Osteoarthritis year in review 2015: mechanics

High-resolution microCT analysis of sclerotic subchondral bone beneath bone-on-bone wear grooves in severe osteoarthritis

Osteoarthritis (OA) is associated with sclerosis, a thickening of the subchondral bone plate, yet little is known about bone adaptations around full-thickness cartilage defects in severe knee OA, particularly beneath bone-on-bone wear grooves. This high-resolution micro-computed tomography (microCT) study aimed to quantify subchondral bone microstructure relative to cartilage defect location, distance from the joint space, and groove depth. Ten tibial plateaus with full-thickness cartilage defects were microCT-scanned to determine defect location and size. Wear groove depth was estimated as the thickness from its deepest point to a surface interpolated from the defect edges. Two 5 × 5 mm specimens were sampled from three regions (defect, edge, and cartilage-covered areas) and two from the contralateral condyle, then scanned at higher resolution. Bone density profiles were analyzed as a function of distance from the joint space to identify cortical and trabecular regions of interest and and compute their respective bone density and microstructure. Cortical bone beneath defects was four times thicker under wear grooves than beneath cartilage. Bone density profiles significantly differed between the three specimen types at depths up to 5 mm. Below defects, cortical porosity was 85 % higher, and trabecular density 14 % higher, than in cartilage-covered specimens. Some trabecular spaces were filled with woven bone-like tissue, forming a new cortical layer. These changes were confined to the defect region and ceased abruptly at the defect edge. No correlation was found between bone microstructural indices and the estimated groove depth. Our findings suggest an ongoing migration of the cortical layer during formation of the groove from its original position into the underlying trabecular bone, a process we termed "trabecular corticalization." Under deeper wear grooves, the new cortical layer exhibited large pores connecting bone marrow to the joint space, suggesting physiological limits to corticalization. These results highlight specific bone adaptations beneath cartilage defects in severe OA and provide insights into the progression of subchondral bone changes under bone-on-bone contact areas.

Impact of core muscle strengthening on knee pain, patient outcomes, physical function, and cartilage thickness in knee osteoarthritis: Protocol for a randomized controlled trial

Knee Osteoarthritis (KOA) is a degenerative condition that significantly impacts individuals, causing disability. Routine rehabilitation methods primarily involve knee and hip strengthening exercises. While there is limited evidence supporting the potential benefits of core muscle strengthening in KOA rehabilitation, further research is needed to examine the effects of a structured core muscle strengthening protocol on pain, functional abilities, quality of life, and knee cartilage health. This double-blind, randomized controlled trial seeks to investigate the impact of integrating core muscle strengthening into routine rehabilitation. The study will randomly assign 80 participants to either routine rehabilitation or experimental groups, with both groups receiving routine rehabilitation combined with core strengthening exercises in the experimental group over a twelve-week period. The outcomes measured will include pain levels, patient-reported outcomes, physical functional abilities, core muscle and leg muscle strength, and cartilage height of the femur and tibia. Follow-up assessments will occur in the 4th, 8th, and 12th weeks. This novel study aims to provide valuable insights into the role of core strengthening in KOA rehabilitation, potentially influencing rehabilitation approaches and managing disease progression.•Incorporating core muscle strengthening into routine rehabilitation for KOA could open new possibilities for KOA management.•This study employs outcome measures recommended by OARSI for a thorough evaluation.•Additionally, it will investigate the impact on cartilage health, offering fresh insights into disease progression and the effects of exercise.

Key roles of the superficial zone in articular cartilage physiology, pathology, and regeneration

ABSTRACT

The superficial zone (SFZ) of articular cartilage is an important interface that isolates deeper zones from the microenvironment of the articular cavity and is directly exposed to various biological and mechanical stimuli. The SFZ is not only a crucial structure for maintaining the normal physiological function of articular cartilage but also the earliest site of osteoarthritis (OA) cartilage degeneration and a major site of cartilage progenitor cells, suggesting that the SFZ might represent a key target for the early diagnosis and treatment of OA. However, to date, SFZ research has not received sufficient attention, accounting for only about 0.58% of cartilage tissue research. The structure, biological composition, function, and related mechanisms of the SFZ in the physiological and pathological processes of articular cartilage remain unclear. This article reviews the key role of the SFZ in articular cartilage physiology and pathology and focuses on the characteristics of SFZ in articular cartilage degeneration and regeneration in OA, aiming to provide researchers with a systematic understanding of the current research status of the SFZ of articular cartilage, hoping that scholars will give more attention to the SFZ of articular cartilage in the future.

Electrical stimulation for cartilage tissue engineering - A critical review from an engineer's perspective

Cartilage has a limited intrinsic healing capacity. Hence, cartilage degradation and lesions pose a huge clinical challenge, particularly in an ageing society. Osteoarthritis impacts a significant number of the population and requires the development of repair and tissue engineering methods for hyaline articular cartilage. In this context, electrical stimulation has been investigated for more than 50 years already. Yet, no well-established clinical therapy to treat osteoarthritis by means of electrical stimulation exists. We argue that one reason is the lack of replicability of electrical stimulation devices from a technical perspective together with lacking hypotheses of the biophysical mechanism. Hence, first, the electrical stimulation studies reported in the context of cartilage tissue engineering with a special focus on technical details are summarized. Then, an experimental and numerical approach is discussed to make the electrical stimulation experiments replicable. Finally, biophysical hypotheses have been reviewed on the interaction of electric fields and cells that are relevant for cartilage tissue engineering. With that, the aim is to inspire future research to enable clinical electrical stimulation therapies to fight osteoarthritis.

Unraveling the path to osteoarthritis management: targeting chondrocyte apoptosis for therapeutic intervention

Osteoarthritis (OA) is a chronic disease affecting joints and further causing disabilities. This disease affects around 240 million people worldwide. It is a multifactorial disease, and its etiology is difficult to determine. Although numerous therapeutic strategies are available, the therapies are aimed at reducing pain and improving patients' quality of life. Hence, there is an urgent need to develop disease-modifying drugs (DMOAD) that can reverse or halt OA progression. Apoptosis is a cell removal process that is important in maintaining homeostatic mechanisms in the development and sustaining cell population. The apoptosis of chondrocytes is believed to play an important role in OA progression due to poor chondrocytes self-repair abilities to maintain the extracellular matrix (ECM). Hence, targeting chondrocyte apoptosis can be one of the potential therapeutic strategies in OA management. There are various mediators and targets available to inhibit apoptosis such as autophagy, endoplasmic reticulum (ER) stress, oxidative stress, and inflammation. As such, this review highlights the importance and potential targets that can be aimed to reduce chondrocyte apoptosis.

Effects of alendronate on cartilage lesions and micro-architecture deterioration of subchondral bone in patellofemoral osteoarthritic ovariectomized rats with patella-baja

BACKGROUND

Patellofemoral osteoarthritis (PFJOA) is a subtype of knee OA, which is one of the main causes of anterior knee pain. The current study found an increased prevalence of OA in postmenopausal women, called postmenopausal OA. Therefore, we designed the ovariectomized rat model of patella baja-induced PFJOA. Alendronate (ALN) inhibits osteoclast-mediated bone loss, and has been reported the favorable result of a potential intervention option of OA treatment. However, the potential effects of ALN treatment on PFJOA in the ovariectomized rat model are unknown and need further investigation prior to exploration in the clinical research setting. In this study, the effects of ALN on articular cartilage degradation and subchondral bone microstructure were assessed in the ovariectomized PFJOA rat model for 10 weeks.

METHODS

Patella baja and estrogen withdrawal were induced by patellar ligament shortening (PLS) and bilateral ovariectmomy surgeries in 3-month-old female Sprague-Dawley rats, respectively. Rats were randomly divided into five groups (n = 8): Sham + V; OVX + V, Sham + PLS + V, OVX + PLS + V, OVX + PLS + ALN (ALN: 70 μg/kg/week). Radiography was performed to evaluate patellar height ratios, and the progression of PFJOA was assessed by macroscopic and microscopic analyses, immunohistochemistry and micro-computed tomography (micro-CT).

RESULTS

Our results found that the patella baja model prepared by PLS can successfully cause degeneration of articular cartilage and subchondral bone, resulting in changes of PFJOA. OVX caused a decrease in estrogen levels in rats, which aggravated the joint degeneration caused by PFJOA. Early application of ALN can delay the degenerative changes of articular cartilage and subchondral bone microstructure in castrated PFJOA rat to a certain extent, improve and maintain the micrometabolism and structural changes of cartilage and subchondral bone.

CONCLUSION

The early application of ALN can delay the destruction of articular cartilage and subchondral bone microstructure in castrated PFJOA rat to a certain extent.

