Kindlin-2 regulates mesenchymal stem cell differentiation through control of YAP1/TAZ

Exosomal non-coding RNAs in the regulation of bone metabolism homeostasis: Molecular mechanism and therapeutic potential

Bone metabolism is a dynamic balance between bone formation and absorption regulated by osteoblasts/osteoclasts. Bone metabolic disorders can lead to metabolic bone disease. Osteoporosis (OP), osteoarthritis (OA) and femoral head necrosis (ONFH) are common metabolic bone diseases. At present, the treatment of metabolic bone disease is still mainly to relieve pain and improve joint function. However, surgical treatment does not apply to the vast majority of high-risk groups, including postmenopausal women, patients with diabetes, cirrhosis, etc. Exosomes (Exos) are nanoscale membrane vesicles that are released by almost all cells. Exos are rich in a variety of bioactive substances, such as non-coding RNAs, nucleic acids, proteins and lipids. In view of the structure of Exos, it can protect the biologically active molecules can be smoothly delivered to the target cells and involved in the regulation of cell function. In this review, we focus on the regulation mechanism and function of bone homeostasis mediated by exosomal ncRNAs (Exos-ncRNAs), including macrophage polarization, autophagy, angiogenesis, signal transduction and competing endogenous RNA (ceRNA). We summarized the therapeutic strategies and potential drugs of Exos-ncRNAs in metabolic bone disease. Moreover, we discussed the shortcomings and potential research directions of Exos as carrier to deliver ncRNAs to play a role.

RhoA/ROCK-TAZ Axis regulates bone formation within calvarial trans-sutural distraction osteogenesis

BACKGROUND

Craniofacial skeletal deformities can be addressed by applying tensile force to sutures to prompt sutural bone formation. The intricate process of mechanical modulation in craniofacial sutures involves complex biomechanical signal transduction. The small GTPase Ras homolog gene family member A (RhoA) functions as a key mechanotransduction protein, orchestrating the dynamic assembly of the cytoskeleton by activating the Rho-associated coiled-coil containing protein kinase (ROCK). Transcriptional coactivator with PDZ-binding motif (TAZ) serves as a crucial mediator in the regulation of genes and the orchestration of biological functions within the mechanotransduction signaling pathway. However, the role of RhoA/ROCK-TAZ in trans-sutural distraction osteogenesis has not been reported.

METHODS

We utilized pre-osteoblast-specific RhoA deletion mice to establish an in vivo calvarial trans-sutural distraction model and an in vitro mechanical stretch model for pre-osteoblasts isolated from neonatal mice. Micro-CT and histological staining were utilized to detect the formation of new bone in the sagittal suture of the skull as well as the activation of RhoA, Osterix and TAZ. The activation of ROCK-limk-cofilin and the nuclear translocation of TAZ in pre-osteoblasts under mechanical tension were detected through Western blot, qRT-PCR, and immunofluorescence.

RESULTS

The osteogenic differentiation of pre-osteoblasts was facilitated by mechanical tension through the activation of RhoA and Rho-associated kinase (ROCK), while ablation of RhoA impaired osteogenesis by inhibiting pre-osteoblast differentiation after suture expansion. Furthermore, inhibiting RhoA expression could block tensile-stimulated nuclear translocation of TAZ by preventing F-actin assembly through ROCK-LIM-domain kinase (LIMK)-cofilin pathway. In addition, the TAZ agonist TM-25659 could attenuate impaired osteogenesis caused by ablation of RhoA in pre-osteoblasts by increasing TAZ nuclear accumulation.

CONCLUSIONS

This study demonstrates that mechanical stretching promotes the osteogenic differentiation of pre-osteoblasts in trans-sutural distraction osteogenesis, and this process is mediated by the RhoA/ROCK-TAZ signaling axis. Overall, our results may provide an insight for potential treatment strategies for craniosynostosis patients through trans-sutural distraction osteogenesis.

Targeting miR-29 mitigates skeletal senescence and bolsters therapeutic potential of mesenchymal stromal cells

Mesenchymal stromal cell (MSC) senescence is a key factor in skeletal aging, affecting the potential of MSC applications. Identifying targets to prevent MSC and skeletal senescence is crucial. Here, we report increased miR-29 expression in bone tissues of aged mice, osteoporotic patients, and senescent MSCs. Genetic overexpression of miR-29 in Prx1-positive MSCs significantly accelerates skeletal senescence, reducing cortical bone thickness and trabecular bone mass, while increasing femur cross-sectional area, bone marrow adiposity, p53, and senescence-associated secretory phenotype (SASP) levels. Mechanistically, miR-29 promotes senescence by upregulating p53 via targeting Kindlin-2 mRNA. miR-29 knockdown in BMSCs impedes skeletal senescence, enhances bone mass, and accelerates calvarial defect regeneration, also reducing lipopolysaccharide (LPS)-induced organ injuries and mortality. Thus, our findings underscore miR-29 as a promising therapeutic target for senescence-related skeletal diseases and acute inflammation-induced organ damage.

A Novel Lipopeptide-Functionalized Metal-Organic Framework for Periodontitis Therapy through the Htra1/FAK/YAP Pathway

Periodontitis is a chronic inflammatory disease characterized by plaque accumulation, resulting in immune microenvironment disorders and resorption of alveolar bone. To promote bone healing under inflammatory environments, a functional biomaterial based on disease pathophysiology is designed. A novel fatty acid C10-modified polypeptide, C10-KR8, is discovered to have excellent abilities in modulating macrophage repolarization and promoting bone regeneration in periodontitis. To build a multifunctional material localized drug delivery system, C10-KR8@ZIF-8 (C10-KR8-loaded zeolitic imidazolate framework-8) nanoparticles are constructed to sustainedly release the C10-KR8 peptide and Zn elements. By synergistic effects of providing a dynamic immuno-modulatory environment and promoting osteogenesis under pathological conditions, the obtained pH-responsive nanoparticles display excellent bone regeneration capability. Furthermore, coimmunoprecipitation/liquid chromatography-tandem mass spectrometry analysis and proteomics analysis revealed that the C10-KR8 peptide directly interacts with the high-temperature requirement protein A1 (Htra1), and C10-KR8@ZIF-8 nanoparticles promote the osteogenic differentiation of bone mesenchymal stem cells by activating the focal adhesion kinase (FAK)/phosphatidylinositide 3-kinase (PI3K)/AKT pathway and enhancing the nuclear localization of Yes-associated protein (YAP). Taken together, this study demonstrates C10-KR8 peptide regulate osteoimmunology and bone regeneration by Htra1/FAK/YAP pathway and that ZIF-8-based peptide loading platform is a promising strategy for periodontitis.

Loss of Pinch Proteins Causes Severe Degenerative Disc Disease-Like Lesions in Mice

Degenerative disc disease (DDD) is one of the most common skeletal disorders affecting aged populations. DDD is the leading cause of low back/neck pain, resulting in disability and huge socioeconomic burdens. However, the molecular mechanisms underlying DDD initiation and progression remain poorly understood. Pinch1 and Pinch2 are LIM-domain-containing proteins with crucial functions in mediating multiple fundamental biological processes, such as focal adhesion, cytoskeletal organization, cell proliferation, migration, and survival. In this study, we found that Pinch1 and Pinch2 were both highly expressed in healthy intervertebral discs (IVDs) and dramatically downregulated in degenerative IVDs in mice. Deleting Pinch1 in aggrecan-expressing cells and Pinch2 globally (AggrecanCreERT2; Pinch1fl/fl; Pinch2-/-) caused striking spontaneous DDD-like lesions in lumbar IVDs in mice. Pinch loss inhibited cell proliferation and promoted extracellular matrix (ECM) degradation and apoptosis in lumbar IVDs. Pinch loss markedly enhanced the production of pro-inflammatory cytokines, especially TNFα, in lumbar IVDs and exacerbated instability-induced DDD defects in mice. Pharmacological inhibition of TNFα signaling mitigated the DDD-like lesions caused by Pinch loss. In human degenerative NP samples, reduced expression of Pinch proteins was correlated with severe DDD progression and a markedly upregulated expression of TNFα. Collectively, we demonstrate the crucial role of Pinch proteins in maintaining IVD homeostasis and define a potential therapeutic target for DDD.

Myoblast-derived exosomal Prrx2 attenuates osteoporosis via transcriptional regulation of lncRNA-MIR22HG to activate Hippo pathway

BACKGROUND

Sarcopenia and osteoporosis are common diseases that predominantly affect older individuals. The interaction between muscle and skeleton exerts pivotal roles in bone remodeling. This study aimed to explore the function of myoblast-derived exosomal Prrx2 in osteogenic differentiation and its potential mechanisms.

