Photoactivation of TAZ via Akt/GSK3β signaling pathway promotes osteogenic differentiation

Noggin promotes osteogenesis in human adipose-derived mesenchymal stem cells via FGFR2/Src/Akt and ERK signaling pathway

The balance between Noggin and bone morphogenetic proteins (BMPs) is important during early development and skeletal regenerative therapies. Noggin binds BMPs in the extracellular space, thereby preventing BMP signaling. However, Noggin may affect cell response not necessarily through the modulation of BMP signaling, raising the possibility of direct Noggin signaling through yet unspecified receptors. Here we show that in osteogenic cultures of adipose-derived stem cells (ASCs), Noggin activates fibroblast growth factor receptors (FGFRs), Src/Akt and ERK kinases, and it stabilizes TAZ proteins in the presence of dexamethasone. Overall, this leads ASCs to increased expression of osteogenic markers and robust mineral deposition. Our results also indicate that Noggin can induce osteogenic genes expression in normal human bone marrow stem cells and alkaline phosphatase activity in normal human dental pulp stem cells. Besides, Noggin can specifically activate FGFR2 in osteosarcoma cells. We believe our findings open new research avenues to further explore the involvement of Noggin in cell fate modulation by FGFR2/Src/Akt/ERK signaling and potential applications of Noggin in bone regenerative therapies.

The Skeletal Cellular and Molecular Underpinning of the Murine Hindlimb Unloading Model

Bone adaptation to spaceflight results in bone loss at weight bearing sites following the absence of the stimulus represented by ground force. The rodent hindlimb unloading model was designed to mimic the loss of mechanical loading experienced by astronauts in spaceflight to better understand the mechanisms causing this disuse-induced bone loss. The model has also been largely adopted to study disuse osteopenia and therefore to test drugs for its treatment. Loss of trabecular and cortical bone is observed in long bones of hindlimbs in tail-suspended rodents. Over the years, osteocytes have been shown to play a key role in sensing mechanical stress/stimulus via the ECM-integrin-cytoskeletal axis and to respond to it by regulating different cytokines such as SOST and RANKL. Colder experimental environments (~20-22°C) below thermoneutral temperatures (~28-32°C) exacerbate bone loss. Hence, it is important to consider the role of environmental temperatures on the experimental outcomes. We provide insights into the cellular and molecular pathways that have been shown to play a role in the hindlimb unloading and recommendations to minimize the effects of conditions that we refer to as confounding factors.

Photobiomodulation therapy ameliorates hyperglycemia and insulin resistance by activating cytochrome c oxidase-mediated protein kinase B in muscle

Ameliorating hyperglycemia and insulin resistance are major therapeutic strategies for type 2 diabetes. Previous studies have indicated that photobiomodulation therapy (PBMT) attenuates metabolic abnormalities in insulin-resistant adipose cells and tissues. However, it remains unclear whether PBMT ameliorates glucose metabolism in skeletal muscle in type 2 diabetes models. Here we showed that PBMT reduced blood glucose and insulin resistance, and reversed metabolic abnormalities in skeletal muscle in two diabetic mouse models. PBMT accelerated adenosine triphosphate (ATP) and reactive oxygen species (ROS) generation by elevating cytochrome c oxidase (CcO) activity. ROS-induced activation of phosphatase and tensin homolog (PTEN)/ protein kinase B (AKT) signaling after PBMT promoted glucose transporter GLUT4 translocation and glycogen synthase (GS) activation, accelerating glucose uptake and glycogen synthesis in skeletal muscle. CcO subunit III deficiency, ROS elimination, and AKT inhibition suppressed the PBMT effects of glucose metabolism in skeletal muscle. This study indicated amelioration of glucose metabolism after PBMT in diabetic mouse models and revealed the metabolic regulatory effects and mechanisms of PBMT on skeletal muscle.

