Sex differences of chondrogenic progenitor cells in late stages of osteoarthritis

Epigenomic differences between osteoarthritis grades in primary cartilage

OBJECTIVE

Osteoarthritis is a common and complex joint disorder that shows higher prevalence and greater disease severity in women. Here, we investigate genome-wide methylation profiles of primary chondrocytes from osteoarthritis patients.

DESIGN

We compare genome-wide methylation profiles of macroscopically intact (low-grade) and degraded (high-grade) osteoarthritis cartilage samples matched from osteoarthritis patients undergoing knee replacement surgery. We perform an epigenome-wide association study for cartilage degeneration across 170 patients and separately in 96 women and 74 men.

RESULTS

We reveal widespread epigenetic differences with enrichments of nervous system and apoptosis-related processes. We further identify substantial similarities between sexes, but also sex-specific markers and pathways.

CONCLUSIONS

Together, we provide the largest genome-wide methylation profiles of primary cartilage to date with enhanced and sex-specific insights into epigenetic processes underlying osteoarthritis progression.

Effect of biological sex and short-term high-fat diet on cellular proliferation, ribosomal biogenesis, and targeted protein abundance in murine articular cartilage

Objective

To identify factors contributing to sex-differences in OA risk by evaluating the short-term effect of high-fat (HF) diet on sex-specific changes in cartilage cell proliferation, ribosomal biogenesis, and targeted extra-cellular and cellular protein abundance.

Materials and methods

Knee cartilage was harvested to the subchondral bone from 20-week-old female and male C57BL/6J mice fed a low-fat or HF diet for 4 weeks and labeled with deuterium oxide for 1, 3, 5, 7, 15, or 21 days. Deuterium enrichment was quantified in isolated DNA and RNA to measure cell proliferation and ribosomal biogenesis, respectively. Protein concentration was measured using targeted high resolution accurate mass spectrometry.

Results

HF diet increased the maximal deuterium incorporation into DNA from approximately 40 to 50%, albeit at a slower rate. These findings, which were magnified in female versus male mice, indicate a greater number of proliferating cells with longer half-lives under HF diet conditions. HF diet caused distinct sex-dependent effects on deuterium incorporation into RNA, increasing the fraction of ribosomes undergoing biogenesis in male mice and doubling the rate of ribosome biogenesis in female mice. HF diet altered cartilage protein abundance similarly in both sexes, except for matrilin-3, which was more abundant in HF versus LF conditions in female mice only. Overall, HF diet treatment had a stronger effect than sex on cartilage protein abundance, with most changes involving extracellular matrix and matrix-associated proteins.

Conclusions

Short-term HF diet broadly altered cartilage matrix protein abundance, while sex-dependent effects primarily involved differences in cell proliferation and ribosomal biogenesis.

Phenotype and energy metabolism differ between osteoarthritic chondrocytes from male compared to female patients: Implications for sexual dimorphism in osteoarthritis development?

OBJECTIVES

The prevalence and severity of knee osteoarthritis (OA) are greater in females than males. The purpose of this study was to determine whether there is an underlying difference in the biology of OA chondrocytes between males and females.

METHODS

Chondrocytes were obtained following knee arthroplasty from male and female patients with primary OA. Phenotype marker expression, glucose and fat consumption, and rates of glycolysis and oxidative phosphorylation were compared between females and males. RNAi was used to determine the consequences of differential expression of Sry-box transcription factor 9 (SOX9) and PGC1α between males and females.

RESULTS

OA chondrocytes from male donors showed elevated ribonucleic acid (RNA) and protein levels of SOX9, elevated COL2A1 protein synthesis, higher glucose consumption, and higher usage of glycolysis compared to females. OA chondrocytes from females had higher PGC1α protein levels, higher fat consumption, and higher oxidative energy metabolism than males. Knockdown of SOX9 reduced expression of COL2A1 to a greater extent in male OA chondrocytes than females whereas knockdown of PGC1α reduced COL2A1 expression in females but not males. Expression of ACAN and the glycolytic enzyme PGK1 was also reduced in males but not females following SOX9 knockdown.

CONCLUSIONS

OA chondrocyte phenotype and energy metabolism differ between males and females. Our results indicate transcriptional control of COL2A1 differs between the two. Differences in chondrocyte biology between males and females imply the underlying mechanisms involved in OA may also differ, highlighting the need to consider sex and gender when investigating pathogenesis and potential treatments for OA.

Response eQTLs, chromatin accessibility, and 3D chromatin structure in chondrocytes provide mechanistic insight into osteoarthritis risk

Osteoarthritis (OA) poses a significant healthcare burden with limited treatment options. While genome-wide association studies (GWAS) have identified over 100 OA-associated loci, translating these findings into therapeutic targets remains challenging. Integrating expression quantitative trait loci (eQTL), 3D chromatin structure, and other genomic approaches with OA GWAS data offers a promising approach to elucidate disease mechanisms; however, comprehensive eQTL maps in OA-relevant tissues and conditions remain scarce. We mapped gene expression, chromatin accessibility, and 3D chromatin structure in primary human articular chondrocytes in both resting and OA-mimicking conditions. We identified thousands of differentially expressed genes, including those associated with differences in sex and age. RNA-seq in chondrocytes from 101 donors across two conditions uncovered 3782 unique eGenes, including 420 that exhibited strong and significant condition-specific effects. Colocalization with OA GWAS signals revealed 13 putative OA risk genes, 10 of which have not been previously identified. Chromatin accessibility and 3D chromatin structure provided insights into the mechanisms and conditional specificity of these variants. Our findings shed light on OA pathogenesis and highlight potential targets for therapeutic development.

Highlights

∘ Comprehensive analysis of sex- and age-related global gene expression in human chondrocytes revealed differences that correlate with osteoarthritis ∘ First response eQTLs in chondrocytes treated with an OA-related stimulus ∘ Deeply sequenced Hi-C in resting and activated chondrocytes helps connect OA risk variants to their putative causal genes ∘ Colocalization analysis reveals 13 (including 10 novel) putative OA risk genes.

Lower serum testosterone is associated with increased likelihood of arthritis

Studies have suggested that serum testosterone levels may be strongly correlated with the pathogenesis of arthritis. Therefore, the aim of this study was to assess the relationship between serum testosterone levels and arthritis in US adults using the National Health and Nutrition Examination Survey (NHANES). We used the database from NHANES, 2013-2016 to perform a cross-sectional study. This study investigated the relationship between serum testosterone and arthritis using multivariate logistic regression models and also used smoothed curve fitting and generalized additivity models. A total of 10,439 adults were included in this analysis. A significant negative association between serum testosterone and arthritis was found in a linear regression analysis. The study showed that the arthritis group had lower testosterone levels than the non-arthritis group. The univariate multivariate analyses of Q4, using Q1 as a reference, all showed a significantly lower risk of developing arthritis. In subgroup analyses, the negative correlation between serum testosterone levels and arthritis was more significant in women and those with a body mass index (BMI) ≥ 30 kg/m2. After controlling for various variables, we found a significant association between serum testosterone and arthritis in this analysis. Further study of the relationship between testosterone and arthritis is necessary to clarify the specific mechanism of serum testosterone action on arthritis.