METHODS

Exosomes were isolated from myogenic differentiated C2C12 cells. qRT-PCR and Western blotting were used to determine target molecule expression. Osteogenic differentiation of BMSCs was evaluated by Alizarin red staining, ALP activity and levels of OCN, OPN, RUNX2, and BMP2. Dual-luciferase reporter assay, RIP, and ChIP assays were performed to verify the interaction between molecules. The nuclear translocation of YAP1 was observed by immunofluorescence staining. In vivo osteoporotic model was established by ovariectomy in mice. Bone loss was examined using HE staining.

RESULTS

Prrx2 expression was elevated in myogenic differentiated C2C12 cells and their exosomes. Myoblast-derived exosomal Prrx2 enhanced osteogenic differentiation of BMSCs. Delivering exosomal Prrx2 directly bond to MIR22HG promoter and promoted its transcription and expression. MIR22HG enhanced expression and nuclear translocation of YAP via sponging miR-128, thus facilitating BMSC osteogenic differentiation. Knockdown of exosomal Prrx2 suppressed osteogenic differentiation, which could be abolished by MIR22HG overexpression. Similarly, miR-128 inhibitor or YAP overexpression reversed the inhibitory effect of MIR22HG depletion or miR-128 mimics on osteogenic differentiation. Finally, myoblast-derived exosomal Prrx2 alleviated osteoporosis in mice via up-regulating MIR22HG and activating the Hippo pathway.

CONCLUSION

Myoblast-derived exosomal Prrx2 contributes to transcriptional activation of MIR22HG to activate YAP pathway via sponging miR-128, thereby facilitating osteogenic differentiation of BMSCs.

Roles of focal adhesion proteins in skeleton and diseases

The skeletal system, which contains bones, joints, tendons, ligaments and other elements, plays a wide variety of roles in body shaping, support and movement, protection of internal organs, production of blood cells and regulation of calcium and phosphate metabolism. The prevalence of skeletal diseases and disorders, such as osteoporosis and bone fracture, osteoarthritis, rheumatoid arthritis, and intervertebral disc degeneration, increases with age, causing pain and loss of mobility and creating a huge social and economic burden globally. Focal adhesions (FAs) are macromolecular assemblies that are composed of the extracellular matrix (ECM), integrins, intracellular cytoskeleton and other proteins, including kindlin, talin, vinculin, paxillin, pinch, Src, focal adhesion kinase (FAK) and integrin-linked protein kinase (ILK) and other proteins. FA acts as a mechanical linkage connecting the ECM and cytoskeleton and plays a key role in mediating cell-environment communications and modulates important processes, such as cell attachment, spreading, migration, differentiation and mechanotransduction, in different cells in skeletal system by impacting distinct outside-in and inside-out signaling pathways. This review aims to integrate the up-to-date knowledge of the roles of FA proteins in the health and disease of skeletal system and focuses on the specific molecular mechanisms and underlying therapeutic targets for skeletal diseases.

Biomineralization inspired 3D printed bioactive glass nanocomposite scaffolds orchestrate diabetic bone regeneration by remodeling micromilieu

Type II diabetes mellitus (TIIDM) remains a challenging clinical issue for both dentists and orthopedists. By virtue of persistent hyperglycemia and altered host metabolism, the pathologic diabetic micromilieu with chronic inflammation, advanced glycation end products accumulation, and attenuated biomineralization severely impairs bone regeneration efficiency. Aiming to "remodel" the pathologic diabetic micromilieu, we 3D-printed bioscaffolds composed of Sr-containing mesoporous bioactive glass nanoparticles (Sr-MBGNs) and gelatin methacrylate (GelMA). Sr-MBGNs act as a biomineralization precursor embedded in the GelMA-simulated extracellular matrix and release Sr, Ca, and Si ions enhancing osteogenic, angiogenic, and immunomodulatory properties. In addition to angiogenic and anti-inflammatory outcomes, this innovative design reveals that the nanocomposites can modulate extracellular matrix reconstruction and simulate biomineralization by activating lysyl oxidase to form healthy enzymatic crosslinked collagen, promoting cell focal adhesion, modulating osteoblast differentiation, and boosting the release of OCN, the noncollagenous proteins (intrafibrillar mineralization dependent), and thus orchestrating osteogenesis through the Kindlin-2/PTH1R/OCN axis. This 3D-printed bioscaffold provides a multifunctional biomineralization-inspired system that remodels the "barren" diabetic microenvironment and sheds light on the new bone regeneration approaches for TIIDM.

Osteoarthritis: pathogenic signaling pathways and therapeutic targets

Osteoarthritis (OA) is a chronic degenerative joint disorder that leads to disability and affects more than 500 million population worldwide. OA was believed to be caused by the wearing and tearing of articular cartilage, but it is now more commonly referred to as a chronic whole-joint disorder that is initiated with biochemical and cellular alterations in the synovial joint tissues, which leads to the histological and structural changes of the joint and ends up with the whole tissue dysfunction. Currently, there is no cure for OA, partly due to a lack of comprehensive understanding of the pathological mechanism of the initiation and progression of the disease. Therefore, a better understanding of pathological signaling pathways and key molecules involved in OA pathogenesis is crucial for therapeutic target design and drug development. In this review, we first summarize the epidemiology of OA, including its prevalence, incidence and burdens, and OA risk factors. We then focus on the roles and regulation of the pathological signaling pathways, such as Wnt/β-catenin, NF-κB, focal adhesion, HIFs, TGFβ/ΒΜP and FGF signaling pathways, and key regulators AMPK, mTOR, and RUNX2 in the onset and development of OA. In addition, the roles of factors associated with OA, including MMPs, ADAMTS/ADAMs, and PRG4, are discussed in detail. Finally, we provide updates on the current clinical therapies and clinical trials of biological treatments and drugs for OA. Research advances in basic knowledge of articular cartilage biology and OA pathogenesis will have a significant impact and translational value in developing OA therapeutic strategies.

Mechanotransduction through adhesion molecules: Emerging roles in regulating the stem cell niche

Stem cells have been shown to play an important role in regenerative medicine due to their proliferative and differentiation potential. The challenge, however, lies in regulating and controlling their potential for this purpose. Stem cells are regulated by growth factors as well as an array of biochemical and mechanical signals. While the role of biochemical signals and growth factors in regulating stem cell homeostasis is well explored, the role of mechanical signals has only just started to be investigated. Stem cells interact with their niche or to other stem cells via adhesion molecules that eventually transduce mechanical cues to maintain their homeostatic function. Here, we present a comprehensive review on our current understanding of the influence of the forces perceived by cell adhesion molecules on the regulation of stem cells. Additionally, we provide insights on how this deeper understanding of mechanobiology of stem cells has translated toward therapeutics.

Polyelectrolyte Complex Hydrogels with Controlled Mechanics Affect Mesenchymal Stem Cell Differentiation Relevant to Growth Plate Injuries

The growth plate is a complex cartilage structure in long bones that mediates growth in children. When injured, the formation of a "bony bar" can occur which impedes normal growth and can cause angular deformities or growth arrest. Current treatments for growth plate injuries are limited and result in poor patient outcomes, necessitating research toward novel treatments that can prevent bony bar formation and stimulate cartilage regeneration. This study investigates alginate-chitosan polyelectrolyte complex (PEC) hydrogels as an injectable biomaterial system to prevent bony bar formation. Biomaterial properties including stiffness and degradation are quantified, and the effect that material properties have on mesenchymal stem cell (MSC) fate is quantified in vitro. Specifically, this study aims to elucidate the effectiveness of biomaterial-based control over the differentiation behavior of MSCs toward osteogenic or chondrogenic lineages using biochemical metabolite assays and quantitative real time PCR. Further, the PEC hydrogels are employed in a rat growth plate injury model to determine their effectiveness in preventing bony bar formation in vivo. Results indicate that hydrogel composition and material properties affect the differentiation tendency of MSCs in vitro, and the PEC hydrogels show promise as an injectable biomaterial for growth plate injuries.

CLP36 promotes p53 deficient sarcoma progression through suppression of atrophin-1 interacting protein-4 (AIP-4)-dependent degradation of YAP1

Background: p53 deficiency is a key causal factor for tumor development and progression. p53 acts in this process through, at least in part, cooperation with YAP1 but the underlying molecular mechanism is incompletely understood. In this paper, we show that CLP36, an actinin-binding cytoskeletal protein, links p53 deficiency to up-regulation of YAP1 expression and sarcoma progression.

