Low bone mass resulting from impaired estrogen signaling in bone increases severity of load-induced osteoarthritis in female mice

Joint damage is more severe following a single bout than multiple bouts of high magnitude loading in mice

OBJECTIVE

While physiological loads maintain cartilage health, both joint overload and abnormal joint mechanical loading contribute to osteoarthritis (OA) development. Here, we examined the role of abnormal mechanical loading on joint health by comparing the severity of OA development following a single overload event and repetitive joint overloads.

METHOD

Cyclic tibial compression was applied to the left limbs of 26-week-old male mice at a peak load of 9N for either a single bout or daily bouts to initiate OA disease. Joint damage severity was morphologically examined using histology and microcomputed tomography at 6 weeks following the start of loading. Early-stage transcriptomic responses to loading were evaluated.

RESULTS

Joint damage was more severe at 6 weeks following a single bout of loading than after daily loading bouts. Severe cartilage damage, subchondral plate erosions, and soft tissue calcifications occurred following the single bout of loading. Daily loading bouts resulted in less severe cartilage damage and preserved subchondral plate integrity. A diverging transcriptomic response was identified in cartilage at 1 week with increased expression of fibrosis- and inflammation-related genes following a single bout of loading compared to daily loading.

CONCLUSIONS

Even applied at hyperphysiological load magnitudes known to initiate cartilage damage, repetitive loading may induce protective effects in the joint and attenuate OA progression over time relative to a single bout of loading. Our findings suggest the potential of mechanotherapies that use repetitive loading as disease-modifying treatments for OA disease.

Single-cell transcriptomics reveals novel chondrocyte and osteoblast subtypes and their role in knee osteoarthritis pathogenesis

Research on treating knee osteoarthritis (KOA) is becoming more challenging due to a growing number of younger patients being affected. The pathogenesis of KOA is complex for being a multifactorial disease affecting the entire joint, with remodeling of subchondral bone playing a key role in the degeneration of the overlying cartilage. Therefore, this study constructed a bipedal postmenopausal KOA mouse model to better understand how the interplay between subchondral bone remodeling and cartilage degeneration contributes to KOA development. A single-cell atlas of the osteochondral composite tissue was established. Furthermore, three novel subtypes of chondrocytes, including Smoc2+ angiogenic chondrocytes, Angptl7+ angiogenic chondrocytes, and Col1a1+ osteogenic chondrocytes, were identified in femoral condyles of KOA mice. In addition, the Angptl7+ chondrocytes promoted angiogenesis in the subchondral bone of KOA mice by interacting with endothelial cells via the FGF2-FGFR2 signaling pathway. The number of H-type vessels was increased in the subchondral bone, recruiting osteoprogenitor cells and facilitating osteogenesis in KOA mice. Sparc+ osteoblasts have negatively regulated bone mineralization and osteoblastic differentiation, aggravated the pathological remodeling of subchondral bone, and promoted the progression of KOA. The above findings have offered new targets and opened up an avenue for the therapeutic intervention of KOA.

Ferroptosis and its role in osteoarthritis: mechanisms, biomarkers, and therapeutic perspectives

Osteoarthritis (OA) is one of the leading causes of disability worldwide, characterized by a complex pathological process involving cartilage degradation, synovial inflammation, and subchondral bone remodeling. In recent years, ferroptosis, a form of programmed cell death driven by iron-dependent lipid peroxidation, has been recognized as playing a critical role in the onset and progression of OA. Investigating the molecular mechanisms of ferroptosis and its involvement in OA may offer novel strategies for diagnosing and treating this disease. This review first outlines the core mechanisms of ferroptosis, with a particular focus on the roles of critical molecules such as Glutathione Peroxidase 4 (GPX4), Transferrin Receptor 1 (TfR1), and Nuclear Receptor Coactivator 4 (NCOA4). Subsequently, this study examines the specific impacts of ferroptosis on the pathophysiology of OA. Building on this, the potential of ferroptosis-related biomarkers for OA diagnosis and treatment is highlighted, along with proposed therapeutic strategies targeting ferroptosis regulation. This review aims to deepen the understanding of ferroptosis mechanisms and advance the clinical application of regulatory therapies for OA.