Understanding the Influence of Local Physical Stimuli on Chondrocyte Behavior

Investigating the mechanobiology of chondrocytes is challenging due to the complex micromechanical environment of cartilage tissue. The innate zonal differences and poroelastic properties of the tissue combined with its heterogeneous composition create spatial- and temporal-dependent cell behavior, which further complicates the investigation. Despite the numerous challenges, understanding the mechanobiology of chondrocytes is crucial for developing strategies for treating cartilage related diseases as chondrocytes are the only cell type within the tissue. The effort to understand chondrocyte behavior under various mechanical stimuli has been ongoing over the last 50 years. Early studies examined global biosynthetic behavior under unidirectional mechanical stimulus. With the technological development in high-speed confocal imaging techniques, recent studies have focused on investigating real-time individual and collective cell responses to multiple / combined modes of mechanical stimuli. Such efforts have led to tremendous advances in understanding the influence of local physical stimuli on chondrocyte behavior. In addition, we highlight the wide variety of experimental techniques, spanning from static to impact loading, and analysis techniques, from biochemical assays to machine learning, that have been utilized to study chondrocyte behavior. Finally, we review the progression of hypotheses about chondrocyte mechanobiology and provide a perspective on the future outlook of chondrocyte mechanobiology.

Effects of computer-aided rowing exercise systems on improving muscle strength and function in older adults with mild knee osteoarthritis: a randomized controlled clinical trial

Background

Osteoarthritis (OA) is common in aged adults and can result in muscle weakness and function limitations in lower limbs. Knee OA affects the quality of life in the elderly. Technology-supported feedback to achieve lower impact on knee joints and individualized exercise could benefit elderly patients with knee OA. Herein, a computer-aided feedback rowing exercise system is proposed, and its effects on improving muscle strength, health conditions, and knee functions of older adults with mild knee OA were investigated.

Methods

Thirty-eight older adults with mild knee OA and satisfying the American College of Rheumatology (ACR) clinical criteria participated in this randomized controlled clinical trial. Each subject was randomly assigned to a computer-aided rowing exercise (CRE) group (n = 20) or a control group (CON) (n = 18) that received regular resistance exercise programs two times per week for 12 weeks. Outcome measurements, including the Western Ontario and MacMaster Universities (WOMAC), muscle strength and functional fitness of the lower limbs, were evaluated before and after the intervention.

Results

Participants’ functional fitness in the CRE group exhibited significantly higher adjusted mean post-tests scores, including the WOMAC (p = 0.006), hip abductors strength (kg) (MD = 2.36 [1.28, 3.44], p = 5.67 × 10^–5), hip adductors strength (MD = 3.04 [1.38, 4.69], p = 0.001), hip flexors strength (MD = 4.01 [2.24, 5.78], p = 6.46 × 10⁻⁵), hip extensors strength (MD = 2.88 [1.64, 4.12], p = 4.43 × 10⁻⁵), knee flexors strength (MD = 2.03 [0.66, 3.41], p = 0.005), knee extensors strength (MD = 1.80 [0.65, 2.94], p = 0.003), and functional-reach (cm) (MD = 3.74 [0.68, 6.80], p = 0.018), with large effect sizes (η² = 0.17–0.42), than those in the CON group after the intervention.

Conclusions

Older adults with knee OA in the CRE group exhibited superior muscle strength, health conditions, and functional fitness improvements after the 12-week computer-aided rowing exercise program than those receiving the conventional exercise approach.

Trial registration

The Institutional Review Board of the Taipei Medical University approved the study protocol (no. N201908020, 27/05/2020) and retrospectively registered at ClinicalTrials.gov (trial registry no. NCT04919486, 09/06/2021).

Silencing of Angiopoietin-Like Protein 4 (Angptl4) Decreases Inflammation, Extracellular Matrix Degradation, and Apoptosis in Osteoarthritis via the Sirtuin 1/NF-κB Pathway

Osteoarthritis (OA) is a frequently observed condition in aged people. OA cartilage is characterized by chondrocyte apoptosis, chondrocyte inflammation, and hyperactive catabolism of extracellular matrix. However, the specific molecular mechanisms remain unclear. Recent data has shown that Angptl4, a multifunctional cytokine, is involved in the regulation of inflammatory and apoptosis responses in different tissues. This study is aimed at defining the role of Angptl4 in the development of OA. We employed X-ray analysis, safranin O-fast green (S-O) staining, and hematoxylin staining to evaluate histomorphological characteristics in the knee joint of mice. Real-time quantitative polymerase chain reaction, Western blot assays, immunofluorescence staining, and enzyme-linked immunosorbent assays (ELISA) were performed to analyze the changes in gene and protein expression. Mechanically, our data demonstrated that Angptl4 knockdown improved the degradation of extracellular matrix and reduced TNF-α-mediated chondrocyte inflammation and apoptosis by suppressing sirtuin 1/NF-κB signaling pathway. In addition, animal studies showed that the suppression of Angptl4 expression might alleviate OA development. In conclusion, our findings revealed the underlying mechanisms of Angptl4 regulation in chondrocytes and its potential value in the treatment of OA.

The articular cartilage surface is impaired by a loss of thick collagen fibers and formation of type I collagen in early osteoarthritis

Osteoarthritis (OA) is a joint disease affecting millions of patients worldwide. During OA onset and progression, the articular cartilage is destroyed, but the underlying complex mechanisms remain unclear. Here, we uncover changes in the thickness of collagen fibers and their composition at the onset of OA. For articular cartilage explants from knee joints of OA patients, we find that type I collagen-rich fibrocartilage-like tissue was formed in macroscopically intact cartilage, distant from OA lesions. Importantly, the number of thick fibers (>100 nm) has decreased early in the disease, followed by complete absence of thick fibers in advanced OA. We have obtained these results by a combination of high-resolution atomic force microscopy imaging under near-native conditions, immunofluorescence, scanning electron microscopy and a fluorescence-based classification of the superficial chondrocyte spatial organization. Taken together, our data suggests that the loss of tissue functionality in early OA cartilage is caused by a reduction of thick type II collagen fibers, likely due to the formation of type I collagen-rich fibrocartilage, followed by the development of focal defects in later OA stages. We anticipate that such an integrative characterization will be very beneficial for an in-depth understanding of other native biological tissues and the development of sustainable biomaterials. STATEMENT OF SIGNIFICANCE: In early osteoarthritis (OA) the cartilage appears macroscopically intact. However, this study demonstrates that the collagen network already changes in early OA by collagen fiber thinning and the formation of fibrocartilage-like tissue. Both nanoscopic deficiencies already occur in macroscopically intact regions of the human knee joint and are likely connected to processes that result in a weakened extracellular matrix. This study enhances the understanding of earliest progressive cartilage degeneration in the absence of external damage. The results suggest a determination of the mean collagen fiber thickness as a new target for the detection of early OA and a regulation of type I collagen synthesis as a new path for OA treatment.

Current concepts and perspectives for articular cartilage regeneration

Articular cartilage injuries are common in the population. The increment in the elderly people and active life results in an increasing demand for new technologies and good outcomes to satisfy longer and healthier life expectancies. However, because of cartilage's low regenerative capacity, finding an efficacious treatment is still challenging for orthopedics.

Since the pioneering studies based on autologous cell transplantation, regenerative medicine has opened new approaches for cartilage lesion treatment.

Tissue engineering combines cells, biomaterials, and biological factors to regenerate damaged tissues, overcoming conventional therapeutic strategies. Cells synthesize matrix structural components, maintain tissue homeostasis by modulating metabolic, inflammatory, and immunologic pathways. Scaffolds are well acknowledged by clinicians in regenerative applications since they provide the appropriate environment for cells, can be easily implanted, reduce surgical morbidity, allow enhanced cell proliferation, maturation, and an efficient and complete integration with surrounding articular cartilage. Growth factors are molecules that facilitate tissue healing and regeneration by stimulating cell signal pathways.

To date, different cell sources and a wide range of natural and synthetic scaffolds have been used both in pre-clinical and clinical studies with the aim to find the suitable solution for recapitulating cartilage microenvironment and inducing the formation of a new tissue with the biochemical and mechanical properties of the native one. Here, we describe the current concepts for articular cartilage regeneration, highlighting the key actors of this process trying to identify the best perspectives.

Hip abductor strengthening in patients diagnosed with knee osteoarthritis - a systematic review and meta-analysis

BACKGROUND

Globally osteoarthritis of the knee is a leading cause of disability. Hip abductor strength and activation are essential for maintaining postural balance during transfers and are related to joint loading and progression during weight-bearing activities. Strength deficits in the hip abductors might cause a reduction in the lower extremity force generation, thereby causing stress on the medial tibiofemoral joint. The aim of this systematic review is to assess the effectiveness of hip abductor strengthening on knee joint loading, knee pain and functional outcome measures in patients with knee osteoarthritis.

