Leptin-mediated cytoskeletal remodeling in chondrocytes occurs via the RhoA/ROCK pathway

Novel perspectives on leptin in osteoarthritis: Focus on aging

Osteoarthritis (OA) is a common chronic joint disease characterized by articular cartilage degeneration, subchondral sclerosis, synovitis, and osteophyte formation. OA is associated with disability and impaired quality of life, particularly among the elderly. Leptin, a 16-kD non-glycosylated protein encoded by the obese gene, is produced on a systemic and local basis in adipose tissue and the infrapatellar fat pad located in the knee. The metabolic mechanisms employed by leptin in OA development have been widely studied, with attention being paid to aging as a corroborative risk factor for OA. Hence, in this review, we have attempted to establish a potential link between leptin and OA, by focusing on aging-associated mechanisms and proposing leptin as a potential diagnostic and therapeutic target in aging-related mechanisms of OA that may provide fruitful guidance and emphasis for future research.

Effect of Traditional Chinese Non-Pharmacological Therapies on Knee Osteoarthritis: A Narrative Review of Clinical Application and Mechanism

Knee osteoarthritis (KOA) stands as a degenerative ailment with a substantial and escalating prevalence. The practice of traditional Chinese non-pharmacological therapy has become a prevalent complementary and adjunctive approach. A mounting body of evidence suggests its efficacy in addressing KOA. Recent investigations have delved into its underlying mechanism, yielding some headway. Consequently, this comprehensive analysis seeks to encapsulate the clinical application and molecular mechanism of traditional Chinese non-pharmacological therapy in KOA treatment. The review reveals that various therapies, such as acupuncture, electroacupuncture, warm needle acupuncture, tuina, and acupotomy, primarily target localized knee components like cartilage, subchondral bone, and synovium. Moreover, their impact extends to the central nervous system and intestinal flora. More perfect experimental design and more comprehensive research remain a promising avenue in the future.

Molecular and Cellular Mechanisms Underlying the Cardiac Hypertrophic and Pro-Remodelling Effects of Leptin

Since its initial discovery in 1994, the adipokine leptin has received extensive interest as an important satiety factor and regulator of energy expenditure. Although produced primarily by white adipocytes, leptin can be synthesized by numerous tissues including those comprising the cardiovascular system. Cardiovascular function can thus be affected by locally produced leptin via an autocrine or paracrine manner but also by circulating leptin. Leptin exerts its effects by binding to and activating specific receptors, termed ObRs or LepRs, belonging to the Class I cytokine family of receptors of which six isoforms have been identified. Although all ObRs have identical intracellular domains, they differ substantially in length in terms of their extracellular domains, which determine their ability to activate cell signalling pathways. The most important of these receptors in terms of biological effects of leptin is the so-called long form (ObRb), which possesses the complete intracellular domain linked to full cell signalling processes. The heart has been shown to express ObRb as well as to produce leptin. Leptin exerts numerous cardiac effects including the development of hypertrophy likely through a number of cell signaling processes as well as mitochondrial dynamics, thus demonstrating substantial complex underlying mechanisms. Here, we discuss mechanisms that potentially mediate leptin-induced cardiac pathological hypertrophy, which may contribute to the development of heart failure.

Leptin Induces MMP-1 Expression Through the RhoA/ERK1/2/NF-κB Axis in Human Intervertebral Disc Cartilage Endplate-Derived Stem Cells

Purpose

Intervertebral disc (IVD) degeneration, associated with aging, may cause low back pain and disability, with obesity as a significant risk factor. In a prior study, we found a positive correlation between IVD degeneration and levels of matrix metalloproteinase-1 (MMP-1) and leptin. Yet, the interaction between MMP-1 and leptin in IVD degeneration is unclear. Our research seeks to explore leptin's influence on MMP-1 expression and the underlying mechanisms in human intervertebral disc cartilage endplate-derived stem cells, specifically SV40 cells.

Methods

The mRNA and protein expression in leptin-stimulated SV40 cells were assessed using RT-real-time PCR and Western blotting or ELISA, respectively. We examined leptin-mediated RhoA activation through a GTP-bound RhoA pull-down assay. Furthermore, the phosphorylation levels of mitogen-activated protein kinases and AKT in leptin-stimulated SV40 cells were analyzed using Western blotting. The activation of NF-κB by leptin was investigated by assessing phosphorylation of IKKα/β, IκBα, and NF-κB p65, along with the nuclear translocation of NF-κB p65. To understand the underlying mechanism behind leptin-mediated MMP-1 expression, we employed specific inhibitors.

Results

Leptin triggered the mRNA and protein expression of MMP-1 in SV40 cells. In-depth mechanistic investigations uncovered that leptin heightened RhoA activity, promoted ERK1/2 phosphorylation, and increased NF-κB activity. However, leptin did not induce phosphorylation of JNK1/2, p38, or AKT. When we inhibited RhoA, ERK1/2, and NF-κB, it resulted in a decrease in MMP-1 expression. Conversely, inhibition of reactive oxygen species and NADPH oxidase did not yield the same outcome. Additionally, inhibiting RhoA or ERK1/2 led to a reduction in leptin-induced NF-κB activation. Moreover, inhibiting RhoA also decreased leptin-mediated ERK1/2 phosphorylation.

Conclusion

These results indicated that leptin induced MMP-1 expression in SV40 cells through the RhoA/ERK1/2/NF-κB axis. This study provided the pathogenic role of leptin and suggested the potential therapeutic target for IVD degeneration.

Obesity, Metabolic Syndrome, and Osteoarthritis-An Updated Review

PURPOSE OF REVIEW

Metabolic syndrome (MetS), also called the 'deadly quartet' comprising obesity, diabetes, dyslipidemia, and hypertension, has been ascertained to have a causal role in the pathogenesis of osteoarthritis (OA). This review is aimed at discussing the current knowledge on the contribution of metabolic syndrome and its various components to OA pathogenesis and progression.

