Refractory Skin Injury in Complex Knock-out Mice Expressing Only the GM3 Ganglioside

Abstract

We generated double knock-out mice lacking the GM2/ GD2 and the GD3 synthase gene by mating single gene mutants, and we analyzed the abnormal phenotypes of the mutant mice expressing only the GM3 ganglioside. We observed a refractory skin lesion that appeared primarily on the face of the mutant mice at 25 weeks after birth or later. Frequent scratching of the wound sites was observed in mutant mice with the skin injury, suggesting that it is a triggering factor that exacerbates the injury. This was confirmed by isolating mice in special cages for metabolic study in which the skin injury developed more rapidly. Characteristic proliferation of nerve fibers was found in the epidermis and subepidermis at the injured sites of the mutants, probably a result of continuous skin injury. Peripheral nerve degeneration was observed in young mutant mice, suggesting that reduced sensory function induced over-scratching and the resulting skin lesion. The fact that sensory response to mechanical stimuli decreased while that to hot stimuli increased in the mutant mice supports this interpretation. Thus, only GM3-expressing mice displayed the important role of gangliosides in maintaining skin integrity via regulation of the peripheral nerves.Acidic glycosphingolipids, gangliosides, are ubiquitously expressed in the various tissues of vertebrates and play important roles in the regulation of highly organized multicellular systems (1). In particular, they are very much enriched in the nervous system and have been considered to control development, proliferation, differentiation, and maintenance of the neural tissues and cells (2, 3). Expression patterns of various ganglioside species in the nervous system vary during development and are strictly regulated in a spatio-temporal manner (4), suggesting that individual structures of gangliosides contain significant implications for individual situations.A number of studies have been performed to demonstrate the biological function of gangliosides primarily by modifying their structures with enzymes or using inhibitors to block some steps of synthesis (5). Otherwise, the effects of addition of gangliosides to the culture medium or injection into the conditioned animals have been the primary approaches in addressing the significance of gangliosides. However, recent success in the molecular cloning of glycosyltransferase genes brought about an evolutional change in the experimental approaches for carbohydrate function analysis. Availability of glycosyltransferase genes responsible for the synthesis of gangliosides enabled us to remodel ganglioside compositions of cells and tissues in vivo (6, 7) and in vitro (8).Because we isolated GM2/GD2 synthase (EC 2.4.1.92) cDNA (9) and GD3 synthase (EC 2.4.99.8) cDNA (10), we established gene knock-out mice lines of the individual glycosyltransferases. GM2/GD2 synthase gene knock-out mice lacking all complex gangliosides showed almost normal morphogenesis of the nervous system and no definite abnormal behaviors (11), although they showed nerve degene...

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