Increased PLEKHO1 within osteoblasts suppresses Smad-dependent BMP signaling to inhibit bone formation during aging

Epigenetic regulations of cellular senescence in osteoporosis

Osteoporosis (OP) is a prevalent age-related disease that is characterized by a decrease in bone mineral density (BMD) and systemic bone microarchitectural disorders. With age, senescent cells accumulate and exhibit the senescence-associated secretory phenotype (SASP) in bone tissue, leading to the imbalance of bone homeostasis, osteopenia, changes in trabecular bone structure, and increased bone fragility. Cellular senescence in the bone microenvironment involves osteoblasts, osteoclasts, and bone marrow mesenchymal stem cells (BMSCs), whose effects on bone homeostasis are regulated by epigenetics. Therefore, the epigenetic regulatory mechanisms of cellular senescence have received considerable attention as potential targets for preventing and treating osteoporosis. In this paper, we systematically review the mechanisms of aging-associated epigenetic regulation in osteoporosis, emphasizing the impact of epigenetics on cellular senescence, and summarize three current methods of targeting cellular senescence, which is helpful better to understand the pathogenic mechanisms of cellular senescence in osteoporosis and provides strategies for the development of epigenetic drugs for the treatment of osteoporosis.

CKIP-1-Loaded Cartilage-Affinitive Nanoliposomes Reverse Osteoarthritis by Restoring Chondrocyte Homeostasis

Osteoarthritis (OA) is a chronic joint disease characterized by cartilage imbalance and disruption of cartilage extracellular matrix secretion. Identifying key genes that regulate cartilage differentiation and developing effective therapeutic strategies to restore their expression is crucial. In a previous study, we observed a significant correlation between the expression of the gene encoding casein kinase-2 interacting protein-1 (CKIP-1) in the cartilage of OA patients and OA severity scores, suggesting its potential involvement in OA development. To test this hypothesis, we synthesized a chondrocyte affinity plasmid, liposomes CKIP-1, to enhance CKIP-1 expression in chondrocytes. Our results demonstrated that injection of CAP-Lipos-CKIP-1 plasmid significantly improved OA joint destruction and restored joint motor function by enhancing cartilage extracellular matrix (ECM) secretion. Histological and cytological analyses confirmed that CKIP-1 maintains altered the phosphorylation of the signal transduction molecule SMAD2/3 of the transforming growth factor-β (TGF-β) pathway by promoting the phosphorylation of the 8T, 416S sit. Taken together, this work highlights a novel approach for the precise modulation of chondrocyte phenotype from an inflammatory to a noninflammatory state for the treatment of OA and may be broadly applicable to patients suffering from other arthritic diseases.

Asian-European differentiation of schizophrenia-associated genes driven by admixture and natural selection

The European-centered genome-wide association studies of schizophrenia (SCZ) may not be well applied to non-European populations. We analyzed 1,592 reported SCZ-associated genes using the public genome data and found an overall higher Asian-European differentiation on the SCZ-associated variants than at the genome-wide level. Notable examples included 15 missense variants, a regulatory variant SLC5A10-rs1624825, and a damaging variant TSPAN18-rs1001292. Independent local adaptations in recent 25,000 years, after the Asian-European divergence, could have contributed to such genetic differentiation, as were identified at a missense mutation LTN1-rs57646126-A in Asians, and a non-risk allele ZSWIM6-rs72761442-G in Europeans. Altai-Neanderthal-derived alleles may have opposite effects on SCZ susceptibility between ancestries. Furthermore, adaptive introgression was detected on the non-risk haplotype at 1q21.2 in Europeans, while in Asians it was observed on the SCZ risk haplotype at 3p21.31 which is also potentially ultra-violet protective. This study emphasizes the importance of including more representative Asian samples in future SCZ studies.