RECENT FINDINGS

Lately, an increased association identified between the various components of metabolic syndrome (obesity, diabetes, dyslipidemia, and hypertension) with OA has led to the identification of the 'metabolic phenotype' of OA. These metabolic perturbations alongside low-grade systemic inflammation have been identified to inflict detrimental effects upon multiple tissues of the joint including cartilage, bone, and synovium leading to complete joint failure in OA. Recent epidemiological and clinical findings affirm that adipokines significantly contribute to inflammation, tissue degradation, and OA pathogenesis mediated through multiple signaling pathways. OA is no longer perceived as just a 'wear and tear' disease and the involvement of the metabolic components in OA pathogenesis adds up to the complexity of the disease. Given the global surge in obesity and its allied metabolic perturbations, this review aims to throw light on the current knowledge on the pathophysiology of MetS-associated OA and the need to address MetS in the context of metabolic OA management. Better regulation of the constituent factors of MetS could be profitable in preventing MetS-associated OA. The identification of key roles for several metabolic regulators in OA pathogenesis has also opened up newer avenues in the recognition and development of novel therapeutic agents.

Hypoxia Preconditioned Serum (HPS) Promotes Proliferation and Chondrogenic Phenotype of Chondrocytes In Vitro

Autologous chondrocyte implantation (ACI) for the treatment of articular cartilage defects remains challenging in terms of maintaining chondrogenic phenotype during in vitro chondrocyte expansion. Growth factor supplementation has been found supportive in improving ACI outcomes by promoting chondrocyte redifferentiation. Here, we analysed the chondrogenic growth factor concentrations in the human blood-derived secretome of Hypoxia Preconditioned Serum (HPS) and assessed the effect of HPS-10% and HPS-40% on human articular chondrocytes from osteoarthritic cartilage at different time points compared to normal fresh serum (NS-10% and NS-40%) and FCS-10% culture conditions. In HPS, the concentrations of TGF-beta1, IGF-1, bFGF, PDGF-BB and G-CSF were found to be higher than in NS. Chondrocyte proliferation was promoted with higher doses of HPS (HPS-40% vs. HPS-10%) and longer stimulation (4 vs. 2 days) compared to FCS-10%. On day 4, immunostaining of the HPS-10%-treated chondrocytes showed increased levels of collagen type II compared to the other conditions. The promotion of the chondrogenic phenotype was validated with quantitative real-time PCR for the expression of collagen type II (COL2A1), collagen type I (COL1A1), SOX9 and matrix metalloproteinase 13 (MMP13). We demonstrated the highest differentiation index (COL2A1/COL1A1) in HPS-10%-treated chondrocytes on day 4. In parallel, the expression of differentiation marker SOX9 was elevated on day 4, with HPS-10% higher than NS-10/40% and FCS-10%. The expression of the cartilage remodelling marker MMP13 was comparable across all culture conditions. These findings implicate the potential of HPS-10% to improve conventional FCS-based ACI culture protocols by promoting the proliferation and chondrogenic phenotype of chondrocytes during in vitro expansion.

Cell morphology as a biological fingerprint of chondrocyte phenotype in control and inflammatory conditions

Introduction

Little is known how inflammatory processes quantitatively affect chondrocyte morphology and how single cell morphometric data could be used as a biological fingerprint of phenotype.

Methods

We investigated whether trainable high-throughput quantitative single cell morphology profiling combined with population-based gene expression analysis can be used to identify biological fingerprints that are discriminatory of control vs. inflammatory phenotypes. The shape of a large number of chondrocytes isolated from bovine healthy and human osteoarthritic (OA) cartilages was quantified under control and inflammatory (IL-1β) conditions using a trainable image analysis technique measuring a panel of cell shape descriptors (area, length, width, circularity, aspect ratio, roundness, solidity). The expression profiles of phenotypically relevant markers were quantified by ddPCR. Statistical analysis, multivariate data exploration, and projection-based modelling were used for identifying specific morphological fingerprints indicative of phenotype.

Results

Cell morphology was sensitive to both cell density and IL-1β. In both cell types, all shape descriptors correlated with expression of extracellular matrix (ECM)- and inflammatory-regulating genes. A hierarchical clustered image map revealed that individual samples sometimes responded differently in control or IL-1β conditions than the overall population. Despite these variances, discriminative projection-based modeling revealed distinct morphological fingerprints that discriminated between control and inflammatory chondrocyte phenotypes: the most essential morphological characteristics attributable to non-treated control cells was a higher cell aspect ratio in healthy bovine chondrocytes and roundness in OA human chondrocytes. In contrast, a higher circularity and width in healthy bovine chondrocytes and length and area in OA human chondrocytes indicated an inflammatory (IL-1β) phenotype. When comparing the two species/health conditions, bovine healthy and human OA chondrocytes exhibited comparable IL-1β-induced morphologies in roundness, a widely recognized marker of chondrocyte phenotype, and aspect ratio.

Discussion

Overall, cell morphology can be used as a biological fingerprint for describing chondrocyte phenotype. Quantitative single cell morphometry in conjunction with advanced methods for multivariate data analysis allows identifying morphological fingerprints that can discriminate between control and inflammatory chondrocyte phenotypes. This approach could be used to assess how culture conditions, inflammatory mediators, and therapeutic modulators regulate cell phenotype and function.

Rutin Inhibits the Progression of Osteoarthritis Through CBS-Mediated RhoA/ROCK Signaling

Osteoarthritis (OA) is a chronic joint disease characterized by the deterioration of cartilage and subchondral bone in the joints. Currently, there is no complete cure for OA, only treatments designed to temporarily relieve pain and improve function. Compared with the high cost of surgical treatment, medical treatment of OA is more acceptable and cost-effective. Rutin, as a flavonoid, has been shown to have anti-OA properties. We evaluated the effects of rutin on chondrocytes in lipopolysaccharide (LPS)-induced OA and on OA in rats induced by anterior cruciate ligament transection. We found that rutin effectively reduced the expression levels of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), tumor necrosis factor-α (TNF-α), and matrix metalloproteinase 13 (MMP-13) and increased the expression of Col II and aggrecan (p < 0.001). In addition, we also found that rutin increased the expression of cystathionine-β-synthase (CBS) and inhibited the expression of Rho-related coiled-coil protein kinase (ROCK) in chondrocytes (p < 0.05), thereby effectively inhibiting the inflammatory progression of OA. We concluded that rutin inhibits the inflammatory progression of OA through the CBS-mediated RhoA/ROCK signaling pathway.

