Dysregulation of YAP by the Hippo pathway is involved in intervertebral disc degeneration, cell contact inhibition, and cell senescence

Emerging Perspectives of YAP/TAZ in Human Skin Epidermal and Dermal Aging

Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are key downstream effectors of the Hippo signaling pathway, which plays a central role in tissue homeostasis, organ development, and regeneration. While the dysregulation of YAP/TAZ has been linked to various human diseases, their involvement in the aging of human skin has only recently begun to manifest. In the skin, the YAP/TAZ effectors emerge as central regulators in maintaining homeostasis of epidermal stem cells and dermal extracellular matrix, and thus intimately linked to skin aging processes. This review underscores recent molecular breakthroughs highlighting how age-related decline of YAP/TAZ activity impacts human epidermal and dermal aging. Gaining insight into the evolving roles of YAP/TAZ in human skin aging presents a promising avenue for the development of innovative therapeutic approaches aimed at enhancing skin health and addressing age-related skin conditions.

SEPHS1 attenuates intervertebral disc degeneration by delaying nucleus pulposus cell senescence through the Hippo-Yap/Taz pathway

Nucleus pulposus cell (NPC) senescence is a major cause of intervertebral disc degeneration (IVDD). Oxidative stress and reactive oxygen species (ROS) play critical roles in regulating cell senescence. Selenophosphate synthetase 1 (SEPHS1) was reported to play an important role in mitigating oxidative stress in an osteoarthritis (OA) model by reducing the production of ROS, thereby, delaying the occurrence and development of osteoarthritis. In this study, we explored the, hitherto unknown, role of SEPHS1 in IVDD in vitro and in vivo using an interleukin-1β (IL-1β)-induced NPC senescence model and a rat needle puncture IVDD model, respectively. SEPHS1 delayed NPC senescence in vitro by reducing ROS production. Age-related dysfunction was also ameliorated by the overexpression of SEPHS1 and inhibition of the Hippo-Yap/Taz signaling pathway. In vivo experiments revealed that the overexpression of SEPHS1 and inhibition of Hippo-Yap/Taz alleviated IVDD in rats. Moreover, a selenium (Se)-deficient diet and lack of SEPHS1 synergistically aggravated IVDD progression. Taken together, our results demonstrate that SEPHS1 plays a significant role in NPC senescence. Overexpression of SEPHS1 and inhibition of Hippo-Yap/Taz can delay NPC senescence, restore the balance of extracellular matrix metabolism, and attenuate IVDD. SEPHS1 could be a promising therapeutic target for IVDD.NEW & NOTEWORTHY Selenophosphate synthetase 1 (SEPHS1) deficiency leads to an increase in reactive oxygen species levels and in the subsequent activation of the Hippo-Yap/Taz signaling pathway. In the rat model of intervertebral disc degeneration (IVDD), overexpression of SEPHS1 and inhibition of Hippo-YAP/Taz mitigated the progression of disc degeneration indicating the involvement of SEPHS1 in IVDD. SEPHS1 is a promising therapeutic target for IVDD.

3-D culture of human lung fibroblasts decreases proliferative and increases extracellular matrix remodeling genes

Fibroblasts are the main producers of extracellular matrix (ECM) responsible for ECM maintenance and repair, a process often disrupted in chronic lung diseases. The accompanying mechanical changes adversely affect resident cells and overall lung function. Numerous models have been used to elucidate fibroblast behavior that are now evolving toward complex three-dimensional (3-D) models incorporating ECM, aiming to replicate the cells' native environment. Little is known about the cellular changes that occur when moving from two-dimensional (2-D) to 3-D cell culture. This study compared the gene expression profiles of primary human lung fibroblasts from seven subjects with normal lung function, that were cultured for 24 h on 2-D collagen I-coated tissue culture plastic and in 3-D collagen I hydrogels, which are commonly used to mimic ECM in various models, from contraction assays to intricate organ-on-a-chip models. Comparing 3-D with 2-D cell culture, 6,771 differentially expressed genes (2,896 up, 3,875 down) were found; enriched gene sets within the downregulated genes, identified through Gene Set Enrichment Analysis and Ingenuity Pathway Analysis, were involved in the initiation of DNA replication which implied downregulation of fibroblast proliferation in 3-D. Observation of cells for 72 h in 2-D and 3-D environments confirmed the reduced progression through the cell cycle in 3-D. A focused analysis, examining the Hippo pathway and ECM-associated genes, showed differential patterns of gene expression in the 3-D versus 2-D culture. Altogether, the transcriptional response of fibroblasts cultured in 3-D indicated inhibition of proliferation, and alterations in Hippo and ECM pathways indicating a complete switch from proliferation to ECM remodeling.NEW & NOTEWORTHY With the introduction of complex three-dimensional (3-D) lung models, comes a need for understanding cellular behavior in these models. We compared gene expression profiles of human lung fibroblasts grown on two-dimensional (2-D) collagen I-coated surfaces with those in 3-D collagen I hydrogels. RNA sequencing and subsequent pathway analyses showed decreased proliferation, increased extracellular matrix (ECM) remodeling, and altered Hippo signaling and ECM deposition-related gene signatures. These findings highlight unique responses of fibroblasts in 3-D models.

Divergent roles of the Hippo pathway in the pathogenesis of idiopathic pulmonary fibrosis: tissue homeostasis and fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive aging-related lung disease with a poor prognosis. Despite extensive research, the cause of IPF remains largely unknown and treatment strategies are limited. Proposed mechanisms of the pathogenesis of IPF are a combination of excessive accumulation of the extracellular matrix and dysfunctional lung tissue regeneration. Epithelial cell dysfunction, in addition to fibroblast activation, is considered a key process in the progression of IPF. Epithelial cells normally maintain homeostasis of the lung tissue through regulated proliferation, differentiation, cell death, and cellular senescence. However, various stresses can cause repetitive damage to lung epithelial cells, leading to dysfunctional regeneration and acquisition of profibrotic functions. The Hippo pathway is a central signaling pathway that maintains tissue homeostasis and plays an essential role in fundamental biological processes. Dysregulation of the Hippo pathway has been implicated in various diseases, including IPF. However, the role of the Hippo pathway in the pathogenesis of IPF remains unclear, particularly given the pathway's opposing effects on the 2 key pathogenic mechanisms of IPF: epithelial cell dysfunction and fibroblast activation. A deeper understanding of the relationship between the Hippo pathway and the pathogenesis of IPF will pave the way for novel Hippo-targeted therapies.

