Effect Of Mechanical Stress On Proliferation And Differentiation Of Epidermal Stem Cells

Skin soft-tissue expansion,a technique to enlarge the skin surface area with an expandable balloon,has been widely used in reconstructive surgery.Although the effect of tissue expansion on in vivo skin physiology and histology has been well documented,it remains unclear whether keratinocytes or other cell types are responsible for these changes. Recognized as a cell that remains and retains the ability to proliferate throughout life, epidermal stem cells are responsible for the precise balance between regeneration and loss. However,which role that the epidermal stem cells play during the expansion process is unknown by the time.It is an exciting prospect,therefore,we investigate the mechanism of epidermal proliferation and differentiation of rats under the influence of skin soft-tissue expansion and the mechanism of proliferation and differentiation of human epidermal stem cells cultured in vitro under the influence of compressive stress,so that we can provide experimental bases to disclose the internal relations for riching the theory of skin soft-tissue expansion.Methods1.72 expanders were implanted on the back of 36 male Wistar rats,and the rats were randomly divided into two groups:sham-operation(SO) and intervention group(IG).The animals of intervention group were brought into effect of conventional intermittent skin expansion.Samples were collected at 1^st,2^nd,3^th,7^th and 10^th day during expansion process, and 7^th day post-expansion.2.HE staining was applied to observed the morphological changes of epidermis.3.p63,Keratin 19,14 and PCNA were employed to determine epidermal stem cells or transit amplifying cells with immunohistochemical SP method.4.Epidermal stem cells were isolated by adhering to typeâ…£collagen and were cultured with conditional medium,then were detected by immunohistochemical SP method with keratin 19 and cell cycle analysis.5.The cultured epidermal stem cells transplanted on silica gel membranes,which were put in a new apparatus was designed to offer cell culture and intermittent compressive stress (4kPa,6kPa,8kPa,10kPa,12kPa) for 2h,3 times a day simultaneously.A week later,cells on silica gel membranes were identified with keratin 19 and 10 by immunohistochemical SP method.Results1.The thickness of the expanded epidermis was increased,which was thicker than that of control group(P＜0.01).2.The numbers of epidermal stem cells and transit amplifying cells of the expanded epidermis were increased and both cells were found in the stratum spinosum and stratum granulosum of epidermis.3.Having established a new apparatus,which can offer cell culture and intermittent compressive stress simultaneously.4.The isolated and cultured epidermal stem cells were identified with keratin 19 positive and 84.80 percent of them were showed in G₁ period with cell cycle analysis.5.Cells on silica gel membranes had been subjected intermittent compressive stress above 8kPa for a week.,the number of the cells was increased,which was more than that of control group,however,some cells identified by immunohistochemical staining with keratin 10 positive were detected among the disposed epidermal stem cells.ConclusionsSkin soft-tissue expansion and the intermittent compressive stress above 8kPa can induce and promote epidermal stem cells to proliferate and differentiate,which indicates that epidermal stem cells respond to mechanical stress probably is its major biological basis.