The role of muscle cells in regulating cartilage matrix production

Bone-muscle crosstalk under physiological and pathological conditions

Anatomically connected bones and muscles determine movement of the body. Forces exerted on muscles are then turned to bones to promote osteogenesis. The crosstalk between muscle and bone has been identified as mechanotransduction previously. In addition to the mechanical features, bones and muscles are also secretory organs which interact closely with one another through producing myokines and osteokines. Moreover, besides the mechanical features, other factors, such as nutrition metabolism, physiological rhythm, age, etc., also affect bone-muscle crosstalk. What's more, osteogenesis and myogenesis within motor system occur almost in parallel. Pathologically, defective muscles are always detected in bone associated diseases and induce the osteopenia, inflammation and abnormal bone metabolism, etc., through biomechanical or biochemical coupling. Hence, we summarize the study findings of bone-muscle crosstalk and propose potential strategies to improve the skeletal or muscular symptoms of certain diseases. Altogether, functional improvement of bones or muscles is beneficial to each other within motor system.

Amyloid Beta Peptides Lead to Mast Cell Activation in a Novel 3D Hydrogel Model

Alzheimer's disease (AD) is a prevalent neurodegenerative disease and the world's primary cause of dementia among the elderly population. The aggregation of toxic amyloid-beta (Aβ) is one of the main pathological hallmarks of the AD brain. Recently, neuroinflammation has been recognized as one of the major features of AD, which involves a network of interactions between immune cells. The mast cell (MC) is an innate immune cell type known to serve as a first responder to pathological changes and crosstalk with microglia and neurons. Although an increased number of mast cells were found near the sites of Aβ deposition, how mast cells are activated in AD is not clear. We developed a 3D culture system to culture MCs and investigated the activation of MCs by Aβ peptides. Because collagen I is the major component of extracellular matrix (ECM) in the brain, we encapsulated human LADR MCs in gels formed by collagen I. We found that 3D-cultured MCs survived and proliferated at the same level as MCs in suspension. Additionally, they can be induced to secrete inflammatory cytokines as well as MC proteases tryptase and chymase by typical MC activators interleukin 33 (IL-33) and IgE/anti-IgE. Culturing with peptides Aβ1-42, Aβ1-40, and Aβ25-35 caused MCs to secrete inflammatory mediators, with Aβ1-42 inducing the maximum level of activation. These data indicate that MCs respond to amyloid deposition to elicit inflammatory responses and demonstrate the validity of collagen gel as a model system to investigate MCs in a 3D environment to understand neuroinflammation in AD.

Quadriceps strength is negatively associated with knee joint structural abnormalities-data from osteoarthritis initiative

OBJECTIVE

The aim of this study was to explore the longitudinal associations between baseline quadriceps strength and knee joint structural abnormalities in knee osteoarthritis (KOA).

METHODS

This study is a longitudinally observational study based on Osteoarthritis Initiative (OAI) cohort, including men and women aged 45-79. Quadriceps strength was measured by isometric knee extension testing at baseline. Knee joint structural abnormalities, including cartilage damage, bone marrow lesions (BMLs), effusion-synovitis and Hoffa-synovitis, were evaluated by Magnetic Resonance Imaging Osteoarthritis Knee Score (MOAKS) at baseline and 1-year follow-up. Generalized estimating equations were employed to examine the associations between quadriceps strength and knee structural abnormalities. All analyses were stratified by sex.

RESULTS

One thousand three hundred thirty-eight participants (523 men and 815 women) with a mean age of 61.8 years and a mean BMI of 29.4 kg/m² were included in this study. For men, no significantly longitudinal association of quadriceps strength with structural abnormalities was detected. In contrast, quadriceps strength was significantly and negatively associated with changes in cartilage damage and BMLs in lateral patellofemoral joint (PFJ) (cartilage damage: OR: 0.91, 95% CI 0.84 to 0.99, P = 0.023; BMLs: OR: 0.85, 95% CI 0.74 to 0.96, P = 0.011) and effusion-synovitis (OR = 0.88, 95% CI 0.78 to 0.99, P = 0.045) among females longitudinally. Higher quadriceps strength was significantly associated with less progression of lateral PFJ cartilage damage, BMLs and effusion-synovitis in females.