Photobiomodulation reduces hepatic lipogenesis and enhances insulin sensitivity through activation of CaMKKβ/AMPK signaling pathway

Photobiomodulation (PBM) could improve systemic blood glucose and insulin resistance in diet-induced diabetic mice. A few possible molecular mechanisms for the beneficial effects of PBM on diabetes have been proposed, but there is still an urgent need to explore the underlying mechanisms that support the application of PBM in the treatment of diabetes. Our study aimed to evaluate the effects of PBM on lipid metabolism in the liver of high-fat diet (HFD)-induced mice and explore the potential mechanisms of PBM on obesity and type 2 diabetes. Here, we administered PBM therapy (wavelength: 635 nm, energy density: 8 J/cm²) daily for eight weeks to HFD-induced mice. We detected that eight-week daily administration of PBM ameliorated HFD-induced gain weight, hyperlipidemia, and hyperglycemia, but also protected against diet-induced hepatic steatosis and insulin resistance. Furthermore, PBM increased AMP-activated protein kinase (AMPK) activation, lowered nuclear translocation of sterol regulatory element binding protein 1 (SREBP1), decreased aberrant lipogenesis, and enhanced insulin sensitive in HFD-induced mice livers. We also observed that Ca²⁺/calmodulin-dependent protein kinase kinase β (CaMKKβ) activation was responsible for AMPK activation in insulin-resistant HepG2 cells exposed to PBM. In summary, PBM at 635 nm and 8 J/cm² improved hepatic lipid metabolism and inhibited the development of HFD-induced obesity and type 2 diabetes. Moreover, increased intracellular Ca²⁺ content and CaMKKβ-dependent AMPK activation were possible molecular mechanisms underlying the PBM-induced improvement on obesity and type 2 diabetes.

Gone Caving: Roles of the Transcriptional Regulators YAP and TAZ in Skeletal Development

PURPOSE OF REVIEW

The development of the skeleton is controlled by cellular decisions determined by the coordinated activation of multiple transcription factors. Recent evidence suggests that the transcriptional regulator proteins, Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ), could have important roles in directing the activity of these transcriptional programs. However, in vitro evidence for the roles of YAP and TAZ in skeletal cells has been hopelessly contradictory. The goals of this review are to provide a cross-sectional view on the state of the field and to synthesize the available data toward a unified perspective.

RECENT FINDINGS

YAP and TAZ are regulated by diverse upstream signals and interact downstream with multiple transcription factors involved in skeletal development, positioning YAP and TAZ as important signal integration nodes in an hourglass-shaped signaling pathway. Here, we provide a survey of putative transcriptional co-effectors for YAP and TAZ in skeletal cells. Synthesizing the in vitro data, we conclude that TAZ is consistently pro-osteogenic in function, while YAP can exhibit either pro- or anti-osteogenic activity depending on cell type and context. Synthesizing the in vivo data, we conclude that YAP and TAZ combinatorially promote developmental bone formation, bone matrix homeostasis, and endochondral fracture repair by regulating a variety of transcriptional programs depending on developmental stage. Here, we discuss the current understanding of the roles of the transcriptional regulators YAP and TAZ in skeletal development, and provide recommendations for continued study of molecular mechanisms, mechanotransduction, and therapeutic implications for skeletal disease.

Thymine DNA glycosylase-regulated TAZ promotes radioresistance by targeting nonhomologous end joining and tumor progression in esophageal cancer

Radiation resistance is a major cause of esophageal cancer relapse or metastasis. Transcriptional coactivator with PDZ binding domain (TAZ) is a final effector of the Hippo signaling pathway and plays critical roles in several types of cancer, but how it participates in the progression and radiation resistance of esophageal cancer remains unclear. Here, we revealed that TAZ was the strongest prognostic factor among Hippo pathway members. Overexpression of TAZ predicted poor outcome and adverse pathological features. In cell and animal models, TAZ facilitated cell proliferation, motility, and radiation resistance. Additionally, TAZ promoted expression of nonhomologous end joining (NHEJ)‐related genes, which are the main contributors to repair irradiation‐induced DNA breaks and result in radiation resistance. Amplification of the TAZ gene occurred in 2.5%‐3.2% of esophageal cancers. In addition, the CpG islands of the TAZ gene were demethylated in esophageal cancer under thymine DNA glycosylase (TDG) regulation. Knockdown of TDG inhibited cell growth, motility, and radiation resistance, which were overridden by TAZ overexpression. Collectively, these findings suggest that the TDG/TAZ/NHEJ axis is a critical player in esophageal cancer progression and radiation resistance, as well as a potential target for radiotherapy.

Role of YAP/TAZ in Cell Lineage Fate Determination and Related Signaling Pathways

The penultimate effectors of the Hippo signaling pathways YAP and TAZ, are transcriptional co-activator proteins that play key roles in many diverse biological processes, ranging from cell proliferation, tumorigenesis, mechanosensing and cell lineage fate determination, to wound healing and regeneration. In this review, we discuss the regulatory mechanisms by which YAP/TAZ control stem/progenitor cell differentiation into the various major lineages that are of interest to tissue engineering and regenerative medicine applications. Of particular interest is the key role of YAP/TAZ in maintaining the delicate balance between quiescence, self-renewal, proliferation and differentiation of endogenous adult stem cells within various tissues/organs during early development, normal homeostasis and regeneration/healing. Finally, we will consider how increasing knowledge of YAP/TAZ signaling might influence the trajectory of future progress in regenerative medicine.