Adipokine Signaling Pathways in Osteoarthritis

Osteoarthritis (OA) is a debilitating joint disease that affects millions of individuals. The pathogenesis of OA has not been fully elucidated. Obesity is a well-recognized risk factor for OA. Multiple studies have demonstrated adipokines play a key role in obesity-induced OA. Increasing evidence show that various adipokines may significantly affect the development or clinical course of OA by regulating the pro/anti-inflammatory and anabolic/catabolic balance, matrix remodeling, chondrocyte apoptosis and autophagy, and subchondral bone sclerosis. Several signaling pathways are involved but still have not been systematically investigated. In this article, we review the cellular and molecular mechanisms of adipokines in OA, and highlight the possible signaling pathways. The review suggested adipokines play important roles in obesity-induced OA, and exert downstream function via the activation of various signaling pathways. In addition, some pharmaceuticals targeting these pathways have been applied into ongoing clinical trials and showed encouraging results. However, these signaling pathways are complex and converge into a common network with each other. In the future work, more research is warranted to further investigate how this network works. Moreover, more high quality randomised controlled trials are needed in order to investigate the therapeutic effects of pharmaceuticals against these pathways for the treatment of OA. This review may help researchers to better understand the pathogenesis of OA, so as to provide new insight for future clinical practices and translational research.

Restoring the dampened expression of the core clock molecule BMAL1 protects against compression-induced intervertebral disc degeneration

The circadian clock participates in maintaining homeostasis in peripheral tissues, including intervertebral discs (IVDs). Abnormal mechanical loading is a known risk factor for intervertebral disc degeneration (IDD). Based on the rhythmic daily loading pattern of rest and activity, we hypothesized that abnormal mechanical loading could dampen the IVD clock, contributing to IDD. Here, we investigated the effects of abnormal loading on the IVD clock and aimed to inhibit compression-induced IDD by targeting the core clock molecule brain and muscle Arnt-like protein-1 (BMAL1). In this study, we showed that BMAL1 KO mice exhibit radiographic features similar to those of human IDD and that BMAL1 expression was negatively correlated with IDD severity by systematic analysis based on 149 human IVD samples. The intrinsic circadian clock in the IVD was dampened by excessive loading, and BMAL1 overexpression by lentivirus attenuated compression-induced IDD. Inhibition of the RhoA/ROCK pathway by Y-27632 or melatonin attenuated the compression-induced decrease in BMAL1 expression. Finally, the two drugs partially restored BMAL1 expression and alleviated IDD in a diurnal compression model. Our results first show that excessive loading dampens the circadian clock of nucleus pulposus tissues via the RhoA/ROCK pathway, the inhibition of which potentially protects against compression-induced IDD by preserving BMAL1 expression. These findings underline the importance of the circadian clock for IVD homeostasis and provide a potentially effective therapeutic strategy for IDD.

Enhanced autophagy suppresses inflammation-mediated bone loss through ROCK1 signaling in bone marrow mesenchymal stem cells

Bone marrow mesenchymal stem cells (BMSCs) have strong proliferative ability and multi-directional differentiation potential. Osteoarthritis is a degenerative joint disease that is closely related to the loss of osteogenic differentiation function of BMSCs. Autophagy, plays a crucial role in the maintenance of cellular functions, but its regulatory mechanism during the osteogenic differentiation of BMSCs remains unclear. In this study, we analyzed the differential gene networks and pathways during BMSC osteogenesis using bioinformatics, and further validated the regulatory roles of autophagy during the osteogenic differentiation of BMSCs in inflammatory condition in vitro. We found that Tumor necrosis factor alpha (TNF-α) treatment led to actin cytoskeleton rearrangements and inhibited osteogenic differentiation in BMSCs. In addition, TNF-α enhanced Rho-associated protein kinase 1 (ROCK1) expression and decreased autophagy activation. ROCK1 knockdown reduced Endoplasmic Reticulum stress (ER stress) and promoted autophagy, resulting reversion of osteogenic differentiation in BMSCs under inflammatory condition. Rapamycin reversed the TNF-α-induced decrease in osteogenesis of BMSCs, assessed by alkaline phosphatase (ALP) activity and Alizarin staining. Autophagy treated with inhibitor 3-Methyladenine (3-MA) further increased TNF-α-induced osteogenesis inhibition of BMSCs. Collectively, these results indicate that ER stress and dysfunction of autophagy promote inflammation-induced bone loss through the activation of ROCK1 signaling in BMSCs.

Involvement of Rho-kinase/IκB-α/NF-κB activation in IL-1β-induced inflammatory response and oxidative stress in human chondrocytes

It has been clearly indicated that osteoarthritis (OA) is an inflammatory and degenerative disease that could be promoted by Rho-kinase (ROCK); however, little is known about the role of ROCK/inhibitor κB alpha (IκB-α)/nuclear factor-κB (NF-κB) p65 pathway activation in interleukin-1β (IL-1β) induced inflammatory response and oxidative stress in primary human chondrocytes. To test this hypothesis, we focused on determining ROCK-II, IκB-α, p-IκB-α, NF-κB p65, p-NF-κB p65, IL-6, tumor necrosis factor alpha (TNF-α), cyclooxygenase-2 (COX-2), p22phox, and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subtype 4 (NOX4) protein expression, ROCK-II activity, NADPH oxidase levels, and total antioxidant capacity (TAC) in the presence and absence of ROCK-inhibitor fasudil. IL-1β (2 ng·mL-1, 24 h) increased the expression of ROCK-II, p-IκB-α, NF-κB p65, p-NF-κB p65, IL-6, TNF-α, COX-2, and p22phox proteins, and decreased the expression of IκB-α, and the NOX4 protein level did not alter. ROCK activity and NADPH oxidase levels were increased, whereas the TAC was decreased by IL-1β. Fasudil (10-5-10-7 M) reversed all these changes induced by IL-1β. These results demonstrate that ROCK/IκB-α/NF-κB p65 pathway activation contributes to the IL-1β-induced inflammatory response and oxidative stress, and thus, ROCK inhibition might be a beneficial treatment option for OA patients mainly based on its anti-inflammatory and antioxidant effects.

