Aging-associated loss of subcutaneous fat tissue is mediated on the cellular level by increased cellular turnover. Oxidatively stressed fibroblasts containing high levels of mtDNA deletions show increased apoptosis. (A) Ziehl-Neelsen staining for lipofuscin of subcutaneous fat tissue from 130-wk-old Csb^m/m mice containing high levels of mtDNA deletions (6 WT and 4 Csb^m/m mice were investigated). Increased level of macrophages containing granular lipofuscin (arrowheads) and no increase in normal fat cells (asterisks). Arrow points to hair follicle. Bar, 50 µm. (B) Quantification of histological sections of lipofuscin-positive macrophages from A with 17% (1 of 6 individuals) of histological sections with lipofuscin-positive cells (macrophages) in WT and 75% (3 of 4 individuals) in Csb^m/m mice. (C) FACS analysis for annexin V–positive and propidium iodide (PI) negative (apoptotic) cells with (black bars) or without (gray bars) 2 wk of UVA irradiation. Increase of apoptotic cells in CSA- and CSB-deficient cells compared with WT and nonirradiated controls. Data are representative of at least three separate experiments.