Effects of chronic growth hormone and insulin-like growth factor 1 deficiency on osteoarthritis severity in rat knee joints

Effects of Growth Hormone on Osteoarthritis Development

Osteoarthritis (OA), a chronic joint disease characterized by primary or secondary degeneration of articular cartilage and bone dysplasia, is associated with various risk factors and is the leading cause of musculoskeletal pain and disability, severely impacting the quality of life. Growth hormone (GH), secreted by the anterior pituitary gland, is essential in mediating the growth and development of bone and cartilage. Reportedly, osteoarthritis increases, and the growth hormone decreases with age. A negative correlation between GH and OA suggests that GH may be related to the occurrence and development of OA. Considering that abnormal growth hormone levels can lead to many diseases related to bone growth, we focus on the relationship between GH and OA. In this review, we will explain the effects of GH on the growth and deficiency of bone and cartilage based on the local pathological changes of osteoarthritis. In addition, the potential feasibility of treating OA with GH will be further explored and summarized.

IGF1 drives Wnt-induced joint damage and is a potential therapeutic target for osteoarthritis

Osteoarthritis is the most common joint disease and a global leading cause of pain and disability. Current treatment is limited to symptom relief, yet there is no disease-modifying therapy. Its multifactorial etiology includes excessive activation of Wnt signaling, but how Wnt causes joint destruction remains poorly understood. Here, we identify that Wnt signaling promotes the transcription of insulin-like growth factor 1 (IGF1) in articular chondrocytes and that IGF1 is a major driver of Wnt-induced joint damage. Male mice with cartilage-specific Igf1 deficiency are protected from Wnt-triggered joint disease. Mechanistically, Wnt-induced IGF1 transcription depends on β-catenin and binding of Wnt transcription factor TCF4 to the IGF1 gene promoter. In a clinically relevant mouse model of post-traumatic osteoarthritis, cartilage-specific deletion of Igf1 protects against the disease in male mice. IGF1 silencing in chondrocytes from patients with osteoarthritis restores a healthy molecular profile. Our findings reveal that reducing Wnt-induced IGF1 is a potential therapeutic strategy for osteoarthritis.

Bone-brain crosstalk in osteoarthritis: pathophysiology and interventions

Osteoarthritis (OA) is a prevalent articular disorder characterized by joint degeneration and persistent pain; it imposes a significant burden on both individuals and society. While OA has traditionally been viewed as a localized peripheral disorder, recent preclinical and clinical studies have revealed the crucial interconnections between the bone and the brain, highlighting the systemic nature of OA. The neuronal pathway, molecular signaling, circadian rhythms, and genetic underpinnings within the bone-brain axis play vital roles in the complex interplay that contributes to OA initiation and progression. This review explores emerging evidence of the crosstalk between the bone and brain in OA progression, and discusses the potential contributions of the bone-brain axis to the development of effective interventions for managing OA.

Growth hormone-receptor disruption in mice reduces osteoarthritis and chondrocyte hypertrophy

Excessive growth hormone (GH) has been shown to promote joint degeneration in both preclinical and clinical studies. Little is known about the effect of disrupted GH or GH receptor (GHR) on joint health. The goal of this study is to investigate joint pathology in mice with either germline (GHR-/-) or adult inducible (iGHR-/-) GHR deficiency. Knee joints from male and female GHR-/- and WT mice at 24 months of age were processed for histological analysis. Also, knee joints from male and female iGHR-/- and WT mice at 22 months of age were scanned by micro-CT (μCT) for subchondral bone changes and characterized via histology for cartilage degeneration. Joint sections were also stained for the chondrocyte hypertrophy marker, COLX, and the cartilage degeneration marker, ADAMTS-5, using immunohistochemistry. Compared to WT mice, GHR-/- mice had remarkably smooth articular joint surfaces and an even distribution of proteoglycan with no signs of degeneration. Quantitatively, GHR-/- mice had lower OARSI and Mankin scores compared to WT controls. By contrast, iGHR-/- mice were only moderately protected from developing aging-associated OA. iGHR-/- mice had a significantly lower Mankin score compared to WT. However, Mankin scores were not significantly different between iGHR-/- and WT when males and females were analyzed separately. OARSI scores did not differ significantly between WT and iGHR-/- in either individual or combined sex analyses. Both GHR-/- and iGHR-/- mice had fewer COLX+ hypertrophic chondrocytes compared to WT, while no significant difference was observed in ADAMTS-5 staining. Compared to WT, a significantly lower trabecular thickness in the subchondral bone was observed in the iGHR-/- male mice but not in the female mice. However, there were no significant differences between WT and iGHR-/- mice in the bone volume to total tissue volume (BV/TV), bone mineral density (BMD), and trabecular number in either sex. This study identified that both germline and adult-induced GHR deficiency protected mice from developing aging-associated OA with more effective protection in GHR-/- mice.

Identification of osteoblastic autophagy-related genes for predicting diagnostic markers in osteoarthritis

The development of osteoarthritis (OA) involves subchondral bone lesions, but the role of osteoblastic autophagy-related genes (ARGs) in osteoarthritis is unclear. Through integrated analysis of single-cell dataset, Bulk RNA dataset, and 367 ARGs extracted from GeneCards, 40 ARGs were found. By employing multiple machine learning algorithms and PPI networks, three key genes (DDIT3, JUN, and VEGFA) were identified. Then the RF model constructed from these genes indicated great potential as a diagnostic tool. Furthermore, the model's effectiveness in predicting OA has been confirmed through external validation datasets. Moreover, the expression of ARGs was examined in osteoblasts subject to excessive mechanical stress, human and mouse tissues. Finally, the role of ARGs in OA was confirmed through co-culturing explants and osteoblasts. Thus, osteoblastic ARGs could be crucial in OA development, providing potential diagnostic and treatment strategies.

Cartilage-specific Sirt6 deficiency represses IGF-1 and enhances osteoarthritis severity in mice

OBJECTIVES

Prior studies noted that chondrocyte SIRT6 activity is repressed in older chondrocytes rendering cells susceptible to catabolic signalling events implicated in osteoarthritis (OA). This study aimed to define the effect of Sirt6 deficiency on the development of post-traumatic and age-associated OA in mice.

METHODS

Male cartilage-specific Sirt6-deficient mice and Sirt6 intact controls underwent destabilisation of the medial meniscus (DMM) or sham surgery at 16 weeks of age and OA severity was analysed at 6 and 10 weeks postsurgery. Age-associated OA was assessed in mice aged 12 and 18 months of age. OA severity was analysed by micro-CT, histomorphometry and scoring of articular cartilage structure, toluidine blue staining and osteophyte formation. SIRT6-regulated pathways were analysed in human chondrocytes by RNA-sequencing, qRT-PCR and immunoblotting.

RESULTS

Sirt6-deficient mice displayed enhanced DMM-induced OA severity and accelerated age-associated OA when compared with controls, characterised by increased cartilage damage, osteophyte formation and subchondral bone sclerosis. In chondrocytes, RNA-sequencing revealed that SIRT6 depletion significantly repressed cartilage extracellular matrix (eg, COL2A1) and anabolic growth factor (eg, insulin-like growth factor-1 (IGF-1)) gene expression. Gain-of-function and loss-of-function studies in chondrocytes demonstrated that SIRT6 depletion attenuated, whereas adenoviral overexpression or MDL-800-induced SIRT6 activation promoted IGF-1 signalling by increasing Aktser473 phosphorylation.