Role and Mechanism of Mechanical Load in the Homeostasis of the Subchondral Bone in Knee Osteoarthritis: A Comprehensive Review

Osteoarthritis (OA) is one of the most prevalent degenerative joint diseases, and the knee joint is particularly susceptible to it. It typically affects the entire joint and is marked by the erosion of cartilage integrity, chondrocytopenia, subchondral bone sclerosis and the mild synovial inflammation. Pathological changes in the subchondral bone often serve as initiating factors for joint degeneration. Various predisposing factors, including metabolic disorders, oxidative stress, and abnormal mechanical loading, regulate OA pathogenesis. Of them, mechanical loading is closely associated with the maintenance of the subchondral bone. Disrupted mechanical loading, leading to subchondral bone remodeling, can potentially trigger OA, whereas appropriate loading might ameliorate its progression. Therefore, this narrative review aimed to discuss existing knowledge and explore how mechanical loading mediates changes in the subchondral bone, influencing the development of knee osteoarthritis. Special emphasis is placed on its role and underlying mechanisms in maintaining joint homeostasis.

Associations between urinary phytoestrogen mixed metabolites and osteoarthritis risk

BACKGROUND

This study aims to explore the relationship between urinary phytoestrogen mixed metabolites and the risk of osteoarthritis (OA).

METHODS

Using data from the National Health and Nutrition Examination Survey (NHANES), a Weighted Quantile Sum (WQS) regression analysis was conducted to determine the dominant metabolites. Additionally, a Bayesian kernel machine regression (BKMR) model was utilized to explore the combined effects of phytoestrogen mixed metabolites on OA.

RESULTS

Compared to the lowest quartile group, the highest quartile group of Enterodiol showed a 46% increased risk of OA (OR = 1.46, 95% CI: 1.09-1.96), while the highest quartile group of Enterlactone showed a 30% decreased risk of OA (OR = 0.70, 95% CI: 0.52-0.96). The WQS regression model analysis revealed a positive relationship between urinary phytoestrogen mixed metabolites and OA risk, with Enterodiol found to have the highest weight in this association. The BKMR model indicated that the association between urinary phytoestrogens and OA increased with concentration but did not reach statistical significance. The univariate exposure-response function demonstrated a positive association between Enterodiol and OA.

CONCLUSIONS

There is a positive relationship between urinary phytoestrogen mixed metabolites and OA, with Enterodiol being an important factor influencing OA risk.

Osteocytes contribute to sex-specific differences in osteoarthritic pain

Osteoarthritic (OA) pain affects 18% of females and 9.6% of males aged over 60 worldwide, with 62% of all OA patients being women. The molecular drivers of sex-based differences in OA are unknown. Bone is intricately coupled with the sensory nervous system and one of the only joint tissues known to show changes that correlate with patient pain in OA. There are fundamental sex differences in pain sensation and bone biology which may be intrinsic to OA disease progression, however these differences are vastly under researched. We have utilised three data sets to investigate the hypothesis that potential mediators responsible for sex dependent pain mechanisms displayed in OA are derived from mechanically stimulated osteocytes. Our published dataset of the in vitro human osteocyte mechanosome was independently compared with published data from, sex-based gene expression differences in human long bone, the sex-based gene expression differences during the skeletal maturation of the mouse osteocyte transcriptome and sex specific OA risk factors and effector genes in a large human GWAS. 80 of the 377 sex-specific genes identified in the mouse osteocyte transcriptome were mechanically regulated in osteocytes with enrichment associated with neural crest migration and axon extension, and DISEASES analysis enrichment for the rheumatoid arthritis pathway. 3861 mechanically regulated osteocytic genes displayed sex-specific differences in human long bone with enrichment for genes associated with the synapse, sensory perception of pain, axon guidance, immune responses, distal peripheral sensory neuropathy, sensory neuropathy, and poor wound healing. 32 of 77 effector genes and 1 of 3 female specific OA risk factor genes identified in the human GWAS were differentially expressed in the osteocyte mechanosome and male and female bone. This analysis lends support to the hypothesis that mechanically regulated genes in osteocytes could influence sex specific differences in osteoarthritic pain and highlights pain pathways with approved drugs that could potentially treat elevated pain susceptibility in females with OA.

