Multiple functions of BMPs in chondrogenesis

A novel mechanism behind irreversible development of cartilage degradation driven articular cartilage defects revealed by rat model: The chain reaction initiated by extracellular vesicles delivered LOC102546541

BACKGROUND

Articular cartilage defects (ACD) are injuries with a diameter greater than 3 mm, resulting from wear and tear on joints. When the diameter of the defect exceeds 6 mm, it can further damage the surrounding joint cartilage, causing osteoarthritis (OA). Try to explain why OA is an irreversible disease, we hypothesize that damaged articular chondrocytes (DAC) may have reduced capacities to repair cartilage because its extracellular vesicle (EVs) that might directly contribute to OA formation.

METHODS

In this study, DAC-EVs and AC-EVs were isolated using ultracentrifugation. Next-generation sequencing was employed to screen for a pathogenic long non-coding RNA (lncRNA). After verifying its function in vitro, the corresponding small interfering RNA (siRNA) was constructed and loaded into extracellular vesicles, which were then injected into the knee joint cavities of rats.

RESULTS

The results revealed that DAC-EVs packaged lncRNA LOC102546541 acts as a competitive endogenous RNA (ceRNA) of MMP13, down-regulating miR-632. Consequently, the function of MMP13 in degrading the extracellular matrix is enhanced, promoting the development of osteoarthritis.

CONCLUSIONS

This study uncovered a novel mode of OA pathogenesis using rat models, which DAC deliver pathogenic LOC102546541 packaged EVs to normal articular chondrocytes, amplifying the degradation of the extracellular matrix. Nonetheless, the functions of highly homologous human gene of LOC102546541 need to be verified in the future.

CRISPR-GEM: A Novel Machine Learning Model for CRISPR Genetic Target Discovery and Evaluation

CRISPR gene editing strategies are shaping cell therapies through precise and tunable control over gene expression. However, achieving reliable therapeutic effects with improved safety and efficacy requires informed target gene selection. This depends on a thorough understanding of the involvement of target genes in gene regulatory networks (GRNs) that regulate cell phenotype and function. Machine learning models have been previously used for GRN reconstruction using RNA-seq data, but current techniques are limited to single cell types and focus mainly on transcription factors. This restriction overlooks many potential CRISPR target genes, such as those encoding extracellular matrix components, growth factors, and signaling molecules, thus limiting the applicability of these models for CRISPR strategies. To address these limitations, we have developed CRISPR-GEM, a multi-layer perceptron (MLP)-based synthetic GRN constructed to accurately predict the downstream effects of CRISPR gene editing. First, input and output nodes are identified as differentially expressed genes between defined experimental and target cell/tissue types respectively. Then, MLP training learns regulatory relationships in a black-box approach allowing accurate prediction of output gene expression using only input gene expression. Finally, CRISPR-mimetic perturbations are made to each input gene individually and the resulting model predictions are compared to those for the target group to score and assess each input gene as a CRISPR candidate. The top scoring genes provided by CRISPR-GEM therefore best modulate experimental group GRNs to motivate transcriptomic shifts towards a target group phenotype. This machine learning model is the first of its kind for predicting optimal CRISPR target genes and serves as a powerful tool for enhanced CRISPR strategies across a range of cell therapies.

Biomimetic Hydrogels as the Inductive Endochondral Ossification Template for Promoting Bone Regeneration

Repairing critical size bone defects (CSBD) is a major clinical challenge and requires effective intervention by biomaterial scaffolds. Inspired by the fact that the cartilaginous template-based endochondral ossification (ECO) process is crucial to bone healing and development, developing biomimetic biomaterials to promote ECO is recognized as a promising approach for repairing CSBD. With the unique highly hydrated 3D polymeric network, hydrogels can be designed to closely emulate the physiochemical properties of cartilage matrix to facilitate ECO. In this review, the various preparation methods of hydrogels possessing the specific physiochemical properties required for promoting ECO are introduced. The materiobiological impacts of the physicochemical properties of hydrogels, such as mechanical properties, topographical structures and chemical compositions on ECO, and the associated molecular mechanisms related to the BMP, Wnt, TGF-β, HIF-1α, FGF, and RhoA signaling pathways are further summarized. This review provides a detailed coverage on the materiobiological insights required for the design and preparation of hydrogel-based biomaterials to facilitate bone regeneration.

3D Bioprinting Strategies for Articular Cartilage Tissue Engineering

Articular cartilage is the avascular and aneural tissue which is the primary connective tissue covering the surface of articulating bone. Traumatic damage or degenerative diseases can cause articular cartilage injuries that are common in the population. As a result, the demand for new therapeutic options is continually increasing for older people and traumatic young patients. Many attempts have been made to address these clinical needs to treat articular cartilage injuries, including osteoarthritis (OA); however, regenerating highly qualified cartilage tissue remains a significant obstacle. 3D bioprinting technology combined with tissue engineering principles has been developed to create biological tissue constructs that recapitulate the anatomical, structural, and functional properties of native tissues. In addition, this cutting-edge technology can precisely place multiple cell types in a 3D tissue architecture. Thus, 3D bioprinting has rapidly become the most innovative tool for manufacturing clinically applicable bioengineered tissue constructs. This has led to increased interest in 3D bioprinting in articular cartilage tissue engineering applications. Here, we reviewed current advances in bioprinting for articular cartilage tissue engineering.

Gli1 labels progenitors during chondrogenesis in postnatal mice

Skeletal growth promoted by endochondral ossification is tightly coordinated by self-renewal and differentiation of chondrogenic progenitors. Emerging evidence has shown that multiple skeletal stem cells (SSCs) participate in cartilage formation. However, as yet, no study has reported the existence of common long-lasting chondrogenic progenitors in various types of cartilage. Here, we identify Gli1+ chondrogenic progenitors (Gli1+ CPs), which are distinct from PTHrP+ or FoxA2+ SSCs, are responsible for the lifelong generation of chondrocytes in the growth plate, vertebrae, ribs, and other cartilage. The absence of Gli1+ CPs leads to cartilage defects and dwarfishness phenotype in mice. Furthermore, we show that the BMP signal plays an important role in self-renewal and maintenance of Gli1+ CPs. Deletion of Bmpr1α triggers Gli1+ CPs quiescence exit and causes the exhaustion of Gli1+ CPs, consequently disrupting columnar cartilage. Collectively, our data demonstrate that Gli1+ CPs are common long-term chondrogenic progenitors in multiple types of cartilage and are essential to maintain cartilage homeostasis.

In vitro inflammatory multi-cellular model of osteoarthritis

Objective

Osteoarthritis (OA) is a chronic joint disease, with limited treatment options, characterized by inflammation and matrix degradation, and resulting in severe pain or disability. Progressive inflammatory interaction among key cell types, including chondrocytes and macrophages, leads to a cascade of intra- and inter-cellular events which culminate in OA induction. In order to investigate these interactions, we developed a multi-cellular in vitro OA model, to characterize OA progression, and identify and evaluate potential OA therapeutics in response to mediators representing graded levels of inflammatory severity.

Methods

We compared macrophages, chondrocytes and their co-culture responses to "low" Interleukin-1 (IL-1) or "high" IL-1/tumor necrosis factor (IL-1/TNF) levels of inflammation. We also investigated response changes following the administration of dexamethasone (DEX) or mesenchymal stromal cell (MSC) treatment via a combination of gene expression and secretory changes, reflecting not only inflammation, but also chondrocyte function.

Results

Inflamed chondrocytes presented an osteoarthritic-like phenotype characterized by high gene expression of pro-inflammatory cytokines and chemokines, up-regulation of ECM degrading proteases, and down-regulation of chondrogenic genes. Our results indicate that while MSC treatment attenuates macrophage inflammation directly, it does not reduce chondrocyte inflammatory responses, unless macrophages are present as well. DEX however, can directly attenuate chondrocyte inflammation.

Conclusions

Our results highlight the importance of considering multi-cellular interactions when studying complex systems such as the articular joint. In addition, our approach, using a panel of both inflammatory and chondrocyte functional genes, provides a more comprehensive approach to investigate disease biomarkers, and responses to treatment.

Advancements in tissue engineering for articular cartilage regeneration

Articular cartilage injury is a prevalent clinical condition resulting from trauma, tumors, infection, osteoarthritis, and other factors. The intrinsic lack of blood vessels, nerves, and lymphatic vessels within cartilage tissue severely limits its self-regenerative capacity after injury. Current treatment options, such as conservative drug therapy and joint replacement, have inherent limitations. Achieving perfect regeneration and repair of articular cartilage remains an ongoing challenge in the field of regenerative medicine. Tissue engineering has emerged as a key focus in articular cartilage injury research, aiming to utilize cultured and expanded tissue cells combined with suitable scaffold materials to create viable, functional tissues. This review article encompasses the latest advancements in seed cells, scaffolds, and cytokines. Additionally, the role of stimulatory factors including cytokines and growth factors, genetic engineering techniques, biophysical stimulation, and bioreactor systems, as well as the role of scaffolding materials including natural scaffolds, synthetic scaffolds, and nanostructured scaffolds in the regeneration of cartilage tissues are discussed. Finally, we also outline the signaling pathways involved in cartilage regeneration. Our review provides valuable insights for scholars to address the complex problem of cartilage regeneration and repair.