Histone demethylase KDM7A regulates bone homeostasis through balancing osteoblast and osteoclast differentiation

Histone methylation plays a crucial role in various cellular processes. We previously reported the in vitro function of histone lysine demethylase 7 A (KDM7A) in osteoblast and adipocyte differentiation. The current study was undertaken to investigate the physiological role of KDM7A in bone homeostasis and elucidate the underlying mechanisms. A conditional strategy was employed to delete the Kdm7a gene specifically in osterix-expressing osteoprogenitor cells in mice. The resulting mutant mice exhibited a significant increase in cancellous bone mass, accompanied by an increase in osteoblasts and bone formation, as well as a reduction in osteoclasts, marrow adipocytes and bone resorption. The bone marrow stromal cells (BMSCs) and calvarial pre-osteoblastic cells derived from the mutant mice exhibited enhanced osteogenic differentiation and suppressed adipogenic differentiation. Additionally, osteoclastic precursor cells from the mutant mice exhibited impaired osteoclast differentiation. Co-culturing BMSCs from the mutant mice with wild-type osteoclast precursor cells resulted in the inhibition of osteoclast differentiation. Mechanistic investigation revealed that KDM7A was able to upregulate the expression of fibroblast activation protein α (FAP) and receptor activator of nuclear factor κB ligand (RANKL) in BMSCs through removing repressive di-methylation marks of H3K9 and H3K27 from Fap and Rankl promoters. Moreover, recombinant FAP attenuated the dysregulation of osteoblast and adipocyte differentiation in BMSCs from Kdm7a deficient mice. Finally, Kdm7a deficiency prevented ovariectomy-induced bone loss in mice. This study establish the role of KDM7A in bone homeostasis through its epigenetic regulation of osteoblast and osteoclast differentiation. Consequently, inhibiting KDM7A may prove beneficial in ameliorating osteoporosis. KDM7A suppresses osteoblast differentiation and bone formation through. upregulating FAP expression and inactivating canonical Wnt signaling, and conversely promotes osteoclast differentiation and bone resorption through upregulating RANKL expression. These are based on its epigenetic removal of the repressive H3K9me2 and H3K27me2 marks from Fap and Rankl promoters. As a result, the expression of KDM7A in osteoprogenitor cells tends to negatively modulate bone mass.

The roles and regulatory mechanisms of TGF-β and BMP signaling in bone and cartilage development, homeostasis and disease

Transforming growth factor-βs (TGF-βs) and bone morphometric proteins (BMPs) belong to the TGF-β superfamily and perform essential functions during osteoblast and chondrocyte lineage commitment and differentiation, skeletal development, and homeostasis. TGF-βs and BMPs transduce signals through SMAD-dependent and -independent pathways; specifically, they recruit different receptor heterotetramers and R-Smad complexes, resulting in unique biological readouts. BMPs promote osteogenesis, osteoclastogenesis, and chondrogenesis at all differentiation stages, while TGF-βs play different roles in a stage-dependent manner. BMPs and TGF-β have opposite functions in articular cartilage homeostasis. Moreover, TGF-β has a specific role in maintaining the osteocyte network. The precise activation of BMP and TGF-β signaling requires regulatory machinery at multiple levels, including latency control in the matrix, extracellular antagonists, ubiquitination and phosphorylation in the cytoplasm, nucleus-cytoplasm transportation, and transcriptional co-regulation in the nuclei. This review weaves the background information with the latest advances in the signaling facilitated by TGF-βs and BMPs, and the advanced understanding of their diverse physiological functions and regulations. This review also summarizes the human diseases and mouse models associated with disordered TGF-β and BMP signaling. A more precise understanding of the BMP and TGF-β signaling could facilitate the development of bona fide clinical applications in treating bone and cartilage disorders.

Regulation of the immune microenvironment by pioglitazone-loaded polylactic glycolic acid nanosphere composite scaffolds to promote vascularization and bone regeneration

Osteogenesis is caused by multiple factors, and the inflammatory response, osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs), regeneration of blood vessels, and other factors must be considered in bone tissue engineering. To effectively repair bone defect, it is important to decrease excessive inflammation, enhance the differentiation of mesenchymal stem cells into osteoblasts, and stimulate angiogenesis. Herein, nano-attapulgite (ATP), polyvinyl alcohol (PVA), and gelatin (GEL) scaffolds were produced using 3D printing technology and pioglitazone (PIO)-containing polylactic acid-glycolic acid (PLGA) nanospheres were added. In both in vitro and in vivo studies, material scaffolds with PIO-loaded polylactic acid-glycolic acid nanospheres could reduce the inflammatory response by encouraging macrophage polarization from M1 to M2 and promoting the osteogenic differentiation of BMSCs by activating the BMP2/Smad/RUNX2 signal pathway to repair bone defects. The vascularization of human umbilical vein endothelial cells (HUVECs) through the PI3K/AKT/HIF1-/VEGF pathway was also encouraged. In vivo research using PIO-containing PLGA nanospheres revealed massive collagen deposition in skin models. These findings indicate a potentially effective scaffold for bone healing, when PLGA nanospheres-which contain the drug PIO-are combined with ATP/PVA/GEL scaffolds.

