Ultraviolet B-induced apoptosis of keratinocytes in murine skin is reduced by mild local hyperthermia.
Two components of sunlight, ultraviolet (UV) B (290-320 nm) and infrared (greater than 700 nm), each cause damage to the skin. However, we recently identified a protective response in which heat reduces UVB-induced killing of cultured keratinocytes. Here, this investigation is extended to the living epidermis. The effects of hyperthermic preconditioning upon UVB-induced apoptosis were studied morphologically with hematoxylin and eosin staining, and biochemically with TUNEL (terminal deoxynucleotide transferase nick-end labeling) to measure endonucleolytic cleavage of DNA in situ. Anesthetized SKH-1 hairless mice were exposed to UVB light (0 to 120 mJ/cm2), after which their skin was biopsied at 24 h and paraffin sections were stained with hematoxylin and eosin or with TUNEL. Apoptotic keratinocytes were found to increase after UVB in a dose-related manner. In contrast, if one flank of the mouse was pretreated at 40 degrees C for 1 h and both flanks subsequently were UVB-irradiated at 6 h, the resulting formation of apoptotic cells was reduced twofold or more in the heated flank. Protection appeared by 3 h, reached a maximum at 6 h, and disappeared by 12 h. In summary, heat induces a transient protective effect that reduces UVB-mediated death of keratinocytes in skin at physiologically attainable doses of heat and UVB.
Kane
K S
KS
Department of Dermatology, Massachusetts General Hospital, Boston 02114.
Maytin
E V
EV
D000818:Animals; D017209:Apoptosis / Q000528:radiation effects*; D004249:DNA Damage; D004253:DNA Nucleotidylexotransferase / Q000378:metabolism; D005260:Female; D005334:Fever / Q000503:physiopathology*; D006651:Histocytochemistry; D015603:Keratinocytes / Q000502:physiology*; D051379:Mice; D013473:Sunscreening Agents / Q000494:pharmacology; D014466:Ultraviolet Rays
D013473:Sunscreening Agents; D004253:DNA Nucleotidylexotransferase