Lioba Ester

Key Points: Podocyte-specific knockout of YAP but not TAZ led to proteinuria. Knockout of more than two alleles of YAP and TAZ resulted in neonatal death, revealing compensation between the two cotranscription factors. Although YAP fully compensated for the loss of TAZ, TAZ did not entirely compensate for YAP functions related to Rho-GTPase and ERBB4 signaling. 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 (YAP ^pKO ), Taz (TAZ ^pKO ), or both (YAP ^pKO /TAZ ^pKO ) 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 . YAP ^pKO mice displayed podocyte damage and progressive kidney failure. By contrast, TAZ ^pKO 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 YAP ^pKO and TAZ ^pKO 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 YAP ^pKO . Furthermore, we observed loss of ERBB4 expression exclusively in YAP ^pKO, 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.

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.

Significance Statement: Treatment of acute, crescentic glomerulonephritis (GN) consists of unspecific and potentially toxic immunosuppression. T cells are central in the pathogenesis of GN, and various checkpoint molecules control their activation. The immune checkpoint molecule B and T-lymphocyte attenuator (BTLA) has shown potential for restraining inflammation in other T-cell–mediated disease models. To investigate its role in GN in a murine model of crescentic nephritis, the authors induced nephrotoxic nephritis in BTLA-deficient mice and wild-type mice. They found that BTLA has a renoprotective role through suppression of local Th1-driven inflammation and expansion of T regulatory cells and that administration of an agonistic anti-BTLA antibody attenuated experimental GN. These findings suggest that antibody-based modulation of BTLA may represent a treatment strategy in human glomerular disease. Background: Modulating T-lymphocytes represents a promising targeted therapeutic option for glomerulonephritis (GN) because these cells mediate damage in various experimental and human GN types. The immune checkpoint molecule B and T-lymphocyte attenuator (BTLA) has shown its potential to restrain inflammation in other T-cell–mediated disease models. Its role in GN, however, has not been investigated. Methods: We induced nephrotoxic nephritis (NTN), a mouse model of crescentic GN, in Btla-deficient (Btla ^KO) mice and wild-type littermate controls and assessed disease severity using functional and histologic parameters at different time points after disease induction. Immunologic changes were comprehensively evaluated by flow cytometry, RNA sequencing, and in vitro assays for dendritic cell and T-cell function. Transfer experiments into Rag1 ^KO mice confirmed the observed in vitro findings. In addition, we evaluated the potential of an agonistic anti-BTLA antibody to treat NTN in vivo. Results: The Btla ^KO mice developed aggravated NTN, driven by an increase of infiltrating renal Th1 cells. Single-cell RNA sequencing showed increased renal T-cell activation and positive regulation of the immune response. Although BTLA-deficient regulatory T cells (Tregs) exhibited preserved suppressive function in vitro and in vivo, Btla ^KO T effector cells evaded Treg suppression. Administration of an agonistic anti-BTLA antibody robustly attenuated NTN by suppressing nephritogenic T effector cells and promoting Treg expansion. Conclusions: In a model of crescentic GN, BTLA signaling effectively restrained nephritogenic Th1 cells and promoted regulatory T cells. Suppression of T-cell–mediated inflammation by BTLA stimulation may prove relevant for a broad range of conditions involving acute GN.