Effect of a retinoic acid analogue on BMP-driven pluripotent stem cell chondrogenesis

Osteoarthritis is the most common degenerative joint condition, leading to articular cartilage (AC) degradation, chronic pain and immobility. The lack of appropriate therapies that provide tissue restoration combined with the limited lifespan of joint-replacement implants indicate the need for alternative AC regeneration strategies. Differentiation of human pluripotent stem cells (hPSCs) into AC progenitors may provide a long-term regenerative solution but is still limited due to the continued reliance upon growth factors to recapitulate developmental signalling processes. Recently, TTNPB, a small molecule activator of retinoic acid receptors (RARs), has been shown to be sufficient to guide mesodermal specification and early chondrogenesis of hPSCs. Here, we modified our previous differentiation protocol, by supplementing cells with TTNPB and administering BMP2 at specific times to enhance early development (referred to as the RAPID-E protocol). Transcriptomic analyses indicated that activation of RAR signalling significantly upregulated genes related to limb and embryonic skeletal development in the early stages of the protocol and upregulated genes related to AC development in later stages. Chondroprogenitors obtained from RAPID-E could generate cartilaginous pellets that expressed AC-related matrix proteins such as Lubricin, Aggrecan, and Collagen II, but additionally expressed Collagen X, indicative of hypertrophy. This protocol could lay the foundations for cell therapy strategies for osteoarthritis and improve the understanding of AC development in humans.

Directed differentiation of human pluripotent stem cells into articular cartilage reveals effects caused by absence of WISP3, the gene responsible for progressive pseudorheumatoid arthropathy of childhood

OBJECTIVES

Progressive pseudorheumatoid arthropathy of childhood (PPAC), caused by deficiency of WNT1 inducible signalling pathway protein 3 (WISP3), has been challenging to study because no animal model of the disease exists and cartilage recovered from affected patients is indistinguishable from common end-stage osteoarthritis. Therefore, to gain insights into why precocious articular cartilage failure occurs in this disease, we made in vitro derived articular cartilage using isogenic WISP3-deficient and WISP3-sufficient human pluripotent stem cells (hPSCs).

METHODS

We generated articular cartilage-like tissues from induced-(i) PSCs from two patients with PPAC and one wild-type human embryonic stem cell line in which we knocked out WISP3. We compared these tissues to in vitro-derived articular cartilage tissues from two isogenic WISP3-sufficient control lines using histology, bulk RNA sequencing, single cell RNA sequencing and in situ hybridisation.

RESULTS

WISP3-deficient and WISP3-sufficient hPSCs both differentiated into articular cartilage-like tissues that appeared histologically similar. However, the transcriptomes of WISP3-deficient tissues differed significantly from WISP3-sufficient tissues and pointed to increased TGFβ, TNFα/NFκB, and IL-2/STAT5 signalling and decreased oxidative phosphorylation. Single cell sequencing and in situ hybridisation revealed that WISP3-deficient cartilage contained a significantly higher fraction (~4 fold increase, p<0.001) of superficial zone chondrocytes compared with deeper zone chondrocytes than did WISP3-sufficient cartilage.

CONCLUSIONS

WISP3-deficient and WISP3-sufficient hPSCs can be differentiated into articular cartilage-like tissues, but these tissues differ in their transcriptomes and in the relative abundances of chondrocyte subtypes they contain. These findings provide important starting points for in vivo studies when an animal model of PPAC or presymptomatic patient-derived articular cartilage becomes available.

Directed differentiation of human pluripotent stem cells into articular cartilage reveals effects caused by absence of WISP3 , the gene responsible for Progressive Pseudorheumatoid Arthropathy of Childhood

Objectives

Progressive Pseudorheumatoid Arthropathy of Childhood (PPAC), caused by deficiency of WNT1 inducible signaling pathway protein 3 ( WISP3 ), has been challenging to study because no animal model of the disease exists and cartilage recovered from affected patients is indistinguishable from common end-stage osteoarthritis. Therefore, to gain insights into why precocious articular cartilage failure occurs in this disease, we made in vitro derived articular cartilage using isogenic WISP3 -deficient and WISP3 -sufficient human pluripotent stem cells (hPSCs).

Methods

We generated articular cartilage-like tissues from induced-(i)PSCs from 2 patients with PPAC and 1 wild-type human embryonic stem cell line in which we knocked out WISP3. We compared these tissues to in vitro -derived articular cartilage tissues from 2 isogenic WISP3 -sufficient control lines using histology, bulk RNA sequencing, single cell RNA sequencing, and in situ hybridization.

Results

WISP3 -deficient and WISP3 -sufficient hPSCs both differentiated into articular cartilage-like tissues that appeared histologically similar. However, the transcriptomes of WISP3 -deficient tissues differed significantly from WISP3 -sufficient tissues and pointed to increased TGFβ, TNFα/NFkB, and IL-2/STAT5 signaling and decreased oxidative phosphorylation. Single cell sequencing and in situ hybridization revealed that WISP3 -deficient cartilage contained a significantly higher fraction (∼ 4-fold increase, p < 0.001) of superficial zone chondrocytes compared to deeper zone chondrocytes than did WISP3 -sufficient cartilage. Conclusions WISP3 -deficient and WISP3 -sufficient hPSCs can be differentiated into articular cartilage-like tissues, but these tissues differ in their transcriptomes and in the relative abundances of chondrocyte sub-types they contain. These findings provide important starting points for in vivo studies when an animal model of PPAC or presymptomtic patient-derived articular cartilage becomes available.

KEY MESSAGES

What is already known on this topic: Loss-of-function mutations in WISP3 cause Progressive Pseudorheumatoid Arthropathy of Childhood (PPAC), yet the precise function of WISP3 in cartilage is unknown due to the absence of cartilage disease Wisp3 knockout mice and the lack of available PPAC patient cartilage that is not end-stage. Thus, most functional studies of WISP3 have been performed in vitro using WISP3 over-expressing cell lines (i.e., not wild-type) and WISP3 -deficient chondrocytes. What this study adds: We describe 3 new WISP3 -deficient human pluripotent stem cell (hPSC) lines and show they can be differentiated into articular cartilage-like tissue. We compare in vitro -derived articular cartilage made from WISP3 -deficient and isogenic WISP3 - sufficient hPSCs using bulk RNA sequencing, single cell RNA sequencing, and in situ hybridization. We observe significant differences in the expression of genes previously associated with cartilage formation and homeostasis in the TGFβ, TNFα/NFkB, and IL-2/STAT5 signaling pathways. We also observe that WISP3-deficient cartilage-like tissues contain significantly higher fractions of chondrocytes that express superficial zone transcripts. These data suggest precocious cartilage failure in PPAC is the result of abnormal articular cartilage formation, dysregulated homeostatic signaling, or both.How this study might affect research, practice or policy: This study uses in vitro -derived articular cartilage to generate hypotheses for why cartilage fails in children with PPAC. This work prioritizes downstream studies to be performed when pre-symptomatic patient-derived cartilage samples or animal model of PPAC becomes available. It is essential to know how WISP3 functions in cartilage to develop therapies that benefit patients with PPAC and other degenerative joint diseases.

Glis1 and oxaloacetate in nucleus pulposus stromal cell somatic reprogramming and survival

Regenerative medicine aims to repair degenerate tissue through cell refurbishment with minimally invasive procedures. Adipose tissue (FAT)-derived stem or stromal cells are a convenient autologous choice for many regenerative cell therapy approaches. The intervertebral disc (IVD) is a suitable target. Comprised of an inner nucleus pulposus (NP) and an outer annulus fibrosus (AF), the degeneration of the IVD through trauma or aging presents a substantial socio-economic burden worldwide. The avascular nature of the mature NP forces cells to reside in a unique environment with increased lactate levels, conditions that pose a challenge to cell-based therapies. We assessed adipose and IVD tissue-derived stromal cells through in vitro transcriptome analysis in 2D and 3D culture and suggested that the transcription factor Glis1 and metabolite oxaloacetic acid (OAA) could provide NP cells with survival tools for the harsh niche conditions in the IVD.

Articulation inspired by nature: A review of biomimetic and biologically active 3D printed scaffolds for cartilage tissue engineering

In the human body, articular cartilage facilitates the frictionless movement of synovial joints. However, due to its avascular and aneural nature, it has a limited ability to self-repair when damaged due to injury or wear and tear over time. Current surgical treatment options for cartilage defects often lead to the formation of fibrous, non-durable tissue and thus a new solution is required. Nature is the best innovator and so recent advances in the field of tissue engineering have aimed to recreate the microenvironment of native articular cartilage using biomaterial scaffolds. However, the inability to mirror the complexity of native tissue has hindered the clinical translation of many products thus far. Fortunately, the advent of 3D printing has provided a potential solution. 3D printed scaffolds, fabricated using biomimetic biomaterials, can be designed to mimic the complex zonal architecture and composition of articular cartilage. The bioinks used to fabricate these scaffolds can also be further functionalised with cells and/or bioactive factors or gene therapeutics to mirror the cellular composition of the native tissue. Thus, this review investigates how the architecture and composition of native articular cartilage is inspiring the design of biomimetic bioinks for 3D printing of scaffolds for cartilage repair. Subsequently, we discuss how these 3D printed scaffolds can be further functionalised with cells and bioactive factors, as well as looking at future prospects in this field.

