Selective Targeting of Vascular Endothelial YAP Activity Blocks EndMT and Ameliorates Unilateral Ureteral Obstruction-Induced Kidney Fibrosis

Verteporfin combined with ROCK inhibitor promotes the restoration of corneal endothelial cell dysfunction in rats

Corneal endothelial cells (CECs) dysfunction frequently results in a hazy, edematous cornea due to corneal endothelial decompensation and is a major cause of corneal blindness. Drug interventions provide a less invasive alternative to corneal transplantation surgery. However, endothelial-to-mesenchymal transition (EndMT) limits CECs function. Rho-kinase (ROCK) inhibitors, shown in numerous studies to be an adjunctive therapy for CECs dysfunction, cannot completely reverse pathological EndMT caused by inflammatory environmental damage. Verteporfin (VP) is an inhibitor of Yes-associated protein (YAP) and has significant inhibitory effects on cell fibrosis and mesenchymal transition. Here, we explored VP's utility in mitigating EndMT during ROCK inhibitors treatment of corneal endothelial dysfunction. We surgically constructed a rat model of CECs injury and studied VP and ROCK inhibitors' effects on EndMT, cell proliferation, and corneal edema using RNA-Seq sequencing, immunofluorescence, optical coherence tomography, and qPCR. The results indicated that YAP expression in human fetal CECs was higher than in adults and decreased with age in rats. Moreover, YAP expression in human CECs was negatively correlated with functional genes, such as AQP1 and ATP1A1. VP effectively reversed EndMT and accelerated corneal hydration regression. However, it inhibited CECs proliferation. We also confirmed that the optimal ratio of VP combined with Y-27632 (ROCK inhibitor) was 1:1, promoting CECs proliferation and reversing EndMT by down-regulating transcription factors downstream of TGF-β signaling, thereby increasing CECs functional and intercellular adhesion proteins. These combined effects promote corneal endothelial damage repair, providing a new treatment strategy.

F2RL1 Inhibition Alleviates Lipotoxicity-Induced Kidney Injury Through the Hippo Pathway in Diabetic Kidney Disease

Diabetic kidney disease (DKD), which is emerging as a pervasive global health concern and a considerable economic burden, is characterized by a detrimental effect on renal function and structure. Recent research indicates that the progression of DKD is facilitated by lipotoxic injury to tubular epithelial cells (TECs). However, the specific mechanisms that contribute to this cellular damage have yet to be fully elucidated. Our results revealed a significant upregulation of F2RL1 in vivo and in vitro models, which was positively correlated with the expression of inflammatory factors. Knockdown of F2RL1 significantly reduced inflammatory response in palmitate-stimulated HK-2 cells. Mechanistically, F2RL1 might exacerbate lipotoxicity-induced DKD through the modulation of the Hippo signaling pathway. Collectively, these findings suggest that modulating F2RL1 expression may be a strategic approach to mitigate the inflammatory damage to RTECs associated with DKD, potentially through its involvement in the Hippo signaling pathway. Given these findings, F2RL1 merits consideration as a candidate therapeutic target for DKD.

Zhilong Huoxue Tongyu capsule protects against atherosclerosis by suppressing EndMT via modulating Hippo/YAP signaling pathway

Background and aim

Zhilong Huoxue Tongyu Capsule (ZL capsule) has been demonstrated to be an effective and widely-used traditional Chinese medicine (TCM) formula for the treatment of various diseases, especially for atherosclerosis (AS) related cardiovascular and cerebrovascular diseases. Reversal of endothelial-mesenchymal transition (EndMT) plays a crucial role in the cure of AS. But the curative impact of ZL capsule on EndMT remains obscure during the development of AS. The purpose of this study is to explore the effect of ZL capsule on AS and to study the regulation mechanism on EndMT in AS by ZL capsule in vivo and in vitro.

Experimental procedure

An in vivo model of AS was induced in ApoE-/- mice by administrating them with an 8-week period of high-fat diet (HFD). After oral gavage of different doses of ZL capsule and Atorvastatin calcium tablets (ATO) for 4 weeks, the lipid levels, plaque area, lipid deposition, and EndMT were evaluated using standard assays. In order to simulate EndMT in vitro, human umbilical vein endothelial cells (HUVECs) were subjected to oxidized low-density lipoprotein (ox-LDL). Western blotting (WB) and immunofluorescence techniques were used to evaluate the intervention effect of ZL capsule on EndMT and Hippo/YAP pathways.

