YAP Translocation Precedes Cytoskeletal Rearrangement in Podocyte Stress Response: A Podometric Investigation of Diabetic Nephropathy

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.

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.

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.

Not too much, not too little-just the right amount: the story of YAP in the podocyte

Chen et al. identify dysregulation of the transcriptional activator Yes-associated protein in the podocytes of diabetic mouse and human kidneys. Podocyte Yes-associated protein deficiency led to downregulation of the key transcription factor Wilms' tumor 1, and worsened podocyte injury in a mouse model of diabetic kidney injury. Yes-associated protein may therefore play a critical role in diabetic podocyte injury via regulation of Wilms' tumor 1 expression.

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.