Articular Chondrocyte Phenotype Regulation through the Cytoskeleton and the Signaling Processes That Originate from or Converge on the Cytoskeleton: Towards a Novel Understanding of the Intersection between Actin Dynamics and Chondrogenic Function

Numerous studies have assembled a complex picture, in which extracellular stimuli and intracellular signaling pathways modulate the chondrocyte phenotype. Because many diseases are mechanobiology-related, this review asked to what extent phenotype regulators control chondrocyte function through the cytoskeleton and cytoskeleton-regulating signaling processes. Such information would generate leverage for advanced articular cartilage repair. Serial passaging, pro-inflammatory cytokine signaling (TNF-α, IL-1α, IL-1β, IL-6, and IL-8), growth factors (TGF-α), and osteoarthritis not only induce dedifferentiation but also converge on RhoA/ROCK/Rac1/mDia1/mDia2/Cdc42 to promote actin polymerization/crosslinking for stress fiber (SF) formation. SF formation takes center stage in phenotype control, as both SF formation and SOX9 phosphorylation for COL2 expression are ROCK activity-dependent. Explaining how it is molecularly possible that dedifferentiation induces low COL2 expression but high SF formation, this review theorized that, in chondrocyte SOX9, phosphorylation by ROCK might effectively be sidelined in favor of other SF-promoting ROCK substrates, based on a differential ROCK affinity. In turn, actin depolymerization for redifferentiation would “free-up” ROCK to increase COL2 expression. Moreover, the actin cytoskeleton regulates COL1 expression, modulates COL2/aggrecan fragment generation, and mediates a fibrogenic/catabolic expression profile, highlighting that actin dynamics-regulating processes decisively control the chondrocyte phenotype. This suggests modulating the balance between actin polymerization/depolymerization for therapeutically controlling the chondrocyte phenotype.

Chronic exposure to methylmercury enhances the anorexigenic effects of leptin in C57BL/6J male mice

Several studies have demonstrated that heavy metals disrupt energy homeostasis. Leptin inhibits food intake and decreases body weight through activation of its receptor in the hypothalamus. The impact of heavy metals on leptin signaling in the hypothalamus is unclear. Here, we show that the environmental pollutant, methylmercury (MeHg), favors an anorexigenic profile in wild-type males. C57BL/6J mice were exposed to MeHg via drinking water (5 ppm) up to 30 days. Our data shows that MeHg exposure was associated with changes in leptin induced activation of Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling pathway in the hypothalamus. In males, the activation of JAK2/STAT3 signaling pathway was sustained by an increase in SOCS3 protein levels. In females, MeHg-activated STAT3 was inhibited by a concomitant increase in PTP1B. Taken together, our data suggest that MeHg enhanced leptin effects in males, favoring an anorexigenic profile in males, which notably, have been shown to be more sensitive to the neurological effects of this organometal than females. A better understanding of MeHg-induced molecular mechanism alterations in the hypothalamus advances the understanding of its neurotoxicity and provides molecular sites for novel therapies.

The EphA4 Signaling is Anti-catabolic in Synoviocytes but Pro-anabolic in Articular Chondrocytes

The expression and activation of EphA4 in the various cell types in a knee joint was upregulated upon an intraarticular injury. To determine if EphA4 signaling plays a role in osteoarthritis, we determined whether deficient EphA4 expression (in EphA4 knockout mice) or upregulation of the EphA4 signaling (with the EfnA4-fc treatment) would alter cellular functions of synoviocytes and articular chondrocytes. In synoviocytes, deficient EphA4 expression enhanced, whereas activation of the EphA4 signaling reduced, expression and secretion of key inflammatory cytokines and matrix metalloproteases. Conversely, in articular chondrocytes, activation of the EphA4 signaling upregulated, while deficient EphA4 expression reduced, expression levels of chondrogenic genes (e.g., aggrecan, lubricin, type-2 collagen, and Sox9). EfnA4-fc treatment in wildtype, but not EphA4-deficient, articular chondrocytes promoted the formation and activity of acidic proteoglycan-producing colonies. Activation of the EphA4 signaling in articular chondrocytes upregulated Rac1/2 and downregulated RhoA via enhancing Vav1 and reducing Ephexin1 activation, respectively. However, activation of the EphA4 signaling in synoviocytes suppressed the Vav/Rac signaling while upregulated the Ephexin/Rho signaling. In summary, the EphA4 signaling in synoviocytes is largely of anti-catabolic nature through suppression of the expression of inflammatory cytokines and matrix proteases, but in articular chondrocytes the signaling is pro-anabolic in that it promotes the biosynthesis of articular cartilage. The contrasting action of the EphA4 signaling in synoviocytes as opposing to articular chondrocytes may in part be mediated through the opposite differential effects of the EphA4 signaling on the Vav/Rac signaling and Ephexin/Rho signaling in the two skeletal cell types.

Serum levels of leptin, osteopontin, and sclerostin in patients with and without knee osteoarthritis

OBJECTIVE

To investigate the relationship between leptin, osteopontin (OPN), sclerostin (SOST) and severity of knee osteoarthritis (KOA).

METHODS

The study included 148 consecutive patients with knee OA and 101 non-KOA subjects enrolled in this cross-sectional study. All patients fulfilled the American College of Rheumatology criteria for primary knee OA. Severity of the disease was assessed using plain radiography of the affected knee, according to the Kellgren and Lawrence classification. Fasting blood samples were obtained from all patients and controls; the serum samples were kept at - 80 °C before assessment of leptin, OPN, and SOST using a multiplex particle-based flow cytometric assay.