Results and conclusion

ZL capsule demonstrated therapeutic effects on dyslipidemia and EndMT among atherosclerotic mice. To be specific, ZL capusle diminished the total cholesterol (TC), total triglyceride (TG) and low-density lipoprotein (LDL-C) levels, whereas increased that of high-density lipoproteins (HDL-C). Meanwhile, ZL capusle upregulated the expression of endothelial markers (CD31 and VE-cadherin) and reduced that of mesenchymal markers (ɑ-SMA and FSP1), indicating that ZL capusle could inhibit EndMT during the development of AS. Furthermore, molecular docking results indicated that active ingredients including formononetin, calycosin, astragaloside III, astragaloside A in ZL capsule have strong affinity with YAP proteins, and ZL capsule can significantly repress the initiation of Hippo/YAP pathway during AS. In conclusion, ZL capsule effectively attenuated AS progression by exerting inhibitory effects on EndMT through modulation of the Hippo/YAP signaling pathway.

Angiotensin II depends on hippo/YAP signaling to reprogram angiogenesis and promote liver fibrosis

Liver fibrosis is a chronic pathological process in which the abnormal proliferation of connective tissue is induced by various pathogenic factors. During the process of fibrosis, excessive angiogenesis is observed. Physiological angiogenesis has the potential to impede the progression of liver fibrosis through augmenting matrix metalloenzyme activity; however, pathological angiogenesis can exacerbate liver fibrosis by promoting collagen accumulation. Therefore, a key scientific research focus in the treatment of liver diseases is to search for the "on-off" mechanism that regulates angiogenesis from normal proliferation to pathological proliferation. In this study, we found that excessive angiogenesis appeared during the initial phase of hepatic fibrosis without mesenchymal characteristics. In addition, angiogenesis accompanied by significant endothelial-to-mesenchymal transition (EndMT) was observed in mice after the intraperitoneal injection of angiotensin II (Ang II). Interestingly, the changes in Yes-associated protein (YAP) activity in endothelial cells (ECs) can affect the regulation of angiogenesis by Ang II. The results of in vitro experiments revealed that the regulatory influence of Ang II on ECs was significantly attenuated upon suppression of YAP activity. Furthermore, the function of Ang II in regulating angiogenesis during fibrosis was investigated in liver-specific transgenic mice. The results revealed that Ang II gene deletion could restrain liver fibrosis and EndMT. Meanwhile, Ang II deletion downregulated the profibrotic YAP signaling pathway in ECs. The small molecule AT1R agonist olmesartan targeting Ang II-YAP signaling could also alleviate liver fibrosis. In conclusion, this study identified Ang II as a pivotal regulator of EndMT during the progression of liver fibrosis and evaluated the therapeutic effect of the Ang II-targeted drug olmesartan on liver fibrosis.

Huoxue Jiedu Huayu recipe inhibits macrophage-secreted vascular endothelial growth factor-a on angiogenesis and alleviates renal fibrosis in the contralateral kidneys of unilateral ureteral obstruction rats

OBJECTIVE：To elucidate the mechanism by which Huoxue Jiedu Huayu recipe (, HJHR) regulates angiogenesis in the contralateral kidney of unilateral ureteral obstruction (UUO) rats and the mechanism by which it reduces of renal fibrosis.

METHODS

Male Wistar rats were randomly divided into 4 groups: the sham group, UUO group (180 d of left ureter ligation), UUO plus eplerenone (EPL) group, and UUO plus HJHR group. After 180 d of oral drug administration, blood and contralateral kidneys were collected for analysis. Angiogenesis- and fibrosis-related indexes were detected.

RESULTS

HJHR and EPL improved structural damage and renal interstitial fibrosis in the contralateral kidney and reduced the protein expression levels of α-smooth muscle actin (α-SMA), vimentin and collagen I. Moreover, these treatments could reduce the expression of vascular endothelial growth factor-A (VEGFA) by inhibiting the infiltration of macrophages. Furthermore, HJHR and EPL significantly reduced the expression of CD34 and CD105 by downregulating VEGFA production, which inhibited angiogenesis. Finally, the coexpressions of CD34, CD105 and α-SMA were decreased in the HJHR and EPL groups, indicating that endothelial-to-mesenchymal transition was inhibited.

CONCLUSIONS

These findings confirm that HJHR alleviates contralateral renal fibrosis by inhibiting VEGFA-induced angiogenesis, encourage the use of HJHR against renal interstitial fibrosis and provide a theoretical basis for the clinical management of patients with CKD.