METHODS

Database such as Scopus, PubMed, EMBASE, Cochrane Central Register of Controlled Trials (CENTRAL) database and PEDro were reviewed to recognize the trials published in English from inception to December 2020. Randomized controlled trials that studied the effectiveness of hip abductor strengthening in subjects with knee osteoarthritis and its impact on knee joint loading, knee pain and functional outcome measures were included. RevMan 5.4 was used for meta-analysis and forest plot construction. Quality assessment of the included studies was carried out using the PEDro scale.

RESULTS AND DISCUSSION

The search yielded 260 results of which 29 full-text articles were screened. The review includes 7 randomized controlled trials and 3 studies with good methodological quality were included for meta-analysis. The meta-analysis of the articles favored hip abductor strengthening intervention over the control group. Hip abductor strengthening had significantly reduced the VAS [ SMD = -0.60[-0.88, -0.33] p < 0.0001]at 95% CI and improved the WOMAC scores [SMD - 0.75[-1.05,-0.45] p < 0.0001] at 95% CI. All of the included studies concluded that strengthening the hip abductor muscle had a positive impact on knee pain and functional outcomes.

CONCLUSION

The current study found high-quality evidence to support the use of hip abductor muscle strengthening exercises as a rehabilitative treatment for subjects with knee osteoarthritis.

TRIAL REGISTRATION

CRD42021256251 .

MMPs in tissues retrieved during surgery from patients with TMJ disorders relate to pain more than to radiological damage score

Orofacial pain is among the most common chronic pain conditions and can result from temporomandibular disorders (TMDs) of the temporomandibular joint (TMJ). Matrix metalloproteinases (MMPs) drive degeneration of TMJ tissues and likely mediate pain in TMJ disorders given their role in nociception. However, few studies have assessed MMPs in the TMJ innervated tissues nor in the context of pain. This study defined the extent of MMP-1, MMP-9, and MMP-2 in TMJ tissues from patients undergoing total joint replacement (TJR) or arthroplasty discectomy for painful TMJ disorders. Protein expression was probed by Western blot in TMJ disc and capsular ligaments taken during TJR (n = 6) or discectomy (n = 3) for osteoarthritis or internal derangement in an IRB-approved study. Pro- and active MMP-1, active MMP-9, and pro- and active MMP-2 are detectable. MMP-1 and MMP-9 correlate positively to each other (Kendall's τ = 0.63; p = 0.01), strengthening the hypothesis that they are mechanistically related in regulatory cascades. Active MMP-1 and active MMP-9 correlate positively with self-reported pain scores (τ ≥ 0.51; p ≤ 0.04), suggesting their involvement in peripheral nociception. Overall, neither MMPs nor pain correlate with the functional vertical opening of the jaw. MMP-1 varies with the observed stage of degeneration during surgery (p = 0.04). Neither overall MMPs nor pain correlate with the overall magnetic resonance imaging scores, corroborating the longstanding, but confounding, clinical observation that pain and radiological evidence of joint damage are not always related. Clinical significance: These findings suggest that MMPs mediate pain in innervated soft tissues and may be targets for diagnosing disease stage and treatments in painful TMJ disorders.

Sprifermin: Effects on Cartilage Homeostasis and Therapeutic Prospects in Cartilage-Related Diseases

When suffering from osteoarthritis (OA), articular cartilage homeostasis is out of balance and the living quality declines. The treatment of knee OA has always been an unsolved problem in the world. At present, symptomatic treatment is mainly adopted for OA. Drug therapy is mainly used to relieve pain symptoms, but often accompanied with adverse reactions; surgical treatment involves the problem of poor integration between the repaired or transplanted tissues and the natural cartilage, leading to the failure of repair. Biotherapy which aims to promote cartilage in situ regeneration and to restore endochondral homeostasis is expected to be an effective method for the prevention and treatment of OA. Disease-modifying osteoarthritis drugs (DMOADs) are intended for targeted treatment of OA. The DMOADs prevent excessive destruction of articular cartilage through anti-catabolism and stimulate tissue regeneration via excitoanabolic effects. Sprifermin (recombinant human FGF18, rhFGF18) is an effective DMOAD, which can not only promote the proliferation of articular chondrocyte and the synthesis of extracellular matrix, increase the thickness of cartilage in a dose-dependent manner, but also inhibit the activity of proteolytic enzymes and remarkedly slow down the degeneration of cartilage. This paper reviews the unique advantages of Sprifermin in repairing cartilage injury and improving cartilage homeostasis, aiming to provide an important strategy for the effective prevention and treatment of cartilage injury-related diseases.

Sparstolonin B suppresses free fatty acid palmitate-induced chondrocyte inflammation and mitigates post-traumatic arthritis in obese mice

Abnormal lipid metabolism, such as systemic increased free fatty acid, results in overproduction of pro‐inflammatory enzymes and cytokines, which is crucial in the development of obesity‐related osteoarthritis (OA). However, there are only a few drugs that target the lipotoxicity of OA. Recent researches have documented that the traditional Chinese medicine, Sparstolonin B (Ssn B), exerted anti‐inflammatory effects in various diseases, but not yet in OA. On the basis of this evidence, our works purposed to evaluate the effect of Ssn B on free fatty acid (FFA) palmitate (PA)‐stimulated human osteoarthritic chondrocytes and obesity‐associated mouse OA model. We found that Ssn B suppressed PA‐triggered inflammatory response and extracellular matrix catabolism in a concentration‐dependent approach. In vivo, Ssn B treatment inhibited cartilage degeneration and subchondral bone calcification caused by joint mechanical imbalance and alleviated metabolic inflammation in obesity. Mechanistically, co‐immunoprecipitine and molecular docking analysis showed that the formation of toll­like receptor 4 (TLR4)/myeloid differentiation protein‐2 (MD‐2) complex caused by PA was blocked by Ssn B. Subsequently, it leads to inactivation of PA‐caused myeloid differentiation factor 88 (MyD88)‐dependent nuclear factor‐kappaB (NF‐κB) cascade. Together, these findings demonstrated that Ssn B is a potential treatment agent for joint degenerative diseases in obese individuals.

Integrins, cadherins and channels in cartilage mechanotransduction: perspectives for future regeneration strategies

Articular cartilage consists of hyaline cartilage, is a major constituent of the human musculoskeletal system and has critical functions in frictionless joint movement and articular homoeostasis. Osteoarthritis (OA) is an inflammatory disease of articular cartilage, which promotes joint degeneration. Although it affects millions of people, there are no satisfying therapies that address this disease at the molecular level. Therefore, tissue regeneration approaches aim at modifying chondrocyte biology to mitigate the consequences of OA. This requires appropriate biochemical and biophysical stimulation of cells. Regarding the latter, mechanotransduction of chondrocytes and their precursor cells has become increasingly important over the last few decades. Mechanotransduction is the transformation of external biophysical stimuli into intracellular biochemical signals, involving sensor molecules at the cell surface and intracellular signalling molecules, so-called mechano-sensors and -transducers. These signalling events determine cell behaviour. Mechanotransducing ion channels and gap junctions additionally govern chondrocyte physiology. It is of great scientific and medical interest to induce a specific cell behaviour by controlling these mechanotransduction pathways and to translate this knowledge into regenerative clinical therapies. This review therefore focuses on the mechanotransduction properties of integrins, cadherins and ion channels in cartilaginous tissues to provide perspectives for cartilage regeneration.

Impacts of tai chi exercise on functional fitness in community-dwelling older adults with mild degenerative knee osteoarthritis: a randomized controlled clinical trial

Background

Degenerative osteoarthritis (OA) often leads to pain and stiffness of the affected joints, which may affect the physical performance and decrease the quality of life of people with degenerative knee OA. Compared to traditional exercise, tai chi is a safe exercise with slow movements which can facilitate physical functioning and psychological well being, and might be suitable for improving the physical activities of older adults with knee OA. Therefore, this study investigated the impacts of tai chi exercise on the functional fitness of community-dwelling older adults with degenerative knee OA.

Methods

Sixty-eight community-dwelling older adults with knee OA were recruited from the local community to participate in this randomized controlled clinical trial. All subjects were randomly assigned to either an TCE group that practiced tai chi exercise (TCE) (n = 36) or a control group (CON) (n = 32) that received regular health education programs twice per week for 12 weeks. Outcome measurements were determined using functional fitness tests before and after the intervention, including a 30-s chair stand (number of repeats), 30-s arm-curl (number of repeats), 2-min step (number of steps), chair sit-and-reach (reaching distance, cm), back-scratch flexibility (distance between hands, cm), single-leg stand (time, s), functional reach (reaching distance, cm), 8-foot up-and-go (time, s), and 10-m walk tests (time, s). Pre-post comparisons of functional fitness were analyzed using the ANCOVA test with SPSS software version 18.0.