The tissue engineering triad of biomaterials, cells and therapeutics as it applies to the formulation of biomimetic bioinks for cartilage repair. These bioinks can be functionalised with cells or cellular therapeutics to promote cartilage repair.

Impact of perlecan, a core component of basement membrane, on regeneration of cartilaginous tissues

As an indispensable component of the extracellular matrix, perlecan (Pln) plays an essential role in cartilaginous tissue function. Although there exist studies suggesting that Pln expressed by cartilaginous tissues is critical for chondrogenesis, few papers have discussed the potential impact Pln may have on cartilage regeneration. In this review, we delineate Pln structure, biomechanical properties, and interactive ligands-which together contribute to the effect Pln has on cartilaginous tissue development. We also review how the signaling pathways of Pln affect cartilage development and scrutinize the potential application of Pln to divisions of cartilage regeneration, spanning vascularization, stem cell differentiation, and biomaterial improvement. The aim of this review is to deepen our understanding of the spatial and temporal interactions that occur between Pln and cartilaginous tissue and ultimately apply Pln in scaffold design to improve cell-based cartilage engineering and regeneration. STATEMENT OF SIGNIFICANCE: As a key component of the basement membrane, Pln plays a critical role in tissue development and repair. Recent findings suggest that Pln existing in the pericellular matrix surrounding mature chondrocytes is actively involved in cartilage regeneration and functionality. We propose that Pln is essential to developing an in vitro matrix niche within biological scaffolds for cartilage tissue engineering.

Applications of Bacterial Cellulose as a Natural Polymer in Tissue Engineering

Choosing the material with the best regeneration potential and properties closest to that of the extracellular matrix is one of the main challenges in tissue engineering and regenerative medicine. Natural polymers, such as collagen, elastin, and cellulose, are widely used for this purpose in tissue engineering. Cellulose derived from bacteria has excellent mechanical properties, high hydrophilicity, crystallinity, and a high degree of polymerization and, therefore, can be used as scaffold/membrane for tissue engineering. In the current study, we reviewed the latest trends in the application of bacterial cellulose (BC) polymers as a scaffold in different types of tissue, including bone, vascular, skin, and cartilage. Also, we mentioned the biological and mechanical advantages and disadvantages of BC polymers. Given the data presented in this study, BC polymer could be suggested as a favorable natural polymer in the design of tissue scaffolds. Implementing novel composites that combine this polymer with other materials through modern or rapid prototyping methods can open up a great prospect in the future of tissue engineering and regenerative medicine.

Mammalian tracheal development and reconstruction: insights from in vivo and in vitro studies

The trachea delivers inhaled air into the lungs for gas exchange. Anomalies in tracheal development can result in life-threatening malformations, such as tracheoesophageal fistula and tracheomalacia. Given the limitations of current therapeutic approaches, development of technologies for the reconstitution of a three-dimensional trachea from stem cells is urgently required. Recently, single-cell sequencing technologies and quantitative analyses from cell to tissue scale have been employed to decipher the cellular basis of tracheal morphogenesis. In this Review, recent advances in mammalian tracheal development and the generation of tracheal tissues from pluripotent stem cells are summarized.

Nanoparticle-Cartilage Interaction: Pathology-Based Intra-articular Drug Delivery for Osteoarthritis Therapy

Osteoarthritis is the most prevalent chronic and debilitating joint disease, resulting in huge medical and socioeconomic burdens. Intra-articular administration of agents is clinically used for pain management. However, the effectiveness is inapparent caused by the rapid clearance of agents. To overcome this issue, nanoparticles as delivery systems hold considerable promise for local control of the pharmacokinetics of therapeutic agents. Given the therapeutic programs are inseparable from pathological progress of osteoarthritis, an ideal delivery system should allow the release of therapeutic agents upon specific features of disorders. In this review, we firstly introduce the pathological features of osteoarthritis and the design concept for accurate localization within cartilage for sustained drug release. Then, we review the interactions of nanoparticles with cartilage microenvironment and the rational design. Furthermore, we highlight advances in the therapeutic schemes according to the pathology signals. Finally, armed with an updated understanding of the pathological mechanisms, we place an emphasis on the development of "smart" bioresponsive and multiple modality nanoparticles on the near horizon to interact with the pathological signals. We anticipate that the exploration of nanoparticles by balancing the efficacy, safety, and complexity will lay down a solid foundation tangible for clinical translation.

Sox9 Determines Translational Capacity During Early Chondrogenic Differentiation of ATDC5 Cells by Regulating Expression of Ribosome Biogenesis Factors and Ribosomal Proteins

Introduction

In addition to the well-known cartilage extracellular matrix-related expression of Sox9, we demonstrated that chondrogenic differentiation of progenitor cells is driven by a sharply defined bi-phasic expression of Sox9: an immediate early and a late (extracellular matrix associated) phase expression. In this study, we aimed to determine what biological processes are driven by Sox9 during this early phase of chondrogenic differentiation.

Materials

Sox9 expression in ATDC5 cells was knocked down by siRNA transfection at the day before chondrogenic differentiation or at day 6 of differentiation. Samples were harvested at 2 h and 7 days of differentiation. The transcriptomes (RNA-seq approach) and proteomes (Label-free proteomics approach) were compared using pathway and network analyses. Total protein translational capacity was evaluated with the SuNSET assay, active ribosomes were evaluated with polysome profiling, and ribosome modus was evaluated with bicistronic reporter assays.

Results

Early Sox9 knockdown severely inhibited chondrogenic differentiation weeks later. Sox9 expression during the immediate early phase of ATDC5 chondrogenic differentiation regulated the expression of ribosome biogenesis factors and ribosomal protein subunits. This was accompanied by decreased translational capacity following Sox9 knockdown, and this correlated to lower amounts of active mono- and polysomes. Moreover, cap- versus IRES-mediated translation was altered by Sox9 knockdown. Sox9 overexpression was able to induce reciprocal effects to the Sox9 knockdown.

Conclusion

Here, we identified an essential new function for Sox9 during early chondrogenic differentiation. A role for Sox9 in regulation of ribosome amount, activity, and/or composition may be crucial in preparation for the demanding proliferative phase and subsequent cartilage extracellular matrix production of chondroprogenitors in the growth plate in vivo.

Therapeutic Effects of Human Umbilical Cord Blood-Derived Mesenchymal Stem Cells Combined with Cartilage Acellular Matrix Mediated Via Bone Morphogenic Protein 6 in a Rabbit Model of Articular Cruciate Ligament Transection

Osteoarthritis (OA) is a general joint disease. Cartilage damage is associated with a decrease in the density of chondrocytes. Mesenchymal stem cells (MSCs) differentiate into adipocytes, osteocytes and chondrocytes, and are an excellent source of cell therapy. Cartilage-derived extracellular matrix (ECM) promotes chondrogenesis of MSCs. However, the role of MSCs stimulated by ECM is not well known in OA. The purpose of this study is to determine the role of specific factors generated by the application of ECM and umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs) in managing OA symptoms. Cartilage acellular matrix (CAM), which is a cartilage-derived ECM, was used to promote the chondrogenesis of UCB-MSCs. Induced MSCs were analyzed using chondrogenic markers (aggrecan, collagen type 2, and SOX9) and bone morphogenic protein 6 (BMP6). BMP6 is known to be involved in early chondrogenesis of MSCs. As a result, treatment with CAM significantly increased the expression of chondrogenic markers and BMP6 in UCB-MSCs. Treatment with recombinant human BMP6 also dramatically increased the levels of chondrogenic markers in UCB-MSCs. In addition, UCB-MSCs and CAM were used to evaluate OA symptom improvement in a rabbit articular cruciate ligament transection (ACLT) model. Application of UCB-MSCs and CAM enhanced not only the structure and synthesis of proteoglycan and collagen type 2 but also anti-inflammatory effects in both rabbit joint and synovial fluid. Moreover, the detection of human cells and involvement of BMP6 were confirmed in rabbit cartilage tissues. This study indicates that therapeutic potential of UCB-MSCs with CAM is mediated via BMP6 in OA.

Osteogenic differentiation characteristics of hip joint capsule fibroblasts obtained from patients with ankylosing spondylitis

Background

Autoimmune disease are fairly common and one that has an excessive degree of disability is Ankylosing spondylitis (AS). As the main cells in connective tissues, fibroblasts may play important roles in AS ossification. The conducted research aims to establish the osteogenic disparity characteristics of fibroblasts cultured in vitro, obtained via AS patients hip joint capsule, as well as investigating the pathological osteogenic molecular workings of AS.

Methods

AS patients hip joint capsules were acquired and fracture patients as the control with the finite fibroblast line were established by using tissue culture method. AS fibroblast proliferation, cycle and apoptosis, expression of osteogenic marker genes, osteogenic phenotypes, and the activation degree of the bone morphogenetic protein (BMP)/Smads signalling pathway were detected by flow cytometry, western blotting and real-time fluorescent quantitative polymerase chain reaction.