Endothelial to mesenchymal transition in kidney fibrosis

Fibrotic diseases are characterized by the uncontrolled accumulation of extracellular matrix (ECM) components leading to disruption of tissue homeostasis. Myofibroblasts as the main ECM-producing cells can originate from various differentiated cell types after injury. Particularly, the process of endothelial-to-mesenchymal transition (endMT), describing phenotypic shifts of endothelial cells to adopt a fully mesenchymal identity, may contribute to the pool of myofibroblasts in fibrosis, while leading to capillary rarefaction and exacerbation of tissue hypoxia. In renal disease, incomplete recovery from acute kidney injury (AKI) and the ensuing fibrotic reaction stand out as major contributors to chronic kidney disease (CKD) development. While the focus has largely been on impaired tubular epithelial repair as a potential fibrosis-driving mechanism, alterations in the renal microcirculation post-AKI, and in particular endMT as a maladaptive response, could hold equal significance. Dysfunctional interplays among various cell types in the kidney microenvironment can instigate endMT. Transforming growth factor beta (TGF-β) signaling, with its downstream activation of canonical/Smad-mediated and non-canonical pathways, has been identified as primary driver of this process. However, non-TGF-β-mediated pathways involving inflammatory agents and metabolic shifts in intercellular communication within the tissue microenvironment can also trigger endMT. These harmful, maladaptive cell-cell interactions and signaling pathways offer potential targets for therapeutic intervention to impede endMT and decelerate fibrogenesis such as in AKI-CKD progression. Presently, partial reduction of TGF-β signaling using anti-diabetic drugs or statins may hold therapeutic potential in renal context. Nevertheless, further investigation is warranted to validate underlying mechanisms and assess positive effects within a clinical framework.

An essential signaling cascade for avian auditory hair cell regeneration

Hearing loss is a chronic disease affecting millions of people worldwide, yet no restorative treatment options are available. Although non-mammalian species can regenerate their auditory sensory hair cells, mammals cannot. Birds retain facultative stem cells known as supporting cells that engage in proliferative regeneration when surrounding hair cells die. Here, we investigated gene expression changes in chicken supporting cells during auditory hair cell death. This identified a pathway involving the receptor F2RL1, HBEGF, EGFR, and ERK signaling. We propose a cascade starting with the proteolytic activation of F2RL1, followed by matrix-metalloprotease-mediated HBEGF shedding, and culminating in EGFR-mediated ERK signaling. Each component of this cascade is essential for supporting cell S-phase entry in vivo and is integral for hair cell regeneration. Furthermore, STAT3-phosphorylation converges with this signaling toward upregulation of transcription factors ATF3, FOSL2, and CREM. Our findings could provide a basis for designing treatments for hearing and balance disorders.

Insights into the Mechanism of Supramolecular Self-Assembly in the Astragalus membranaceus-Angelica sinensis Codecoction

Astragalus membranaceus (Fisch.) Bge. (AM) and Angelica sinensis (Oliv.) Diels (AS) constitute a classic herb pair in prescriptions to treat myocardial fibrosis. To date, research on the AM-AS herb pair has mainly focused on the chemical compositions associated with therapeutic efficacy. However, supermolecules actually exist in herb codecoctions, and their self-assembly mechanism remains unclear. In this study, supermolecules originating from AM-AS codoping reactions (AA-NPs) were first reported. The chemical compositions of AA-NPs showed a dynamic self-assembly process. AA-NPs with different decoction times had similar surface groups and amorphous states; however, the size distributions of these nanoparticles might be different. Taking the interaction between Z-ligustilide and astragaloside IV as an example to understand the self-assembly mechanism of AA-NPs, it was found that the complex could be formed with a molar ratio of 2:1. Later, AA-NPs were proven to be effective in the treatment of myocardial fibrosis both in vivo and in vitro, the in-depth mechanisms of which were related to the recovery of cardiac function, reduced collagen deposition, and inhibition of the endothelial-to-mesenchymal transition that occurred in the process of myocardial fibrosis. Thus, AA-NPs may be the chemical material basis of the molecular mechanism of the AM-AS decoction in treating isoproterenol-induced myocardial fibrosis. Taken together, this work provides a supramolecular strategy for revealing the interaction between effective chemical components in herb-pair decoctions.

