OC 36.3 - Type-I Interferon promotes neutrophil-dependent Joint Damage in Hemophilia A

Background: Hemophilic arthropathy (HA) is the predominant pathophysiology resulting from recurrent joint bleeding in individuals with hemophilia and leads to permanent joint damage, chronic pain and reduced quality of life. Although FVIII replacement therapy or FVIII mimetics have significantly improved the disease outcome, joint bleeding continues to occur in severely hemophilic patients (FVIII < 1%). HA starts at an early age and develops progressively, warranting the need for a therapy that can intervene the progression of HA. Unfortunately, such therapy does not exist and the etiological mechanism of HA remains poorly understood.

Aims: To determine whether type-I interferon-dependent neutrophil extracellular traps (NETs) generation promotes HA.

Methods: Knee joints in FVIII-total knockout (F8TKO) or littermate WT male mice were injured using a needle. Scoring of the bleeding severity and histology of injured joints were conducted. Neutrophils from HA patients, F8TKO mice and matched controls were isolated, activation of type-I interferon-pathway components was evaluated in neutrophils using qRT-PCR (gene expression), ELISA and western blotting (protein phosphorylation and cleavage). Imaging-flow-cytometry and ELISA assays were used to evaluate the number of circulating NETs (cNETs) in the blood samples of patients diagnosed with HA and mice with following knee injury.

Results: F8TKO but not control mice manifested unresolved joint injury and severe bleeding 5-days post injury. Principal genes associated with type-1 interferon signaling were significantly elevated in neutrophils of HA patients and injured F8TKO mice compared to controls. Western blot analysis revealed activation of type-1 interferon-signaling in neutrophils isolated from HA patients and injured F8TKO mice but not control humans or uninjured F8TKO mice. cNETs were significantly elevated in the plasma of HA patients and injured F8TKO mice but not plasma of control humans or injured WT or uninjured F8TKO mice.

Conclusion(s): These findings are the first to suggest that type-I interferon-dependent generation of NETs contributes to joint damage in hemophilia-A.