 deletion-induced renal tubule injury promoted the secretion of C-X-C motif chemokine ligand 1 (CXCL1), potentially augmenting M1 macrophage infiltration within the renal microenvironment. These multifaceted events were significantly ameliorated by administrating the YAP1 activator XMU-MP-1 in DKD mice. Consistently, bioinformatic analysis of transcriptomics data from the GEO dataset revealed a noteworthy upregulation of tubule cells-derived chemokine CXCL1 associated with macrophage infiltration among DKD patients. Crucially, overexpression of YAP1 via adenovirus transfection sustained mitochondrial membrane potential, mtDNA copy number, oxygen consumption rate, and activity of mitochondrial respiratory chain complex, but attenuated mitochondrial ROS production, thereby maintaining MQC and subsequently suppressing CXCL1 generation within cultured tubule cells exposed to HG and PA. Collectively, our study establishes a pivotal role of tubule YAP1 inactivation-mediated MQC dysfunction in driving DKD progression, at least in part, facilitated by promoting M1 macrophage polarization through a paracrine-dependent mechanism.

Autophagic inhibitor ROC-325 ameliorates glomerulosclerosis and podocyte injury via inhibiting autophagic flux in experimental FSGS mice

BACKGROUND

Autophagy plays an important role in the pathogenesis of focal segmental glomerulosclerosis (FSGS). Podocyte-specific Yes-associated protein (YAP) deletion mice, referred to as YAP-KO mice, is considered a new animal model to study the underlying mechanism of FSGS. ROC-325 is a novel small-molecule lysosomal autophagy inhibitor that is more effective than chloroquine (CQ) and hydroxychloroquine (HCQ) in suppressing autophagy. In this study, we sought to determine the therapeutic benefit and mechanism of action of ROC-325 in YAP-KO mice, an experimental FSGS model.

METHODS AND RESULTS

YAP-KO mice were treated with ROC-325 (50 mg/kg, p.o.) daily for one month. Our results revealed that albuminuria, mesangial matrix expension, and focal segmental glomerulosclerosis in YAP-KO mice were significantly attenuated by ROC-325 administration. Transmission electron microscopy and immunofluorescence staining showed that ROC-325 treatment significantly inhibited YAP-KO-induced autophagy activation by decreasing autophagosome-lysosome fusion and increasing LC3A/B and p62/SQSTM. Meanwhile, Immunofluorescence staining revealed that preapplication of ROC-325 in podocyte with YAP-targeted siRNA and mRFP-GFP-LC3 adenovirus markedly suppressed autophagic flux in vitro, suggesting that autophagy intervention may serve as a target for FSGS.

CONCLUSIONS

These results showed that the role of autophagic activity in FSGS mice model and ROC-325 could be a novel and promising agent for the treatment of FSGS.

CRB2 Depletion Induces YAP Signaling and Disrupts Mechanosensing in Podocytes

Focal Segmental Glomerulosclerosis (FSGS) is a histologic lesion caused by a variety of injurious stimuli that lead to dysfunction/loss of glomerular visceral epithelial cells (i.e. podocytes). Pathogenic mutations in CRB2, encoding the type 1 transmembrane protein Crumb 2 Homolog Protein, have been shown to cause early-onset corticosteroid-resistant nephrotic syndrome (SRNS)/FSGS. Here, we identified a 2-generation East Asian kindred (DUK40595) with biopsy-proven SRNS/FSGS caused by a compound heterozygous mutation in CRB2 comprised of the previously described truncating mutation p.Gly1036_Alafs*43 and a rare 9-bp deletion mutation p.Leu1074_Asp1076del. Because compound heterozygous mutations involving the truncating p.Gly1036_Alafs*43 variant have been associated with reduced CRB2 expression in podocytes and autosomal recessive SRNS/FSGS, we sought to define the pathogenic effects of CRB2 deficiency in podocytes. We show that CRB2 knockdown induces YAP activity and target gene expression in podocytes. It upregulates YAP-mediated mechanosignaling and increases the density of focal adhesion and F-actin. Using Elastic Resonator Interference Stress Microscopy (ERISM), we demonstrate that CRB2 knockdown also enhances podocyte contractility in a substrate stiffness-dependent manner. The knockdown effect decreases with increasing substrate stiffness, indicating impaired mechanosensing in CRB2 knockdown cells at low substrate stiffness. While the mechanical activation of CRB2 knockdown cells is associated with increased YAP activity, the enhanced cell contractility is not significantly reduced by the selective YAP inhibitors K-975 and verteporfin, suggesting that multiple pathways may be involved in mechanosignaling downstream of CRB2. Taken together, these studies provide the first evidence that CRB2 deficiency may impair podocyte mechanotransduction via disruption of YAP signaling in podocytes.