Concentration-dependent effects of leptin on osteoarthritis-associated changes in phenotype of human chondrocytes

Metabolic syndrome is a risk factor for osteoarthritis. Elevated leptin levels have been implicated as a potential cause of this association. Previous studies have shown that supra-physiological leptin concentrations can induce osteoarthritis-like changes in chondrocyte phenotype. Here, we tested the effects of leptin in the concentration range found in synovial fluid on chondrocyte phenotype. Chondrocytes isolated from macroscopically normal regions of cartilage within osteoarthritic joints from patients undergoing knee arthroplasty, all with body mass index >30 kg/m2 were treated with 2-40 ng/ml leptin for 24 h. Chondrocyte phenotype marker expression was measured by RT-qPCR and western blot. The role of HES1 in mediating the effects of leptin was determined by gene knockdown using RNAi and over-expression using adenoviral-mediated gene delivery. Treatment of chondrocytes with 20 or 40 ng/ml leptin resulted in decreased SOX9 levels and decreased levels of the SOX9-target genes COL2A1 and ACAN. Levels of HES1 were lower and ADAMTS5 higher in chondrocytes treated with 20 or 40 ng/ml leptin. HES1 knockdown resulted in increased ADAMTS5 expression whereas over-expression of HES1 prevented the leptin-induced increase in ADAMTS5. An increase in MMP13 expression was only evident in chondrocytes treated with 40 ng/ml leptin and was not mediated by HES1 activity. High concentrations of leptin can cause changes in chondrocyte phenotype consistent with those seen in osteoarthritis. Synovial fluid leptin concentrations of this level are typically observed in patients with metabolic syndrome and/or women, suggesting elevated leptin levels may form part of the multifactorial network that leads to osteoarthritis development in these patients.

Achieving Nasal Septal Cartilage In Situ Regeneration: Focus on Cartilage Progenitor Cells

The nasal septal cartilage plays an important role in preventing the collapse of the nasal bones and maintaining the appearance of the nose. In the context of inherent difficulties regarding septal cartilage repair and the shortage of cartilage graft resources for regeneration, tissue engineering, especially the in situ strategy based on scaffolds, has become a new prospect and become one of the most promising approaches. Given that it is difficult for chondrocytes to achieve directional migration and secrete matrix components to participate in tissue repair after cartilage injury, cartilage progenitor cells (CPCs), with great migratory ability and stem cell characteristics, have caught the attention of researchers and brought hope for nasal septal cartilage in situ regeneration. In this review, we first summarized the distribution, characteristics, isolation, and culture methods of nasal septal CPCs. Subsequently, we described the roles of migratory CPCs in cartilage regeneration. Finally, we reviewed the existing studies on CPCs-based cartilage tissue engineering and summarized the strategies for promoting the migration and chondrogenesis of CPCs so as to provide ideas for achieving nasal septal cartilage in situ regeneration.

Reasons for the Sex Bias in Osteoarthritis Research: A Review of Preclinical Studies

Osteoarthritis (OA) is one of the most common degenerative diseases of articular cartilage. During OA, all the elements that contribute to the joint undergo physiological and structural changes that impair the joint function and cause joint pain and stiffness. OA can arise naturally, with the aging population witnessing an increase in diagnoses of this pathology, but the root causes of OA have yet to be identified, and increasing interest is arising towards investigating biological sex as a risk factor. Clinical studies show increased prevalence and worse clinical outcomes for female patients, yet most clinical and preclinical studies have disproportionately focused on male subjects. This review provides a critical overview of preclinical practices in the context of OA, highlighting the underlying need for taking biological sex as both a risk factor and an important component affecting treatment outcome. A unique insight into the possible reasons for female underrepresentation in preclinical studies is offered, including factors such as lack of specific guidelines requiring the analysis of sex as a biological variable (SABV), research-associated costs and animal handling, and wrongful application of the reduction principle. Additionally, a thorough investigation of sex-related variables is provided, stressing how each of them could add valuable information for the understanding of OA pathophysiology, as well as sex-dependent treatment strategies.

Sex-dependent variation in cartilage adaptation: from degeneration to regeneration

Despite acknowledgement in the scientific community of sex-based differences in cartilage biology, the implications for study design remain unclear, with many studies continuing to arbitrarily assign demographics. Clinically, it has been well-established that males and females differ in cartilage degeneration, and accumulating evidence points to the importance of sex differences in the field of cartilage repair. However, a comprehensive review of the mechanisms behind this trend and the influence of sex on cartilage regeneration has not yet been presented. This paper aims to summarize current findings regarding sex-dependent variation in knee anatomy, sex hormones' effect on cartilage, and cartilaginous degeneration and regeneration, with a focus on stem cell therapies. Findings suggest that the stem cells themselves, as well as their surrounding microenvironment, contribute to sex-based differences. Accordingly, this paper underscores the contribution of both stem cell donor and recipient sex to sex-related differences in treatment efficacy. Cartilage regeneration is a field that needs more research to optimize strategies for better clinical results; taking sex into account could be a big factor in developing more effective and personalized treatments. The compilation of this information emphasizes the importance of investing further research in sex differences in cartilage biology.

Se(XY) matters: the importance of incorporating sex in microphysiological models

The development of microphysiological models is currently at the forefront of preclinical research. Although these 3D tissue models are being developed to mimic physiological organ function and diseases, which are often sexually dimorphic, sex is usually neglected as a biological variable. For decades, national research agencies have required government-funded clinical trials to include both male and female participants as a means of eliminating male bias. However, this is not the case in preclinical trials, which have been shown to favor male rodents in animal studies and male cell types in in vitro studies. In this Opinion, we highlight the importance of considering sex as a biological variable and outline five approaches for incorporating sex-specific features into current microphysiological models.

From regeneration to osteoarthritis in the knee joint: The role shift of cartilage-derived progenitor cells

A mount of growing evidence has proven that cartilage-derived progenitor cells (CPCs) harbor strong proliferation, migration, andmultiple differentiation potentials over the past 2 decades. CPCs in the stage of immature tissue play an important role in cartilage development process and injured cartilage repair in the young and active people. However, during maturation and aging, cartilage defects cannot be completely repaired by CPCs in vivo. Recently, tissue engineering has revealed that repaired cartilage defects with sufficient stem cell resources under good condition and bioactive scaffolds in vitro and in vivo. Chronic inflammation in the knee joint limit the proliferation and chondrogenesis abilities of CPCs, which further hampered cartilage healing and regeneration. Neocartilage formation was observed in the varus deformity of osteoarthritis (OA) patients treated with offloading technologies, which raises the possibility that organisms could rebuild cartilage structures spontaneously. In addition, nutritionmetabolismdysregulation, including glucose and free fatty acid dysregulation, could influence both chondrogenesis and cartilage formation. There are a few reviews about the advantages of CPCs for cartilage repair, but few focused on the reasons why CPCs could not repair the cartilage as they do in immature status. A wide spectrum of CPCs was generated by different techniques and exhibited substantial differences. We recently reported that CPCs maybe are as internal inflammation sources during cartilage inflammaging. In this review, we further streamlined the changes of CPCs from immature development to maturation and from healthy status to OA advancement. The key words including “cartilage derived stem cells”, “cartilage progenitor cells”, “chondroprogenitor cells”, “chondroprogenitors” were set for latest literature searching in PubMed and Web of Science. The articles were then screened through titles, abstracts, and the full texts in sequence. The internal environment including long-term inflammation, extendedmechanical loading, and nutritional elements intake and external deleterious factors were summarized. Taken together, these results provide a comprehensive understanding of the underlying mechanism of CPC proliferation and differentiation during development, maturation, aging, injury, and cartilage regeneration in vivo.