The interplay between osteoarthritis and osteoporosis: Mechanisms, implications, and treatment considerations - A narrative review

This comprehensive review examines the relationship between osteoarthritis (OA) and osteoporosis (OP), two common disorders in the elderly. OA involves joint cartilage degeneration and pain, while OP leads to fractures due to reduced bone mass. Despite different pathologies, both conditions share risk factors such as age and genetics. Studies reveal mixed results: some show higher bone mineral density (BMD) in OA patients, suggesting an inverse relationship, while others find no significant link. Proposed mechanisms include mechanical loading, bone remodeling, and inflammation. Clinical strategies focus on maintaining bone health in OA and monitoring joint health in OP, with treatments like bisphosphonates and exercise. Understanding these interactions is crucial for developing integrated treatments to improve patient outcomes and quality of life. Further research is needed to clarify these complex mechanisms.

Exploring the mechanism of action of Vanda tessellata extract for the treatment of osteoarthritis through network pharmacology, molecular modelling and experimental assays

The present study employed a comprehensive approach of network pharmacology, molecular dynamic simulation and in-vitro assays to investigate the underlying mechanism of the anti-osteoarthritic potential of Vanda tessellata extract (VTE). Thirteen active compounds of VTE were retrieved from the literature and the IMPPAT database. All of these passed the drug likeness and oral bioavailability parameters. A total of 535 VTE targets and 2577 osteoarthritis related targets were obtained. The compound-target-disease network analysis revealed vanillin, daucosterol, gigantol and syringaldehyde as the core key components. Protein-protein interaction analysis revealed BCL2, FGF2, ICAM 1, MAPK1, MMP1, MMP2, MMP9, COX2, STAT3 and ESR1 as the hub genes. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed AGE-RAGE signalling pathway, HIF-1 signalling pathway and ESR signalling pathway as the major signalling pathway of VTE involved in treating osteoarthritis. Molecular docking analysis showed daucosterol and gigantol to have good binding affinity with BCL2, ESR1 and MMP9, and the results were further confirmed through molecular dynamics simulation analysis. The mechanism predicted by network pharmacology was validated in vitro on IL-1β-induced SW982 synovial cells. VTE did not show any cytotoxicity and inhibited the migration of SW982 cells. VTE inhibited the expression level of IL-6, IL-8, TNF-α, PGE-2, MMP-2 and MMP-9 in a dose-dependent manner. VTE inhibited nuclear translocation of NF- κβ and suppressed phosphorylation of p38, extracellular signal-regulated kinase (ERK), and c-Jun NH2-terminal kinase (JNK) of the mitogen-activated protein kinase (MAPK) signalling pathway. The results showed that VTE exerted an anti-osteoarthritic effect by a multi-target, multi-component and multi-signalling pathway approach.

PTH treatment before cyclic joint loading improves cartilage health and attenuates load-induced osteoarthritis development in mice

Osteoarthritis (OA) treatment is limited by the lack of effective nonsurgical interventions to slow disease progression. Here, we examined the contributions of the subchondral bone properties to OA development. We used parathyroid hormone (PTH) to modulate bone mass before OA initiation and alendronate (ALN) to inhibit bone remodeling during OA progression. We examined the spatiotemporal progression of joint damage by combining histopathological and transcriptomic analyses across joint tissues. The additive effect of PTH pretreatment before OA initiation and ALN treatment during OA progression most effectively attenuated load-induced OA pathology. Individually, PTH directly improved cartilage health and slowed the development of cartilage damage, whereas ALN primarily attenuated subchondral bone changes associated with OA progression. Joint damage reflected early transcriptomic changes. With both treatments, the structural changes were associated with early modulation of immunoregulation and immunoresponse pathways that may contribute to disease mechanisms. Overall, our results demonstrate the potential of subchondral bone-modifying therapies to slow the progression of OA.

Collagen type X expression and chondrocyte hypertrophic differentiation during OA and OS development