Deletion of the chondrocyte glucocorticoid receptor attenuates cartilage degradation through suppression of early synovial activation in murine posttraumatic osteoarthritis

OBJECTIVE

Disruption of endogenous glucocorticoid signalling in bone cells attenuates osteoarthritis (OA) in aged mice, however, the role of endogenous glucocorticoids in chondrocytes is unknown. Here, we investigated whether deletion of the glucocorticoid receptor, specifically in chondrocytes, also alters OA progression.

DESIGN

Knee OA was induced by surgical destabilisation of the medial meniscus (DMM) in male 22-week-old tamoxifen-inducible glucocorticoid receptor knockout (chGRKO) mice and their wild-type (WT) littermates (n = 7-9/group). Mice were harvested 2, 4, 8 and 16 weeks after surgery to examine the spatiotemporal changes in molecular, cellular, and histological characteristics.

RESULTS

At all time points following DMM, cartilage damage was significantly attenuated in chGRKO compared to WT mice. Two weeks after DMM, WT mice exhibited increased chondrocyte and synoviocyte hypoxia inducible factor (HIF)-2α expression resulting in extensive synovial activation characterised by synovial thickening and increased interleukin-1 beta expression. At 2 and 4 weeks after DMM, WT mice displayed pronounced chondrocyte senescence and elevated catabolic signalling (reduced Yes-associated protein 1 (YAP1) and increased matrix metalloprotease [MMP]-13 expression). Contrastingly, at 2 weeks after DMM, HIF-2α expression and synovial activation were much less pronounced in chGRKO than in WT mice. Furthermore, chondrocyte YAP1 and MMP-13 expression, as well as chondrocyte senescence were similar in chGRKO-DMM mice and sham-operated controls.

CONCLUSION

Endogenous glucocorticoid signalling in chondrocytes promotes synovial activation, chondrocyte senescence and cartilage degradation by upregulation of catabolic signalling through HIF-2α in murine posttraumatic OA. These findings indicate that inhibition of glucocorticoid signalling early after injury may present a promising way to slow osteoarthritic cartilage degeneration.

Transient inhibition of meniscus cell migration following acute inflammatory challenge

Meniscus tears represent a common orthopedic injury that often requires surgery to restore pain-free function. The need for surgical intervention is due, in part, to the inflammatory and catabolic environment that inhibits meniscus healing after injury. In other organ systems, healing is dependent on the migration of cells to the site of injury; however, in the meniscus, it is currently unknown how the microenvironment dictates cell migration in the postinjury inflamed setting. Here, we investigated how inflammatory cytokines alter meniscal fibrochondrocyte (MFC) migration and sensation of microenvironmental stiffness. We further tested whether an FDA approved interleukin-1 receptor antagonist (IL-1Ra; Anakinra) could rescue migratory deficits caused by inflammatory challenge. When cultured in the presence of inflammatory cytokines (tumor necrosis factor-α [TNF-α] or interleukin-1β [IL-1β]) for 1 day, MFC migration was inhibited for 3 days before returning to control levels at Day 7. This migratory deficit was clear in three-dimensional as well, where fewer MFCs exposed to inflammatory cytokines migrated from a living meniscal explant compared with control. Notably, addition of IL-1Ra to MFCs previously exposed to IL-1β restored migration to baseline levels. This study demonstrates that joint inflammation can have negative impacts on meniscus cell migration and mechanosensation, affecting their potential for repair, and that resolution of this inflammation with concurrent anti-inflammatories can reverse these deficits. Future work will apply these findings to mitigate the negative consequences of joint inflammation and promote repair in a clinically relevant meniscus injury model.

The mitophagy receptor BNIP3 is critical for the regulation of metabolic homeostasis and mitochondrial function in the nucleus pulposus cells of the intervertebral disc

The contribution of mitochondria to the metabolic function of hypoxic NP cells has been overlooked. We have shown that NP cells contain networked mitochondria and that mitochondrial translocation of BNIP3 mediates hypoxia-induced mitophagy. However, whether BNIP3 also plays a role in governing mitochondrial function and metabolism in hypoxic NP cells is not known. BNIP3 knockdown altered mitochondrial morphology, and number, and increased mitophagy. Interestingly, BNIP3 deficiency in NP cells reduced glycolytic capacity reflected by lower production of lactate/H+ and lower ATP production rate. Widely targeted metabolic profiling and flux analysis using 1-2-13C-glucose showed that the BNIP3 loss resulted in redirection of glycolytic flux into pentose phosphate and hexosamine biosynthesis as well as pyruvate resulting in increased TCA flux. An overall reduction in one-carbon metabolism was noted suggesting reduced biosynthesis. U13C-glutamine flux analysis showed preservation of glutamine utilization to maintain TCA intermediates. The transcriptomic analysis of the BNIP3-deficient cells showed dysregulation of cellular functions including membrane and cytoskeletal integrity, ECM-growth factor signaling, and protein quality control with an overall increase in themes related to angiogenesis and innate immune response. Importantly, we observed strong thematic similarities with the transcriptome of a subset of human degenerative samples. Last, we noted increased autophagic flux, decreased disc height index and aberrant COL10A1/collagen X expression, signs of early disc degeneration in young adult bnip3 knockout mice. These results suggested that in addition to mitophagy regulation, BNIP3 plays a role in maintaining mitochondrial function and metabolism, and dysregulation of mitochondrial homeostasis could promote disc degeneration.Abbreviations: ECAR extracellular acidification rate; HIF hypoxia inducible factor; MFA metabolic flux analysis; NP nucleus pulposus; OCR oxygen consumption rate; ShBnip3 short-hairpin Bnip3.

Mechanism of YAP1 in the senescence and degeneration of endplate chondrocytes induced by intermittent cyclic mechanical tension

BACKGROUND

This study aimed to investigate the potential mechanism of YAP1 in the senescence and degeneration of endplate chondrocytes induced by intermittent cyclic mechanical tension (ICMT).

