Onset of re-epithelialization after skin injury correlates with a reorganization of keratin filaments in wound edge keratinocytes: defining a potential role for keratin 16.

Abstract

Abstract. Injury to stratified epithelia causes a strong induction of keratins 6 (K6) and 16 (K16) in post-mitotic keratinocytes located at the wound edge. We show that induction of K6 and K16 occurs within 6 h after injury to human epidermis. Their subsequent accumulation in keratinocytes correlates with the profound reorganization of keratin filaments from a pan-cytoplasmic distribution to one in which filaments are aggregated in a juxtanuclear location, opposite to the direction of cell migration. This filament reorganization coincides with additional cytoarchitectural changes and the onset of re-epithelialization after 18 h post-injury. By following the assembly of K6 and K16 in vitro and in cultured cells, we find that relative to K5 and K14, a well-characterized keratin pair that is constitutively expressed in epidermis, K6 and K16 polymerize into short 10-nm filaments that accumulate near the nucleus, a property arising from K16. Forced expression of human K16 in skin keratinocytes of transgenic mice causes a retraction of keratin filaments from the cell periphery, often in a polarized fashion. These results imply that K16 may not have a primary structural function akin to epidermal keratins. Rather, they suggest that in the context of epidermal wound healing, the function of K16 could be to promote a reorganization of the cytoplasmic array of keratin filaments, an event that precedes the onset of keratinocyte migration into the wound site. ~]~ typical stratified squamous epithelium, the epidermis shows a polarity in its functional organization and morphology. This polarity reflects the maintenance of an optimal balance between proliferation and differentiation, such that this self-renewing tissue maintains an architecture that is ideal for a barrier function. Progenitor cells reside in the basal layer, where keratinocytes are mitotically active, have a low columnar shape, appear relatively undifferentiated, and express specific markers such as the type II keratin K5 and type I keratins K14 (Nelson and Sun, 1983). Upon commitment to differentiation, basal keratinocytes exit the cell cycle and migrate upward to the suprabasal compartment (Fuchs, 1993). This commitment triggers a specific program of gene expression during which suprabasal keratinocytes steadily progress towards a cytoarchitecture in which they are completely flattened, have lost their organelles and nucleus, and have most of their protein content covalently cross-linked via the action of transglutaminases (Rice and Green, 1979). It is believed that commitment to terminal differentiation, which is accompanied by a switch in keratin gene expression from

Complete Cytolysis and Neonatal Lethality in Keratin 5 Knockout Mice Reveal Its Fundamental Role in Skin Integrity and in Epidermolysis Bullosa Simplex

“…The induction of these keratins occurs within 6 -12 h in suprabasal cells after epidermis full-thickness injury (McGowan and Coulombe, 1998a) and takes place at the mRNA level (Coulombe, 1997;Takahashi et al, 1998). With the accumulation of K6, K16, and K17, the protein levels of K1 and K10 are decreased (Mansbridge and Knapp, 1987;Paladini et al, 1996). First insights into the regulation of the K6 induction in wound healing came from in vitro studies with the use of human skin keratinocytes, which revealed AP-1 and epidermal growth factor-responsive elements in the human and bovine K6 promoter region (Jiang et al, 1993;Navarro et al, 1995).…”

K15 Expression Implies Lateral Differentiation within Stratified Epithelial Basal Cells

“…During wound healing, keratinocytes at the wound edge undergo cell shape changes and become migratory (Gabbiani et al, 1978;Paladini et al, 1996) and changes in keratin expression take place (Mansbridge and Knapp, 1987). Suction blister (epidermal) wounds were therefore examined for changes in K15 expression, using LHK15 to monitor K15 expression at various time points up to 96 hours after injury.…”

Comparison of advanced therapy medicinal product gingiva and skin substitutes and their in vitro wound healing potentials

“…For example, keratin 16 is expressed in native gingiva, but is absent in native skin (Figure 3). Furthermore, keratins 16 and 17 are described to be upregulated during wound healing as they disrupt the rigid structure of the epithelium, thus allowing keratinocytes to migrate over each other and over the connective tissue matrix (Paladini, Takahashi, Bravo, & Coulombe, 1996). Notably, both keratins were expressed in the midsections of the SS as well as the GS.…”

“…It is thought that these keratins may promote reorganization of the cytoplasmic array of keratin filaments (Paladini et al, 1996). This is an event that precedes the onset of keratinocyte migration into the wound site.…”