Self-Improvement of Keratinocyte Differentiation Defects During Skin Maturation in ABCA12-Deficient Harlequin Ichthyosis Model Mice

Abstract

Harlequin ichthyosis (HI) is caused by loss-of-function mutations in the keratinocyte lipid transporter ABCA12. The patients often die in the first 1 or 2 weeks of life, although HI survivors' phenotypes improve within several weeks after birth. In order to clarify the mechanisms of phenotypic recovery, we studied grafted skin and keratinocytes from Abca12-disrupted (Abca12 ؊/؊ ) mice showing abnormal lipid transport. Abca12 ؊/؊ neonatal epidermis showed significantly reduced total ceramide amounts and aberrant ceramide composition. Immunofluorescence and immunoblotting of Abca12 ؊/؊ neonatal epidermis revealed defective profilaggrin/filaggrin conversion and reduced protein expression of the differentiation-specific molecules, loricrin, kallikrein 5, and transglutaminase 1, although their mRNA expression was up-regulated. In contrast, Abca12 ؊/؊ skin grafts kept in a dry environment exhibited dramatic improvements in all these abnormalities. Increased transepidermal water loss, a parameter representing barrier defect, was remarkably decreased in grafted Abca12 ؊/؊ skin. Ten-passage sub-cultured Abca12 Harlequin ichthyosis (HI) (OMIM 242500) is one of the most severe genetic skin disorders, and its clinical features at birth include severe ectropion, eclabium, flattening of the ears, and large thick plate-like scales over the entire body. 1Infants affected with HI frequently die within the early neonatal period, although an increasing survival rate for HI newborns has recently been highlighted. 2 In 2005, we and another independent research group identified mutations in the ATP-binding cassette transporter A12 (ABCA12) gene as the cause of HI. 3,4 We previously demonstrated that a severe ABCA12 deficiency causes defective lipid transport in lamellar granules in the upper spinous and granular layer keratinocytes, resulting in malformation of intercellular lipid layers at the granular/cornified layer interface and epidermal lipid barrier disruption resulting in HI phenotype. 3 We recently generated Abca12-disrupted (Abca12 Ϫ/Ϫ ) mice by targeting Abca12, which closely reproduced the human HI phenotype and died soon after birth. 5 We tried systemic retinoid administration to the pregnant female mice as a form of fetal therapy, although no therapeutic effect was

ABCA12 mutations and autosomal recessive congenital ichthyosis: A review of genotype/phenotype correlations and of pathogenetic conceptsa

“…Furthermore, in the mutant mice carrying a homozygous spontaneous missense mutation, loss of Abca12 function led to premature differentiation of basal keratinocytes [Smyth et al, 2008]. In contrast, in our Abca12 À/À HI model mice, immunofluorescence and immunoblotting of Abca12 À/À neonatal epidermis revealed defective profilaggrin/filaggrin conversion and reduced expression of the differentiation-specific molecules, loricrin, kallikrein 5, and transglutaminase 1, although their mRNA expression was upregulated [Yanagi et al, 2010]. These data suggest that ABCA12 deficiency may lead to disturbed keratinocyte differentiation during fetal development, resulting in an ichthyotic phenotype at birth.…”

“…Increased transepidermal water loss, a parameter of barrier defect, was remarkably decreased in grafted Abca12 À/À skin. 10 passage-subcultured Abca12 À/À keratinocytes showed restoration of intact ceramide distribution, differentiation-specific protein expression, and profilaggrin/filaggrin conversion, which were defective in the primary culture [Yanagi et al, 2010]. These observations suggested that, during maturation, Abca12 À/À epidermal keratinocytes regain normal differentiation processes, although the exact mechanisms of this restoration is still unknown [Yanagi et al, 2010].…”

“…Retinoids were also ineffective in in vivo studies using cultured keratinocytes from the model mice [Yanagi et al, 2010].…”

“…However, once they survive beyond the neonatal period, HI survivors' phenotypes improve within several weeks after birth. In order to clarify mechanisms of the phenotype recovery, we studied grafted skin and keratinocytes from Abca12-disrupted (Abca12 À/À ) mouse [Yanagi et al, 2010]. Abca12 À/À skin grafts kept in a dry environment exhibited dramatic improvements in all the abnormalities seen in the model mice.…”

Endogenous β-glucocerebrosidase activity in Abca12epidermis elevates ceramide levels after topical lipid application but does not restore barrier function

“…In normal skin, ABCA12 localizes to LB ( 33 ), and keratinocytes demonstrate a widely distributed pattern of cellular GlcCer expression ( 1,12 ). In contrast, in HI skin, GlcCer fails to localize to the periphery of the keratinocyte cytoplasm ( 34 ), and there is a loss of lamellae structure in the stratum corneum and LB ( 1,(11)(12)(13). These data, together with our observations of the enzymatic processing of de novo-synthesized ceramides in the Abca12 Ϫ / Ϫ skin and the partial circumvention of the GlcCer processing defect via topical application of exogenous precursors, are consistent with a critical role for ABCA12 in transporting GlcCer to the extracellular space via its action at the lamellar body membrane ( 1, 7, 11-13, 35, 36 ).…”