Increased spectrin proteolysis in fibroblasts from aged and Alzheimer donors.

Since calcium homeostasis is altered in cultured skin fibroblasts from aged and Alzheimer donors, the present study examined the degradation of spectrin, a substrate of the calcium dependent protease calpain. Spectrin proteolysis was estimated as the percentage of spectrin breakdown products (e.g., 150 + 155 kDa bands) per total spectrin immunoreactivity. In the baseline condition (e.g., unstimulated fibroblasts), spectrin breakdown was 53% greater in cells from aged donors when compared to cells from either young or Alzheimer donors. Compared to unstimulated cells, serum increased spectrin breakdown in cells from aged (22.4%) or Alzheimer (92.1%) donors but was ineffective in cells from young donors. Thus, when compared to young donors (100%), serum stimulation increased spectrin proteolysis by 183.9% (aged) or 231.7% (Alzheimer) after serum stimulation. Treatment of unstimulated cells with carbonyl cyanide 4-trifluoromethoxy-phenylhydrazone (FCCP), an uncoupler of mitochondrial function, increased spectrin degradation by 360.6% (young), 242.4% (aged) or 239.7% (Alzheimer) when compared to unstimulated cells of the same group. The combination of FCCP and serum stimulation enhanced spectrin breakdown in cells from aged (123.6%) and Alzheimer (154.0%) donors when compared to young cells (100%). Thus, changes in the regulation of calcium dependent proteases may contribute to decreased cell spreading and may play a role in the altered cytoskeletal dynamics characteristic of Alzheimer's disease.