Evaluation of Wnt/β-Catenin Pathway Circulating Proteins in Children and Adolescents with Hemophilia: Correlation with the Degree of Hemophilic Arhtropathy

Introduction: The pathophysiology of hemophilic arthropathy (HAP) establishes a hallmark of heterogeneous mechanisms related with the joint degeneration which has not been fully elucidated especially in reference to the development of inflammatory and catabolic processes occurring within the articular cartilage and synovial membrane. Crucial pathways regulating bone remodeling are the Wnt/β-catenin and the Receptor Activator of Nuclear factor kB (RANK) Ligand (RANKL)/Osteoprotegerin (OPG) systems. The Wnt/β-catenin pathway plays a major role in osteoblast differentiation and calcium homoeostasis. Sclerostin (SOST) and Dickkopf-1 (DKK-1) are soluble antagonists of the Wnt/β-catenin pathway secreted solely by the osteocytes. Osteopontin (OPN) acts as a secreted protein that is referred to many aspects of bone metabolism. OPN participates in bone regulation through neurology, endocrine and immunity. In this context, we aimed to investigate the clinical significance of peripheral biomarkers implicated in HAP severity and correlate with HAP features in children and adolescents with hemophilia A and B.

Patients and Methods: Οne hundred sixty two children and adolescents (mean age: 11.7 years, range 1-18.5 years) with severe, moderate and mild (n= 8) hemophilia A or B (n=11), on prophylaxis or on demand treatment (n= 6) were included in the study. Of them, 69 patients with median age of 11 years had no signs of HA (NHAP), 70 patients with median age of 14 years had arthropathy (HAP), while 23 patients with median age of 15.5 years presented with acute bleeding -hemarthrosis or muscle bleed- at the time of the biomarkers’ measurement- (AB). In all patients along with standard care laboratory evaluation, measurements of plasma circulating levels of DKK-1, RANKL, OPG, SOST and OPN were performed using immunoenzymatic techniques. Data are presented as mean ± SEM.

Results: We found that a) DKK-1 levels were higher in patients with NHAP and AB compared to patients with HAP, 3.396.0±194.0 pg/mL and 3.221±282.2 pg/mL vs 2.544±172.7 pg/mL (p=0.002); b) SOST levels in patients with NHAP (192.5±27.0 pg/mL), HAP (205.5±22.3 pg/mL) and AB (188.9±30.3 pg/mL) did not differ between the groups of patients (p>0.950); c) OPG levels in patients with NHAP (9.6±0.2 pg/mL), HAP (9.3±0.3 pg/mL) and AB (8.5±0.3 pg/mL) and RANKL levels in patients with NHAP (673.0±53.9 pg/mL), HAP (717.6±53.0 pg/mL) and AB (728.0±75.0 pg/mL) did not differ between the groups of patients (p>0.148 and p>0.515, respectively); d) Similarly, OPN levels in patients with NHAP (57.6±6.9 pg/mL), HAP (65.2±7.3 pg/mL) and AB (59.4±5.9 pg/mL) did not differ between the groups of patients (p>0.822) and e) DKK-1 and OPG levels correlated significantly with FVIII/FIX levels at the time of measurement (r=-0.553, p=0.014 and r=-0.540, p=0.017, respectively).

Conclusions: In this study, no significant perturbations of the crucial pathways regulating bone remodeling such as Wnt/β-catenin and RANKL/OPG systems were identified, by measuring circulating levels of key proteins involved in these pathways. Circulating DKK-1 seems to be a more sensitive biomarker indicating a potential decrease in osteoblastic activity. It appears that bone loss is rather rare in well-treated children and adolescents with hemophilic arthropathy comparing to young patients without arthropathy. Further studies are needed in order to determine how biomarkers in serum could play a prognostic role in the evolution of arthropathy from an early age in children and adolescents with hemophilia A or B, as well as the role of FVIII and FIX in bone metabolism, with the aim to ameliorate treatment strategies and prevent joint damage.