CONCLUSIONS

Higher quadriceps strength was associated with changes in cartilage damage and BMLs within the lateral PFJ and effusion-synovitis among females, suggesting the potential protective role of quadriceps strength on joint structures in women.

Automatic hip abductor muscle fat fraction estimation and association with early OA cartilage degeneration biomarkers

The aim of this study was to develop an automatic segmentation method for hip abductor muscles and find their fat fraction associations with early stage hip osteoarthritis (OA) cartilage degeneration biomarkers. This Institutional Review Board approved, Health Insurance Portability and Accountability Act compliant prospective study recruited 61 patients with evidence of hip OA or Femoroacetabular Impingement (FAI). Magnetic resonance (MR) images were acquired for cartilage segmentation, T_1ρ and T₂ relaxation times computation and grading of cartilage lesion scores. A 3D V-Net (Dice loss, Adam optimizer, learning rate = 1e^-4 , batch size = 3) was trained to segment the three muscles (gluteus medius, gluteus minimus, and tensor fascia latae). The V-Net performance was measured using Dice, distance maps between manual and automatic masks, and Bland-Altman plots of the fat fractions and volumes. Associations between muscle fat fraction and T_1ρ , T₂ relaxation times values were found using voxel based relaxometry (VBR). A p < 0.05 was considered significant. The V-Net had a Dice of 0.90, 0.88, and 0.91 (GMed, GMin, and TFL). The VBR results found associations of fat fraction of all three muscles in early stage OA and FAI patients with T_1ρ , T₂ relaxation times. Using an automatic, validated segmentation model, the associations derived between OA biomarkers and muscle fat fractions provide insight into early changes that occur in OA, and show that hip abductor muscle fat is associated with markers of cartilage degeneration.

A quantitative analysis of 3D-cell distribution in regenerating muscle-skeletal system with synchrotron X-ray computed microtomography

One of the greatest enigmas of modern biology is how the geometry of muscular and skeletal structures are created and how their development is controlled during growth and regeneration. Scaling and shaping of vertebrate muscles and skeletal elements has always been enigmatic and required an advanced technical level in order to analyse the cell distribution in 3D. In this work, synchrotron X-ray computed microtomography (µCT) and chemical contrasting has been exploited for a quantitative analysis of the 3D-cell distribution in tissues of a developing salamander (Pleurodeles waltl) limb – a key model organism for vertebrate regeneration studies. We mapped the limb muscles, their size and shape as well as the number and density of cells within the extracellular matrix of the developing cartilage. By using tomographic approach, we explored the polarity of the cells in 3D, in relation to the structure of developing joints. We found that the polarity of chondrocytes correlates with the planes in joint surfaces and also changes along the length of the cartilaginous elements. Our approach generates data for the precise computer simulations of muscle-skeletal regeneration using cell dynamics models, which is necessary for the understanding how anisotropic growth results in the precise shapes of skeletal structures.

Sarcopenic osteoarthritis: a new entity in geriatric medicine?

PURPOSE

Osteoarthritis, a disease characterized by cartilage degradation, abnormal subchondral bone remodeling and some grade of inflammation, and sarcopenia, a condition of low muscle mass associated with reduced strength and function, are prevalent disorders in older adults. In this review, we examine what is known about the relationship between osteoarthritis and sarcopenia, with particular focus on the older population. We also discuss how osteoarthritis and sarcopenia may interact and affect each other in clinical progression and the potential benefits from developing treatments that address such muscular-skeletal interaction.

METHODS

We searched in Pubmed and Scopus through a combination of search and MESH terms, for osteoarthritis and sarcopenia.

RESULTS

Even if more literature is needed, there is increasing evidence that decline in lower limb muscle strength is associated with knee or hip osteoarthritis in a pathological network of pain, altered joint stability, maladapted postures and defective neuromuscular communication. At the cellular levels, chondrocytes and myoblasts share common pathways, and the close anatomical location of both cell types also suggest the possibility of paracrine communication.

CONCLUSIONS

Sarcopenia and osteoarthritis are significantly intercorrelated and in the near future should be considered as an only entity, as we have recently proposed for sarcopenia and osteoporosis. The treatment of both sarcopenia and osteoarthritis is based on physical exercise and nutritional interventions with the aim of improving cartilage, bone and muscle health. Future studies are needed, particularly to know the exact prevalence of sarcopenia in people with osteoarthritis, its peculiar consequences and the most appropriate treatments.