Estrogen Signaling Dictates Musculoskeletal Stem Cell Behavior: Sex Differences in Tissue Repair

Sexual dimorphisms in humans and other species exist in visually evident features such as body size and less apparent characteristics, including disease prevalence. Current research is adding to a growing understanding of sex differences in stem cell function and response to external stimuli, including sex hormones such as estrogens. These differences are proving significant and directly impact both the understanding of stem cell processes in tissue repair and the clinical implementation of stem cell therapies. Adult stem cells of the musculoskeletal system, including those used for development and repair of muscle, bone, cartilage, fibrocartilage, ligaments, and tendons, are no exception. Both in vitro and in vivo studies have found differences in stem cell number, proliferative and differentiation capabilities, and response to estrogen treatment between males and females of many species. Maintaining the stemness and reducing senescence of adult stem cells is an important topic with implications in regenerative therapy and aging. As such, this review discusses the effect of estrogens on musculoskeletal system stem cell response in multiple species and highlights the research gaps that still need to be addressed. The following evidence from investigations of sex-related phenotypes in adult progenitor and stem cells are pieces to the big puzzle of sex-related effects on aging and disease and critical information for both fundamental tissue repair and regeneration studies and safe and effective clinical use of stem cells. Impact Statement This review summarizes current knowledge of sex differences in and the effects of estrogen treatment on musculoskeletal stem cells in the context of tissue engineering. Specifically, it highlights the impact of sex on musculoskeletal stem cell function and ability to regenerate tissue. Furthermore, it discusses the varying effects of estrogen on stem cell properties, including proliferation and differentiation, important to tissue engineering. This review aims to highlight the potential impact of estrogens and the importance of performing sex comparative studies in the field of tissue engineering.

Is gender a factor affecting long-term heterotopic ossification incidence after single-level cervical disc arthroplasty?

BACKGROUND

Cervical disc diseases have been treated by means of cervical disc arthroplasty (CDA). Nevertheless, some patients will experience a mobility failure in their cervical prostheses over time because of heterotopic ossification (HO). Aim of this study is to investigate the role of gender in long-term outcomes after CDA.

MATERIALS AND METHODS

A retrospective, single-center study including patients who underwent single-level CDA with a Bryan prosthesis was performed, including a narrative review about gender differences in both structural and biomechanical features of the cervical spine.

RESULTS

Study patients (14M, 30F) had an average follow-up period of 9,8 ± 3,2 years. Significant differences emerged between genders for specific items in Neck Disability Index (NDI) preoperative evaluation, with females reporting worse pain scores (p=0.05). After stratification by age we report a higher preoperative overall NDI score for female patients under 36 years of age (p=0.03). In an intergender, BMI-specific comparison we also found a significant difference in NDI preoperative score with normal-weight male patients faring worse than overweight ones (p= 0.05). At a radiological level, we found a tendency towards a higher HO incidence in male patients (62% males, 17% females, p=0.06). Women's cervical spine has peculiar features including bone structure, muscular action, soft-tissue response, genetic and epigenetic response to osteoarthritis.

CONCLUSION

The incidence of mobility failure in our series of single-level CDA was lower in females. Several gender specific factors both in static and dynamic features may play a significant role in spinal pathology and CDA long-term radiological outcome.

Gender-Related Aspects in Osteoarthritis Development and Progression: A Review

Osteoarthritis (OA) is a common degenerative joint disease treated mostly symptomatically before approaching its definitive treatment, joint arthroplasty. The rapidly growing prevalence of OA highlights the urgent need for a more efficient treatment strategy and boosts research into the mechanisms of OA incidence and progression. As a multifactorial disease, many aspects have been investigated as contributors to OA onset and progression. Differences in gender appear to play a role in the natural history of the disease, since female sex is known to increase the susceptibility to its development. The aim of the present review is to investigate the cues associated with gender by analyzing various hormonal, anatomical, molecular, and biomechanical parameters, as well as their differences between sexes. Our findings reveal the possible implications of gender in OA onset and progression and provide evidence for gaps in the current state of art, thus suggesting future research directions.

The clinical potential of articular cartilage-derived progenitor cells: a systematic review

Over the past two decades, evidence has emerged for the existence of a distinct population of endogenous progenitor cells in adult articular cartilage, predominantly referred to as articular cartilage-derived progenitor cells (ACPCs). This progenitor population can be isolated from articular cartilage of a broad range of species, including human, equine, and bovine cartilage. In vitro, ACPCs possess mesenchymal stromal cell (MSC)-like characteristics, such as colony forming potential, extensive proliferation, and multilineage potential. Contrary to bone marrow-derived MSCs, ACPCs exhibit no signs of hypertrophic differentiation and therefore hold potential for cartilage repair. As no unique cell marker or marker set has been established to specifically identify ACPCs, isolation and characterization protocols vary greatly. This systematic review summarizes the state-of-the-art research on this promising cell type for use in cartilage repair therapies. It provides an overview of the available literature on endogenous progenitor cells in adult articular cartilage and specifically compares identification of these cell populations in healthy and osteoarthritic (OA) cartilage, isolation procedures, in vitro characterization, and advantages over other cell types used for cartilage repair. The methods for the systematic review were prospectively registered in PROSPERO (CRD42020184775).

Pondering the Potential of Hyaline Cartilage-Derived Chondroprogenitors for Tissue Regeneration: A Systematic Review

OBJECTIVE

Chondroprogenitors have recently gained prominence due to promising results seen in in vitro and animal studies as a potential contender in cell-based therapy for cartilage repair. Lack of consensus regarding nomenclature, isolation techniques, and expansion protocols create substantial limitations for translational research, especially given the absence of distinct markers of identification. The objective of this systematic review was to identify and collate information pertaining to hyaline cartilage-derived chondroprogenitors, with regard to their isolation, culture, and outcome measures.

DESIGN

As per Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, a web-based search of Scopus and PubMed databases was performed from January 2000 to May 2020, which yielded 509 studies. A total of 65 studies were identified that met the standardized inclusion criteria which comprised of, but was not limited to, progenitors derived from fibronectin adhesion, migrated subpopulation from explant cultures, and single-cell sorting.

