Pain in osteoarthritis: Driven by intrinsic rather than extrinsic joint afferents and why this should impact treatment.

Pain in osteoarthritis (OA) results from erosion of joint cartilage, resulting in bone contacting bone without an intervening cushion. The periosteum, including its nociceptive innervation, ends at the border of the cartilage. No other innervated tissue is present between the denuded articular bone ends that could serve as a neuronal pathway to carry a bone-on-bone pain signal to the brain. The pain signaling pathway must therefore originate in afferent axons with electrogenic nociceptive sensory endings that reside within the bone itself, specifically in the opposing surfaces of epiphyseal subchondral bone. Selective ablation of this intrinsic nerve pathway, using any of a variety of approaches, is expected to permanently eliminate OA pain.

Intra-articular and intraosseous approach to temporomandibular joint-targeted injections: a cadaveric investigation.

PURPOSE: Temporomandibular joint osteoarthritis (TMJ-OA) management is complex, and several conservative and minimally invasive protocols have been proposed. Intra-articular injections of medications directed at OA have been performed, but in some cases, these medications do not directly contact the tissue lesion sites. Here, we propose a new real-time ultrasound-guided technique to inject medications directly into the subchondral bone. METHODS: Ultrasound image screening was carried out with the point-of-care Clarius L15 device. Then, with the patient's mouth closed, a stainless-steel cannula with a concentric trocar was US-guided using an in-plane approach until the perforating tip of the internal trocar touched the lateral pole of the mandibular condyle. Then, the trocar was inserted through the medullary bone, where a posterior injection was made. RESULTS: The technique's precision was confirmed by capturing an iodine contrast solution that imaged the medullary condyle of fresh anatomical specimens processed by computed tomography. CONCLUSION: The proposed technique was effective in accessing the mandibular condyle subchondral bone in the inferior TMJ space for the simultaneously intra-articular (IA) and intra-osseous (IO) in-plane US-guided injections. Thus, its implementation may represent an important advance in early TMJ-OA treatment. This may be a promising approach, especially in OA cases in which the cortical bone is still preserved.

PLCγ1 deficiency in chondrocytes accelerates the age-related changes in articular cartilage and subchondral bone.

Ageing is the most prominent risk for osteoarthritis (OA) development. This study aimed to investigate the role of phosphoinositide-specific phospholipase Cγ (PLCγ) 1, previously linked to OA progression, in regulating age-related changes in articular cartilage and subchondral bone. d-galactose (d-Gal) was employed to treat chondrocytes from rats and mice or injected intraperitoneally into C57BL/6 mice. RTCA, qPCR, Western blot and immunohistochemistry assays were used to evaluate cell proliferation, matrix synthesis, senescence genes and senescence-associated secretory phenotype, along with PLCγ1 expression. Subchondral bone morphology was assessed through micro-CT. In mice with chondrocyte-specific Plcg1 deficiency (Plcg1flox/flox; Col2a1-CreERT), articular cartilage and subchondral bone were examined over different survival periods. Our results showed that d-Gal induced chondrocyte senescence, expedited articular cartilage ageing and caused subchondral bone abnormalities. In d-Gal-induced chondrocytes, diminished PLCγ1 expression was observed, and its further inhibition by U73122 exacerbated chondrocyte senescence. Plcg1flox/flox; Col2a1-CreERT mice exhibited more pronounced age-related changes in articular cartilage and subchondral bone compared to Plcg1flox/flox mice. Therefore, not only does d-Gal induce senescence in chondrocytes and age-related changes in articular cartilage and subchondral bone, as well as diminished PLCγ1 expression, but PLCγ1 deficiency in chondrocytes may also accelerate age-related changes in articular cartilage and subchondral bone. PLCγ1 may be a promising therapeutic target for mitigating age-related changes in joint tissue.

A Preliminary Study of Quantitative MRI Cartilage Loss Fraction and Its Association With Future Arthroplasty Using the Osteoarthritis Initiative Database.

