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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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Ultrastructural defects in Abca12el12/el12 mice.Thin sections of Abca12el12/el12 epidermis illustrated hyperkeratosis and expansion of the stratum granulosum (A). Nile red staining shows reduced intercellular lamellae lipids at E18.5 (B). In wild type epidermis intercellular lipid lamellae (white arrow and inset) were noted as well as LBs fusing with the surface of granular cells (red arrow) (C). Lamellar bodies in wild type and heterozygous embryonic epidermis were normally loaded with lipid (D). In mutant skin, LBs lacked lamellar cargo (E, F arrowheads) but fused with the granular cell membrane (F; arrows). Mutant epidermis had a normal cornified envelope (G,H) with persistent corneodesmosomes in distal layers of the stratum corneum (G, H, red arrowheads) and the cornified layer had multiple lipid inclusions (G, black arrowheads). Unlike the uniform contents of wild type cornified cells mutant cell layers contained vesicular fibrillar structures (I, red arrows) and frequent inclusion bodies (I, black arrows). EM scale bars in C–F, H, I equal 200 nm and 2 µm in G. C–F and I were stained with ruthenium tetroxide, G and H with osmium tetroxide.
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pgen-1000192-g005: Ultrastructural defects in Abca12el12/el12 mice.Thin sections of Abca12el12/el12 epidermis illustrated hyperkeratosis and expansion of the stratum granulosum (A). Nile red staining shows reduced intercellular lamellae lipids at E18.5 (B). In wild type epidermis intercellular lipid lamellae (white arrow and inset) were noted as well as LBs fusing with the surface of granular cells (red arrow) (C). Lamellar bodies in wild type and heterozygous embryonic epidermis were normally loaded with lipid (D). In mutant skin, LBs lacked lamellar cargo (E, F arrowheads) but fused with the granular cell membrane (F; arrows). Mutant epidermis had a normal cornified envelope (G,H) with persistent corneodesmosomes in distal layers of the stratum corneum (G, H, red arrowheads) and the cornified layer had multiple lipid inclusions (G, black arrowheads). Unlike the uniform contents of wild type cornified cells mutant cell layers contained vesicular fibrillar structures (I, red arrows) and frequent inclusion bodies (I, black arrows). EM scale bars in C–F, H, I equal 200 nm and 2 µm in G. C–F and I were stained with ruthenium tetroxide, G and H with osmium tetroxide.

Mentions: Histologically all epidermal cell layers were apparent in Abca12el12/e1l2 embryos, although the size of the granular layer progressively increased at the expense of the spinous layer (Figure 2B, 5A). By parturition the cornified layers had coalesced into thick sheets of 20–30 enucleate corneocytes. The basal layer in Abca12el12/el12 mice also lost the dense palisaded nuclear organisation apparent in wild type and Abca12el12/+ mice (Figures 2B, 4A). Consistent with the apparently restrictive nature of the cornified layer, the epidermis as a whole was 30% thinner at E17.5 and P1 in Abca12el12/el12 animals (data not shown). Despite this constriction, hair follicles formed and differentiated relatively normally (Figure 2B, 3F) and complete histological examination of E18.5 embryos did not identify overt anomalies in other organs. Adult and embryonic Abca12el12/+ mice had no overt phenotype, no obvious histological abnormalities and were healthy and fertile.


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)

Ultrastructural defects in Abca12el12/el12 mice.Thin sections of Abca12el12/el12 epidermis illustrated hyperkeratosis and expansion of the stratum granulosum (A). Nile red staining shows reduced intercellular lamellae lipids at E18.5 (B). In wild type epidermis intercellular lipid lamellae (white arrow and inset) were noted as well as LBs fusing with the surface of granular cells (red arrow) (C). Lamellar bodies in wild type and heterozygous embryonic epidermis were normally loaded with lipid (D). In mutant skin, LBs lacked lamellar cargo (E, F arrowheads) but fused with the granular cell membrane (F; arrows). Mutant epidermis had a normal cornified envelope (G,H) with persistent corneodesmosomes in distal layers of the stratum corneum (G, H, red arrowheads) and the cornified layer had multiple lipid inclusions (G, black arrowheads). Unlike the uniform contents of wild type cornified cells mutant cell layers contained vesicular fibrillar structures (I, red arrows) and frequent inclusion bodies (I, black arrows). EM scale bars in C–F, H, I equal 200 nm and 2 µm in G. C–F and I were stained with ruthenium tetroxide, G and H with osmium tetroxide.
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Related In: Results  -  Collection

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pgen-1000192-g005: Ultrastructural defects in Abca12el12/el12 mice.Thin sections of Abca12el12/el12 epidermis illustrated hyperkeratosis and expansion of the stratum granulosum (A). Nile red staining shows reduced intercellular lamellae lipids at E18.5 (B). In wild type epidermis intercellular lipid lamellae (white arrow and inset) were noted as well as LBs fusing with the surface of granular cells (red arrow) (C). Lamellar bodies in wild type and heterozygous embryonic epidermis were normally loaded with lipid (D). In mutant skin, LBs lacked lamellar cargo (E, F arrowheads) but fused with the granular cell membrane (F; arrows). Mutant epidermis had a normal cornified envelope (G,H) with persistent corneodesmosomes in distal layers of the stratum corneum (G, H, red arrowheads) and the cornified layer had multiple lipid inclusions (G, black arrowheads). Unlike the uniform contents of wild type cornified cells mutant cell layers contained vesicular fibrillar structures (I, red arrows) and frequent inclusion bodies (I, black arrows). EM scale bars in C–F, H, I equal 200 nm and 2 µm in G. C–F and I were stained with ruthenium tetroxide, G and H with osmium tetroxide.
Mentions: Histologically all epidermal cell layers were apparent in Abca12el12/e1l2 embryos, although the size of the granular layer progressively increased at the expense of the spinous layer (Figure 2B, 5A). By parturition the cornified layers had coalesced into thick sheets of 20–30 enucleate corneocytes. The basal layer in Abca12el12/el12 mice also lost the dense palisaded nuclear organisation apparent in wild type and Abca12el12/+ mice (Figures 2B, 4A). Consistent with the apparently restrictive nature of the cornified layer, the epidermis as a whole was 30% thinner at E17.5 and P1 in Abca12el12/el12 animals (data not shown). Despite this constriction, hair follicles formed and differentiated relatively normally (Figure 2B, 3F) and complete histological examination of E18.5 embryos did not identify overt anomalies in other organs. Adult and embryonic Abca12el12/+ mice had no overt phenotype, no obvious histological abnormalities and were healthy and fertile.

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