Small interfering RNAs in the management of human osteoporosis

BACKGROUND

Osteoporosis results in reduced bone mass and consequent bone fragility. Small interfering RNAs (siRNAs) can be used for therapeutic purposes, as molecular targets or as useful markers to test new therapies.

SOURCES OF DATA

A systematic search of different databases to May 2023 was performed to define the role of siRNAs in osteoporosis therapy. Fourteen suitable studies were identified.

AREAS OF AGREEMENT

SiRNAs may be useful in studying metabolic processes in osteoporosis and identify possible therapeutic targets for novel drug therapies.

AREAS OF CONTROVERSY

The metabolic processes of osteoporosis are regulated by many genes and cytokines that can be targeted by siRNAs. However, it is not easy to predict whether the in vitro responses of the studied siRNAs and drugs are applicable in vivo.

GROWING POINTS

Metabolic processes can be affected by the effect of gene dysregulation mediated by siRNAs on various growth factors.

AREAS TIMELY FOR DEVELOPING RESEARCH

Despite the predictability of pharmacological response of siRNA in vitro, similar responses cannot be expected in vivo.

Cellular senescence in skeletal disease: mechanisms and treatment

The musculoskeletal system supports the movement of the entire body and provides blood production while acting as an endocrine organ. With aging, the balance of bone homeostasis is disrupted, leading to bone loss and degenerative diseases, such as osteoporosis, osteoarthritis, and intervertebral disc degeneration. Skeletal diseases have a profound impact on the motor and cognitive abilities of the elderly, thus creating a major challenge for both global health and the economy. Cellular senescence is caused by various genotoxic stressors and results in permanent cell cycle arrest, which is considered to be the underlying mechanism of aging. During aging, senescent cells (SnCs) tend to aggregate in the bone and trigger chronic inflammation by releasing senescence-associated secretory phenotypic factors. Multiple signalling pathways are involved in regulating cellular senescence in bone and bone marrow microenvironments. Targeted SnCs alleviate age-related degenerative diseases. However, the association between senescence and age-related diseases remains unclear. This review summarises the fundamental role of senescence in age-related skeletal diseases, highlights the signalling pathways that mediate senescence, and discusses potential therapeutic strategies for targeting SnCs.

Inactivation of Ihh in Sp7-Expressing Cells Inhibits Osteoblast Proliferation, Differentiation, and Bone Formation, Resulting in a Dwarfism Phenotype with Severe Skeletal Dysplasia in Mice

Indian hedgehog (Ihh) is an indispensable paracrine factor for proper tissue patterning, skeletogenesis, and cellular proliferation. Recent genetic studies have revealed critical roles of chondrocyte-derived Ihh in regulating chondrocyte proliferation, hypertrophy and cartilage ossification. However, the functions of Sp7-expressing cell-derived Ihh in osteoblast differentiation and bone formation remain unclear. Sp7 is an essential transcription factor for osteoblast differentiation. In the current study, we generated Sp7-iCre; Ihh^fl/fl mice, in which the Ihh gene was specifically deleted in Sp7-expressing cells to investigate the roles of Ihh. Ihh ablation in Sp7-expressing cells resulted in a dwarfism phenotype with severe skeletal dysplasia and lethality at birth, but with normal joint segmentation. Sp7-iCre; Ihh^fl/fl mice had fewer osteoblasts, almost no cortical and trabecular bones, smaller skulls, and wider cranial sutures. Additionally, the levels of osteogenesis- and angiogenesis-related genes, and of major bone matrix protein genes were significantly reduced. These results demonstrated that Ihh regulates bone formation in Sp7-expressing cells. Ihh deficiency in primary osteoblasts cultured in vitro inhibited their proliferation, differentiation, and mineralization ability, and reduced the expression of osteogenesis-related genes. Moreover, the deletion of Ihh also attenuated the Bmp2/Smad/Runx2 pathway in E18.5 tibial and primary osteoblasts. The activity of primary osteoblasts in mutant mice was rescued after treatment with rhBMP2. In summary, our data revealed that Ihh in Sp7-expressing cells plays an indispensable role in osteoblast differentiation, mineralization, and embryonic osteogenesis, further implicated that its pro-osteogenic role may be mediated through the canonical Bmp2/Smad/Runx2 pathway.

