Depletion of ceramides with very long chain fatty acids causes defective skin permeability barrier function, and neonatal lethality in ELOVL4 deficient mice

Abstract

Very long chain fatty acids (VLCFA), either free or as components of glycerolipids and sphingolipids, are present in many organs. Elongation of very long chain fatty acids-4 (ELOVL4) belongs to a family of 6 members of putative fatty acid elongases that are involved in the formation of VLCFA. Mutations in ELOVL4 were found to be responsible for an autosomal dominant form of Stargardt's-like macular dystrophy (STGD3) in human. We have previously disrupted the mouse Elovl4 gene, and found that Elovl4 +/-mice were developmentally normal, suggesting that haploinsufficiency of ELOVL4 is not a cause for the juvenile retinal degeneration in STGD3 patients. However, Elovl4 -/-mice died within several hours of birth for unknown reason(s). To study functions of ELOVL4 further, we have explored the causes for the postnatal lethality in Elovl4 -/-mice. Our data indicated that the mutant mice exhibited reduced thickness of the dermis, delayed differentiation of keratinocytes, and abnormal structure of the stratum corneum. We showed that all Elovl4 -/-mice exhibited defective skin water permeability barrier function, leading to the early postnatal death. We further showed that the absence of ELOVL4 results in depletion in the epidermis of ceramides with ω-hydroxy very long chain fatty acids (≥C28) and accumulation of ceramides with non ω-hydroxy fatty acids of C26, implicating C26 fatty acids as possible substrates of ELOVL4. These data demonstrate that ELOVL4 is required for VLCFA synthesis that is essential for water permeability barrier function of skin.

Biosynthesis of very long-chain fatty acids (C>24) in Atlantic salmon: Cloning, functional characterisation, and tissue distribution of an Elovl4 elongase

“…Investigations on genetically-modified mice suggested a role for Elovl4 in the biosynthesis of saturated VLC-FA. Thus, mice lacking a functional ELOVL4 exhibited lower saturated VLC-FA (C > 24) in skin acyl-ceramides, which resulted in severe skin permeability disruptions in the pups that died perinatally (Cameron et al, 2007;Li et al, 2007;Vasireddy et al, 2007). Similarly, mutated Elovl4-knockin mice exhibited depleted levels of C32-C36 VLC-PUFA in retinal phosphatidylcholine (PC), indicating that mammalian ELOVL4 is also involved in the biosynthesis of VLC-PUFA (McMahon et al, 2007).…”

Role of Stargardt-3 macular dystrophy protein (ELOVL4) in the biosynthesis of very long chain fatty acids

“…Also, transgenic mice expressing the mutant form of human ELOVL4 that causes STGD3 accumulate undigested phagosomes and lipofuscin-derived fluorophores in the retinal pigment epithelium (RPE), followed by RPE atrophy and subsequent photoreceptor degeneration in the central retina (4), as observed in human dominant STGD3 (1, 24), recessive Stargardt disease (25), and age-related macular degeneration (26,27). Furthermore, homozygous Elovl4 knockout and knockin neonates, which died within hours of birth, exhibited scaly wrinkled skin and a severely compromised epidermal permeability barrier, most likely resulting from a global reduction in very long chain saturated and monounsaturated fatty acids (VLC-FA, chain length Ն26:0) in both omega hydroxyl ceramides/glucosylceramides and free fatty acids (19)(20)(21)(22).To establish the specific step(s) that the ELOVL4 protein catalyzes in very long chain fatty acid elongation, we overexpressed transgenic ELOVL4 protein in rat neonatal cardiomyocytes and a human RPE cell line (ARPE-19), neither of which express detectable levels of endogenous ELOVL4 protein, and treated them with several fatty acid precursors. Results obtained by gas chromatography-mass spectrometry (GC-MS) show that ELOVL4 protein is indeed a component of a fatty acid elongation system that catalyzes synthesis of 28:0 and 30:0 VLC-FA and of C28-C38 VLC-PUFA, the latter being uniquely found in retina (28, 29), sperm (29, 30), and brain (31).…”

“…Also, transgenic mice expressing the mutant form of human ELOVL4 that causes STGD3 accumulate undigested phagosomes and lipofuscin-derived fluorophores in the retinal pigment epithelium (RPE), followed by RPE atrophy and subsequent photoreceptor degeneration in the central retina (4), as observed in human dominant STGD3 (1, 24), recessive Stargardt disease (25), and age-related macular degeneration (26,27). Furthermore, homozygous Elovl4 knockout and knockin neonates, which died within hours of birth, exhibited scaly wrinkled skin and a severely compromised epidermal permeability barrier, most likely resulting from a global reduction in very long chain saturated and monounsaturated fatty acids (VLC-FA, chain length Ն26:0) in both omega hydroxyl ceramides/glucosylceramides and free fatty acids (19)(20)(21)(22).…”

“…Based on the abundant expression of ELOVL4 protein in photoreceptor cells of the retina (15-17) and to lesser extents in brain, testis, and skin (17), it was first hypothesized that ELOVL4 may be involved in the biosynthetic pathway of docosahexaenoic acid (22:6n3, DHA), the most abundant PUFA in the retina and the brain (1,16,18). A series of experiments carried out in our laboratory (unpublished data) does not support this hypothesis.Recent reports establish ELOVL4 as an essential protein for growth and development, as neonatal lethality is observed in both homozygous Elovl4 knockout and knockin mouse models (19)(20)(21)(22). Heterozygous knockin animals carrying a mutant mouse gene, a condition similar to human STGD3, showed slow but significant changes in retinal morphology (23), accumulation of lipofuscin (23), and altered visual function (22, 23).…”

“…Recent reports establish ELOVL4 as an essential protein for growth and development, as neonatal lethality is observed in both homozygous Elovl4 knockout and knockin mouse models (19)(20)(21)(22). Heterozygous knockin animals carrying a mutant mouse gene, a condition similar to human STGD3, showed slow but significant changes in retinal morphology (23), accumulation of lipofuscin (23), and altered visual function (22,23).…”