Results

Proliferative activity in AS fibroblasts were abnormally high, and the apoptotic rate decreased. Compared with normal fibroblasts, the mRNA expression of osteogenic marker genes, expression of osteogenic phenotypes, protein expression of core-binding factor a1 (Cbfa1), Smad1, Smad4, Smad5, phosphorylated (p) Smad1, and pSmad5 in AS fibroblasts were higher; however, the expression of Smad6 was lower. Moreover, recombinant human bone morphogenetic protein-2(rhBMP-2) stimulated Cbfa1 expression by normal and AS fibroblasts through the BMP/Smads signalling pathway.

Conclusions

The fibroblasts of hip joint capsules in patients with AS cultured in vitro have biologic characteristics of osteogenic differentiation and may be important target cells of AS ossification. The Activated BMP/Smads signalling pathway could potentially be a mechanism relating to fibroblasts differentiating into osteoblasts and an ossification mechanism for AS.

Effect of Mechanical Strain on Cells Involved in Fracture Healing

Secondary fracture healing is a complex multi‐stage process in which the mechanical environment plays a key role. The use of an appropriate mechanical stimulation such as strain is conducive to tissue formation between fracture ends, thus aiding the healing process. However, if the strain is too large or too small, the biological behavior of the cells involved in bone healing will be affected, resulting in non‐union or delayed healing. In this review, we summarize the current state of knowledge regarding the effect of strain on cells that play a role in the fracture‐healing process. Overall, the related literature suggests that selection of an adequate strain promotes fracture healing through the stimulation of angiogenesis and osteogenesis, along with inhibition of osteoclast differentiation and bone resorption. However, standardized methods for the application of mechanical stimulation are lacking, and a unified consensus on the mechanism by which strain promotes cell differentiation has not yet been reached. These issues, therefore, deserve further investigation.

A SMOC2 variant inhibits BMP signaling by competitively binding to BMPR1B and causes growth plate defects

Endochondral ossification is the major process of long bone formation, and chondrogenesis is the final step of this process. Several studies have indicated that bone morphogenetic proteins (BMPs) are required for chondrogenesis and regulate multiple growth plate features. Abnormal BMP pathways lead to growth plate defects, resulting in osteochondrodysplasia. The SPARC-related modular calcium binding 2 (SMOC2) gene encodes an extracellular protein that is considered to be an antagonist of BMP signaling. In this study, we generated a mouse model by knocking-in the SMOC2 mutation (c.1076 T > G), which showed short-limbed dwarfism, reduced, disorganized, and hypocellular proliferative zones and expanded hypertrophic zones in tibial growth plates. To determine the underlying pathophysiological mechanism of SMOC2 mutation, we used knock-in mice to investigate the interaction between SMOC2 and the BMP-SMAD1/5/9 signaling pathway in vivo and in vitro. Eventually, we found that mutant SMOC2 could not bind to COL9A1 and HSPG. Furthermore, mutant SMOC2 inhibited BMP signaling by competitively binding to BMPR1B, which lead to defects in growth plates and short-limbed dwarfism in knock-in mice.

Dysregulated BMP signaling through ACVR1 impairs digit joint development in fibrodysplasia ossificans progressiva (FOP)

The development of joints in the mammalian skeleton depends on the precise regulation of multiple interacting signaling pathways including the bone morphogenetic protein (BMP) pathway, a key regulator of joint development, digit patterning, skeletal growth, and chondrogenesis. Mutations in the BMP receptor ACVR1 cause the rare genetic disease fibrodysplasia ossificans progressiva (FOP) in which extensive and progressive extra-skeletal bone forms in soft connective tissues after birth. These mutations, which enhance BMP-pSmad1/5 pathway activity to induce ectopic bone, also affect skeletal development. FOP can be diagnosed at birth by symmetric, characteristic malformations of the great toes (first digits) that are associated with decreased joint mobility, shortened digit length, and absent, fused, and/or malformed phalanges. To elucidate the role of ACVR1-mediated BMP signaling in digit skeletal development, we used an Acvr1^R206H/+;Prrx1-Cre knock-in mouse model that mimics the first digit phenotype of human FOP. We have determined that the effects of increased Acvr1-mediated signaling by the Acvr1^R206H mutation are not limited to the first digit but alter BMP signaling, Gdf5+ joint progenitor cell localization, and joint development in a manner that differently affects individual digits during embryogenesis. The Acvr1^R206H mutation leads to delayed and disrupted joint specification and cleavage in the digits and alters the development of cartilage and endochondral ossification at sites of joint morphogenesis. These findings demonstrate an important role for ACVR1-mediated BMP signaling in the regulation of joint and skeletal formation, show a direct link between failure to restrict BMP signaling in the digit joint interzone and failure of joint cleavage at the presumptive interzone, and implicate impaired, digit-specific joint development as the proximal cause of digit malformation in FOP.

Temporal TGF-β Supergene Family Signalling Cues Modulating Tissue Morphogenesis: Chondrogenesis within a Muscle Tissue Model?

Temporal translational signalling cues modulate all forms of tissue morphogenesis. However, if the rules to obtain specific tissues rely upon specific ligands to be active or inactive, does this mean we can engineer any tissue from another? The present study focused on the temporal effect of “multiple” morphogen interactions on muscle tissue to figure out if chondrogenesis could be induced, opening up the way for new tissue models or therapies. Gene expression and histomorphometrical analysis of muscle tissue exposed to rat bone morphogenic protein 2 (rBMP-2), rat transforming growth factor beta 3 (rTGF-β₃₎, and/or rBMP-7, including different combinations applied briefly for 48 h or continuously for 30 days, revealed that a continuous rBMP-2 stimulation seems to be critical to initiate a chondrogenesis response that was limited to the first seven days of culture, but only in the absence of rBMP-7 and/or rTGF-β₃. After day 7, unknown modulatory effects retard rBMP-2s’ effect where only through the paired-up addition of rBMP-7 and/or rTGF-β₃ a chondrogenesis-like reaction seemed to be maintained. This new tissue model, whilst still very crude in its design, is a world-first attempt to better understand how multiple morphogens affect tissue morphogenesis with time, with our goal being to one day predict the chronological order of what signals have to be applied, when, for how long, and with which other signals to induce and maintain a desired tissue morphogenesis.

BMP9 exhibits dual and coupled roles in inducing osteogenic and angiogenic differentiation of mesenchymal stem cells

Bone morphogenetic protein (BMP) 9 (BMP9) is one of most potent BMPs in inducing osteogenic differentiation of mesenchymal stem cells (MSCs). Recently, evidence has shown that osteogenesis and angiogenesis are coupled, however, it is unclear whether BMP9 induces MSC differentiation into endothelial-like cells and further promotes blood vessel formation. In the present study, we explored the potential of BMP9-induced angiogenic differentiation of MSCs, and the relationship between BMP9-induced osteogenic and angiogenic differentiation of MSCs. Osteogenic activities and angiogenic differentiation markers were analyzed at mRNA and protein levels. In vivo osteogenic and angiogenic differentiation of MSCs were tested by the ectopic bone formation model. We identified that adenoviral vectors effectively transduced in immortalized mouse embryonic fibroblasts (iMEFs) and expressed BMP9 with high efficiency. We found that BMP9 induces early and late osteogenic differentiation, and it up-regulated osteogenic marker expression in MSCs. Meanwhile, BMP9 induces angiogenic differentiation of MSCs via the expression of vascular endothelial growth factor a (VEGFa) and CD31 at both mRNA and protein levels. CD31-positive cells were also increased with the stimulation of BMP9. The ectopic bone formation tests found that BMP9-induced trabecular bone formation was coupled with the expression of blood vessel formation markers and sinusoid capillary formation. These findings suggest that BMP9 exhibits dual and coupled roles in inducing osteogenic and angiogenic differentiation of MSCs.

Current knowledge of pituitary adenylate cyclase activating polypeptide (PACAP) in articular cartilage

Pituitary adenylate cyclase activating polypeptide (PACAP) is an evolutionally well conserved neuropeptide, mainly expressed by neuronal and peripheral cells. It proves to be an interesting object of study both for its trophic functions during the development of several tissues and for its protective effects against oxidative stress, hypoxia, inflammation and apoptosis in different degenerative diseases. This brief review summarises the recent findings concerning the role of PACAP in the articular cartilage. PACAP and its receptors are expressed during chondrogenesis and are shown to activate the pathways involved in regulating cartilage development. Moreover, this neuropeptide proves to be chondroprotective against those stressors that determine cartilage degeneration and contribute to the onset of osteoarthritis (OA), the most common form of degenerative joint disease. Indeed, the degenerated cartilage exhibits low levels of PACAP, suggesting that its endogenous levels in adult cartilage may play an essential role in maintaining physiological properties. Thanks to its peculiar characteristics, exogenous administration of PACAP could be suggested as a potential tool to slow down the progression of OA and for cartilage regeneration approaches.