METHODS

According to the Pfirrmann grade evaluation classification, 30 human endplate cartilage tissues were divided into the lumbar vertebra fracture (LVF) group and lumbar disc herniation (LDH) group. Then, quantitative reverse transcription polymerase chain reaction, western blot, flow cytometry, hematoxylin-eosin staining, and senescence-associated β-galactosidase staining were performed. The difference in extracellular matrix expression between LVF and LDH endplate cartilage was detected. Second, the effect of ICMT on endplate chondrocytes degeneration was observed. Finally, the key regulatory role of YAP1 in ICMT-induced endplate cartilage degeneration was further verified.

RESULTS

In degraded human endplate cartilage and tension-induced degraded endplate chondrocytes, the expression of YAP1, COL-2A, and Sox9 was decreased. Conversely, the expression of p53 and p21 was increased. By regulating YAP1 in vivo and in vitro, we can achieve alleviation of ICMT-induced senescence of endplate chondrocytes and effective treatment of disc degeneration.

CONCLUSIONS

ICMT could induce senescence and degeneration of endplate chondrocytes, and ICMT-induced senescence and degeneration of endplate chondrocytes could be alleviated by regulating YAP1 expression.

Targeting Hippo pathway: A novel strategy for Helicobacter pylori-induced gastric cancer treatment

The Hippo pathway plays an important role in cell proliferation, apoptosis, and differentiation; it is a crucial regulatory pathway in organ development and tumor growth. Infection with Helicobacter pylori (H. pylori) increases the risk of developing gastric cancer. In recent years, significant progress has been made in understanding the mechanisms by which H. pylori infection promotes the development and progression of gastric cancer via the Hippo pathway. Exploring the Hippo pathway molecules may yield new diagnostic and therapeutic targets for H. pylori-induced gastric cancer. The current article reviews the composition and regulatory mechanism of the Hippo pathway, as well as the research progress of the Hippo pathway in the occurrence and development of H. pylori-related gastric cancer, in order to provide a broader perspective for the study and prevention of gastric cancer.

Roles of Hippo-YAP/TAZ signalling in intervertebral disc degeneration

Intervertebral disc degeneration (IVDD), a common cartilage-degenerative disease, is considered the main cause of low back pain (LBP). Owing to the complex aetiology and pathophysiology of IVDD, its molecular mechanisms and definitive treatment of IVDD remain unclear. As an evolutionarily and functionally conserved signalling pathway, Hippo-YAP/TAZ signalling plays a crucial role in IVDD progression. In this review, we discuss the regulation of Hippo-YAP/TAZ signalling and summarise the recent research progress on its role in cartilage homeostasis and IVDD. We also discuss the current application and future prospects of IVDD treatments based on Hippo-YAP/TAZ signalling.

Microtubule stabilization promotes the synthesis of type 2 collagen in nucleus pulposus cell by activating hippo-yap pathway

Intervertebral disc degeneration (IDD) is the cardinal pathological mechanism that underlies low back pain. Mechanical stress of the intervertebral disc may result in a change in nucleus pulposus cells state, matrix degradation, and degeneration of the disc. Microtubules, which are components of the cytoskeleton, are involved in driving or regulating signal pathways, which sense and transmit mechano-transduction. Microtubule and the related proteins play an important role in the development of many diseases, while little is known about the role of microtubules in nucleus pulposus cells. Researchers have found that type II collagen (COL2) expression is promoted by microtubule stabilization in synovial mesenchymal stem cells. In this study, we demonstrated that microtubule stabilization promotes the expression of COL2 in nucleus pulposus cells. Stabilized microtubules stimulating Hippo signaling pathway, inhibiting YAP protein expression and activity. In addition, microtubules stabilization promotes the expression of COL2 and alleviates disc degeneration in rats. In summary, our study for the first time, identifies microtubule as a promising therapeutic target for IDD, up-regulating the synthesis of COL2 via Hippo-Yap pathway. Our findings may provide new insights into the etiologies and pathology for IDD, further, targeting of microtubule acetylation may be an effective strategy for the treatment of IDD.

TAZ Reduces UVA-mediated Photoaging through Regulates Cell Proliferation in Skin Fibroblasts

The transcriptional co-activator with PDZ-binding motif (TAZ) is a significant transcription factor downstream of the Hippo pathway regulating organ size, tissue regeneration, cell proliferation and apoptosis. Here, we report on TAZ in response to photoaging mediated by repeated UVA irradiation in skin fibroblasts. Continuous UVA irradiation caused a decrease in TAZ and targeted CTGF mRNA and protein expression in fibroblasts, accompanied by reduced cell proliferation, DNA damage, and cell cycle arrest in G1 phase and S phase reduction. Furthermore, P16 and P21 expression levels were increased, whereas Lamin B1 and Lamin A/C expression were decreased as a result of repeated UVA exposure. We further demonstrated that TAZ reduction enables photoaging caused by continuously UVA-irradiated fibroblasts. TAZ overexpression decreases G1 phase, augments the S phase and reduces P16 and P21 protein expression levels in fibroblasts. However, TAZ overexpressing cells exposed to chronic-UVA radiation show induced G1 phase arrest, an S phase reduction, and elevated P16 and P21 protein levels in fibroblasts, compared with TAZ overexpression cells. These findings suggest a novel function of TAZ to reduce photoaging in fibroblasts. This regulation implies that TAZ might be a viable therapeutic target for photoaging or UVA-related skin disorders.

A20 ameliorates disc degeneration by suppressing mTOR/BNIP3 axis-mediated mitophagy

BACKGROUND

The pathological mechanism of intervertebral disc degeneration (IDD) is an unanswered question that we are committed to exploring. A20 is an anti-inflammatory protein of nucleus pulposus (NP) cells and plays a protective role in intervertebral disc degeneration.

OBJECTIVE

This study aims to investigate the molecular mechanism by which A20 attenuates disc degeneration.

METHODS

The proteins of interest were measured by immunoblotting, immunofluorescence, ELISA assay, and immunohistochemical technique to conduct related experiments. Immunofluorescence assays and mitochondrial membrane potential (JC-1) were used to assess mitophagy and mitochondrial fitness, respectively.