NEDD4 E3 Ligases: Functions and Mechanisms in Bone and Tooth

Protein ubiquitination is a precisely controlled enzymatic cascade reaction belonging to the post-translational modification of proteins. In this process, E3 ligases catalyze the binding of ubiquitin (Ub) to protein substrates and define specificity. The neuronally expressed developmentally down-regulated 4 (NEDD4) subfamily, belonging to the homology to E6APC terminus (HECT) class of E3 ligases, has recently emerged as an essential determinant of multiple cellular processes in different tissues, including bone and tooth. Here, we place special emphasis on the regulatory role of the NEDD4 subfamily in the molecular and cell biology of osteogenesis. We elucidate in detail the specific roles, downstream substrates, and upstream regulatory mechanisms of the NEDD4 subfamily. Further, we provide an overview of the involvement of E3 ligases and deubiquitinases in the development, repair, and regeneration of another mineralized tissue—tooth.

Bu-Gu-Sheng-Sui decoction promotes osteogenesis via activating the ERK/Smad signaling pathways

Osteoporosis is a systemic metabolic skeletal disease, which becomes a common public health problem that seriously endangers people’s health. Bu-Gu-Sheng-Sui decoction (BGSSD) is a safe and effective Chinese medicine formulation for the treatment of osteoporosis. Numerous studies have indicated that it played a significant role in bone anabolism. However, the underlying mechanism remains unclear. Herein, we selected senescence-accelerated mice prone 6 (SAMP6) and MC3T3-E1 cells to study the effects of BGSSD on osteogenesis and then investigated the potential mechanism of BGSSD. Our research found that BGSSD protected the bone mass in SAMP6, increased the expression of osteogenic specific factor Runx2, and improved bone trabecular structure. In vitro, BGSSD accelerated the proliferation and differentiation of MC3T3-E1 cells, which was characterized by stimulating the activity of Alkaline phosphatase (ALP) and raising the expression of Runx2. Moreover, BGSSD could effectively boost the expression levels of ERK and Smad in SAMP6 and MC3T3-E1. Therefore, we speculate that BGSSD may promote bone formation through ERK/Smad pathways. Collectively, our results highlight the importance of BGSSD as a compound in promoting osteogenic differentiation and osteogenesis, demonstrating that BGSSD may become a latent drug to prevent and treat osteoporosis.

Improved repair of rabbit calvarial defects with hydroxyapatite/chitosan/polycaprolactone composite scaffold-engrafted EPCs and BMSCs

Endothelial progenitor cells (EPCs) expressing vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) and bone marrow mesenchymal stem cells (BMSCs) expressing endogenous bone morphogenetic protein-2 (BMP-2) play the important role in new bone formation. This study investigated the effects of a porous hydroxyapatite (HA)/chitosan (CS)/polycaprolactone (PCL) composite scaffold-engrafted EPCs and BMSCs on the expression of BMP-2, VEGF, and PDGF in the calvarial defect rabbit model in vivo. It showed that a three-dimensional composite scaffold was successfully constructed by physical interaction with a pore size of 250 μm. The HA/CS/PCL scaffold degraded slowly within 10 weeks and showed non-cytotoxicity. By X-ray, micro-CT examination, and H&E staining, compared with the HA/CS/PCL group, HA/CS/PCL + EPCs, HA/CS/PCL + BMSCs, and HA/CS/PCL + EPCs + BMSCs groups performed a more obvious repair effect, and the dual factor group presented particularly significant improvement on the percentages of bone volume at week 4 and week 8, with evident bone growth. Osteogenesis marker (BMP-2) and vascularization marker (VEGF and PDGF) expression in the dual factor group were much better than those of the HA/CS/PCL control group and single factor groups. Collectively, the HA/CS/PCL composite scaffold-engrafting EPCs and BMSCs is effective to repair calvarial defects by regulating endogenous expression of BMP-2, VEGF, and PDGF. Thus, this study provides important implications for the potential clinical application of biomaterial composite scaffold-engrafted engineering cells.