Endothelial cell plasticity in kidney fibrosis and disease

Renal endothelial cells demonstrate an impressive remodeling potential during angiogenic sprouting, vessel repair or while transitioning into mesenchymal cells. These different processes may play important roles in both renal disease progression or regeneration while underlying signaling pathways of different endothelial cell plasticity routes partly overlap. Angiogenesis contributes to wound healing after kidney injury and pharmaceutical modulation of angiogenesis may home a great therapeutic potential. Yet, it is not clear whether any differentiated endothelial cell can proliferate or whether regenerative processes are largely controlled by resident or circulating endothelial progenitor cells. In the glomerular compartment for example, a distinct endothelial progenitor cell population may remodel the glomerular endothelium after injury. Endothelial-to-mesenchymal transition (EndoMT) in the kidney is vastly documented and often associated with endothelial dysfunction, fibrosis, and kidney disease progression. Especially the role of EndoMT in renal fibrosis is controversial. Studies on EndoMT in vivo determined possible conclusions on the pathophysiological role of EndoMT in the kidney, but whether endothelial cells really contribute to kidney fibrosis and if not what other cellular and functional outcomes derive from EndoMT in kidney disease is unclear. Sequencing data, however, suggest no participation of endothelial cells in extracellular matrix deposition. Thus, more in-depth classification of cellular markers and the fate of EndoMT cells in the kidney is needed. In this review, we describe different signaling pathways of endothelial plasticity, outline methodological approaches and evidence for functional and structural implications of angiogenesis and EndoMT in the kidney, and eventually discuss controversial aspects in the literature.

YAP/TAZ: Molecular pathway and disease therapy

The Yes-associated protein and its transcriptional coactivator with PDZ-binding motif (YAP/TAZ) are two homologous transcriptional coactivators that lie at the center of a key regulatory network of Hippo, Wnt, GPCR, estrogen, mechanical, and metabolism signaling. YAP/TAZ influences the expressions of downstream genes and proteins as well as enzyme activity in metabolic cycles, cell proliferation, inflammatory factor expression, and the transdifferentiation of fibroblasts into myofibroblasts. YAP/TAZ can also be regulated through epigenetic regulation and posttranslational modifications. Consequently, the regulatory function of these mechanisms implicates YAP/TAZ in the pathogenesis of metabolism-related diseases, atherosclerosis, fibrosis, and the delicate equilibrium between cancer progression and organ regeneration. As such, there arises a pressing need for thorough investigation of YAP/TAZ in clinical settings. In this paper, we aim to elucidate the signaling pathways that regulate YAP/TAZ and explore the mechanisms of YAP/TAZ-induce diseases and their potential therapeutic interventions. Furthermore, we summarize the current clinical studies investigating treatments targeting YAP/TAZ. We also address the limitations of existing research on YAP/TAZ and propose future directions for research. In conclusion, this review aims to provide fresh insights into the signaling mediated by YAP/TAZ and identify potential therapeutic targets to present innovative solutions to overcome the challenges associated with YAP/TAZ.

Targeting endothelial coagulation signaling ameliorates liver obstructive cholestasis and dysfunctional angiogenesis

Cholestatic fibrogenesis is a pathobiological process in which cumulative injury to the bile ducts coincides with progressive liver fibrosis. The pathobiologic mechanisms underlying fibrogenesis and disease progression remain poorly understood. Currently, there is no effective treatment for liver fibrosis. In this study, we discovered that components of the coagulation cascade were associated with the advanced progression of obstructive cholestasis, and anticoagulant therapy could improve liver cholestasis-induced fibrosis. In a mouse model of common bile duct ligation (BDL), which mimics cholestatic liver injury, RNA sequencing analysis revealed an increased expression of coagulation factors in endothelial cells. Pharmacological targeting of the coagulation signaling by hirudin, an anticoagulatory antagonist of thrombin, ameliorated obstructive cholestasis, and attenuated liver fibrosis symptoms. Hirudin attenuated fibrosis-associated angiogenesis, endothelial-to-mesenchymal transition (EndMT), and tissue hypoxia and reduced liver inflammation after BDL. Furthermore, hirudin suppressed YAP (Yes-associated protein) signaling and its downstream effectors in vascular endothelial cells, which are considered with profibrotic characteristics. In conclusion, we demonstrated that pharmacological targeting of coagulation signaling by hirudin has the potential to alleviate liver obstructive cholestasis and fibrosis.

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.