Chondrocyte hypertrophy and the expression of its specific marker, the collagen type X gene (COL10A1), constitute key terminal differentiation stages during endochondral ossification in long bone development. Mutations in the COL10A1 gene are known to cause schmid type metaphyseal chondrodysplasia (SMCD) and spondyloepiphyseal dyschondrodysplasia (SMD). Moreover, abnormal COL10A1 expression and aberrant chondrocyte hypertrophy are strongly correlated with skeletal diseases, notably osteoarthritis (OA) and osteosarcoma (OS). Throughout the progression of OA, articular chondrocytes undergo substantial changes in gene expression and phenotype, including a transition to a hypertrophic-like state characterized by the expression of collagen type X, matrix metalloproteinase-13, and alkaline phosphatase. This state is similar to the process of endochondral ossification during cartilage development. OS, the most common pediatric bone cancer, exhibits characteristics of abnormal bone formation alongside the presence of tumor tissue containing cartilaginous components. This observation suggests a potential role for chondrogenesis in the development of OS. A deeper understanding of the shifts in collagen X expression and chondrocyte hypertrophy phenotypes in OA or OS may offer novel insights into their pathogenesis, thereby paving the way for potential therapeutic interventions. This review systematically summarizes the findings from multiple OA models (e.g., transgenic, surgically-induced, mechanically-loaded, and chemically-induced OA models), with a particular focus on their chondrogenic and/or hypertrophic phenotypes and possible signaling pathways. The OS phenotypes and pathogenesis in relation to chondrogenesis, collagen X expression, chondrocyte (hypertrophic) differentiation, and their regulatory mechanisms were also discussed. Together, this review provides novel insights into OA and OS therapeutics, possibly by intervening the process of abnormal endochondral-like pathway with altered collagen type X expression.

Mechanical loading of joint modulates T cells in lymph nodes to regulate osteoarthritis

OBJECTIVE

The crosstalk of joint pathology with local lymph nodes in osteoarthritis (OA) is poorly understood. We characterized the change in T cells in lymph nodes following load-induced OA and established the association of the presence and migration of T cells to the onset and progression of OA.

METHODS

We used an in vivo model of OA to induce mechanical load-induced joint damage. After cyclic tibial compression of mice, we analyzed lymph nodes for T cells using flow cytometry and joint pathology using histology and microcomputed tomography. The role of T-cell migration and the presence of T-cell type was examined using T-cell receptor (TCR)α-/- mice and an immunomodulatory drug, Sphingosine-1-phosphate (S1P) receptor inhibitor-treated mice, respectively.

RESULTS

We demonstrated a significant increase in T-cell populations in local lymph nodes in response to joint injury in 10, 16, and 26-week-old mice, and as a function of load duration, 1, 2, and 6 weeks. T-cell expression of inflammatory cytokine markers increased in the local lymph nodes and was associated with load-induced OA progression in the mouse knee. Joint loading in TCRα-/- mice reduced both cartilage degeneration (Osteoarthritis Research Society International (OARSI) scores: TCRα 0.568, 0.981-0.329 confidence interval (CI); wild type (WT) 1.328, 2.353-0.749 CI) and osteophyte formation. Inhibition of T-cell egress from lymph nodes attenuated load-induced cartilage degradation (OARSI scores: Fingolimod: 0.509, 1.821-0.142 CI; Saline 1.210, 1.932-0.758 CI) and decreased localization of T cells in the synovium.

CONCLUSIONS

These results establish the association of lymph node-resident T cells in joint damage and suggest that the S1P receptor modulators and T-cell immunotherapies could be used to treat OA.

Wnt5a deficiency in osteocalcin-expressing cells could not alleviate the osteoarthritic phenotype in a mouse model of post-traumatic osteoarthritis

Objectives

Wnt5a, which regulates the activities of osteoblasts and osteoclasts, is reportedly overexpressed in osteoarthritis (OA) tissues. The purpose of this study was to elucidate its role in the development of OA by deleting Wnt5a in osteocalcin (OCN)-expressing cells.

Materials and Methods

Knee OA was induced by anterior cruciate ligament transection (ACLT) in OCN-Cre;Wnt5afl/fl knockout (Wnt5a-cKO) mice and control littermates. Eight weeks after surgery, histological changes, cell apoptosis, and matrix metabolism of cartilage were evaluated by toluidine blue, TUNEL staining, and im-immunohistochemistry analyses, respectively. In addition, the subchondral bone microarchitecture of mice was examined by micro-computed tomography (micro-CT).

Results

Histological scores show substantial cartilage degeneration occurred in ACLT knees, coupled with decreased collagen type II expression and enhanced matrix metalloproteinase 13 expression, as well as higher proportions of apoptotic cells. Micro-CT results show that ACLT resulted in decreased bone mineral density, bone volume/trabecular volume, trabecular number, and structure model index of subchondral bones in both Wnt5a-cKO and control littermates; although Wnt5a-cKO mice display lower BMD and BV/TV values, no significant difference was observed between Wnt5a-cKO and control mice for any of these values.

Conclusion

Our findings indicate that Wnt5a deficiency in OCN-expressing cells could not prevent an osteoarthritic phenotype in a mouse model of post-traumatic OA.