Mechanosensitive Differentiation of Human iPS Cell-Derived Podocytes

Stem cell fate decisions, including proliferation, differentiation, morphological changes, and viability, are impacted by microenvironmental cues such as physical and biochemical signals. However, the specific impact of matrix elasticity on kidney cell development and function remains less understood due to the lack of models that can closely recapitulate human kidney biology. An established protocol to differentiate podocytes from human-induced pluripotent stem (iPS) cells provides a promising avenue to elucidate the role of matrix elasticity in kidney tissue development and lineage determination. In this study, we synthesized polyacrylamide hydrogels with different stiffnesses and investigated their ability to promote podocyte differentiation and biomolecular characteristics. We found that 3 kPa and 10 kPa hydrogels significantly support the adhesion, differentiation, and viability of podocytes. Differentiating podocytes on a more compliant (0.7 kPa) hydrogel resulted in significant cell loss and detachment. Further investigation of the mechanosensitive proteins yes-associated protein (YAP) and synaptopodin revealed nuanced molecular distinctions in cellular responses to matrix elasticity that may otherwise be overlooked if morphology and cell spreading alone were used as the primary metric for selecting matrices for podocyte differentiation. Specifically, hydrogels with kidney-like rigidities outperformed traditional tissue culture plates at modulating the molecular-level expression of active mechanosensitive proteins critical for podocyte health and function. These findings could guide the development of physiologically relevant platforms for kidney tissue engineering, disease modeling, and mechanistic studies of organ physiology and pathophysiology. Such advances are critical for realizing the full potential of in vitro platforms in accurately predicting human biological responses.

Role of biophysics and mechanobiology in podocyte physiology

Podocytes form the backbone of the glomerular filtration barrier and are exposed to various mechanical forces throughout the lifetime of an individual. The highly dynamic biomechanical environment of the glomerular capillaries greatly influences the cell biology of podocytes and their pathophysiology. Throughout the past two decades, a holistic picture of podocyte cell biology has emerged, highlighting mechanobiological signalling pathways, cytoskeletal dynamics and cellular adhesion as key determinants of biomechanical resilience in podocytes. This biomechanical resilience is essential for the physiological function of podocytes, including the formation and maintenance of the glomerular filtration barrier. Podocytes integrate diverse biomechanical stimuli from their environment and adapt their biophysical properties accordingly. However, perturbations in biomechanical cues or the underlying podocyte mechanobiology can lead to glomerular dysfunction with severe clinical consequences, including proteinuria and glomerulosclerosis. As our mechanistic understanding of podocyte mechanobiology and its role in the pathogenesis of glomerular disease increases, new targets for podocyte-specific therapeutics will emerge. Treating glomerular diseases by targeting podocyte mechanobiology might improve therapeutic precision and efficacy, with potential to reduce the burden of chronic kidney disease on individuals and health-care systems alike.

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.

Identification of Plasma hsa_circ_0001230 and hsa_circ_0023879 as Potential Novel Biomarkers for Focal Segmental Glomerulosclerosis and circRNA-miRNA-mRNA Network Analysis

INTRODUCTION

Focal segmental glomerulosclerosis (FSGS) is a common glomerulopathy with an unclear mechanism. The demand for FSGS clinical diagnostic biomarkers has not yet been met. Circular RNA (circRNA) is a novel non-coding RNA with multiple functions, but its diagnostic value for FSGS remains unexplored. This study aimed to identify circRNAs that could aid in early clinical diagnosis and to investigate their mechanisms in podocyte injury.

METHODS

The signature of plasma circRNAs for FSGS was identified by circRNA microarray. The existence of circRNAs was confirmed by quantitative real-time polymerase chain reaction (qRT-PCR), RNase R assay, and DNA sequencing. Plasma levels of circRNAs were evaluated by qRT-PCR. The diagnostic value was appraised by the receiver operating characteristic curve. The circRNA-miRNA-mRNA network was built with Cytoscape 7.3.2. Statistically significant differences were calculated by the Mann-Whitney U test.

RESULTS

A total of 493 circRNAs (165 upregulated, 328 downregulated) were differentially expressed in the plasma of FSGS patients (n = 3) and normal controls (n = 3). Eight candidate circRNAs were demonstrated to be circular and stable transcripts. Among them, hsa_circ_0001230 and hsa_circ_0023879 were significantly upregulated in FSGS patients (n = 29) compared to normal controls (n = 51). The areas under the curve value of hsa_circ_0001230 and hsa_circ_0023879 were 0.668 and 0.753, respectively, while that of the two-circRNA panel was 0.763. The RNA pull-down analysis revealed that hsa_circ_0001230 and hsa_circ_0023879 could sponge hsa-miR-106a. Additionally, hsa_circ_0001230 and hsa_circ_0023879 positively regulated hsa-miR-106a target genes phosphatase and tensin homolog (PTEN) and Bcl-2-like protein 11 (BCL2L11) in podocytes.

