Permeability barrier requirements regulate epidermal beta-glucocerebrosidase.

The intercellular spaces of the outermost layers of the epidermis (stratum corneum, SC) of terrestrial mammals con- tain a mixture of lipids, enriched in ceramides that are critical for the epidermal permeability barrier. Whereas glucosyl- ceramides (GlcCer) are synthesized in abundance in the epidermis, they disappear coincident with an increase of cera- mides (Cer) in the SC. Hence, hydrolysis of GlcCer to Cer by @-glucocerebrosidase (GlcCer'ase), may be required for per- meability barrier homeostasis. We determined first whether modulations in epidermal GlcCer'ase activity and mRNA levels occur in response to barrier disruption; and second, how GlcCer'ase inhibitors influence barrier hnction and SC mem- brane ultrastructure. Barrier disruption significantly increased epidermal GlcCer'ase mRNA levels, with a 2.8-fold increase over untreated control levels at 8 h (P < 0.01). GlcCer'ase ac- tivity was increased in whole epidermis (34%; P < 0.02) 24 h after barrier disruption. Localization of GlcCer'ase activity showed an increase (33%; P < 0.05) in the outer epidermis (SC and stratum granulosum), without a change in lower epidermal activity (stratum spinosum and stratum basale). Furthermore, a single topical application of the GlcCer'ase inhibitor, bromo- conduritol-B-epoxide (BrCBE), inhibited enzyme activity (98%) and significantly delayed permeability barrier recovery after ace- tone treatment. In addition, BrCBE treatment disrupted SC intercellular lamellar bilayers, without evidence of cellular toxicity. These results indicate that epidermal processing of GlcCer to Cer by GlcCer'ase is required for barrier homeostasis, and that this important enzymatic step is regulated by barrier requirements.-Holleran, W. M., Y. Takagi, G. K. Menon, S. M. Jackson, J. M. Lee, K. R. Feingold, and P. M. Elias. Permeability barrier requirements regulate epidermal 0-gluco- cerebrosidase. J Lipid Res. 1994. 35: 905-912. pholipids associated with bilayer formation in other cellu- lar membranes (2-4). These hydrophobic species derive, in part, from a mixture of precursors, including phospho- lipids and glucosylceramides, contained in the epidermal lamellar body (5, S), a distinctive secretory organelle that delivers these lipids, along with co-packaged hydrolytic enzymes (7, 8), to the intercellular spaces at the base of the stratum corneum. After secretion, lamellar body con- tents undergo a series of morphologic transformations leading to the formation of intercellular lamellar unit structures characteristic of the stratum corneum of terres- trial mammals (1, 9). These structural alterations are ac- companied by depletion of glucosylceramides and phos- pholipids, with an increase in ceramides and free fatty acids within the stratum corneum interstices (2-4, 10). In both mucosal epithelia (11) and marine cetacean epi- dermis (E), which display less stringent barrier require- ment, glycosylceramides predominate over ceramides, perhaps due to a paucity of epithelial glycosidases (13), and basic lamellar unit structures do not form. These observations suggest that transformation of glucosylceramides to ceramides may be an important pre- requisite of permeability barrier competence. We recently demonstrated large quantities of P-glucocerebrosidase (GlcCer'ase) in murine epidermis, with the highest levels of activity in stratum corneum (14). Moreover, when bromoconduritol-B-epoxide (BrCBE), a covalent inhibi- tor of GlcCer'ase (15), was applied topically to intact skin, a progressive defect in permeability barrier function oc- curred, which was accompanied by both the accumulation