Strontium chloride improves bone mass by affecting the gut microbiota in young male rats

Introduction

Bone mass accumulated in early adulthood is an important determinant of bone mass throughout the lifespan, and inadequate bone deposition may lead to associated skeletal diseases. Recent studies suggest that gut bacteria may be potential factors in boosting bone mass. Strontium (Sr) as a key bioactive element has been shown to improve bone quality, but the precise way that maintains the equilibrium of the gut microbiome and bone health is still not well understood.

Methods

We explored the capacity of SrCl2 solutions of varying concentrations (0, 100, 200 and 400 mg/kg BW) on bone quality in 7-week-old male Wistar rats and attempted to elucidate the mechanism through gut microbes.

Results

The results showed that in a Wistar rat model under normal growth conditions, serum Ca levels increased after Sr-treatment and showed a dose-dependent increase with Sr concentration. Three-point mechanics and Micro-CT results showed that Sr exposure enhanced bone biomechanical properties and improved bone microarchitecture. In addition, the osteoblast gene markers BMP, BGP, RUNX2, OPG and ALP mRNA levels were significantly increased to varying degrees after Sr treatment, and the osteoclast markers RANKL and TRAP were accompanied by varying degrees of reduction. These experimental results show that Sr improves bones from multiple angles. Further investigation of the microbial population revealed that the composition of the gut microbiome was changed due to Sr, with the abundance of 6 of the bacteria showing a different dose dependence with Sr concentration than the control group. To investigate whether alterations in bacterial flora were responsible for the effects of Sr on bone remodeling, a further pearson correlation analysis was done, 4 types of bacteria (Ruminococcaceae_UCG-014, Lachnospiraceae_NK4A136_group, Alistipes and Weissella) were deduced to be the primary contributors to Sr-relieved bone loss. Of these, we focused our analysis on the most firmly associated Ruminococcaceae_UCG-014.

Discussion

To summarize, our current research explores changes in bone mass following Sr intervention in young individuals, and the connection between Sr-altered intestinal flora and potentially beneficial bacteria in the attenuation of bone loss. These discoveries underscore the importance of the "gut-bone" axis, contributing to an understanding of how Sr affects bone quality, and providing a fresh idea for bone mass accumulation in young individuals and thereby preventing disease due to acquired bone mass deficiency.

Missing link between tissue specific expressing pattern of ERβ and the clinical manifestations in LGBLEL

Purpose

Lacrimal gland benign lymphoepithelial lesion (LGBLEL) is an IgG4-related disease of unknown etiology with a risk for malignant transformation. Estrogen is considered to be related to LGBLEL onset.

Methods

Seventy-eight LGBLEL and 13 control clinical samples were collected and studied to determine the relationship between estrogen and its receptors and LGBLEL development.

Results

The serological analysis revealed no significant differences in the levels of three estrogens be-tween the LGBLEL and control groups. However, immunohistochemical analyses indicated that the expression levels of ERβ and its downstream receptor RERG were relatively lower in LGBLEL samples than in control samples, with higher expression in the lacrimal gland and lower expression in the lymphocyte infiltration region. However, low expression of ERα was detected. The transcriptome sequence analysis revealed upregulated genes associated with LGBLEL enriched in lymphocyte proliferation and activation function; downregulated genes were enriched in epithelial and vascular proliferation functions. The key genes and gene networks were further analyzed. Interactions between B cells and epithelial cells were analyzed due to the identified involvement of leukocyte subsets and epithelial cells. B cell proliferation was found to potentially contribute to lacrimal gland apoptosis.

Conclusion

Therefore, the tissue-heterogeneous expression pattern of ERβ is potentially related to the clinical manifestations and progression of LGBLEL, although further investigations are required to confirm this finding.

The influence of sex hormones on musculoskeletal pain and osteoarthritis

The association of female sex with certain rheumatic symptoms and diseases is now indisputable. Some of the most striking examples of this association occur in individuals with musculoskeletal pain and osteoarthritis, in whom sex-dependent changes in incidence and prevalence of disease are seen throughout the lifecourse. Joint and muscle pain are some of the most common symptoms of menopause, and there is increasingly compelling evidence that changes in or loss of sex hormones (be it natural, autoimmune, pharmacological, or surgical) influence musculoskeletal pain propensity and perhaps disease. However, the effects of modulation or replacement of sex hormones in this context are far less established, particularly whether these approaches could represent a preventative or therapeutic opportunity once symptoms have developed. In this Review, we present evidence for the association of changes in sex hormones with musculoskeletal pain and painful osteoarthritis, discussing data from diverse natural, therapeutic, and experimental settings in humans and relevant animal models relating to hormone loss or replacement and the consequent effects on health, pain, and disease. We also postulate mechanisms by which sex hormones could mediate these effects. Further research is needed; however, increased scientific understanding of this complex area could lead to real benefits in musculoskeletal and women's health.

