Accumulation of lipofuscin (age pigment) in aging skeletal connective tissues as revealed by electron microscopy

An EM survey of aging skeletal connective tissue was made for the presence of lipofuscin accumulation. Twenty-six mice of both sexes, 5 to 130 weeks of age were perfused with glutaraldehyde. Femoral periosteal samples were fixed in cold glutaraldehyde, decalcified in EDTA, and post-fixed in osmium tetroxide. Sections were stained with uranyl acetate and lead citrate. Lipofuscin was absent in all cell types in mice 5 and 26 weeks of age. At 52 weeks, single membrane-bound lipofuscin granules were observed in fibrocytes, precursor osteogenic cells (preosteoblasts), osteoblasts, and osteocytes. With increasing age (78 to 104 weeks) lipofuscin was observed more frequently, as well as the number of granules per cell. At 104 and 130 weeks, many of the remaining cells revealed age pigment. These observations point to a wider distribution of age pigment in various tissues than previously realized. The presence of lipofuscin in connective tissue may facilitate a reevaluation of the role of this pigment in cellular aging.