Essential role of the cytochrome P450 CYP4F22 in the production of acylceramide, the key lipid for skin permeability barrier formation

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Ceramide and complex sphingolipids regulate important cellular functions including cell growth, apoptosis, and signaling. Dysregulation of sphingolipid metabolism leads to pathological consequences such as sphingolipidoses and insulin resistance. Ceramides in mammals vary greatly in their acyl-chain composition: six different ceramide synthase isozymes (CERS1-6) that exhibit distinct substrate specificity and tissue distribution account for this diversity. In the present study, we demonstrated that CERS2-6 were phosphorylated at the cytoplasmic C-terminal regions. Most of the phosphorylated residues conformed to a consensus motif for phosphorylation by casein kinase 2 (CK2), and treatment of cells with the CK2-specific inhibitor CX-4945 lowered the phosphorylation levels of CERS2, -4, -5, and -6. Phosphorylation of CERS2 was especially important for its catalytic activity, acting mainly by increasing its V max value. Phosphorylation modestly increased the catalytic activities of CERS4 and -5 and mildly increased those of CERS3 and -6. Dephosphorylation of endogenous ceramide synthases in the mouse brain led to severely reduced activity toward the Cers2 substrates C22:0/C24:0-CoAs and modestly reduced activity toward the Cers5/6 substrate C16:0-CoA. These results suggest that the phosphorylation of ceramide synthases may be a key regulatory point in the control of the distribution and levels of sphingolipids of various acyl-chain lengths.Sphingolipids, one of the major lipid constituents of eukaryotic membranes, mediate a number of cellular and physiological functions such as cell growth, apoptosis, immune responses, and the epidermal permeability barrier, whereas their abnormal metabolism is involved in diseases such as sphingolipidoses, neural disorders, and diabetes (1-7). Ceramides are located in the hub of sphingolipid metabolism. Ceramides are precursors for complex sphingolipids, whereas their hydrolysis releases a sphingoid long-chain base and a fatty acid (FA).2 The released long-chain base can then be recycled to synthesize new ceramide, or metabolized further into other lipids such as sphingosine 1-phosphate (8 -10). Ceramide synthases catalyze the formation of an amide bond between the long-chain base and the FA in the endoplasmic reticulum. In most tissues, the chain lengths of the FA moieties of ceramides are C16 -

Section: Methodsmentioning

confidence: 99%

“…were analyzed by reversed-phase LC/MS using ultra-performance liquid chromatography coupled with electrospray ionization tandem triple quadrupole MS (Xevo TQ-S, Waters, Milford, MA) as described previously (29). Each ceramide species was detected by multiple reaction monitoring by selecting the m/z…”

Section: Lipid Analysis Using Lc/ms-ceramidesmentioning

confidence: 99%

Enzyme Activities of the Ceramide Synthases CERS2–6 Are Regulated by Phosphorylation in the C-terminal Region

Sassa

Hirayama

Kihara

2016

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“…A variety of ceramide species exist in the epidermis. Among them, acylceramides are a class of epidermis-specific ceramides that play an essential role in skin barrier formation (7,8). Ceramides are normally composed of a long-chain base (LCB) and a FA (9).…”

Section: Sjögren-larsson Syndrome (Sls)mentioning

confidence: 99%

“…LC/MS/MS analyses were performed as described previously (8). Lipids were resolved by ultra-performance LC on a reversephase column (ACQUITY UPLC BEH C18 column, length 150 mm; Waters, Milford, MA) coupled with electrospray ionization tandem triple quadrupole MS (Xevo TQ-S, Waters) and detected by multiple reaction monitoring by selecting the specific m/z at quadrupole mass filters Q1 and Q3 (Tables 2-4).…”

Section: Generation Of Aldh3a2mentioning

confidence: 99%

Disruption of the Sjögren-Larsson Syndrome Gene Aldh3a2 in Mice Increases Keratinocyte Growth and Retards Skin Barrier Recovery