RESULTS

Here, we demonstrated that A20 promoted mitophagy, attenuated pyroptosis, and inhibited the degradation of the extracellular matrix, consequently significantly ameliorating disc degeneration. Mechanistically, A20 reduces pyroptosis and further suppresses cellular mTOR activity. On the one hand, A20-induced mTOR inhibition triggers BNIP3-mediated mitophagy to ensure mitochondrial fitness under LPS stimulation, as a result of mitigating mitochondrial dysfunction induced by LPS. On the other hand, A20-induced mTOR inhibition reduces the loss of mitochondrial membrane potential and the generation of Mitochondrial ROS.

CONCLUSION

The study revealed that A20 promotes BNIP3-mediated mitophagy by suppressing mTOR pathway activation against LPS-induced pyroptosis.

Morroniside attenuates nucleus pulposus cell senescence to alleviate intervertebral disc degeneration via inhibiting ROS-Hippo-p53 pathway

Intervertebral disc (IVD) degeneration (IVDD) which is highly prevalent within the elderly population, is a leading cause of chronic low back pain and disability. Nucleus pulposus (NP) cell senescence plays an indispensable role in the pathogenesis of IVDD. Morroniside is a major iridoid glycoside and one of the quality control metrics of Cornus officinalis Siebold & Zucc (CO). An increasing body of evidence suggests that morroniside and CO-containing formulae share many similar biological effects, including anti-inflammatory, anti-oxidative, and anti-apoptotic properties. In a previous study, we reported that Liuwei Dihuang Decoction, a CO-containing formula, is effective for treating IVDD by targeting p53 expression; however, the therapeutic role of morroniside on IVDD remains obscure. In this study, we assessed the pharmacological effects of morroniside on NP cell senescence and IVDD pathogenesis using a lumbar spine instability surgery-induced mouse IVDD model and an in vitro H2O2-induced NP cell senescence model. Our results demonstrated that morroniside administration could significantly ameliorate mouse IVDD progression, concomitant with substantial improvement in extracellular matrix metabolism and histological grading score. Importantly, in vivo and in vitro experiments revealed that morroniside could significantly reduce the increase in SA-β-gal activities and the expression of p53 and p21, which are the most widely used indicators of senescence. Mechanistically, morroniside suppressed ROS-induced aberrant activation of Hippo signaling by inhibiting Mst1/2 and Lats1/2 phosphorylation and reversing Yap/Taz reduction, whereas blockade of Hippo signaling by Yap/Taz inhibitor-1 or Yap/Taz siRNAs could antagonize the anti-senescence effect of morroniside on H2O2-induced NP cell senescence model by increasing p53 expression and activity. Moreover, the inhibition of Hippo signaling in the IVD tissues by morroniside was further verified in mouse IVDD model. Taken together, our findings suggest that morroniside protects against NP cell senescence to alleviate IVDD progression by inhibiting the ROS-Hippo-p53 pathway, providing a potential novel therapeutic approach for IVDD.

Irisin Ameliorates Intervertebral Disc Degeneration by Activating LATS/YAP/CTGF Signaling

Unbalanced metabolism of an extracellular matrix (ECM) in nucleus pulposus cells (NPCs) is widely acknowledged as the primary cause of intervertebral disc degeneration (IDD). Irisin, a novel myokine, is cleaved from fibronectin type III domain-containing 5 (FNDC5) and has recently been proven to regulate the metabolism of ECM. However, little is known about its potential on NPCs and the development of IDD. Therefore, this study sought to examine the protective effects and molecular mechanism of irisin on IDD in vivo and in vitro. Decreased expression levels of FNDC5 and anabolism markers (COL2A1 and ACAN) but increased levels of catabolism markers (ADAMTS4) were found in degenerative nucleus pulposus (NP) tissues. In a punctured-induced rat IDD model, irisin treatment was found to significantly slow the development of IDD, and in TNF-α-stimulated NPCs, irisin treatment partly reversed the disorder of ECM metabolism. In mechanism, RNA-seq results suggested that irisin treatment affected the Hippo signaling pathway. Further studies revealed that with irisin treatment, the phosphorylation levels of key factors (LATS and YAP) were downregulated, while the expression level of CTGF was upregulated. Moreover, CTGF knockdown partially eliminated the protective effects of irisin on the metabolism of ECM in NPCs, including inhibiting the anabolism and promoting the catabolism. Taken together, this study demonstrated that the expression levels of FNDC5 were decreased in degenerative NP tissues, while irisin treatment promoted the anabolism, inhibited the catabolism of the ECM in NPCs, and delayed the progression of IDD via LATS/YAP/CTGF signaling. These results shed light on the protective actions of irisin on NPCs, leading to the development of a novel therapeutic target for treating IDD.

YAP1 controls degeneration of human cartilage chondrocytes in response to mechanical tension

Disc herniation is a kind of disease caused by degenerative discs, which is common in the elderly, bringing substantial financial burden to families and society. Mechanical tension has a vital effect on the maintenance of cartilage function, however, the molecular mechanism by which mechanical tension causes degenerative discs to remain unclear. This study was the first to reveal Yes-associated protein 1(YAP1) is a key regulator in mechanical tension-mediated degenerative discs. Activation of YAP1 may be a valuable strategy to delays the degeneration of human cartilage chondrocytes. We found that YAP1 expression was significantly decreased in degenerative human endplate cartilage and tissue with the strength and time of mechanical stimulation, but the cell cycle distribution was significantly changed under the 10% cyclic mechanical tension(CMT). Besides, the degeneration of endplate cartilage can be delayed by activating the expression level of YAP1 in vitro and it has also been verified in the cartilage endplate tissue in vitro. Furthermore, We found that YAP1 and TEAD1 overexpression increased the activity of the ACAN or COL2A1 promoter to enhance the transcriptional activity of human chondrocyte collagen. The CMT activates the classic Hippo signaling pathway of YAP1, and piezo1 may regulate YAP1 expression through the Hippo signaling pathway. In conclusion, these results suggest the novel mechanism of YAP contributes to delaying the degeneration of endplate cartilage and targeting YAP in combination with Piezo1 is a potential therapeutic approach for the treatment of endplate cartilage degeneration.