RESULTS

KOA patients group compared with the control group, serum leptin (KOA, 26581.7 ± 2011.5 pg/ml, vs control,6936.4 ± 702.2 pg/ml),OPN (KOA, 4908.3 ± 769.4 pg/ml, vs control, 2182.5 ± 217.8 pg/ml), and SOST (KOA, 2481.9 ± 543.5 pg/ml, vs control, 1288.9 ± 267.7 pg/ml) in the KOA group were higher than control group; there were also differences in three bone metabolic factors between male and female in the KOA group; meanwhile, there was correlation between each factor and the incidence of KOA.

CONCLUSION

Our study of 249 serum samples was conducted. Serum leptin, OPN, and SOST were significantly increased in KOA patients, and there was an internal correlation; these findings could, at best, contribute to the identification of novel targets for medical interventions. Key Points • The aim of this study was to assess the relationships of radiographic knee OA with altered serum levels of leptin, OPN, and SOST. Our study of 249 serum samples was conducted. Serum leptin, OPN, and SOST were significantly increased in KOA patients compared with control group. There were gender differences in the concentration of three serum bone turnover factors in KOA group and control group. Serum SOST concentration increased with Kellgren-Lawrence (K-L) grading. We found that serum leptin, OPN, and SOST were significantly increased in KOA patients, and there was an internal correlation. Leptin had a remarkable diagnostic value in the incidence of KOA.

An update on the association between metabolic syndrome and osteoarthritis and on the potential role of leptin in osteoarthritis

Metabolic syndrome (MetS) has been associated with osteoarthritis (OA). Leptin, which is one of the markers of MetS, has been associated with OA pathophysiology. This study aimed to provide an update on the association between MetS and OA and on the potential role of leptin in OA. In this review, we summarized the current knowledge of the association between MetS and OA and updated the evidence on the potential role of leptin in OA. Clinical studies have investigated the epidemiologic association between MetS or its components and OA. Results suggested strong epidemiologic associations between MetS and OA, especially in the Asian population. Animal studies also indicated that metabolic dysregulation may lead to OA pathogenesis. The systemic role of MetS in OA pathophysiology is associated with obesity-related inflammation, the beneficial role of n-3 polyunsaturated fatty acids and deleterious role of cholesterol, physical inactivity, hypertension-induced subchondral ischemia, dyslipidemia-induced ectopic lipid deposition in chondrocytes, hyperglycemia-induced local effects of oxidative stress and advanced glycation end-products, low-grade systemic inflammation, and obesity-related adipokines by inducing the expression of proinflammtory factors. Leptin levels in serum/plasma and synovial fluid were associated with joint pain, radiographic progression, bone formation biomarkers, cartilage volume, knee OA incidence, and total joint arthroplasty in OA patients. Elevated leptin expression and increased effect of leptin on infrapatellar fat pad, synovium, articular cartilage, and bone were also involved in the pathogenesis of OA. Current knowledge indicates a convincing epidemiologic association between MetS and OA, especially in the Asian population. Animal studies have also shown that metabolic dysregulation may lead to OA pathogenesis. Accumulating evidence suggests that leptin may play a potential role in OA pathogenesis. Therefore, leptin and its receptor may be an emerging target for intervention in metabolic-associated OA.

Leptin Promotes Expression of EMT-Related Transcription Factors and Invasion in a Src and FAK-Dependent Pathway in MCF10A Mammary Epithelial Cells

Leptin is one of the main adipokines secreted in breast tissue. Leptin promotes epithelial-mesenchymal transition (EMT), cell migration and invasion in epithelial breast cells, leading to tumor progression. Although, the molecular mechanisms that underlie these events are not fully understood, the activation of different signaling pathways appears to be essential. In this sense, the effects of leptin on the activation of kinases like Src and FAK, which regulate signaling pathways that activate the EMT program, are not completely described. Therefore, we investigated the involvement of these kinases using an in vitro model for leptin-induced EMT process in the non-tumorigenic MCF10A cell line. To this end, MCF10A cells were stimulated with leptin, and Src and FAK activation was assessed. Specific events occurring during EMT were also evaluated in the presence or absence of the kinases' chemical inhibitors PP2 and PF-573228. For instance, we tested the expression and subcellular localization of the EMT-related transcription factors Twist and β-catenin, by western blot and immunofluorescence. We also evaluated the secretion and activation of matrix metalloproteases (MMP-2 and MMP-9) by gelatin zymography. Invasiveness properties of leptin-stimulated cells were determined by invadopodia formation assays, and by the Transwell chamber method. Our results showed that leptin promotes EMT through Src and FAK activation, which leads to the secretion and activation of MMP-2 and MMP-9, invadopodia formation and cell invasion in MCF10A cells. In conclusion, our data suggest that leptin promotes an increase in the expression levels of Twist and β-catenin, the secretion of MMP-2, MMP-9, the invadopodia formation and invasion in MCF10A cells in a Src and FAK-dependent manner.

Platelet-Rich Plasma Supports Proliferation and Redifferentiation of Chondrocytes during In Vitro Expansion