Background and objective  Osteoarthritis (OA) is the most common arthritis in the world. Despite the high disease burden, there is no therapy to prevent, halt, or reverse OA, and many clinical trials relied on radiographic biomarkers for therapy response. It is important to identify patients with early OA who will eventually need arthroplasty, the end-stage treatment for osteoarthritis. This pilot study evaluates a novel MRI biomarker, cartilage loss fraction, for association with future arthroplasty and evaluates its feasibility of use and effect size estimates. Materials and methods Publicly available knee MRIs from the Osteoarthritis Initiative were used. A total of 38 participants with Kellgren-Lawrence (K-L) grade >1 and 38 participants with K-L grade ≤ 1 at enrollment were matched in age, sex, race, and BMI, and assessed for the degree of full-thickness cartilage loss, or cartilage loss fraction. Univariate conditional logistic regression analysis was performed for differences in cartilage loss fractions between groups. Receiver operating characteristic (ROC) curve analysis was performed to assess the association of MRI biomarkers and knee arthroplasty during the eight-year follow-up. Results The medial femoral condyle, medial tibial plateau, total, and two-year progression cartilage loss fractions were significantly higher in participants with K-L grade >1 (p < 0.01 for all) and showed high area under the curve (AUC) values on ROC analysis (812, 0.827, 0.917, and 0.933, respectively). These results were comparable or more strongly associated with other OA grading schemes. Conclusion MRI biomarker cartilage loss fractions are significantly higher in subjects with K-L grade >1 and show a strong association with arthroplasty. After further validation, cartilage loss fracture may be used to predict future arthroplasty.

Zoledronate alleviates subchondral bone collapse and articular cartilage degeneration in a rat model of rotator cuff tear arthropathy.

OBJECTIVE: To evaluate the humeral head bone volume of patients with cuff tear arthropathy (CTA) and examine the therapeutic effect of zoledronate in a rat modified model of CTA (mCTA). DESIGN: The bone mass in patients with CTA was measured using Hounsfield units from CT images. The mCTA was induced by transecting the rotator cuff, biceps brachii tendon, and superior half of the joint capsule in adult rat shoulders. A single subcutaneous injection of zoledronate was followed by bone histomorphometry and immunohistochemistry of the humeral head, as well as the Murine Shoulder Arthritis Score (MSAS) assessment. RESULTS: The humeral head bone volume was decreased in patients with CTA. In the mCTA model, M1 macrophages were increased in the synovium and were decreased by zoledronate treatment. The increased expressions of TNF-α, IL-1ß and IL-6 in mCTA synovium and articular cartilage were suppressed in the zoledronate-treated mCTA group. The expression of catabolic enzymes in the articular cartilage and MSAS showed similar results. The zoledronate-treated mCTA group showed a decreased subchondral bone collapse with a decreased RANKL/OPG expression ratio and a suppressed number of osteoclasts compared with the control mCTA group. The enhanced expressions of HMGB1 and S100A9 in the mCTA shoulders were eliminated in the zoledronate-treated mCTA group. CONCLUSIONS: The humeral head subchondral bone was decreased in patients with CTA. In the mCTA model, the collapse and osteoarthritic changes were prevented by zoledronate administration. Zoledronate seemed to suppress the number of M1 macrophages in the synovium and osteoclasts in the subchondral bone.

Subchondral bone: An emerging target for the treatment of articular surface lesions of the knee.

Purpose: When dealing with the health status of the knee articular surface, the entire osteochondral unit has gained increasing attention, and in particular the subchondral bone, which plays a key role in the integrity of the osteochondral unit. The aim of this article was to discuss the current evidence on the role of the subchondral bone. Methods: Experts from different geographical regions were involved in performing a review on highly discussed topics about the subchondral bone, ranging from its etiopathogenetic role in joint degeneration processes to its prognostic role in chondral and osteochondral defects, up to treatment strategies to address both the subchondral bone and the articular surface. Discussion: Subchondral bone has a central role both from an aetiologic point of view and as a diagnostic tool, and its status was found to be relevant also as a prognostic factor in the follow-up of chondral treatment. Finally, the recognition of its importance in the natural history of these lesions led to consider subchondral bone as a treatment target, with the development of osteochondral scaffolds and procedures to specifically address osteochondral lesions. Conclusion: Subchondral bone plays a central role in articular surface lesions from different points of view. Several aspects still need to be understood, but a growing interest in subchondral bone is to be expected in the upcoming future towards the optimization of joint preservation strategies. Level of Evidence: Level V, expert opinion.