CONCLUSIONS

SIRT6 deficiency increases post-traumatic and age-associated OA severity in vivo. SIRT6 profoundly regulated the pro-anabolic and pro-survival IGF-1/Akt signalling pathway and suggests that preserving the SIRT6/IGF-1/Akt axis may be necessary to protect cartilage from injury-associated or age-associated OA. Targeted therapies aimed at increasing SIRT6 function could represent a novel strategy to slow or stop OA.

Promotion of Joint Degeneration and Chondrocyte Metabolic Dysfunction by Excessive Growth Hormone in Mice

OBJECTIVE

Many patients with acromegaly, a hormonal disorder with excessive growth hormone (GH) production, report pain in joints. We undertook this study to characterize the joint pathology of mice with overexpression of bovine GH (bGH) or a GH receptor antagonist (GHa) and to investigate the effect of GH on regulation of chondrocyte cellular metabolism.

METHODS

Knee joints from mice overexpressing bGH or GHa and wild-type (WT) control mice were examined using histology and micro-computed tomography for osteoarthritic (OA) pathologies. Additionally, cartilage from bGH mice was used for metabolomics analysis. Mouse primary chondrocytes from bGH and WT mice, with or without pegvisomant treatment, were used for quantitative polymerase chain reaction and Seahorse respirometry analyses.

RESULTS

Both male and female bGH mice at ~13 months of age had increased knee joint degeneration, which was characterized by loss of cartilage structure, expansion of hypertrophic chondrocytes, synovitis, and subchondral plate thinning. The joint pathologies were also demonstrated by significantly higher Osteoarthritis Research Society International and Mankin scores in bGH mice compared to WT control mice. Metabolomics analysis revealed changes in a wide range of metabolic pathways in bGH mice, including beta-alanine metabolism, tryptophan metabolism, lysine degradation, and ascorbate and aldarate metabolism. Also, bGH chondrocytes up-regulated fatty acid oxidation and increased expression of Col10a. Joints of GHa mice were remarkably protected from developing age-associated joint degeneration, with smooth articular joint surface.

CONCLUSION

This study showed that an excessive amount of GH promotes joint degeneration in mice, which was associated with chondrocyte metabolic dysfunction and hypertrophic changes, whereas antagonizing GH action through a GHa protects mice from OA development.

The role of mechano growth factor in chondrocytes and cartilage defects: a concise review

Mechano growth factor (MGF), an isoform of insulin-like growth factor 1 (IGF-1), is recognized as a typical mechanically sensitive growth factor and has been shown to play an indispensable role in the skeletal system. In the joint cavity, MGF is highly expressed in chondrocytes, especially in the damaged cartilage tissue caused by trauma or degenerative diseases such as osteoarthritis (OA). Cartilage is an extremely important component of joints because it functions as a shock absorber and load distributer at the weight-bearing interfaces in the joint cavity, but it can hardly be repaired once injured due to its lack of blood vessels, lymphatic vessels, and nerves. MGF has been proven to play an important role in chondrocyte behaviors, including cell proliferation, migration, differentiation, inflammatory reactions and apoptosis, in and around the injury site. Moreover, under the normalized mechanical microenvironment in the joint cavity, MGF can sense and respond to mechanical stimuli, regulate chondrocyte activity, and maintain the homeostasis of cartilage tissue. Recent reports continue to explain its effects on various cell types and sport-related tissues, but its role in cartilage development, homeostasis and disease occurrence is still controversial, and its internal biological mechanism is still elusive. In this review, we summarize recent discoveries on the role of MGF in chondrocytes and cartilage defects, including tissue repair at the macroscopic level and chondrocyte activities at the microcosmic level, and discuss the current state of research and potential gaps in knowledge.

Recombinant protein drugs-based intra articular drug delivery systems for osteoarthritis therapy

Osteoarthritis (OA) is the most prevalent chronic degenerative joint disease. It weakens the motor function of patients and imposes a significant economic burden on society. The current medications commonly used in clinical practice do not meet the need for the treatment of OA. Recombinant protein drugs (RPDs) can treat OA by inhibiting inflammatory pathways, regulating catabolism/anabolism, and promoting cartilage repair, thereby showing promise as disease-modifying OA drugs (DMOADs). However, the rapid clearance and short half-life of them in the articular cavity limit their clinical translation. Therefore, the reliable drug delivery systems for extending drug treatment are necessary for the further development. This review introduces RPDs with therapeutic potential for OA, and summarizes their research progress on related drug delivery systems, and make proper discussion on the certain keys for optimal development of this area.

Pentraxin 3 regulated by miR-224-5p modulates macrophage reprogramming and exacerbates osteoarthritis associated synovitis by targeting CD32

Emerging evidence has shown an imbalance in M1/M2 macrophage polarization to play an essential role in osteoarthritis (OA) progression. However, the underlying mechanistic basis for this polarization is unknown. RNA sequencing of OA M1-polarized macrophages found highly expressed levels of pentraxin 3 (PTX3), suggesting a role for PTX3 in OA occurrence and development. Herein, PTX3 was found to be increased in the synovium and articular cartilage of OA patients and OA mice. Intra-articular injection of PTX3 aggravated, while PTX3 neutralization reversed synovitis and cartilage degeneration. No metabolic disorder or proteoglycan loss were observed in cartilage explants when treated with PTX3 alone. However, cartilage explants exhibited an OA phenotype when treated with culture supernatants of macrophages stimulated with PTX3, suggesting that PTX3 did not have a direct effect on chondrocytes. Therefore, the OA anti-chondrogenic effects of PTX3 are primarily mediated through macrophages. Mechanistically, PTX3 was upregulated by miR-224-5p deficiency, which activated the p65/NF-κB pathway to promote M1 macrophage polarization by targeting CD32. CD32 was expressed by macrophages, that when stimulated with PTX3, secreted abundant pro-inflammation cytokines that induced severe articular cartilage damage. The paracrine interaction between macrophages and chondrocytes produced a feedback loop that enhanced synovitis and cartilage damage. The findings of this study identified a functional pathway important to OA development. Blockade of this pathway and PTX3 may prevent and treat OA.

Musculoskeletal Effects of Altered GH Action

Growth hormone (GH) is a peptide hormone that can signal directly through its receptor or indirectly through insulin-like growth factor 1 (IGF-1) stimulation. GH draws its name from its anabolic effects on muscle and bone but also has distinct metabolic effects in multiple tissues. In addition to its metabolic and musculoskeletal effects, GH is closely associated with aging, with levels declining as individuals age but GH action negatively correlating with lifespan. GH’s effects have been studied in human conditions of GH alteration, such as acromegaly and Laron syndrome, and GH therapies have been suggested to combat aging-related musculoskeletal diseases, in part, because of the decline in GH levels with advanced age. While clinical data are inconclusive, animal models have been indispensable in understanding the underlying molecular mechanisms of GH action. This review will provide a brief overview of the musculoskeletal effects of GH, focusing on clinical and animal models.