Articular cartilage regeneration is insufficient to restore sports injuries or defects that can occur from trauma. Treatment options for cartilage repair include autologous chondrocyte implantation (ACI) by isolation, expansion, and reimplantation of healthy donor chondrocytes. Chondrocyte expansion onto 2D substrates leads to dedifferentiation and loss of the cellular phenotype. We aimed to overcome the state of dedifferentiation by biochemical stimuli with platelet derivatives such as platelet-rich plasma (PRP) and hyperacute serum (HAS) to achieve sufficient cell numbers in combination with variable oxygen tension. Human articular chondrocytes from osteoarthritic (OA) cartilage chondrocytes were switched from 10% FCS supplementation to either 10% PRP or 10% HAS after initial passaging for further experiments under normoxic (20% O₂) or hypoxic (1% O₂) conditions. An XTT assay measured the effect of PRP or HAS on the cell proliferation at 3, 6, and 9 days. The chondrogenic redifferentiation potential of dedifferentiated chondrocytes was determined with reverse transcriptase quantitative real-time PCR for markers of expression for type II collagen (COL2A1), type I collagen (COL1A1), and matrix metalloproteinases MMP3, matrix metalloproteinase 13 (MMP13) at 24 and 72 h. Measured protein levels of 100% PRP or HAS by multiplex quantification revealed basic fibroblast growth factor, G-CSF, and PDGF were significantly higher in PRP than in HAS (p < 0.05) but LEPTIN levels did not differ. The quantified protein levels did not differ when isolated from same donors at a different time. Chondrocyte proliferation indicated that supplementation of 10% HAS enhanced the proliferation rate compared to 10% PRP or 10% FCS at 6 and 9 days significantly (p < 0.05). mRNA levels for expression of COL1A1 were significantly downregulated (p < 0.05) when cultured with 10% PRP than 10% HAS or 10% FCS under normoxic/hypoxic conditions. COL2A1 was significantly upregulated (p < 0.05) in PRP than 10% HAS or 10% FCS. MMP3 expression was downregulated after 72 h under all conditions. MMP13 was upregulated with 10% PRP at both 24 and 72 h but significantly downregulated under hypoxia (1% O₂) for all circumstances. While HAS has its effect on chondrocyte proliferation, PRP enhances both proliferation and redifferentiation of dedifferentiated chondrocytes. PRP can replace standard usage of FCS for chondrogenic priming and expansion as implications for clinical use such as ACI procedures.

Functions of Rho family of small GTPases and Rho-associated coiled-coil kinases in bone cells during differentiation and mineralization

BACKGROUND

Members of Rho-associated coiled-coil kinases (ROCKs) are effectors of Rho family of small GTPases. ROCKs have multiple functions that include regulation of cellular contraction and polarity, adhesion, motility, proliferation, apoptosis, differentiation, maturation and remodeling of the extracellular matrix (ECM).

SCOPE OF THE REVIEW

Here, we focus on the action of RhoA and RhoA effectors, ROCK1 and ROCK2, in cells related to tissue mineralization: mesenchymal stem cells, chondrocytes, preosteoblasts, osteoblasts, osteocytes, lining cells and osteoclasts.

MAJOR CONCLUSIONS

The activation of the RhoA/ROCK pathway promotes stress fiber formation and reduces chondrocyte and osteogenic differentiations, in contrast to that in mesenchymal stem cells which stimulated the osteogenic and the chondrogenic differentiation. The effects of Rac1 and Cdc42 in promoting chondrocyte hypertrophy and of Rac1, Rac2 and Cdc42 in osteoclast are discussed. In addition, members of the Rho family of GTPases such Rac1, Rac2, Rac3 and Cdc42, acting upstream of ROCK and/or other protein effectors, may compensate the actions of RhoA, affecting directly or indirectly the actions of ROCKs as well as other protein effectors.

GENERAL SIGNIFICANCE

ROCK activity can trigger cartilage degradation and affect bone formation, therefore these kinases may represent a possible therapeutic target to treat osteoarthritis and osseous diseases. Inhibition of Rho/ROCK activity in chondrocytes prevents cartilage degradation, stimulate mineralization of osteoblasts and facilitate bone formation around implanted metals. Treatment with osteoprotegerin results in a significant decrease in the expression of Rho GTPases, ROCK1 and ROCK2, reducing bone resorption. Inhibition of ROCK signaling increases osteoblast differentiation in a topography-dependent manner.

P120-Catenin Protects Endplate Chondrocytes From Intermittent Cyclic Mechanical Tension Induced Degeneration by Inhibiting the Expression of RhoA/ROCK-1 Signaling Pathway

STUDY DESIGN

The changes of endplate chondrocytes induced by intermittent cyclic mechanical tension (ICMT) were observed by realtime reverse transcription-polymerase chain reaction, immunofluorescence, and Western blot analysis.

OBJECTIVE

To investigate the role of RhoA/ROCK-1 signaling pathway and E-cadherin/P120-catenin complex in endplate chondrocytes degeneration induced by ICMT.

SUMMARY OF BACKGROUND DATA

ICMT can induce the endplate chondrocyte degeneration. However, the relationship between P120-catenin or RhoA/ROCK-1 signaling pathway and endplate chondrocytes degeneration induced by ICMT is not clear.

METHODS

ICMT (strain at 0.5 Hz sinusoidal curve at 8% elongation) was applied to rat endplate chondrocytes for 6 days, 16 hours a day. The cell viability and apoptosis were examined by the LIVE/DEAD assay and flow cytometry. Histological staining was used to examine the lumbar disc tissue morphology and extracellular matrix. To regulate RhoA/ROCK-1 signaling pathway and the expression of E-cadherin and P120-catenin, RhoA/ROCK-1 pathway-specific inhibitors, E-cadherin, and p120-catenin plasmid were applied. Coimmunoprecipitation was employed to examine the interaction between E-cadherin and P120-catenin, P120-catenin, and RhoA. The related gene expression and protein location was examined by realtime reverse transcription-polymerase chain reaction, Western blot, and immunofluorescence.

RESULTS

There was no change of viability verified by LIVE/DEAD assay and flow cytometry after ICMT loading. ICMT loading led to RhoA/ROCK-1 signaling activation and the loss of the chondrogenic phenotype of endplate chondrocytes. Inhibition of RhoA/ROCK-1 signaling pathway significantly ameliorated the degeneration induced by ICMT. The expression of P120-catenin and E-cadherin were inhibited by ICMT. ICMT reduced the interaction between P120-catenin and E-cadherin. Furthermore, over-expression of P120-catenin and E-cadherin can suppress the expression of chondrogenic gene, over-expression of P120-catenin can suppress the RhoA/ROCK-1 signaling pathway, but over-expression of E-cadherin cannot do it.

CONCLUSION

P120-catenin protects endplate chondrocytes from ICMT Induced degeneration by inhibiting the expression of RhoA/ROCK-1 signaling pathway.

LEVEL OF EVIDENCE

N/A.