Effects of resveratrol on biochemical and structural outcomes in osteoarthritis: A systematic review and meta-analysis of preclinical studies.

Background and objective: Osteoarthritis (OA) is the most common age-related disease of joints with increasing global prevalence. Persistent inflammation within the joint space is speculated to be the cause of OA. Resveratrol is an anti-inflammatory and antioxidant compound which can influence cartilage metabolism through multiple signalling pathways. This systematic review and meta-analysis aimed to summarize the therapeutic effects of resveratrol in animal models of OA. Methods: A comprehensive literature search was performed using PubMed, Embase, Web of Science, Cochrane Library, China National Knowledge Infrastructure, China Wanfang and VIP databases in May 2023. Studies on the effects of resveratrol in animal models of OA written in English or Mandarin, published from the inception of databases until the date of the search were considered. Results: Fifteen eligibility studies were included and analysed. Resveratrol was shown to inhibit the secretion of interleukin-1ß, tumour necrosis factor-α, interleukin-6, nitric oxide, and apoptosis of articular chondrocytes. Joint structure as indicated by Mankin scores was restored with resveratrol in animal OA models. Conclusion: Resveratrol is a potential therapeutic agent for OA based on animal studies. Further evidence from well-planned human studies would be required to validate its clinical efficacies.

Treatment of osteoarthritis by implantation of Mg- and WE43-cylinders - A preclinical study on bone and cartilage changes and their influence on pain sensation in rabbits.

With its main features of cartilage degeneration, subchondral bone sclerosis and osteophyte formation, osteoarthritis represents a multifactorial disease with no effective treatment options. As biomechanical shift in the trabecular network may be a driver for further cartilage degeneration, bone enhancement could possibly delay OA progression. Magnesium is known to be osteoconductive and already showed positive effects in OA models. We aimed to use magnesium cylinders to enhance subchondral bone quality, condition of cartilage and pain sensation compared to sole drilling in vivo. After eight weeks of implantation in rabbits, significant increase in subchondral bone volume and trabecular thickness with constant bone mineral density was found indicating favored biomechanics. As representative for pain, a higher number of CD271+ vessels were present in control samples without magnesium. However, this result could not be confirmed by sensitive, objective lameness evaluation using a pressure sensing mat and no positive effect could be shown on either cartilage degeneration evaluated by OARSI score nor the presence of regenerative cells in CD271-stained samples. The presented results show a relevant impact of implanted magnesium on key structures in OA pain with missing clinical relevance regarding pain. Further studies with shifted focus should examine additional structures as joint capsule or osteophytes.

Histological and Histopathological Features of the Third Metacarpal/Tarsal Parasagittal Groove and Proximal Phalanx Sagittal Groove in Thoroughbred Horses with Racing History.

Information regarding the histopathology of the proximal phalanx (P1) sagittal groove in racehorses is limited. Twenty-nine cadaver limbs from nine Thoroughbred racehorses in racing/race-training underwent histological examination. Histological specimens of the third metacarpal/metatarsal (MC3/MT3) parasagittal grooves and P1 sagittal grooves were graded for histopathological findings in hyaline cartilage (HC), calcified cartilage (CC), and subchondral plate and trabecular bone (SCB/TB) regions. Histopathological grades were compared between (1) fissure and non-fissure locations observed in a previous study and (2) dorsal, middle, and palmar/plantar aspects. (1) HC, CC, and SCB/TB grades were more severe in fissure than non-fissure locations in the MC3/MT3 parasagittal groove (p < 0.001). SCB/TB grades were more severe in fissure than non-fissure locations in the P1 sagittal groove (p < 0.001). (2) HC, CC, and SCB/TB grades including SCB collapse were more severe in the palmar/plantar than the middle aspect of the MC3/MT3 parasagittal groove (p < 0.001). SCB/TB grades including SCB collapse were more severe in the dorsal and middle than the palmar/plantar aspect of the P1 sagittal groove (p < 0.001). Histopathology in the SCB/TB region including bone fatigue injury was related to fissure locations, the palmar/plantar MC3/MT3 parasagittal groove, and the dorsal P1 sagittal groove.

