Abstract 227: Intravital Multiphoton Microscopy Reveals Increased Capillary Patrolling by Leukocytes and Cardiomyocyte Dysfunction in High Fat Diet Induced Hypertrophy

Abstract

Background: The study of functional cardiomyocyte adaptation and inflammatory cell behavior at the micro-scale in vivo has been challenging due to limited imaging tools. We recently developed intravital multiphoton microscopy (MPM) methods that enable visualization and quantification of cardiac dynamics at a cell-scale throughout the cardiac cycle. We aimed to determine the dynamic cellular changes that occur due to high fat diet (HFD) induced hypertrophy using intravital cardiac MPM. Methods: ApoE -/- C57Bl6 mice started a HFD at 6 weeks of age (ApoE -/- -HFD, n=11), while age-matched wild-type mice (WT-ND, n=10) were fed a normal chow diet. At 26-weeks, mice were assessed by cardiac echocardiography and intravital MPM in the intact beating heart. Intravenous injections of rhodamine-6G (R6g) labeled cardiomyocytes and leukocytes, and Texas-Red dextran labeled vasculature. 3D volumes were reconstructed throughout the cardiac cycle to quantify cell motion using automated algorithms. Results: ApoE -/- -HFD hearts underwent hypertrophy compared to WT-ND with increased heart weight-to-tibial length ratio (10±0.8 vs 13±1.1) and left ventricle wall thickness (1.07±0.03 mm vs 1.13±0.06 mm, respectively, p<0.05 for both) while ejection fraction remained similar (66±3 % vs 59±3 %). In vivo MPM demonstrated that cells move a greater total distance in each cardiac cycle in ApoE -/- -HFD vs WT-ND. Maximum displacement in the apex-base and anterior-posterior directions increased by 46 % in ApoE -/- -HFD compared to WT-ND (30 μm vs 14 μm). R6g+ leukocytes were visible moving in capillaries. The incidence of patrolling behavior (defined as slowing moving cells, visible for longer than one heart beat) increased in capillaries of ApoE -/- -HFD compared to WT-ND (3.4±0.5/min vs 0.12±0.1/min, p<0.01). Conclusion: These results suggest that hypertrophied cardiomyocytes increase myocardial displacement, and increased leukocyte patrolling behavior is associated with HFD induced cardiac hypertrophy. Intravital cardiac MPM provides a novel perspective to study HFD induced cardiac hypertrophy by capturing the simultaneous contributions of inflammatory cells and myocyte function in the beating heart.