Characterization of a novel compound that promotes myogenesis via Akt and transcriptional co-activator with PDZ-binding motif (TAZ) in mouse C2C12 cells

Transcriptional co-activator with PDZ-binding motif (TAZ) plays versatile roles in the regulation of cell proliferation and differentiation. TAZ activity changes in response to the cellular environment such as mechanic and nutritional stimuli, osmolarity, and hypoxia. To understand the physiological roles of TAZ, chemical compounds that activate TAZ in cells are useful as experimental reagents. Kaempferol, TM-25659, and ethacridine are reported as TAZ activators. However, as each TAZ activator has a distinct property in cellular functions, additional TAZ activators are awaiting. We screened for TAZ activators and previously reported IB008738 as a TAZ activator that promotes myogenesis in C2C12 cells. In this study, we have characterized IBS004735 that was obtained in the same screening. IBS004735 also promotes myogenesis in C2C12 cells, but is not similar to IBS008738 in the structure. IBS004735 activates TAZ via Akt and has no effect on TAZ phosphorylation, which is the well-described key modification to regulate TAZ activity. Thus, we introduce IBS004735 as a novel TAZ activator that regulates TAZ in a yet unidentified mechanism.

Overexpressed miR-196a accelerates osteogenic differentiation in osteoporotic mice via GNAS-dependent Hedgehog signaling pathway

Osteoporosis (OP), a common metabolic bone disease, is accompanied by reduced bone mass, bone mineral density (BMD), as well as microstructure destruction of bone. Previously, microRNA-196a-2 (miR-196a-2) and miR-196a-3p were reported for its involvement in BMD. Herein, this study set out to identify the functional relevance of miR-196a in osteogenic differentiation in osteoporotic mice and explore the associated mechanism by establishing an OP mouse model. Guanine nucleotide binding protein, alpha stimulating (GNAS) was verified as a target gene of miR-196a, which was decreased in OP mice. Furthermore, the bone marrow stromal cells (BMSCs) were then extracted from OP mice and treated with miR-196 mimic/inhibitor or small interfering RNA against GNAS to investigate miR-196a interaction with GNAS and the Hedgehog signaling pathway. BMSCs in OP mice transfected with miR-196a mimic or si-GNAS displayed the elevated expression of Smo, ALP, Runx2, and OPN, as well as bone gla protein and tartrate-resistant acid phosphatase, elevated ALP vitality and bone formation ability as well as reduced expression of GNAS and PTCH. Taken conjointly, overexpression of miR-196a repressed GNAS expression by activating the Hedgehog signaling pathway, thus promoting osteogenic differentiation in mice with OP.

ATP6V1H facilitates osteogenic differentiation in MC3T3-E1 cells via Akt/GSK3β signaling pathway

Type 2 diabetes mellitus (T2DM) accounts for approximately 90% of all diabetic patients, and osteoporosis is one of the complications during T2DM process. ATP6V1H (V-type proton ATPase subunit H) displays crucial roles in inhibiting bone loss, but its role in osteogenic differentiation remains unknown. Therefore in this study, we aimed to explore the biological role of ATP6V1H in osteogenic differentiation. OM (osteogenic medium) and HG (high glucose and free fatty acids) were used to induce the MC3T3-E1 cells into osteogenic differentiation in a T2DM simulating environment. CCK8 assay was used to detect cell viability. Alizarin Red staining was used to detect the influence of ATP6V1H on osteogenic differentiation. ATP6V1H expression increased in OM-MC3T3-E1 cells, while decreased in OM+HG-MC3T3-E1 cells. ATP6V1H promoted osteogenic differentiation of OM+HG-MC3T3-E1 cells. Overexpression of ATP6V1H inhibited Akt/GSK3β signaling pathway, while knockdown of ATP6V1H promoted Akt/GSK3β signaling pathway. ATP6V1H overexpression promoted osteogenic differentiation of OM+HG-MC3T3-E1 cells. The role of ATP6V1H in osteogenic differentiation in a T2DM simulating environment involved in Akt/GSK3β signaling pathway. These data demonstrated that ATP6V1H could serve as a potential target for osteogenic differentiation in a T2DM simulating environment.

