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A mouse model of harlequin ichthyosis delineates a key role for Abca12 in lipid homeostasis.

Smyth I, Hacking DF, Hilton AA, Mukhamedova N, Meikle PJ, Ellis S, Satterley K, Slattery K, Collinge JE, de Graaf CA, Bahlo M, Sviridov D, Kile BT, Hilton DJ - PLoS Genet. (2008)

Bottom Line: We have used this model to follow disease progression in utero and present evidence that loss of Abca12 function leads to premature differentiation of basal keratinocytes.These cells have severely impaired lipid efflux leading to intracellular accumulation of neutral lipids.Furthermore, we identify Abca12 as a mediator of Abca1-regulated cellular cholesterol efflux, a finding that may have significant implications for other diseases of lipid metabolism and homeostasis, including atherosclerosis.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, Monash University, Melbourne, Australia. ian.smyth@med.monash.edu.au

ABSTRACT
Harlequin Ichthyosis (HI) is a severe and often lethal hyperkeratotic skin disease caused by mutations in the ABCA12 transport protein. In keratinocytes, ABCA12 is thought to regulate the transfer of lipids into small intracellular trafficking vesicles known as lamellar bodies. However, the nature and scope of this regulation remains unclear. As part of an original recessive mouse ENU mutagenesis screen, we have identified and characterised an animal model of HI and showed that it displays many of the hallmarks of the disease including hyperkeratosis, loss of barrier function, and defects in lipid homeostasis. We have used this model to follow disease progression in utero and present evidence that loss of Abca12 function leads to premature differentiation of basal keratinocytes. A comprehensive analysis of lipid levels in mutant epidermis demonstrated profound defects in lipid homeostasis, illustrating for the first time the extent to which Abca12 plays a pivotal role in maintaining lipid balance in the skin. To further investigate the scope of Abca12's activity, we have utilised cells from the mutant mouse to ascribe direct transport functions to the protein and, in doing so, we demonstrate activities independent of its role in lamellar body function. These cells have severely impaired lipid efflux leading to intracellular accumulation of neutral lipids. Furthermore, we identify Abca12 as a mediator of Abca1-regulated cellular cholesterol efflux, a finding that may have significant implications for other diseases of lipid metabolism and homeostasis, including atherosclerosis.

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Barrier defects in Abca12el12/el12 mice.Abca12el12/el12 mice have defects in barrier formation as evidenced by dye exclusion (A) and trans-epidermal water loss (B) assays at E18.5. Cornified envelopes prepared from Abca12el12/el12 mice are fragile and reduced in size compared with wild type littermate controls (Abca12el12/el12 CEs concentrated 15 times, C, D: p = 6×10−23). Western blotting indicates defects in filaggrin processing in Abca12el12/el12 epidermis (E, arrow) while expression of other CE proteins such as loricrin is unaffected. Expression of “proliferative” keratin VI is present only in the differentiating hair follicle of both mutant and wild type epidermis (F) and cell proliferation at E17.5 is normal as assayed by phospho-histone H3 staining (G; p = 0.27).
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pgen-1000192-g003: Barrier defects in Abca12el12/el12 mice.Abca12el12/el12 mice have defects in barrier formation as evidenced by dye exclusion (A) and trans-epidermal water loss (B) assays at E18.5. Cornified envelopes prepared from Abca12el12/el12 mice are fragile and reduced in size compared with wild type littermate controls (Abca12el12/el12 CEs concentrated 15 times, C, D: p = 6×10−23). Western blotting indicates defects in filaggrin processing in Abca12el12/el12 epidermis (E, arrow) while expression of other CE proteins such as loricrin is unaffected. Expression of “proliferative” keratin VI is present only in the differentiating hair follicle of both mutant and wild type epidermis (F) and cell proliferation at E17.5 is normal as assayed by phospho-histone H3 staining (G; p = 0.27).

Mentions: Consistent with the results of the genetic screen, at weaning no Abca12el12/el12 mice were detected from heterozygous crosses however examination of litters at E18.5 found normal mendelian ratios of viable but phenotypically abnormal Abca12el12/el12 embryos (n = 17/57 embryos). Abca12el12/el12 pups were occasionally found in the first few hours after birth but were often dead or severely dehydrated and had failed to suckle normally. Recent studies by Yanagi et al., indicate a role for Abca12 in lung development and defects in this organ may contribute to neonatal death [16]. To follow the development of the phenotype we examined cohorts of embryos from various developmental stages. At E14.5 and E15.5 homozygous embryos appeared normal; however from E16.5 onwards they were characterised by an absence of normal skin folds around the trunk and limbs. As development progressed, Abca12el12/el12 embryos developed a taut, thick epidermis and multiple contractures affecting the limbs (Figure 2A,3A). Late stage Abca12el12/el12 embryos were also found to be smaller than their wild type or heterozygous littermates (Figure 2A, 3A), a phenotype we assayed in newborn mice (p = 0.0023, data not shown). Skin sections from affected embryos revealed a hyperkeratotic phenotype from E16, and confirmed the absence of normal folding (Figure 2B).


