Biglycan neo-epitope (BGN262), a novel biomarker for screening early changes in equine osteoarthritic subchondral bone

OBJECTIVE

Native biglycan (BGN), which can undergo proteolytic cleavage in pathological conditions, is well known to be involved in bone formation and mineralization. This study aimed to delineate the specific cleavage fragment, a neo-epitope for BGN (BGN²⁶²), in synovial fluid (SF) from young racehorses in training, osteoarthritic (OA) joints with subchondral bone sclerosis (SCBS), and chip fracture joints.

DESIGN

A custom-made inhibition ELISA was developed to quantify BGN²⁶² in SF. Cohort 1: A longitudinal study comprising 10 racehorses undergoing long-term training. Cohort 2: A cross-sectional study comprising joints from horses (N = 69) with different stages of OA and radiographically classified SCBS. Cohort 3: A cross-sectional study comprising horses (N = 9) with chip fractures. Receiver operating characteristic (ROC) curve analysis was performed (healthy joints vs chip joints) to evaluate BGN²⁶² robustness.

RESULTS

Cohort 1: SF BGN²⁶² levels from racehorses showed a statistical increase during the first 6 months of the training period. Cohort 2: BGN²⁶² levels were significantly higher in the SF from severe SCBS joints. Cohort 3: SF BGN²⁶² levels in chip fracture joints showed a significant increase compared to normal joints. The ROC analysis showed an AUC of 0.957 (95% C.I 0.868-1.046), indicating good separation between the groups.

CONCLUSIONS

The data presented show that BGN²⁶² levels increase in SF in correlation with the initiation of training, severity of SCBS, and presence of chip fractures. This suggests that BGN²⁶² is a potential predictor and a novel biomarker for early changes in subchondral bone (SCB), aiming to prevent catastrophic injuries in racehorses.

Knocking out or pharmaceutical inhibition of fatty acid binding protein 4 (FABP4) alleviates osteoarthritis induced by high-fat diet in mice

OBJECTIVES

Adipokines play roles in the pathogenesis of osteoarthritis (OA). Fatty acid binding protein 4 (FABP4) is a novel adipokine that is closely associated with obesity and metabolic diseases. The aim of this study was to discover the potential role of FABP4 in OA.

METHODS

Seventy-two FABP4 knockout mice (KO) in C57BL/6N background and wild-type littermates (WT) (male, 6-week-old) were fed with a high-fat diet (HFD, 60% calorie) or standard diet (STD, 11.6% calorie) for 3 months, 6 months and 9 months (n = 6 each). In the parallel study, forty-eight 6-week-old male WT mice were fed with HFD or STD, and simultaneously treated with daily oral gavage of selective FABP4 inhibitor BMS309403 (15 mg/kg/d) or vehicle for 4 months and 6 months (n = 6 each). Serum FABP4 and cartilage oligomeric matrix protein (COMP) concentration was quantified. Histological assessment of knee OA and micro-CT analysis of subchondral bone were performed.

RESULTS

HFD induced obesity in mice. After 3 months and 6 months of HFD, KO mice showed alleviated cartilage degradation and synovitis, with significantly lower COMP, modified Mankin OA score, and MMP-13/ADAMTS4 expression. After 6 months and 9 months of HFD, KO mice showed less osteophyte formation and subchondral bone sclerosis. Chronic treatment of BMS309403 for 4 months and 6 months significantly alleviated cartilage degradation, but had no effects on the subchondral bone. Knocking out or pharmaceutical inhibition of FABP4 did not have significant effects on lean mice fed with STD.

CONCLUSIONS

Knocking out or pharmaceutical inhibition of FABP4 alleviates OA induced by HFD in mice.

Subchondral bone sclerosis and cancellous bone loss following OA induction depend on the underlying bone phenotype

OBJECTIVES

Osteoarthritis (OA) is increasingly considered a disease of the whole joint, yet the interplay between the articular cartilage and the subchondral bone remains obscure. We here set out to investigate the impact of bone mass on the progression of surgically induced knee OA in the mouse.

METHODS

OA was induced in the right knees of female C57BL/6 (low bone mass) and STR/ort (high bone mass) mice via anterior cruciate ligament transection and destabilization of the medial meniscus. At 36 weeks of age, left and right knee joints were histologically compared for cartilage degeneration and via microCT analysis for subchondral bone plate thickness. In addition, femora were analyzed for bone mass at diaphysis and distal meta- and epiphysis.

RESULTS

The severity of cartilage deterioration did not differ under high and low bone mass conditions. However, the extent of bone sclerosis differed and was proportional to the baseline subchondral bone plate thickness. Moreover, the cancellous bone loss following OA progression was inversely related to the bone mass: high bone mass restricted the loss to the epiphysis, whereas low bone mass allowed for a more widespread loss extending into the metaphysis.

CONCLUSIONS

Our results suggest that cartilage degeneration is independent of the underlying bone mass. In contrast, subchondral bone remodeling associated with OA progression seem to correlate with the initial bone mass and suggest an enhanced crosstalk between the deteriorating cartilage and the subchondral bone under low bone mass conditions.