Identification of pancreatic type I secreted phospholipase A2 in human epidermis and its determination by tape stripping

Abstract

Phospholipases A2 (PLA2) catalyse the release of fatty acids from the sn-2 position of phospholipids and have been suggested to play a key part in permeability barrier homeostasis. Using a sensitive and versatile fluorometric method, significant PLA2 activity has been detected in both human skin homogenates and tape strippings of stratum corneum. Based on various properties (resistance to heat and sulphuric acid treatment, neutral optimal pH, absolute requirement for millimolar calcium concentrations, inhibition by dithiothreitol and p-bromophenacyl bromide, and resistance to a trifluoromethyl ketone derivative of arachidonic acid, AACOCF3, a specific inhibitor of cytosolic PLA2), this enzyme was characterized as a secretory PLA2 (sPLA2). Immunohistochemistry revealed strong labelling of type I pancreatic sPLA2 at the stratum corneum-stratum granulosum junction, type II sPLA2 being undetectable. An increase in PLA2 activity in tape-stripped material from the deepest level of the stratum corneum was correlated with partial morphological disappearance of type I sPLA2 immunolabelling. Our data thus provide the first convincing evidence that pancreatic sPLA2 is significantly expressed in human epidermis, where it might participate in the accumulation of free fatty acids contributing to the permeability barrier. In addition, our method for determining PLA2 activity in easily available tape strippings should allow further clinical studies aimed to explore possible PLA2 abnormalities in various dermatoses.

Variability of Enzyme Markers during Clinical Regression of Atopic Dermatitis

“…It has been reported that type I PLA2, the pancreatic form, is essentially located at the interface between the stratum granulosum and the stra-tum corneum [9]. This location coincides with that of the lysis of phospholipids into free fatty acids, i.e.…”

“…Concerning phospholipase A2-like activity (table 2), it has been shown as resulting from the presence of both type I PLA2 [9] and type II PLA2 [10].…”

“…trypsin-like activity [5], which is involved in desquamation, acid-phosphataselike activity, which is a marker for the degree of regeneration of the barrier function and, finally, the activity of the phospholipase-A2-like enzymes, in particular that involved in the release of arachidonate, a precursor of inflammation mediators [6]. Recent studies have indicated the presence of two secretory PLA2 activities in the upper layers of the epidermis: one similar to pancreatic PLA2 (type I) [7][8][9] and the other resembling synovial PLA2 (type II) [10].…”

Different modulation of phospholipase A2 activity by saturated and monounsaturated N-acylethanolamines

“…Moreover, studies on this protein are interesting because the presence of type I PLA 2 proteins was demonstrated in various tissues, including kidney, small intestine, spleen, lung, and stomach (55). A pancreatic type I PLA 2 was recently identified in the human epidermis (56). Moreover, the presence of a PLA 2 , which is revealed by immunostaining with antibodies raised against the porcine pancreatic enzyme, was detected in the acrosomal region of human spermatozoa (57).…”

Stratum corneum pH: Formation and Function of the ‘Acid Mantle’

“…Whereas epidermis also expresses two other sPLA 2 isoforms [42,43,48,49], group II and group X sPLA 2 , neither of these sPLA 2 are expressed in the outer epidermis under basal conditions. Moreover, based upon its inhibitor profile, its sensitivity to dithiothreitol, its pH optimum (= 7), its resistance to both heat and sulfuric acid, its Ca 2+ requirement and its immunohistochemical localization, much if not all of the sPLA 2 activity in the SC comprises the group 1 (pancreatic-type) sPLA 2 [44,45]. Like its lipid substrates, sPLA 2 activity localizes to lamellar bodies and within the SC interstices [34,37,[50][51][52][53], while in contrast, other potential epidermal sources of FFA (e.g.…”