The regenerative therapies of the ankle degeneration: a focus on multipotential mesenchymal stromal cells

The ankle degeneration ranging from focal osteochondral lesions to osteoarthritis can cause a total joint function loss. With rising life expectancy and activity of the patients, various regenerative therapies were introduced aiming to preserve the joint function via the induction of cartilage and bone repair. Here, biological events and mechanical changes of the ankle degeneration were discussed. The regenerative therapies were reviewed versus the standard surgical treatment. We especially focused on the use of mesenchymal (multipotential) stromal cells (MSCs) highlighting their dual functions of regeneration and cell modulation with an emphasis on the emerging MSC-based clinical studies. Being at an early step, more basic and clinical research is needed to optimize the applications of all ankle regenerative therapies including MSC-based methods.

Cartilage regeneration and ageing: Targeting cellular plasticity in osteoarthritis

Ageing processes play a major contributing role for the development of Osteoarthritis (OA). This prototypic degenerative condition of ageing is the most common form of arthritis and is accompanied by a general decline, chronic pain and mobility deficits. The disease is primarily characterized by articular cartilage degradation, followed by subchondral bone thickening, osteophyte formation, synovial inflammation and joint degeneration. In the early stages, osteoarthritic chondrocytes undergo phenotypic changes that increase cell proliferation and cluster formation and enhance the production of matrix-remodelling enzymes. In fact, chondrocytes exhibit differentiation plasticity and undergo phenotypic changes during the healing process. Current studies are focusing on unravelling whether OA is a consequence of an abnormal wound healing response. Recent investigations suggest that alterations in different proteins, such as TGF-ß/BMPs, NF-Kß, Wnt, and Cx43, or SASP factors involved in signalling pathways in wound healing response, could be directly implicated in the initiation of OA. Several findings suggest that osteoarthritic chondrocytes remain in an immature state expressing stemness-associated cell surface markers. In fact, the efficacy of new disease-modifying OA drugs that promote chondrogenic differentiation in animal models indicates that this may be a drug-sensible state. In this review, we highlight the current knowledge regarding cellular plasticity in chondrocytes and OA. A better comprehension of the mechanisms involved in these processes may enable us to understand the molecular pathways that promote abnormal repair and cartilage degradation in OA. This understanding would be advantageous in identifying novel targets and designing therapies to promote effective cartilage repair and successful joint ageing by preventing functional limitations and disability.

Association between grip strength and hand and knee radiographic osteoarthritis in Korean adults: Data from the Dong-gu study

Objectives

We assessed whether grip strength was related to various types of radiographic damage in Korean adults with osteoarthritis (OA).

Methods

Data from 2,251 subjects enrolled in the Dong-gu study, who had no hand joint pain, were analyzed to investigate the relationship between grip strength and OA. Hand grip strength was measured using a hand-held dynamometer, and radiographs of the hand and knee were scored according to a semi-quantitative grading system. Multiple linear regressions were used to explore associations between grip strength and radiographic features of OA.

Results

Grip strength in men and women was negatively related to hand (both p < 0.001) and knee (men, p < 0.001; women, p = 0.010) OA after adjusting for confounders. Hand (men, p < 0.001; women, p = 0.001) and knee (both p < 0.001) joint space narrowing (JSN) showed the strongest associations with low grip strength, regardless of gender. Moreover, the severity of hand osteophytes in women (p = 0.001), and subchondral cysts (men, p < 0.001) was correlated with low grip strength in both genders.

Conclusions

Among subjects without hand joint pain, low grip strength was associated significantly with hand and knee radiographic OA, regardless of gender. Among all types of OA radiographic damage, low grip strength showed the strongest association with JSN.

