Vascular remodeling underlies rebleeding in hemophilic arthropathy Vikas Bhat, 1,2 Merissa Olmer, 1 Shweta Joshi, 3 Donald L. Durden, 3 Thomas J. Cramer, 2 Richard FW Barnes, 2 Scott T. Ball, 4 Tudor H. Hughes, 5 Mauricio Silva, 6 James V. Luck, 6 Randy E. Moore, 7 Laurent O. Mosnier, 1 and Annette von Drygalski 1,2 * Hemophilic arthropathy is a debilitating condition that can develop as a consequence of frequent joint bleeding despite adequate clotting factor replacement. The mechanisms leading to repeated spontaneous bleeding are unknown. We investigated synovial, vascular, stromal, and cartilage changes in response to a single induced hemarthrosis in the FVIII-deficient mouse. We found soft-tissue hyperproliferation with marked induction of neoangiogenesis and evolving abnormal vascular architecture. While soft-tissue changes were rapidly reversible, abnormal vascularity persisted for months and, surprisingly, was also seen in uninjured joints. Vascular changes in FVIII-deficient mice involved pronounced remodeling with expression of a-Smooth Muscle Actin (SMA), Endoglin (CD105), and vascular endothelial growth factor, as well as alterations of joint perfusion as determined by in vivo imaging. Vascular architecture changes and pronounced expression of a- SMA appeared unique to hemophilia, as these were not found in joint tissue obtained from mouse models of rheumatoid arthritis and osteoarthritis and from patients with the same conditions. Evidence that vascular changes in hemophilia were significantly associated with bleeding and joint deterioration was obtained prospectively by dynamic in vivo imaging with musculoskeletal ultrasound and power Doppler of 156 joints (elbows, knees, and ankles) in a cohort of 26 patients with hemophilia at baseline and during painful episodes. These observations support the hypothesis that vascular remodeling contributes significantly to bleed propagation and development of hemophilic arthropathy. Based on these findings, the development of molecular targets for angiogenesis inhibition may be considered in this disease. Am. J. Hematol. 90:1027–1035, 2015. V C 2015 Wiley Periodicals, Inc.  Introduction Factor (F)VIII-(Hemophilia A) or FIX-deficiency (Hemophilia B) manifests with spontaneous joint bleeding in childhood [1] that results in “target joints,” defined as joints with several consecutive bleeds within a 6-month period [2]. Target joints often progress to hemophilic arthropathy [2,3] characterized by joint deformities, synovial hypertrophy, and cartilage and bone destruction. Prophylactic clotting factor replacement can reduce joint bleeding and the development of hemophilic arthropathy markedly, but cannot entirely prevent it [3–6]. Therefore, hemophilic arthropathy is an important disabling comorbidity in adult patients, whereby the timing and intensity of prophylaxis in childhood appears to influence disease burden later in life [5,7]. While early start and intensity as well as adherence and continued access to clotting factor all weigh in favor of joint health in hemo- philia, there is evidence that once a target joint has formed prophylaxis cannot halt progressive range of motion deficits [3]. Also, despite access to pro- phylaxis in childhood, 30–50% of young adults with hemophilia living in industrialized countries suffer from hemophilic arthropathy [8–10], which has become an important focus of management outside of clotting factor replacement [11]. Since clotting factor replacement alone is only partially effective for the prevention and treatment of hemophilic arthropathy, additional treatment strategies are desirable and their development could be enabled by a better understanding of the pathobiology of disease progression. However, information about such pathobiological processes is limited Additional Supporting Information may be found in the online version of this article. 1 Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, California; 2 Department of Medicine, University of California San Diego, San Diego, California; 3 Department of Pediatrics, University of California San Diego, California; 4 Department of Orthopaedic Surgery, University of California San Diego, San Diego, California; 5 Department of Radiology, University of California San Diego, San Diego, California; 6 Orthopedic Institute for Children University of California Los Angeles, Los Angeles, California; 7 General Musculoskeletal Imaging Inc, Cincinnati, Ohio Conflict of interest: A.v.D. has received honoraria for participating in scientific advisory board panels, consulting and speaking engagements for Baxalta, Pfizer, Biogen, CSL-Behring, Novo Nordisk and Grifols. This work was funded by grant support from Biogen for “prevalence and etiology of subclinical joint bleeding and ’joint microbleeding’ in adults with hemophilic arthropathy” (A.v.D), an Early Career Development Award from Bayer Hemophilia (A.v.D. and V.B.), a Novo Nordisk Career Development Award from the National Hemophilia Foundation (A.v.D.), by National Institutes of Health grants HL091385, CA94233, CA192658 (D.L.D.) and HL104165 (L.O.M.). *Correspondence to: Annette von Drygalski; Hemophilia and Thrombosis Treatment Center, University of California San Diego, Department of Medicine, Division of Hematology/Oncology, 8929 University Center Ln. Ste. 201, San Diego, CA 92122. E-mail: avondrygalski@ucsd.edu Contract grant sponsor: Biogen for “prevalence and etiology of subclinical joint bleeding and ‘joint microbleeding’ in adults with hemophilic arthropathy” (A.v.D). Contract grant sponsor: An Early Career Development Award from Bayer Hemophilia (A.v.D. and V.B.). Contract grant sponsor: A Novo Nordisk Career Development Award from the National Hemophilia Foundation (A.v.D.). Contract grant sponsor: National Institutes of Health; Contract grant numbers: HL091385; CA94233; CA192658 (D.L.D.); HL104165 (L.O.M.). Received for publication: 8 July 2015; Revised: 17 July 2015; Accepted: 20 July 2015 Am. J. Hematol. 90:1027–1035, 2015. Published online: 7 August 2015 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/ajh.24133 V C 2015 Wiley Periodicals, Inc. doi:10.1002/ajh.24133 American Journal of Hematology, Vol. 90, No. 11, November 2015 1027 RESEARCH ARTICLE A JH A JH