Methods: Immunohistochemical staining and Western blotting were used to investigate the effect of p53 deficiency on CLP36 expression in sarcoma tissues and cells. Furthermore, molecular, cellular, and genetic knockout and knockdown approaches were employed to investigate the functions of CLP36 in regulation of sarcoma cell behavior in culture and tumor growth in mice. Finally, biochemical approaches were used to investigate the molecular mechanism by which CLP36 regulates the malignant behavior of p53 deficient sarcoma cells.

Results: We have found that the expression of CLP36 is up-regulated in response to loss of p53 in sarcoma tissues and cells. Depletion of CLP36 inhibited malignant behavior of p53 deficient sarcoma cells. Furthermore, knockout of CLP36 in mice markedly inhibited p53 deficiency-induced tumorigenesis and improved the survival of the p53 deficient mice. Mechanistically, CLP36 promoted p53 deficiency-induced tumorigenesis through inhibition of E3 ligase atrophin-1 interacting protein-4 (AIP-4)-dependent proteasomal degradation of YAP1 and consequently increase of YAP1 expression.

Conclusions: Our results reveal a crucial role of CLP36 in linking p53 deficiency to up-regulation of YAP1 expression and sarcoma progression. Our findings suggest that therapeutic targeting the CLP36/YAP1 signaling axis may provide an effective strategy for alleviation of p53 deficient sarcoma progression.

Kindlin-2 loss in condylar chondrocytes causes spontaneous osteoarthritic lesions in the temporomandibular joint in mice

The progressive destruction of condylar cartilage is a hallmark of the temporomandibular joint (TMJ) osteoarthritis (OA); however, its mechanism is incompletely understood. Here, we show that Kindlin-2, a key focal adhesion protein, is strongly detected in cells of mandibular condylar cartilage in mice. We find that genetic ablation of Kindlin-2 in aggrecan-expressing condylar chondrocytes induces multiple spontaneous osteoarthritic lesions, including progressive cartilage loss and deformation, surface fissures, and ectopic cartilage and bone formation in TMJ. Kindlin-2 loss significantly downregulates the expression of aggrecan, Col2a1 and Proteoglycan 4 (Prg4), all anabolic extracellular matrix proteins, and promotes catabolic metabolism in TMJ cartilage by inducing expression of Runx2 and Mmp13 in condylar chondrocytes. Kindlin-2 loss decreases TMJ chondrocyte proliferation in condylar cartilages. Furthermore, Kindlin-2 loss promotes the release of cytochrome c as well as caspase 3 activation, and accelerates chondrocyte apoptosis in vitro and TMJ. Collectively, these findings reveal a crucial role of Kindlin-2 in condylar chondrocytes to maintain TMJ homeostasis.

Kindlin-2 promotes Src-mediated tyrosine phosphorylation of androgen receptor and contributes to breast cancer progression

Androgen receptor (AR) signaling plays important roles in breast cancer progression. We show here that Kindlin-2, a focal adhesion protein, is critically involved in the promotion of AR signaling and breast cancer progression. Kindlin-2 physically associates with AR and Src through its two neighboring domains, namely F1 and F0 domains, resulting in formation of a Kindlin-2-AR-Src supramolecular complex and consequently facilitating Src-mediated AR Tyr-534 phosphorylation and signaling. Depletion of Kindlin-2 was sufficient to suppress Src-mediated AR Tyr-534 phosphorylation and signaling, resulting in diminished breast cancer cell proliferation and migration. Re-expression of wild-type Kindlin-2, but not AR-binding-defective or Src-binding-defective mutant forms of Kindlin-2, in Kindlin-2-deficient cells restored AR Tyr-534 phosphorylation, signaling, breast cancer cell proliferation and migration. Furthermore, re-introduction of phosphor-mimic mutant AR-Y534D, but not wild-type AR reversed Kindlin-2 deficiency-induced inhibition of AR signaling and breast cancer progression. Finally, using a genetic knockout strategy, we show that ablation of Kindlin-2 from mammary tumors in mouse significantly reduced AR Tyr-534 phosphorylation, breast tumor progression and metastasis in vivo. Our results suggest a critical role of Kindlin-2 in promoting breast cancer progression and shed light on the molecular mechanism through which it functions in this process.

Prevention of collagen hydrogel contraction using polydopamine-coating and alginate outer shell increases cell contractile force

Collagen is the most abundant protein in the extracellular matrix of mammals and has a great effect on various cell behaviors including adhesion, differentiation, and migration. However, it is difficult to utilize collagen gel as a physical scaffold in vitro because of its severe contraction. Decrease in the overall hydrogel volume induces changes in cell distribution, and mass transfer within the gel. Uncontrolled mechanical and physiological factors in the fibrous matrix result in uncontrolled cell behaviors in the surrounding cells. In this study, two strategies were used to minimize the contraction of collagen gel. A disk-shaped frame made of polydopamine-coated polydimethylsiloxane (PDMS) prevented horizontal contraction at the edge of the hydrogel. The sequentially cross-linked collagen gel with alginate outer shell (CA-shell) structure inhibited the vertical gel contraction. The combined method synergistically prevented the hydrogel from shrinkage in long-term 3D cell culture. We observed the shift in balance of differentiation from adipogenesis to osteogenesis in mesenchymal stem cells under the environment where gel contraction was prevented, and confirmed that this phenomenon is closely associated with the mechanotransduction based on Yes-associated protein (YAP) localization. Development of this contraction inhibition platform made it possible to investigate the influence of regulation of cellular microenvironments. The physical properties of the hydrogel fabricated in this study were similar to that of pure collagen gel but completely changed the cell behavior within the gel by inhibition of gel contraction. The platform can be used to broaden our understanding of the fundamental mechanism underlying cell-matrix interactions and reproduce extracellular matrix in vivo.

Antioxidant Effects of Irisin in Liver Diseases: Mechanistic Insights

Oxidative stress is a crucial factor in the development of various liver diseases. Irisin, a metabolic hormone discovered in 2012, is mainly produced by proteolytic cleavage of fibronectin type III domain containing 5 (FNDC5) in skeletal muscles. Irisin is induced by physical exercise, and a rapidly growing body of literature suggests that irisin is, at least partially, responsible for the beneficial effects of regular exercise. The major biological function of irisin is believed to be involved in the maintenance of metabolic homeostasis. However, recent studies have suggested the therapeutic potential of irisin against a variety of liver diseases involving its antioxidative function. In this review, we aim to summarize the accumulating evidence demonstrating the antioxidative effects of irisin in liver diseases, with an emphasis on the current understanding of the potential molecular mechanisms.

Quercetin attenuates the proliferation, inflammation, and oxidative stress of high glucose-induced human mesangial cells by regulating the miR-485-5p/YAP1 pathway

Background

Diabetic nephropathy (DN) is a kidney damage caused by diabetes and the main cause of end-stage renal disease. However, the current treatment of DN has many limitations. Quercetin is a bioflavonoid compound with therapeutic benefits in metabolic diseases. This study aims to determine the therapeutic potentials and underlying mechanism of quercetin on DN.

Methods

We collected blood samples from DN patients and healthy controls and treated human mesangial cells (HMCs) with high glucose (HG) to establish an in vitro model of DN. Then we assessed the expression difference of miR-485-5p as well as YAP1 in serum of DN patients and healthy controls and between HG-induced HMCs and control cells. qRT-PCR and western blot were performed to assess miR-485-5p and YAP1 expression levels; CCK-8 and ELISAs were used to examine cell proliferation, inflammation, and oxidative stress. Dual luciferase reporter assay was implemented to detect the binding of miR-485-5p and YAP1 mRNA sequence.

Results

Quercetin suppressed proliferation, inflammation, and oxidative stress of HMCs induced by HG. As for mechanism, miR-485-5p directly bound to YAP1 and inhibited YAP1 expression. The downregulation of miR-485-5p and upregulation of YAP1 were also observed in the serum of DN patients. Quercetin modulated miR-485-5p/YAP1 axis to regulate HG-induced inflammation and oxidative stress.

Conclusion:

Quercetin inhibits the proliferation, inflammation, and oxidative stress of HMCs induced by HG through miR-485-5p/YAP1 axis, which might provide a novel treatment strategy for DN.