RESULT

Literature search revealed that progenitors demonstrated inherent chondrogenesis and minimal tendency for hypertrophy. Multiple sources also demonstrated significantly better outcomes that bone marrow-derived mesenchymal stem cells and comparable results to chondrocytes. With regard to progenitor subgroups, collated evidence points to better and consistent outcomes with the use of migratory progenitors when compared to fibronectin adhesion assay-derived progenitors, although a direct comparison between the two cell populations is warranted.

CONCLUSION

Since chondroprogenitors exhibit favorable properties for cartilage repair, efficient characterization of progenitors is imperative, to complete their phenotypic profile, so as to optimize their use in translational research for neocartilage formation.

The future of basic science in orthopaedics and traumatology: Cassandra or Prometheus?

Orthopaedic and trauma research is a gateway to better health and mobility, reflecting the ever-increasing and complex burden of musculoskeletal diseases and injuries in Germany, Europe and worldwide. Basic science in orthopaedics and traumatology addresses the complete organism down to the molecule among an entire life of musculoskeletal mobility. Reflecting the complex and intertwined underlying mechanisms, cooperative research in this field has discovered important mechanisms on the molecular, cellular and organ levels, which subsequently led to innovative diagnostic and therapeutic strategies that reduced individual suffering as well as the burden on the society. However, research efforts are considerably threatened by economical pressures on clinicians and scientists, growing obstacles for urgently needed translational animal research, and insufficient funding. Although sophisticated science is feasible and realized in ever more individual research groups, a main goal of the multidisciplinary members of the Basic Science Section of the German Society for Orthopaedics and Trauma Surgery is to generate overarching structures and networks to answer to the growing clinical needs. The future of basic science in orthopaedics and traumatology can only be managed by an even more intensified exchange between basic scientists and clinicians while fuelling enthusiasm of talented junior scientists and clinicians. Prioritized future projects will master a broad range of opportunities from artificial intelligence, gene- and nano-technologies to large-scale, multi-centre clinical studies. Like Prometheus in the ancient Greek myth, transferring the elucidating knowledge from basic science to the real (clinical) world will reduce the individual suffering from orthopaedic diseases and trauma as well as their socio-economic impact.

Donor variation and sex hormone receptors in periodontal ligament cells

OBJECTIVE

This study evaluated the gene expression and protein synthesis of sex hormone receptors in human periodontal ligament cells (PDLCs) in relation to donor- and tooth-specific factors with the aim to clarify the debate about sex hormone receptors in PDLCs.

DESIGN

The expression patterns of estrogen receptors (genes: ESR1 and ESR2; proteins: ERα and ERβ), androgen receptor (AR) and progesterone receptor (PR) were investigated in the context of immortalization status, previous orthodontic tooth movement (OTM), donor age, sex and hormonal stimulation in PDLCs from 14 healthy donors (male: n = 8, female: n = 6; adolescents: n = 8, adults: n = 6) using quantitative real-time polymerase chain reaction, Western blot and immunocytochemistry.

RESULTS

For ERβ, the full-length isoform ERβ1 and truncated variants were detected. For ERα, the expected isoform ERα66 was not observed, but a novel isoform ERα36 was detected. Immortalization status, previous OTM and donor age had no impact on ESR1 and ESR2 expression. Estradiol stimulation for 24 h doubled the ratio of ESR2/ESR1 in PDLCs from female but not male donors, indicating sex-specific patterns of receptor expression. AR and PR demonstrated insufficient protein synthesis in PDLCs.

CONCLUSIONS

The data revealed a pivotal role for and complex interplay between ERα and ERβ in human PDLCs regardless of variable donor characteristics. Therefore, PDLC biology might be altered in patients of each age group and both sexes due to hormonal changes. This should be kept in mind during periodontic and orthodontic treatment of patients with special hormonal status.

Total Serum Testosterone and Western Ontario and McMaster Universities Osteoarthritis Index Pain and Function Among Older Men and Women With Severe Knee Osteoarthritis

OBJECTIVE

To investigate whether serum total testosterone level is associated with knee pain and function in men and women with severe knee osteoarthritis (OA).

METHODS

We enrolled 272 adults age ≥60 years (mean ± SD age 70.4 ± 4.4 years, 53% women) who underwent unilateral total knee replacement (TKR) due to severe knee OA. Serum testosterone levels and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain and function of the operated and contralateral knee were measured at 6-8 weeks after surgery. At the nonoperated knee, 56% of participants had radiographic knee OA with a Kellgren/Lawrence grade ≥2. Cross-sectional analyses were performed by sex and body mass index (BMI) subgroups, using multivariable regression adjusted for age, physical activity, and BMI.

RESULTS

At the operated knee, higher testosterone levels were associated with less WOMAC pain in men (B = -0.62, P = 0.046) and women (B = -3.79, P = 0.02), and less WOMAC disability scores in women (B = -3.62, P = 0.02) and obese men (B = -1.99, P = 0.02). At the nonoperated knee, testosterone levels were not associated with WOMAC pain in men or women, but higher testosterone levels were associated with less disability in women (B = -0.95, P = 0.02). Testosterone levels were inconsistently associated with pain and disability in BMI subgroups among men. Only among obese women, testosterone levels were inversely associated with radiographic knee OA (odds ratio = 0.10, P = 0.003).

CONCLUSION

Higher total testosterone levels were associated with less pain in the operated knee in men and women undergoing TKR and less disability in women. At the nonoperated knee, higher testosterone levels were inconsistently associated with less pain and disability.

The Relative Expression of ERα Isoforms ERα66 and ERα36 Controls the Cellular Response to 24R,25-Dihydroxyvitamin D3 in Breast Cancer

Vitamin D3 and its metabolites have antitumorigenic properties in vitro and in vivo; however, clinical trials and retrospective studies on the effectiveness of vitamin D3 oral supplementation against cancer have been inconclusive. One reason for this may be that clinical trials ignore the complex vitamin D metabolome and the many active vitamin D3 metabolites present in the body. Recent work by our lab showed that 24R,25(OH)₂D₃, a vitamin D₃ metabolite that is active in chondrocyte proliferation and differentiation, has antitumorigenic properties in estrogen receptor alpha-66 (ERα66)-positive (ER⁺) breast cancer, but not in ERα66-negative (ER^-) breast cancer. Here we show that 24R,25(OH)₂D₃ is protumorigenic in an in vivo mouse model (NOD.Cg-Prkdc^scidIl2rg^tm1Wjl /SzJ (NSG) mice) of ER^- breast cancer, causing greater tumor growth than in mice treated with vehicle alone. In vitro results indicate that the effect of 24R,25(OH)₂D₃ is via a membrane-associated mechanism involving ERs and phospholipase D. 24R,25(OH)₂D₃ increased proliferation and reduced apoptosis in ERα66-negative HCC38 breast cancer cells, and stimulated expression of metastatic markers. Overexpressing ESRI, which encodes ERα66, ERα46, and ERα36, reduced the proapoptotic response of ERα66^- cells to 24R,25(OH)₂D₃, possibly by upregulating ERα66. Silencing ESR1 in ERα66⁺ cells increased apoptosis. This suggests 24R,25(OH)₂D₃ is differentially tumorigenic in cancers with different ERα isoform profiles. Antiapoptotic actions of 24R,25(OH)₂D₃ require ERα36 and proapoptotic actions require ERα66. IMPLICATIONS: These results suggest that 24R,25(OH)₂D₃, which is a major circulating metabolite of vitamin D, is functionally active in breast cancer and that the regulatory properties of 24R,25(OH)₂D₃ are dependent upon the relative expression of ERα66 and ERα36.