Uncovering the "riddle of femininity" in osteoarthritis: a systematic review and meta-analysis of menopausal animal models and mathematical modeling of estrogen treatment

OBJECTIVE

Post-menopausal women are disproportionately affected by osteoarthritis (OA). As such, the purpose of this study was to (1) summarize the state-of-the-science aimed at understanding the effects of menopause on OA in animal models and (2) investigate how dosage and timing of initiation of estrogen treatment affect cartilage degeneration.

DESIGN

A systematic review identified articles studying menopausal effects on cartilage in preclinical models. A meta-analysis was performed using overlapping cartilage outcomes in conjunction with a rigor and reproducibility analysis. Ordinary differential equation models were used to determine if a relationship exists between cartilage degeneration and the timing of initiation or dosage of estrogen treatment.

RESULTS

Thirty-eight manuscripts were eligible for inclusion. The most common menopause model used was ovariectomy (92%), and most animals were young at the time of menopause induction (86%). Most studies did not report inclusion criteria, animal monitoring, protocol registration, or data accessibility. Cartilage outcomes were worse in post-menopausal animals compared to age-matched, non-menopausal animals, as evidenced by cartilage histological scoring [0.75, 1.72], cartilage thickness [-4.96, -0.96], type II collagen [-4.87, -0.56], and c-terminal cross-linked telopeptide of type II collagen (CTX-II) [2.43, 5.79] (95% CI of Effect Size (+greater in menopause, -greater in non-menopause)). Moreover, modeling suggests that cartilage health may be improved with early initiation and higher doses of estrogen treatment.

CONCLUSIONS

To improve translatability, animal models that consider aging and natural menopause should be utilized, and more attention to rigor and reproducibility is needed. Timing of initiation and dosage may be important factors modulating therapeutic effects of estrogen on cartilage.

Mechanotransduction pathways in articular chondrocytes and the emerging role of estrogen receptor-α

In the synovial joint, mechanical force creates an important signal that influences chondrocyte behavior. The conversion of mechanical signals into biochemical cues relies on different elements in mechanotransduction pathways and culminates in changes in chondrocyte phenotype and extracellular matrix composition/structure. Recently, several mechanosensors, the first responders to mechanical force, have been discovered. However, we still have limited knowledge about the downstream molecules that enact alterations in the gene expression profile during mechanotransduction signaling. Recently, estrogen receptor α (ERα) has been shown to modulate the chondrocyte response to mechanical loading through a ligand-independent mechanism, in line with previous research showing that ERα exerts important mechanotransduction effects on other cell types, such as osteoblasts. In consideration of these recent discoveries, the goal of this review is to position ERα into the mechanotransduction pathways known to date. Specifically, we first summarize our most recent understanding of the mechanotransduction pathways in chondrocytes on the basis of three categories of actors, namely mechanosensors, mechanotransducers, and mechanoimpactors. Then, the specific roles played by ERα in mediating the chondrocyte response to mechanical loading are discussed, and the potential interactions of ERα with other molecules in mechanotransduction pathways are explored. Finally, we propose several future research directions that may advance our understanding of the roles played by ERα in mediating biomechanical cues under physiological and pathological conditions.

In vitro study to identify ligand-independent function of estrogen receptor-α in suppressing DNA damage-induced chondrocyte senescence

