THE J OURNAL m- I NVEST IGATIVE DEIlMATOLOGY, 65:259- 27 1, 1975 Vol. 65, No. 3 Copyright © 1975 by The Williams & Wilkins Co. Printed in U.S.A . REVIEW ARTICLE James H. Herndon, Jr., M.D. Review Article Editor LYSOSOMES AND THE SKIN GERALD S. LAZARUS , M.D. · , VICTOR B. HATCHER , PH.D., AND NORMAN LEVINE , M .D. D epartments of M edicine and Biochemistry, Albert Einstein College of M edicine, and DiVl:sion of Dermatology, Department of M edicine, Montefi ore Hospital and Medical Center, Bron.x , New York The importance of lysosomes in cutaneous phys­ as a secondary lysosome or digestive vacuole (Fig. iology was a ppreciated early. The studies of Fell 1) . and Mellanby [1) on vitamin A induction of The substrate containing organell es can ori gi­ mucouS meta plasia in chick skin and the investiga­ nate by several distinct mechanisms . Heterophagy tions of Weissman and Fell [2] on lysosomal is a process by which t he cell can engulf foreign labilization by ultraviolet light, were landmarks in material into h eterophagoso mes (Fig. 1) by either our understanding of lysoso mal physiology. Subse­ phagocytosis, which is the uptake of larger, insolu­ quently lysosomes have been shown to be impor­ ble substances, or pinocytosis, which is the inges­ tant in keratinization, pigmentat ion, and seba­ tion of sma ll er soluble material. The two processes ceous secretion. The lysosomal system also partici­ are known coll ectively as endocytosis. The fusion pates in numerous pathologic processes in skin of a heterophagosome with a primary lysosome incl uding epidermal phagocytosis, inflammation, produces a digestive vacuole. and neoplasia. Autophagy is a met hod by which the cell can sequester part of its own cytoplasm in auto­ DEFINIT ION OF LYSOSOMES phagosom es for digestion (Fig. 1). In this way, the cell is able to rid itself of damaged constituents. Lysosomes were first d escribed in 1955 by Fusion of the autophagic vacuole with a primary deDuve et a l [3]. They are cytoplasmic organelles lysosome results in the formation of a digestive which contain hydrolytic enzymes that are capable vacuole. of digesting many tissue constituents. Most diges­ The membrane that delimits the digestive vacu­ tion occurs intracellularly , but hydrolytic enzymes ole is ideally suited for cellular economy. Large can be secreted by exocy tosis, into the extracell ul ar macromolec ules readily enter the lysosome by com partment where they may also act on extracel­ heterophagy or autophagy but they are unabl e to lular macromolecules (Fig. 1) . diffuse from the vacuole because of their size. After Lysosomal enzymes are produced in the rough extensive enzymic digestion, the breakdown prod­ endoplasmic reticulum (6] and are then trans­ ucts of proteins, carbohydrates, nucleic acids, ported to a specialized re gion of the smooth endo­ mucopolysaccharides, and glycoproteins are s mall plasmic reticulum located at the inner surface of enough to pass through the lysosomal membrane the Golgi stack (GERL) (7]. Here these proteins where they may be used in biosynthetic processes are concentrated a nd packaged into membrane­ in other parts of the cell (8]. bound primary lysosomes. Primary lysosomes can A residual body or telolysosome is formed when fuse with organell es containing substrates for di­ substances in the digestive vacuole are incom­ gestion; the s ingle membrane-bound vacuole pletely digested so that they are too large to pass which contains hydrolases and substrate is shown through the lysosomal membrane. When these organell es have no further demonstrable hydrolytic Manuscript received December 18, 1974; in revised enzyme activity, they are call ed postlysosomes form April 11, 1975; accepted for publication April 14, (Fig. 1) . The residual body can be extruded from 1975. the cell by the process of exocytosis or it may i This work was supported by grants from the National rema in within the cytoplasm of the cell . Institute of Arthritis, Metabolism, and Di gestive Dis­ eases (IRO I AM 17370 01), t he National Institute of Heart and Lung (HL 16387 01) , and a grant from the MORPHOLOGIC EVIDENCE FOR THE PRESENCE OF Syntex Corporation to Dr. Norman Levine. LYSOSOMES IN SK IN * Senior Investi gator, The Arthritis Foundation U.S.A. Reprint requests to: Dr. G. S. Lazarus, Division of Dermatology, Duke University Medical Center, Durham, In this section we will discuss the morphologic Nort h Carolina 27708. evidence for the presence of lysosomes in the 259 260 LAZARUS, HATCHER, AND LEVINE Vol. 65, No.3 BIOCHEM ICAL STUDIES OF LYSOSOMAL ENZYMES IN SKIN n seque .. ,o,;ot r.~ Preparation of Lysosomal Fractions from Skin Endoplasmic :~ • :: Typical lysosomal hydrolases have been found i space '====' n '\. AUlophogosame / homogenates of whole s kin [1 8- 26 ]. T he specif· P,;mo,y Iysosomes ~ activity of these enzymes is highest in the l ysos~~ !