Sex Specific Determinants in Osteoarthritis: A Systematic Review of Preclinical Studies

Osteoarthritis (OA) is a highly prevalent joint disease that primarily affects about 10% of the world's population over 60 years old. The purpose of this study is to systematically review the preclinical studies regarding sex differences in OA, with particular attention to the molecular aspect and gene expression, but also to the histopathological aspects. Three databases (PubMed, Scopus, and Web of Knowledge) were screened for eligible studies. In vitro and in vivo papers written in English, published in the last 11 years (2009-2020) were eligible. Participants were preclinical studies, including cell cultures and animal models of OA, evaluating sex differences. Independent extraction of articles and quality assessments were performed by two authors using predefined data fields and specific tools (Animals in Research Reporting In Vivo Experiments (ARRIVE) guideline and Systematic Review Centre for Laboratory animal Experimentation (SYRCLE) tool). Twenty-three studies were included in the review: 4 in vitro studies, 18 in vivo studies, and 1 both in vitro and in vivo study. From in vitro works, sex differences were found in the gene expression of inflammatory molecules, hormonal receptors, and in responsiveness to hormonal stimulation. In vivo research showed a great heterogeneity of animal models mainly focused on the histopathological aspects rather than on the analysis of sex-related molecular mechanisms. This review highlights that many gaps in knowledge still exist; improvementsin the selection and reporting of animal models, the use of advanced in vitro models, and multiomics analyses might contribute to developing a personalized gender-based medicine.

The Signaling Pathways Project, an integrated 'omics knowledgebase for mammalian cellular signaling pathways

Mining of integrated public transcriptomic and ChIP-Seq (cistromic) datasets can illuminate functions of mammalian cellular signaling pathways not yet explored in the research literature. Here, we designed a web knowledgebase, the Signaling Pathways Project (SPP), which incorporates community classifications of signaling pathway nodes (receptors, enzymes, transcription factors and co-nodes) and their cognate bioactive small molecules. We then mapped over 10,000 public transcriptomic or cistromic experiments to their pathway node or biosample of study. To enable prediction of pathway node-gene target transcriptional regulatory relationships through SPP, we generated consensus 'omics signatures, or consensomes, which ranked genes based on measures of their significant differential expression or promoter occupancy across transcriptomic or cistromic experiments mapped to a specific node family. Consensomes were validated using alignment with canonical literature knowledge, gene target-level integration of transcriptomic and cistromic data points, and in bench experiments confirming previously uncharacterized node-gene target regulatory relationships. To expose the SPP knowledgebase to researchers, a web browser interface was designed that accommodates numerous routine data mining strategies. SPP is freely accessible at https://www.signalingpathways.org .

Hand tendinopathy risk factors in Taiwan: A population-based cohort study

De Quervain's disease, carpal tunnel syndrome (CTS), and trigger finger (digit) are three common pathological conditions of the hand. They are considered overuse syndromes and occur predominantly in females. The prevalence rate and cause-specific risks of these three tendinopathies have not yet been clarified. Data from 41,871 cases listed in the Taiwan National Health Insurance Research Database (NHIRD) from 2010 to 2014 were analyzed. The prevalence rate of these 3 conditions by age, sex, and the risk factors of female-dominant diseases (e.g., osteoporosis, rheumatoid arthritis [RA], and tendinopathy), diabetes mellitus, and hormone antagonist treatment was evaluated. We found that 1.59% of the population developed CTS, 0.49% developed de Quervain's, and 1.07% developed trigger finger. Cases were more likely to develop the three hand tendinopathies if they were female, between 50 and 59 years old, and, according to a multivariate analysis, comorbid with RA, diabetes, using hormone antagonists. Our findings should provide an understanding of the risk factors associated with hand tendinopathy.

Characterization of osteoarthritic human knees indicates potential sex differences

BACKGROUND

The prevalence of osteoarthritis is higher in women than in men in every age group, and overall prevalence increases with advancing age. Sex-specific differences in the properties of osteoarthritic joint tissues may permit the development of sex-specific therapies. Sex hormones regulate cartilage and bone development and homeostasis in a sex-dependent manner. Recent in vitro studies show that the vitamin D3 metabolite 1α,25-dihydroxyvitamin D3 [1α,25(OH)2D3] also has sex-specific effects on musculoskeletal cells, suggesting that vitamin D3 metabolites may play a role in osteoarthritis-related sex-specific differences. The purpose of this study was to determine if sex-specific differences exist in synovial fluid and knee tissues isolated from male and female patients with severe knee osteoarthritis. We determined the presence of vitamin D3 metabolites, inflammatory cytokines, growth factors, and matrix metalloproteinases (MMPs) in synovial fluid and assessed responses of articular chondrocytes and subchondral osteoblasts to 17β-estradiol, dihydrotestosterone, and 1α,25(OH)2D3.

METHODS

Samples from knee joints of 10 Caucasian male and 10 Caucasian female patients with advanced osteoarthritis aged 65 to 75 years were obtained from total knee arthroplasty. Vitamin D metabolites, cytokines, MMPs, and growth factors in the synovial fluid were measured. Primary cultures of chondrocytes were isolated from fibrillated articular cartilage adjacent to osteoarthritis lesions and minimally affected cartilage distal to the lesion. Osteoblasts were isolated from the subchondral bone. Expression of receptors for 17β-estradiol and 1α,25(OH)2D3 was assessed by real-time PCR. Chondrocytes and osteoblasts were treated with 10(-8) M 17β-estradiol, dihydrotestosterone, or 1α,25(OH)2D3 and effects on gene expression and protein synthesis determined.

RESULTS

Histology of the articular cartilage confirmed advanced osteoarthritis. Sex differences were found in synovial fluid levels of vitamin D metabolites, cytokines, and metalloproteinases as well as in the cellular expression of receptors for 17β-estradiol and 1α,25(OH)2D3. Male cells were more responsive to 1α,25(OH)2D3 and dihydrotestosterone, whereas 17β-estradiol-affected female cells.

CONCLUSIONS

These results demonstrate that there are underlying sex differences in knee tissues affected by osteoarthritis. Our findings do not address osteoarthritis etiology but have implications for different prevention methods and treatments for men and women. Further research is needed to better understand these sex-based differences.

