VGLL4 relieves TEADs-mediated RUNX2 transcriptional inhibition by impairing TEADs-RUNX2 interaction.

Heart valve disease is a major clinical problem worldwide. Cardiac valve development and homeostasis need to be precisely controlled. Hippo signaling is essential for organ development and tissue homeostasis, while its role in valve formation and morphology maintenance remains unknown. VGLL4 is a transcription cofactor in vertebrates and we found it was mainly expressed in valve interstitial cells at the post-EMT stage and was maintained till the adult stage. Tissue specific knockout of VGLL4 in different cell lineages revealed that only loss of VGLL4 in endothelial cell lineage led to valve malformation with expanded expression of YAP targets. We further semi-knockout YAP in VGLL4 ablated hearts, and found hyper proliferation of arterial valve interstitial cells was significantly constrained. These findings suggest that VGLL4 is important for valve development and manipulation of Hippo components would be a potential therapy for preventing the progression of congenital valve disease. VGLL4, a new member of the Hippo pathway, is intensively investigated in inhibition of tumor progression via competing with YAP to bind TEADs, but its role in cardiovascular field remains unclear. Here we generated VGLL4 knockout mouse line and VGLL4-eGFP reporter mouse line. VGLL4-eGFP reporter mouse line showed VGLL4 was mainly expressed in valve interstitial cells from post-EMT stage to adult stage. Genetic loss of function and lineage tracing data demonstrated only endothelial loss of VGLL4 led to valve malformation with up-regulation of YAP targets. Of note, semi-knockout YAP could rescue this phenotype of VGLL4 knockouts. This is the first study to show the Hippo pathway plays a critical role in valve remodeling, maturation and homeostasis. Our findings suggest that mutations in VGLL4 may underlie human congenital heart valve dysplasia.

The Hippo signalling pathway is a conserved kinase cascade that orchestrates diverse cellular processes, such as proliferation, apoptosis, lineage commitment and stemness. With the onset of society ages, research on skeletal aging‐mechanics‐bone homeostasis has exploded. In recent years, aging and mechanical force in the skeletal system have gained groundbreaking research progress. Under the regulation of mechanics and aging, the Hippo signalling pathway has a crucial role in the development and homeostasis of bone. We synthesize the current knowledge on the role of the Hippo signalling pathway, particularly its downstream effectors yes‐associated protein (YAP) and transcriptional co‐activator with PDZ‐binding motif (TAZ), in bone homeostasis. We discuss the regulation of the lineage specification and function of different skeletal cell types by the Hippo signalling pathway. The interactions of the Hippo signalling pathway with other pathways, such as Wnt, transforming growth factor beta and nuclear factor kappa‐B, are also mentioned because of their importance for modulating bone homeostasis. Furthermore, YAP/TAZ have been extensively studied as mechanotransducers. Due to space limitations, we focus on reviewing how mechanical forces and aging influence cell fate, communications and homeostasis through a dysregulated Hippo signalling pathway.

Chromobox protein homolog 4 (CBX4) is a component of the Polycomb group (PcG) multiprotein Polycomb repressive complexes 1 (PRC1), which is participated in several processes including growth, senescence, immunity, and tissue repair. CBX4 has been shown to have diverse, even opposite functions in different types of tissue and malignancy in previous studies. In this study, we found that CBX4 deletion promoted lung adenocarcinoma (LUAD) proliferation and progression in Kras^G12D mutated background. In vitro, over 50% Cbx4^L/L, Kras^G12D mouse embryonic fibroblasts (MEFs) underwent apoptosis in the initial period after Adeno-Cre virus treatment, while a small portion of survival cells got increased proliferation and transformation abilities, which we called selected Cbx4^−/−, Kras^G12D cells. Karyotype analysis and RNA-seq data revealed chromosome instability and genome changes in selected Cbx4^−/−, Kras^G12D cells compared with Kras^G12D cells. Further study showed that P15, P16 and other apoptosis-related genes were upregulated in the primary Cbx4^−/−, Kras^G12D cells due to chromosome instability, which led to the large population of cell apoptosis. In addition, multiple pathways including Hippo pathway and basal cell cancer-related signatures were altered in selected Cbx4^−/−, Kras^G12D cells, ultimately leading to cancer. We also found that low expression of CBX4 in LUAD was associated with poorer prognosis under Kras mutation background from the human clinical data. To sum up, CBX4 deletion causes genomic instability to induce tumorigenesis under Kras^G12D background. Our study demonstrates that CBX4 plays an emerging role in tumorigenesis, which is of great importance in guiding the clinical treatment of lung adenocarcinoma.

Extracellular matrix homeostasis is crucial for hyaline cartilage integrity, however, the mechanism of extracellular matrix homeostasis in hyaline cartilage is poorly understood. Single-cell sequencing shows that VGLL4 is highly expressed in chondrocytes but declines after injury/aging. VGLL4 deficiency impairs collagen/elastin formation, causes extracellular matrix disorganization and osteoarthritis in Col2-CreERT2; Vgll4^fl/fl mice, and is exacerbated by destabilization of the medial meniscus surgery. Mechanistically, the VGLL4-TEAD-SMAD3 complex maintains extracellular matrix homeostasis through specific interactions: TEAD4 (E263/D266/ Q269/H427) binds SMAD3 (K81/F260) via hydrogen bonds and hydrophobic contacts, while VGLL4 (H240/F241) engages TEAD4 (F337/F373) through π-stacking. Notably, intra-articular delivery of adeno-associated virus encoding either SMAD3 or VGLL4 effectively ameliorates osteoarthritis pathology, whereas interaction-deficient mutants lose therapeutic efficacy. This study demonstrates that VGLL4 serves as a critical regulator of extracellular matrix homeostasis in chondrocytes. The VGLL4 complex represents a potential therapeutic target for treating osteoarthritis and cartilage fibrosis.