The negatively charged microenvironment of collagen hydrogels regulates the chondrogenic differentiation of bone marrow mesenchymal stem cells in vitro and in vivo

The differentiation of bone marrow mesenchymal stem cells (BMSCs) into functional chondrocytes is crucial for successful cartilage tissue engineering. Since the extracellular matrix (ECM) microenvironment can regulate the behaviours of BMSCs and guide their differentiation, it is important to simulate the natural cartilage ECM to induce the chondrogenesis of BMSCs. As the most abundant protein in the ECM, collagen hydrogels were found to provide a structural and chemical microenvironment for natural cartilage, and regulate the chondrogenic differentiation of BMSCs. However, as the negatively charged ECM microenvironment is crucial for chondrogenesis and homeostasis within cells in cartilage tissue, the electrical properties of collagen hydrogels need to be further optimized. In this study, three collagen hydrogels with different electrical properties were fabricated using methacrylic anhydride (MA) and succinic anhydride (SA) modification. The collagen hydrogels had a similar composition, storage modulus and integral triple helix structure of collagen, but their different negatively charged microenvironments significantly impacted the hydrophilicity, protein diffusion and binding, and consequently influenced BMSC adhesion and spreading on the surface of the hydrogels. Moreover, the BMSCs encapsulated in the collagen hydrogels also demonstrated improved sGAG secretion and chondrogenic and integrin gene expression with the increased negative charge in vitro. Similar results were also observed in subcutaneous implantation in vivo, where higher secretions of sGAG, SOX9 and collagen type II proteins were found in the collagen hydrogels with higher negative charge. Together, our results demonstrated that more negative charges introduced into the collagen hydrogel microenvironment would enhance the chondrogenic differentiation of BMSCs in vitro and in vivo. This revealed that the electrical properties are an important consideration in designing future collagen hydrogels for cartilage regeneration.

Toxic effects of dechlorane plus on the common carp (Cyprinus carpio) embryonic development

Dechlorane Plus (DP) is a widely used chlorinated flame retardant, which has been extensively detected in the environment. Although DP content in the surface water is low, it can pose a continuous exposure risk to aquatic organisms due to its strong bioaccumulation. Considering that the related studies on the toxicity mechanism of DP exposure are limited, the effect of DP on carp embryo development was evaluated. In the present work, carp embryos were exposed to different concentrations (0, 30, 60, and 120 μg/L) of DP at 3 h post-fertilization (hpf). The expression levels of neural and skeletal development-associated genes, such as sox2, sox19a, Mef2c and BMP4, were detected with quantitative PCR, and the changes in different developmental toxicity endpoints were observed. Our results demonstrated that the expression levels of sox2, sox19a, Mef2c and BMP4 were significantly altered and several developmental abnormalities were found in DP-exposed carp embryos, such as DNA damage, increased mortality rate, delayed hatching time, reduced hatching rate, decreased body length, and increased morphological deformities. In addition, the activities of reactive oxygen species and malondialdehyde were remarkably higher in 60 and 120 μg/L DP exposure groups than in control group. These results suggest that DP can exhibit a unique modes of action, which lead to aberration occurrence in the early development stage of common carps, which may be related to some gene damage and oxidative stress. Besides, the parameters evaluated here can be used as tools to access the environmental risk for biota and humans exposed to DP.

Improving Cell Therapy Survival and Anabolism in Harsh Musculoskeletal Disease Environments

Cell therapies are an up and coming technology in orthopedic medicine that has the potential to provide regenerative treatments for musculoskeletal disease. Despite numerous cell therapies showing preclinical success for common musculoskeletal indications of disc degeneration and osteoarthritis, there have been mixed results when testing these therapies in humans during clinical trials. A theory behind the mixed success of these cell therapies is that the harsh microenvironments of the disc and knee they are entering inhibit their anabolism and survival. Therefore, there is much ongoing research looking into how to improve the survival and anabolism of cell therapies within these musculoskeletal disease environments. This includes research into improving cell function under specific microenvironmental conditions known to exist in the intervertebral disc (IVD) and knee environment such as hypoxia, low-nutrient conditions, hyperosmolarity, acidity, and inflammation. This research also includes improving differentiation of cells into desired native cell phenotypes to better enhance their survival and anabolism in the knee and IVD. This review highlights the effects of specific musculoskeletal microenvironmental challenges on cell therapies and what research is being done to overcome these challenges. Impact statement While there has been significant clinical interest in using cell therapies for musculoskeletal pathologies in the knee and intervertebral disc, cell therapy clinical trials have had mixed outcomes. The information presented in this review includes the environmental challenges (i.e., acidic pH, inflammation, hyperosmolarity, hypoxia, and low nutrition) that cell therapies experience in these pathological musculoskeletal environments. This review summarizes studies that describe various approaches to improving the therapeutic capability of cell therapies in these harsh environments. The result is an overview of what approaches can be targeted and/or combined to develop a more consistent cell therapy for musculoskeletal pathologies.

Local modulation of the Wnt/β-catenin and bone morphogenic protein (BMP) pathways recapitulates rib defects analogous to cerebro-costo-mandibular syndrome

Ribs are seldom affected by developmental disorders, however, multiple defects in rib structure are observed in the spliceosomal disease cerebro-costo-mandibular syndrome (CCMS). These defects include rib gaps, found in the posterior part of the costal shaft in multiple ribs, as well as missing ribs, shortened ribs and abnormal costotransverse articulations, which result in inadequate ventilation at birth and high perinatal mortality. The genetic mechanism of CCMS is a loss-of-function mutation in SNRPB, a component of the major spliceosome, and knockdown of this gene in vitro affects the activity of the Wnt/β-catenin and bone morphogenic protein (BMP) pathways. The aim of the present study was to investigate whether altering these pathways in vivo can recapitulate rib gaps and other rib abnormalities in the model animal. Chick embryos were implanted with beads soaked in Wnt/β-catenin and BMP pathway modulators during somitogenesis, and incubated until the ribs were formed. Some embryos were harvested in the preceding days for analysis of the chondrogenic marker Sox9, to determine whether pathway modulation affected somite patterning or chondrogenesis. Wnt/β-catenin inhibition manifested characteristic rib phenotypes seen in CCMS, including rib gaps (P < 0.05) and missing ribs (P < 0.05). BMP pathway activation did not cause rib gaps but yielded missing rib (P < 0.01) and shortened rib phenotypes (P < 0.05). A strong association with vertebral phenotypes was also noted with BMP4 (P < 0.001), including scoliosis (P < 0.05), a feature associated with CCMS. Reduced expression of Sox9 was detected with Wnt/β-catenin inhibition, indicating that inhibition of chondrogenesis precipitated the rib defects in the presence of Wnt/β-catenin inhibitors. BMP pathway activators also reduced Sox9 expression, indicating an interruption of somite patterning in the manifestation of rib defects with BMP4. The present study demonstrates that local inhibition of the Wnt/β-catenin and activation of the BMP pathway can recapitulate rib defects, such as those observed in CCMS. The balance of Wnt/β-catenin and BMP in the somite is vital for correct rib morphogenesis, and alteration of the activity of these two pathways in CCMS may perturb this balance during somite patterning, leading to the observed rib defects.

A combination insecticide at sub-lethal dose debilitated the expression pattern of crucial signalling molecules that facilitate craniofacial patterning in domestic chick Gallus domesticus

Pesticides despite being agents that protect the plants and humans from noxious pests, are infamous for their potential to cause detrimental health issues in nontargeted species. In order to ascertain the latter, a set of experiments were conducted by exposing early chick embryos to a widely used combination insecticide (Ci, 50% chlorpyrifos and 5% cypermethrin). The results revealed a myriad of congenital defects pertaining to craniofacial development such as anophthalmia, microphthalmia, exencephaly as well as deformed beak and cranial structures. These teratological manifestations could be attributed to the Ci induced alteration in the titre of major regulators of neurulation and ossification. Therefore, the mRNA and/or the protein level expression pattern of genes which are reported to be involved in the craniofacial development were studied at selected time points of embryonic development. The analysis of the result showed that there have been significant alternations in the expression patterns of the signalling molecules such as SHH, WNTs, CDH1, CDH2, L1CAM, PAX6, HOX, PCNA, GLI3, BMP7, FGF8, GLIs, SOX9, RUNX2, DLX5, COL10A1, CASPASE3 etc. on embryonic days 2, 4 and/or 10. Concurrently, on day 10, whole-mount skeletal staining and biochemical estimation of hydroxyproline were carried out in the cranial tissues of the embryos. The overall result of the current study indicates that exposure to Ci during early development impede the crucial regulatory signals that orchestrate the morphogenesis of cranial neural crest cells thereby hindering the normal progression of neural tube and endochondral ossification which collectively lead to craniofacial dysmorphism in domestic chicks.

Homozygous missense variant in BMPR1A resulting in BMPR signaling disruption and syndromic features

Background

The bone morphogenetic protein (BMP) pathway is known to play an imperative role in bone, cartilage, and cardiac tissue formation. Truncating, heterozygous variants, and deletions of one of the essential receptors in this pathway, Bone Morphogenetic Protein Receptor Type1A (BMPR1A), have been associated with autosomal dominant juvenile polyposis. Heterozygous deletions have also been associated with cardiac and minor skeletal anomalies. Populations with atrioventricular septal defects are enriched for rare missense BMPR1A variants.