Transcriptomic Analysis of Laying Hens Revealed the Role of Aging-Related Genes during Forced Molting

Molting in birds provides us with an ideal genetic model for understanding aging and rejuvenation since birds present younger characteristics for reproduction and appearance after molting. Forced molting (FM) by fasting in chickens causes aging of their reproductive system and then promotes cell redevelopment by providing water and feed again. To reveal the genetic mechanism of rejuvenation, we detected blood hormone indexes and gene expression levels in the hypothalamus and ovary of hens from five different periods during FM. Three hormones were identified as participating in FM. Furthermore, the variation trends of gene expression levels in the hypothalamus and ovary at five different stages were found to be basically similar using transcriptome analysis. Among them, 45 genes were found to regulate cell aging during fasting stress and 12 genes were found to promote cell development during the recovery period in the hypothalamus. In addition, five hub genes (INO80D, HELZ, AGO4, ROCK2, and RFX7) were identified by WGCNA. FM can restart the reproductive function of aged hens by regulating expression levels of genes associated with aging and development. Our study not only enriches the theoretical basis of FM but also provides insights for the study of antiaging in humans and the conception mechanism in elderly women.

E3 Ubiquitin Ligase-Mediated Regulation of Osteoblast Differentiation and Bone Formation

The ubiquitin–proteasome system (UPS) is an essential pathway that regulates the homeostasis and function of intracellular proteins and is a crucial protein-degradation system in osteoblast differentiation and bone formation. Abnormal regulation of ubiquitination leads to osteoblast differentiation disorders, interfering with bone formation and ultimately leading to osteoporosis. E3 ubiquitin ligases (E3) promote addition of a ubiquitin moiety to substrate proteins, specifically recognizing the substrate and modulating tyrosine kinase receptors, signaling proteins, and transcription factors involved in the regulation of osteoblast proliferation, differentiation, survival, and bone formation. In this review, we summarize current progress in the understanding of the function and regulatory effects of E3 ligases on the transcription factors and signaling pathways that regulate osteoblast differentiation and bone formation. A deep understanding of E3 ligase-mediated regulation of osteoblast differentiation provides a scientific rationale for the discovery and development of novel E3-targeting therapeutic strategies for osteoporosis.

CDC20 promotes bone formation via APC/C dependent ubiquitination and degradation of p65

The E3 ubiquitin ligase complex CDC20‐activated anaphase‐promoting complex/Cyclosome (APC/C^CDC20) plays a critical role in governing mitotic progression by targeting key cell cycle regulators for degradation. Cell division cycle protein 20 homolog (CDC20), the co‐activator of APC/C, is required for full ubiquitin ligase activity. In addition to its well‐known cell cycle‐related functions, we demonstrate that CDC20 plays an essential role in osteogenic commitment of bone marrow mesenchymal stromal/stem cells (BMSCs). Cdc20 conditional knockout mice exhibit decreased bone formation and impaired bone regeneration after injury. Mechanistically, we discovered a functional interaction between the WD40 domain of CDC20 and the DNA‐binding domain of p65. Moreover, CDC20 promotes the ubiquitination and degradation of p65 in an APC11‐dependent manner. More importantly, knockdown of p65 rescues the bone loss in Cdc20 conditional knockout mice. Our current work reveals a cell cycle‐independent function of CDC20, establishes APC11^CDC20 as a pivotal regulator for bone formation by governing the ubiquitination and degradation of p65, and may pave the way for treatment of bone‐related diseases.

The Smad Dependent TGF-β and BMP Signaling Pathway in Bone Remodeling and Therapies

Bone remodeling is a continuous process that maintains the homeostasis of the skeletal system, and it depends on the homeostasis between bone-forming osteoblasts and bone-absorbing osteoclasts. A large number of studies have confirmed that the Smad signaling pathway is essential for the regulation of osteoblastic and osteoclastic differentiation during skeletal development, bone formation and bone homeostasis, suggesting a close relationship between Smad signaling and bone remodeling. It is known that Smads proteins are pivotal intracellular effectors for the members of the transforming growth factor-β (TGF-β) and bone morphogenetic proteins (BMP), acting as transcription factors. Smad mediates the signal transduction in TGF-β and BMP signaling pathway that affects both osteoblast and osteoclast functions, and therefore plays a critical role in the regulation of bone remodeling. Increasing studies have demonstrated that a number of Smad signaling regulators have potential functions in bone remodeling. Therefore, targeting Smad dependent TGF-β and BMP signaling pathway might be a novel and promising therapeutic strategy against osteoporosis. This article aims to review recent advances in this field, summarizing the influence of Smad on osteoblast and osteoclast function, together with Smad signaling regulators in bone remodeling. This will facilitate the understanding of Smad signaling pathway in bone biology and shed new light on the modulation and potential treatment for osteoporosis.