Engineered extracellular vesicle-delivered TGF-ß inhibitor for attenuating osteoarthritis by targeting subchondral bone.

Osteoarthritis (OA) is a disease that affects the entire joint. To treat OA, it may be beneficial to inhibit the activity of TGF-ß in the subchondral bone. However, delivering drugs to the subchondral bone using conventional methods is challenging. In this study, we developed an extracellular vesicle delivery system. The utilization of macrophage-derived extracellular vesicles as a drug-carrying platform enables drugs to evade immune clearance and cross biological barriers. By incorporating targeting peptides on the surface of extracellular vesicles, the drug platform becomes targeted. The combination of these two factors results in the successful delivery of the drug to the subchondral bone. The study evaluated the stability, cytotoxicity, and bone targeting capability of the engineered extracellular vesicle platform (BT-EV-G). It also assessed the effects of BT-EV-G on the differentiation, proliferation, and migration of bone mesenchymal stem cells (BMSCs). Additionally, the researchers administered BT-EV-G to anterior cruciate ligament transection (ACLT)-induced OA mice. The results showed that BT-EV-G had low toxicity and high bone targeting ability both in vitro and in vivo. BT-EV-G can restore coupled bone remodeling in subchondral bone by inhibiting pSmad2/3-dependent TGF-ß signaling. This work provides new insights into the treatment of OA.

Advantages of cone beam computed tomography for evaluation of subchondral insufficiency fractures of the knee compared to MRI.

To determine the diagnostic yield of cone beam computed tomography (CBCT) compared with 3 T magnetic resonance imaging (MRI) for the evaluation of subchondral insufficiency fractures of the knee. Consecutive patients with subchondral insufficiency fractures of the knee examined by 3 T MRI and CBCT of the femoral condyles were reviewed. Two experienced raters graded the lesion severity on 3 T MRI and CBCT images: grade 1: no signs of a subchondral bone lesion; grade 2: subchondral trabecular fracture or cystic changes, but without infraction of the subchondral bone plate; grade 3: collapse of the subchondral bone plate. Ratings were repeated after six weeks to determine reliability. In addition, the bone lesion size was measured as elliptical area (mm2) and compared between CBCT and T1-weighted MRI sequences. Among 30 patients included (43.3% women; mean age: 60.9 ± 12.8 years; body mass index (BMI) 29.0 ± 12.8 kg/m2), the medial femoral condyle was affected in 21/30 patients (70%). The grading of subchondral lesions between MRI and CBCT did not match in 12 cases (40%). Based on MRI images, an underestimation (i.e., undergrading) compared with CBCT was observed in nine cases (30%), whereas overgrading occurred in three cases (10%). Compared to CBCT, routine T1-weighted 3 T sequences significantly overestimated osseus defect zones in sagittal (84.7 ± 68.9 mm2 vs. 35.9 ± 38.2 mm2, p < 0.01, Cohen's d = 1.14) and coronal orientation (53.1 ± 24.0 mm2 vs. 22.0 ± 15.2 mm2, p < 0.01, Cohen's d = 1.23). The reproducibility of the grading determined by intra- and inter-rater agreement was very high in MRI (intra-class correlation coefficient (ICC) 0.78 and 0.90, respectively) and CBCT (ICC 0.96 and 0.96, respectively). In patients with subchondral insufficiency fractures of the knee, the use of CBCT revealed discrepancies in lesion grading compared with MRI. These findings are clinically relevant, as precise determination of subchondral bone plate integrity may influence the decision about conservative or surgical treatment. CBCT represents our imaging modality of choice for grading the lesion and assessing subchondral bone plate integrity. MRI remains the gold standard modality to detect especially early stages.

An HFD negatively influences both joint and liver health in rabbits with and without an enzymatically-induced model of arthritis.

