Autoantibodies to type VII collagen recognize epitopes in a fibronectin-like region of the noncollagenous (NC1) domain.

Autoantibodies to type VII collagen are characteristic of the blistering diseases epidermolysis bullosa acquisita and bullous systemic lupus erythematosus (SLE). Blisters in those diseases are due to defective adhesion of the lamina densa subregion of the epithelial basement membrane to the underlying dermis. Previous studies indicating that type VII collagen contributes to lamina densa-dermal adhesion by cross-linking lamina densa and dermal matrix proteins suggests that autoantibodies may contribute to blisters by interfering with type VII collagen function. That hypothesis is supported by previous studies showing autoantibodies from a small number of epidermolysis bullosa acquisita patients recognize proteolytic fragments containing the 145-kD noncollagenous domain of type VII collagen. In this study, we examined reactivity of autoantibodies from a large number of epidermolysis bullosa acquisita and bullous SLE patients with fusion proteins representing most of the noncollagenous domain of type VII collagen and that those regions are homologous to type III repeats of fibronectin. These results suggest autoantibodies binding to fibronectin homology regions within the 145-kD noncollagenous domain may interfere with the adhesion function of type VII collagen and contribute to lamina densa-dermal dysadhesion in epidermolysis bullous acquisita and bullous SLE.

Arterial prostaglandins and lysosomal function during atherogenesis. I. Homogenates of diet-induced atherosclerotic aortas of rabbit.

Homogenates of control and diet-induced atherosclerotic aortas of rabbit were prepared and the levels of DNA, protein, free and esterified cholesterol, and six enzymes known to be associated with various subcellular organelles [N-acetyl-beta-glucosaminidase, beta-galactosidase (lysosomes); cytochrome oxidase (mitochondria); neutral alpha-glucosidase (endoplasmic reticulum); 5'-nucleotidase (plasma membrane); catalase (peroxisomes)] were compared between control and atherosclerotic preparations. The levels of prostaglandins I2, E2, and F2 alpha, based on DNA, also were measured by radioimmunoassay. Atherosclerotic aortas were significantly enriched in catalase activity (440%) and in each of the acid hydrolases (395 and 630%), based on DNA, as well as in free (630%) and esterified cholesterol (930%), based on tissue wet weight, compared to control aortas. The control level of prostaglandin I2 was 10-fold higher than that of prostaglandin E2, which was 3-fold higher than that of prostaglandin F 2 alpha. Prostaglandin I2 doubled in amount with advanced atherosclerosis, while prostaglandin E2 increased over 10-fold, resulting in twice the amount of prostaglandin I2 than E2 in advanced atherosclerosis; the level of prostaglandin F2 alpha did not appear to change significantly with atherosclerosis. Increased levels of prostaglandins I2 and E2 were correlated significantly with increased aortic total cholesterol content (based on DNA) but not increased serum cholesterol levels. N-Acetyl-beta-glucosaminidase activity also was correlated significantly to aortic total cholesterol content and beta-galactosidase activity, as well as to the level of prostaglandin I2; in contrast, N-acetyl-beta-glucosaminidase was not significantly correlated to prostaglandin E2. The association of prostaglandins I2 and E2 with aortic total cholesterol suggests the participation of prostaglandins in the response of arterial cells to lipid accumulation in atherosclerosis. The specific association of aortic prostaglandin I2 level and N-acetyl-beta-glucosaminidase activity further suggests a possible role for this prostaglandin during arterial intralysosomal cholesterol accumulation.

Arterial prostaglandins and lysosomal function during atherogenesis. II. Isolated cells of diet-induced atherosclerotic aortas of rabbit.

This report validates and expands further the interpretation of our findings on prostaglandins and lysosomes in rabbit aortic homogenates (see paper I of this series) to enzymatically isolated and separated aortic cell populations during atherogenesis. Evidence is provided by which isolated arterial cells may be considered representative of in situ increases of diseased aortic tissue prostaglandin I2 and E2 levels, as well as lysosomal acid hydrolase activities and total cholesterol content based on DNA. Increasing latency of aortic lysosomal N-acetyl-beta-glucosaminidase activity was confirmed and correlated with increasing severity of atherosclerosis, in parallel to increasing levels of prostaglandin I2 but not increasing levels of prostaglandin E2. Ultrastructural observations also confirmed aortic intracellular lipid accumulation within lysosomes and as lipid droplets. Consistent with these relationships, separated low density, lipid-filled aortic cells were especially increased in total (197%) and latent (15%) lysosomal acid hydrolase activities, catalase activity (274%), total cholesterol (151%), and in both prostaglandin I2 (67%) and E2 (325%) levels based on DNA, as compared to control aortic cells or more normal-appearing high-density diseased aortic smooth muscle cells; high-density diseased aortic cells were increased in prostaglandin E2 but similar in latent acid hydrolase activity compared to control aortic cells. Since the total cholesterol content of rabbit atherosclerotic aortas was evidenced more intracellularly (75%) than extracellularly (25%) in this study, the association of increased prostaglandin I2 and E2 levels with low-density lipid-filled cells suggest the participation of these prostaglandins in the genesis of aortic foam cells during arterial lipid accumulation in rabbit atherosclerosis. The association of increasing prostaglandin I2 levels and increasing latent lysosomal N-acetyl-beta-glucosaminidase activities also implicates a possible relationship between this prostaglandin and lysosomal membranes of aortic cells, either primary or secondary to intralysosomal lipid accumulation.