In osteoarthritis (OA), chondrocytes undergo many pathological alternations that are linked with cellular senescence. However, the exact pathways that lead to the generation of a senescence-like phenotype in OA chondrocytes are not clear. Previously, we found that loss of estrogen receptor-α (ERα) was associated with an increased senescence level in human chondrocytes. Since DNA damage is a common cause of cellular senescence, we aimed to study the relationship among ERα levels, DNA damage, and senescence in chondrocytes. We first examined the levels of ERα, representative markers of DNA damage and senescence in normal and OA cartilage harvested from male and female human donors, as well as from male mice. The influence of DNA damage on ERα levels was studied by treating human chondrocytes with doxorubicin (DOX), which is an often-used DNA-damaging agent. Next, we tested the potential of overexpressing ERα in reducing DNA damage and senescence levels. Lastly, we explored the interaction between ERα and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway. Results indicated that the OA chondrocytes contained DNA damage and displayed senescence features, which were accompanied by significantly reduced ERα levels. Overexpression of ERα reduced the levels of DNA damage and senescence in DOX-treated normal chondrocytes and OA chondrocytes. Moreover, DOX-induced the activation of NF-κB pathway, which was partially reversed by overexpressing ERα. Taken together, our results demonstrated the critical role of ERα in maintaining the health of chondrocytes by inhibiting DNA damage and senescence. This study also suggests that maintaining the ERα level may represent a new avenue to prevent and treat OA.

Aromatase Inhibition Eliminates Sexual Receptivity Without Enhancing Weight Gain in Ovariectomized Marmoset Monkeys

Context

Ovarian estradiol supports female sexual behavior and metabolic function. While ovariectomy (OVX) in rodents abolishes sexual behavior and enables obesity, OVX in nonhuman primates decreases, but does not abolish, sexual behavior, and inconsistently alters weight gain.

Objective

We hypothesize that extra-ovarian estradiol provides key support for both functions, and to test this idea, we employed aromatase inhibition to eliminate extra-ovarian estradiol biosynthesis and diet-induced obesity to enhance weight gain.

Methods

Thirteen adult female marmosets were OVX and received (1) estradiol-containing capsules and daily oral treatments of vehicle (E2; n = 5); empty capsules and daily oral treatments of either (2) vehicle (VEH, 1 mL/kg, n = 4), or (3) letrozole (LET, 1 mg/kg, n = 4).

Results

After 7 months, we observed robust sexual receptivity in E2, intermediate frequencies in VEH, and virtually none in LET females (P = .04). By contrast, few rejections of male mounts were observed in E2, intermediate frequencies in VEH, and high frequencies in LET females (P = .04). Receptive head turns were consistently observed in E2, but not in VEH and LET females. LET females, alone, exhibited robust aggressive rejection of males. VEH and LET females demonstrated increased % body weight gain (P = .01). Relative estradiol levels in peripheral serum were E2 >>> VEH > LET, while those in hypothalamus ranked E2 = VEH > LET, confirming inhibition of local hypothalamic estradiol synthesis by letrozole.

Conclusion

Our findings provide the first evidence for extra-ovarian estradiol contributing to female sexual behavior in a nonhuman primate, and prompt speculation that extra-ovarian estradiol, and in particular neuroestrogens, may similarly regulate sexual motivation in other primates, including humans.

Novel role of estrogen receptor-α on regulating chondrocyte phenotype and response to mechanical loading

OBJECTIVE

In knee cartilage from patients with osteoarthritis (OA), both preserved cartilage and damaged cartilage are observed. In this study, we aim to compare preserved with damaged cartilage to identify the molecule(s) that may be responsible for the mechanical loading-induced differences within cartilage degradation.

METHODS

Preserved and damaged cartilage were harvested from the same OA knee joint. RNA Sequencing was performed to examine the transcriptomic differences between preserved and damaged cartilage cells. Estrogen receptor-α (ERα) was identified, and its function of was tested through gene knockin and knockout. The role of ERα in mediating chondrocyte response to mechanical loading was examined via compression of chondrocyte-laded hydrogel in a strain-controlled manner. Findings from the studies on human samples were verified in animal models.

RESULTS

Level of estrogen receptor α (ERα) was significantly reduced in damaged cartilage compared to preserved cartilage, which were observed in both human and mice samples. Knockdown of ESR1, the gene encoding ERα, resulted in an upregulation of senescence- and OA-relevant markers in chondrocytes. Conversely, knockin of ESR1 partially reversed the osteoarthritic and senescent phenotype of OA chondrocytes. Using a three-dimensional (3D) culture model, we demonstrated that mechanical overload significantly suppressed ERα level in chondrocytes with concomitant upregulation of osteoarthritic phenotype. When ESR1 expression was suppressed, mechanical loading enhanced hypertrophic and osteogenic transition.

CONCLUSION

Our study demonstrates a new estrogen-independent role of ERα in mediating chondrocyte phenotype and its response to mechanical loading, and suggests that enhancing ERα level may represent a new method to treat osteoarthritis.