Leptin in osteoarthritis: Focus on articular cartilage and chondrocytes

Osteoarthritis (OA) is a complex joint disorder with a number of underlying physical, biochemical, biomechanical and genetic causes. Obesity is considered to be one of the major risk factors for the development and progression of OA. It actively contributes to the inflammatory status and to cartilage degradation in the OA joints. Recent data suggests that metabolic factors produced by white adipose tissue, such as leptin, may provide a mechanistic link between obesity and OA, providing an explanation for the high prevalence of OA among obese and over-weight individuals. The unbalanced production of catabolic and anabolic mediators by chondrocytes, the only cell type present in cartilage, determines cartilage degradation, which is the central pathological feature of OA. Evidence is accumulating to support a key role for leptin in the pathogenesis and/or progression of OA. The goal of this focused review is to summarize the current knowledge on the role of leptin in OA with particular emphasis on the effects of this adipokine in cartilage and chondrocyte pathophysiology.

Interleukin-1β and tumor necrosis factor-α increase stiffness and impair contractile function of articular chondrocytes

Interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) are major proinflammatory cytokines involved in osteoarthritis (OA). These cytokines disturb chondrocyte metabolism by suppressing the synthesis of extracellular matrix proteins and stimulating the release of catabolic proteases, but little is known about their role in chondrocyte mechanics. Thus, the aim of this study was to measure the effects of IL-1β and TNF-α on the mechanical properties of the chondrocytes. Chondrocytes from goat knee joints were cultured in 96-well plates. The cellular stiffness and contractile function were probed using optical magnetic twisting cytometry, the cytoskeleton and the expression of extracellular matrix proteins were visualized using immunofluorescent staining, and chondrocyte phenotypical expression was measured by western blot analysis. Results showed that chondrocyte stiffness was dramatically decreased by disruption of F-actin but was unaffected by disruption of the intermediate filament vimentin. Treatment with 10 ng/ml IL-1β or 40 ng/ml TNF-α for 24 h substantially increased the expression level of F-actin and cellular stiffness, and impaired cell stiffening in response to the contractile agonist histamine, but these effects were blocked by the Rho-associated protein kinase inhibitor Y27632. In conclusion, IL-1β and TNF-α substantially change the mechanical properties of the chondrocytes in vitro. While changes of chondrocyte mechanics in vivo during OA progression remain unclear, this finding reveals a prominent role of these cytokines in cellular mechanics and provides insight for anti-cytokine therapies of OA.

Connecting metabolism to intestinal barrier function: The role of leptin

Structure and function of the intestinal epithelial barrier (IEB) are dependent upon the integrity of junctional protein structures sealing the apical surface between epithelial cells. Tight junctions (TJ) and the surrounding apical F-actin cytoskeleton are involved in the regulation of paracellular permeability. The regulation of actin cytoskeleton organization by RhoA/Rho-kinase (ROCK) pathway plays an important role in TJ assembly and function. There is mounting evidence that the adipocyte-derived hormone leptin exerts pleiotropic effects on the intestinal epithelium including nutrient absorption, epithelial growth, inflammation and injury. Leptin activates multiple cell signaling pathways in intestinal epithelial cells (IEC) that can explain these pleiotropic effects. However, these pathways are also involved in the primary role of leptin that is the regulation of energy and glucose metabolism homeostasis. In this commentary, we examine how the interplay between leptin signaling pathways that regulate cell metabolism could impact upon IEB function.

Adipokines: Biomarkers for osteoarthritis?

Osteoarthritis (OA) is one of the most common degenerative joint diseases in aging population. Obesity is an important risk factor for initiation and progression of OA. It is accepted that excess body weight may lead to cartilage degeneration by increasing the mechanical forces across weight-bearing joints. However, emerging data suggest that additional metabolic factors released mainly by white adipose tissue may also be responsible for the high prevalence of OA among obese people. Adipocyte-derived molecules ‘‘adipokines’’ have prompt much interest in OA pathophysiological research over the past decade since they play an important role in cartilage and bone homeostasis. Therefore, the aim of this review is to summarize the current knowledge on the role of adipokines including leptin, adiponectin, visfatin and resistin in OA and their potential to be used as biomarkers for earlier diagnosis, classifying disease severity, monitoring disease progression, and testing pharmacological interventions for OA. In OA patients, leptin, visfatin and resistin showed increased production whereas adiponectin showed decreased production. Leptin and adiponectin are far more studied than visfatin and resistin. Importantly, altered adipokine levels also contribute to a wide range of diseases. Further experiments are still crucial for understanding the relationship between adipokines and OA.

Leptin activates RhoA/ROCK pathway to induce cytoskeleton remodeling in nucleus pulposus cells

Hyperleptinemia is implicated in obesity-associated lumbar disc degeneration. Nevertheless, the effect of leptin on the intracellular signaling of nucleus pulposus cells is not clear. The current study sought to delineate the possible involvement of the RhoA/ROCK pathway in leptin-mediated cytoskeleton reorganization in nucleus pulposus cells. Nucleus pulposus cells isolated from scoliosis patients were treated with 10 ng/mL of leptin. Fluorescent resonance energy transfer analysis was used to determine the activation of RhoA signaling in nucleus pulposus cells. The protein expression of LIMK1 and cofilin-2 were analyzed by western blot analysis. F-actin cytoskeletal reorganization was assessed by rhodamine-conjugated phalloidin immunoprecipitation. Leptin induced F-actin reorganization and stress fiber formation in nucleus pulposus cells, accompanied by localized RhoA activation and phosphorylation of LIMK1 and cofilin. The RhoA inhibitor C3 exoenzyme or the ROCK inhibitor Y-27632 potently attenuated the effects of leptin on F-actin reorganization and stress fiber formation. Both inhibitors also prevented leptin-induced phosphorylation of LIMK1 and cofilin-2. Our study demonstrated that leptin activated the RhoA/ROCK/LIMK/cofilin-2 cascade to induce cytoskeleton reorganization in nucleus pulposus cells. These findings may provide novel insights into the pathogenic mechanism of obesity-associated lumbar disc degeneration.