Melatonin Promotes Antler Growth by Accelerating MT1-Mediated Mesenchymal Cell Differentiation and Inhibiting VEGF-Induced Degeneration of Chondrocytes

The sika deer is one type of seasonal breeding animal, and the growth of its antler is affected by light signals. Melatonin (MLT) is a neuroendocrine hormone synthesized by the pineal gland and plays an important role in controlling the circadian rhythm. Although the MLT/MT1 (melatonin 1A receptor) signal has been identified during antler development, its physiological function remains almost unknown. The role of MLT on antler growth in vivo and in vitro is discussed in this paper. In vivo, MLT implantation was found to significantly increase the weight of antlers. The relative growth rate of antlers showed a remarkable increased trend as well. In vitro, the experiment showed MLT accelerated antler mesenchymal cell differentiation. Further, results revealed that MLT regulated the expression of Collage type II (Col2a) through the MT1 binding mediated transcription of Yes-associated protein 1 (YAP1) in antler mesenchymal cells. In addition, treatment with vascular endothelial growth factor (VEGF) promoted chondrocytes degeneration by downregulating the expression of Col2a and Sox9 (SRY-Box Transcription Factor 9). MLT effectively inhibited VEGF-induced degeneration of antler chondrocytes by inhibiting the Signal transducers and activators of transcription 5/Interleukin-6 (STAT5/IL-6) pathway and activating the AKT/CREB (Cyclin AMP response-element binding protein) pathway dependent on Sox9 expression. Together, our results indicate that MLT plays a vital role in the development of antler cartilage.

Kindlin-2 deletion in osteoprogenitors causes severe chondrodysplasia and low-turnover osteopenia in mice

BACKGROUND

Our recent studies demonstrate that the focal adhesion protein Kindlin-2 exerts crucial functions in the mesenchymal stem cells, mature osteoblasts and osteocytes in control of early skeletal development and bone homeostasis in mice. However, whether Kindlin-2 plays a role in osteoprogenitors remains unclear.

MATERIALS AND METHODS

Mice lacking Kindlin-2 expression in osterix (Osx)-expressing cells (i.e., osteoprogenitors) were generated. Micro-computerized tomography (μCT) analyses, histology, bone histomorphometry and immunohistochemistry were performed to determine the effects of Kindlin-2 deletion on skeletal development and bone mass accrual and homeostasis. Bone marrow stromal cells (BMSCs) from mutant mice (Kindlin-2 fl/fl ; Osx Cre ) and control littermates were isolated and determined for their osteoblastic differentiation capacity.

RESULTS

Kindlin-2 was highly expressed in osteoprogenitors during endochondral ossification. Deleting Kindlin-2 expression in osteoprogenitors impaired both intramembranous and endochondral ossifications. Mutant mice displayed multiple severe skeletal abnormalities, including unmineralized fontanel, limb shortening and growth retardation. Deletion of Kindlin-2 in osteoprogenitors impaired the growth plate development and largely delayed formation of the secondary ossification center in the long bones. Furthermore, adult mutant mice displayed a severe low-turnover osteopenia with a dramatic decrease in bone formation which exceeded that in bone resorption. Primary BMSCs isolated from mutant mice exhibited decreased osteoblastic differentiation capacity.

CONCLUSIONS

Our study demonstrates an essential role of Kinlind-2 expression in osteoprogenitors in regulating skeletogenesis and bone mass accrual and homeostasis in mice.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

This study reveals that Kindlin-2 through its expression in osteoprogenitor cells controls chondrogenesis and bone mass. We may define a novel therapeutic target for treatment of skeletal diseases, such as chondrodysplasia and osteoporosis.

Proteogenomic Analysis Reveals Proteins Involved in the First Step of Adipogenesis in Human Adipose-Derived Stem Cells

Background

Obesity is characterized as a disease that directly affects the whole-body metabolism and is associated with excess fat mass and several related comorbidities. Dynamics of adipocyte hypertrophy and hyperplasia play an important role in health and disease, especially in obesity. Human adipose-derived stem cells (hASC) represent an important source for understanding the entire adipogenic differentiation process. However, little is known about the triggering step of adipogenesis in hASC. Here, we performed a proteogenomic approach for understanding the protein abundance alterations during the initiation of the adipogenic differentiation process.

Methods

hASC were isolated from adipose tissue of three donors and were then characterized and expanded. Cells were cultured for 24 hours in adipogenic differentiation medium followed by protein extraction. We used shotgun proteomics to compare the proteomic profile of 24 h-adipogenic, differentiated, and undifferentiated hASC. We also used our previous next-generation sequencing data (RNA-seq) of the total and polysomal mRNA fractions of hASC to study posttranscriptional regulation during the initial steps of adipogenesis.

Results

We identified 3420 proteins out of 48,336 peptides, of which 92 proteins were exclusively identified in undifferentiated hASC and 53 proteins were exclusively found in 24 h-differentiated cells. Using a stringent criterion, we identified 33 differentially abundant proteins when comparing 24 h-differentiated and undifferentiated hASC (14 upregulated and 19 downregulated, respectively). Among the upregulated proteins, we shortlisted several adipogenesis-related proteins. A combined analysis of the proteome and the transcriptome allowed the identification of positive correlation coefficients between proteins and mRNAs.

Conclusions

These results demonstrate a specific proteome profile related to adipogenesis at the beginning (24 hours) of the differentiation process in hASC, which advances the understanding of human adipogenesis and obesity. Adipogenic differentiation is finely regulated at the transcriptional, posttranscriptional, and posttranslational levels.

Fermitin family member 2 promotes melanoma progression by enhancing the binding of p-α-Pix to Rac1 to activate the MAPK pathway

We identified fermitin family member 2 (FERMT2, also known as kindlin-2) as a potential target in A375 cell line by siRNA library screening. Drugs that target mutant BRAF kinase lack durable efficacy in the treatment of melanoma because of acquired resistance, thus the identification of novel therapeutic targets is needed. Immunohistochemistry was used to identify kindlin-2 expression in melanoma samples. The interaction between kindlin-2 and Rac1 or p-Rac/Cdc42 guanine nucleotide exchange factor 6 (α-Pix) was investigated. Finally, the tumor suppressive role of kindlin-2 was validated in vitro and in vivo. Analysis of clinical samples and Oncomine data showed that higher levels of kindlin-2 predicted a more advanced T stage and M stage and facilitated metastasis and recurrence. Kindlin-2 knockdown significantly inhibited melanoma growth and migration, whereas kindlin-2 overexpression had the inverse effects. Further study showed that kindlin-2 could specifically bind to p-α-Pix(S13) and Rac1 to induce a switch from the inactive Rac1-GDP conformation to the active Rac1-GTP conformation and then stimulate the downstream MAPK pathway. Moreover, we revealed that a Rac1 inhibitor suppressed melanoma growth and metastasis and the combination of the Rac1 inhibitor and vemurafenib resulted in a better therapeutic outcome than monotherapy in melanoma with high kindlin-2 expression and BRAF mutation. Our results demonstrated that kindlin-2 promoted melanoma progression, which was attributed to specific binding to p-α-Pix(S13) and Rac1 to stimulate the downstream MAPK pathway. Thus, kindlin-2 could be a potential therapeutic target for treating melanoma.

Fermitin family homolog 2 (Kindlin-2) affects vascularization during the wound healing process by regulating the Wnt/β-catenin signaling pathway in vascular endothelial cells

Kindlin-2 is a member of the FERM-containing cytoskeletal protein family that regulates cell–matrix interactions. Previous studies have shown that Kindlin-2 recruits focal adhesion proteins and regulates integration by binding to the focal adhesion region of the integrin β-segment. Although Kindlin-2 has been reported to be involved in various skin diseases and many kinds of tumors, its role in the skin wound healing process remains unclear. The aim of the present study was to investigate the role of Kindlin-2 in the regulation of wound healing. The effects of Kindlin-2 on wound healing were studied by a wound healing model, kindlin-2 (±) mice. The effects of Kindlin-2 on cell migration, cellular tube formation, and cell adhesion and spreading were evaluated in human umbilical vein endothelial cells (HUVECs) with downregulated Kindlin-2 expression. We found that the expression of kindlin-2 was elevated in wound healing tissues and that interfering with the expression of Kindlin-2 delayed the wound healing process and reduced neovascularization. We found that the wound healing of kindlin-2 (±) mice was delayed, with a decreased number of new blood vessels. Furthermore, depletion of Kindlin-2 impaired HUVEC spreading, migration and tube formation. Intriguingly, we found that kindlin-2 binds to β-catenin in the Wnt/β-catenin signaling pathway and cooperates with β-catenin to enter the nucleus from the cytoplasm, activating the downstream Wnt/β-catenin signaling pathway. Taken together, these results help to elucidate the mechanism of Kindlin-2 in the regulation of the wound healing process and provide a theoretical basis for further study of wound healing and abnormal healing.