Cartilage repair in vivo: the role of migratory progenitor cells

The most common diseases of the joints and its tissues are osteoarthritis and rheumatoid arthritis, with osteoarthritis being anticipated to be the fourth leading cause of disability by the year 2020. To date, no truly causal therapies are available, and this has promoted tissue engineering attempts mainly involving mesenchymal stem cells. The goal of all tissue repairs would be to restore a fully functional tissue, here a hyaline articular cartilage. The hyaline cartilage is the most affected in osteoarthritis, where altered cell–matrix interactions gradually destroy tissue integrity. In rheumatoid arthritis, the inflammatory aspect is more important, and the cartilage tissue is destroyed by the invasion of tumor-like pannus tissue arising from the inflamed synovia. Furthermore, the fibrocartilage of the meniscus is clearly involved in the initiation of osteoarthritis, especially after trauma. Recent investigations have highlighted the role of migratory progenitor cells found in diseased tissues in situ. In osteoarthritis and rheumatoid arthritis, these chondrogenic progenitor cells are involved in regeneration efforts that are largely unsuccessful in diseased cartilage tissue. However, these progenitor cells are interesting targets for a cell-based regenerative therapy for joint diseases.

Human migratory meniscus progenitor cells are controlled via the TGF-β pathway

Degeneration of the knee joint during osteoarthritis often begins with meniscal lesions. Meniscectomy, previously performed extensively after meniscal injury, is now obsolete because of the inevitable osteoarthritis that occurs following this procedure. Clinically, meniscus self-renewal is well documented as long as the outer, vascularized meniscal ring remains intact. In contrast, regeneration of the inner, avascular meniscus does not occur. Here, we show that cartilage tissue harvested from the avascular inner human meniscus during the late stages of osteoarthritis harbors a unique progenitor cell population. These meniscus progenitor cells (MPCs) are clonogenic and multipotent and exhibit migratory activity. We also determined that MPCs are likely to be controlled by canonical transforming growth factor β (TGF-β) signaling that leads to an increase in SOX9 and a decrease in RUNX2, thereby enhancing the chondrogenic potential of MPC. Therefore, our work is relevant for the development of novel cell biological, regenerative therapies for meniscus repair.

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Progenitor cells are found in the inner avascular part of human osteoarthritic menisci

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These meniscus progenitor cells (MPCs) are clonogenic, migratory, and multipotent

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MPCs are governed via the canonical TGF-β pathway

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TGF-β3 via Smad2 reduces Runx2 to enhance the chondrogenic potential of MPCs

Interleukin-1 beta and tumor necrosis factor alpha inhibit migration activity of chondrogenic progenitor cells from non-fibrillated osteoarthritic cartilage

Introduction

The repair capability of traumatized articular cartilage is highly limited so that joint injuries often lead to osteoarthritis. Migratory chondrogenic progenitor cells (CPC) might represent a target cell population for in situ regeneration. This study aims to clarify, whether 1) CPC are present in regions of macroscopically intact cartilage from human osteoarthritic joints, 2) CPC migration is stimulated by single growth factors and the cocktail of factors released from traumatized cartilage and 3) CPC migration is influenced by cytokines present in traumatized joints.

Methods

We characterized the cells growing out from macroscopically intact human osteoarthritic cartilage using a panel of positive and negative surface markers and analyzed their differentiation capacity. The migratory response to platelet-derived growth factor (PDGF)-BB, insulin-like growth factor 1 (IGF-1), supernatants obtained from in vitro traumatized cartilage and interleukin-1 beta (IL-1β) as well as tumor necrosis factor alpha (TNF-α) were tested with a modified Boyden chamber assay. The influence of IL-1β and TNF-α was additionally examined by scratch assays and outgrowth experiments.

Results

A comparison of 25 quadruplicate marker combinations in CPC and bone-marrow derived mesenchymal stromal cells showed a similar expression profile. CPC cultures had the potential for adipogenic, osteogenic and chondrogenic differentiation. PDGF-BB and IGF-1, such as the supernatant from traumatized cartilage, induced a significant site-directed migratory response. IL-1β and TNF-α significantly reduced basal cell migration and abrogated the stimulative effect of the growth factors and the trauma supernatant. Both cytokines also inhibited cell migration in the scratch assay and primary outgrowth of CPC from cartilage tissue. In contrast, the cytokine IL-6, which is present in trauma supernatant, did not affect growth factor induced migration of CPC.

Conclusion

These results indicate that traumatized cartilage releases chemoattractive factors for CPC but IL-1β and TNF-α inhibit their migratory activity which might contribute to the low regenerative potential of cartilage in vivo.

A discoidin domain receptor 1 knock-out mouse as a novel model for osteoarthritis of the temporomandibular joint

Discoidin domain receptor 1 (DDR-1)-deficient mice exhibited a high incidence of osteoarthritis (OA) in the temporomandibular joint (TMJ) as early as 9 weeks of age. They showed typical histological signs of OA, including surface fissures, loss of proteoglycans, chondrocyte cluster formation, collagen type I upregulation, and atypical collagen fibril arrangements. Chondrocytes isolated from the TMJs of DDR-1-deficient mice maintained their osteoarthritic characteristics when placed in culture. They expressed high levels of runx-2 and collagen type I, as well as low levels of sox-9 and aggrecan. The expression of DDR-2, a key factor in OA, was increased. DDR-1-deficient chondrocytes from the TMJ were positively influenced towards chondrogenesis by a three-dimensional matrix combined with a runx-2 knockdown or stimulation with extracellular matrix components, such as nidogen-2. Therefore, the DDR-1 knock-out mouse can serve as a novel model for temporomandibular disorders, such as OA of the TMJ, and will help to develop new treatment options, particularly those involving tissue regeneration.

Physiological testosterone levels enhance chondrogenic extracellular matrix synthesis by male intervertebral disc cells in vitro, but not by mesenchymal stem cells

BACKGROUND CONTEXT

Testosterone (T) is a hormone and regulator involved in the processes of development of the organism (ie, promoting development of bone and muscle mass). Although T effects on the mesenchyme-derived muscle, bone, and adipose tissues are well studied, T effects on intervertebral disc (IVD) have not been reported.

PURPOSE

The aim was to test the following hypothesis: if a physiological concentration of T (∼30 nM) can improve in vitro chondrogenesis of human IVD cells and mesenchymal stem cells (MSCs).

STUDY DESIGN/SETTING

Human IVD cells and MSCs were differentiated to chondrogenic lineage on gelatin scaffolds for 4 weeks, in the presence or absence of T.

METHODS

Chondrogenesis was assessed by cell viability, by measuring gene expression with quantitative polymerase chain reaction and extracellular matrix (ECM) accumulation with immunoblotting, immunohistochemical, and biochemical methods.

RESULTS

Supplementation of T to chondrogenic culture did not affect viability. In male IVD cells, T had a beneficial impact on chondrogenesis, particularly in nucleus pulposus cells, demonstrated by an increased expression of aggrecan, collagen type I, and especially collagen type II. Conversely, T had no effects on chondrogenesis of female IVD cells or MSCs from both genders. A gene expression array of transforming growth factor β/bone morphogenetic protein signaling cascade showed that in male IVD cells, T promoted a stable general but nonsignificant increase in gene expression. Furthermore, aromatase inhibitor anastrazole repressed the effect of T on ECM expression by IVD cells. The results suggest that T increased ECM accumulation in male IVD cells in combination with its conversion to estradiol by the enzyme aromatase.