Let-7i-5p functions as a putative osteogenic differentiation promoter by targeting CKIP-1

MicroRNA (miRNA) is an endogenous regulatory small molecule RNA. Growing evidence shows that miRNA plays an important regulatory role in gene expression. Although miRNA is a more intensive regulatory noncoding RNA in recent years, few studies have investigated the regulation of targeting genes involved in bone repair. Meanwhile, as a negative bone regulator, previous studies showed that casein kinase 2-interacting protein 1 (CKIP-1) is closely associated with bone formation and regeneration. However, the gene knockout method may not be suitable for clinical application. Therefore, it was hypothesized that miRNA molecules can inhibit the expression of CKIP-1 and ultimately promote the osteogenesis process. The present study revealed that let-7i-5p plays an important role in the process of fracture healing by inhibiting the expression of CKIP-1. Related research provides a novel gene target for fracture healing.

Supplementary information

The online version of this article (10.1007/s10616-020-00444-1) contains supplementary material, which is available to authorized users.

Targeted overexpression of the long noncoding RNA ODSM can regulate osteoblast function in vitro and in vivo

Ameliorating bone loss caused by mechanical unloading is a substantial clinical challenge, and the role of noncoding RNAs in this process has attracted increasing attention. In this study, we found that the long noncoding RNA osteoblast differentiation-related lncRNA under simulated microgravity (lncRNA ODSM) could inhibit osteoblast apoptosis and promote osteoblast mineralization in vitro. The increased expression level of the lncRNA ODSM partially reduced apoptosis and promoted differentiation in MC3T3-E1 cells under microgravity unloading conditions, and the effect was partially dependent on miR-139-3p. LncRNA ODSM supplementation in hindlimb-unloaded mice caused a decrease in the number of apoptotic cells in bone tissue and an increase in osteoblast activity. Furthermore, targeted overexpression of the lncRNA ODSM in osteoblasts partially reversed bone loss induced by mechanical unloading at the microstructural and biomechanical levels. These findings are the first to suggest the potential value of the lncRNA ODSM in osteoporosis therapy and the treatment of pathological osteopenia.

Deficiency of Macf1 in osterix expressing cells decreases bone formation by Bmp2/Smad/Runx2 pathway

Microtubule actin cross-linking factor 1 (Macf1) is a spectraplakin family member known to regulate cytoskeletal dynamics, cell migration, neuronal growth and cell signal transduction. We previously demonstrated that knockdown of Macf1 inhibited the differentiation of MC3T3-E1 cell line. However, whether Macf1 could regulate bone formation in vivo is unclear. To study the function and mechanism of Macf1 in bone formation and osteogenic differentiation, we established osteoblast-specific Osterix (Osx) promoter-driven Macf1 conditional knockout mice (Macf1^f/f Osx-Cre). The Macf1^f/f Osx-Cre mice displayed delayed ossification and decreased bone mass. Morphological and mechanical studies showed deteriorated trabecular microarchitecture and impaired biomechanical strength of femur in Macf1^f/f Osx-Cre mice. In addition, the differentiation of primary osteoblasts isolated from calvaria was inhibited in Macf1^f/f Osx-Cre mice. Deficiency of Macf1 in primary osteoblasts inhibited the expression of osteogenic marker genes (Col1, Runx2 and Alp) and the number of mineralized nodules. Furthermore, deficiency of Macf1 attenuated Bmp2/Smad/Runx2 signalling in primary osteoblasts of Macf1^f/f Osx-Cre mice. Together, these results indicated that Macf1 plays a significant role in bone formation and osteoblast differentiation by regulating Bmp2/Smad/Runx2 pathway, suggesting that Macf1 might be a therapeutic target for bone disease.