CONCLUSION

hsa_circ_0001230 and hsa_circ_0023879 are novel blood biomarkers for FSGS. They may regulate podocyte apoptosis by competitively binding to hsa-miR-106a.

Identification of RP11-770J1.4 as immune-related lncRNA regulating the CTXN1-cGAS-STING axis in histologically lower-grade glioma

Human gliomas are lethal brain cancers. Emerging evidence revealed the regulatory role of long noncoding RNAs (lncRNAs) in tumors. Here, we performed a comprehensive analysis of the expression profiles of RNAs in histologically lower-grade glioma (LGG). Enrichment analysis revealed that glioma is influenced by immune-related signatures. Survival analysis further established the close correlation between network features and glioma prognosis. Subsequent experiments showed lncRNA RP11-770J1.4 regulates CTXN1 expression through hsa-miR-124-3p. Correlation analysis identified lncRNA RP11-770J1.4 was immune related, specifically involved in the cytosolic DNA sensing pathway. Downregulated lncRNA RP11-770J1.4 resulted in increased spontaneous gene expression of the cGAS-STING pathway. Single-cell RNA sequencing analysis, along with investigations in a glioblastoma stem cell model and patient sample analysis, demonstrated the predominant localization of CTXN1 within tumor cores rather than peripheral regions. Immunohistochemistry staining established a negative correlation between CTXN1 expression and infiltration of CD8+ T cells. In vivo, Ctxn1 knockdown in GL261 cells led to decreased tumor burden and improved survival while increasing infiltration of CD8+ T cells. These findings unveil novel insights into the lncRNA RP11-770J1.4-CTXN1 as a potential immune regulatory axis, highlighting its therapeutic implications for histologically LGGs.

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.

Proximal Tubular Lats2 Ablation Exacerbates Ischemia/Reperfusion Injury (IRI)-Induced Renal Maladaptive Repair through the Upregulation of P53

The Hippo pathway mediates renal maladaptive repair after acute kidney injury (AKI), which has been considered a driving force in the progression to chronic kidney disease (CKD). LATS2, a core kinase of the Hippo pathway, exerts non-Hippo-dependent functions in the regulation of the cell cycle and cell fate, providing new insights into AKI and further repair. However, its role remains unknown. Here, we utilized a proximal tubular Lats2 conditional knockout mouse strain (Lats2-CKO) to evaluate the effect of LATS2 deficiency on ischemia/reperfusion-induced AKI-to-CKD transition. Lats2-CKO mice presented with more severe tubular maladaptive repair, inflammatory infiltration, interstitial fibrosis, and apoptosis following AKI. Importantly, we discovered that Lats2 ablation caused the activation of p53, with increased levels of cellular apoptotic molecules (p21, Bax, and cleaved caspase-3), and decreased levels of anti-apoptotic molecules (Bcl-2 and Bcl-xL). Pifithirin-α (p53 inhibitor) effectively attenuated renal fibrosis, inflammation, and apoptosis in Lats2-CKO mice after AKI. Consistently, in vitro Lats2 overexpression decreased p53, p21, Bax and cleaved caspase 3 expression after hypoxia/reoxygenation (H/R) treatment. Of note, the phosphorylation of MDM2, which promotes the ubiquitination degradation of p53, at site Ser186 was decreased in Lats2-CKO kidneys, but increased by Lats2 overexpression in vitro. Therefore, LATS2 deficiency aggravated ischemia/reperfusion injury (IRI)-induced maladaptive repair via regulating the tubular MDM2-p53 axis in AKI-to-CKD transition.

Hippo signaling in acute kidney injury to chronic kidney disease transition: current understandings and future targets

Acute kidney injury (AKI)-to-chronic kidney disease (CKD) transition is a slow but persistent progression toward end-stage kidney disease. Earlier reports have shown that Hippo components, such as Yes-associated protein (YAP) and its homolog TAZ (Transcriptional coactivator with PDZ-binding motif), regulate inflammation and fibrogenesis during the AKI-to-CKD transition. Notably, the roles and mechanisms of Hippo components vary during AKI, AKI-to-CKD transition, and CKD. Hence, it is important to understand these roles in detail. This review addresses the potential of Hippo regulators or components as future therapeutic targets for halting the AKI-to-CKD transition.

Verteporfin inhibits the dedifferentiation of tubular epithelial cells via TGF-β1/Smad pathway but induces podocyte loss in diabetic nephropathy

AIMS

The dedifferentiation of tubular epithelial cells has been identified as an important trigger of renal fibrosis. The Hippo pathway is a crucial regulator of cell proliferation and differentiation. In this study, we determined the role of Hippo proteins in tubular dedifferentiation in diabetic nephropathy (DN).