Hippo signaling pathway and respiratory diseases

The hippo signaling pathway is a highly conserved evolutionary signaling pathway that plays an important role in regulating cell proliferation, organ size, tissue development, and regeneration. Increasing evidences consider that the hippo signaling pathway is involved in the process of respiratory diseases. Hippo signaling pathway is mainly composed of mammalian STE20-like kinase 1/2 (MST1/2), large tumor suppressor 1/2 (LATS1/2), WW domain of the Sav family containing protein 1 (SAV1), MOB kinase activator 1 (MOB1), Yes-associated protein (YAP) or transcriptional coactivator with PDZ-binding motif (TAZ), and members of the TEA domain (TEAD) family. YAP is the cascade effector of the hippo signaling pathway. The activation of YAP promotes pulmonary arterial vascular smooth muscle cells (PAVSMCs) proliferation, which leads to pulmonary vascular remodeling; thereby the pulmonary arterial hypertension (PAH) is aggravated. While the loss of YAP leads to high expression of inflammatory genes and the accumulation of inflammatory cells, the pneumonia is consequently exacerbated. In addition, overexpressed YAP promotes the proliferation of lung fibroblasts and collagen deposition; thereby the idiopathic pulmonary fibrosis (IPF) is promoted. Moreover, YAP knockout reduces collagen deposition and the senescence of adult alveolar epithelial cells (AECs); hence the IPF is slowed. In addition, hippo signaling pathway may be involved in the repair of acute lung injury (ALI) by promoting the proliferation and differentiation of lung epithelial progenitor cells and intervening in the repair of pulmonary capillary endothelium. Moreover, the hippo signaling pathway is involved in asthma. In conclusion, the hippo signaling pathway is involved in respiratory diseases. More researches are needed to focus on the molecular mechanisms by which the hippo signaling pathway participates in respiratory diseases.

Whole-genome resequencing to investigate the determinants of the multi-lumbar vertebrae trait in sheep

Multi-lumbar vertebrae trait is a beneficial mutation that can significantly improve livestock meat production. However, the genetic basis of the multi-lumbar vertebrae in sheep is still unclear. Here, we analysed the number of lumbar vertebrae of Duolang sheep and found three different traits of lumbar vertebrae number. Compared with the normal sheep, the length and weight of animal carcass from the multi-lumbar vertebrae sheep increased by 2.21 cm and 0.78 kg, respectively. We performed high-throughput genome resequencing on multi-lumbar vertebrae (n = 18) and normal (n = 11) Duolang sheep and obtained a total of more than 528.87 GB data. We found that the most significantly selective region were located in the 49.68-49.74 MB of chromosome 4 by selective-sweep analysis. We annotated this region and found that it contains SFRP4 which is known to regulate bone development. We further used the PCR-SSCP technology to detect the single nucleotide polymorphism (SNP) of the putative candidate SFRP4 and found that the two SNPs (rs600370085:C > T and rs415133338: A > G) of this gene were significantly associated with the multi-lumbar vertebrae of Duolang sheep. Our study indicates that the SFRP4 may be a potential major gene that affects the number of lumbar vertebrae in Duolang sheep, and has the potential to be utilized for sheep breeding in the future.

In Situ Cell Signalling of the Hippo-YAP/TAZ Pathway in Reaction to Complex Dynamic Loading in an Intervertebral Disc Organ Culture

Recently, a dysregulation of the Hippo-YAP/TAZ pathway has been correlated with intervertebral disc (IVD) degeneration (IDD), as it plays a key role in cell survival, tissue regeneration, and mechanical stress. We aimed to investigate the influence of different mechanical loading regimes, i.e., under compression and torsion, on the induction and progression of IDD and its association with the Hippo-YAP/TAZ pathway. Therefore, bovine IVDs were assigned to one of four different static or complex dynamic loading regimes: (i) static, (ii) "low-stress", (iii) "intermediate-stress", and (iv) "high-stress" regime using a bioreactor. After one week of loading, a significant loss of relative IVD height was observed in the intermediate- and high-stress regimes. Furthermore, the high-stress regime showed a significantly lower cell viability and a significant decrease in glycosaminoglycan content in the tissue. Finally, the mechanosensitive gene CILP was significantly downregulated overall, and the Hippo-pathway gene MST1 was significantly upregulated in the high-stress regime. This study demonstrates that excessive torsion combined with compression leads to key features of IDD. However, the results indicated no clear correlation between the degree of IDD and a subsequent inactivation of the Hippo-YAP/TAZ pathway as a means of regenerating the IVD.

Bioinformatics-Based Research on Key Genes and Pathways of Intervertebral Disc Degeneration

OBJECTIVE

To find out the pathways and key genes and to reveal disc degeneration pathogenesis based on bioinformatic analyses.

DESIGN

The GSE70362 dataset was downloaded from the GEO (Gene Expression Omnibus) database. Differentially expressed genes (DEGs) between the patients having disc degeneration and healthy controls were screened by Limma package in R language. Critical genes were identified by adopting gene ontologies (GOs), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, and protein-protein interaction (PPI) networks.

RESULTS

We identified 112 DEGs, including 60 genes which were upregulated and 52 that were downregulated. Analyses, such as GO and KEGG demonstrated that the DEGs got enriched in 4 biological processes and 2 signaling pathways, mainly related to disc degeneration. The PPI network analyses identified 5 key proteins, CCND1 (cyclin D1), GATA3, TNFSF11, LEF1, and DKK1 (Dickkopf related protein 1).

CONCLUSION

In this study, the DEGs and pathways determined promoted us understand the disc degeneration mechanisms. Also, the study may contribute novel biomarkers for the diagnosis and prevention of disc degeneration, and seek new treatment methods to repair and even regenerate degenerative intervertebral disc.