Methods

We report on a patient with a homozygous missense variant in BMPR1A causing skeletal abnormalities, growth failure a large atrial septal defect, severe subglottic stenosis, laryngomalacia, facial dysmorphisms, and developmental delays.

Results

Functional analysis of this variant shows increased chondrocyte death for cells with the mutated receptor, increased phosphorylated R‐Smads1/5/8, and loss of Sox9 expression mediated by decreased phosphorylation of p38.

Conclusion

This homozygous missense variant in BMPR1A appears to cause a distinct clinical phenotype.

Hox11 expressing regional skeletal stem cells are progenitors for osteoblasts, chondrocytes and adipocytes throughout life

Multipotent mesenchymal stromal cells (MSCs) are required for skeletal formation, maintenance, and repair throughout life; however, current models posit that postnatally arising long-lived adult MSCs replace transient embryonic progenitor populations. We previously reported exclusive expression and function of the embryonic patterning transcription factor, Hoxa11, in adult skeletal progenitor-enriched MSCs. Here, using a newly generated Hoxa11-CreERT2 lineage-tracing system, we show Hoxa11-lineage marked cells give rise to all skeletal lineages throughout the life of the animal and persist as MSCs. Hoxa11 lineage-positive cells give rise to previously described progenitor-enriched MSC populations marked by LepR-Cre and Osx-CreER, placing them upstream of these populations. Our studies establish that Hox-expressing cells are skeletal stem cells that arise from the earliest stages of skeletal development and self-renew throughout the life of the animal.

Blockade of RGMb inhibits allergen-induced airways disease

BACKGROUND

Allergic asthma causes morbidity in many subjects, and novel precision-directed treatments would be valuable.

OBJECTIVE

We sought to examine the role of a novel innate molecule, repulsive guidance molecule b (RGMb), in murine models of allergic asthma.

METHODS

In models of allergic asthma using ovalbumin or cockroach allergen, mice were treated with anti-RGMb or control mAb and examined for airway inflammation and airway hyperreactivity (AHR), a cardinal feature of asthma. The mechanisms by which RGMb causes airways disease were also examined.

RESULTS

We found that blockade of RGMb by treatment with anti-RGMb mAb effectively blocked the development of airway inflammation and AHR. Importantly, blockade of RGMb completely blocked the development of airway inflammation and AHR, even if treatment occurred only during the challenge (effector) phase. IL-25 played an important role in these models of asthma because IL-25 receptor-deficient mice did not develop disease after sensitization and challenge with allergen. RGMb was expressed primarily by innate cells in the lungs, including bronchial epithelial cells (known producers of IL-25), activated eosinophils, and interstitial macrophages, which in the inflamed lung expressed the IL-25 receptor and produced IL-5 and IL-13. We also found that neogenin, the canonical receptor for RGMb, was expressed by interstitial macrophages and bronchial epithelial cells in the inflamed lung, suggesting that an innate RGMb-neogenin axis might modulate allergic asthma.

CONCLUSIONS

These results demonstrate an important role for a novel innate pathway in regulating type 2 inflammation in patients with allergic asthma involving RGMb and RGMb-expressing cells, such as interstitial macrophages and bronchial epithelial cells. Moreover, targeting this previously unappreciated innate pathway might provide an important treatment option for allergic asthma.

Influence of hydrogel network microstructures on mesenchymal stem cell chondrogenesis in vitro and in vivo

Hydrogels, which provide three-dimensional (3D) niches for encapsulating bone marrow mesenchymal stem cells (BMSCs), are becoming a promising tissue engineering solution for chondrogenic differentiation of BMSCs. However, it remains a challenge to design a hydrogel material for effective chondrogenesis of BMSCs because of the complexity of cartilage ECM and cell-matrix interactions. Thus far, various studies have shown the physical-chemical cues of hydrogel materials to impact BMSCs chondrogenesis, but the design of the 3D network microstructure of the hydrogel to induce BMSCs chondrogenesis is still far from optimized. In this study, we successfully prepared two types of collagen hydrogels, namely, the fibrous network and porous network, with the same chemical composition and similar mechanical strength but with two distinct network microstructures. The two different network microstructures significantly influenced mass transfer, protein adsorption, degradability, and contraction of the collagen hydrogels. Moreover, the cells presented distinct proliferation and morphology in the two hydrogels, which consequently modulated chondrogenic differentiation of BMSCs derived from rat. Collagen hydrogels with a fibrous network promoted more chondrogenic differentiation of BMSCs without additional growth factors in vitro and subcutaneous implantation in vivo than those with a porous network. Moreover, fibrous network resulted in less ECM calcification than porous network. However, the fibrous network could not prevent hypertrophy of the chondrogenic cells induced by BMSCs. Overall, these results revealed that the 3D network microstructure of a hydrogel was a key design parameter for the chondrogenic differentiation of BMSCs. STATEMENT OF SIGNIFICANCE: Hydrogels had been used to induce the chondrogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) in cartilage tissue engineering, but the key design parameters remain unoptimized. This was mainly due to the different material properties including composition, strength, and microstructure, which would interplay with each other and result in difficulties to investigate the effects for one factor. In this study, we fabricated two collagen hydrogels with the same chemical composition and mechanical strength, but two distinct network microstructures. The effects of the two network microstructures on the chondrogenic differentiation of BMSCs were investigated by in vitro and in vivo assays. The results highlight the effects of network microstructures and provide important information about optimizing the design of future hydrogels in cartilage tissue engineering.

Toxic effects of cyhalofop-butyl on embryos of the Yellow River carp (Cyprinus carpio var.): alters embryos hatching, development failure, mortality of embryos, and apoptosis

As a universal environmental contaminant, the herbicide cyhalofop-butyl is considered to have infested effects on the embryonic development of aquatic species. The present study focused on an assessment of the impacts of cyhalofop-butyl on Yellow River carp embryos. It was found that cyhalofop-butyl inhibited the hatching of the embryos, and the hatching rate decreased with higher concentrations of the herbicide. The mortality rate was increased on exposure to cyhalofop-butyl and was significantly higher in the 1.6 and 2 mg/L treatment groups over 48 h. All of the embryos of the 2 mg/L treatment group died within the 48 h post-hatching stage. And the transcription of several embryos related to apoptosis was also influenced by cyhalofop-butyl exposure. Further, cyhalofop-butyl exposure leads to a series of morphological changes (pericardial edema, tail deformation, and spine deformation) in embryos, which were consistent with significant modifications in the associated genes. These results provided a scientific basis for further studies into the effects of cyhalofop-butyl on aquatic organisms.

Osteostimulation scaffolds of stem cells: BMP-7-derived peptide-decorated alginate porous scaffolds promote the aggregation and osteo-differentiation of human mesenchymal stem cells

The scaffolds for stem cell-based bone tissue engineering should hold the ability to guide stem cells osteo-differentiating. Otherwise, stem cells will differentiate into unwanted cell types or will form tumors in vivo. Alginate, a natural polysaccharide with great biocompatibility, was widely used in biomedical applications. However, the limited bioactivity and poor osteogenesis capability of pristine alginate hampered its further application in tissue engineering. In this work, a bone forming peptide-1 (BFP-1), derived from bone morphogenetic protein-7, was grafted to alginate polymer chains to prepare peptide-decorated alginate porous scaffolds (pep-APS) for promoting osteo-differentiation of human mesenchymal stem cells (hMSCs). SEM images of pep-APS exhibited porous structure with about 90% porosity (pore size 100-300 μm), which was appropriate for hMSCs ingrowth. The adhesion, proliferation and aggregation of hMSCs grown on pep-APS were enhanced in vitro. Moreover, pep-APS promoted the alkaline phosphatase (ALP) activity of hMSCs, and the osteo-related genes expression was obviously up-regulated. The immunochemical staining and western blot analysis results showed high expression level of OCN and Col1a1 in the hMSCs grown on pep-APS. This work provided a facile and valid strategy to endow the alginate polymers themselves with specific bioactivity and prepare osteopromoting scaffold with enhanced osteogenesis ability, possessing potential applications in stem cell therapy and regenerative medicine.