Macrophage-Derived Extracellular Vesicles as Carriers of Alarmins and Their Potential Involvement in Bone Homeostasis

Extracellular vesicles are a heterogeneous group of cell-derived membranous structures, which facilitate intercellular communication. Recent studies have highlighted the importance of extracellular vesicles in bone homeostasis, as mediators of crosstalk between different bone-resident cells. Osteoblasts and osteoclasts are capable of releasing various types of extracellular vesicles that promote both osteogenesis, as well as, osteoclastogenesis, maintaining bone homeostasis. However, the contribution of immune cell-derived extracellular vesicles in bone homeostasis remains largely unknown. Recent proteomic studies showed that alarmins are abundantly present in/on macrophage-derived EVs. In this review we will describe these alarmins in the context of bone matrix regulation and discuss the potential contribution macrophage-derived EVs may have in this process.

Physiological functions of CKIP-1: From molecular mechanisms to therapy implications

The casein kinase 2 interacting protein-1 (CKIP-1, also known as PLEKHO1) is initially identified as a specific CK2α subunit-interacting protein. Subsequently, various proteins, including CPα, PAK1, Arp2/3, HDAC1, c-Jun, ATM, Smurf1, Rpt6, Akt, IFP35, TRAF6, REGγ and CARMA1, were reported to interact with CKIP-1. Owing to the great diversity of interacted proteins, CKIP-1 exhibits multiple biologic functions in cell morphology, cell differentiation and cell apoptosis. Besides, these functions are subcellular localization, cell type, and regulatory signaling dependent. CKIP-1 is involved in biological processes consisting of bone formation, tumorigenesis and immune regulation. Importantly, deregulation of CKIP-1 results in osteoporosis, tumor, and atherosclerosis. In this review, we introduce the molecular functions, biological processes and promising of therapeutic strategies. Through summarizing the intrinsic mechanisms, we expect to open new therapeutic avenues for CKIP-1.

Osteoblastic PLEKHO1 contributes to joint inflammation in rheumatoid arthritis

Background

Osteoblasts participating in the inflammation regulation gradually obtain concerns. However, its role in joint inflammation of rheumatoid arthritis (RA) is largely unknown. Here, we investigated the role of osteoblastic pleckstrin homology domain-containing family O member 1 (PLEKHO1), a negative regulator of osteogenic lineage activity, in regulating joint inflammation in RA.

Methods

The level of osteoblastic PLEKHO1 in RA patients and collagen-induced arthritis (CIA) mice was examined. The role of osteoblastic PLEKHO1 in joint inflammation was evaluated by a CIA model and a K/BxN serum-transfer arthritis (STA) model which were induced in osteoblast-specific Plekho1 conditional knockout mice and mice expressing high Plekho1 exclusively in osteoblasts, respectively. The effect of osteoblastic PLEKHO1 inhibition was explored in a CIA mice model and a non-human primate arthritis model. The mechanism of osteoblastic PLEKHO1 in regulating joint inflammation were performed by a series of in vitro studies.

Results

PLEKHO1 was highly expressed in osteoblasts from RA patients and CIA mice. Osteoblastic Plekho1 deletion ameliorated joint inflammation, whereas overexpressing Plekho1 only within osteoblasts exacerbated local inflammation in CIA mice and STA mice. PLEKHO1 was required for TRAF2-mediated RIP1 ubiquitination to activate NF-κB for inducing inflammatory cytokines production in osteoblasts. Moreover, osteoblastic PLEKHO1 inhibition diminished joint inflammation and promoted bone formation in CIA mice and non-human primate arthritis model.

Conclusions

These data strongly suggest that the highly expressed PLEKHO1 in osteoblasts contributes to joint inflammation in RA. Targeting osteoblastic PLEKHO1 may exert dual therapeutic action of alleviating joint inflammation and promoting bone formation in RA.