Osteoarthritis (OA) is a common arthritis types in animals that causes persistent pain and reduces quality of life. Although a high-fat diet (HFD) is widely believed to induce obesity and have adverse effects on the body, the connection between HFD and joint health is not well understood. Therefore, in this study, 32 healthy male New Zealand rabbits were randomly divided into four groups: healthy rabbits fed a standard diet (NDG, n=8) or an HFD (HDG, n=8), rabbits fed a standard diet (OAG, n=8) and an HFD (HOG, n=8), and arthritis was induced by intra-articular enzyme injection. After 12 weeks of HFD feeding, articular cartilage, synovium, and subchondral bone were isolated and collected. Joint tissue damage was evaluated using histopathological and imaging tests. The results showed that there was no significant difference in body weight between rabbits fed a normal diet and those fed an HFD. However, the HFD led to an increase in joint injuries in both induced and non-induced arthritis rabbits. Specifically, the HFD induced lipid metabolism disorders and liver damage in vivo, significantly elevating the levels of serum inflammatory cytokines and bone metabolism markers. Moreover, HFD exacerbated articular cartilage damage in the joints and increased the accumulation of inflammatory cells in synovial tissue, resulting in a notable increase in synovial macrophages and inflammatory cytokines. Additionally, HFD accelerated the bone resorption process in subchondral bone, leading to the destruction of bone mass and subchondral bone microstructure. In summary, the results of this study indicate that an HFD can cause histological damage to the articular cartilage, synovium, and subchondral bone in rabbits, exacerbating arthritis in pre-existing joint damage. Notably, weight is not the primary factor in this effect.

Intra-articular sustained-release of pirfenidone as a disease-modifying treatment for early osteoarthritis.

Osteoarthritis (OA) is a major clinical challenge, and effective disease-modifying drugs for OA are still lacking due to the complicated pathology and scattered treatment targets. Effective early treatments are urgently needed to prevent OA progression. The excessive amount of transforming growth factor ß (TGFß) is one of the major causes of synovial fibrosis and subchondral bone sclerosis, and such pathogenic changes in early OA precede cartilage damage. Herein we report a novel strategy of intra-articular sustained-release of pirfenidone (PFD), a clinically-approved TGFß inhibitor, to achieve disease-modifying effects on early OA joints. We found that PFD effectively restored the mineralization in the presence of excessive amount of TGFß1 (as those levels found in patients' synovial fluid). A monthly injection strategy was then designed of using poly lactic-co-glycolic acid (PLGA) microparticles and hyaluronic acid (HA) solution to enable a sustained release of PFD (the "PLGA-PFD + HA" strategy). This strategy effectively regulated OA progression in destabilization of the medial meniscus (DMM)- induced OA mice model, including preventing subchondral bone loss in early OA and subchondral bone sclerosis in late OA, and reduced synovitis and pain with cartilage preservation effects. This finding suggests the promising clinical application of PFD as a novel disease-modifying OA drug.

Aging alters the subchondral bone response 7 days after noninvasive traumatic joint injury in C57BL/6JN mice.

Posttraumatic osteoarthritis (PTOA) commonly develops following anterior cruciate ligament (ACL) injuries, affecting around 50% of individuals within 10-20 years. Recent studies have highlighted early changes in subchondral bone structure after ACL injury in adolescent or young adult mice, which could contribute to the development of PTOA. However, ACL injuries do not only occur early in life. Middle-aged and older patients also experience ACL injuries and PTOA, but whether the aged subchondral bone also responds rapidly to injury is unknown. This study utilized a noninvasive, single overload mouse injury model to assess subchondral bone microarchitecture, turnover, and material properties in both young adults (5 months) and early old age (22 months) female C57BL/6JN mice at 7 days after injury. Mice underwent either joint injury (i.e., produces ACL tears) or sham injury procedures on both the loaded and contralateral limbs, allowing evaluation of the impacts of injury versus loading. The subchondral bone response to ACL injury is distinct for young adult and aged mice. While 5-month mice show subchondral bone loss and increased bone resorption postinjury, 22-month mice did not show loss of bone structure and had lower bone resorption. Subchondral bone plate modulus increased with age, but not with injury. Both ages of mice showed several bone measures were altered in the contralateral limb, demonstrating the systemic skeletal response to joint injury. These data motivate further investigation to discern how osteochondral tissues differently respond to injury in aging, such that diagnostics and treatments can be refined for these demographics.