Control of tissue homeostasis, tumorigenesis, and degeneration by coupled bidirectional bistable switches

The Hippo-YAP/TAZ signaling pathway plays a critical role in tissue homeostasis, tumorigenesis, and degeneration disorders. The regulation of YAP/TAZ levels is controlled by a complex regulatory network, where several feedback loops have been identified. However, it remains elusive how these feedback loops contain the YAP/TAZ levels and maintain the system in a healthy physiological state or trap the system in pathological conditions. Here, a mathematical model was developed to represent the YAP/TAZ regulatory network. Through theoretical analyses, three distinct states that designate the one physiological and two pathological outcomes were found. The transition from the physiological state to the two pathological states is mechanistically controlled by coupled bidirectional bistable switches, which are robust to parametric variation and stochastic fluctuations at the molecular level. This work provides a mechanistic understanding of the regulation and dysregulation of YAP/TAZ levels in tissue state transitions.

Tissue development and homeostasis require well-controlled cell proliferation. Lack of this control could lead to degenerative or tumorigenic diseases. Signaling pathways have been explored in promoting or inhibiting these diseases. The Hippo signaling pathway is one of these, which has been found to control tissue homeostasis and organ size through cell proliferation and apoptosis, as evidenced by extensive experimental data. However, the question remains of how tissue can transition from a homeostatic state to either a degenerative or tumorigenic state. By theoretically analyzing a mathematical model of its regulatory network, we present a mechanism that underlies Hippo signaling to control tissue transition from a homeostatic state to a disease state. This provides us with a mechanistic understanding of how the parts of the regulatory network are coordinated for the transitions between the homeostasis state and the disease states. In addition, we looked at the role of system noise and found that it could promote the transition to one of the disease states. Our model allows for experimental hypotheses to be generated and could lead to the development of therapeutic strategies by targeting the Hippo signaling pathway.

DNMT3B decreases extracellular matrix degradation and alleviates intervertebral disc degeneration through TRPA1 methylation to inhibit the COX2/YAP axis

Intervertebral disc degeneration (IVDD) is a main cause of low back pain that is associated with extracellular matrix (ECM) degradation and inflammation. This study aims to investigate the role of DNMT3B and its regulatory mechanisms in IVDD. IVDD rat models were constructed followed by transfections with oe-DNMT3B or oe-YAP in order to explore the role of DNMT3B in the development of IVDD. After that transfection, nucleus pulposus (NP) cells were isolated and transfected with oe-DNMT3B, oe-TRPA1, si-YAP, oe-YAP or oe-COX2 in order to investigate the functions of DNMT3B in NP cells. DNMT3B was poorly expressed in IVDD tissues and NP cells whereas TRPA1, COX2, and YAP were highly expressed. The proliferation or apoptosis of NP cells was detected through CCK-8 assay or flow cytometry, respectively. Overexpression of DNMT3B promoted the proliferation of NP cells, inhibited their apoptosis, as well as increasing the expression of collagen II and aggrecan and decreasing expression of MMP3 and MMP9. Besides, DNMT3B suppressed inflammation and alleviated IVDD. Mechanistically, DNMT3B modified the TRPA1 promoter by methylation to inhibit the expression of COX2. Overexpression of COX2 promoted the apoptosis of NP cells and decreased the expression of YAP, which was reversed by upregulating DNMT3B. DNMT3B may promote the proliferation of NP cells and prevent their ECM degradation through the TRPA1/COX2/YAP axis, thereby alleviating IVDD in rats.

Inverse Agonist of Retinoid-Related Orphan Receptor-Alpha Prevents Apoptosis and Degeneration in Nucleus Pulposus Cells via Upregulation of YAP

Intervertebral disc degenerative disease (IDD) is the most common degenerative spine disease, which leads to chronic low back pain and symptoms in the lower extremities. In this study, we found that RORα, a member of the retinoid-related orphan receptor family, is significantly elevated in nucleus pulposus tissue in IDD patients. The elevation of RORα is associated with increased apoptosis of nucleus pulposus (NP) cells. Therefore, we applicated a well-established inverse agonist of RORα, SR3335, to investigate its role in regulating NP cell metabolism and apoptosis. To further investigate the mechanism that SR3335 regulates the pathogenesis of IDD in vitro, tumor necrosis factor alpha (TNF-α) stimulation was used in human NP cells to mimic the hostile environment that leads to degeneration. We found that SR3335 treatment reversed the trend of increased apoptosis in NP cells induced by TNF-α treatment. Next, TNF-α treatment upregulated the expression of type II collagen and aggrecan and downregulated MMP13 (matrix-degrading enzyme matrix metalloproteinase 13) and ADAMTS4 (a disintegrin and metalloproteinase with thrombospondin motifs 4). However, these effects were reversed after SR3335 treatment. Furthermore, we find that SR3335 mediated the effect in NP cells by regulating the YAP signaling pathway, especially by affecting the phosphorylation state of YAP. In conclusion, the reduction of matrix degradation enzymes and apoptosis upon SR3335 treatment suggests that SR3335 is a promising drug in reversing the deleterious microenvironment in IDD patients.

LncRNA JPX regulates proliferation and apoptosis of nucleus pulposus cells by targeting the miR-18a-5p/HIF-1α/Hippo-YAP pathway

With the aggravation of global aging, the rapid rise in the obesity rate, and the increasing number of patients with intervertebral disc degeneration (IDD), the principles and mechanism of this disease remain unclear. This study explored the molecular mechanism of IDD treatment through interactions of the lncRNA-miRNA-mRNA-signaling pathways and the effects on the proliferation and apoptosis of human nucleus pulposus cells (HNPCs) cultured in vitro. Our study revealed that lncRNA JPX is expressed at low levels in HNPCs under normoxic conditions. Luciferase and RNA pull-down assays were used to verify that lncRNA JPX directly bound to miR-18a-5p and influenced HNPC proliferation and apoptosis. Subsequently, a luciferase assay confirmed the direct binding of miR-18a-5p to HIF-1α and demonstrated a negative correlation between miR-18a-5p and HIF-1α. In addition, the HIF-1α antagonist reversed the inhibition of the Hippo-YAP pathway by the miR-18a-5p inhibitor. In conclusion, overexpression of lncRNA JPX upregulated HIF-1α by inhibiting the expression of miR-18a-5p, thereby inhibiting the Hippo-YAP pathway. By inhibiting this pathway, JPX overexpression promoted the proliferation of HNPCs and decreased their apoptosis. Therefore, the lncRNA JPX is a potential new target.