CONCLUSIONS

We demonstrated that T effectively enhances in vitro chondrogenesis in male IVD cells, rising the interest in the possible role of sex hormones in IVD degeneration. Nevertheless, T does not affect chondrogenic differentiation of female IVD cells and MSCs from both genders.

Sonic hedgehog improves redifferentiation of dedifferentiated chondrocytes for articular cartilage repair

Sonic hedgehog (Shh) is involved in the induction of early cartilaginous differentiation of mesenchymal cells in the limb. We investigated whether Shh could promote redifferentiation of dedifferentiated chondrocytes and have a favorable effect on the regeneration of cartilage. Articular chondrocytes of rats were separated and cultured. The redifferentiation of dedifferentiated chondrocytes transfected with Shh was evaluated using monolayer and pellet culture system. The signaling molecules (Ptc 1, Gli 1 and Sox9) of the hedgehog pathway were investigated. A rat model of articular cartilage defect was used to evaluate cartilage repair after transplantation with dedifferentiated chondrocytes. After Shh gene transfer, the hedgehog pathway was upregulated in dedifferentiated chondrocytes. Real time-PCR and western blot analysis verified the stronger expression of Ptc1, Gli1 and Sox9 in Shh transfected cells. Shh upregulates the Shh signaling pathway and multiple cytokines (bone morphogenetic protein 2 and insulin-like growth factor 1) in dedifferentiated chondrocytes. After transplantation in the joint, histologic analysis of the regenerative tissues revealed that significantly better cartilage repair in rats transplanted with Shh transfected cells. These data suggest that Shh could induce redifferentiation of dedifferentiated chondrocytes through up-regulating Shh signaling pathway, and have considerable therapeutic potential in cartilage repair.

Hormonal modulation of connective tissue homeostasis and sex differences in risk for osteoarthritis of the knee

Young female athletes experience a higher incidence of ligament injuries than their male counterparts, females experience a higher incidence of joint hypermobility syndrome (a risk factor for osteoarthritis development), and post-menopausal females experience a higher prevalence of osteoarthritis than age-matched males. These observations indicate that fluctuating sex hormone levels in young females and loss of ovarian sex hormone production due to menopause likely contribute to observed sex differences in knee joint function and risk for loss of function. In studies of osteoarthritis, however, there is a general lack of appreciation for the heterogeneity of hormonal control in both women and men. Progress in this field is limited by the relatively few preclinical osteoarthritis models, and that most of the work with established models uses only male animals. To elucidate sex differences in osteoarthritis, it is important to examine sex hormone mechanisms in cells from knee tissues and the sexual dimorphism in the role of inflammation at the cell, tissue, and organ levels. There is a need to determine if the risk for loss of knee function and integrity in females is restricted to only the knee or if sex-specific changes in other tissues play a role. This paper discusses these gaps in knowledge and suggests remedies.

Current concepts in stem cell therapy for articular cartilage repair

INTRODUCTION

Hyaline articular cartilage is the connective tissue responsible for frictionless joint movement. Its degeneration ultimately results in complete loss of joint function in the late stages of osteoarthritis. Intrinsic repair is compromised, and cartilage tissue regeneration is difficult. However, new options are available to repair cartilage tissue by applying ESCs, MSCs and CPCs.

AREAS COVERED

In this review, the authors shed light on the different concepts currently under investigation for cartilage repair.

EXPERT OPINION

So far, there is no way to derive a chondrogenic lineage from stem cells that forms functional hyaline cartilage tissue in vivo. One alternative might be to enhance the chondrogenic potential of repair cells, which are already present in diseased cartilage tissue. CPCs found in diseased cartilage tissue in situ are biologically driven toward the osteochondrogenic lineage and can be directed toward chondrogenesis at least in vitro.

Increased Femoral Cartilage Thickness in Patients With Klinefelter Syndrome

The objective of this study was to determine femoral cartilage thickness (FCT) in patients with Klinefelter syndrome (KS), which is the most common sex chromosome disorder in men with varying degrees of androgen deficiency. This cross-sectional controlled study was conducted in a tertiary care center. Participants were 33 male patients (mean age = 36.2 years) with KS and 35 aged-matched healthy male controls (mean age = 32.9 years). Femoral condyle cartilage was measured by ultrasonography at three locations in each knee. Total testosterone, estradiol, sex hormone binding globulin, free androgen index, bioavailable testosterone, and albumin levels were measured. Femoral cartilage of patients at right and left knee lateral (3.03 and 2.99 mm), mid (3.81 and 3.74 mm), and medial (3.01 and 3.20 mm) were statistically thicker than in controls (right and left knee lateral 2.29 and 2.36 mm, mid 2.64 and 2.53 mm, medial 2.39 and 2.32 mm, respectively, p < .001). There was no significant correlation between FCT and sex hormones. In conclusion, patients with KS had thicker femoral cartilage. Relatively low testosterone levels in these patients and altered estrogen metabolism may hypothetically explain increased cartilage thickness in these patients.

Dietary polyphenols and mechanisms of osteoarthritis

Osteoarthritis is a condition caused in part by injury, loss of cartilage structure and function, and an imbalance in inflammatory and anti-inflammatory pathways. It primarily affects the articular cartilage and subchondral bone of synovial joints and results in joint failure, leading to pain upon weight bearing including walking and standing. There is no cure for osteoarthritis, as it is very difficult to restore the cartilage once it is destroyed. The goals of treatment are to relieve pain, maintain or improve joint mobility, increase the strength of the joints and minimize the disabling effects of the disease. Recent studies have shown an association between dietary polyphenols and the prevention of osteoarthritis-related musculoskeletal inflammation. This review discusses the effects of commonly consumed polyphenols, including curcumin, epigallocatechin gallate and green tea extract, resveratrol, nobiletin and citrus fruits, pomegranate, as well as genistein and soy protein, on osteoarthritis with an emphasis on molecular antiosteoarthritic mechanisms.

Multi-layered environmental regulation on the homeostasis of stem cells: the saga of hair growth and alopecia

Stem cells are fascinating because of their potential in regenerative medicine. Stem cell homeostasis has been thought to be mainly regulated by signals from their adjacent micro-environment named the "stem cell niche". However, recent studies reveal that there can be multiple layers of environmental controls. Here we review these environmental controls using the paradigm of hair stem cells, because to observe and analyze the growth of hair is easier due to their characteristic cyclic regeneration pattern. The length of hair fibers is regulated by the duration of the growth period. In the hair follicles, hair stem cells located in the follicle bulge interact with signals from the dermal papilla. Outside of the follicle, activation of hair stem cells has been shown to be modulated by molecules released from the intra-dermal adipose tissue as well as body hormone status, immune function, neural activities, and aging. The general physiological status of an individual is further influenced by circadian rhythms and changing seasons. The interactive networks of these environmental factors provide new understanding on how stem cell homeostasis is regulated, inspiring new insights for regenerative medicine. Therapies do not necessarily have to be achieved by using stem cells themselves which may constitute a higher risk but by modulating stem cell activity through targeting one or multiple layers of their micro- and macro-environments.