Temporal progression of subchondral bone alterations in OA models involving induction of compromised meniscus integrity in mice and rats: A scoping review.

OBJECTIVE: To categorize the temporal progression of subchondral bone alterations induced by compromising meniscus integrity in mouse and rat models of knee osteoarthritis (OA). METHOD: Scoping review of investigations reporting subchondral bone changes with appropriate negative controls in the different mouse and rat models of OA induced by compromising meniscus integrity. RESULTS: The available literature provides appropriate temporal detail on subchondral changes in these models, covering the entire spectrum of OA with an emphasis on early and mid-term time points. Microstructural changes of the subarticular spongiosa are comprehensively described; those of the subchondral bone plate are not. In mouse models, global subchondral bone alterations are unidirectional, involving an advancing sclerosis of the trabecular structure over time. In rats, biphasic subchondral bone alterations begin with an osteopenic degeneration and loss of subchondral trabeculae, progressing to a late sclerosis of the entire subchondral bone. Rat models, independently from the applied technique, relatively faithfully mirror the early bone loss detected in larger animals, and the late subchondral bone sclerosis observed in human advanced OA. CONCLUSION: Mice and rats allow us to study the microstructural consequences of compromising meniscus integrity at high temporal detail. Thickening of the subchondral bone plate, an early loss of thinner subarticular trabecular elements, followed by a subsequent sclerosis of the entire subchondral bone are all important and reliable hallmarks that occur in parallel with the advancing articular cartilage degeneration. Thoughtful decisions on the study design, laterality, selection of controls and volumes of interest are crucial to obtain meaningful data.

Three-gene signature revealing the dynamics of lymphocyte infiltration in subchondral bone during osteoarthritis progression.

Osteoarthritis (OA), a degenerative joint disorder, has an unclear immune infiltration mechanism in subchondral bone (SCB). Thus, this study aims to discern immune infiltration variations in SCB between early- and late-stages of OA and identify pertinent biomarkers. Utilizing the GSE515188 bulk-seq profile from the Gene Expression Omnibus database, we performed single-sample gene-set enrichment analysis alongside weighted gene co-expression network analysis to identify key cells and immune-related genes (IRGs) involved in SCB at both stages. At the meanwhile, differentially expressed genes (DEGs) were identified in the same dataset and intersected with IRGs to find IR-DEGs. Protein-protein interaction network and enrichment analyses and further gene filtering using LASSO regression led to the discovery of potential biomarkers, which were then validated by ROC curve analysis, single-cell RNA sequencing, qRT-PCR, western blot and immunofluorescence. ScRNA-seq analysis using GSE196678, qRT-PCR, western blot and immunofluorescence results confirmed the upregulation of their expression levels in early-stage OA SCB samples. Our comprehensive analysis revealed lymphocytes infiltration as a major feature in early OA SCB. A total of 13 IR-DEGs were identified, showing significant enrichment in T- or B-cell activation pathways. Three of them (CD247, POU2AF1, and TNFRSF13B) were selected via the LASSO regression analysis, and results from the ROC curve analyses indicated the diagnostic efficacy of these 3 genes as biomarkers. These findings may aid in investigating the mechanisms of SCB immune infiltration in OA, stratifying OA progression, and identifying relevant therapeutic targets.

Parathyroid hormone (1-34) retards the lumbar facet joint degeneration and activates Wnt/ß-catenin signaling pathway in ovariectomized rats.