The role of accelerated growth plate fusion in the absence of SOCS2 on osteoarthritis vulnerability

AIMS

Osteoarthritis (OA) is the most prevalent systemic musculoskeletal disorder, characterized by articular cartilage degeneration and subchondral bone (SCB) sclerosis. Here, we sought to examine the contribution of accelerated growth to OA development using a murine model of excessive longitudinal growth. Suppressor of cytokine signalling 2 (SOCS2) is a negative regulator of growth hormone (GH) signalling, thus mice deficient in SOCS2 (Socs2 -/-) display accelerated bone growth.

METHODS

We examined vulnerability of Socs2 -/- mice to OA following surgical induction of disease (destabilization of the medial meniscus (DMM)), and with ageing, by histology and micro-CT.

RESULTS

We observed a significant increase in mean number (wild-type (WT) DMM: 532 (SD 56); WT sham: 495 (SD 45); knockout (KO) DMM: 169 (SD 49); KO sham: 187 (SD 56); p < 0.001) and density (WT DMM: 2.2 (SD 0.9); WT sham: 1.2 (SD 0.5); KO DMM: 13.0 (SD 0.5); KO sham: 14.4 (SD 0.7)) of growth plate bridges in Socs2 -/- in comparison with WT. Histological examination of WT and Socs2 -/- knees revealed articular cartilage damage with DMM in comparison to sham. Articular cartilage lesion severity scores (mean and maximum) were similar in WT and Socs2 -/- mice with either DMM, or with ageing. Micro-CT analysis revealed significant decreases in SCB thickness, epiphyseal trabecular number, and thickness in the medial compartment of Socs2 -/-, in comparison with WT (p < 0.001). DMM had no effect on the SCB thickness in comparison with sham in either genotype.

CONCLUSION

Together, these data suggest that enhanced GH signalling through SOCS2 deletion accelerates growth plate fusion, however this has no effect on OA vulnerability in this model. Cite this article: Bone Joint Res 2022;11(3):162-170.

Strategies for Articular Cartilage Repair and Regeneration

Articular cartilage is an avascular tissue, with limited ability to repair and self-renew. Defects in articular cartilage can induce debilitating degenerative joint diseases such as osteoarthritis. Currently, clinical treatments have limited ability to repair, for they often result in the formation of mechanically inferior cartilage. In this review, we discuss the factors that affect cartilage homeostasis and function, and describe the emerging regenerative approaches that are informing the future treatment options.

Insulin-like growth factor-1 in articular cartilage repair for osteoarthritis treatment

Articular cartilage repair is a critical issue in osteoarthritis (OA) treatment. The insulin-like growth factor (IGF) signaling pathway has been implicated in articular cartilage repair. IGF-1 is a member of a family of growth factors that are structurally closely related to pro-insulin and can promote chondrocyte proliferation, enhance matrix production, and inhibit chondrocyte apoptosis. Here, we reviewed the role of IGF-1 in cartilage anabolism and catabolism. Moreover, we discussed the potential role of IGF-1 in OA treatment. Of note, we summarized the recent progress on IGF delivery systems. Optimization of IGF delivery systems will facilitate treatment application in cartilage repair and improve OA treatment efficacy.

Changes of the condylar cartilage and subchondral bone in the temporomandibular joints of rats under unilateral mastication and expression of Insulin-like Growth Factor-1

OBJECTIVES

This study aimed to define changes in the rat condylar cartilage and subchondral bone using the unilateral mastication model.

MATERIALS AND METHODS

In this study, forty 4-week-old Wistar rats were randomly divided into experimental (n = 20) and control group (n = 20). In the experimental group, unilateral dental splints were placed on the occlusal surface of left maxillary molars. The rats were sacrificed at 1, 2, 3, and 4 weeks after placement of the splint. Micro-CT scanning and histological staining were performed to observe the changes in the mandibular condylar cartilage and subchondral bone. Levels of insulin-like growth factor-1 (IGF-1) were determined via immunohistochemistry to analyse the occurrence of osteogenic changes.

RESULTS

Micro-CT scanning findings demonstrated the occurrence of asymmetric growth of condyle in the experimental group. The condylar cartilage and subchondral bone exhibited degradation on the chewing side of the experimental group and showed decreased bone mineral density, thinner cartilage thickness, and increased degree of degeneration and osteoclast activity. Compared with the control group, the expression of IGF-1 was remarkably higher on the non-chewing side.

CONCLUSION

Long-term unilateral mastication can lead to the occurrence of degenerative changes in the condylar cartilage and subchondral bone during growth and development. IGF-1 may play a role in promoting the process of osteogenesis.

Sexual dimorphic impact of adult-onset somatopause on life span and age-induced osteoarthritis

Osteoarthritis (OA), the most prevalent joint disease, is a major cause of disability worldwide. Growth hormone (GH) has been suggested to play significant roles in maintaining articular chondrocyte function and ultimately articular cartilage (AC) homeostasis. In humans, the age-associated decline in GH levels was hypothesized to play a role in the etiology of OA. We studied the impact of adult-onset isolated GH deficiency (AOiGHD) on the life span and skeletal integrity including the AC, in 23- to 30-month-old male and female mice on C57/BL6 genetic background. Reductions in GH during adulthood were associated with extended life span and reductions in body temperature in female mice only. However, end-of-life pathology revealed high levels of lymphomas in both sexes, independent of GH status. Skeletal characterization revealed increases in OA severity in AOiGHD mice, evidenced by AC degradation in both femur and tibia, and significantly increased osteophyte formation in AOiGHD females. AOiGHD males showed significant increases in the thickness of the synovial lining cell layer that was associated with increased markers of inflammation (IL-6, iNOS). Furthermore, male AOiGHD showed significant increases in matrix metalloproteinase-13 (MMP-13), p16, and β-galactosidase immunoreactivity in the AC as compared to controls, indicating increased cell senescence. In conclusion, while the life span of AOiGHD females increased, their health span was compromised by high-grade lymphomas and the development of severe OA. In contrast, AOiGHD males, which did not show extended life span, showed an overall low grade of lymphomas but exhibited significantly decreased health span, evidenced by increased OA severity.

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

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

IGF-1-releasing PLGA nanoparticles modified 3D printed PCL scaffolds for cartilage tissue engineering

The aim of this study is to fabricate and test a 3D-printed PCL scaffold incorporating IGF-1-releasing PLGA nanoparticles for cartilage tissue engineering. IGF-1 loaded PLGA nanoparticles were produced by the double-emulsion method, and were incorporated onto 3D printed PCL scaffolds via PDA. Particle size, loading effciency (LE) and encapsulation effciency (EE) of the nanoparticles were examined. SEM, pore size, porosity, compression testing, contact angle, IGF-1 release kinetics of the composite scaffolds were also determined. For cell culture studies, CCK-8, Live/dead, MTT, GAG content and expression level of chondrocytes specific proteins and genes and HIF-1α were also tested. There was no difference of the nanoparticle size. And the LE and EE of IGF-1 in PLGA nanoparticles was about 5.53 ± 0.12% and 61.26 ± 2.71%, respectively. There was a slower, sustained release for all drug-loaded nanoparticles PLGA/PDA/PCL scaffolds. There was no difference of pore size, porosity, compressive strength of each scaffold. The contact angles PCL scaffolds were significant decreased when coated with PDA and PLGA nanoparticales. (p < .05) Live/dead staining showed more cells attached to the IGF-1 PLGA/PDA/PCL scaffolds. The CCK-8 and MTT assay showed higher cell proliferation and better biocompatibility of the IGF-1 PLGA/PDA/PCL scaffolds. (p < .05) GAG content, chondrogenic protein and gene expression level of SOX-9, COL-II, ACAN, and HIF pathway related gene (HIF-1α) were significantly higher in IGF-1 PLGA/PDA/PCL scaffolds group compared to other groups. (p < .05) IGF-1 PLGA/PDA/PCL scaffolds may be a better method for sustained IGF-1 administration and a promising scaffold for cartilage tissue engineering.