PINCH-1 promotes Δ1-pyrroline-5-carboxylate synthase expression and contributes to proline metabolic reprogramming in lung adenocarcinoma

Proline metabolic reprogramming is intimately involved in cancer progression. We recently identified a critical role of PINCH-1, a cell-extracellular matrix (ECM) adhesion protein whose expression is elevated in lung adenocarcinoma, in the promotion of proline biosynthesis, fibrosis and lung adenocarcinoma growth. How PINCH-1 promotes proline biosynthesis, however, was incompletely understood. In this study, we show that PINCH-1 promotes the expression of Δ¹-pyrroline-5-carboxylate synthase (P5CS), a key enzyme that links glutamate metabolism to proline biosynthesis. Depletion of PINCH-1 from lung adenocarcinoma cells reduced the protein but not mRNA level of P5CS, resulting in down-regulation of the cellular level of P5C and cell proliferation. Treatment of the cells with protease inhibitor leupeptin effectively reversed PINCH-1 deficiency-induced reduction of the P5CS level. At the molecular level, PINCH-1, through its LIM2 domain, physically associated with P5CS in lung adenocarcinoma cells. Re-expression of wild type PINCH-1, but not that of the PINCH-1 LIM2 deletion mutant, in PINCH-1 deficient lung adenocarcinoma cells restored P5CS expression, proline biosynthesis and cell proliferation. Finally, P5CS expression, like that of PINCH-1, is elevated in human and mouse lung adenocarcinoma. Using a mouse model of lung adenocarcinoma in which PINCH-1 is conditionally ablated, we show that knockout of PINCH-1 from lung adenocarcinoma effectively reduced the P5CS level in vivo. Our results reveal an important role of PINCH-1 in the promotion of P5CS expression, which likely contributes to proline metabolic reprogramming and consequently lung adenocarcinoma progression.

How signaling pathways link extracellular mechano-environment to proline biosynthesis: A hypothesis: PINCH-1 and kindlin-2 sense mechanical signals from extracellular matrix and link them to proline biosynthesis

We propose a signaling pathway in which cell-extracellular matrix (ECM) adhesion components PINCH-1 and kindlin-2 sense mechanical signals from ECM and link them to proline biosynthesis, a vital metabolic pathway for macromolecule synthesis, redox balance, and ECM remodeling. ECM stiffening promotes PINCH-1 expression via integrin signaling, which suppresses dynamin-related protein 1 (DRP1) expression and mitochondrial fission, resulting in increased kindlin-2 translocation into mitochondria and interaction with Δ¹ -pyrroline-5-carboxylate (P5C) reductase 1 (PYCR1). Kindlin-2 interaction with PYCR1 protects the latter from proteolytic degradation, leading to elevated PYCR1 level. Additionally, PINCH-1 promotes P5C synthase (P5CS) expression and P5C synthesis, which, together with increased PYCR1 level, support augmented proline biosynthesis. This signaling pathway is frequently activated in fibrosis and cancer, resulting in increased proline biosynthesis and excessive collagen matrix production, which in turn further promotes ECM stiffening. Targeting this signaling pathway, therefore, may provide an effective strategy for alleviating fibrosis and cancer progression.

Kindlin-2 Acts as a Key Mediator of Lung Fibroblast Activation and Pulmonary Fibrosis Progression

Pulmonary fibrosis is a progressive and fatal lung disease characterized by activation of lung fibroblasts and excessive deposition of collagen matrix. We show here that the concentrations of kindlin-2 and its binding partner PYCR1, a key enzyme for proline synthesis, are significantly increased in the lung tissues of human patients with pulmonary fibrosis. Treatment of human lung fibroblasts with TGF-β1 markedly increased the expression of kindlin-2 and PYCR1, resulting in increased kindlin-2 mitochondrial translocation, formation of the kindlin-2-PYCR1 complex, and proline synthesis. The concentrations of the kindlin-2-PYCR1 complex and proline synthesis were markedly reduced in response to pirfenidone or nintedanib, two clinically approved therapeutic drugs for pulmonary fibrosis. Furthermore, depletion of kindlin-2 alone was sufficient to suppress TGF-β1-induced increases of PYCR1 expression, proline synthesis, and fibroblast activation. Finally, using a bleomycin mouse model of pulmonary fibrosis, we show that ablation of kindlin-2 effectively reduced the concentrations of PYCR1, proline, and collagen matrix and alleviate the progression of pulmonary fibrosis in vivo. Our results suggest that kindlin-2 is a key promoter of lung fibroblast activation, collagen matrix synthesis, and pulmonary fibrosis, underscoring the therapeutic potential of targeting the kindlin-2 signaling pathway for control of this deadly lung disease.

Kindlin-2 in Sertoli cells is essential for testis development and male fertility in mice

Kindlin-2 is known to play important roles in the development of mesoderm-derived tissues including myocardium, smooth muscle, cartilage and blood vessels. However, nothing is known for the role of Kindlin-2 in mesoderm-derived reproductive organs. Here, we report that loss of Kindlin-2 in Sertoli cells caused severe testis hypoplasia, abnormal germ cell development and complete infertility in male mice. Functionally, loss of Kindlin-2 inhibits proliferation, increases apoptosis, impairs phagocytosis in Sertoli cells and destroyed the integration of blood-testis barrier structure in testes. Mechanistically, Kindlin-2 interacts with LATS1 and YAP, the key components of Hippo pathway. Kindlin-2 impedes LATS1 interaction with YAP, and depletion of Kindlin-2 enhances LATS1 interaction with YAP, increases YAP phosphorylation and decreases its nuclear translocation. For clinical relevance, lower Kindlin-2 expression and decreased nucleus localization of YAP was found in SCOS patients. Collectively, we demonstrated that Kindlin-2 in Sertoli cells is essential for sperm development and male reproduction.

Circ-ITCH sponges miR-214 to promote the osteogenic differentiation in osteoporosis via upregulating YAP1

Osteoporosis is the most prevailing primary bone disease and a growing health care burden. The aim of this study was to clarify the functional roles and mechanisms of the circ-ITCH regulating osteogenic differentiation of osteoporosis. Circ-ITCH and yes-associated protein 1 (YAP1) levels were downregulated, but the miR‐214 level was upregulated in osteoporotic mice and patients. Knockdown of circ-ITCH inhibited the alkaline phosphatase (ALP) activity, mineralized nodule formation, and expression of runt-related transcription factor 2 (RUNX2), osteopontin (OPN), and osteocalcin (OCN) during osteogenic induction. Furthermore, miR-214 was a target of circ-ITCH, knockdown of miR-214 could impede the regulatory effects of sh-circ-ITCH on osteogenic differentiation. Moreover, miR-214 suppressed hBMSCs osteogenic differentiation by downregulating YAP1. Finally, in vivo experiments indicated that overexpression of circ-ITCH could improve osteogenesis in ovariectomized mice. In conclusion, circ-ITCH upregulated YAP1 expression to promote osteogenic differentiation in osteoporosis via sponging miR-214. Circ-ITCH could act as a novel therapeutic target for osteoporosis.

Kindlin-2 mediates mechanotransduction in bone by regulating expression of Sclerostin in osteocytes

Osteocytes act as mechanosensors in bone; however, the underlying mechanism remains poorly understood. Here we report that deleting Kindlin-2 in osteocytes causes severe osteopenia and mechanical property defects in weight-bearing long bones, but not in non-weight-bearing calvariae. Kindlin-2 loss in osteocytes impairs skeletal responses to mechanical stimulation in long bones. Control and cKO mice display similar bone loss induced by unloading. However, unlike control mice, cKO mice fail to restore lost bone after reloading. Osteocyte Kindlin-2 deletion impairs focal adhesion (FA) formation, cytoskeleton organization and cell orientation in vitro and in bone. Fluid shear stress dose-dependently increases Kindlin-2 expression and decreases that of Sclerostin by downregulating Smad2/3 in osteocytes; this latter response is abolished by Kindlin-2 ablation. Kindlin-2-deficient osteocytes express abundant Sclerostin, contributing to bone loss in cKO mice. Collectively, we demonstrate an indispensable novel role of Kindlin-2 in maintaining skeletal responses to mechanical stimulation by inhibiting Sclerostin expression during osteocyte mechanotransduction.