Bromodomain-containing protein 7 regulates matrix metabolism and apoptosis in human nucleus pulposus cells through the BRD7-PI3K-YAP1 signaling axis

Intervertebral disc degeneration (IDD) results from dysregulated metabolism of the extracellular matrix of the nucleus pulposus (NP) and involves the participation of inflammatory factors such as TNF-α. Bromodomain-containing protein 7 (BRD7) shows considerable potential for anti-inflammatory applications. Herein, we investigated the role of BRD7 in IDD. The immunohistochemistry results demonstrated decreased BRD7 expression in severely degenerated human NP tissues compared to those showing mild degeneration. Lentiviruses and adenoviruses were used to knock down or overexpress BRD7 and YAP1, respectively. Our results revealed that BRD7 knockdown promoted matrix degradation and suppressed PI3K and YAP1 expression, while BRD7 overexpression alleviated matrix degradation and promoted YAP1 and PI3K expression. In addition, PI3K inhibition augmented matrix degradation, enhanced apoptosis, and reduced YAP1 expression, whereas YAP1 overexpression promoted matrix synthesis, suppressed apoptosis and promoted PI3K expression. Besides, BRD7 overexpression reversed the reductions in sulfated glycosaminoglycan levels induced by TNF-α, but this effect was blocked by PI3K or YAP1 inhibitors. Moreover, YAP1 and PI3K were shown to interact through coimmunoprecipitation analysis. In summary, our results demonstrate that BRD7 can regulate matrix metabolism and apoptosis in human NP cells through the BRD7-PI3K-YAP1 signaling axis. This study might provide new insights into the prevention and treatment of IDD.

Multiscale Regulation of the Intervertebral Disc: Achievements in Experimental, In Silico, and Regenerative Research

Intervertebral disc (IVD) degeneration is a major risk factor of low back pain. It is defined by a progressive loss of the IVD structure and functionality, leading to severe impairments with restricted treatment options due to the highly demanding mechanical exposure of the IVD. Degenerative changes in the IVD usually increase with age but at an accelerated rate in some individuals. To understand the initiation and progression of this disease, it is crucial to identify key top-down and bottom-up regulations' processes, across the cell, tissue, and organ levels, in health and disease. Owing to unremitting investigation of experimental research, the comprehension of detailed cell signaling pathways and their effect on matrix turnover significantly rose. Likewise, in silico research substantially contributed to a holistic understanding of spatiotemporal effects and complex, multifactorial interactions within the IVD. Together with important achievements in the research of biomaterials, manifold promising approaches for regenerative treatment options were presented over the last years. This review provides an integrative analysis of the current knowledge about (1) the multiscale function and regulation of the IVD in health and disease, (2) the possible regenerative strategies, and (3) the in silico models that shall eventually support the development of advanced therapies.

Hypoxia Protects Rat Bone Marrow Mesenchymal Stem Cells Against Compression-Induced Apoptosis in the Degenerative Disc Microenvironment Through Activation of the HIF-1α/YAP Signaling Pathway

Stem cell therapy provides an attractive solution for intervertebral disc (IVD) degeneration. However, the degenerative microenvironment, characterized by excessive mechanical loading and hypoxia, remains an obstacle for the long-lasting survival of exogenous transplanted stem cells. Whether and how bone marrow mesenchymal stem cells (BMSCs) adapt to the hostile microenvironment remain unclear. In this study, CoCl₂ and mechanical compression were simultaneously used to simulate the hypoxic and overloaded microenvironment of IVDs in vitro. Compression had a proapoptotic effect through activation of the mitochondrial apoptotic pathway, while hypoxia exerted a prosurvival effect counteracting compression-induced apoptosis. Inhibiting the transcriptional activity of hypoxia inducible factor 1 subunit alpha (HIF-1α) by chetomin reversed the antiapoptotic effect of hypoxia. Furthermore, HIF-1α promoted dephosphorylation and activation of yes-associated protein (YAP) in hypoxic conditions. Conversely, both YAP inhibition and increased cell apoptosis were observed after inhibition through chetomin or YAP inhibitor verteporfin. Immunofluorescence staining and coimmunoprecipitation assays revealed that YAP could interact directly with HIF-1α and colocalize in the nucleus. Taken together, our results demonstrated that hypoxia protected BMSCs against compression-induced apoptosis in the degenerative disc microenvironment through activation of the HIF-1α/YAP signaling pathway. Thus, regulation of HIF-1α/YAP signaling might provide novel insights for promoting long-lasting BMSC survival and optimizing stem cell therapy for IVD degeneration.

The HIPPO pathway in gynecological malignancies

The Hippo pathway has been initially discovered by screening genes that regulate organ size in Drosophila. Recent studies have highlighted the role of the Hippo pathway in controlling organ size, tissue homeostasis and regeneration, and signaling dysregulation, especially the overactivation of the transcriptional coactivator YAP/TAZ, which leads to uncontrolled cell growth and malignant transformation. The core components of the Hippo pathway may initiate tumorigenesis by inducing tumor stem cells and proliferation, ultimately leading to metastasis and drug resistance, which occurs extensively in gynecological malignancies, including cervical cancer, ovarian cancer, and endometrial cancer. In this review, we attempt to systematically summarize recent progress in our understanding of the mechanism of Hippo pathway regulation in tumorigenesis and the mechanisms that underlie alterations during gynecological malignancies, as well as new therapeutic strategies.

PDK-1 mediated Hippo-YAP-IRS2 signaling pathway and involved in the apoptosis of non-small cell lung cancer cells

Pyruvate dehydrogenase kinase-1 (PDK-1), a gatekeeper enzyme, was involved in cancer progression, such as tumor angiogenesis, cell survival, and growth. Recent evidence indicated that PDK-1 may be involved in lung cancer, however, the function and underlying mechanism of PDK-1 is remaining unclear. In the present study, our aim was to investigate the role and mechanisms of PDK-1 in human non-small cell lung cancer (NSCLC) cells. We first observed that PDK-1 was highly expressed in NSCLC cell lines. PDK-1 silence resulted in the inhibition of NSCLC cell survival. Also, cell apoptosis and caspase-3 activity were increased by PDK-1 knockdown in H1299 and A549 cells. Attenuation of PDK-1 expression blocked YAP and insulin receptor substrate 2 (IRS2) expression, and PDK-1 silence suppressed IRS2 expression dependent on Hippo-YAP signaling pathway. Moreover, further studies confirmed that YAP or IRS2 overexpression reversed the action of PDK-1 in NSCLC cells. In conclusion, our findings indicate that PDK1/Hippo-YAP/IRS2 signaling pathway plays a critical role in NSCLC cell survival and apoptosis.

