EPIDERMAL GROWTH-FACTOR AND TEMPERATURE REGULATE KERATINOCYTE DIFFERENTIATION

The limited life-span and irregularities in epidermal differentiation and barrier function that have restricted the utility of presently ava ilable skin culture models for pharmacological and toxicological studi es indicate that further modifications of culture conditions are requi red for optimization of these models, In the present study epidermis r econstructed on de-epidermized dermis was used to investigate the effe cts of temperature and epidermal growth factor (EGF) on epidermal diff erentiation and lipogenesis, When cultured at 37 degrees C, keratinocy tes formed a well-differentiated epidermis whether EGF was present or not, However, the thickness of the epidermis, particularly of the stra tum corneum, was higher in the presence of EGF, Both the differentiati on-specific protein markers (keratins 1 and 10, involucrin and transgl utaminase) and lipid markers (ceramides) were synthesized, EGF-induced increases in triglyceride content caused accumulation of lipid drople ts within the stratum corneum which is indicative of a hyperproliferat ive effect of EGF. In the absence of EGF, a well-differentiated epider mis was generated at 33 degrees C with a morphology showing a higher r esemblance to native epidermis than cultures grown at 37 degrees C, Th e stratum corneum was less compact and with practically no lipid dropl ets, irregularly shaped keratohyalin granules were abundant in the str atum granulosum, lamellar body extrusion was improved and the number o f stratum corneum layers was reduced to normal levels, However, EGF su pplementation had a deleterious effect on epidermal morphogenesis and differentiation of cultures grown at 33 degrees C, The epidermis lacke d a stratum granulosum and the stratum corneum contained a high number of nuclear remnants, The synthesis of the early specific protein diff erentiation markers (keratins 1 and 10) was suppressed on both the pro tein and mRNA levels without significant interference with the synthes is of late differentiation lipid markers, such as ceramides, From this observation it can be concluded that the synthesis of keratins associ ated with terminal differentiation is profoundly affected by the prese nce of EGF and is sensitive to temperature and that of ceramides is no t, The finding that TGF alpha did not modulate the morphogenesis and s ynthesis of keratins 1 and 10 in cultures grown at 33 degrees C indica tes possible differences between the postreceptor binding processes of these EGF receptor ligands.