Periostin Promotes Colorectal Tumorigenesis through Integrin-FAK-Src Pathway-Mediated YAP/TAZ Activation

Periostin is a multifunctional extracellular matrix protein involved in various inflammatory diseases and tumor metastasis; however, evidence regarding whether and how periostin actively contributes to inflammation-associated tumorigenesis remains elusive. Here, we demonstrate that periostin deficiency significantly inhibits the occurrence of colorectal cancer in azoxymethane/dextran sulfate sodium-treated mice and in Apc^Min/+ mice. Moreover, periostin deficiency attenuates the severity of colitis and reduces the proliferation of tumor cells. Mechanistically, stromal fibroblast-derived periostin activates FAK-Src kinases through integrin-mediated outside-in signaling, which results in the activation of YAP/TAZ and, subsequently, IL-6 expression in tumor cells. Conversely, IL-6 induces periostin expression in fibroblasts by activating STAT3, which ultimately facilitates colorectal tumor development. These findings provide the evidence that periostin promotes colorectal tumorigenesis, and identify periostin- and IL-6-mediated tumor-stroma interaction as a promising target for treating colitis-associated colorectal cancer.

Extracellular Matrix Stiffness: New Areas Affecting Cell Metabolism

In recent years, in-depth studies have shown that extracellular matrix stiffness plays an important role in cell growth, proliferation, migration, immunity, malignant transformation, and apoptosis. Most of these processes entail metabolic reprogramming of cells. However, the exact mechanism through which extracellular matrix stiffness leads to metabolic reprogramming remains unclear. Insights regarding the relationship between extracellular matrix stiffness and metabolism could help unravel novel therapeutic targets and guide development of clinical approaches against a myriad of diseases. This review provides an overview of different pathways of extracellular matrix stiffness involved in regulating glucose, lipid and amino acid metabolism.

Biomimetic Culture Strategies for the Clinical Expansion of Mesenchymal Stromal Cells

Mesenchymal stromal/stem cells (MSCs) typically require significant ex vivo expansion to achieve the high cell numbers required for research and clinical applications. However, conventional MSC culture on planar (2D) plastic surfaces has been shown to induce MSC senescence and decrease cell functionality over long-term proliferation, and usually, it has a high labor requirement, a high usage of reagents, and therefore, a high cost. In this Review, we describe current MSC-based therapeutic strategies and outline the important factors that need to be considered when developing next-generation cell expansion platforms. To retain the functional value of expanded MSCs, ex vivo culture systems should ideally recapitulate the components of the native stem cell microenvironment, which include soluble cues, resident cells, and the extracellular matrix substrate. We review the interplay between these stem cell niche components and their biological roles in governing MSC phenotype and functionality. We discuss current biomimetic strategies of incorporating biochemical and biophysical cues in MSC culture platforms to grow clinically relevant cell numbers while preserving cell potency and stemness. This Review summarizes the current state of MSC expansion technologies and the challenges that still need to be overcome for MSC clinical applications to be feasible and sustainable.

Kindlin-2 regulates the differentiation of 3T3-L1 preadipocytes: implications for wound healing

Background

Adipose tissue has been proven to play a crucial role in wound healing, while kindlin-2, an integrin-associated protein, has been shown to regulate cell adhesion, migration, and differentiation. This study aimed to explore its involvement in the cell differentiation of 3T3-L1 preadipocytes and its role in wound healing.

Methods

Cell adhesion, Cell Counting Kit-8 (CCK-8), Transwell, and in vitro wound healing assays, along with adipogenic and osteogenic differentiation induction were performed in 3T3-L1 preadipocytes in which kindlin-2 was knocked down or overexpressed. In vivo, kindlin-2 (+/−) transgenic mice were constructed, and wound healing was analyzed by immunohistochemistry (IHC) in a mouse dorsal wound model. Real-time polymerase chain reaction (RT-PCR) and western blotting were performed to analyze the expression of adipokines and adipogenic markers in mouse wound tissues. Adipogenic differentiation induction of adipose tissue stromal vascular fraction (SVF) were performed, and the expression of adipogenic markers in SVF was detected by western blotting. The target signaling pathway highly related to adipogenic differentiation was explored by computational biology and verified by western blotting.

Results

Knockdown of kindlin-2 was found to inhibit the adhesion, migration, and adipogenic differentiation of 3T3-L1 preadipocytes while promoting their osteogenic differentiation. In contrast, kindlin-2 overexpression resulted in increased adhesion, migration, and adipogenic differentiation of 3T3-L1 preadipocytes while reducing osteogenic differentiation. In vivo, downregulation of kindlin-2 inhibited adipogenesis in kindlin-2 transgenic mice, resulting in delayed wound healing by inhibiting inflammation, angiogenesis, collagen remodeling, and wound contraction. Mechanistically, we found that kindlin-2 could regulate adipogenic differentiation through PI3K/AKT/mTOR signaling pathway.

Conclusions

Our study revealed the essential role that kindlin-2 has in the differentiation and wound healing of 3T3-L1 preadipocytes, which offers a theoretical basis for further research and a novel strategy for wound healing.

Kindlin-2 promotes rear focal adhesion disassembly and directional persistence during cell migration

Cell migration involves front-to-rear asymmetric focal adhesion (FA) dynamics, which facilitates trailing edge detachment and directional persistence. Here, we show that kindlin-2 is crucial for FA sliding and disassembly in migrating cells. Loss of kindlin-2 markedly reduced FA number and selectively impaired rear FA sliding and disassembly, resulting in defective rear retraction and reduced directional persistence during cell migration. Kindlin-2-deficient cells failed to develop serum-induced actomyosin-dependent tension at FAs. At the molecular level, kindlin-2 directly interacted with myosin light chain kinase (MYLK, hereafter referred to as MLCK), which was enhanced in response to serum stimulation. Serum deprivation inhibited rear FA disassembly, which was released in response to serum stimulation. Overexpression of the MLCK-binding kindlin-2 F0F1 fragment (amino acid residues 1-167), which inhibits the interaction of endogenous kindlin-2 with MLCK, phenocopied kindlin-2 deficiency-induced migration defects. Inhibition of MLCK, like loss of kindlin-2, also impaired trailing-edge detachment, rear FA disassembly and directional persistence. These results suggest a role of kindlin-2 in promoting actomyosin contractility at FAs, leading to increased rear FA sliding and disassembly, and directional persistence during cell migration.

Paracrine Interactions Involved in Human Induced Pluripotent Stem Cells Differentiation into Chondrocytes

Osteoarthritis (OA), as a degenerative joint disease, is the most common form of joint disorder that causes pain, stiffness, and other symptoms associated with OA. Various genetic, biomechanical, and environmental factors have a relevant role in the development of OA. To date, extensive efforts are currently being made to overcome the poor self-healing capacity of articular cartilage. Despite the pivotal role of chondrocytes, their proliferation and repair capacity after tissue injury are limited. Therefore, the development of new strategies to overcome these constraints is urgently needed. Recent advances in regenerative medicine suggest that pluripotent stem cells are promising stem cell sources for cartilage repair. Pluripotent stem cells are undifferentiated cells that have the capacity to differentiate into different types of cells and can self-renew indefinitely. In the past few decades, numerous attempts have been made to regenerate articular cartilage by using induced pluripotent stem cells (iPSCs). The potential applications of patient-specific iPSCs hold great promise for regenerative medicine and OA treatment. However, there are different culture conditions for the preparation and characterization of human iPSCs-derived chondrocytes (hiChondrocytes). Recent biochemical analyses reported that several paracrine factors such as TGFb, BMPs, WNT, Ihh, and Runx have been shown to be involved in cartilage cell proliferation and differentiation from human iPSCs. In this review, we summarize and discuss the paracrine interactions involved in human iPSCs differentiation into chondrocytes in different cell culture media.