MFG-E8 regulated by miR-99b-5p protects against osteoarthritis by targeting chondrocyte senescence and macrophage reprogramming via the NF-κB pathway

Milk fat globule-epidermal growth factor (EGF) factor 8 (MFG-E8), as a necessary bridging molecule between apoptotic cells and phagocytic cells, has been widely studied in various organs and diseases, while the effect of MFG-E8 in osteoarthritis (OA) remains unclear. Here, we identified MFG-E8 as a key factor mediating chondrocyte senescence and macrophage polarization and revealed its role in the pathology of OA. We found that MFG-E8 expression was downregulated both locally and systemically as OA advanced in patients with OA and in mice after destabilization of the medial meniscus surgery (DMM) to induce OA. MFG-E8 loss caused striking progressive articular cartilage damage, synovial hyperplasia, and massive osteophyte formation in OA mice, which was relieved by intra-articular administration of recombinant mouse MFG-E8 (rmMFG-E8). Moreover, MFG-E8 restored chondrocyte homeostasis, deferred chondrocyte senescence and reprogrammed macrophages to the M2 subtype to alleviate OA. Further studies showed that MFG-E8 was inhibited by miR-99b-5p, expression of which was significantly upregulated in OA cartilage, leading to exacerbation of experimental OA partially through activation of NF-κB signaling in chondrocytes. Our findings established an essential role of MFG-E8 in chondrocyte senescence and macrophage reprogramming during OA, and identified intra-articular injection of MFG-E8 as a potential therapeutic target for OA prevention and treatment.

Effects of GH/IGF axis on bone and cartilage

Growth hormone (GH) and its mediator, the insulin-like growth factor-1 (IGF-1) regulate somatic growth, metabolism and many aspects of aging. As such, actions of GH/IGF have been studied in many tissues and organs over decades. GH and IGF-1 are part of the hypothalamic/pituitary somatotrophic axis that consists of many other regulatory hormones, receptors, binding proteins, and proteases. In humans, GH/IGF actions peak during pubertal growth and regulate skeletal acquisition through stimulation of extracellular matrix production and increases in bone mineral density. During aging the activity of these hormones declines, a state called somatopaguss, which associates with deleterious effects on the musculoskeletal system. In this review, we will focus on GH/IGF-1 action in bone and cartilage. We will cover many studies that have utilized congenital ablation or overexpression of members of this axis, as well as cell-specific gene-targeting approaches used to unravel the nature of the GH/IGF-1 actions in the skeleton in vivo.

Pathophysiological landscape of osteoarthritis

A sharp rise in osteoarthritis (OA) incidence is expected as over 25% of world population ages in the coming decade. Although OA is considered a degenerative disease, mounting evidence suggests a strong connection with chronic metabolic conditions and low-grade inflammation. OA pathology is increasingly understood as a complex interplay of multiple pathological events including oxidative stress, synovitis and immune responses revealing its intricate nature. Cellular, biochemical and molecular aspects of these pathological events along with major outcomes of the relevant research studies in this area are discussed in the present review. With reference to their published and unpublished work, the authors strongly propose synovitis as a central OA pathology and the key OA pathological events are described in connection with it. Recent research outcomes also have succeeded to establish a linkage between metabolic syndrome and OA, which has been precisely included in the present review. Impact of aging process cannot be neglected in OA. Cell senescence is an important mechanism of aging through which it facilitates development of OA like other degenerative disorders, also discussed within a frame of OA. Conclusively, the reviewers urge low-grade inflammation linked to aging and derailed immune function as a pathological platform for OA development and progression. Thus, interventions targeted to prevent inflammaging hold a promising potential in effective OA management and efforts should be invested in this direction.

Activation of the SOX-5, SOX-6, and SOX-9 Trio of Transcription Factors Using a Gene-Activated Scaffold Stimulates Mesenchymal Stromal Cell Chondrogenesis and Inhibits Endochondral Ossification

Current treatments for articular cartilage defects relieve symptoms but often only delay cartilage degeneration. Mesenchymal stem cells (MSCs) have shown chondrogenic potential but tend to undergo endochondral ossification when implanted in vivo. Harnessing factors governing joint development to functionalize biomaterial scaffolds, termed developmental engineering, might allow to prime host MSCs to regenerate mature articular cartilage in situ without requiring cell isolation or ex vivo expansion. Therefore, the aim of this study is to develop a gene-activated scaffold capable of delivering developmental cues to host MSCs, thus priming MSCs for articular cartilage differentiation and inhibiting endochondral ossification. It is shown that delivery of the SOX-Trio induced MSCs to over-express COL2A1 and ACAN and deposit a sulfated and collagen type II rich extracellular matrix while hypertrophic gene expression and collagen type X deposition is inhibited. When cell-free SOX-Trio-activated scaffolds are implanted ectopically in vivo, they induced spontaneous chondrogenesis without evidence of hypertrophy. MSCs pre-cultured on SOX-Trio-activated scaffolds prior to implantation differentiate into phenotypically stable chondrocytes as evidenced by a lack of collagen X expression or vascular invasion. This SOX-trio-activated scaffold represents a potent, single treatment, developmentally inspired strategy to prime MSCs in situ for articular cartilage defect repair.

Secreted Factors and EV-miRNAs Orchestrate the Healing Capacity of Adipose Mesenchymal Stem Cells for the Treatment of Knee Osteoarthritis

Mesenchymal stem cells (MSCs) derived from adipose tissue and used either as expanded cells or minimally manipulated cell preparations showed positive clinical outcomes in regenerative medicine approaches based on tissue restoration and inflammation control, like in osteoarthritis (OA). Recently, MSCs’ healing capacity has been ascribed to the large array of soluble factors, including soluble cytokines/chemokines and miRNAs conveyed within extracellular vesicles (EVs). Therefore, in this study, 200 secreted cytokines, chemokines and growth factors via ELISA, together with EV-embedded miRNAs via high-throughput techniques, were scored in adipose-derived MSCs (ASCs) cultivated under inflammatory conditions, mimicking OA synovial fluid. Both factors (through most abundantly expressed TIMP1, TIMP2, PLG and CTSS) and miRNAs (miR-24-3p, miR-222-3p and miR-193b-3p) suggested a strong capacity for ASCs to reduce matrix degradation activities, as those activated in OA cartilage, and switch synovial macrophages, often characterized by an M1 inflammatory polarization, towards an M2 phenotype. Moreover, the crucial importance of selecting the target tissue is discussed, showing how a focused search may greatly improve potency prediction and explain clinical outcomes. In conclusion, herein presented data shed light about the way ASCs regulate cell homeostasis and regenerative pathways in an OA-resembling environment, therefore suggesting a rationale for the use of MSC-enriched clinical products, such as stromal vascular fraction and microfragmented adipose tissue, in joint pathologies.

