Sarsasapogenin inhibits YAP1-dependent chondrocyte ferroptosis to alleviate osteoarthritis

The involvement of chondrocyte ferroptosis in the development of osteoarthritis (OA) has been observed, and Sarsasapogenin (Sar) has therapeutic promise in a variety of inflammatory diseases. This study investigates the potential influence of Sar on the mechanism of chondrocyte ferroptotic cell death in the progression of osteoarthritic cartilage degradation. An in vivo medial meniscus destabilization (DMM)-induced OA animal model as well as an in vitro examination of chondrocytes in an OA microenvironment induced by interleukin-1β (IL-1β) exposure were employed. Histology, immunofluorescence, quantitative RT-PCR, Western blot, cell viability, and Micro-CT analysis were utilized in conjunction with gene overexpression and knockdown to evaluate the chondroprotective effects of Sar in OA progression and the role of Yes-associated protein 1 (YAP1) in Sar-induced ferroptosis resistance of chondrocytes. In this study we found Sar reduced chondrocyte ferroptosis and OA progression. And Sar-induced chondrocyte ferroptosis resistance was mediated by YAP1. Furthermore, infection of siRNA specific to YAP1 in chondrocytes reduced Sar's chondroprotective and ferroptosis-suppressing effects during OA development. The findings suggest that Sar mitigates the progression of osteoarthritis by decreasing the sensitivity of chondrocytes to ferroptosis through the promotion of YAP1, indicating that Sar has the potential to serve as a therapeutic approach for diseases associated with ferroptosis.

YAP/TAZ activity in stromal cells prevents ageing by controlling cGAS-STING

Ageing is intimately connected to the induction of cell senescence1,2, but why this is so remains poorly understood. A key challenge is the identification of pathways that normally suppress senescence, are lost during ageing and are functionally relevant to oppose ageing3. Here we connected the structural and functional decline of ageing tissues to attenuated function of the master effectors of cellular mechanosignalling YAP and TAZ. YAP/TAZ activity declines during physiological ageing in stromal cells, and mimicking such decline through genetic inactivation of YAP/TAZ in these cells leads to accelerated ageing. Conversely, sustaining YAP function rejuvenates old cells and opposes the emergence of ageing-related traits associated with either physiological ageing or accelerated ageing triggered by a mechano-defective extracellular matrix. Ageing traits induced by inactivation of YAP/TAZ are preceded by induction of tissue senescence. This occurs because YAP/TAZ mechanotransduction suppresses cGAS-STING signalling, to the extent that inhibition of STING prevents tissue senescence and premature ageing-related tissue degeneration after YAP/TAZ inactivation. Mechanistically, YAP/TAZ-mediated control of cGAS-STING signalling relies on the unexpected role of YAP/TAZ in preserving nuclear envelope integrity, at least in part through direct transcriptional regulation of lamin B1 and ACTR2, the latter of which is involved in building the peri-nuclear actin cap. The findings demonstrate that declining YAP/TAZ mechanotransduction drives ageing by unleashing cGAS-STING signalling, a pillar of innate immunity. Thus, sustaining YAP/TAZ mechanosignalling or inhibiting STING may represent promising approaches for limiting senescence-associated inflammation and improving healthy ageing.

Dopamine receptor D2 antagonism normalizes profibrotic macrophage-endothelial crosstalk in non-alcoholic steatohepatitis

BACKGROUND & AIMS

Currently there is no effective treatment for liver fibrosis, which is one of the main histological determinants of non-alcoholic steatohepatitis (NASH). While Hippo/YAP (Yes-associated protein) signaling is essential for liver regeneration, its aberrant activation frequently leads to fibrosis and tumorigenesis. Unravelling "context-specific" contributions of YAP in liver repair might help selectively bypass fibrosis and preserve the pro-regenerative YAP function in hepatic diseases.

METHODS

We used murine liver fibrosis and minipig NASH models, and liver biopsies from patients with cirrhosis. Single-cell RNA-sequencing (scRNA-Seq) was performed, and a G-protein-coupled receptor (GPCR) ligand screening system was used to identify cell-selective YAP inhibitors.

RESULTS

YAP levels in macrophages are increased in the livers of humans and mice with liver fibrosis. The increase in type I interferon and attenuation of hepatic fibrosis observed in mice specifically lacking Yap1 in myeloid cells provided further evidence for the fibrogenic role of macrophage YAP. ScRNA-Seq further showed that defective YAP pathway signaling in macrophages diminished a fibrogenic vascular endothelial cell subset that exhibited profibrotic molecular signatures such as angiocrine CTGF and VCAM1 expression. To specifically target fibrogenic YAP in macrophages, we utilized a GPCR ligand screening system and identified a dopamine receptor D2 (DRD2) antagonist that selectively blocked YAP in macrophages but not hepatocytes. Genetic and pharmacological targeting of macrophage DRD2 attenuated liver fibrosis. In a large animal (minipig) NASH model recapitulating human pathology, the DRD2 antagonist blocked fibrosis and restored hepatic architecture.

CONCLUSIONS

DRD2 antagonism selectively targets YAP-dependent fibrogenic crosstalk between macrophages and CTGF⁺VCAM1⁺ vascular niche, promoting liver regeneration over fibrosis in both rodent and large animal models.