Identifying potential biomarkers for the diagnosis and treatment of IgA nephropathy based on bioinformatics analysis

BACKGROUND

IgA nephropathy (IgAN) has become the leading cause of end-stage renal disease in young adults. Nevertheless, the current diagnosis exclusively relies on invasive renal biopsy, and specific treatment is deficient. Thus, our study aims to identify potential crucial genes, thereby providing novel biomarkers for the diagnosis and therapy of IgAN.

METHODS

Three microarray datasets were downloaded from GEO official website. Differentially expressed genes (DEGs) were identified by limma package. GO and KEGG analysis were conducted. Tissue/organ-specific DEGs were distinguished via BioGPS. GSEA was utilized to elucidate the predominant enrichment pathways. The PPI network of DEGs was established, and hub genes were mined through Cytoscape. The CTD database was employed to determine the association between hub genes and IgAN. Infiltrating immune cells and their relationship to hub genes were evaluated based on CIBERSORT. Furthermore, the diagnostic effectiveness of hub markers was subsequently predicted using the ROC curves. The CMap database was applied to investigate potential therapeutic drugs. The expression level and diagnostic accuracy of TYROBP was validated in the cell model of IgAN and different renal pathologies.

RESULTS

A total of 113 DEGs were screened, which were mostly enriched in peptidase regulator activity, regulation of cytokine production, and collagen-containing extracellular matrix. Among these DEGs, 67 genes manifested pronounced tissue and organ specificity. GSEA analysis revealed that the most significant enriched gene sets were involved in proteasome pathway. Ten hub genes (KNG1, FN1, ALB, PLG, IGF1, EGF, HRG, TYROBP, CSF1R, and ITGB2) were recognized. CTD showed a close connection between ALB, IGF, FN1 and IgAN. Immune infiltration analysis elucidated that IGF1, EGF, HRG, FN1, ITGB2, and TYROBP were closely associated with infiltrating immune cells. ROC curves reflected that all hub genes, especially TYROBP, exhibited a good diagnostic value for IgAN. Verteporfin, moxonidine, and procaine were the most significant three therapeutic drugs. Further exploration proved that TYROBP was not only highly expressed in IgAN, but exhibited high specificity for the diagnosis of IgAN.

CONCLUSIONS

This study may offer novel insights into the mechanisms involved in IgAN occurrence and progression and the selection of diagnostic markers and therapeutic targets for IgAN.

Endothelial to Mesenchymal Transition in Health and Disease

The endothelium is one of the largest organ systems in the body, and data continue to emerge regarding the importance of endothelial cell (EC) dysfunction in vascular aging and a range of cardiovascular diseases (CVDs). Over the last two decades and as a process intimately related to EC dysfunction, an increasing number of studies have also implicated endothelial to mesenchymal transition (EndMT) as a potentially disease-causal pathobiologic process that is involved in a multitude of differing CVDs. However, EndMT is also involved in physiologic processes (e.g., cardiac development), and transient EndMT may contribute to vascular regeneration in certain contexts. Given that EndMT involves a major alteration in the EC-specific molecular program, and that it potentially contributes to CVD pathobiology, the clinical translation opportunities are significant, but further molecular and translational research is needed to see these opportunities realized.

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.

Pharmacological targeting of cGAS/STING-YAP axis suppresses pathological angiogenesis and ameliorates organ fibrosis

Organ fibrosis is accompanied by pathological angiogenesis. Discovering new ways to ameliorate pathological angiogenesis may bypass organ fibrosis. The cyclic guanosine monophosphate (GMP)-adenosine monophosphate (AMP) synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway has been implicated in organ injuries and its activation inhibits endothelial proliferation. Currently, a controversy exists as to whether cGAS/STING activation exacerbates inflammation and tissue injury or mitigates damage, and whether one of these effects predominates under specific context. This study unveiled a new antifibrotic cGAS/STING signaling pathway that suppresses pathological angiogenesis in liver and kidney fibrosis. We showed that cGAS expression was induced in fibrotic liver and kidney, but suppressed in endothelial cells. cGAS genetic deletion promoted liver and kidney fibrosis and pathological angiogenesis, including occurrence of endothelial-to-mesenchymal transition. Meanwhile, cGAS deletion upregulated profibrotic Yes-associated protein (YAP) signaling in endothelial cells, which was evidenced by the attenuation of organ fibrosis in mice specifically lacking endothelial YAP. Pharmacological targeting of cGAS/STING-YAP signaling by both a small-molecule STING agonist, SR-717, and a G protein-coupled receptor (GPCR)-based antagonist that blocks the profibrotic activity of endothelial YAP, attenuated liver and kidney fibrosis. Together, our data support that activation of cGAS/STING signaling mitigates organ fibrosis and suppresses pathological angiogenesis. Further, pharmacological targeting of cGAS/STING-YAP axis exhibits the potential to alleviate liver and kidney fibrosis.

