Regulation of Keratinocyte Proliferation in Rats With Deep, Partial-Thickness Scald: Modulation of Cyclin D1-Cyclin-Dependent Kinase 4 and Histone H1 Kinase Activity of M-Phase Promoting Factor

Abstract

Keratinocyte proliferation, which is undergone by its cell cycle transition, is considered a major event during re-epithelialization over the wound size. Cyclins, cyclin-dependent kinases, and cyclin-dependent kinase inhibitors interact to regulate the cell cycle. We investigated proliferative events associated with cell-cycle control in keratinocytes during wound healing in rats with deep, partial scald injuries. Male Sprague Dawley rats with starting weights of 200 to 220 g were inflicted with standardized deep partial-thickness burns by scalding 10% of the skin surface. The full thickness skin biopsies were harvested for histological evaluation at following time points: 0 d, post-burn day 3, post-burn day 7, and post-burn day 14. Keratinocytes from wound edge were isolated for cell cycle examination. The cell cycle regulators and their activity were detected. Keratinocytes tended to proliferate and had enlarged nuclei and nucleoli from day 3 after injury. Morphological features became evident on day 14, with an increase in keratinocytes. The percentage of S-phase keratinocytes tended to increase on day 14. The percentage G2/M-phase keratinocytes increased from day 3 and significantly increased on days 7 and 14. Cyclin D1 expression markedly increased from day 3, with down-regulation of cyclin-dependent kinase 4, which re-elevated on day 14. Cyclin B1 expression did not dramatically vary. Histone H1 kinase activity of mitosis phase promoting factor markedly increased on day 14. These findings suggested early, active DNA synthesis and mitosis in keratinocytes, with marked proliferation on day 14, that depended on the modulation of cyclin D1-cyclin-dependent kinase 4 and histone H1 kinase activity of mitosis phase promoting factor. During wound healing, patterns of cell-cycle control expression differed from those previously known.