Results

Results revealed that participants’ functional fitness in the TCE group had significantly higher adjusted mean post-tests scores than that in the CON group after the intervention, including the 8-foot up-and-go (s) (mean difference [MD]=-2.92 [-3.93, -1.91], p = 2.39*10^− 7), 30-s arm curl (MD = 4.75 (2.76, 6.73), p = 1.11*10^− 5), 2-min step (MD = 36.94 [23.53, 50.36], p = 7.08*10^− 7), 30-s chair stand (MD = 4.66 [2.97, 6.36], p = 6.96*10^− 7), functional-reach (MD = 5.86 [3.52, 8.20], p = 4.72*10^− 6), single-leg stand with eyes closed (MD = 3.44 [1.92, 4.97], p = 2.74*10^− 5), chair sit-and-reach (MD = 3.93 [1.72, 6.15], p = 0.001), and single-leg stand with eyes opened (MD = 17.07 [6.29, 27.85], p = 0.002), with large effect sizes (η²=0.14 ~ 0.34).

Conclusions

Community-dwelling older adults with knee OA in the TCE group had better functional fitness performances after the 12-week tai chi intervention than those receiving only health education.

α-Cyperone (CYP) down-regulates NF-κB and MAPKs signaling, attenuating inflammation and extracellular matrix degradation in chondrocytes, to ameliorate osteoarthritis in mice

Inflammation and extracellular matrix (ECM) degradation have been implicated in the pathological process of osteoarthritis (OA). α-Cyperone is the main active component of the traditional Chinese medicine Cyperus rotundus L. In this study, we found that α-Cyperone abolished the IL-1β-induced production of inflammatory cytokines in isolated rat chondrocytes, such as cyclooxygenase-2 (COX-2), tumor necrosis factor alpha (TNF-α), interleukin-6 (IL-6) and inducible nitric oxide synthase (iNOS), in a dose-dependent manner (0.75, 1.5 or 3 μM). Also, the results showed that α-Cyperone downregulated the expression of metalloproteinases (MMPs) and thrombospondin motifs 5 (ADAMTS5), and upregulated the expression of type-2 collagen. Mechanistically, molecular docking tests revealed that α-Cyperone stably and effectively binds to p65, p38, extracellular signal-regulated kinase (ERK), and c-Jun N-terminal kinase (JNK). α-Cyperone inhibited NF-κB activation by blocking its nuclear transfer, and decreasing the phosphorylation of mitogen-activated protein kinase (MAPKs). In addition, in vivo studies based on a mouse model of arthritis showed that α-Cyperone prevented the development of osteoarthritis. Therefore, α-Cyperone may be a potential anti-OA drug.

A Stretchable Scaffold with Electrochemical Sensing for 3D Culture, Mechanical Loading, and Real-Time Monitoring of Cells

In the field of three-dimensional (3D) cell culture and tissue engineering, great advance focusing on functionalized materials and desirable culture systems has been made to mimic the natural environment of cells in vivo. Mechanical loading is one of the critical factors that affect cell/tissue behaviors and metabolic activities, but the reported models or detection methods offer little direct and real-time information about mechanically induced cell responses. Herein, for the first time, a stretchable and multifunctional platform integrating 3D cell culture, mechanical loading, and electrochemical sensing is developed by immobilization of biomimetic peptide linked gold nanotubes on porous and elastic polydimethylsiloxane. The 3D scaffold demonstrates very good compatibility, excellent stretchability, and stable electrochemical sensing performance. This allows mimicking the articular cartilage and investigating its mechanotransduction by 3D culture, mechanical stretching of chondrocytes, and synchronously real-time monitoring of stretch-induced signaling molecules. The results disclose a previously unclear mechanotransduction pathway in chondrocytes that mechanical loading can rapidly activate nitric oxide signaling within seconds. This indicates the promising potential of the stretchable 3D sensing in exploring the mechanotransduction in 3D cellular systems and engineered tissues.

Hybrid fluorescence-AFM explores articular surface degeneration in early osteoarthritis across length scales

Atomic force microscopy (AFM) has become a powerful tool for the characterization of materials at the nanoscale. Nevertheless, its application to hierarchical biological tissue like cartilage is still limited. One reason is that such samples are usually millimeters in size, while the AFM delivers much more localized information. Here a combination of AFM and fluorescence microscopy is presented where features on a millimeter sized tissue sample are selected by fluorescence microscopy on the micrometer scale and then mapped down to nanometer precision by AFM under native conditions. This served us to show that local changes in the organization of fluorescent stained cells, a marker for early osteoarthritis, correlate with a significant local reduction of the elastic modulus, local thinning of the collagen fibers, and a roughening of the articular surface. This approach is not only relevant for cartilage, but in general for the characterization of native biological tissue from the macro- to the nanoscale. STATEMENT OF SIGNIFICANCE: Different length scales have to be studied to understand the function and dysfunction of hierarchically organized biomaterials or tissues. Here we combine a highly stable AFM with fluorescence microscopy and precisely motorized movement to correlate micro- and nanoscopic properties of articular cartilage on a millimeter sized sample under native conditions. This is necessary for unraveling the relationship between microscale organization of chondrocytes, micrometer scale changes in articular cartilage properties and nanoscale organization of collagen (including D-banding). We anticipate that such studies pave the way for a guided design of hierarchical biomaterials.

Biomechanical characteristics of tibio-femoral joint after partial medial meniscectomy in different flexion angles: a finite element analysis

BACKGROUND

Recent studies have pointed out that arthroscopy, the commonly-used surgical procedure for meniscal tears, may lead to an elevated risk of knee osteoarthritis (KOA). The biomechanical factors of KOA can be clarified by the biomechanical analysis after arthroscopic partial meniscectomy (APM). This study aimed to elucidate the cartilage stress and meniscus displacement of the tibiofemoral joint under flexion and rotation loads after APM.

METHODS

A detailed finite element model of the knee bone, cartilage, meniscus, and major ligaments was established by combining computed tomography and magnetic resonance images. Vertical load and front load were applied to simulate different knee buckling angles. At the same time, by simulating flexion of different degrees and internal and external rotations, the stresses on tibiofemoral articular cartilage and meniscus displacement were evaluated.

RESULTS

Generally, the contact stress on both the femoral tibial articular cartilage and the meniscus increased with the increased flexion degree. Moreover, the maximum stress on the tibial plateau gradually moved backward. The maximum position shift value of the lateral meniscus was larger than that of the medial meniscus.

CONCLUSION

Our finite element model provides a realistic three-dimensional model to evaluate the influence of different joint range of motion and rotating tibiofemoral joint stress distribution. The decreased displacement of the medial meniscus may explain the higher pressure on the knee components. These characteristics of the medial tibiofemoral joint indicate the potential biomechanical risk of knee degeneration.

Expression and Localization of Thrombospondins, Plastin 3, and STIM1 in Different Cartilage Compartments of the Osteoarthritic Varus Knee

Osteoarthritis (OA) is a multifactorial disease which is characterized by a change in the homeostasis of the extracellular matrix (ECM). The ECM is essential for the function of the articular cartilage and plays an important role in cartilage mechanotransduction. To provide a better understanding of the interaction between the ECM and the actin cytoskeleton, we investigated the localization and expression of the Ca²⁺-dependent proteins cartilage oligomeric matrix protein (COMP), thrombospondin-1 (TSP-1), plastin 3 (PLS3) and stromal interaction molecule 1 (STIM1). We investigated 16 patients who suffered from varus knee OA and performed a topographical analysis of the cartilage from the medial and lateral compartment of the proximal tibial plateau. In a varus knee, OA is more pronounced in the medial compared to the lateral compartment as a result of an overloading due to the malalignment. We detected a location-dependent staining of PLS3 and STIM1 in the articular cartilage tissue. The staining intensity for both proteins correlated with the degree of cartilage degeneration. The staining intensity of TSP-1 was clearly reduced in the cartilage of the more affected medial compartment, an observation that was confirmed in cartilage extracts by immunoblotting. The total amount of COMP was unchanged; however, slight changes were detected in the localization of the protein. Our results provide novel information on alterations in OA cartilage suggesting that Ca²⁺-dependent mechanotransduction between the ECM and the actin cytoskeleton might play an essential role in the pathomechanism of OA.

Proof-of-concept for the detection of early osteoarthritis pathology by clinically applicable endomicroscopy and quantitative AI-supported optical biopsy

OBJECTIVE

Clinical trials for osteoarthritis (OA), the leading cause of global disability, are unable to pinpoint the early, potentially reversible disease with clinical technology. Hence, disease-modifying drug candidates cannot be tested early in the disease. To overcome this obstacle, we asked whether early OA-pathology detection is possible with current clinical technology.

METHODS

We determined the relationship between two sensitive early OA markers, atomic force microscopy (AFM)-measured human articular cartilage (AC) surface stiffness, and location-matched superficial zone chondrocyte spatial organizations (SCSOs), asking whether a significant loss of surface stiffness can be detected in early OA SCSO stages. We then tested whether current clinical technology can visualize and accurately diagnose the SCSOs using an approved probe-based confocal laser-endomicroscope and a random forest (RF) model.

