Abstract 17530: Characterization of Cardiac-resident Leukocyte Populations in the Steady-state and During Aging

Abstract

Although it is well acknowledged that immunological phenomena participate in several cardiac diseases, it has been deeply neglected the fact that the heart is already populated by resident leukocytes before the onset of any sign of disease. In the present work we comprehensively characterized the cardiac-resident leukocyte populations and addressed for the first time in the literature how these cells take part in cardiac physiology and aging. We compared cardiac function, structure and gene expression of healthy naïve C57BL6/J (WT) mice 10 (young), 30 (mid-aged) and 60 (aged) wk old. Flow cytometrical analysis of perfused-digested murine hearts revealed a cardiac-resident leukocyte population comprised of approx. 103 cells/mg (M2-macrophages > B-cells > T-cells > granulocytes). The frequency of resident leukocytes found in cardiac muscle was 17.4 fold higher than in skeletal muscle, suggesting that they might be relevant for cardiac physiology. Importantly, cardiac-resident leukocyte composition shifted towards a pro-inflammatory profile during aging. Additionally, qPCR analysis indicated a significant up-regulation of pro-inflammatory genes such as TNF, IL-1β and IFN-γ in aged mice (e.g. TNF mRNA expression level: 2.1 .10-4 ± 2.0 10-5 in young vs 1.5 .10-3 ± 2.6 .10-4 in aged mice; P < 0.05). Similar results were found regarding to pro-fibrotic and pro-hypertrophic genes expression (e.g. Coll-III, TGF-β and βMyHC). Furthermore, aged WT mice presented increased serum levels of autoantibodies against myosin and higher frequencies of activated T helper cells (CD4+CD69+) in mediastinal lymph nodes as compared to young mice. Echocardiographic and hemodynamic studies revealed that in parallel with increased inflammation, 60 wk old naïve mice spontaneously develop severe cardiac dysfunction (e.g. ejection fraction: 34.6% ± 5.19%). Altogether, these data demonstrated that the heart comprises an important and yet underappreciated resident leukocyte population in the steady-state and that shifts in its composition occur in parallel with the cardiac deterioration observed in aged mice.