Abstract 3401: Hypoxia, Inflammatory Cells, and Hyaluronan Homeostasis in Aortic Valve Calcification
Objectives: The glycosaminoglycan hyaluronan (HA) is a well known participant in inflammatory cell invasion and extracellular matrix remodeling. Given the role of HA in the delivery of bone morphogenic protein (BMP)-2, HA may link remodeling, inflammation, and ossification in calcific aortic valve disease (CAVD). Excess BMP-2 is also linked with production of brown fat cells that stimulate hypoxic conditions in heterotopic ossification. The objective of this study was to determine the extent to which these inflammatory, HA-driven, and hypoxic mechanisms were present in CAVD.
Methods: Calcified human aortic valves (n=14, mean age 65±15) were immunohistochemically stained for proteins involved in matrix remodeling, hypoxia, and cell differentiation. Staining intensity was evaluated within and surrounding mature calcified nodules, immature pre-nodules, and non-calcified regions of the leaflet. Inflammatory cell infiltration was assessed by the percentage of CD32, CD44, and CD45RO positive cells.
Results: There were numerous correlations (p<0.05) linking chondrogenic and osteogenic markers (S100, BMP-2) with markers for brown adipocytes (uncoupling protein-1, PPARgamma co-activator 1alpha) and hypoxia (HIF-1alpha). These relationships were strong (r>0.5) on the edge of mature nodules and in surrounding tissues, even stronger (r>0.75) in pre-nodules, and absent or inversely correlated in control regions. Interactions were also present between HA homeostatic regulators, BMP-2, and TNF-alpha-stimulated gene-6 (TSG-6). Binding of HA to TSG-6 prevents TSG-6 from inhibiting BMP-2 mediated ossification; our data suggests that ossification was promoted by this relationship in mature nodules but not in pre-nodules, where BMP-2 was associated with TSG-6 but not HA. Finally, the percentage of CD32 and CD45RO positive inflammatory cells was tenfold greater in regions surrounding the nodule compared to uncalcified regions (p<0.05).
Conclusions: Mature and immature nodules within CAVD demonstrate evidence for hypoxia-, matrix-, and inflammatory cell-driven remodeling. These newly identified mechanisms interact with more well known pathways leading to CAVD, and may reveal new information about possible therapeutic approaches.