RESULTS

We demonstrated a correlation between AC surface stiffness and the SCSO (r_rm = -0.91; 95%CI: -0.97, -0.73), and an extensive loss of surface stiffness specifically in those ACs with early OA-typical SCSO (95%CIs: string SCSO: 269-173 kPa, double string SCSO: 77-46 kPa). This established the SCSO as a visualizable, functionally relevant surrogate marker of early OA AC surface pathology. Moreover, SCSO-based stiffness discrimination worked well in each patient's AC. We then demonstrated feasibility of visualizing the SCSO by clinical laser-endomicroscopy and, importantly, accurate SCSO diagnosis using RF.

CONCLUSION

We present the proof-of-concept of early OA-pathology detection with available clinical technology, introducing a future-oriented, AI-supported, non-destructive quantitative optical biopsy for early disease detection. Operationalizing SCSO recognition, this approach allows testing for correlations between local tissue architectures with other experimental and clinical read-outs, but needs clinical validation and a larger sample size for defining diagnostic thresholds.

Range-of-motion affects cartilage fluid load support: functional implications for prolonged inactivity

OBJECTIVE

Joint movements sustain cartilage fluid load support (FLS) through a combination of contact migration and periodic bath exposure. Although there have been suggestions that small involuntary movements may disrupt load-induced exudation during prolonged inactivity, theoretical studies have shown otherwise. This work used well-controlled explant measurements to experimentally test an existing hypothesis that the range-of-motion must exceed the contact length to sustain non-zero FLS.

METHOD

Smooth glass spheres (1.2-3.2 mm radius) were slid at 1.5 mm/s (Péclet number >100) against bovine osteochondral explants under varying normal loads (0.05-0.1 N) and migration lengths (0.05-7 mm) using a custom instrument. In situ deformation measurements were used to quantify FLS.

RESULTS

Non-zero FLS was maintained at migration lengths as small as 0.05 mm or <10% the typical contact diameter. FLS peaked when track lengths exceeded 10 times the contact diameter. For migration lengths below this threshold, FLS decreased with increased contact stress.

CONCLUSIONS

Migration lengths far smaller than the contact diameter can sustain non-zero FLS, which, from a clinical perspective, indicates that fidgeting and drifting can mitigate exudation and loss of FLS during prolonged sitting and standing. Nonetheless, FLS decreased monotonically with decreased migration length when migration lengths were less than 10 times the contact diameter. The results demonstrate: (1) potential biomechanical benefits from small movement (e.g., drifting and fidgeting); (2) the quantitative limits of those benefits; (3) and how loads, movement patterns, and mobility likely impact long term FLS.

Heterogeneous Strain Distribution in the Subchondral Bone of Human Osteoarthritic Femoral Heads, Measured with Digital Volume Correlation

Osteoarthritis (OA) is a chronic disease, affecting approximately one third of people over the age of 45. Whilst the etiology and pathogenesis of the disease are still not well understood, mechanics play an important role in both the initiation and progression of osteoarthritis. In this study, we demonstrate the application of stepwise compression, combined with microCT imaging and digital volume correlation (DVC) to measure and evaluate full-field strain distributions within osteoarthritic femoral heads under uniaxial compression. A comprehensive analysis showed that the microstructural features inherent in OA bone did not affect the level of uncertainties associated with the applied methods. The results illustrate the localization of strains at the loading surface as well as in areas of low bone volume fraction and subchondral cysts. Trabecular thickness and connectivity density were identified as the only microstructural parameters with any association to the magnitude of local strain measured at apparent yield strain or the volume of bone exceeding yield strain. This work demonstrates a novel approach to evaluating the mechanical properties of the whole human femoral head in case of severe OA.

Correlation between single nucleotide polymorphisms in CXCR4 microRNA binding site and the susceptibility to knee osteoarthritis in Han Chinese population

Background

This study aimed to investigate the relationship between single nucleotide polymorphisms (SNPs) at the microRNA target sequence in CXCR4 and the susceptibility to knee osteoarthritis (KOA).

Methods

A total of 305 patients with KOA and 305 healthy controls were recruited into this study. The genotypes of CXCR4 rs1804029 and rs17848060 loci were analyzed.

Results

The susceptibility to KOA of CXCR4 rs1804029 G allele carriers was 1.33 times (95% CI: 1.09‐1.54, P = .006) that of T allele carriers. The KOA susceptibility in individuals carrying T allele at CXCR4 rs17848060 locus was 1.38 times that of individuals carrying A allele (95% CI: 1.17‐1.57, P < .001). The G allele at CXCR4 rs1804029 locus was the target of hsa‐miR‐146a‐3p, while the A allele at CXCR4 rs17848060 locus could be targeted by hsa‐miR‐20a‐3p. The plasma level of hsa‐miR‐146a‐3p was lower in rs1804029 G allele carriers than T allele carriers (P < .001), whereas plasma level of hsa‐miR‐20a‐3p was higher in rs17848060 T allele carriers than A allele carriers (P < .001).

Conclusion

The SNPs at rs1804029 and rs17848060 loci in CXCR4 were significantly associated with the susceptibility to KOA in Han Chinese population.

Jumonji domain containing-3 (JMJD3) inhibition attenuates IL-1β-induced chondrocytes damage in vitro and protects osteoarthritis cartilage in vivo

OBJECTIVES

This study aimed to explore the effects and relative mechanism of JMJD3 on knee osteoarthritis (OA).

METHODS

In this study, we first analyzed the expression of JMJD3 in OA cartilage using western blot and immunohistochemistry. In an in vitro study, the effects of GSK-J4, JMJD3 inhibitor, on ATDC-5 chondrocytes were evaluated by CCK-8 assay. Real-time PCR and western blot were used to examine the inhibitory effect of GSK-J4 on the inflammation and ECM degradation of chondrocytes. NF-κB p65 phosphorylation and nuclear translocation were measured by western blot and immunofluorescence. In the animal study, twenty mice were randomized into four experimental groups: sham group, DMM-induced OA + DMSO group, OA + low-dose GSK-J4 group, and OA + high-dose GSK-J4 group. After the treatment, hematoxylin-eosin and safranin O/fast green staining were used to evaluate cartilage degradation of knee joint, with OARSI scores for quantitative assessment of cartilage damage.

RESULTS

Our results revealed that JMJD3 was overexpressed in OA cartilage and GSK-J4 could suppress the IL-1β-induced production of pro-inflammatory cytokines and catabolic enzymes, including IL-6, IL-8, MMP-9 and ADAMTS-5. Consistent with these findings, GSK-J4 could inhibit IL-1β-induced degradation of collagen II and aggrecan. Mechanistically, GSK-J4 dramatically suppressed IL-1β-stimulated NF-κB signal pathway activation. In vivo, GSK-J4 prevented cartilage damage in mouse DMM-induced OA model.

CONCLUSIONS

This study elucidates the important role of JMJD3 in cartilage degeneration in OA, and our results indicate that JDJM3 may become a novel therapeutic target in OA therapy.

Esculentoside A protects against osteoarthritis by ameliorating inflammation and repressing osteoclastogenesis

Osteoarthritis is a relatively common disorder of articular deterioration related to cartilage damage, subchondral bone remodelling, inflammation and metabolism. Agents that can inhibit cartilage degradation and osteoclastogenesis are required for the prevention and treatment of osteoarthritis. Esculentoside A, the highest concentration triterpene saponin isolated from the root of Phytolacca esculenta, has commonly been used for the treatment of chronic bronchitis. However, the role esculentoside A plays in ameliorating osteoarthritis has not been reported. We found that esculentoside A suppresses the expression of IL-1β-induced inflammatory and metabolic factors (IL-6, IL-8, TNF-α, MMP2, MMP3 and MMP13). In addition, esculentoside A restrains osteoclast formation by inhibiting the marker gene expression of NFATc1 and c-Fos. Our results indicate that esculentoside A markedly suppresses IL-1β-induced NF-κB and MAPK signalling pathway activation in chondrocytes, and inhibits RANKL-induced osteoclast precursor generation. Finally, treatment with esculentoside A inhibits the progressive cartilage degeneration and osteoclastogenesis in osteoarthritis mouse models. In summary, these results demonstrate that esculentoside A could be a latent therapeutic reagent for the treatment of osteoarthritis.