The adiponectin paralog C1q/TNF-related protein 3 (CTRP3) stimulates testosterone production through the cAMP/PKA signaling pathway

CTRP3, a paralog of adiponectin, is a member of the C1q and tumor necrosis factor (TNF)-related protein (CTRP) superfamily. It is expressed at high levels in adipose tissue and has recently emerged as a novel adipokine. In the present study, we provide the first evidence for a physiological role of the new adipokine, CTRP3, in the reproductive system. CTRP3 was specifically expressed in interstitial Leydig cells, where testosterone is produced, in the adult mouse testis. CTRP3 increased testosterone production by TM3 mouse Leydig cells in a dose-dependent manner. The increased testosterone production was linked to upregulation of steroidogenic proteins expression, such as steroidogenic acute regulatory (StAR) protein and cholesterol side-chain cleavage cytochrome P450 (P450scc). Moreover, increases in intracellular cyclic AMP (cAMP) concentrations and the phosphorylation of cAMP-response element binding protein (CREB) in CTRP3-stimulated TM3 Leydig cells were observed. Inhibition of this signaling pathway by a specific protein kinase A (PKA) inhibitor, H89, blocked testosterone production in CTRP3-stimulated Leydig cells, suggesting that the stimulatory effect of CTRP3 on testosterone production is associated with activation of the cAMP/PKA signaling pathway. Thus, our results demonstrate a physiological role for CTRP3 in testicular steroidogenesis and provide novel insights in the intracellular mechanisms activated by this protein.

New insights into cartilage repair - the role of migratory progenitor cells in osteoarthritis

Osteoarthritis is one of the most common musculo-skeletal diseases with a complex patholoy and a strong impact on cell biology, differentiation and migration behavior of mesenchymal stem cell-derived progenitor cells. In this review, we elucidate the influence of the pathologically altered extracellular matrix on progenitor cell behavior. Moreover, we discuss the modulation of progenitor cells especially of previously characterized chondrogenic progenitor cells (Koelling et al., 2009) in situ to enhance their regeneration potential. These options comprise the application of growth factors like fibroblast growth factor-2, a Runx-2 knock down and a contemporary anti-inflammatory therapy. This supports endogenous regeneration on behalf of the diseased osteoarthritic cartilage, which otherwise results mainly in an insufficient fibro-cartilaginous repair tissue. Furthermore, new results indicate a role of pericytes in osteoarthritis for these repair attempts. We discuss the biological mechanisms potentially leading to new therapeutic options in osteoarthritis to enhance regeneration in situ.

The primary cilium as a dual sensor of mechanochemical signals in chondrocytes

The primary cilium is an immotile, solitary, and microtubule-based structure that projects from cell surfaces into the extracellular environment. The primary cilium functions as a dual sensor, as mechanosensors and chemosensors. The primary cilia coordinate several essential cell signaling pathways that are mainly involved in cell division and differentiation. A primary cilium malfunction can result in several human diseases. Mechanical loading is sense by mechanosensitive cells in nearly all tissues and organs. With this sensation, the mechanical signal is further transduced into biochemical signals involving pathways such as Akt, PKA, FAK, ERK, and MAPK. In this review, we focus on the fundamental functional and structural features of primary cilia in chondrocytes and chondrogenic cells.

The associations between finger length pattern, osteoarthritis, and knee injury: data from the Framingham community cohort

OBJECTIVE

To investigate the associations of index finger-to-ring finger (2D:4D) length ratio with radiographic knee and hand osteoarthritis (OA), previous knee injury, and meniscal lesions in the general population.

METHODS

We measured the length of the right second and fourth phalangeal and metacarpal bones on hand radiographs from 1,020 randomly recruited subjects (ages 51-92 years). Knee radiography and magnetic resonance imaging (MRI) were performed on subjects. Women and men were divided into tertiles according to their 2D:4D phalangeal and metacarpal ratios. We assessed the odds ratios (ORs) and 95% confidence intervals (95% CIs) for radiographic knee OA, severe symptomatic knee OA, radiographic hand OA, previous knee injury, and MRI-defined meniscal lesion, using logistic regression with adjustment for age and body mass index. Because hand OA may affect the 2D:4D phalangeal ratio, we performed sensitivity analyses in subjects without joint space narrowing in the second and fourth interphalangeal joints.

RESULTS

We found no significant associations between 2D:4D length ratio and radiographic knee OA, severe symptomatic knee OA, or meniscal lesions. Low 2D:4D phalangeal ratio was associated with hand OA in women (OR 1.80, 95% CI 1.11-2.93), but in the sensitivity analysis, the association was attenuated (OR 1.35, 95% CI 0.79-2.32). Low 2D:4D phalangeal ratios were associated with knee injury in men (OR 1.78, 95% CI 1.02-3.10). We found no significant associations for 2D:4D metacarpal ratios.

CONCLUSION

Low 2D:4D phalangeal ratios in men are associated with knee injury, but we did not find any significant association with knee OA. Low 2D:4D length ratio may be a consequence, rather than a cause, of hand OA in women.

Prospects of stem cell therapy in osteoarthritis

Osteoarthritis is a common disorder in which there is not only extensive degeneration but also an aberrant attempt at repair in joints. Stem cell therapy could provide a permanent, biological solution, with all sources of stem cells (embryonic, fetal and adult) showing some degree of potential. Mesenchymal stromal/stem cells, however, appear to be the leading candidates because of their ability to be sourced from many or all joint tissues. They may also modulate the immune response of individuals, in a manner influenced by local factors. This biological behavior of stem cells renders the application of regulatory standardizations challenging in comparison to pharmaceutical therapies. However, this would not be an issue if endogenous stem cells were activated to effect repair of an arthritic joint.

New developments in osteoarthritis. Sex differences in magnetic resonance imaging-based biomarkers and in those of joint metabolism

Sex differences in the prevalence, incidence, and severity of osteoarthritis (OA) have long been known. Some differences in the evaluation of this issue across studies may be related to differences in study design, sampling, study size, study populations, targeted joint sites, and definitions of OA. This report highlights recent studies of sex differences in individual joint components imaged by magnetic resonance imaging and in systemic biomarkers of joint metabolism. Particularly important are those studies that examine this issue in young unaffected adults and children before the development of disease. Despite some variation across studies, women appear for the most part to have a thinner and more reduced volume of cartilage in the knee than men, and this may occur from early childhood. It is not clear whether women have a more accelerated rate of cartilage volume loss than men. Few data exist on sex differences in systemic biomarkers of joint metabolism. In these studies, it is critically important to characterize the total body burden of OA and the presence of comorbid conditions likely to influence a given biomarker. Lastly, future research should dovetail studies of sex differences in imaging and biochemical biomarkers with genetics to maximize insight into the mechanisms behind observed sex differences.