Differential enzymatic digestion of cytoplasmic components of keratinocytes: electron microscopic observations

The effect of the proteolytic enzyme savinase on human plantar skin in vitro

The effect of the proteolytic enzyme savinase on human plantar skin in vitro was examined by light and electron microscopy to elucidate the morphological involvement of activated savinase in human epidermis. Light microscopic examination of incubated skin fragments demonstrated that the histological changes produced by savinase in the epidermis, including the stratum corneum, depended upon pH value, enzyme concentration and incubation time. After incubation in 0.1% savinase in phosphate buffer, pH 8.0, for 2 h at 35 degrees C, the stratum corneum revealed a serrated appearance at the free edges, the viable cell layers showed acantholysis, particularly in the suprabasal area. Digestion of cytoplasmic components of horny cells was observed by electron microscopy, but both cell membranes and desmosomes remained intact. Detachment of basal and spinous cells was found in the viable epidermal cell layers. The main cytoplasmic changes consisted of the presence of numerous cytoplasmic processes and vesicular formations. The results of this study indicate that activated savinase digests the intercellular substance in the viable cell layers, but it does not digest horny cells without physical rupture of the cell membrane.

Fate of Mallory body-containing hepatocytes: disappearance of Mallory bodies and restoration of the hepatocytic intermediate filament cytoskeleton after drug withdrawal in the griseofulvin-treated mouse

Mallory bodies are characteristic morphological features of alcoholic hepatitis in man and can be produced in the mouse by chronic griseofulvin intoxication. The appearance of Mallory bodies in hepatocytes is associated with derangement of the cytokeratin intermediate filament cytoskeleton, at least as revealed by immunofluorescence and suggested by immunoelectron microscopy. Immunohistochemical studies were performed to answer the question whether Mallory body formation and cytoskeleton alterations finally lead to cell death or are reversible phenomena. Chronically griseofulvin-intoxicated mice killed at different stages of recovery on a normal diet served as experimental animals. It could be shown that (a) Mallory bodies are very durable structures and are found for up to 6 mo after griseofulvin withdrawal as a result of persistence and neoformation; (b) new Mallory bodies can appear even several months after cessation of griseofulvin feeding; (c) Mallory body formation and cytoskeletal changes by themselves do not lead to irreversible cell damage; (d) the cytoskeletal changes are reversible within 7 mo after griseofulvin withdrawal; (e) a dissociation between disappearance of Mallory bodies and restoration of a regularly immunostained cytoplasmic cytokeratin meshwork is observed.

Lipid composition and acid hydrolase content of lamellar granules of fetal rat epidermis

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.

Effect of enzyme digestion on the permeability barrier in keratinizing and non-keratinizing epithelia

In an attempt to characterize the permeability barrier of the oral mucosa and skin, small pieces of keratinized and non-keratinized oral epithelia and epidermis were digested with specific enzymes. These enzymes were selected for their effect on carbohydrate-protein, or carbohydrate-lipid compounds and phospholipids. The effect of the enzyme treatment was monitored by exposing the digested tissue to horseradish peroxidase. Electron microscopic examination of tissue treated with phospholipases revealed considerable damage to membrane structures but not to the integrity of the permeability barrier. Hyaluronidase and neuraminidase caused less structural damage but did not impair barrier function; this was only seen after treatment with chondroitinase ABC. This enzyme may degrade certain of the polar molecules thought to be necessary to stabilize the neutral lipid bilayers of the intercellular barrier and thus disrupt its barrier properties.

A method for partial purification of lamellar granules from fetal rat epidermis

A subcellular fraction enriched with lamellar granules was obtained from homogenates of fetal rat epidermis by means of density gradient fractionation in metrizamide. 62% of organelles in this fraction were bounded by single membranes and measured 80-130 nm in the shorter diameter. About 10% of these had characteristic lamellae. Other structures in this fraction were larger vesicles (20%) or smaller organelles and vesicles (18%). The fraction had a low buoyant density (1.08-1.10) suggesting a high lipid content and contained a sharply localized peak of acid phosphatase activity. The 80-130 nm organelles reacted with bismuth after oxidation with periodic acid and were positive for acid phosphatase. Other intracellular organelles (e.g., lysosomes, mitochondria, ribosomes) as well as keratin fibrils and keratohyalin were not present. It is concluded that most of this fraction consists of lamellar granules, permitting for the first time detailed investigations of the composition and metabolism of these organelles.

Trends in electron microscopy of skin

Some trends in electron microscopy of skin have emerged and should be pursued in the future. The fine structure and some basic cellular reaction patterns of epidermal cells are discussed to illustrate the interplay of morphologic, cytochemical, and tracer studies. Intracytoplasmic membranes and secretory granules, lysosomes and endocytic mechanisms, cytomembranes and cell surface specialization are discussed to show how these can be used to arrive at a more meaningful interpretation of structure. Despite all advances, however, a great deal more needs to be done before the details of skin structure are completely elucidated.

Histochemistry of the keratohyalin granules in human oral leukoplakia

The keratohyalin granules from 25 human oral leukoplakias, showing benign hyperorthokeratosis histologically, were examined employing a series of histochemical techniques. The tissues were fixed in 10% neutral buffered formalin, 80% methanol, or Carnoy's fluid. The keratohyalin granules stained intensely with Pauly's reagent, Congo red and Harris hematoxylin, indicating the presence of proteins. This was confirmed by abolishing the staining reaction by pretreatment with proteolytic enzymes. The keratohyalin granules also reacted with methyl green-pyronin by staining pink at their peripheries; this staining was abolished by pretreatment with ribonuclease, indicating the presence of ribonucleotides. The keratohyalin granules partially stained with toluidine blue and colloidal iron, indicating the presence of acid polysaccharides. The keratohyalin granules did not react with the Feulgen reagent, suggesting the absence of DNA. Our studies indicate that the keratohyalin granules in human oral leukoplakia are primarily protein(s) complexed with polyribonucleotides. The presence of a carbohydrate moiety suggests the possibility of a protein-polysaccharide component in the granules.

Aspects of epidermal ultrastructure

Some problems posed by primarily ultrastructural studies of the epidermis are highlighted and discussed, and on the whole it is concluded that purely morphologic observations are unlikely further to elucidate such questions as the nature and function of keratohyalin, or the dynamic aspects of the general keratinization process. The contribution of freeze-fracture studies to the understanding of the functional morphology of the epidermis is assessed, with particular reference to specialized contacts, and the stratum corneum. Passing reference is made to the epidermal nonkeratinocytes.