Calcified Rheumatic Valve Neoangiogenesis Is Associated With Vascular Endothelial Growth Factor Expression and Osteoblast-Like Bone Formation

Abstract

Background-Rheumatic heart disease is the most common cause of valvular disease in developing countries. Despite the high prevalence of this disease, the cellular mechanisms are not well known. We hypothesized that rheumatic valve calcification is associated with an osteoblast bone formation and neoangiogenesis. Methods and Results-To test this hypothesis, we examined human rheumatic valves replaced at surgery (nϭ23), normal human valves (nϭ20) removed at cardiac transplantation, and degenerative mitral valve leaflets removed during surgical valve repair (nϭ15). Microcomputed tomography was used to assess mineralization fronts to reconstruct the extents of mineralization. Immunohistochemistry was used to localize osteopontin protein, ␣-actin, osteocalcin, vascular endothelial growth factor, von Willebrand factor, and CD68 (human macrophage). Microcomputed tomography demonstrated complex calcification developing within the heavily calcified rheumatic valves, not in the degenerative mitral valves and control valves. Immunohistochemistry localized osteopontin and osteocalcin to areas of smooth muscle cells within microvessels and proliferating myofibroblasts. Vascular endothelial growth factor was present in areas of inflammation and colocalized with the CD68 stain primarily in the calcified rheumatic valves. Alizarin red, osteopontin, and osteocalcin protein expression was upregulated in the calcified rheumatic valves and was present at low levels in the degenerative mitral valves. Conclusions-These findings support the concept that rheumatic valve calcification is not a random passive process but a regulated, inflammatory cellular process associated with the expression of osteoblast markers and neoangiogenesis. Key Words: angiogenesis Ⅲ calcification Ⅲ cardiovascular diseases Ⅲ rheumatic heart disease Ⅲ valves R heumatic valvular heart disease is the most common cause of valvular heart disease in developing countries. Improvement in living standards and the aggressive treatment of penicillin-sensitive group A ␤-hemolytic Streptococcus are changing the epidemiology of rheumatic valve disease throughout the world. In 1924, Dr Carey Coombs wrote the first systematic textbook on rheumatic heart disease, describing the inflammatory lesion in the rheumatic valve leaflet and the presence of new vessels developing within the valve. 1 Since 1924, a number of studies have demonstrated the histopathology of this disease with correlations of the degree of rheumatic activity, which include the presence of Aschoff bodies, nonspecific edema, and leukocyte infiltration. 2,3 Despite the high prevalence, increased morbidity, and well-described histopathological findings of this disease, little is known about the cellular mechanisms responsible for calcification in these valves. Recently, our laboratory and others have demonstrated that calcification in nonrheumatic, "degenerative" stenotic aortic valves removed at the time of surgical valve replacement is associated with an osteoblast-like phenotype. 4,5 We hypothesized that the i...

Differential cell-matrix responses in hypoxia-stimulated aortic versus mitral valves

“…The role of angiogenesis in CAVD and MS remains unclear, though there is growing evidence of its involvement in calcification [10,14]. HIF-1a, a marker frequently associated with angiogenesis, has recently been identified histologically in CAVD [21,22].…”

“…MMVD involves glycosaminoglycan and proteoglycan accumulation resulting in leaflet weakening and valve prolapse, whereas MS is associated with fibrotic remodelling, collagen accumulation and leaflet stiffening [9,10]. Angiogenic remodelling is a hallmark of both CAVD and MS, but it is not observed during MMVD [10][11][12][13][14]. During CAVD and MS, both valves also & 2016 The Author(s) Published by the Royal Society.…”

Extracellular Matrix Organization, Structure, and Function

“…Its traditional role as a product of bone indicates that valve calcification may actually be a result of active bone formation in the valve tissue [86]. This bone formation may be the result of VEGF secretion by endothelial cells during neoangiogenesis occurring in response to inflammation, as seen in rheumatic valve calcification [89]. Additionally, increased serum levels of osteocalcin were shown to be indicative of aortic valve disease in patients [90].…”

Periostin advances atherosclerotic and rheumatic cardiac valve degeneration by inducing angiogenesis and MMP production in humans and rodents

“…The cartilage and tendons are known to have unique angioinhibitory mechanisms (19), disruption of which results in angiogenesis and destruction of the joint, leading to arthritis (20). In contrast, angiogenesis and VEGF expression are increased in calcified aortic valves (21,22). Previously, we showed that chondromodulin I (encoded by Lect1) and tenomodulin, angioinhibitory factors expressed in the cartilage and tendon, respectively, were expressed in the cardiac valves and chordae tendineae cordis (23,24), respectively.…”