Caloric restriction minimizes aging effects on the femoral medial condyle

This study aimed to analyze the effects of caloric restriction on aged femoral articular cartilage of Wistar rats. Three groups of eight animals each were considered: young (YC) and old (OC) control groups fed with a normal diet and old caloric restriction group (OCR) composed of 18-month-old animals fed with a 31% less caloric diet from 6-months of age. Articular cartilage was studied through morphometry and immunohistochemistry. Body mass was 12% less in the OCR group than in the OC group. The articular cartilage from OC rats show thinner medial condyles, fewer chondrocytes, smaller chondrocytes nuclear volume and, in both condyles, a predominance of collagen type II and less collagen density compared to both YC and OCR groups (p < .001). In contrast, OCR articular cartilage show thicker medial condyles, larger chondrocytes nuclear volume and increased collagen density compared to OC group (p < 0.001). We concluded that caloric restriction minimizes the effects of aging on medial condyles of the femoral articular cartilage.

In vivo immunological properties research on mesenchymal stem cells based engineering cartilage by a dialyzer pocket model

As the seed cells, the immune properties of the mesenchymal stem cells are important for the tissue engineering restoring effect. But the in vivo research model is lacking. In the study, based on a dialyzer pocket model, changes in immunological properties and the differentiation of seeded mesenchymal stem cells (MSCs) in collagen hydrogel were studied in muscle and articular cavity implantation, respectively. The results showed that collagen hydrogel can induce MSCs to form cartilage tissue, followed by alteration of immunological properties. In muscle implantation, relatively low expression of major histocompatibility complex (MHC) molecules and low level of one-way mixed lymphocyte reactions (MLR) on the seeded MSCs were observed, but only a little cartilage tissue formed. In articular cavity implantation, more cartilage tissue formed, but higher MHC expressions and MLR level were found. Results indicated that the immunomodulation and the cartilage formation of the seeded MSCs will be impacted by the scaffold and the environment of the in vivo implanted site. The dialyzer pocket model can be used for the in vivo research for the MSC-based strategy of the tissue engineering, especially for the optimization of the immunomodulation.

Peritoneum and omentum are natural reservoirs for chondrocytes of osteochondral autografts: A comparative animal study

Objective

The purpose of this study was to investigate the effects of the omentum, peritoneum, paratenon and skeletal muscle on the proliferation of the cartilage tissue using rabbit model as an in vivo culture medium.

Methods

6 months old forty-five New Zealand rabbits were randomized into omentum, peritoneum, muscle, and Achilles paratenon groups. Standard sized osteochondral grafts were harvested from right knees and immediately placed into the specified tissues. Control group was fresh cartilage at the end of follow-up. After five months, samples were collected and evaluated macroscopically by measuring their dimensions (vertical = D1, horizontal = D2, and depth = D3) and volumes, and histologically by counting the chondrocyte number using camera lucida method.

Results

Macroscopically, increase in mean values for D1 and D2 dimensions of specimens from paratenon and omentum compared to pretransplant dimensions was statistically significant (p < 0.05). Although, volume measurements were higher in omentum and peritoneum group compared to pretransplant dimensions, increase was not significant (p > 0.05). Histologically, mean chondrocyte count was 14.0 ± 0.6 in fresh articular cartilage. Mean chondrocyte counts were 14.4 ± 0.9 in omentum group, 15.4 ± 1.0 in peritoneum group, 9.7 ± 1.3 in muscle group and 9.2 ± 0.4 in Achilles paratenon group respectively. However, mean chondrocyte counts were higher in samples of omentum and peritoneum group compared to fresh articular cartilage, increase was not statistically significant (p > 0.05).

Discussion

Transplantation of the cartilage grafts into mesothelium enhanced the chondrocyte counts and volumes compared with the pretransplant measurements. Mesothelium may have the potential to be used as an in vivo culture medium for osteochondral tissue growth.

Association of sarcopenia and physical activity with femur bone mineral density in elderly women

[Purpose]

This study examined the association of femur bone mineral density (BMD) with body composition and physical activity in elderly women.

[Methods]

This was a cross sectional study involving 119 women with mean age of 73.1±5.5 years. Body composition parameters including body mass index (BMI), percent of body fat (%BF), appendicular skeletal muscle mass (ASM) index and femur BMD was measured by dual-energy X-ray absorptiometry (DXA). Physical activity was assessed by the uniaxial accelerometer for 7 consecutive days including weekends. Based on femur BMD T-scores, subjects were classified as optimal group, osteopenia group, and osteoporosis group. Based on ASM index, subjects were classified as normal group and sarcopenia group. According to WHO recommendations of physical activity for elderly, the subjects were classified as active group or inactive group. Logistic regression analyses were used to determine the odds ratio (OR) for osteopenia and osteoporosis.