PURPOSE: Facet joint degeneration (FJD) is a major cause of low back pain. Parathyroid hormone (PTH) (1-34) is commonly used to treat osteoporosis. However, little is known about its effects on FJD induced by estrogen deficiency. This study aims to investigate the effects of PTH (1-34) on FJD induced by estrogen deficiency and the underlying pathogenesis of the disease. METHODS: Forty 3-month-old female Sprague-Dawley rats were randomly divided into four groups: 30 received bilateral ovariectomy (OVX) followed by 12 weeks of treatment with normal saline, PTH (1-34) or 17ß-estradiol (E2), and 10 received sham surgery followed by administration of normal saline. Status and Wnt/ß-catenin signaling activity in the cartilage and subchondral bone of the L4-L5 FJs and serum biomarkers were analyzed. RESULTS: Administration of PTH (1-34) and E2 ameliorated cartilage lesions, and significantly decreased MMP-13 and caspase-3 levels and chondrocyte apoptosis. PTH (1-34) but not E2 significantly increased cartilage thickness, number of chondrocytes, and the expression of aggrecan. PTH (1-34) significantly improved microarchitecture parameters of subchondral bone, increased the expression of collagen I and osteocalcin, and decreased RANKL/OPG ratio. E2 treatment significantly increased the OPG level and decreased the RANKL/OPG ratio in the subchondral bone of ovariectomized rats, but it did not significantly improve the microarchitecture parameters of subchondral bone. Wnt3a and ß-catenin expression was significantly reduced in the articular cartilage and subchondral bone in OVX rats, but PTH (1-34) could increase the expression of these proteins. E2 significantly increased the activity of Wnt/ß-catenin pathway only in cartilage, but not in subchondral bone. The restoration of Wnt/ß-catenin signaling had an obvious correlation with the improvement of some parameters associated with the FJs status. CONCLUSION: Wnt/ß-catenin signaling may be a potential therapeutic target for FJD induced by estrogen deficiency. PTH (1-34) is effective in treating this disease with better efficacy than 17ß-estradiol, and the efficacy may be attributed to its restoration of Wnt/ß-catenin signaling.

Long-term haplodeficency of DSPP causes temporomandibular joint osteoarthritis in mice.

BACKGROUND: Extracellular matrix (ECM) protein malfunction or defect may lead to temporomandibular joint osteoarthritis (TMJ OA). Dentin sialophophoprotein (DSPP) is a mandibular condylar cartilage ECM protein, and its deletion impacted cell proliferation and other extracellular matrix alterations of postnatal condylar cartilage. However, it remains unclear if long-term loss of function of DSPP leads to TMJ OA. The study aimed to test the hypothesis that long-term haploinsufficiency of DSPP causes TMJ OA. MATERIALS AND METHODS: To determine whether Dspp+/- mice exhibit TMJ OA but no severe tooth defects, mandibles of wild-type (WT), Dspp+/-, and Dspp homozygous (Dspp-/-) mice were analyzed by Micro-computed tomography (micro-CT). To characterize the progression and possible mechanisms of osteoarthritic degeneration over time in Dspp+/- mice over time, condyles of Dspp+/- and WT mice were analyzed radiologically, histologically, and immunohistochemically. RESULTS: Micro-CT and histomorphometric analyses revealed that Dspp+/- and Dspp-/- mice had significantly lower subchondral bone mass, bone volume fraction, bone mineral density, and trabecular thickness compared to WT mice at 12 months. Interestingly, in contrast to Dspp-/- mice which exhibited tooth loss, Dspp+/- mice had minor tooth defects. RNA sequencing data showed that haplodeficency of DSPP affects the biological process of ossification and osteoclast differentiation. Additionally, histological analysis showed that Dspp+/- mice had condylar cartilage fissures, reduced cartilage thickness, decreased articular cell numbers and severe subchondral bone cavities, and with signs that were exaggerated with age. Radiographic data showed an increase in subchondral osteoporosis up to 18 months and osteophyte formation at 21 months. Moreover, Dspp+/- mice showed increased distribution of osteoclasts in the subchondral bone and increased expression of MMP2, IL-6, FN-1, and TLR4 in the mandibular condylar cartilage. CONCLUSIONS: Dspp+/- mice exhibit TMJ OA in a time-dependent manner, with lesions in the mandibular condyle attributed to hypomineralization of subchondral bone and breakdown of the mandibular condylar cartilage, accompanied by upregulation of inflammatory markers.

Subchondral Bone Osteocyte Lacunae Morphology in End-Stage Osteoarthritis of the Human Tibial Plateau.