New Insights into Hippo/YAP Signaling in Fibrotic Diseases

Fibrosis results from defective wound healing processes often seen after chronic injury and/or inflammation in a range of organs. Progressive fibrotic events may lead to permanent organ damage/failure. The hallmark of fibrosis is the excessive accumulation of extracellular matrix (ECM), mostly produced by pathological myofibroblasts and myofibroblast-like cells. The Hippo signaling pathway is an evolutionarily conserved kinase cascade, which has been described well for its crucial role in cell proliferation, apoptosis, cell fate decisions, and stem cell self-renewal during development, homeostasis, and tissue regeneration. Recent investigations in clinical and pre-clinical models has shown that the Hippo signaling pathway is linked to the pathophysiology of fibrotic diseases in many organs including the lung, heart, liver, kidney, and skin. In this review, we have summarized recent evidences related to the contribution of the Hippo signaling pathway in the development of organ fibrosis. A better understanding of this pathway will guide us to dissect the pathophysiology of fibrotic disorders and develop effective tissue repair therapies.

YAP is critical to inflammation, endothelial-mesenchymal transition and subretinal fibrosis in experimental choroidal neovascularization

Subretinal fibrosis causes local damage to the retina and irreversible vision loss, as the final stage of neovascular age-related macular degeneration (nAMD). More recently, the endothelial-to-mesenchymal transition (EndoMT) has been considered one of the most significant sources of myofibroblasts in subretinal fibrosis, though the underpinning molecular mechanisms remain unclear. In this study, a series of experiments were performed to test the hypothesis that Yes-associated protein (YAP) may be involved in EndoMT and subretinal fibrosis. We demonstrated that transforming growth factor (TGF)-β2 stimulation induces YAP dephosphorylation (activated) and nuclear transcription in human umbilical vein endothelial cells (HUVECs) by increasing reactive oxygen species (ROS) levels. Moreover, TGF-β2-mediated EndoMT and proinflammatory cytokine production in HUVECs were reduced by ROS clearance or YAP knockdown. Furthermore, the severity of subretinal fibrosis was markedly relieved by intravitreal administration of a small interfering RNA targeting YAP in the mouse laser-induced choroidal neovascularization (CNV) model. Our findings provide novel insights into a previously unknown effect of YAP on the EndoMT process and reveal YAP as a potential target for suppressing CNV-related subretinal fibrosis and protect vision.

Targeted inhibition of the immunoproteasome blocks endothelial MHC class II antigen presentation to CD4+ T cells in chronic liver injury

Chronic or overwhelming liver injury is frequently associated with fibrosis, which is the main histological characteristic of non-alcoholic steatohepatitis (NASH). Currently, there is no effective treatment for liver fibrosis. Adaptive immunity is one of the perpetrators of liver inflammation and involves the antigen-specific activation of lymphocytes. Targeting adaptive immunity has been proposed as a novel therapeutic approach for NASH. In this study, we demonstrated that liver endothelial cells contribute to MHC class II (MHC-II) antigen presentation to CD4⁺ T cells after chronic liver injury. In human cirrhotic liver samples, we observed an increased expression of endothelial MHC-II and of the antigen presentation-associated protein LMP7, which is one of the proteolytically active subunits of the immunoproteasome. In a CCl₄-induced chronic injury model or a diet- and chemical-induced NASH model, endothelial MHC-II and LMP7 expression was induced to increase. PR-957, a selective inhibitor of the immunoproteasome, inhibited MHC-II expression in endothelial cells and CD4⁺ T cell response after chronic liver injury. In vitro experiment demonstrated PR-957 also reversed IFN-γ-induced upregulation of MHC-II in endothelial cells. Furthermore, PR-957 treatment or CD4⁺ T cell depletion in chronic liver injury alleviated liver fibrosis and reduced inflammation, as indicated by the downregulation of inflammatory response markers (F4/80, IL-1, IL-6 and IL-18). In conclusion, targeted inhibition of the immunoproteasome blocks endothelial MHC-II antigen presentation to CD4⁺ T cells in chronic liver injury. In this regard, the PR-957 inhibitor is a promising candidate for the development of future therapies against NASH.