[Results]

There were linear decreases for body composition parameters including weight (P=.023), BMI (P=.039), lean mass (P=.032), ASM index (P=.007) and physical activity parameters including daily of step (P<.001), low intensity physical activity (P<.001), moderate intensity physical activity (P=.001) across femur BMD levels. Compared to the normal group (OR=1), the sarcopenia group had a significantly higher OR (OR=4.823; P=.042), and the inactive group had a significantly higher OR (OR=5.478; P=.005) having osteopenia and osteoporosis when compared to the active group (OR=1).

[Conclusion]

The findings of this study suggested that physical activity along with a healthy nutrition should be promoted as a preventive strategy against osteopenia and osteoporosis in elderly women.

Muscle and bone, two interconnected tissues

As bones are levers for skeletal muscle to exert forces, both are complementary and essential for locomotion and individual autonomy. In the past decades, the idea of a bone-muscle unit has emerged. Numerous studies have confirmed this hypothesis from in utero to aging works. Space flight, bed rest as well as osteoporosis and sarcopenia experimentations have allowed to accumulate considerable evidence. Mechanical loading is a key mechanism linking both tissues with a central promoting role of physical activity. Moreover, the skeletal muscle secretome accounts various molecules that affect bone including insulin-like growth factor-1 (IGF-1), basic fibroblast growth factor (FGF-2), interleukin-6 (IL-6), IL-15, myostatin, osteoglycin (OGN), FAM5C, Tmem119 and osteoactivin. Even though studies on the potential effects of bone on muscle metabolism are sparse, few osteokines have been identified. Prostaglandin E2 (PGE2) and Wnt3a, which are secreted by osteocytes, osteocalcin (OCN) and IGF-1, which are produced by osteoblasts and sclerostin which is secreted by both cell types, might impact skeletal muscle cells. Cartilage and adipose tissue are also likely to participate to this control loop and should not be set aside. Indeed, chondrocytes are known to secrete Dickkopf-1 (DKK-1) and Indian hedgehog (Ihh) and adipocytes produce leptin, adiponectin and IL-6, which potentially modulate bone and muscle metabolisms. The understanding of this system will enable to define new levers to prevent/treat sarcopenia and osteoporosis at the same time. These strategies might include nutritional interventions and physical exercise.

Scaffold structure and fabrication method affect proinflammatory milieu in three-dimensional-cultured chondrocytes

Cartilage tissue engineering has emerged as an attractive therapeutic option for repairing damaged cartilage tissue in the arthritic joint. High levels of proinflammatory cytokines present at arthritic joints can cause cartilage destruction and instability of the engineered cartilage tissue, and thus it is critical to engineer strong and stable cartilage that is resistant to the inflammatory environment. In this study, we demonstrate that scaffolding materials with different pore sizes and fabrication methods influence the microenvironment of chondrocytes and the response of these cells to proinflammatory cytokines, interleukin-1beta, and tumor necrosis factor alpha. Silk scaffolds prepared using the organic solvent hexafluoroisopropanol as compared to an aqueous-based method, as well as those with larger pore sizes, supported the deposition of higher cartilage matrix levels and lower expression of cartilage matrix degradation-related genes, as well as lower expression of endogenous proinflammatory cytokines IL-1β in articular chondrocytes. These biochemical properties could be related to the physical properties of the scaffolds such as the water uptake and the tendency to leach or adsorb proinflammatory cytokines. Thus, scaffold structure may influence the behavior of chondrocytes by influencing the microenvironment under inflammatory conditions, and should be considered as an important component for bioengineering stable cartilage tissues.