Melatonin Suppresses Estrogen Deficiency-Induced Osteoporosis and Promotes Osteoblastogenesis by Inactivating the NLRP3 Inflammasome

Postmenopausal osteoporosis induced by estrogen deficiency causes inadequate new bone formation and affects millions of women worldwide. Melatonin can improve bone mineral density at the femoral neck in postmenopausal women with osteopenia. This study aimed to investigate the mechanism of melatonin in estrogen deficiency-induced osteoporosis by focusing on osteoblast differentiation. 12-week-old female C57BL/6J mice were ovariectomized (OVX) and intraperitoneally injected with 10 or 50 mg/kg of melatonin for 8 weeks. Micro-computerized tomography scanning demonstrated that melatonin alleviated OVX-induced bone loss in a dose-dependent manner. Serum levels of ALP and osteocalcin (OCN) were further increased, whereas tartrate-resistant acid phosphatase level was decreased by melatonin in OVX-treated mice. Melatonin promoted osteoblast differentiation in primary bone marrow mesenchymal stem cells from OVX mice. It also inhibited activation of NLRP3 inflammasome in femoral bone protein and in induced osteoblasts stimulated by OVX. Knockdown of NLRP3 attenuated OVX-induced repression of osteogenic differentiation. The NLRP3 inflammasome activator monosodium urate partly abrogated the effect of melatonin on the expression of osteoblastogenic markers, including Runx2 and OCN. Additionally, the results showed that melatonin suppressed NLRP3 inflammasome activation by regulating Wnt/β-catenin signaling, which was confirmed by the Wnt/β-catenin inhibitor recombinant DKK1. These results indicated that melatonin ameliorates estrogen deficiency-induced osteoporosis and impaired osteogenic differentiation potential by suppressing activation of the NLRP3 inflammasome via mediating the Wnt/β-catenin pathway.

New pathway of icariin-induced MSC osteogenesis: transcriptional activation of TAZ/Runx2 by PI3K/Akt

Icariin has been demonstrated to stimulate mesenchymal stem cell (MSC) osteogensis and activate several signals, such as PI3K/Akt, but how the osteogenesis was sequentially mediated is unclear. Runx2 is one of the osteogenic regulators in MSC and is regulated by the TAZ gene. The purpose of this study was to investigate whether icariin-activated PI3K/Akt crosstalked with the TAZ-Runx2 pathway to regulate MSC osteogenesis. Adipose-derived MSCs were treated with icariin alone, together with TAZ silencing or PI3K/Akt inhibitor. Normal MSCs were used as a control. The activation of PI3K/Akt, expression of TAZ and downstream expression of Runx2 were analyzed. Induction of MSC osteogenesis under different treatments was detected. The results demonstrated that icariin treatment significantly activated PI3K/Akt and TAZ expression, as well as the downstream Runx2 expression. When activation of PI3K/Akt by icariin was inhibited by LY294002, upregulated TAZ expression was reversed, as well as the downstream expression of Runx2. Consequently, with the osteogenic counteracting effects of icariin on MSCs, inhibition of TAZ upregulation by siRNA did not significantly influence PI3K/ Akt activation in icariin-treated MSCs, but icariin-induced upregulation of Runx2 and osteogenic differentiation in MSCs was counteracted. It could be concluded from these findings that icariin treatment activated PI3K/Akt and further mediated the transcriptional activation of the TAZ/Runx2 pathway to induce osteogenic differentiation of MSCs.

Sox9 Protects against Human Lung Fibroblast Cell Apoptosis Induced by LPS through Activation of the AKT/GSK3β Pathway

Sex-determining region Y-box 9 (Sox9) is an important transcription factor that has been identified as a key regulator of several types of diseases. In this study, we explored the correlation of Sox9 with cell proliferation, apoptosis, inflammatory factor expression, and the possible signaling pathway in human lung fibroblast cell line to investigate the possible mechanism of neonatal pneumonia. Therefore, in the present study, pc-Sox9 and si-Sox9 were transfected into MRC-5 (human fetal lung fibroblast cell line) to promote or inhibit expression of Sox-9. Quantitative reverse-transcription polymerase chain reaction and Western blot were used to determine the expression level of Sox-9 at mRNA and protein level. Then 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay and flow cytometry were used to explore, respectively, proliferation and apoptosis in vitro. We found that Sox9 could significantly upregulate the proliferation rate and inhibit apoptosis rate and inflammatory factor expression of MRC-5 cells compared with a control group. Moreover, the signaling pathway study confirmed that Sox9 protected MRC-5 from lipopolysaccharide injury through the AKT/GSK3β pathway. All these findings suggest that Sox9 acts as a novel marker for neonatal pneumonia and could be a new therapeutic target for this disease.