Osteoarthritis year in review 2019: mechanics

Mechanics play a critical - but not sole - role in the pathogenesis of osteoarthritis, and recent research has highlighted how mechanical constructs are relevant at the cellular, joint, and whole-body level related to osteoarthritis outcomes. This review examined papers from April 2018 to April 2019 that reported on the role of mechanics in osteoarthritis etiology, with a particular emphasis on studies that focused on the interaction between movement and tissue biomechanics with other clinical outcomes relevant to the pathophysiology of osteoarthritis. Studies were grouped by themes that were particularly prevalent from the past year. Results of the search highlighted the large exposure of knee-related research relative to other body areas, as well as studies utilizing laboratory-based motion capture technology. New research from this past year highlighted the important role that rate of exerted loads and rate of muscle force development - rather than simply force capacity (strength) - have in OA etiology and treatment. Further, the role of muscle activation patterns in functional and structural aspects of joint health has received much interest, though findings remain equivocal. Finally, new research has identified potential mechanical outcome measures that may be related to osteoarthritis disease progression. Future research should continue to combine knowledge of mechanics with other relevant research techniques, and to identify mechanical markers of joint health and structural and functional disease progression that are needed to best inform disease prevention, monitoring, and treatment.

Osteoarthritis and type 2 diabetes: From pathogenetic factors to therapeutic intervention

Over the last decades, osteoarthritis (OA) and type 2 diabetes (T2D) prevalence increased due to the global ageing population and the pandemic obesity. They currently affect a substantial part of the Western world population and are characterized by enhancing the risk of disability and reduction of quality of life. OA is a multifactorial condition whose development derives from the interaction between individual and environmental factors: The best known primarily include age, female gender, genetic determinants, articular biomechanics, and obesity (OB). Given the high prevalence of OA and T2D and their association with OB and inflammation, several studies have been conducted to investigate the causative role of biological characteristics proper to T2D on the development of OA. This review aims to analyse the relationship between of OA and T2D, in order to explain the pathophysiological drivers of the degenerative process and to delineate possible targets to which appropriate treatments may be addressed in the near future.

The relationship between urinary C-Telopeptide fragments of type II collagen, knee joint load, pain, and physical function in individuals with medial knee osteoarthritis

OBJECTIVE

Considering the osteoarthritis (OA) model that integrates the biological, mechanical, and structural components of the disease, the present study aimed to investigate the association between urinary C-Telopeptide fragments of type II collagen (uCTX-II), knee joint moments, pain, and physical function in individuals with medial knee OA.

METHODS

Twenty-five subjects radiographically diagnosed with knee OA were recruited. Participants were evaluated through three-dimensional gait analysis, uCTX-II level, the WOMAC pain and physical function scores, and the 40m walk test. The association between these variables was investigated using Pearson's product-moment correlation, followed by a hierarchical linear regression, controlled by OA severity and body mass index (BMI).

RESULTS

No relationship was found between uCTX-II level and knee moments. A significant correlation between uCTX-II level and pain, physical function, and the 40m walk test was found. The hierarchical linear regression controlling for OA severity and BMI showed that uCTX-II level explained 9% of the WOMAC pain score, 27% of the WOMAC physical function score, and 7% of the 40m walk test.

CONCLUSION

Greater uCTX-II level is associated with higher pain and reduced physical function and 40m walk test performance in individuals with medial knee OA.

Nifedipine inhibits oxidative stress and ameliorates osteoarthritis by activating the nuclear factor erythroid-2-related factor 2 pathway

Nifedipine is a voltage-gated calcium channel inhibitor widely used in the treatment of hypertension. Nifedipine has been reported to have antioxidant and anti-apoptotic effects and promotes cell proliferation. However, the effects of nifedipine on oxidative stress and apoptosis in osteoarthritic (OA) chondrocytes are still unclear. In this study, we sought to investigate whether nifedipine alleviates oxidative stress and apoptosis in OA through nuclear factor erythroid-2-related factor 2 (Nrf2) activation. The cytotoxicity of nifedipine against human chondrocytes was detected using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) kit, whereas mRNA and protein expression levels were measured using reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting, respectively. The oxidative stress level was analyzed by measuring reactive oxygen species (ROS), glutathione peroxidase (GSH-px), catalase (CAT) and superoxide dismutase (SOD) activities. The role of Nrf2 in the effect of nifedipine on OA was analyzed using an Nrf2 inhibitor brusatol (BR). The result showed that nifedipine inhibited the expression of matrix metalloprotein(MMP)-13, interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)-α, cyclooxygenase (COX)-2, inducible nitric oxide (NO) synthase (iNOS), and prostaglandin E2 (PGE2), as well as reduced ROS production in human OA chondrocytes, which was partially reversed by BR. Nifedipine prevented cartilage degeneration and contributed to the expression of Nrf-2 in chondrocytes. These results indicate that nifedipine inhibited inflammation and oxidative stress in chondrocytes via activation of Nrf-2/HO-1 signaling.

Effects of Controlling Abnormal Joint Movement on Expression of MMP13 and TIMP-1 in Osteoarthritis

OBJECTIVE

Abnormal joint movement is associated with osteoarthritis (OA). Previous studies using the controlling abnormal joint movement (CAJM) model of OA reported delayed cartilage degeneration; however, none of them focused on gait performance and the localization of matrix metalloproteinase 13 (MMP13) and tissue inhibitor of metalloproteinase-1 (TIMP-1) in chondrocytes. Therefore, we aimed to investigate the effect of controlling abnormal joint movement on gait performance and the localization of MMP13 and TIMP-1, using kinematic and histological analyses.

DESIGN

Rats were assigned to 2 groups: anterior cruciate ligament transection (ACL-T) group and CAJM group (n = 5/group); contralateral hind limbs of ACL-T rats were designated as intact. After 1, 2, and 4 weeks, step length was analyzed, and after 2, 4, and 8 weeks, Safranin O-Fast Green staining and immunohistochemical staining for MMP13 and TIMP-1 were performed.

RESULTS

Step length did not differ significantly between the groups. However, degeneration of articular cartilage was higher in the ACL-T group than in the intact group (P < 0.05). There was no significant difference in the CAJM group at all time points. Immunohistochemical analysis of the MMP13/TIMP-1 relationship revealed a significant increase in the expression ratio of MMP13 after 4 weeks in the ACL-T group compared to the CAJM group (P < 0.05).

CONCLUSIONS

Controlling abnormal joint movement may reduce mechanical stress owing to kinematic elements of small articulation including joint instability and delayed cartilage degeneration, despite the lack of kinematic change in step length.

MicroRNA-365 functions as a mechanosensitive microRNA to inhibit end plate chondrocyte degeneration by targeting histone deacetylase 4

End plate chondrocyte degeneration is a major cause of intervertebral disc degeneration. Mechanical biophysical forces, including intermittent cyclic mechanical tension (ICMT), exacerbate end plate chondrocyte degeneration. However, the underlying molecular mechanism of mechanical stretch-induced end plate chondrocyte degeneration is still unclear. This study sought to determine whether microRNAs (miRNAs) respond to mechanical stretch and play a role in regulating mechanically-induced end plate chondrocyte degeneration. We identified miR-365 as a mechanoresponsive miRNA in primary human end plate chondrocytes after ICMT application by miRNA microarray analysis. The expression of miR-365 was down-regulated in the disc samples obtained from patients with disc degeneration. We also found that the miR-365 stimulates chondrocyte proliferation but does not promote end plate chondrocyte death. Using bioinformatic analyses and subsequent confirmation by real-time RT-PCR, we identified multiple candidate target genes of miR-365 that responded to in vitro mechanical stimulation; among them, HDAC4 was fully characterized. Mutation of putative miR-365 binding sites in HDAC4 mRNA abolished miR-365 mediated repression of HDAC4 3'-untranslated region (3'UTR) luciferase reporter activity, suggesting that miR-365 binds to the HDAC4 3'UTR. Overexpression of miR-365 significantly decreased the HDAC4 protein level, suggesting that miR-365 acts as an endogenous attenuator of HDAC4 in human end plate chondrocytes. Further, perturbation of miR-365 expression also had a significant effect on the expression of COL2A and ACAN and on matrix degeneration. Overexpression of HDAC4 abolished miR-365 rescued end plate chondrocyte degeneration during ICMT application. Furthermore, we found that the wnt/β-catenin signal pathway was related to HDAC4 and promoted end plate chondrocyte degeneration. Overall, our results suggest that miR-365 is a mechanosensitive miRNA that regulates human chondrocyte degeneration by directly targeting HDAC4. We propose that therapeutic regulation of miR-365 may be an efficient anabolic strategy for inhibiting end plate chondrocyte degeneration.

Proteoglycan degradation mimics static compression by altering the natural gradients in fibrillar organisation in cartilage

Structural and associated biomechanical gradients within biological tissues are important for tissue functionality and preventing damaging interfacial stress concentrations. Articular cartilage possesses an inhomogeneous structure throughout its thickness, driving the associated variation in the biomechanical strain profile within the tissue under physiological compressive loading. However, little is known experimentally about the nanostructural mechanical role of the collagen fibrils and how this varies with depth. Utilising a high-brilliance synchrotron X-ray source, we have measured the depth-wise nanostructural parameters of the collagen network in terms of the periodic fibrillar banding (D-period) and associated parameters. We show that there is a depth dependent variation in D-period reflecting the pre-strain and concurrent with changes in the level of intrafibrillar order. Further, prolonged static compression leads to fibrillar changes mirroring those caused by removal of extrafibrillar proteoglycans (as may occur in aging or disease). We suggest that fibrillar D-period is a sensitive indicator of localised changes to the mechanical environment at the nanoscale in soft connective tissues.