Muscle-bone interactions: basic and clinical aspects

Muscle and bone are anatomically and functionally closely connected. The traditional concept that skeletal muscles serve to load bone and transform skeletal segments into a system of levers has been further refined into the mechanostat theory, according to which striated muscle is essential for bone development and maintenance, modelling and remodelling. Besides biomechanical function, skeletal muscle and bone are endocrine organs able to secrete factors capable of modulating biological function within their microenvironment, in nearby tissues or in distant organs. The endocrine properties of muscle and bone may serve to sense and transduce biomechanical signals such as loading, unloading or exercise, or systemic hormonal stimuli into biochemical signals. Nonetheless, given the close anatomical relationship between skeletal muscle and bone, paracrine interactions particularly at the periosteal interface can be hypothesized. These mechanisms can assume particular importance during bone and muscle healing after musculoskeletal injury. Basic studies in vitro and in rodents have helped to dissect the multiple influences of skeletal muscle on bone and/or expression of inside-organ metabolism and have served to explain clinical observations linking muscle-to-bone quality. Recent evidences pinpoint that also bone tissue is able to modulate directly or indirectly skeletal muscle metabolism, thus empowering the crosstalk hypothesis to be further tested in humans in vivo.

Bearing arms against osteoarthritis and sarcopenia: when cartilage and skeletal muscle find common interest in talking together

Osteoarthritis, a disease characterized by cartilage degradation, abnormal subchondral bone remodelling and some grade of inflammation, and sarcopenia, a condition of pathological muscle weakness associated with altered muscle mass, strength, and function, are prevalent disorders in elderly people. There is increasing evidence that decline in lower limb muscle strength is associated with knee or hip osteoarthritis in a context of pain, altered joint stability, maladapted postures and defective neuromuscular communication. At the cellular and molecular levels, chondrocytes and myoblasts share common pathological targets and pathways, and the close anatomical location of both cell types suggest a possibility of paracrine communication. In this review, we examine the relationship between osteoarthritis and sarcopenia in the musculoskeletal field, and discuss the potential advantage of concomitant therapies, or how each disorder may benefit from treatment of the other.

Muscle cell-derived factors inhibit inflammatory stimuli-induced damage in hMSC-derived chondrocytes

OBJECTIVE

Pro-inflammatory cytokines play an important role in inducing cartilage degradation during osteoarthritis pathogenesis. Muscle is a tissue that lies near cartilage in situ. However, muscle's non-loading biochemical effect on cartilage has been largely unexplored. Here, we tested the hypothesis that muscle cells can regulate the response to pro-inflammatory cytokine-mediated damage in chondrocytes derived from human bone marrow-derived mesenchymal stem cells (hMSCs).

METHOD

hMSCs were allowed to undergo chondrogenic differentiation in porous silk scaffolds in the typical chondrogenic medium for 12 days. For the next 9 days, the cells were cultured in chondrogenic medium containing 50% conditioned medium derived from C2C12 muscle cells or fibroblast control cells, and were subject to treatments of pro-inflammatory cytokines IL-1β or TNFα.

RESULTS

Both IL-1β and TNFα-induced strong expression of multiple MMPs and hypertrophic markers Runx2 and type X collagen. Strikingly, culturing hMSC-derived chondrocytes in C2C12 muscle cell-conditioned medium strongly inhibited the expression of all these genes, a result further confirmed by GAG content and histological evaluation of matrix protein. To determine whether these effects were due to altered chondrocyte growth and survival, we assayed the expression of cell proliferation marker Ki67, cell cycle arrest markers p21 and p53, and apoptosis marker caspase 3. Muscle cell-conditioned medium promoted proliferation and inhibited apoptosis, thereby suggesting a possible decrease in the cellular aging and death that typically accompanies cartilage inflammation.

CONCLUSION

Our findings suggest the role of muscle in cartilage homeostasis and provide insight into designing strategies for promoting resistance to pro-inflammatory cytokines in hMSC-derived chondrocytes.