Liver-derived IGF-I is not required for protection against osteoarthritis in male mice

Insulin-like growth factor-I (IGF-I) is anabolic for cartilage and important for cartilage integrity, which might suggest a connection between IGF-I and osteoarthritis (OA) development. However, the results of studies performed so far are conflicting, and we aimed to clarify the role of endocrine IGF-I in rodent OA. Male mice with inducible inactivation of circulating, liver-derived IGF-I (LI-IGF-I^-/- mice, serum IGF-I reduced by ~80%) were used. Experimental OA was induced in young adult LI-IGF-I^-/- and control mice by destabilization of the medial meniscus (DMM); age-related OA was also evaluated in 1-yr-old mice. DMM-operated LI-IGF-I^-/- mice had thinner lateral subchondral bone plate in tibia compared with control mice, whereas osteophyte volume and articular cartilage damage were unaffected at the medial side of the DMM knee. However, the control mice but not the LI-IGF-I^-/- mice also developed mild OA on the lateral side of the DMM knee compared with the unoperated knee. One-year-old LI-IGF-I^-/- mice had lower mid-diaphyseal cortical bone area than the 1-yr-old control mice, whereas analyses of joint tissues displayed smaller osteophyte volume and thicker calcified cartilage than the control mice. There was no difference in OA severity in the articular cartilage between old LI-IGF-I^-/- and control mice. Our study is the first to investigate whether there is an association between circulating IGF-I and OA in mice. We conclude that, although there is an ~80% reduction of circulating IGF-I and a decrease in cortical bone in male LI-IGF-I^-/- mice, cartilage damage is clearly not intensified and may instead be slightly reduced.

Skeletal maturation and predicted adult height in adolescents with temporomandibular joint osteoarthritis

BACKGROUND

The occurrence of osteoarthritis (OA) of the temporomandibular joint (TMJ) in juveniles could be associated with fluctuating levels of oestrogen and growth hormone (GH) during adolescence.

OBJECTIVE

To investigate extent of skeletal maturation and predicted adult height in adolescents with TMJ OA.

METHOD

In total, 155 adolescents (54 males, 101 females; mean age, 14.1 ± 2.0 years) were enrolled. Among them, 19 adolescents (CON) showed no sign of TMD, 50 adolescents exhibited signs of disc displacement but did not have TMJ OA (TMDnoOA), 23 adolescents exhibited the initial stage of TMJ OA (TMJOAini) and 63 adolescents exhibited the severe stage of TMJ OA (TMJOApro). TMJ OA was diagnosed based on the Research Diagnostic Criteria axis I and bone age was estimated using the Greulich-Pyle method. The height, weight and body mass index of participated adolescents were measured and statistically converted to z-scores. The predicted adult height and age of peak height velocity (APHV) were calculated using the BoneXpert® software.

RESULTS

In female adolescents, the differences between the chronological and bone ages were significantly higher and the z-score for height was significantly lower in the TMJOApro. Female adolescents with TMJOA exhibited a significantly shorter predicted adult height and earlier APHV than those in the CON and TMDnoOA.

CONCLUSION

The adolescents with TMJ OA exhibited premature skeletal maturations and short predicted adult stature, particularly the female adolescents.

Ageing and Osteoarthritis

The increase in global lifespan has in turn increased the prevalence of osteoarthritis which is now the most common type of arthritis. Cartilage tissue located on articular joints erodes during osteoarthritis which causes pain and may lead to a crippling loss of function in patients. The pathophysiology of osteoarthritis has been understudied and currently no disease modifying treatments exist. The only current end-point treatment remains joint replacement surgery. The primary risk factor for osteoarthritis is age. Clinical and basic research is now focused on understanding the ageing process of cartilage and its role in osteoarthritis. This chapter will outline the physiology of cartilage tissue, the clinical presentation and treatment options for the disease and the cellular ageing processes which are involved in the pathophysiology of the disease.

miRNA‑27a regulates arthritis via PPARγ in vivo and in vitro

The present study investigated the role of microRNA (miR)‑27a in the development of arthritis and its mechanism of action. Initially, collagen was used to develop an in vivo rat model of arthritis. Changes in the miRs in the rats were analyzed. It was subsequently observed that miR‑27a expression was reduced in patients with arthritis, compared with the control group. In the present study an in vitro miR‑27a overexpression model of arthritis was established and it was observed that miR‑27a increased the proliferation of osteoblast‑like cells in vitro. miR‑27a overexpression promoted osteogenic differentiation, increased alkaline phosphatase (ALP) and osteoporosis (OST) content, induced insulin‑like growth factor binding protein-5 (IGFBP‑5) protein expression, reduced inflammation and suppressed peroxisome proliferator‑activated receptor γ (PPARγ) and matrix metalloproteinase-17 (MMP‑17) protein expression in arthritis. However, miR‑27a downregulation inhibited osteogenic differentiation, increased inflammation and PPARγ and MMP‑17 protein expression and suppressed ALP and OST content in an in vitro model of arthritis. The PPARγ inhibitor reduced the function of miR‑27a downregulation on arthritis. Therefore the results of the present study revealed that miR‑27a regulates arthritis via PPARγ.

Adding Intra-Articular Growth Hormone to Platelet Rich Plasma under Ultrasound Guidance in Knee Osteoarthritis: A Comparative Double-Blind Clinical Trial

Introduction

Intra-articular injections of platelet rich plasma (PRP) for the treatment of knee osteoarthritis have been shown to reduce pain and improve joint function. The aim of this study is to examine the joint function by adding intra-articular growth hormone to platelet rich plasma. This study was performed on the individuals with knee osteoarthritis and under ultrasound guidance.

Methods

Fifty four patients who were scheduled for ultra-sound guided intra-articular injection were enrolled in the study. The patients were randomly allocated to groups P (platelet rich plasma) and PS (platelet rich plasma and Somatropin). Group P and PS were injected with 5 mL of platelet rich plasma, and 4 IU growth hormone (Somatropin) added to platelet rich plasma, respectively. Intra-articular injection was performed in two steps; the onset of study and one month after. Knee joint function based on Western Ontario and McMaster osteoarthritis index (WOMAC) score at the baseline, 1 and 2 month later, and complications were evaluated.

Results

WOMAC score in both groups has been significantly reduced after injections (P = 0.030). WOMAC score reduction in group PS in first month was significantly higher than group P, but in second month 2, the difference between two groups was not significant (P = 0.235). No complication was observed.

Conclusions

These results showed that adding growth hormone to platelet rich plasma for intra-articular injection improved function of the osteoarthritic knee joint in short period of time.

Cartilage tissue engineering: Role of mesenchymal stem cells along with growth factors & scaffolds

Articular cartilage injury poses a major challenge for both the patient and orthopaedician. Articular cartilage defects once formed do not regenerate spontaneously, rather replaced by fibrocartilage which is weaker in mechanical competence than the normal hyaline cartilage. Mesenchymal stem cells (MSCs) along with different growth factors and scaffolds are currently incorporated in tissue engineering to overcome the deficiencies associated with currently available surgical methods and to facilitate cartilage healing. MSCs, being readily available with a potential to differentiate into chondrocytes which are enhanced by the application of different growth factors, are considered for effective repair of articular cartilage after injury. However, therapeutic application of MSCs and growth factors for cartilage repair remains in its infancy, with no comparative clinical study to that of the other surgical techniques. The present review covers the role of MSCs, growth factors and scaffolds for the repair of articular cartilage injury.