Rheumatic diseases and obesity: adipocytokines as potential comorbidity biomarkers for cardiovascular diseases

Inflammation has been recognized as a common trait in the pathogenesis of multifactorial diseases including obesity, where a low-grade inflammation has been established and may be responsible for the cardiovascular risk related to the disease. Obesity has also been associated with the increased incidence and a worse outcome of rheumatoid arthritis (RA) and osteoarthritis (OA). RA is characterized by systemic inflammation, which is thought to play a key role in accelerated atherosclerosis and in the increased incidence of cardiovascular disease, an important comorbidity in patients with RA. The inflammatory process underlying the cardiovascular risk both in obesity and RA may be mediated by adipocytokines, a heterogeneous group of soluble proteins mainly secreted by the adipocytes. Many adipocytokines are mainly produced by white adipose tissue. Adipocytokines may also be involved in the pathogenesis of OA since a positive association with obesity has been found for weight-bearing and nonweight-bearing joints, suggesting that, in addition to local overload, systemic factors may contribute to joint damage. In this review we summarize the current knowledge on experimental models and clinical studies in which adipocytokines were examined in obesity, RA, and OA and discuss the potential of adipocytokines as comorbidity biomarkers for cardiovascular risk.

ROCKing the JAKs

The endocrine cytokine leptin is mainly secreted by white adipose tissue and plasma leptin levels positively correlate with body fat mass. Via its action on neurons in the hypothalamic arcuate nucleus (ARC), leptin regulates body weight by stimulating energy expenditure and inhibiting food intake. The main signaling pathway of the leptin receptor is the JAK2-STAT3 pathway. A recent publication of Huang et al. in Nature Neuroscience shows that leptin’s hypothalamic signaling via JAK2 requires the kinase ROCK1 (Rho-associated coiled-coil-containing protein kinase 1). ROCK1 directly phosphorylates JAK2, and this phosphorylation is required for the JAK2-STAT3 pathway of the leptin receptor. Gene deletion of ROCK1 in ARC neurons targeted by leptin makes these neurons less sensitive to leptin. This is reflected by a pronounced weight gain with hyperphagia, reduced locomotor activity, and increased fat accumulation. In this article we comment on the article of Huang et al. While the mechanism of ROCK1 activation in the neurons remains uncharacterized for the moment, a literature survey suggests that the interplay between ROCK1 and a JAK kinase may be a common theme for receptors that function via a JAK2 and even for other members of the JAK kinase family.

Wnt and Rho GTPase signaling in osteoarthritis development and intervention: implications for diagnosis and therapy

Wnt and Rho GTPase signaling play critical roles in governing numerous aspects of cell physiology, and have been shown to be involved in endochondral ossification and osteoarthritis (OA) development. In this review, current studies of canonical Wnt signaling in OA development, together with the differential roles of Rho GTPases in chondrocyte maturation and OA pathology are critically summarized. Based on the current scientific literature together with our preliminary results, the strategy of targeting Wnt and Rho GTPase for OA prognosis and therapy is suggested, which is instructive for clinical treatment of the disease.

The role of leptin on the organization and expression of cytoskeleton elements in nucleus pulposus cells

Obesity is an important risk factor for intervertebral disc degeneration and leptin is a biomarker of obesity. However, the expression of leptin receptors has not been determined in disc tissue. It is not known whether leptin has a direct effect on the nucleus pulposus (NP) cells. To determine whether the NP tissues and cells express leptin receptors (OBRa and OBRb) and whether leptin affects the organization and the expression of major cytoskeletal elements in NP cells. Messenger RNA (mRNA) and protein levels of OBRa and OBRb were measured by real-time PCR and Western blot, respectively, in NP tissues and cells. Immunofluorescence and real-time PCR and Western blot were performed to investigate the effect of leptin on cytoskeleton reorganization and expression. Results show that mRNA and proteins of OBRa and OBRb were expressed in all NP tissues and cells, and that OBRb expression was correlated with patients' body weight. Increased expression of β-actin and reorganization of F-actin were evident in leptin-stimulated NP cells. Leptin also induced vimentin expression but had no effect on β-tubulin in NP cells. These findings provide novel evidence supporting the possible involvement of leptin in the pathogenesis of intervertebral disc degeneration.

Biomechanical influence of cartilage homeostasis in health and disease

There is an urgent demand for long term solutions to improve osteoarthritis treatments in the ageing population. There are drugs that control the pain but none that stop the progression of the disease in a safe and efficient way. Increased intervention efforts, augmented by early diagnosis and integrated biophysical therapies are therefore needed. Unfortunately, progress has been hampered due to the wide variety of experimental models which examine the effect of mechanical stimuli and inflammatory mediators on signal transduction pathways. Our understanding of the early mechanopathophysiology is poor, particularly the way in which mechanical stimuli influences cell function and regulates matrix synthesis. This makes it difficult to identify reliable targets and design new therapies. In addition, the effect of mechanical loading on matrix turnover is dependent on the nature of the mechanical stimulus. Accumulating evidence suggests that moderate mechanical loading helps to maintain cartilage integrity with a low turnover of matrix constituents. In contrast, nonphysiological mechanical signals are associated with increased cartilage damage and degenerative changes. This review will discuss the pathways regulated by compressive loading regimes and inflammatory signals in animal and in vitro 3D models. Identification of the chondroprotective pathways will reveal novel targets for osteoarthritis treatments.

HIV-1 proteins join the family of LIM kinase partners. New roads open up for HIV-1 treatment

LIM kinases (LIMK) exert their functions by recruiting many macromolecular partners that could contribute to modulate LIMK activity in a positive or negative manner. In addition to proteins that interact with LIMK in human or animal cells and tissues, recent data show that LIMK activity is also influenced by HIV-1 viral proteins. These results suggest new strategies for the treatment of HIV-1 infection, based on the inhibition of LIMK-mediated cofilin inactivation and consequent actin depolymerization. Further efforts are however required to unravel the mechanism by which the virus interferes with LIMK activity and with the right balance of actin remodeling.