Statement of Significance

Collagen plays a significant role in both the structural and mechanical integrity of articular cartilage, allowing the tissue to withstand highly repetitive loading. However, the fibrillar mechanics of the collagen network in cartilage are not clear. Here we find that cartilage has a spatial gradient in the nanostructural collagen fibril pre-strain, with an increase in the fibrillar pre-strain with depth. Further, the fibrillar gradient changes similarly under compression when compared to an enzymatically degraded tissue which mimics age-related changes. Given that the fibrils potentially have a finite capacity to mechanically respond and alter their configuration, these findings are significant in understanding how collagen may alter in structure and gradient in diseased cartilage, and in informing the design of cartilage replacements.

Ex vivo physiological compression of human osteoarthritis cartilage modulates cellular and matrix components

Mechanical stimulation appears to play a key role in cartilage homeostasis maintenance, but it can also contribute to osteoarthritis (OA) pathogenesis. Accumulating evidence suggests that cartilage loading in the physiological range contributes to tissue integrity maintenance, whereas excessive or reduced loading have catabolic effects. However, how mechanical stimuli can regulate joint homeostasis is still not completely elucidated and few data are available on human cartilage. We aimed at investigating human OA cartilage response to ex vivo loading at physiological intensity. Cartilage explants from ten OA patients were subjected to ex vivo controlled compression, then recovered and used for gene and protein expression analysis of cartilage homeostasis markers. Compressed samples were compared to uncompressed ones in presence or without interleukin 1β (IL-1β) or interleukin 4 (IL-4). Cartilage explants compressed in combination with IL-4 treatment showed the best histological scores. Mechanical stimulation was able to significantly modify the expression of collagen type II (collagen 2), aggrecan, SOX9 transcription factor, cartilage oligomeric matrix protein (COMP), collagen degradation marker C2C and vascular endothelial growth factor (VEGF). Conversely, ADAMTS4 metallopeptidase, interleukin 4 receptor alpha (IL4Rα), chondroitin sulfate 846 epitope (CS846), procollagen type 2 C-propeptide (CPII) and glycosaminoglycans (GAG) appeared not modulated. Our data suggest that physiological compression of OA human cartilage modulates the inflammatory milieu by differently affecting the expression of components and homeostasis regulators of the cartilage extracellular matrix.

Ibuprofen attenuates interleukin-1β-induced inflammation and actin reorganization via modulation of RhoA signaling in rabbit chondrocytes

Ibuprofen, a medication in the nonsteroidal anti-inflammatory drug class, is widely used for treating inflammatory diseases such as osteoarthritis. It has been shown in recent years that ibuprofen has a strong effect on Ras homolog gene family, member A (RhoA) inhibition in multiple cell types. Our previous finding also demonstrated that interleukin-1β (IL-1β) increases filamentous actin (F-actin) of chondrocytes via RhoA pathway. Therefore, we hypothesized that ibuprofen may suppress the IL-1β-induced F-actin upregulation in chondrocytes by inhibiting RhoA pathway. To this end, in this study, articular chondrocytes from New Zealand White rabbits were pretreated with 500 μM ibuprofen for 2 h, then with 10 ng/ml IL-1β for 24 h. Results showed that pretreatment with ibuprofen inhibited the IL-1β-induced nitric oxide (NO) and prostaglandin E2 (PGE2) production, protected the chondrocyte phenotype from IL-1β stimulation, and inhibited the IL-1β-induced actin remodeling via RhoA signaling modulation. In conclusion, ibuprofen showed not only anti-inflammatory function, but also RhoA inhibition in articular chondrocytes.

Concentration-Dependent Effects of Fibroblast-Like Synoviocytes on Collagen Gel Multiscale Biomechanics and Neuronal Signaling: Implications for Modeling Human Ligamentous Tissues

Abnormal loading of a joint's ligamentous capsule causes pain by activating the capsule's nociceptive afferent fibers, which reside in the capsule's collagenous matrix alongside fibroblast-like synoviocytes (FLS) and transmit pain to the dorsal root ganglia (DRG). This study integrated FLS into a DRG-collagen gel model to better mimic the anatomy and physiology of human joint capsules; using this new model, the effect of FLS on multiscale biomechanics and cell physiology under load was investigated. Primary FLS cells were co-cultured with DRGs at low or high concentrations, to simulate variable anatomical FLS densities, and failed in tension. Given their roles in collagen degradation and nociception, matrix-metalloproteinase (MMP-1) and neuronal expression of the neurotransmitter substance P were probed after gel failure. The amount of FLS did not alter (p > 0.3) the gel failure force, displacement, or stiffness. FLS doubled regional strains at both low (p < 0.01) and high (p = 0.01) concentrations. For high FLS, the collagen network showed more reorganization at failure (p < 0.01). Although total MMP-1 and neuronal substance P were the same regardless of FLS concentration before loading, protein expression of both increased after failure, but only in low FLS gels (p ≤ 0.02). The concentration-dependent effect of FLS on microstructure and cellular responses implies that capsule regions with different FLS densities experience variable microenvironments. This study presents a novel DRG-FLS co-culture collagen gel system that provides a platform for investigating the complex biomechanics and physiology of human joint capsules, and is the first relating DRG and FLS interactions between each other and their surrounding collagen network.

Lateral Meniscal Graft Transplantation: Effect of Fixation Method on Joint Contact Mechanics During Simulated Gait

BACKGROUND

Controversy exists regarding the optimal bony fixation technique for lateral meniscal allografts.

PURPOSE/HYPOTHESIS

The objective was to quantify knee joint contact mechanics across the lateral plateau for keyhole and bone plug meniscal allograft transplant fixation techniques throughout simulated gait. It was hypothesized that both methods of fixation would improve contact mechanics relative to the meniscectomized condition, while keyhole fixation would restore the distribution of contact stress closer to that of the intact knee.

STUDY DESIGN

Controlled laboratory study.

METHODS

Six human cadaveric knees were mounted on a multidirectional dynamic simulator and subjected to the following conditions: (1) native intact meniscus, (2) keyhole fixation of the native meniscus, (3) bone plug fixation of the native meniscus, and (4) meniscectomy. Contact area, peak contact stress, and the distribution of stress across the tibial plateau were computed at 14% and 45% of the gait cycle, at which axial forces are at their highest. Translation of the weighted center of contact stress throughout simulated gait was computed.

RESULTS

Both bony fixation techniques improved contact mechanics relative to the meniscectomized condition. The keyhole technique was not significantly different from the intact condition for the following metrics: contact area, peak contact stress, distribution of force between the meniscal footprint and cartilage-to-cartilage contact, and the position of the weighted center of contact. In contrast, bone plug fixation resulted in a significant decrease of 21% to 28% in contact area at 14% and 45% of the simulated gait cycle, a significant increase in peak contact stresses of 34% at 45% of the gait cycle, and a shift in the weighted center of contact, which increased forces in the cartilage-to-cartilage contact area at 45% of the gait cycle.

CONCLUSION

While both keyhole and bone plug fixation methods improved lateral compartment contact mechanics relative to the meniscectomized knee, keyhole fixation restored contact mechanics closer to that of the intact knee.

CLINICAL RELEVANCE

Method of meniscal fixation is under the direct control of the surgeon. From a biomechanics perspective, keyhole fixation is advocated for its ability to mimic intact knee joint contact mechanics.

Isofraxidin targets the TLR4/MD-2 axis to prevent osteoarthritis development

Osteoarthritis (OA) is a major cause of joint pain and disability, resulting in large socioeconomic costs worldwide. Isofraxidin (ISO), a bioactive coumarin compound isolated from the functional foods Siberian ginseng and Apium graveolens, exerts anti-inflammatory effects in a variety of diseases. However, no studies have reported the protective effects of ISO against OA development. Accordingly, this study aimed to assess the therapeutic effect of ISO in human OA chondrocytes, and in a mouse model of OA induced by destabilisation of the medial meniscus (DMM). In vitro, lipopolysaccharide (LPS)-induced overproduction of nitric oxide (NO), prostaglandin E2 (PGE2), tumour necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) was decreased by ISO pre-treatment. Furthermore, ISO attenuated the increased expression of inflammatory enzymes, including inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), in response to LPS stimulation. Meanwhile, LPS-induced extracellular matrix (ECM) degradation was also reversed by ISO treatment. Mechanistically, ISO competitively inhibited Toll-like receptor 4 (TLR4)/myeloid differentiation protein-2 (MD-2) complex formation, and thus TLR4/nuclear factor kappa B (NF-κB) signalling cascades. In vivo, ISO treatment not only prevented the calcification and erosion of cartilage, as well as the thickening of subchondral bone, but also reduced the serum levels of inflammatory cytokines in the mouse OA model. Taken together, these data suggest that ISO has potential in the treatment of OA.

