Lamellar bodies as delivery systems of hydrolytic enzymes: implications for normal and abnormal desquamation

Lamellar body secretion results in the delivery of a selected array of hydrolytic enzymes to the extracellular domains of stratum corneum (SC). Deposition and activation of these enzymes in the interstices presumably is associated with the transformation of lamellar body-derived lipids from a relatively polar to a non-polar mixture, as well as the degradation of other non-lipid intercellular substrates. To determine whether abnormal desquamation might result from failure of hydrolytic enzyme delivery to the SC interstices, we localized one catabolic enzyme, acid lipase, previously shown to be a reproducible marker for the lamellar body secretory system, by cytochemical methods within the epidermis of selected human (congenital ichthyosiform erythroderma, CIE) and animal (essential fatty-acid deficient (EFAD) mouse epidermis and mouse tail epidermis) models associated with abnormal scaling or unusual SC retention. In addition, we compared the persistence of desmosomes within normal SC vs. the various models. Normal human and murine epidermis displayed abundant lipase activity both in lamellar bodies (LB) and in association with secreted lamellar body contents in the SC interstices. Despite normal quantities of LB in CIE, EFAD, and mouse tail epidermis, lipase activity was markedly deficient both in LB and in the SC intercellular domains. These studies support the hypothesis that normal desquamation is mediated by enzymatic modulations in lipid and/or protein content of the SC interstices, and that some forms of pathological or excessive scaling may be due to desmosomal persistence that results from defective or limited delivery of lamellar body-derived, hydrolytic enzymes to the SC intercellular domains.