A mouse model of harlequin ichthyosis delineates a key role for Abca12 in lipid homeostasis.

Smyth I, Hacking DF, Hilton AA, Mukhamedova N, Meikle PJ, Ellis S, Satterley K, Slattery K, Collinge JE, de Graaf CA, Bahlo M, Sviridov D, Kile BT, Hilton DJ - PLoS Genet. (2008)

Barrier defects in Abca12el12/el12 mice.Abca12el12/el12 mice have defects in barrier formation as evidenced by dye exclusion (A) and trans-epidermal water loss (B) assays at E18.5. Cornified envelopes prepared from Abca12el12/el12 mice are fragile and reduced in size compared with wild type littermate controls (Abca12el12/el12 CEs concentrated 15 times, C, D: p = 6×10−23). Western blotting indicates defects in filaggrin processing in Abca12el12/el12 epidermis (E, arrow) while expression of other CE proteins such as loricrin is unaffected. Expression of “proliferative” keratin VI is present only in the differentiating hair follicle of both mutant and wild type epidermis (F) and cell proliferation at E17.5 is normal as assayed by phospho-histone H3 staining (G; p = 0.27).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2529452&req=5

pgen-1000192-g003: Barrier defects in Abca12el12/el12 mice.Abca12el12/el12 mice have defects in barrier formation as evidenced by dye exclusion (A) and trans-epidermal water loss (B) assays at E18.5. Cornified envelopes prepared from Abca12el12/el12 mice are fragile and reduced in size compared with wild type littermate controls (Abca12el12/el12 CEs concentrated 15 times, C, D: p = 6×10−23). Western blotting indicates defects in filaggrin processing in Abca12el12/el12 epidermis (E, arrow) while expression of other CE proteins such as loricrin is unaffected. Expression of “proliferative” keratin VI is present only in the differentiating hair follicle of both mutant and wild type epidermis (F) and cell proliferation at E17.5 is normal as assayed by phospho-histone H3 staining (G; p = 0.27).
Mentions: Consistent with the results of the genetic screen, at weaning no Abca12el12/el12 mice were detected from heterozygous crosses however examination of litters at E18.5 found normal mendelian ratios of viable but phenotypically abnormal Abca12el12/el12 embryos (n = 17/57 embryos). Abca12el12/el12 pups were occasionally found in the first few hours after birth but were often dead or severely dehydrated and had failed to suckle normally. Recent studies by Yanagi et al., indicate a role for Abca12 in lung development and defects in this organ may contribute to neonatal death [16]. To follow the development of the phenotype we examined cohorts of embryos from various developmental stages. At E14.5 and E15.5 homozygous embryos appeared normal; however from E16.5 onwards they were characterised by an absence of normal skin folds around the trunk and limbs. As development progressed, Abca12el12/el12 embryos developed a taut, thick epidermis and multiple contractures affecting the limbs (Figure 2A,3A). Late stage Abca12el12/el12 embryos were also found to be smaller than their wild type or heterozygous littermates (Figure 2A, 3A), a phenotype we assayed in newborn mice (p = 0.0023, data not shown). Skin sections from affected embryos revealed a hyperkeratotic phenotype from E16, and confirmed the absence of normal folding (Figure 2B).

Bottom Line: We have used this model to follow disease progression in utero and present evidence that loss of Abca12 function leads to premature differentiation of basal keratinocytes.These cells have severely impaired lipid efflux leading to intracellular accumulation of neutral lipids.Furthermore, we identify Abca12 as a mediator of Abca1-regulated cellular cholesterol efflux, a finding that may have significant implications for other diseases of lipid metabolism and homeostasis, including atherosclerosis.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, Monash University, Melbourne, Australia. ian.smyth@med.monash.edu.au

ABSTRACT
Harlequin Ichthyosis (HI) is a severe and often lethal hyperkeratotic skin disease caused by mutations in the ABCA12 transport protein. In keratinocytes, ABCA12 is thought to regulate the transfer of lipids into small intracellular trafficking vesicles known as lamellar bodies. However, the nature and scope of this regulation remains unclear. As part of an original recessive mouse ENU mutagenesis screen, we have identified and characterised an animal model of HI and showed that it displays many of the hallmarks of the disease including hyperkeratosis, loss of barrier function, and defects in lipid homeostasis. We have used this model to follow disease progression in utero and present evidence that loss of Abca12 function leads to premature differentiation of basal keratinocytes. A comprehensive analysis of lipid levels in mutant epidermis demonstrated profound defects in lipid homeostasis, illustrating for the first time the extent to which Abca12 plays a pivotal role in maintaining lipid balance in the skin. To further investigate the scope of Abca12's activity, we have utilised cells from the mutant mouse to ascribe direct transport functions to the protein and, in doing so, we demonstrate activities independent of its role in lamellar body function. These cells have severely impaired lipid efflux leading to intracellular accumulation of neutral lipids. Furthermore, we identify Abca12 as a mediator of Abca1-regulated cellular cholesterol efflux, a finding that may have significant implications for other diseases of lipid metabolism and homeostasis, including atherosclerosis.

Show MeSH
Related in: MedlinePlus