IGF-1 deficiency in a critical period early in life influences the vascular aging phenotype in mice by altering miRNA-mediated post-transcriptional gene regulation: implications for the developmental origins of health and disease hypothesis

Epidemiological findings support the concept of Developmental Origins of Health and Disease, suggesting that early-life hormonal influences during a sensitive period of development have a fundamental impact on vascular health later in life. The endocrine changes that occur during development are highly conserved across mammalian species and include dramatic increases in circulating IGF-1 levels during adolescence. The present study was designed to characterize the effect of developmental IGF-1 deficiency on the vascular aging phenotype. To achieve that goal, early-onset endocrine IGF-1 deficiency was induced in mice by knockdown of IGF-1 in the liver using Cre-lox technology (Igf1 ^f/f mice crossed with mice expressing albumin-driven Cre recombinase). This model exhibits low-circulating IGF-1 levels during the peripubertal phase of development, which is critical for the biology of aging. Due to the emergence of miRNAs as important regulators of the vascular aging phenotype, the effect of early-life IGF-1 deficiency on miRNA expression profile in the aorta was examined in animals at 27 months of age. We found that developmental IGF-1 deficiency elicits persisting late-life changes in miRNA expression in the vasculature, which significantly differed from those in mice with adult-onset IGF-1 deficiency (TBG-Cre-AAV8-mediated knockdown of IGF-1 at 5 month of age in Igf1 ^f/f mice). Using a novel computational approach, we identified miRNA target genes that are co-expressed with IGF-1 and associate with aging and vascular pathophysiology. We found that among the predicted targets, the expression of multiple extracellular matrix-related genes, including collagen-encoding genes, were downregulated in mice with developmental IGF-1 deficiency. Collectively, IGF-1 deficiency during a critical period during early in life results in persistent changes in post-transcriptional miRNA-mediated control of genes critical targets for vascular health, which likely contribute to the deleterious late-life cardiovascular effects known to occur with developmental IGF-1 deficiency.

Adenoviral vector expressing IGF-1 protects murine chondrogenic ATDC5 cells against hydrogen peroxide-induced mitochondrial dysfunction and apoptosis

Insulin-like growth factor-1 (IGF-1), with an age-related decline, regulates the proliferation and survival of multiple cell types, particularly stimulates cartilage matrix synthesis, and inhibits matrix degradation. The present study was to investigate the regulatory role of IGF-1 against hydrogen peroxide(H2O2)-induced mitochondrial dysfunction and apoptosis in murine chondrocytic ATDC5 cells. We firstly determined mitochondrial dysfunction and apoptosis in ATDC5 cells which were exposed to H2O2. We then constructed an IGF-1-overexpressed adenovirus (IGF-1-Ad) harboring the IGF-1 coding sequence, and investigated the regulatory role of the overexpressed IGF-1 against the H2O2-induced mitochondrial dysfunction and apoptosis in ATDC5 cells. It was demonstrated that H2O2 treatment promoted the mitochondrial dysfunction, and further reduced the viability and induced apoptosis of ATDC5 cells. However, the IGF-1 overexpression by adenovirus inhibited the H2O2-induced mitochondrial dysfunction and further inhibited the H2O2-promoted apoptosis in ATDC5 cells. In conclusion, the present study found that oxidative stress promoted mitochondrial dysfunction and induced apoptosis in the murine chondrocytic ATDC5 cells, and the adenoviral vector-expressed IGF-1 protected the murine chondrocytic ATDC5 cells against such mitochondrial dysfunction and apoptosis. This study implies the protective role of IGF-1 against the oxidative stress in murine chondrocytic ATDC5 cells and demonstrates the promising anti-oxidative stress effect of the recombinant IGF-1-Ad against oxidative stress in chondrocytic cells.

Cellular ageing mechanisms in osteoarthritis

Age is the strongest independent risk factor for the development of osteoarthritis (OA) and for many years this was assumed to be due to repetitive microtrauma of the joint surface over time, the so-called 'wear and tear' arthritis. As our understanding of OA pathogenesis has become more refined, it has changed our appreciation of the role of ageing on disease. Cartilage breakdown in disease is not a passive process but one involving induction and activation of specific matrix-degrading enzymes; chondrocytes are exquisitely sensitive to changes in the mechanical, inflammatory and metabolic environment of the joint; cartilage is continuously adapting to these changes by altering its matrix. Ageing influences all of these processes. In this review, we will discuss how ageing affects tissue structure, joint use and the cellular metabolism. We describe what is known about pathways implicated in ageing in other model systems and discuss the potential value of targeting these pathways in OA.

Signaling pathways in cartilage repair

In adult healthy cartilage, chondrocytes are in a quiescent phase characterized by a fine balance between anabolic and catabolic activities. In ageing, degenerative joint diseases and traumatic injuries of cartilage, a loss of homeostatic conditions and an up-regulation of catabolic pathways occur. Since cartilage differentiation and maintenance of homeostasis are finely tuned by a complex network of signaling molecules and biophysical factors, shedding light on these mechanisms appears to be extremely relevant for both the identification of pathogenic key factors, as specific therapeutic targets, and the development of biological approaches for cartilage regeneration. This review will focus on the main signaling pathways that can activate cellular and molecular processes, regulating the functional behavior of cartilage in both physiological and pathological conditions. These networks may be relevant in the crosstalk among joint compartments and increased knowledge in this field may lead to the development of more effective strategies for inducing cartilage repair.

Serum CTXii Correlates With Articular Cartilage Degeneration After Anterior Cruciate Ligament Transection or Arthrotomy Followed by Standardized Exercise

Background:

Anterior cruciate ligament injury increases risk for accelerated development of osteoarthritis. The effect of exercise on articular cartilage following joint injury is not well understood. Biochemical biomarkers of collagen degradation and proteoglycan turnover are potential indicators for early articular cartilage degeneration.

Hypothesis:

This study tests the hypothesis that serum concentrations of CS846 and CTXii correlate with structural changes to articular cartilage following joint injury in exercised animals.

Study Design:

Controlled laboratory study.

Methods:

Twenty-four Sprague-Dawley rats underwent either arthrotomy alone (sham surgery) or anterior cruciate ligament transection (ACLT). Animals were recovered for 3 weeks and then exercised on a treadmill at 18 m per minute, 1 hour per day, 5 days per week, until sacrifice either 6 or 12 weeks later. Articular cartilage was assessed grossly, and histology was graded using modified Mankin, toluidine blue, and modified David-Vaudey scales. Serum collected preoperatively and at sacrifice was assayed by ELISA for CTXii and CS846.

Results:

At 6 weeks, gross grades (P < 0.01), modified Mankin scores (P < 0.03), and toluidine blue scores (P < 0.04) were higher, reflecting increased degeneration in ACLT animals compared with sham surgery animals. Serum CS846 increased after 6 weeks in ACLT animals (P < 0.05). Serum CTXii levels strongly correlated with Mankin degenerative scores (coefficient = 0.81, P < 0.01) and David-Vaudey histology grades (coefficient = 0.73, P < 0.01) at 6 weeks. While gross grades remained higher at 12 weeks in ACLT animals (P < 0.04), no differences were seen in serum CS846 and CTXii. Histology scores also showed no differences between ACLT and sham due to increasing degeneration in the sham surgery group.

