Collagen Remodeling Of Spontaneously Hypertensive Rats Undergoing Quinapril Treatment Measured By Three Dimensional Shape Analysis

Introduction: Myocardial collagen structure is a complex three dimensional (3D) hierarchy, organizing cardiomyocytes and providing structural integrity. Changes in collagen organization have a crucial role in cardiac remodeling. However, quantitative methods for the analysis of collagen structures are still lacking. Herein, we apply our collagen shape analysis framework to compare within-sheetlet collagen (both endomysial collagen surrounding myocytes and perimysial cords) against sheetlet-surface collagen (perimysial meshwork collagen deposited between sheetlets) in spontaneously hypertensive rats undergoing quinapril treatment. Hypothesis: The different functional properties of endomysial and perimysial meshwork collagen are linked to their structure and will have markedly different features quantifiable by 3D shape analysis. Methods: Rat myocardium was stained for collagen (picrosirius red), and the left ventricular free wall imaged using extended volume confocal microscopy (0.4 μm 3 voxel size). The 3D image volumes were segmented into within-sheetlet and sheetlet-surface regions. Shape analysis was performed using eigenanalysis of the inertia matrix to derive 3D morphological (elongation and flatness) parameters, characterizing the collagen shape in the two regions. Results: Shape analysis revealed marked differences between within-sheetlet and sheetlet-surface collagen organization. Long-term quinapril treatment resulted in notable differences in within-sheetlet collagen shape in rats at 14 months of age (mo) compared with 24 mo. At 14 mo, the within-sheetlet collagen is a mix of sheet-, ribbon-, and rod-like structures (elongation: 0.43, flatness: 0.05), but by 24 mo this has remodeled to predominately thin rod-like structures (elongation: 0.03, flatness: 0.35). The sheetlet-surface collagen consisted of thick sheet-like structures in both 14 and 24 mo rats (elongation: 0.83 vs 0.79, flatness: 0.13 vs 0.09). Conclusion: Shape analysis in 3D showed marked differences between within-sheetlet and sheetlet-surface collagen structure, as well as differences between early treatment and late treatment of diseased hearts.