Effect of degenerative and radial tears of the meniscus and resultant meniscectomy on the knee joint: a finite element analysis

Objective

The objective of this study is to investigate the biomechanics on the knee components caused by degenerative and radial meniscal tears and resultant meniscectomy.

Methods

A detailed finite element model of the knee joint with bones, cartilages, menisci and main ligaments was constructed from a combination of computed tomography and magnetic resonance images. Degenerative and radial tears of both menisci and resultant medial meniscectomy were used and two different kinds of simulations, the vertical and the anterior load, mimicking the static stance and slight flexion simulations, were applied on the model. The compressive and shear stress and meniscus extrusion were evaluated and compared.

Results

Generally, both degenerative and radial tears lead to increased peak compressive and shear stress of both cartilages and menisci and large meniscus extrusion, and the medial meniscal tear induced larger value of stress and extrusion than the lateral meniscal tear. The peak stress and meniscus extrusion further elevated after the medial meniscus meniscectomy. Distribution of stress was shifted from the intact hemi joint to the injured hemi joint with either medial or lateral meniscal tear.

Conclusion

Our finite element model provides a realistic three-dimensional knee model to investigate the effects of degenerative and radial meniscal tears and resultant meniscectomy on the stress distribution of the knee. The stress was increased in meniscal tears and increased significantly when meniscectomy was performed. Increased meniscus extrusion may explain the mechanism for higher stress on the components of the knee.

The translational potential of this article

Meniscal tears are the most common damage associated to the menisci, and meniscectomy is often performed to relieve the pain and instability of the knee. The results of our study indicated increased stress on cartilages and menisci, which may lead to early onset of osteoarthritis. This may guide surgeons to preserve more of the meniscus when performing meniscectomy.

3D printing of musculoskeletal tissues: impact on safety and health at work

Additive manufacturing (commonly referred to as 3D printing) created an attractive approach for regenerative medicine research in musculoskeletal tissue engineering. Given the high number of fabrication technologies available, characterized by different working and physical principles, there are several related risks that need to be managed to protect operators. Recently, an increasing number of studies demonstrated that several types of 3D printers are emitters of ultrafine particles and volatile organic compounds whose harmful effects through inhalation, ingestion and skin uptake are known. Confirmation of danger of these products is not yet final, but this provides a basis to adopt preventive measures in agreement with the precautionary principle. The purpose of this investigation was to provide a useful tool to the researcher for managing the risks related to the use of different kinds of three-dimensional printers (3D printers) in the lab, especiallyconcerning orthopedic applications, and to define appropriate control measures. Particular attention was given to new emerging risks and to developing response strategies for a comprehensive coverage of the health and safety of operators.

Osteoarthritis and intervertebral disc degeneration: Quite different, quite similar

Intervertebral disc degeneration describes the vicious cycle of the deterioration of intervertebral discs and can eventually result in degenerative disc disease (DDD), which is accompanied by low-back pain, the musculoskeletal disorder with the largest socioeconomic impact world-wide. In more severe stages, intervertebral disc degeneration is accompanied by loss of joint space, subchondral sclerosis, and osteophytes, similar to osteoarthritis (OA) in the articular joint. Inspired by this resemblance, we investigated the analogy between human intervertebral discs and articular joints. Although embryonic origin and anatomy suggest substantial differences between the two types of joint, some features of cell physiology and extracellular matrix in the nucleus pulposus and articular cartilage share numerous parallels. Moreover, there are great similarities in the response to mechanical loading and the matrix-degrading factors involved in the cascade of degeneration in both tissues. This suggests that the local environment of the cell is more important to its behavior than embryonic origin. Nevertheless, OA is widely regarded as a true disease, while intervertebral disc degeneration is often regarded as a radiological finding and DDD is undervalued as a cause of chronic low-back pain by clinicians, patients and society. Emphasizing the similarities rather than the differences between the two diseases may create more awareness in the clinic, improve diagnostics in DDD, and provide cross-fertilization of clinicians and scientists involved in both intervertebral disc degeneration and OA.

Mechanical stress contributes to osteoarthritis development through the activation of transforming growth factor beta 1 (TGF-β1)

Objectives

The role of mechanical stress and transforming growth factor beta 1 (TGF-β1) is important in the initiation and progression of osteoarthritis (OA). However, the underlying molecular mechanisms are not clearly known.

Methods

In this study, TGF-β1 from osteoclasts and knee joints were analyzed using a co-cultured cell model and an OA rat model, respectively. Five patients with a femoral neck fracture (four female and one male, mean 73.4 years (68 to 79)) were recruited between January 2015 and December 2015. Results showed that TGF-β1 was significantly upregulated in osteoclasts by cyclic loading in a time- and dose-dependent mode. The osteoclasts were subjected to cyclic loading before being co-cultured with chondrocytes for 24 hours.

Results

A significant decrease in the survival rate of co-cultured chondrocytes was found. Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labelling (TUNEL) assay demonstrated that mechanical stress-induced apoptosis occurred significantly in co-cultured chondrocytes but administration of the TGF-β1 receptor inhibitor, SB-505124, can significantly reverse these effects. Abdominal administration of SB-505124 can attenuate markedly articular cartilage degradation in OA rats.

Conclusion

Mechanical stress-induced overexpression of TGF-β1 from osteoclasts is responsible for chondrocyte apoptosis and cartilage degeneration in OA. Administration of a TGF-β1 inhibitor can inhibit articular cartilage degradation.

Cite this article: R-K. Zhang, G-W. Li, C. Zeng, C-X. Lin, L-S. Huang, G-X. Huang, C. Zhao, S-Y. Feng, H. Fang. Mechanical stress contributes to osteoarthritis development through the activation of transforming growth factor beta 1 (TGF-β1). Bone Joint Res 2018;7:587–594. DOI: 10.1302/2046-3758.711.BJR-2018-0057.R1.

Dehydroepiandrosterone: Molecular mechanisms and therapeutic implications in osteoarthritis

Dehydroepiandrosterone (DHEA), a 19-carbon steroid hormone primarily synthesized in the adrenal gland, exerts a chondroprotective effect against osteoarthritis (OA) and has been considered an effective candidate of disease-modifying OA drugs (DMOADs) that slow disease progression. We and others previously demonstrated that DHEA exerted a beneficial effect on osteoarthritic cartilage by positively modulating the balance between anabolic and catabolic factors (e.g., MMPs/TIMP-1, ADAMTS/TIMP-3 and cysteine proteinases/cystatin C), inhibiting catabolic signaling pathways (e.g., Wnt/β-catenin), and suppressing proinflammatory cytokines-mediated low-grade synovial inflammation (e.g., IL-1β). However, the full picture of the pharmacological molecular mechanism(s) underlying the activity of DHEA against OA is still incomplete, and a comprehensive and up-to-date review article in this field is unavailable. In this review, recent findings (apart from the well documented pathogenesis of OA) regarding disease-related mechanisms involving low grade synovial inflammation, cartilage matrix stiffness, chondrocyte autophagy and the roles of a variety of catabolic cellular signaling pathways are discussed. Moreover, the possible relationship between these disease-related mechanisms and DHEA action is discussed. Emerging evidence from in vivo and in vitro studies were scrutinized and are concisely presented to demonstrate the investigational and putative mechanisms underlying the anti-OA potential of DHEA.

Three-Dimensional Bioprinting of Cartilage by the Use of Stem Cells: A Strategy to Improve Regeneration

Cartilage lesions fail to heal spontaneously, leading to the development of chronic conditions which worsen the life quality of patients. Three-dimensional scaffold-based bioprinting holds the potential of tissue regeneration through the creation of organized, living constructs via a "layer-by-layer" deposition of small units of biomaterials and cells. This technique displays important advantages to mimic natural cartilage over traditional methods by allowing a fine control of cell distribution, and the modulation of mechanical and chemical properties. This opens up a number of new perspectives including personalized medicine through the development of complex structures (the osteochondral compartment), different types of cartilage (hyaline, fibrous), and constructs according to a specific patient's needs. However, the choice of the ideal combination of biomaterials and cells for cartilage bioprinting is still a challenge. Stem cells may improve material mimicry ability thanks to their unique properties: the immune-privileged status and the paracrine activity. Here, we review the recent advances in cartilage three-dimensional, scaffold-based bioprinting using stem cells and identify future developments for clinical translation. Database search terms used to write this review were: "articular cartilage", "menisci", "3D bioprinting", "bioinks", "stem cells", and "cartilage tissue engineering".