Detailed Structure and Composition of Skin

We examine the detailed structure and composition of skin below inasmuch as the ECM in skin is involved in sensing of external forces applied to the epidermis and transducing these forces into changes in skin thickness and composition. It is well known that increased friction on the surface of skin leads to thickening of the epidermis. 

Together with actin microfilaments and microtubules, keratin filaments make up the cytoskeleton of vertebrate epithelial cells. Keratins belong to a family of intermediate filament proteins that form a-helical coiled-coil dimers that associate laterally and end to end to form 10 nm diameter filaments. Keratin and actin filaments and microtubules form an integrated cytoskeleton that preserves the shape and structural integrity of the ker-atinocyte as well as serves to transmit mechanical loads. Keratins account for about 30% of the total protein in basal cells. 

external forces applied to the epidermis and/or internal forces present in dermis are transmitted through the cornified layer and lead to stretching of keratinocyte-keratinocyte cell junctions and the epidermal-dermal junction. These forces appear to be transmitted between epithelial cells via cadherins and may result in activation of secondary messengers which alter gene expression and protein synthesis. 

The hyaluronan content of skin has been estimated to be between 0.03% and 0.09%, and dermatan sulfate represents 30 to 40% of dermal proteoglycans. The GAG content is reported to decrease with respect to the amount of protein with increased age, and a recent report suggests that there is a decrease in the proportion of versican and an increase in decorin with increased age, which is associated with the appearance of a small PG that may be a catabolic fragment of decorin. 

---