Repeated mild heat shock delays ageing in cultured human skin fibroblasts.

The effects of repetitive mild heat shock (30 min, 41 degrees C) on growth and various cellular and biochemical characteristics of human skin fibroblasts undergoing ageing in vitro were analysed. Human skin cells not only tolerated more than 30 repeated heat shocks throughout their replicative lifespan, but also maintained several characteristics of young cells until late in life. Whereas the growth rates, population doubling rates, and cumulative population doubling levels achieved in vitro remained unaffected, age-related changes in cellular morphology, cell size, cytoskeletal organisation, autofluorescence and neutral beta-galactosidase activity were significantly slowed down by repeated mild heat shock. These hormesis-like effects of stress-induced defence processes can be useful to elucidate the role of maintenance and repair mechanisms in ageing.