Subchondral bone remodeling, mediated by osteocytes within the lacuno-canalicular network, plays a crucial role in osteoarthritis (OA) progression. Following cell death, lacunae preserve integrity, offering insights into bone remodeling mechanisms. Limited and controversial data on osteocyte lacuna morphology in OA result from small sample sizes and two-dimensional (2D) techniques that have been used thus far. This study aimed to quantify three-dimensional (3D) osteocyte lacunar characteristics at well-defined tibial plateau locations, known to be differently affected by OA. Specifically, 11 tibial plateaus were obtained from end-stage knee-OA patients with varus deformity. Each plateau provided one sample from the less affected lateral compartment and two samples from the medial compartment, at minimum and maximum bone volume fraction (BV/TV) locations. High-resolution desktop micro-computed tomography (micro-CT) at 0.7 µm voxel resolution imaged the 33 samples. Lacuna number density (Lc.N/BV) and lacuna volume density (Lc.TV/BV) were significantly lower (p < 0.02) in samples from the medial side with maximum BV/TV compared to lateral side samples. In the medial compartment at maximum local BV/TV, mean lacuna volume (Lc.V), total lacuna volume (Lc.TV), and Lc.TV/BV were significantly (p < 0.001) lower than in the region with minimum BV/TV. Lc.N/BV was also significantly lower (p < 0.02) at the maximum local BV/TV location compared to the region with minimum BV/TV. Our findings suggest that subchondral bone lacunae adapt to the changing loads in end-stage OA.

Single Injection AAV2-FGF18 Gene Therapy Reduces Cartilage Loss and Subchondral Bone Damage in a Mechanically Induced Model of Osteoarthritis.

BACKGROUND: Osteoarthritis (OA) is a highly debilitating, degenerative pathology of cartilaginous joints affecting over 500 million people worldwide. The global economic burden of OA is estimated at $260-519 billion and growing, driven by aging global population and increasing rates of obesity. To date, only the multi-injection chondroanabolic treatment regimen of Fibroblast Growth Factor 18 (FGF18) has demonstrated clinically meaningful disease-modifying efficacy in placebo-controlled human trials. Our work focuses on the development of a novel single injection disease-modifying gene therapy, based on FGF18's chondroanabolic activity. METHODS: OA was induced in Sprague-Dawley rats using destabilization of the medial meniscus (DMM) (3 weeks), followed by intra-articular treatment with 3 dose levels of AAV2-FGF18, rh- FGF18 protein, and PBS. Durability, redosability, and biodistribution were measured by quantifying nLuc reporter bioluminescence. Transcriptomic analysis was performed by RNA-seq on cultured human chondrocytes and rat knee joints. Morphological analysis was performed on knee joints stained with Safranin O/Fast Green and anti-PRG antibody. RESULTS: Dose-dependent reductions in cartilage defect size were observed in the AAV2-FGF18- treated joints relative to the vehicle control. Total defect width was reduced by up to 76% and cartilage thickness in the thinnest zone was increased by up to 106%. Morphologically, the vehicle- treated joints exhibited pronounced degeneration, ranging from severe cartilage erosion and bone void formation, to subchondral bone remodeling and near-complete subchondral bone collapse. In contrast, AAV2-FGF18-treated joints appeared more anatomically normal, with only regional glycosaminoglycan loss and marginal cartilage erosion. While effective at reducing cartilage lesions, treatment with rhFGF18 injections resulted in significant joint swelling (19% increase in diameter), as well as a decrease in PRG4 staining uniformity and intensity. In contrast to early-timepoint in vitro RNA-seq analysis, which showed a high degree of concordance between protein- and gene therapy-treated chondrocytes, in vivo transcriptomic analysis, revealed few gene expression changes following protein treatment. On the other hand, the gene therapy treatment exhibited a high degree of durability and localization over the study period, upregulating several chondroanabolic genes while downregulating OA- and fibrocartilage-associated markers. CONCLUSION: FGF18 gene therapy treatment of OA joints can provide benefits to both cartilage and subchondral bone, with a high degree of localization and durability.