KEGG-expressed genes and pathways in intervertebral disc degeneration: Protocol for a systematic review and data mining

miRNAs and genes play significant roles in the etiology and pathogenesis of intervertebral disc degeneration (IDD). This study aimed to identify aberrantly expressed miRNAs, genes, and pathways in IDD through a comprehensive bioinformatics analysis.Data of miRNAs expression microarrays (GSE63492) and genes microarrays (GSE23130) were obtained from GEO database. Similarly, aberrantly expressed miRNAs and genes were obtained using GEO2R. In addition, functional and enrichment analyses of selected miRNAs and genes were performed using the DAVID database. Meanwhile, protein-protein interaction (PPI) network was constructed using STRING, and then visualized in Cytoscape.A total of 98 upregulated miRNAs were identified. They were enriched in biological processes of response to organelle, ion binding, cellular nitrogen compound metabolic process, biosynthetic process, small molecule metabolic process, cellular protein modification process, catabolic process, molecular function, neurotrophin TRK receptor signaling pathway, and protein complex. In addition, 1405 high expression protein genes were detected. It indicated enrichment in biological processes, such as translational initiation, nonsense-mediated decay, viral transcription, cell-cell adhesion, rRNA processing, translation, RP-dependent cotranslational protein targeting to membrane, nuclear-transcribed mRNA catabolic process, regulation of mRNA stability, and mRNA splicing via spliceosome and extracellular matrix organization. In addition, pathway analysis exhibited the common enrichment in focal adhesion, Hippo signaling pathway, ECM-receptor interaction, Wnt signaling pathway, PI3K-Akt signaling pathway, endocytosis, proteoglycans in cancer, and so on. The top 10 central genes of PPI network were POTEE, PPP2CA, RPL17, HSP90AA1, POTEF, RPL13A, ACTB, RPL18, RPS24, and HSPA1A.In conclusion, our research proposed abnormally expressed miRNAs, genes, and pathways in IDD through bioinformatics methods, which may provide new insights into the pathogenesis of IDD. Thus, the Hub gene involving POTEE, PPP2CA, RPL17, HSP90AA1, POTEF, RPL13A, ACTB, RPL18, RPS24, and HSPA1A may be biomarkers for accurate diagnosis and treatment of IDD in the future.

Dysregulation of the Hippo pathway signaling in aging and cancer

Human beings are facing emerging degenerative and cancer diseases, in large part, as a consequence of increased life expectancy. In the near future, researchers will have to put even more effort into fighting these new challenges, one of which will be prevention of cancer while continuing to improve the aging process through this increased life expectancy. In the last few decades, relevance of the Hippo pathway on cancer has become an important study since it is a major regulator of organ size control and proliferation. However, its deregulation can induce tumors throughout the body by regulating cell proliferation, disrupting cell polarity, releasing YAP and TAZ from the Scribble complexes and facilitating survival gene expression via activation of TEAD transcription factors. This pathway is also involved in some of the most important mechanisms that control the aging processes, such as the AMP-activated protein kinase and sirtuin pathways, along with autophagy and oxidative stress response/antioxidant defense. This could be the link between two tightly connected processes that could open a broader range of targeted molecular therapies to fight aging and cancer. Therefore, available knowledge of the processes involved in the Hippo pathway during aging and cancer must necessarily be well understood.

A prospect of cell immortalization combined with matrix microenvironmental optimization strategy for tissue engineering and regeneration

Cellular senescence is a major hurdle for primary cell-based tissue engineering and regenerative medicine. Telomere erosion, oxidative stress, the expression of oncogenes and the loss of tumor suppressor genes all may account for the cellular senescence process with the involvement of various signaling pathways. To establish immortalized cell lines for research and clinical use, strategies have been applied including internal genomic or external matrix microenvironment modification. Considering the potential risks of malignant transformation and tumorigenesis of genetic manipulation, environmental modification methods, especially the decellularized cell-deposited extracellular matrix (dECM)-based preconditioning strategy, appear to be promising for tissue engineering-aimed cell immortalization. Due to few review articles focusing on this topic, this review provides a summary of cell senescence and immortalization and discusses advantages and limitations of tissue engineering and regeneration with the use of immortalized cells as well as a potential rejuvenation strategy through combination with the dECM approach.

AMOT130 linking F-actin to YAP is involved in intervertebral disc degeneration

OBJECTIVES

Dysregulation of YAP by the Hippo signalling is associated with intervertebral disc degeneration (IDD). However, the relationship between the F-actin and Hippo pathway in IDD, and their effects on YAP remain poorly understood.

METHODS

The characteristics of Hippo pathway and F-actin the in the NP (nucleus pulposus) and annulus fibrosus of immature, mature, ageing and disc degeneration model rats were observed by immunofluorescence, western blot and qPCR. Nucleus pulposus cells (NPCs) were transfected with lentivirus Sh-LATS A, Sh-LATS B and harvested for SA-β-gal staining, qPCR, western blotting and immunofluorescence staining to investigate the mechanism of Hippo pathway and F-actin interact in NPCs.

RESULTS

We observed moderate decreases in F-actin and YAP expression with age in healthy intervertebral discs (IVDs). F-actin stress fibres distributed throughout the cytoplasm disappeared following treatment with latrunculin B (Lat B), resulting in a punctate distribution. Depletion of large tumour suppressor homologues 1/2 (LATS1/2) did not decrease the rate of cellular senescence, and YAP remained in the cytoplasm following Lat B treatment. Furthermore, angiomotin 130 (AMOT130) was associated with F-actin through a conserved actin-binding domain to retain YAP in the cytoplasm.

CONCLUSIONS

This study showed that a mechanism by which Hippo pathway and F-actin synergize to modulate YAP activation and localization in the context of IDD and help to control NPCs proliferation.