Figure 2. Primary keratinocytes prepared from aged skin represent a valuable model of aging. Primary keratinocytes were isolated from 3 skin biopsies from young (<5 years) and old individuals (>60 years). Cells were cultured from passage 1 (P1) to late passage 6 (P6) and protein were extracted. (A) Western-blot analysis of p16. Actin is used as a loading control. (B) Western-blot analysis of BIP/GRP78 and p63 at passage 2 (P2) and passage 6 (P6). Actin is used as a loading control.