Abstract 643: Involvement of Osteonectin Protein Expressions in Interstitial Fibrosis in Human Fibrillated Atria
Background: It has been shown that atrial fibrosis creates a substrate that promotes atrial fibrillation (AF). Osteonectin, also known as SPARC (secreted protein acidic and rich in cysteine), is a matricellular glycoprotein that regulates the balance between matrix deposition and degradation, which is related to tissue fibrosis. Expressions of osteonectin remain to be clarified in the remodeled atria. We tested the hypothesis that osteonectin was highly expressed in persistent AF patients (more remodeled atria), which is associated with interstitial fibrosis in the human diseased atria.
Methods: The subjects were 12 subjects (10men, mean age, 61 years) who underwent cardiac surgery for valvular diseases (10 mitral valve regurgitation, 2 atrial septal defect) and resected left atrial appendage with Maze operation for AF (paroxysmal 4, persistent 8). We examined expressions of osteonectin in the samples from left atrial appendages using immunohistological stains and immunofluorescence technique. Masson’s Trichorme was used to stain for collagens.
Results: We found localization of osteonectin predominantly to atrial interstitium in AF patients. Double immunofluorescence stainings demonstrated that osteonectin was expressed on non-myocytes, mainly on αsmooth muscle actin-positive myofibroblasts. The osteonectin protein expressions were significantly greater in persistent AF patients in compared with those in paroxysmal AF patients (p<0.05). The degree of osteonectin protein expression is significantly associated with not only left atrial dimensions, but also the levels of collagen deposition (p<0.05).
Conclusions: This study demonstrated that osteonectin expressions mainly in myofibroblasts are associated with interstitial fibrosis in human atria, suggesting that osteonectin might play an important role in progression of atrial tissue injury.