Lipids and acid hydrolases have been characterized in a subcellular fraction, enriched with lamellar granules (LG), derived from fetal rat epidermis. This fraction contains 23% glycosyl ceramides and ceramides, 15% free sterols, and 34% phospholipids. The lipid/protein ratio is 2.0. The sterols and sphingolipids were present in proportions similar to those previously reported in stratum corneum. These findings provide direct biochemical evidence for the widely accepted hypothesis that stratum corneum lipids are derived from exocytosis of lamellar granules into the intercellular space. The LG fraction was enriched in certain acid hydrolases including glucosidase, acid phosphatase, phospholipases A, and sphingomyelinase; other acid hydrolases, i.e., amino-glycosidases, glactosidase and aryl sulfatase (pH 5.5), and steroid sulfatase were not preferentially localized in this fraction. By modulation of phospholipids, glycolipids, and proteins in the membrane regions of stratum corneum, the acid hydrolases of LG may play a role relevant to the function and desquamation of stratum corneum.

Sphingolipid profiles have been determined for whole epidermis, a subcellular fraction enriched in lamellar granules, and a fraction enriched with stratum corneum derived from fetal rat skin. In each case, 4 groups of glucosylceramides and 6 groups of ceramides have been identified by thin-layer chromatographic comparison with structurally defined sphingolipids from pig epidermis. The relative amounts of the sphingolipids in each preparation have been quantified by photodensitometry of the charred chromatograms. Lamellar granule sphingolipids had elevated proportions, relative to whole epidermis, of acylceramides, acylglucosylceramides, and a glucosylceramide fraction which may be produced by O-deacylation of the acylglucosylceramides. The fetal stratum corneum-enriched samples contain reduced proportions of all glucosylceramides and acylceramides as compared to lamellar granule lipids. The possible functions of these sphingolipids in the assembly and structure of lamellar granules are discussed.

No abstract

Three lysosomal-type acid hydrolases were examined in subcellular fractions of the developing epidermis of fetal rats to assess the relationship of degradative enzymes to cornification. As the granular layer developed and cornified between 18 and 20 days (D) of gestation, epidermal acid phosphatase increased, acid phospholipase A remained constant, and beta-glucuronidase activity declined. The enzymes were present in 3,000, 17,000, and 100,000 g particulate fractions and soluble cytoplasm. However distribution differed: acid phosphatase and phospholipase A were more preferentially localized than was glucuronidase in the 17,000 g fraction which excluded mitochondria and ribosomes and was enriched in lamellar granules. The findings suggested that acid phosphatase and phospholipase were present in membrane-bound organelles (e.g., lamellar granules) in the granular layer. Particulate acid phosphatase increased with granular layers on days 19 and 20 while a 7-fold increase in soluble enzyme coincided with cornification on day 20. As shown by isoelectric focusing, the enzyme became more heterogeneous at day 20 than at day 18, suggesting increased glycosylation. The particulate fraction displayed lysosomal characteristics with respect to release of acid phosphatase, which was inhibited by hydrocortisone and enhanced by retinol. When fetal epidermis was allowed to cornify in organ cultures, similar increases in acid phosphatase occurred. The presence of hydrocortisone did not affect increase in total enzyme but a greater proportion remained in the particulate fraction. The findings suggest that particulate acid phosphatase and phospholipase are compartmentalized in organelles with lysosomal characteristics during development of granular cells and that release of phosphatase is coincident with cornification. This may reflect not only exocytosis of lamellar granules but also intracellular release of the hydrolytic enzyme.

Bullous pemphigoid (BP) is an IgG-mediated autoimmune blistering disease targeting the hemidesmosomal proteins bullous pemphigoid antigens 1 and 2. Currently, there is no active animal model in which to dissect the immunopathogenic mechanism. We noticed that cutaneous blistering arose spontaneously in 12 adult Yucatan minipigs. Skin lesions consisted of turgid, isolated or clustered vesicles that occasionally evolved from erythematous and pruritic patches. Histopathological examination revealed subepidermal vesicles rich in intact and degranulated eosinophils. Antigen mapping and transmission electron microscopy confirmed that dermoepidermal separation took place in the lamina lucida of the epidermal basement membrane zone. Direct immunofluorescence revealed the presence of IgG deposited linearly at the dermoepidermal junction in seven of nine skin specimens examined. Indirect immunofluorescence testing confirmed the presence, in the serum from eight of eight affected pigs, of circulating basement membrane-specific IgG autoantibodies (titers 1 : 50 to 1 : 250). Using uncleaved and salt-split lip substrates, the autoantibodies were shown to target antigens situated not only at the basal, but also at the lateral and apical aspects of stratum basale keratinocytes. Immunoelectron microscopy confirmed that circulating IgG autoantibodies recognized hemidesmosomal antigen(s). ELISA, immunoblotting and immunoadsorption demonstrated that five of eight serum samples exhibited high immunoreactivity against BPAG2-NC16A peptides. This novel porcine acquired blistering dermatosis could be proposed as a valuable model to conduct immunomechanistic studies on the natural progression of BP, correlation of autoreactive T cells or autoantibodies with disease activity, and the role of eosinophils in the blistering process, as these diseases cannot be modeled easily in human patients or in murine passive transfer models.