LAY SUMMARY

Fibrosis in the liver is one of the main histological determinants of non-alcoholic steatohepatitis (NASH), a disease paralleling a worldwide surge in metabolic syndromes. Our study demonstrates that a macrophage-specific deficiency in Yes-associated protein (YAP) attenuates liver fibrosis. Dopamine receptor D2 (DRD2) antagonism selectively blocks YAP in macrophages and thwarts liver fibrosis in both rodent and large animal models, and thus holds potential for the treatment of NASH.

Ibrutinib Blocks YAP1 Activation and Reverses BRAF Inhibitor Resistance in Melanoma Cells

Most B-Raf proto-oncogene (BRAF)-mutant melanoma tumors respond initially to BRAF inhibitor (BRAFi)/mitogen-activated protein kinase kinase 1 inhibitor (MEKi) therapy, although few patients have durable long-term responses to these agents. The goal of this study was to use an unbiased computational approach to identify inhibitors that reverse an experimentally derived BRAFi resistance gene expression signature. Using this approach, we found that ibrutinib effectively reverses this signature, and we demonstrate experimentally that ibrutinib resensitizes a subset of BRAFi-resistant melanoma cells to vemurafenib. Ibrutinib is used clinically as an inhibitor of the Src family kinase Bruton tyrosine kinase (BTK); however, neither BTK deletion nor treatment with acalabrutinib, another BTK inhibitor with reduced off-target activity, resensitized cells to vemurafenib. These data suggest that ibrutinib acts through a BTK-independent mechanism in vemurafenib resensitization. To better understand this mechanism, we analyzed the transcriptional profile of ibrutinib-treated BRAFi-resistant melanoma cells and found that the transcriptional profile of ibrutinib was highly similar to that of multiple Src proto-oncogene kinase inhibitors. Since ibrutinib, but not acalabrutinib, has appreciable off-target activity against multiple Src family kinases, it suggests that ibrutinib may be acting through this mechanism. Furthermore, genes that are differentially expressed in ibrutinib-treated cells are enriched in Yes1-associated transcriptional regulator (YAP1) target genes, and we showed that ibrutinib, but not acalabrutinib, reduces YAP1 activity in BRAFi-resistant melanoma cells. Taken together, these data suggest that ibrutinib, or other Src family kinase inhibitors, may be useful for treating some BRAFi/MEKi-refractory melanoma tumors. SIGNIFICANCE STATEMENT: MAPK-targeted therapies provide dramatic initial responses, but resistance develops rapidly; a subset of these tumors may be rendered sensitive again by treatment with an approved Src family kinase inhibitor-ibrutinub-potentially providing improved clinical outcomes.

RASSF1A-Mediated Suppression of Estrogen Receptor Alpha (ERα)-Driven Breast Cancer Cell Growth Depends on the Hippo-Kinases LATS1 and 2

Around 70% of breast cancers express the estrogen receptor alpha (ERα). This receptor is of central importance for breast cancer development and estrogen-dependent tumor growth. However, the molecular mechanisms that are responsible for the control of ERα expression and function in the context of breast carcinogenesis are complex and not fully understood. In previous work, we have demonstrated that the tumor suppressor RASSF1A suppresses estrogen-dependent growth of breast cancer cells through a complex network that keeps ERα expression and function under control. We observed that RASSF1A mediates the suppression of ERα expression through modulation of the Hippo effector Yes-associated protein 1 (YAP1) activity. Here we report that RASSF1A-mediated alteration of YAP1 depends on the Hippo-kinases LATS1 and LATS2. Based on these results, we conclude that inactivation of RASSF1A causes changes in the function of the Hippo signaling pathway and altered activation of YAP1, and as a consequence, increased expression and function of ERα. Thus, the inactivation of RASSF1A might constitute a fundamental event that supports the initiation of ERα-dependent breast cancer. Furthermore, our results support the notion that the Hippo pathway is important for the suppression of luminal breast cancers, and that the tumor-suppressor function of RASSF1A depends on LATS1 and LATS2.

Hippo-YAP/MCP-1 mediated tubular maladaptive repair promote inflammation in renal failed recovery after ischemic AKI

Acute kidney injury (AKI) is associated with significant morbidity and its chronic inflammation contributes to subsequent chronic kidney disease (CKD) development. Yes-associated protein (YAP), the major transcriptional coactivator of the Hippo pathway, has been shown associated with chronic inflammation, but its role and mechanism in AKI-CKD transition remain unclear. Here we aimed to investigate the role of YAP in AKI-induced chronic inflammation. Renal ischemia/reperfusion (I/R) was used to induce a mouse model of AKI-CKD transition. We used verteporfin (VP), a pharmacological inhibitor of YAP, to treat post-IRI mice for a period, and evaluated the influence of YAP inhibition on long-term outcomes of AKI. In our results, severe IRI led to maladaptive tubular repair, macrophages infiltration, and progressive fibrosis. Following AKI, the Hippo pathway was found significantly altered with YAP persistent activation. Besides, tubular YAP activation was associated with the maladaptive repair, also correlated with interstitial macrophage infiltration. Monocyte chemoattractant protein 1 (MCP-1) was found notably upregulated with YAP activation. Of note, pharmacological inhibition of YAP in vivo attenuated renal inflammation, including macrophage infiltration and MCP-1 overexpression. Consistently, in vitro oxygen-glucose deprivation and reoxygenation (OGD/R) induced YAP activation and MCP-1 overproduction whereas these could be inhibited by VP. In addition, we modulated YAP activity by RNA interference, which further confirmed YAP activation enhances MCP-1 expression. Together, we concluded tubular YAP activation with maladaptive repair exacerbates renal inflammation probably via promoting MCP-1 production, which contributes to AKI-CKD transition.