Conclusion:

The strong correlation between serum CTXii and microstructural changes to articular cartilage following joint injury demonstrates potential use of serum biomarkers for early detection of cartilage degeneration. Increasing cartilage degeneration in exercised sham-surgery animals suggests that early loading may have negative effects on articular cartilage due to either mechanical injury or hemarthrosis after arthrotomy.

Clinical Relevance:

Patients with anterior cruciate ligament injury are at increased risk for development of posttraumatic osteoarthritis. CTXii may be useful for early detection of joint degeneration. Further study on the effects of exercise after injury is important to postinjury and postoperative rehabilitation.

A biological therapy to osteoarthritis treatment using platelet-rich plasma

INTRODUCTION

Osteoarthritis (OA) is a degenerative disease affecting the synovial joint. It is caused by cells exposure to non-physiological stimuli, either mechanical or biochemical, and the loss of bone-cartilage homeostasis. Some of these changes, however, may be reversed by the use of single or combined growth factors, suggesting that the treatment of OA could be addressed using a pool of growth factors.

AREAS COVERED

This review addresses current molecular and biological knowledge and implicates the recapitulation of some developmental processes during endochondral ossification in OA aetiology and pathogenesis. Platelets act as carriers of endogenous morphogens that may modulate cell fate and therefore affect joint tissues structure and function. We shed light on the platelet-rich plasma effects on biological level that might drive the osteoarthritic joint's improvement both in structure and function.

EXPERT OPINION

We present the therapeutic potential of plasma rich in growth factors (PRGF-Endoret), an endogenous biological therapy that might modulate the gene expression of cells such as chondrocytes, synoviocytes, macrophages, and mesenchymal stem cells, and thereby influence an anabolic microenvironment of synovial joint which is conducive to maintaining the homeostatic state of the joint's tissues, and hence reduce pain and improve the joint motion.

Effects of serum and autologous conditioned serum on equine articular chondrocytes treated with interleukin-1β

OBJECTIVE

To compare the effects of autologous equine serum (AES) and autologous conditioned serum (ACS) on equine articular chondrocyte metabolism when stimulated with recombinant human (rh) interleukin (IL)-1β.

SAMPLE

Articular cartilage and nonconditioned and conditioned serum from 6 young adult horses.

PROCEDURES

Cartilage samples were digested, and chondrocytes were isolated and formed into pellets. Chondrocyte pellets were treated with each of the following: 10% AES, 10% AES and rhIL-1β, 20% AES and rhIL-1β, 10% ACS and rhIL-1β, and 20% ACS and rhIL-1β, and various effects of these treatments were measured.

RESULTS

Recombinant human IL-1β treatment led to a decrease in chondrocyte glycosaminoglycan synthesis and collagen II mRNA expression and an increase in medium matrix metalloproteinase-3 activity and cyclooxygenase-2 mRNA expression. When results of ACS and rhIL-1β treatment were compared with those of AES and rhIL-1β treatment, no difference was evident in glycosaminoglycan release, total glycosaminoglycan concentration, total DNA content, or matrix metalloproteinase-3 activity. A significant increase was found in chondrocyte glycosaminoglycan synthesis with 20% AES and rhIL-1β versus 10% ACS and rhIL-1β. The medium from ACS and rhIL-1β treatment had a higher concentration of IL-1β receptor antagonist, compared with medium from AES and rhIL-1β treatment. Treatment with 20% ACS and rhIL-1β resulted in a higher medium insulin-like growth factor-I concentration than did treatment with 10% AES and rhIL-1β. No difference in mRNA expression was found between ACS and rhIL-1β treatment and AES and rhIL-1β treatment.

CONCLUSIONS AND CLINICAL RELEVANCE

Minimal beneficial effects of ACS treatment on proteoglycan matrix metabolism in equine chonrocytes were evident, compared with the effects of AES treatment.

Differential expression of IGF1, IGFR1 and IGFBP3 in mandibular condylar cartilage between male and female rats applied with malocclusion

This study was designed to investigate the expression differences of insulin-like growth factor-1 (IGF1), IGF type 1 receptor (IGFR1) and IGF-binding protein-3 (IGFBP3) in mandibular condylar cartilage between male and female rats with experimentally created malocclusion. A total of 40 male and 40 female rats were used, and malocclusion was created by moving the first molars mesially and the third molars distally in the experimental group. Animals were killed at the end of the second and fourth weeks. Haematoxylin and eosin (HE) staining was performed to monitor the changes in cartilage morphology and thickness. Immunohistochemistry and real-time PCR were used to detect the expression of IGF1, IGFR1 and IGFBP3. Osteoarthritis (OA)-like changes were observed in the experimental groups, with 2-week females showing larger OA-like regions than 2-week males (P < 0·05). Compared to their age- and sex-matched controls, both 2- and 4-week males in the experimental groups displayed increased cartilage thickness in the posterior regions (P < 0·05). Compared to their age- and sex-matched controls, the expression of IGF1 was lower in 2-week female group (P < 0·05), but higher in 4-week female, 2- and 4-week male experimental groups (P < 0.05). Similarly, the expression of IGFR1 was lower in 2-week female experimental group (P < 0.05), but higher in 2-week male experimental group (P < 0.05). The higher expression of IGFBP3 was observed in 2-week female, 2- and 4-week male experimental groups (P < 0·05). These results indicate that condylar cartilage from male and female rats respond differently to the malocclusion in early stage of OA, with more serious degeneration in females.

Proinflammatory actions of visfatin/nicotinamide phosphoribosyltransferase (Nampt) involve regulation of insulin signaling pathway and Nampt enzymatic activity

Visfatin (also termed pre-B-cell colony-enhancing factor (PBEF) or nicotinamide phosphoribosyltransferase (Nampt)) is a pleiotropic mediator acting on many inflammatory processes including osteoarthritis. Visfatin exhibits both an intracellular enzymatic activity (nicotinamide phosphoribosyltransferase, Nampt) leading to NAD synthesis and a cytokine function via the binding to its hypothetical receptor. We recently reported the role of visfatin in prostaglandin E(2) (PGE(2)) synthesis in chondrocytes. Here, our aim was to characterize the signaling pathways involved in this response in exploring both the insulin receptor (IR) signaling pathway and Nampt activity. IR was expressed in human and murine chondrocytes, and visfatin triggered Akt phosphorylation in murine chondrocytes. Blocking IR expression with siRNA or activity using the hydroxy-2-naphthalenyl methyl phosphonic acid tris acetoxymethyl ester (HNMPA-(AM)(3)) inhibitor diminished visfatin-induced PGE(2) release in chondrocytes. Moreover, visfatin-induced IGF-1R(-/-) chondrocytes released higher concentration of PGE(2) than IGF-1R(+/+) cells, a finding confirmed with an antibody that blocked IGF-1R. Using RT-PCR, we found that visfatin did not regulate IR expression and that an increased insulin release was also unlikely to be involved because insulin was unable to increase PGE(2) release. Inhibition of Nampt activity using the APO866 inhibitor gradually decreased PGE(2) release, whereas the addition of exogenous nicotinamide increased it. We conclude that the proinflammatory actions of visfatin in chondrocytes involve regulation of IR signaling pathways, possibly through the control of Nampt enzymatic activity.