Time-dependent regulation of morphological changes and cartilage differentiation markers in the mouse pubic symphysis during pregnancy and postpartum recovery

Animal models commonly serve as a bridge between in vitro experiments and clinical applications; however, few physiological processes in adult animals are sufficient to serve as proof-of-concept models for cartilage regeneration. Intriguingly, some rodents, such as young adult mice, undergo physiological connective tissue modifications to birth canal elements such as the pubic symphysis during pregnancy; therefore, we investigated whether the differential expression of cartilage differentiation markers is associated with cartilaginous tissue morphological modifications during these changes. Our results showed that osteochondral progenitor cells expressing Runx2, Sox9, Col2a1 and Dcx at the non-pregnant pubic symphysis proliferated and differentiated throughout pregnancy, giving rise to a complex osteoligamentous junction that attached the interpubic ligament to the pubic bones until labour occurred. After delivery, the recovery of pubic symphysis cartilaginous tissues was improved by the time-dependent expression of these chondrocytic lineage markers at the osteoligamentous junction. This process potentially recapitulates embryologic chondrocytic differentiation to successfully recover hyaline cartilaginous pads at 10 days postpartum. Therefore, we propose that this physiological phenomenon represents a proof-of-concept model for investigating the mechanisms involved in cartilage restoration in adult animals.

mir-374-5p, mir-379-5p, and mir-503-5p Regulate Proliferation and Hypertrophic Differentiation of Growth Plate Chondrocytes in Male Rats

Growth plate chondrocytes undergo sequential differentiation to form the resting zone, the proliferative zone (PZ), and the hypertrophic zone (HZ). The important role of microRNAs (miRNAs) in the growth plate was previously revealed by cartilage-specific ablation of Dicer, an enzyme essential for biogenesis of many miRNAs. To identify specific miRNAs that regulate differentiation of PZ chondrocytes to HZ chondrocytes, we microdissected individual growth plate zones from juvenile rats and performed miRNA profiling using a solution hybridization method and miRNA sequencing. Thirty-four miRNAs were differentially expressed between the PZ and the HZ, and we hypothesized that some of the miRNAs that are preferentially expressed in the PZ may promote proliferation and inhibit hypertrophic differentiation. Consistent with this hypothesis, transfection of inhibitors for four of these miRNAs (mir-369-3p, mir-374-5p, mir-379-5p, and mir-503-5p) decreased proliferation in primary epiphyseal chondrocytes. The inhibitors for three of these miRNAs (mir-374-5p, mir-379-5p, and mir-503-5p) also increased expression of multiple genes that are associated with chondrocyte hypertrophic differentiation. We next hypothesized that preferential expression of these miRNAs in the PZ is driven by the parathyroid hormone-related protein (PTHrP) concentration gradient across the growth plate. Consistent with this hypothesis, treatment of primary chondrocytes with a parathyroid hormone (PTH)/PTHrP receptor agonist, PTH1-34, increased expression of mir-374-5p, mir-379-5p, and mir-503-5p. Taken together, our findings suggest that the PTHrP concentration gradient across the growth plate induces differential expression of mir-374-5p, mir-379-5p, and mir-503-5p between the PZ and the HZ. In the PZ, the higher expression levels of these miRNAs promote proliferation and inhibit hypertrophic differentiation. In the HZ, downregulation of these miRNAs inhibits proliferation and promotes hypertrophic differentiation.

Distinct metabolic programs induced by TGF-β1 and BMP2 in human articular chondrocytes with osteoarthritis

Objectives

Cellular energy metabolism is important for the function of all tissues, including cartilage. Recent studies indicate that superficial and deep subpopulations of articular chondrocytes (ACs) have distinct metabolic profiles. At the cellular and molecular level, osteoarthritis (OA) is characterised by alteration from a healthy homoeostatic state towards a catabolic state. Several molecular pathways, including transforming growth factor beta (TGF-β) and bone morphogenetic protein (BMP) signalling, have been identified as critical players in the pathogenesis and progression of OA. However, the manner in which these factors influence cellular energy metabolism in ACs is not well understood. This study investigates the effect of TGF-β or BMP signalling on energy metabolism in human articular chondrocytes (hACs).

Methods

ACs were isolated from residual macroscopically full thickness and intact cartilage from the femoral condyle of human samples obtained from patients with OA. ACs were treated with Vehicle (control), TGF-β1 or BMP2 for 48–72 hours. Metabolic assays were performed to determine glucose consumption, lactate production and adenosine triphosphate (ATP) production, whereas the mitochondrial stress test was performed to determine oxygen consumption rate. Protein was isolated to assess translational activity and was evaluated using Western blot.

Results

We showed that TGF-β1, known to maintain chondrocyte homoeostasis, stimulated glycolysis by upregulating key glycolytic factors, such as glucose transporter 1 (Glut1) and hexokinase II, while reducing oxidative phosphorylation in hACs. In contrast, BMP2 enhanced mitochondrial metabolism and oxidative phosphorylation and had a minimal effect on key glycolytic regulators.

Conclusions

Our data revealed distinct metabolic programs induced by TGF-β1 and BMP2 in hACs, suggesting that the regulation of cellular metabolism may represent a new mechanism underlying the pathogenesis of OA.

The translational potential of this article

The findings define the regulation of energy metabolism as a potential novel therapeutic approach for the treatment of OA.

An effective delivery vehicle of demineralized bone matrix incorporated with engineered collagen-binding human bone morphogenetic protein-2 to accelerate spinal fusion at low dose

The aim of this study was to investigate the feasibility and efficacy of a new delivery matrix using demineralized bone matrix (DBM) incorporated with collagen-binding bone morphogenetic protein-2 (CBD-BMP-2) in the rat inter-transverse spinal fusion model. Sixty rats undergoing posterolateral (inter-transverse) spinal fusion were divided into 3 groups according to the fusion materials containing different components (n = 20 per group). Group A were implanted with DBM, Group B with combination of DBM and BMP-2 and Group C with combination of DBM and CBD-BMP-2. After surgery, the spinal fusion of all the rats was assessed by plain radiography, CT + 3D reconstruction, manual palpation and histological evaluation. Significant difference was found in terms of solid fusion rate among the three groups, with 95% in Group C, 65% in Group B and 0% in Group A (P < 0.001). Compared with Groups B and A, new bone formation was observed earlier and was obvious larger, trabecular bone microarchitecture assessment was better and bone mineral density was statistically larger in Group C. In addition, more newly woven bone and osteocytes were shown by histological evaluation in Group C at 4 weeks post-operation. The present study showed CBD domain could help BMP-2 to improve the efficiency of posterolateral spinal fusion. DBM scaffold activated by collagen-binding BMP-2 was a feasible and promising bone repair vehicle. The present study showed better results in terms of plain radiography, CT + 3D reconstruction, manual palpation and histological evaluation in the rat inter-transverse spinal fusion model using DBM+CBD-BMP-2, compared with DBM+BMP-2 and DBM alone, indicating DBM scaffold activated by collagen-binding BMP-2 was a feasible and promising bone repair vehicle.

Combinatorial Analysis of Growth Factors Reveals the Contribution of Bone Morphogenetic Proteins to Chondrogenic Differentiation of Human Periosteal Cells

Successful application of cell-based strategies in cartilage and bone tissue engineering has been hampered by the lack of robust protocols to efficiently differentiate mesenchymal stem cells into the chondrogenic lineage. The development of chemically defined culture media supplemented with growth factors (GFs) has been proposed as a way to overcome this limitation. In this work, we applied a fractional design of experiment (DoE) strategy to screen the effect of multiple GFs (BMP2, BMP6, GDF5, TGF-β1, and FGF2) on chondrogenic differentiation of human periosteum-derived mesenchymal stem cells (hPDCs) in vitro. In a micromass culture (μMass) system, BMP2 had a positive effect on glycosaminoglycan deposition at day 7 (p < 0.001), which in combination with BMP6 synergistically enhanced cartilage-like tissue formation that displayed in vitro mineralization capacity at day 14 (p < 0.001). Gene expression of μMasses cultured for 7 days with a medium formulation supplemented with 100 ng/mL of BMP2 and BMP6 and a low concentration of GDF5, TGF-β1, and FGF2 showed increased expression of Sox9 (1.7-fold) and the matrix molecules aggrecan (7-fold increase) and COL2A1 (40-fold increase) compared to nonstimulated control μMasses. The DoE analysis indicated that in GF combinations, BMP2 was the strongest effector for chondrogenic differentiation of hPDCs. When transplanted ectopically in nude mice, the in vitro-differentiated μMasses showed maintenance of the cartilaginous phenotype after 4 weeks in vivo. This study indicates the power of using the DoE approach for the creation of new medium formulations for skeletal tissue engineering approaches.

Bone morphogenetic protein-2 and -7 mediate the anabolic function of nucleus pulposus cells with discrete mechanisms

Bone morphogenetic proteins (BMPs) play roles in promoting cell anabolism, especially in extracellular matrix production. The difference between BMP members in their capacity to modulate intervertebral disc cell activity is yet to be defined. BMP-7/OP-1 has been shown to retard disc degeneration. We compared the activity of BMP-7 with that of BMP-2 on nucleus pulposus (NP) cell phenotype and function, and investigated how they differentially affect the gene expression profiles of signaling cascade components in human NP cells under degenerative states. We found that while both BMP-2 and BMP-7 enhanced matrix production of bovine NP cells, BMP-7 is more potent than BMP-2 at various dosages (50-800 ng/ml). BMP-7 exerted a relatively stronger stimulation on sulfated glycosaminoglycan production and proliferation in human NP cells. Degenerated NP cells showed an overall weaker response to the BMPs than non-degenerated cells, and were more sensitive to BMP-7 than BMP-2 stimulation. Compared to BMP-2, BMP-7 not only induced the gene expression of canonical BMP components, but also evoked changes in MAPKs as well as CREB1 and EP300 gene expression in degenerated NP cells, suggesting potential activation of the cAMP dependent protein kinase related pathways. In contrast to BMP-2, BMP-7 concomitantly inhibited the expression of profibrotic genes. We propose that BMP-2 and BMP-7, and likely other BMPs, may operate multifaceted but discrete molecular machineries that give rise to their different capacity in regulating NP cell phenotype. Further investigations into such differential capacity may possibly derive alternative cues important for IVD repair or engineering.