Kindlin-2 regulates skeletal homeostasis by modulating PTH1R in mice

In vertebrates, the type 1 parathyroid hormone receptor (PTH1R) is a critical regulator of skeletal development and homeostasis; however, how it is modulated is incompletely understood. Here we report that deleting Kindlin-2 in osteoblastic cells using the mouse 10-kb Dmp1-Cre largely neutralizes the intermittent PTH-stimulated increasing of bone volume fraction and bone mineral density by impairing both osteoblast and osteoclast formation in murine adult bone. Single-cell profiling reveals that Kindlin-2 loss increases the proportion of osteoblasts, but not mesenchymal stem cells, chondrocytes and fibroblasts, in non-hematopoietic bone marrow cells, with concomitant depletion of osteoblasts on the bone surfaces, especially those stimulated by PTH. Furthermore, haploinsufficiency of Kindlin-2 and Pth1r genes, but not that of either gene, in mice significantly decreases basal and, to a larger extent, PTH-stimulated bone mass, supporting the notion that both factors function in the same genetic pathway. Mechanistically, Kindlin-2 interacts with the C-terminal cytoplasmic domain of PTH1R via aa 474–475 and Gsα. Kindlin-2 loss suppresses PTH induction of cAMP production and CREB phosphorylation in cultured osteoblasts and in bone. Interestingly, PTH promotes Kindlin-2 expression in vitro and in vivo, thus creating a positive feedback regulatory loop. Finally, estrogen deficiency induced by ovariectomy drastically decreases expression of Kindlin-2 protein in osteocytes embedded in the bone matrix and Kindlin-2 loss essentially abolishes the PTH anabolic activity in bone in ovariectomized mice. Thus, we demonstrate that Kindlin-2 functions as an intrinsic component of the PTH1R signaling pathway in osteoblastic cells to regulate bone mass accrual and homeostasis.

miRNA-200c-3p promotes endothelial to mesenchymal transition and neointimal hyperplasia in artery bypass grafts

Increasing evidence has suggested a critical role for endothelial‐to‐mesenchymal transition (EndoMT) in a variety of pathological conditions. MicroRNA‐200c‐3p (miR‐200c‐3p) has been implicated in epithelial‐to‐mesenchymal transition. However, the functional role of miR‐200c‐3p in EndoMT and neointimal hyperplasia in artery bypass grafts remains largely unknown. Here we demonstrated a critical role for miR‐200c‐3p in EndoMT. Proteomics and luciferase activity assays revealed that fermitin family member 2 (FERM2) is the functional target of miR‐200c‐3p during EndoMT. FERMT2 gene inactivation recapitulates the effect of miR‐200c‐3p overexpression on EndoMT, and the inhibitory effect of miR‐200c‐3p inhibition on EndoMT was reversed by FERMT2 knockdown. Further mechanistic studies revealed that FERM2 suppresses smooth muscle gene expression by preventing serum response factor nuclear translocation and preventing endothelial mRNA decay by interacting with Y‐box binding protein 1. In a model of aortic grafting using endothelial lineage tracing, we observed that miR‐200c‐3p expression was dramatically up‐regulated, and that EndoMT contributed to neointimal hyperplasia in grafted arteries. MiR‐200c‐3p inhibition in grafted arteries significantly up‐regulated FERM2 gene expression, thereby preventing EndoMT and reducing neointimal formation. Importantly, we found a high level of EndoMT in human femoral arteries with atherosclerotic lesions, and that miR‐200c‐3p expression was significantly increased, while FERMT2 expression levels were dramatically decreased in diseased human arteries. Collectively, we have documented an unexpected role for miR‐200c‐3p in EndoMT and neointimal hyperplasia in grafted arteries. Our findings offer a novel therapeutic opportunity for treating vascular diseases by specifically targeting the miR‐200c‐3p/FERM2 regulatory axis. © 2020 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

Characterization of Phosphopeptide Positional Isomers on the Transcriptional Co-activator TAZ

The transcriptional co-activator with the PDZ binding motif (TAZ) is a critical regulator of numerous cellular processes such as cell differentiation, development, proliferation, and cell growth. Aberrant expression and activity of TAZ are also featured in many human malignancies. A hallmark of TAZ biology is its cytoplasmic retention mediated by 14-3-3 isoforms in response to phosphorylation of Ser⁸⁹ by members of the LATS family of kinases. Following the observation that TAZ is a highly phosphorylated protein even when Ser⁸⁹ is mutated, high-resolution mass spectrometry employing data-independent acquisition and ion mobility separation was conducted to elucidate additional TAZ phosphorylation sites that may play a role in regulating this critical transcriptional rheostat. Numerous phosphorylation sites on TAZ were identified, including several novel modifications. Of notable interest was the identification of positional phosphoisomers on a phosphopeptide containing Ser⁸⁹. Optimized use of a so-called wideband enhancement acquisition technique yielded higher-quality fragmentation data that confirmed the detection of Ser⁹³ as the positional phosphoisomer partner of Ser⁸⁹ and identified diagnostic fragment ions for the phosphorylation events. Functional analysis indicated that Ser⁹³ phosphorylation reduces the level of 14-3-3 association and increases the level of nuclear translocation, indicating this phosphorylation event attenuates the 14-3-3-mediated TAZ cytoplasmic retention mechanism. These findings suggest that the biological activities of TAZ are likely dynamically regulated by multisite phosphorylation.

Yes-Associated Protein 1: Role and Treatment Prospects in Orthopedic Degenerative Diseases

The Hippo/yes-associated protein 1 signaling pathway is an evolutionarily conserved signaling pathway. This signaling pathway is primarily involved in the regulation of stem cell self-renewal, organ size and tissue regeneration by regulating cell proliferation, differentiation and apoptosis. It plays an important role in embryonic development and tissue organ formation. Yes-associated protein 1 (YAP1) is a key transcription factor in the Hippo signaling pathway and is negatively regulated by this pathway. Changes in YAP1 expression levels affect the occurrence and development of a variety of tumors, but the specific mechanism associated with this phenomenon has not been thoroughly studied. Recently, several studies have described the role of YAP1 in osteoarthritis (OA). Indeed, YAP1 is involved in orthopedic degenerative diseases such as osteoporosis (OP) in addition to OA. In this review, we will summarize the significance of YAP1 in orthopedic degenerative diseases and discuss the potential of the targeted modulation of YAP1 for the treatment of these diseases.

LIM domain proteins Pinch1/2 regulate chondrogenesis and bone mass in mice

The LIM domain-containing proteins Pinch1/2 regulate integrin activation and cell–extracellular matrix interaction and adhesion. Here, we report that deleting Pinch1 in limb mesenchymal stem cells (MSCs) and Pinch2 globally (double knockout; dKO) in mice causes severe chondrodysplasia, while single mutant mice do not display marked defects. Pinch deletion decreases chondrocyte proliferation, accelerates cell differentiation and disrupts column formation. Pinch loss drastically reduces Smad2/3 protein expression in proliferative zone (PZ) chondrocytes and increases Runx2 and Col10a1 expression in both PZ and hypertrophic zone (HZ) chondrocytes. Pinch loss increases sclerostin and Rankl expression in HZ chondrocytes, reduces bone formation, and increases bone resorption, leading to low bone mass. In vitro studies revealed that Pinch1 and Smad2/3 colocalize in the nuclei of chondrocytes. Through its C-terminal region, Pinch1 interacts with Smad2/3 proteins. Pinch loss increases Smad2/3 ubiquitination and degradation in primary bone marrow stromal cells (BMSCs). Pinch loss reduces TGF-β-induced Smad2/3 phosphorylation and nuclear localization in primary BMSCs. Interestingly, compared to those from single mutant mice, BMSCs from dKO mice express dramatically lower protein levels of β-catenin and Yap1/Taz and display reduced osteogenic but increased adipogenic differentiation capacity. Finally, ablating Pinch1 in chondrocytes and Pinch2 globally causes severe osteopenia with subtle limb shortening. Collectively, our findings demonstrate critical roles for Pinch1/2 and a functional redundancy of both factors in the control of chondrogenesis and bone mass through distinct mechanisms.

Recapitulation of Human Embryonic Heartbeat to Promote Differentiation of Hepatic Endoderm to Hepatoblasts

Hepatic development requires multiple sequential physicochemical environmental changes in an embryo, and human pluripotent stem cells (hPSCs) allow for the elucidation of this embryonic developmental process. However, the current in vitro methods for hPSC-hepatic differentiation, which employ various biochemical substances, produce hPSC-derived hepatocytes with less functionality than primary hepatocytes, due to a lack of physical stimuli, such as heart beating. Here, we developed a microfluidic platform that recapitulates the beating of a human embryonic heart to improve the functionality of hepatoblasts derived from hepatic endoderm (HE) in vitro. This microfluidic platform facilitates the application of multiple mechanical stretching forces, to mimic heart beating, to cultured hepatic endoderm cells to identify the optimal stimuli. Results show that stimulated HE-derived hepatoblasts increased cytochrome P450 3A (CYP3A) metabolic activity, as well as the expression of hepatoblast functional markers (albumin, cytokeratin 19 and CYP3A7), compared to unstimulated hepatoblasts. This approach of hepatic differentiation from hPSCs with the application of mechanical stimuli will facilitate improved methods for studying human embryonic liver development, as well as accurate pharmacological testing with functional liver cells.