The New Synthetic H2S-Releasing SDSS Protects MC3T3-E1 Osteoblasts against H2O2-Induced Apoptosis by Suppressing Oxidative Stress, Inhibiting MAPKs, and Activating the PI3K/Akt Pathway

Reactive oxygen species (ROS) are important in osteoporosis development. Oxidative stress induces apoptosis of osteoblasts and arrest of their differentiation. Both Danshensu (DSS) and hydrogen sulfide (H₂S) produce significant antioxidant effect in various systems. In this study, we synthesized SDSS, a novel H₂S-releasing compound derived from DSS, and studied its antioxidant effect in an H₂O₂-induced MC3T3-E1 osteoblastic cell injury model. We first characterized the H₂S releasing property of SDSS in both in vivo and in vitro models. HPLC chromatogram showed that intravenous injection of SDSS in adult rats released ADT-OH, a well proved H₂S sustained-release moiety, within several minutes in the rat plasma. Using an H₂S selective fluorescent probe, we further confirmed that SDSS released H₂S in MC3T3-E1 osteoblastic cells. Biological studies revealed that SDSS had no significant toxic effect but produced protective effects against H₂O₂-induced MC3T3-E1 cell apoptosis. SDSS also reversed the arrest of cell differentiation caused by H₂O₂ treatment. This was caused by the stimulatory effect of SDSS on bone sialoprotein, runt-related transcription factor 2, collagen expression, alkaline phosphatase activity, and bone nodule formation. Further studies revealed that SDSS reversed the reduced superoxide dismutase activity and glutathione content, and the increased ROS production in H₂O₂ treated cells. In addition, SDSS significantly attenuated H₂O₂-induced activation of p38-, ERK1/2-, and JNK-MAPKs. SDSS also stimulated phosphatidylinositol 3-kinase/Akt signaling pathway. Blockade of this pathway attenuated the cytoprotective effect of SDSS. In conclusion, SDSS protects MC3T3-E1 cells against H₂O₂-induced apoptosis by suppressing oxidative stress, inhibiting MAPKs, and activating the phosphatidylinositol 3-kinase/Akt pathway.

Regulation of TAZ in cancer

TAZ, a transcriptional coactivator with PDZ-binding motif, is encoded by WWTR1 gene (WW domain containing transcription regulator 1). TAZ is tightly regulated in the hippo pathway-dependent and -independent manner in response to a wide range of extracellular and intrinsic signals, including cell density, cell polarity, F-actin related mechanical stress, ligands of G protein-coupled receptors (GPCRs), cellular energy status, hypoxia and osmotic stress. Besides its role in normal tissue development, TAZ plays critical roles in cell proliferation, differentiation, apoptosis, migration, invasion, epithelial-mesenchymal transition (EMT), and stemness in multiple human cancers. We discuss here the regulators and regulation of TAZ. We also highlight the tumorigenic roles of TAZ and its potential therapeutic impact in human cancers.

Simulated microgravity inhibits osteogenic differentiation of mesenchymal stem cells through down regulating the transcriptional co-activator TAZ

Microgravity induces observed bone loss in space flight or simulated experiments, while the mechanism underlying it is still obscure. Here, we utilized a clinostat to model simulated microgravity (SMG) and found that SMG obviously inhibited osteogenic differentiation of rat bone marrow mesenchymal stem cells (BMSCs). We detected that SMG dramatically inhibited the expression of the transcriptional coactivator with PDZ-binding motif (TAZ), which acts as a vital regulator of osteogenesis. Interestingly, we found that lysophosphatidic acid (LPA) could activate TAZ and retain osteogenic differentiation of BMSCs under SMG. Our data further demonstrated that depletion of TAZ by siRNA blocked the LPA-induced increase in osteogenic differentiation of BMSCs under SMG. Moreover, Y27632 (the Rock inhibitor) abrogated the activation of TAZ and the increased osteogenic differentiation induced by LPA. Taken together, we propose that microgravity inhibits osteogenic differentiation of BMSCs due to decreased TAZ expression and that LPA can efficiently reverse the reduced osteogenic differentiation via the Rock-TAZ pathway.