BMP signaling regulates the skeletal and connective tissue differentiation during caudal fin regeneration in sailfin molly (Poecilia latipinna)

Caudal fin regeneration in sailfin molly, Poecilia latipinna (Lesueur 1821) involves an initial wound healing stage, followed by blastema that is formed of fast proliferating cells. In order to replicate the lost fin, correct differentiation of the blastemal cells into various tissues is the prime essence. Among the molecular signals governing proper differentiation of blastemal cells, members of the bone morphogenetic protein (BMP) family are crucial. Herein, we investigated the specific effects of inhibition of BMP signaling using LDN193189 on skeletal and connective tissue formation in the regenerating tail fin of P. latipinna during early differentiation phase. It was observed that BMP inhibition leads to reduction in the length of regeneration, which can be correlated with compromised proliferation of blastemal cells. Decreased expression of cell proliferation marker like pcna together with reduced BrdU positive cells consolidate the above observation. Further, histological analysis revealed stunted progression of skeletal tissues and this correlated with the reduced expression of sox9, runx2 and dlx5, Osc and Osn genes in response to BMP inhibition. Also, defective bone patterning was observed due to BMP inhibition, which was associated with diminished levels of shh, ptc-1, gli2 and other BMP ligands. Moreover, histochemical analysis revealed that collagen, one of the most prominent components of connective tissue, was formed below par in treated fin tissues which was subsequently confirmed by biochemical and transcript level analyses. Overall our results highlight the importance of the BMP pathway in proper differentiation of skeletal and connective tissues during the differentiation stage of regenerating caudal fin.

ZC4H2 stabilizes Smads to enhance BMP signalling, which is involved in neural development in Xenopus

Bone morphogenetic proteins (BMPs) play vital roles in regulating stem cell maintenance, differentiation and embryonic development. Intracellularly, BMP signalling is mediated by Smad proteins, which are regulated post-transcriptionally through reversible phosphorylation and ubiquitination. ZC4H2 is a small nuclear protein associated with intellectual disability and neural development in humans. Here, we report that ZC4H2 is highly expressed in the developing neural system and is involved in neural patterning and BMP signalling in Xenopus Knockdown of ZC4H2 led to expansion of the expression of the pan neural plate marker Sox2 in Xenopus embryos. In mammalian cells, ZC4H2 promotes BMP signalling and is involved in BMP regulated myogenic and osteogenic differentiation of mouse myoblast cells. Mechanistically, ZC4H2 binds and stabilizes Smad1 and Smad5 proteins through reducing their association with the Smurf ubiquitin ligases and thus their ubiquitination. We also found that a group of ZC4H2 mutations, which have been isolated in patients with intellectual disorders, showed weaker Smad-stabilizing activity, suggesting that the ZC4H2-Smad interaction might contribute to proper neural development in humans.

Expression of Noggin and Gremlin1 and its implications in fine-tuning BMP activities in mouse cartilage tissues

Increasing evidence supports the idea that bone morphogenetic proteins (BMPs) regulate cartilage maintenance in the adult skeleton. The aim of this study is to obtain insight into the regulation of BMP activities in the adult skeletal system. We analyzed expression of Noggin and Gremlin1, BMP antagonists that are known to regulate embryonic skeletal development, in the adult skeletal system by Noggin-LacZ and Gremlin1-LacZ knockin reporter mouse lines. Both reporters are expressed in the adult skeleton in a largely overlapping manner with some distinct patterns. Both are detected in the articular cartilage, pubic symphysis, facet joint in the vertebrae, and intervertebral disk, suggesting that they regulate BMP activities in these tissues. In a surgically induced knee osteoarthritis model in mice, expression of Noggin mRNA was lost from the articular cartilage, which correlated with loss of BMP2/4 and pSMAD1/5/8, an indicator of active BMP signaling. Both reporters are also expressed in the sterna and rib cartilage, suggesting an extensive role of BMP antagonism in adult cartilage tissue. Moreover, Noggin-LacZ was detected in sutures in the skull and broadly in the nasal cartilage, while Gremlin1-LacZ exhibits a weaker and more restricted expression domain in the nasal cartilage. These results suggest broad regulation of BMP activities by Noggin and Gremlin1 in cartilage tissues in the adult skeleton, and that BMP signaling and its antagonism by NOGGIN play a role in osteoarthritis development. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1671-1682, 2017.

Cellular reprogramming for clinical cartilage repair

The repair of articular cartilage needs a sufficient number of chondrocytes to replace the defect tissue, and therefore, expansion of cells is generally required. Chondrocytes derived by cellular reprogramming may provide a solution to the limitations of current (stem) cell-based therapies. In this article, two distinct approaches-induced pluripotent stem cell (iPSC)-mediated reprogramming and direct lineage conversion-are analysed and compared according to criteria that encompass the qualification of the method and the derived chondrocytes for the purpose of clinical application. Progress in iPSC generation has provided insights into the replacement of reprogramming factors by small molecules and chemical compounds. As follows, multistage chondrogenic differentiation methods have shown to improve the chondrocyte yield and quality. Nevertheless, the iPSC 'detour' remains a time- and cost-consuming approach. Direct conversion of fibroblasts into chondrocytes provides a slight advantage over these aspects compared to the iPSC detour. However, the requirement of constitutive transgene expression to inhibit hypertrophic differentiation limits this approach of being translated to the clinic. It can be concluded that the quality of the derived chondrocytes highly depends on the characteristics of the reprogramming method and that this is important to keep in mind during the experimental set-up. Further research into both reprogramming approaches for clinical cartilage repair has to include proper control groups and epigenetic profiling to optimize the techniques and eventually derive functionally stable articular chondrocytes.

Pathophysiology of Aortic Stenosis and Mitral Regurgitation

The global impact of the spectrum of valve diseases is a crucial, fast-growing, and underrecognized health problem. The most prevalent valve diseases, requiring surgical intervention, are represented by calcific and degenerative processes occurring in heart valves, in particular, aortic and mitral valve. Due to the increasing elderly population, these pathologies will gain weight in the global health burden. The two most common valve diseases are aortic valve stenosis (AVS) and mitral valve regurgitation (MR). AVS is the most commonly encountered valve disease nowadays and affects almost 5% of elderly population. In particular, AVS poses a great challenge due to the multiple comorbidities and frailty of this patient subset. MR is also a common valve pathology and has an estimated prevalence of 3% in the general population, affecting more than 176 million people worldwide. This review will focus on pathophysiological changes in both these valve diseases, starting from the description of the anatomical aspects of normal valve, highlighting all the main cellular and molecular features involved in the pathological progression and cardiac consequences. This review also evaluates the main approaches in clinical management of these valve diseases, taking into account of the main published clinical guidelines. © 2017 American Physiological Society. Compr Physiol 7:799-818, 2017.

Analysis and identification of the Grem2 heparin/heparan sulfate-binding motif

Bone morphogenetic proteins (BMPs) are regulated by extracellular antagonists of the DAN (differential screening-selected gene aberrative in neuroblastoma) family. Similar to the BMP ligands, certain DAN family members have been shown to interact with heparin and heparan sulfate (HS). Structural studies of DAN family members Gremlin-1 and Gremlin-2 (Grem2) have revealed a dimeric growth factor-like fold where a series of lysine residues cluster along one face of the protein. In the present study, we used mutagenesis, heparin-binding measurements, and cell surface-binding analysis to identify lysine residues that are important for heparin/HS binding in Grem2. We determined that residues involved in heparin/HS binding, while not necessary for BMP antagonism, merge with the heparin/HS-binding epitope of BMP2. Furthermore, the Grem2-BMP2 complex has higher affinity for heparin than the individual proteins and this affinity is not abrogated when the heparin/HS-binding epitope of Grem2 is attenuated. Overall, the present study shows that the Grem2 heparin/HS and BMP-binding epitopes are unique and independent, where, interestingly, the Grem2-BMP2 complex exhibits a significant increase in binding affinity toward heparin moieties that appear to be partially independent of the Grem2 heparin/HS-binding epitope.

Dynamic changes of epigenetic signatures during chondrogenic and adipogenic differentiation of mesenchymal stem cells

Extensive studies have been performed to clarify the processes during which mesenchymal stem cells (MSCs) differentiate into their lineage fates. In vitro differentiation of MSCs into distinct lineages have attracted the focus of a large number of clinical investigations. Although the gene expression profiling during differentiation of MSC toward bone, cartilage, and adipocytes is well established, the master regulators by which MSC fate can be controlled are not entirely determined. During differentiation of MSCs into a special cell fate, epigenetic mechanisms considered as the primary mediators that suppress the irrelevant genes and activate the genes required for a specific cell lineage. This review dedicated to addressing the changes of various epigenetic mechanisms, including DNA methylation, histone modifications, and micro-RNAs during chondrogenic and adipogenic differentiation of MSC.