~ ~ ~al fr~ct i on [1 8,27,28]. T~ese hydrolases are a lso & \ s,\>Je lIocUOles ~ found. IJ1 t he supernatant fraction , suggesting that va . o,e. / ~\ :~~ <':~ t~ the vlgoro:,s treatment necessary to homogenize @ .~. ~.~ sklJ1 also disrupts lysosomal organell es. Epidermal homogenates contain lysosomal enzymes with ~ higher specific activit ies t han whole skin [27-30 J. .Elcw" Residual Postlysosome o (f'e~ Cathepsin D ~ <1o,y l,sOSO \. bod, IiP\ Cathepsin D is a lysosomal acid proteinase C-J @~ which degrades hemoglobin at ~H 3 and proteogly_ TeIO I YSOS~~m; ~ can at pH 5 [31,32 ]. The use of a potent monospe_ .~~" ~ cific inhibitory antiserum to pure cathepsin D in y' °,c · t issue cult ure and a utolytic experiments has dem_ I o onstrated t hat this enzyme is important in extra_ S cellular matrix degradation [33 ]. Cathepsin D has been positively identified in extracts of rabbit skin [34] and in huma n skin where approximately lO o/c FIG. 1. Schematic representation of lysosomal func­ of the total enzyme wa s found in the epiderm is. t tions. (From Vaes [4] modified from Jacques 15 J with Antiserum to rabbit cathepsin D was capable of permission of the authors) quantitatively precipitating t he enzyme from ex­ tracts of whole rabbit skin. The removal of cathep_ epidermis and its appendages. T he connective s in D from the crude skin extract resulted in t issue cells of t he dermis, s uch as fibroblasts, al most complete loss of proteolytic activity against endotheli al cell s, histiocytes, mast cells, etc., are hemoglobin below pH 5 (Fig. 5) [34]. Autolysis not unique to the s kin and their lysosomes have experi men ts util izing i m m unoinh i bition of cathep_ been adequately reviewed elsewhere [9]. sin D demonstrated t hat t his enzyme was a lso The presence of lysosomes in t he epidermis was respons ibl e for degradation of structural s kin pro­ initiall y suggested fo ll owing the demonstration of tein at acid pH [34 ]. 1m munocytologic studies in t he lysosomal hydrolase, acid phosphatase, in t he rabbit skin demonstrate t hat t he enzyme is local­ granular layer [10] . Subsequent ly, acid phospha­ ized in epidermis, epidermal appendages, and tase [11 - 14] and aryl sulfatase [1 5] were localized fibroblasts [17] (see morphologic evidence above). in vacuoles in epidermal cells . Structures meeting Cathepsin D levels increase dramaticall y at morphologic criteria for lysosomes were observed in times of remodeling in chick skin [35,36 ]. This t he basal epidermal cells of guinea pigs and enzyme, as well as neutral proteinase, a lso in- ' humans (Fig. 2). T hese structures regularly con­ creases dramaticall y in experimental inflamma_ tained acid phosphatase (Fig. 3) . Ac id phosph atase tion induced by turpentine in rabbit skin (see was also locali zed to t he small juxtanuclear Golgi Lysosomes and Cutaneous Inflammation). cisternae of t he basal and s pinous cell s and in Cathepsin D may playa major role in intracellu_ membrane-coating gran ul es (Fig. 2c). Typical acid lar protein digestion. Dingle et al [37] in cubated phosphatase-conta ining lysosomes h ave been rabbit pulmonary alveolar macrophages with ca­ fo und in epidermal Langerhans cells and in mel­ t hepsin D antiserum and were able to a rrest the anosomes (see section on Pigmentation). intracellular digestion of IgG, hemoglobin, a nd Cathepsin D, t he major lysosomal acid protein­ proteoglycan. The antiserum-treated cells devel­ ase responsible for protein degradation at acid pH, oped giant vacuoles which contained un degraded has been locali zed immunocytochemically in chi ck s ubstrate; t he cells remained viable and when t he epidermal cell cultures [1 6] a nd rabbit skin [1 7 ]. a ntiserum was removed t heir morphology returned Immunofluorescent and immunoautoradiographic to normal. T hese results indicated t hat cathepsin techniques (Fig. 4) have been used to demonstrate D co uld be inhibited within t he cell and t hat t his punctate localization of cathepsin D in t he basal acid hydrolase pl ayed a major role in protein I ayer of t he epidermis and a diffuse distribution of catabolism. The locali zation of cathepsin D to the enzyme in the granular layer . Cathepsin D has basal epidermal cells [1 7 ], coupled with t heir also been found in hair fo llicles, sebaceous glands, known phagocytic function [38], suggests t hat a nd mesenchymal cells of t he dermis. These stud­ ies suggest that epidermal lysosomes may be t Levine N, Hatcher VB, Lazarus GS: Unpublished involved in protein catabolism. res ul ts. Sept. 1975 LYSOSOMES AND T H E SKI N 261 FIG. 2. Some morphologic variants of epidermal lysosomes in guinea-pig epidermis. a: Single membrane-limited bodies (L) conta ining granule material of moderate electron density.