Abstract
Macrophages have multiple roles in the heart including immune surveillance and extracellular matrix remodeling. Aging increases both collagen deposition and macrophage number in the heart; however, rodent models used to study cardiac macrophages have age-related comorbidities such as atherosclerosis and hypertension. The Fischer 344 rat does not develop these conditions with aging; therefore, the purpose of this study was to evaluate macrophage number and polarization in the hearts of aged (24-month) and young (6-month) Fischer 344 rats. Paraffin-embedded hearts were assessed for collagen deposition and immunolabeled for CD68, CD163, CD206, and galectin-3. Compared with young rats, significantly greater collagen deposition was observed in the old rats. There were no significant differences in CD68(+) or CD163(+) cells between age groups, but both CD206(+) and galectin-3(+) cells were more numerous in the aged animals. Double-immunofluorescence studies demonstrated that galectin-3 colocalized with both CD68 and CD163, suggesting that galectin-3 is found in cardiac macrophages. Further colocalization studies demonstrated similar proportions of CD68(+)/CD163(-), CD68(+)/CD163(+), and CD68(-)/CD163(+) cells between age groups, suggesting that aging does not affect macrophage polarization. As CD206(+) and galectin-3(+) cells promote fibrosis, these results warrant future studies that delineate the specific roles of these cells in the aged heart.