The influence of scaffold material on chondrocytes under inflammatory conditions

Cartilage tissue engineering aims to repair damaged cartilage tissue in arthritic joints. As arthritic joints have significantly higher levels of pro-inflammatory cytokines (such as IL-1β and TNFα that cause cartilage destruction, it is critical to engineer stable cartilage in an inflammatory environment. Biomaterial scaffolds constitute an important component of the microenvironment for chondrocytes in engineered cartilage. However, it remains unclear how the scaffold material influences the response of chondrocytes seeded in these scaffolds under inflammatory stimuli. Here we have compared the responses of articular chondrocytes seeded within three different polymeric scaffolding materials (silk, collagen and polylactic acid (PLA)) to IL-1β and TNFα. These scaffolds have different physical characteristics and yielded significant differences in the expression of genes associated with cartilage matrix production and degradation, cell adhesion and cell death. The silk and collagen scaffolds released pro-inflammatory cytokines faster and had higher uptake water abilities than PLA scaffolds. Correspondingly, chondrocytes cultured in silk and collagen scaffolds maintained higher levels of cartilage matrix than those in PLA, suggesting that these biophysical properties of scaffolds may regulate gene expression and the response to inflammatory stimuli in chondrocytes. Based on this study we conclude that selecting the proper scaffold material will aid in the engineering of more stable cartilage tissues for cartilage repair, and that silk and collagen are better scaffolds in terms of supporting the stability of three-dimensional cartilage under inflammatory conditions.

Soft-tissue reconstruction of open fractures of the lower limb: muscle versus fasciocutaneous flaps

Early vascularized soft-tissue closure has long been recognized to be essential in achieving eventual infection-free union. The question of whether muscle or fasciocutaneous tissue is superior in terms of promoting fracture healing remains unresolved. In this article, the authors review the experimental and clinical evidence for the different tissue types and advocate that the biological role of flaps should be included as a key consideration during flap selection.

Inflammation and Joint Tissue Interactions in OA: Implications for Potential Therapeutic Approaches

It is increasingly recognized that the pathogenesis of cartilage degradation in osteoarthritis (OA) is multifactorial and involves the interactions between cartilage and its surrounding tissues. These interactions regulate proinflammatory cytokine-mediated cartilage destruction, contributing to OA progression as well as cartilage repair. This review explores the pathogenesis of OA in the context of the multiple tissue types in the joint and discusses the implications of such complex tissue interaction in the development of anti-inflammatory therapeutics for the treatment of OA.

The skeletal muscle secretome: an emerging player in muscle-bone crosstalk

In vitro and in vivo studies provide evidence that a variety of growth factors and cytokines are actively secreted by muscle tissue. Muscle can therefore function as an endocrine and paracrine organ. These peptides characterize the muscle secretome, and many muscle-derived factors such as insulin-like growth factor-1, basic fibroblast growth factor, interleukin-15, myostatin and secreted protein acidic and rich in cysteine (osteonectin) are also known to have significant effects on bone metabolism. The factors secreted by muscle may vary according to muscle activity, in that muscle contraction, muscle atrophy or traumatic muscle injury can alter the type and relative abundance of particular factors released from muscle cells. The molecular and cellular pathways by which muscle-derived factors affect different types of bone cells (for example, osteoblasts, osteoclasts and osteocytes) are, however, poorly understood. Nevertheless, these findings further underscore the complex nature of muscle-bone interactions, and highlight the importance of integrating muscle biology and physiology into our understanding of bone growth, development and aging.

A role for myokines in muscle-bone interactions

This review presents the hypothesis that muscle is a source of secreted factors (myokines) that can influence bone mass in both positive and negative ways. Growth factor secretion by muscle may therefore be one pathway through which mechanical signals are transduced biologically.

Muscle cells enhance resistance to pro-inflammatory cytokine-induced cartilage destruction

Pro-inflammatory cytokines IL-1beta and TNFalpha play important roles in the manifestation of arthritis by disrupting the anabolic and catabolic activities of the chondrocytes. We observed a novel mechanism of cartilage regulation by which muscle cells diminish the response of chondrocytes to IL-1beta and TNFalpha. We found that chondrocytes cocultured with muscle cells or cultured in muscle cell-conditioned medium significantly enhanced the expression of cartilage matrix proteins (collagen II and collagen IX) and resisted IL-1beta and TNFalpha-induced cartilage damage. Our data suggest that this effect is achieved by inhibiting the expression of key components of the signaling pathways of pro-inflammatory cytokines (including NFkappaB, ESE-1, Cox-2, and GADD45beta), leading to attenuated expression of cartilage-degrading enzymes (MMPs and ADAMTS4). Therefore, our work unveils a potential role of muscle in regulating cartilage homeostasis and response to pro-inflammatory stimuli, and provides insights on designing treatment strategies for joint degenerative diseases such as arthritis.