PINCH-1 regulates mitochondrial dynamics to promote proline synthesis and tumor growth

Reprograming of proline metabolism is critical for tumor growth. Here we show that PINCH-1 is highly expressed in lung adenocarcinoma and promotes proline synthesis through regulation of mitochondrial dynamics. Knockout (KO) of PINCH-1 increases dynamin-related protein 1 (DRP1) expression and mitochondrial fragmentation, which suppresses kindlin-2 mitochondrial translocation and interaction with pyrroline-5-carboxylate reductase 1 (PYCR1), resulting in inhibition of proline synthesis and cell proliferation. Depletion of DRP1 reverses PINCH-1 deficiency-induced defects on mitochondrial dynamics, proline synthesis and cell proliferation. Furthermore, overexpression of PYCR1 in PINCH-1 KO cells restores proline synthesis and cell proliferation, and suppresses DRP1 expression and mitochondrial fragmentation. Finally, ablation of PINCH-1 from lung adenocarcinoma in mouse increases DRP1 expression and inhibits PYCR1 expression, proline synthesis, fibrosis and tumor growth. Our results identify a signaling axis consisting of PINCH-1, DRP1 and PYCR1 that regulates mitochondrial dynamics and proline synthesis, and suggest an attractive strategy for alleviation of tumor growth.

Kindlin-2 Inhibits the Hippo Signaling Pathway by Promoting Degradation of MOB1

The Hippo signaling pathway plays a key role in development and cancer progression. However, molecules that intrinsically inhibit this pathway are less well known. Here, we report that the focal adhesion molecule Kindlin-2 inhibits Hippo signaling by interacting with and degrading MOB1 and promoting the interaction between MOB1 and the E3 ligase praja2. Kindlin-2 thus inhibits the phosphorylation of LATS1 and YAP and promotes YAP translocation into the nucleus, where it activates downstream Hippo target gene transcription. Kindlin-2 depletion activates Hippo/YAP signaling and alleviates renal fibrosis in Kindlin-2 knockout mice with unilateral ureteral occlusion (UUO). Moreover, Kindlin-2 levels are negatively correlated with MOB1 and phosphorylated (p) YAP in samples from patients with renal fibrosis. Altogether, these results demonstrate that Kindlin-2 inhibits Hippo signaling through degradation of MOB1. A specific long-lasting siRNA against Kindlin-2 effectively alleviated UUO-induced renal fibrosis and could be a potential therapy for renal fibrosis.

miR-140 inhibits osteogenic differentiation of human periodontal ligament fibroblasts through ras homolog gene family, member A -transcriptional co-activator with PDZ-binding motif pathway

Osteogenesis induced by mechanical stretch is the main factor affecting the orthodontic treatment. Due to the masticatory force transmitted by tooth, human periodontal ligament fibroblasts (hPDLFs) could enhance osteogenic differentiation, and remolding of periodontal. Therefore, in-depth study of hPDLFs osteogenic differentiation and its regulatory mechanism is helpful in the understanding of periodontal remolding promoted by orthodontic force. In the present study, 3-(4,5-dimethylthiazol)-2,5-diphenyltetrazolium bromide showed that miR-140 inhibited the viability of hPDLFs cells. Moreover, we provided evidence that miR-140 inhibited alkaline phosphatase (ALP) activity, Alizarin Red S (ARS) activity and the mRNA expression of osteogenesis associated genes, including ALP, runt-related transcription factor 2, collagen 1, and osteocalcin. Besides, double-luciferase reporter result demonstrated that Ras homolog gene family, member A (RhoA) was a downstream target gene of miR-140, and by inhibiting RhoA-transcriptional co-activator with PDZ-binding motif (TAZ) signaling pathway, miR-140 suppressed the osteogenesis differentiation of hPDLFs. Furthermore, overexpression of RhoA or TAZ promoted ALP activity, ARS activity and osteogenesis associated genes expression, which was inhibited by miR-140 mimics. Our findings not only provided a possible mechanism of hPDLFs osteogenic differentiation but also proposed the clinical application of miR-140 inhibitor to target RhoA-TAZ for orthodontic treatment.

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.

Gli1+ Periodontium Stem Cells Are Regulated by Osteocytes and Occlusal Force

Teeth are attached to alveolar bone by the periodontal ligament (PDL), which contains stem cells supporting tissue turnover. Here, we identified Gli1+ cells in adult mouse molar PDL as multi-potential stem cells (PDLSCs) giving rise to PDL, alveolar bone, and cementum. They support periodontium tissue turnover and injury repair. Gli1+ PDLSCs are surrounding the neurovascular bundle and more enriched in the apical region. Canonical Wnt signaling is essential for their activation. Alveolar bone osteocytes negatively regulate Gli1+ PDLSCs activity through sclerostin, a Wnt inhibitor. Blockage of sclerostin accelerates the PDLSCs lineage contribution rate in vivo. Sclerostin expression is modulated by physiological occlusal force. Removal of occlusal force upregulates sclerostin and inhibits PDLSCs activation. In summary, Gli1+ cells are the multipotential PDLSCs in vivo. Osteocytes provide negative feedback to PDLSCs and inhibit their activities through sclerostin. Physiological occlusal force indirectly regulates PDLSCs activities by fine-tuning this feedback loop.

Mitochondrial metabolism and cancer metastasis

Metastasis is regarded as the most important cause of cancer-related deaths around the world. During the complicated metastatic cascade, altered mitochondrial metabolism adapts to serve distinct conditions and microenvironments. In this review, we discuss how cells regulate their mitochondria metabolism to adapt to environmental cues during the metastasis, as well as how cancer cells and their tumor micro-environment (TME) are metabolically coupled during the metastatic cascade. We place a strong emphasis on how mitochondrial proline metabolism and extracellular matrix (ECM) are coupled.

Role of Kindlin-2 in cancer progression and metastasis

Cancer metastasis is a complex and multistep process whereby cancer cells escape the confines of the primary site to establish a new residency at distant sites. This multistep process is also known as the invasion-metastasis cascade. The biological and molecular mechanisms that control the invasion-metastasis cascade, which ultimately leads to the spread of cancer cells into distant sites, remain poorly understood. Kindlin-2 (K2) belongs to the 4.1-ezrin-ridixin-moesin (FERM) domain family of proteins, which interact with the cytoplasmic tails of β-integrin subunits, leading to the activation of extensive biological functions. These biological functions include cell migration, differentiation, cancer initiation, development, and invasion. In this review, we will discuss the various molecular signaling pathways that are regulated by K2 during the invasion-metastasis cascade of cancer tumors. These signaling pathways include TGFβ, Wnt/β-Catenin, Hedgehog, p53 and senescence, and cancer stem cell (CSC) maintenance. We will also discuss the molecular signaling pathways that regulate K2 function both at the transcriptional and the posttranslational levels. Finally, we will consider molecular mechanisms to specifically target K2 as novel therapeutic options for cancer treatment.

Kindlin-2 modulates MafA and β-catenin expression to regulate β-cell function and mass in mice

β-Cell dysfunction and reduction in β-cell mass are hallmark events of diabetes mellitus. Here we show that β-cells express abundant Kindlin-2 and deleting its expression causes severe diabetes-like phenotypes without markedly causing peripheral insulin resistance. Kindlin-2, through its C-terminal region, binds to and stabilizes MafA, which activates insulin expression. Kindlin-2 loss impairs insulin secretion in primary human and mouse islets in vitro and in mice by reducing, at least in part, Ca²⁺ release in β-cells. Kindlin-2 loss activates GSK-3β and downregulates β-catenin, leading to reduced β-cell proliferation and mass. Kindlin-2 loss reduces the percentage of β-cells and concomitantly increases that of α-cells during early pancreatic development. Genetic activation of β-catenin in β-cells restores the diabetes-like phenotypes induced by Kindlin-2 loss. Finally, the inducible deletion of β-cell Kindlin-2 causes diabetic phenotypes in adult mice. Collectively, our results establish an important function of Kindlin-2 and provide a potential therapeutic target for diabetes.

Beta cell dysfunction and reduction in beta cell mass are hallmark events in the pathogenesis of diabetes mellitus. We identify focal adhesion protein Kindlin-2 as a key factor that controls insulin synthesis and secretion and beta cell mass by modulating MafA and beta-catenin proteins in pancreatic beta cells.