MAIN METHODS

In this study, we measured dedifferentiation markers and Hippo proteins in db/db mice and high glucose treated tubular epithelial cells. Then, verteporfin and knockdown of large tumor suppressor kinase (LATS) 1 and 2 were performed to uncover therapeutic targets for DN.

KEY FINDINGS

Here, we found dedifferentiation and upregulated Hippo proteins in tubular epithelial cells in DN model both in vivo and in vitro. Both verteporfin and LATS knockdown could inhibit the tubular mesenchymal transition, but verteporfin showed broad inhibitory effect on Hippo proteins, especially nuclear YAP, and exacerbated podocyte loss of DN. LATS2 knockdown did not reverse the tubular E-Cadherin loss while it also induced podocyte apoptosis. Overall, intervention of LATS1 inhibited tubular dedifferentiation efficiently without affecting YAP and bringing podocyte apoptosis. Further mechanistic investigations revealed that the TGF-β1/Smad, instead of the YAP-TEAD-CTGF signaling, might be the underlying pathway through which verteporfin and LATS1 engaged in the tubular dedifferentiation.

SIGNIFICANCE

In conclusion, verteporfin is not a suitable treatment for DN owing to evitable podocyte loss and apoptosis. Targeting LATS1 is a better choice worthy of further investigation for DN therapy.

hucMSC-sEVs-Derived 14-3-3ζ Serves as a Bridge between YAP and Autophagy in Diabetic Kidney Disease

As nanoscale membranous vesicles, human umbilical cord mesenchymal stem cell-derived small extracellular vesicles (hucMSC-sEVs) have attracted extensive attention in the field of tissue regeneration. Under the premise that the mechanisms of hucMSC-sEVs on the treatment of diabetic kidney disease (DKD) have not been revealed clearly, we constructed DKD rat model with success. After tail vein injection, hucMSC-sEVs effectively reduced blood glucose, maintained body weight and improved renal function in DKD rats. Notably, we found that hucMSC-sEVs suppressed YAP expression in renal cortical regions. Further in vitro experiments, we confirmed that the expression of YAP in the nucleus of renal podocytes was increased, and the level of autophagy was inhibited in the high-glucose environment, which could be reversed by intervention with hucMSC-sEVs. We screened out the key protein 14-3-3ζ, which could not only promote YAP cytoplasmic retention instead of entering the nucleus, but also enhance the level of autophagy in the cytoplasm. Ultimately, excessive YAP protein was removed by autophagy, a classic way of protein degradation. In conclusion, our study provides new strategies for the prevention of DKD and proposes the possibility of hucMSC-sEVs becoming a new treatment for DKD in the future.

Blocking ribosomal protein S6 phosphorylation inhibits podocyte hypertrophy and focal segmental glomerulosclerosis

Ribosomal protein S6 (rpS6) phosphorylation mediates the hypertrophic growth of kidney proximal tubule cells. However, the role of rpS6 phosphorylation in podocyte hypertrophy and podocyte loss during the pathogenesis of focal segmental glomerulosclerosis (FSGS) remains undefined. Here, we examined rpS6 phosphorylation levels in kidney biopsy specimens from patients with FSGS and in podocytes from mouse kidneys with Adriamycin-induced FSGS. Using genetic and pharmacologic approaches in the mouse model of FSGS, we investigated the role of rpS6 phosphorylation in podocyte hypertrophy and loss during development and progression of FSGS. Phosphorylated rpS6 was found to be markedly increased in the podocytes of patients with FSGS and Adriamycin-induced FSGS mice. Genetic deletion of the Tuberous sclerosis 1 gene in kidney glomerular podocytes activated mammalian target of rapamycin complex 1 signaling to rpS6 phosphorylation, resulting in podocyte hypertrophy and pathologic features similar to those of patients with FSGS including podocyte loss, leading to segmental glomerulosclerosis. Since protein phosphatase 1 is known to negatively regulate rpS6 phosphorylation, treatment with an inhibitor increased phospho-rpS6 levels, promoted podocyte hypertrophy and exacerbated formation of FSGS lesions. Importantly, blocking rpS6 phosphorylation (either by generating congenic rpS6 knock-in mice expressing non-phosphorylatable rpS6 or by inhibiting ribosomal protein S6 kinase 1-mediated rpS6 phosphorylation with an inhibitor) significantly blunted podocyte hypertrophy, inhibited podocyte loss, and attenuated formation of FSGS lesions. Thus, our study provides genetic and pharmacologic evidence indicating that specifically targeting rpS6 phosphorylation can attenuate the development of FSGS lesions by inhibiting podocyte hypertrophy and associated podocyte depletion.