Insights into siRNA Transfection in Suspension: Efficient Gene Silencing in Human Mesenchymal Stem Cells Encapsulated in Hyaluronic Acid Hydrogel

Small interfering RNAs (siRNAs) are powerful tools for post-transcriptional gene silencing, which offers enormous opportunities for tissue engineering applications. However, poor serum stability, inefficient intracellular delivery, and inevitable toxicity of transfection reagents are the key barriers for their clinical translation. Thus, innovative strategies that allow safe and efficient intracellular delivery of the nucleic acid drugs at the desired site is urgently needed for a smooth clinical translation of therapeutically appealing siRNA-based technology. In this regard, we have developed an innovative siRNA transfection protocol that employs a short incubation time of just 5 min. This allows easy transfection in suspension followed by transplantation of the cells in a hyaluronic acid (HA) hydrogel system. We also report here the unique ability of siRNA to bind HA that was quantified by siRNA release and rheological characterization of the HA-hydrogel. Such interactions also showed promising results to deliver functional siRNA in suspension transfection conditions within 30 min using native HA, although removal of excess HA by centrifugation seem to be essential. In the 2D experiments, suspension transfection of hMSCs with RNAiMAX resulted in ≈90% gene silencing (with or without removal of the excess reagent by centrifugation), while HA demonstrated a modest ≈40% gene silencing after removal of excess reagent after 30 min. Transplantation of such transfected cells in the HA-hydrogel system demonstrated an improved knockdown (≈90% and ≈60% with RNAiMAX and HA respectively after 48 h), with lower cytotoxicity (up to 5-days) as determined by PrestoBlue assay. The gene silencing efficiency in the 2D and 3D conditions were also confirmed at the protein levels by Western blot analysis. We postulate this novel transfection method could be applied for in vivo applications as it allows minimal manipulation of cells that are to be transplanted and reduce toxicity.

Extracellular vesicle and mesenchymal stem cells in bone regeneration: recent progress and perspectives

Transplanting mesenchymal stem cells (MSCs) has been widely perceived as an ideal treatment for bone repair and regeneration, owing to their differential potential. However, researchers found that very few intravenous MSCs could stay in the target tissue, whereas the majority of them are trapped in liver, spleen, and lung, largely reducing its therapeutic effects. Recently, extracellular vesicles (EVs) have attracted increased attention due to their function in bone repair and advantages over traditional cell therapy. Also, MSCs-derived EVs are likely to achieve the osteogenic goal via modulating the cells and cytokines involved in bone metabolism. This review aims at summarizing the function of EVs and MSCs in bone metabolism and regeneration. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 243-250, 2019.

Intracellular attenuation of BMP signaling via CKIP-1/Smurf1 is essential during neural crest induction

The neural crest is induced at the neural plate border during gastrulation by combined bone morphogenetic protein (BMP), fibroblast growth factor (FGF), and Wnt signaling. While intermediate BMP levels are critical for this induction, secreted BMP inhibitors are largely absent from the neural plate border. Here, we propose a morphogen model in which intracellular attenuation of BMP signaling sets the required intermediate levels to maintain neural crest induction. We show that the scaffold protein casein kinase interacting protein 1 (CKIP-1) and ubiquitin ligase Smad ubiquitin regulatory factor 1 (Smurf1) are coexpressed with BMP4 at the chick neural plate border. Knockdown of CKIP-1 during a critical period between gastrulation and neurulation causes neural crest loss. Consistent with specific BMP modulation, CKIP-1 loss suppresses phospho-Smads 1/5/8 (pSmad1/5/8) and BMP reporter output but has no effect on Wnt signaling; Smurf1 overexpression (OE) acts similarly. Epistasis experiments further show that CKIP-1 rescues Smurf1-mediated neural crest loss. The results support a model in which CKIP-1 suppresses Smurf1-mediated degradation of Smads, uncovering an intracellular mechanism for attenuation of BMP signaling to the intermediate levels required for maintenance of neural crest induction.

The role of CKIP-1 in osteoporosis development and treatment

Osteoporosis is a systemic skeletal disorder characterized by reduced bone mass and deterioration of bone microarchitecture, which results in increased bone fragility and fracture risk. Casein kinase 2-interacting protein-1 (CKIP-1) is a protein that plays an important role in regulation of bone formation. The effect of CKIP-1 on bone formation is mainly mediated through negative regulation of the bone morphogenetic protein pathway. In addition, CKIP-1 has an important role in the progression of osteoporosis. This review provides a summary of the recent studies on the role of CKIP-1 in osteoporosis development and treatment.

Cite this article: X. Peng, X. Wu, J. Zhang, G. Zhang, G. Li, X. Pan. The role of CKIP-1 in osteoporosis development and treatment. Bone Joint Res 2018;7:173–178. DOI: 10.1302/2046-3758.72.BJR-2017-0172.R1.