Anabolic/Catabolic balance in pathogenesis of osteoarthritis: identifying molecular targets

Osteoarthritis is the most common degenerative musculoskeletal disease. In healthy cartilage, a low turnover of extracellular matrix molecules occurs. Proper balance of anabolic and catabolic activities is thus crucial for the maintenance of cartilage tissue integrity and for the repair of molecular damages sustained during daily usage. In persons with degenerative diseases such as osteoarthritis, this balance of anabolic and catabolic activities is compromised, and the extent of tissue degradation predominates over the capacity of tissue repair. This mismatch eventually results in cartilage loss in persons with osteoarthritis. Tissue homeostasis is controlled by coordinated actions and crosstalk among a number of proanabolic and antianabolic and procatabolic and anticatabolic factors. In osteoarthritis, an elevation of antianabolic and catabolic factors occurs. Interestingly, anabolic activity is also increased, but this response fails to repair the tissue because of both quantitative and qualitative insufficiency. This review presents an overview of the anabolic and catabolic activities involved in cartilage degeneration and the interplay among different signaling and metabolic factors. Understanding the basic molecular mechanisms responsible for tissue degeneration is critical to identifying and developing means to efficiently block or reverse the pathobiological symptoms of osteoarthritis.

The role of growth factors in cartilage repair

BACKGROUND

Full-thickness chondral defects and early osteoarthritis continue to present major challenges for the patient and the orthopaedic surgeon as a result of the limited healing potential of articular cartilage. The use of bioactive growth factors is under consideration as a potential therapy to enhance healing of chondral injuries and modify the arthritic disease process.

QUESTIONS/PURPOSES

We reviewed the role of growth factors in articular cartilage repair and identified specific growth factors and combinations of growth factors that have the capacity to improve cartilage regeneration. Additionally, we discuss the potential use of platelet-rich plasma, autologous-conditioned serum, and bone marrow concentrate preparations as methods of combined growth factor delivery.

METHODS

A PubMed search was performed using key words cartilage or chondrocyte alone and in combination with growth factor. The search was open for original manuscripts and review papers and open for all dates. From these searches we selected manuscripts investigating the effects of growth factors on extracellular matrix synthesis and excluded those investigating molecular mechanisms of action.

RESULTS

By modulating the local microenvironment, the anabolic and anticatabolic effects of a variety of growth factors have demonstrated potential in both in vitro and animal studies of cartilage injury and repair. Members of the transforming growth factor-β superfamily, fibroblast growth factor family, insulin-like growth factor-I, and platelet-derived growth factor have all been investigated as possible treatment augments in the management of chondral injuries and early arthritis.

CONCLUSIONS

The application of growth factors in the treatment of local cartilage defects as well as osteoarthritis appears promising; however, further research is needed at both the basic science and clinical levels before routine application.

The OARSI histopathology initiative - recommendations for histological assessments of osteoarthritis in the rat

OBJECTIVE

During the development of disease-modifying osteoarthritis (OA) drugs, rat models of OA are frequently used for a first assessment of in vivo efficacy. The most efficacious compound in the rat model may then be tested in a larger animal model before entering human trials. The aim of this study was to describe a histologic scoring system for use in different models of OA in rats that allows standardization and comparison of results obtained by different investigators.

METHODS

The experience of the authors with current scoring systems and the range of lesions observed in rat and human OA studies were considered in recommending this common paradigm for rat histologic scoring. Considerations were made for reproducibility and ease of use for new scorers. Additional scoring paradigms may be employed to further identify specific effects of some disease-modifying drugs.

RESULTS

Although the described scoring system is more complex than the modified Mankin scores, which are recommended for some other species, the reliability study showed that it is easily understood and can be reproducibly used, even by inexperienced scorers.

CONCLUSIONS

The scoring paradigm described here has been found to be sufficiently sensitive to discriminate between treatments and to have high reproducibility. Therefore we recommend its use for evaluation of different rat OA models as well as assessment of disease-modifying effects of treatments in these models.

Hypertrophic differentiation of chondrocytes in osteoarthritis: the developmental aspect of degenerative joint disorders

Osteoarthritis is characterized by a progressive degradation of articular cartilage leading to loss of joint function. The molecular mechanisms regulating pathogenesis and progression of osteoarthritis are poorly understood. Remarkably, some characteristics of this joint disease resemble chondrocyte differentiation processes during skeletal development by endochondral ossification. In healthy articular cartilage, chondrocytes resist proliferation and terminal differentiation. By contrast, chondrocytes in diseased cartilage progressively proliferate and develop hypertrophy. Moreover, vascularization and focal calcification of joint cartilage are initiated. Signaling molecules that regulate chondrocyte activities in both growth cartilage and permanent articular cartilage during osteoarthritis are thus interesting targets for disease-modifying osteoarthritis therapies.

Plasmid growth hormone releasing hormone therapy in healthy and laminitis-afflicted horses-evaluation and pilot study

BACKGROUND

In vivo electroporation dramatically improves the potency of plasmid-mediated therapies, including in large animal models. Laminitis and arthritis are common and debilitating diseases in the horse, as well as humans.

METHODS

The effects of growth hormone releasing hormone (GHRH) on healthy horses and on horses with laminitis that were followed for 6 months after a single intramuscular injection and electroporation of 2.5 mg of an optimized myogenic GHRH-expressing plasmid were examined.

RESULTS

In the first study on six healthy horses, we observed a significant increase in body mass by day 180 compared to baseline (P < 0.003), and an increase in erythrocyte production (hematocrit, red blood cells, hemoglobin, P = 0.03). IGF-I levels were increased by 7% by day 120 (P = 0.02). A pilot study was performed on two horses with chronic laminitis, a vascular condition often associated with arthritis, with two horses with similar clinical disease serving as non-treated controls. Treated horses experienced an increase in weight compared to control horses that received standard care (P = 0.007). By 6 months post-treatment, treated subjects were rated pasture sound. Physical and radiographic evaluation demonstrated significant improvement with reduced inflammation and decreased lameness.

CONCLUSIONS

These results demonstrate that a plasmid therapy delivered by electroporation can potentially be used to treat chronic conditions in horses, and possibly other very large mammals. While further studies are needed, overall this proof-of-concept work presents encouraging data for studying gene therapeutic treatments for Raynaud's syndrome and arthritis in humans.

Molecular network of cartilage homeostasis and osteoarthritis

This review article presents the current understanding of the molecular basis of articular cartilaginous homeostasis, and outlines potential areas to focus on within the developing field of therapeutics for cartilage disorders. Articular cartilage, an integral component of joints in extremities and the vertebral column, is essential for locomotion. Disturbance of joint development or cartilage homeostasis causes congenital osteocartilaginous dysplasia or osteoarthritic diseases, respectively. Symptomatic treatments and surgical replacement of joints are effective but can also be problematic in terms of quality of life over time. Recently, new insights into the molecular biological basis of chondrocyte differentiation and cartilage homeostasis have been reported. While joint formation is regulated by several growth factors such as Wnts (wingless-related MMTV integration site) and Gdfs (growth and differentiation factors), the pathology of osteoarthritis is now interpreted as the disruption of balance between anabolic and catabolic signals. Current findings in molecular biology on joint development are reviewed concisely to aid in the understanding of the molecular network that governs articular cartilage development and homeostasis.