Naganuma

Takagi

Kanetake

et al. 2016

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The fatty aldehyde dehydrogenase (FALDH) ALDH3A2 is the causative gene of Sjögren Larsson syndrome (SLS Sjögren-Larsson syndrome (SLS)2 is a hereditary neurocutaneous disorder caused by mutations in the fatty aldehyde dehydrogenase (FALDH) gene, ALDH3A2. The major symptoms of SLS are mental retardation, spastic di-or tetraplegia, and ichthyosis, with crystalline macular dystrophy sometimes comorbid (1). ALDH3A2 catalyzes the conversion of fatty aldehydes with medium-chain (MC) to very-long-chain fatty acids (FA) (MC, C5-C10; long-chain (LC), C11-C20; and very-longchain, ՆC21), with the most preferred substrates being C16 and C18 aldehydes (2, 3). To date, more than 70 mutations have been found in the ALDH3A2 gene of SLS patients, and most of them cause Ͼ90% reduction in enzyme activity (4). Because aldehyde molecules are reactive and toxic in general, it is considered that accumulated fatty aldehydes cause the SLS pathology by reacting with certain important proteins in the nervous system and epidermis and compromising their functions. Furthermore, the literature lacks a detailed description of the characteristics of Aldh3a2 knock-out mice.The skin symptom ichthyosis is characterized by dry, thickened, and scaly skin, often likened to fish scales, and is caused by a skin permeability barrier defect related to multilayered lipids (lipid lamellae) in the epidermis. The epidermis is composed of four cell layers, the stratum basale, stratum spinosum, stratum granulosum, and the stratum corneum, the last of which is the site of these lipid lamellae, and accordingly has the most important role in skin barrier formation (5, 6). Keratinocytes proliferate in the stratum basale and migrate outward, differentiating into cell layer-specific cell types. The major lipid components of lipid lamellae are ceramides, cholesterol, and FAs, with ceramides being the most abundant (5, 6). A variety of ceramide species exist in the epidermis. Among them, acylceramides are a class of epidermis-specific ceramides that play an essential role in skin barrier formation (7,8). Ceramides are normally composed of a long-chain base (LCB) and a FA (9). However, acylceramides contain an additional hydrophobic chain (linoleic acid), which is esterified with the hydroxylated -carbon of the FA. In the epidermis of SLS patients, some ceramide species, including the acylceramide EOS (a combination of an esterified -hydroxy FA and the LCB sphingosine), are greatly reduced (10).Several metabolic pathways generate the substrates of ALDH3A2, fatty aldehydes. These include metabolic pathways of leukotriene B 4 , diet-derived phytol, plasmalogens, and fatty alcohols (11)(12)(13)(14)(15). Furthermore, we recently revealed that metabolism of LCBs also generates fatty aldehydes, i.e. hexadecanal (C16:0 aldehyde) from dihydrosphingosine (DHS) and

“…Although these enzymes often exhibit overlapping substrate specificities, genetic association studies link the -hydroxylase CYP4V2 to the Bietti's crystalline dystrophy, which is characterized by ocular lipid deposits (7,8), suggesting a key role for CYP4V2 in the removal of excess lipids in ocular tissues. Furthermore, CYP4F22 genetic variants are associated with lamellar ichthyosis, which reflects deficiencies in the water permeability barrier of skin (9). This is likely to reflect the capacity of P450 4F22 to catalyze the -hydroxylation of very long chain fatty acids (C28 or greater).…”

mentioning

confidence: 99%

The Crystal Structure of Cytochrome P450 4B1 (CYP4B1) Monooxygenase Complexed with Octane Discloses Several Structural Adaptations for ω-Hydroxylation

Hsu

Baer

Rettie

et al. 2017

Edited by Ruma BanerjeeP450 family 4 fatty acid -hydroxylases preferentially oxygenate primary C-H bonds over adjacent, energetically favored secondary C-H bonds, but the mechanism explaining this intriguing preference is unclear. To this end, the structure of rabbit P450 4B1 complexed with its substrate octane was determined by X-ray crystallography to define features of the active site that contribute to a preference for -hydroxylation. The structure indicated that octane is bound in a narrow active-site cavity that limits access of the secondary C-H bond to the reactive intermediate. A highly conserved sequence motif on helix I contributes to positioning the terminal carbon of octane for -hydroxylation. Glu-310 of this motif auto-catalytically forms an ester bond with the heme 5-methyl, and the immobilized Glu-310 contributes to substrate positioning. The preference for -hydroxylation was decreased in an E310A mutant having a shorter side chain, but the overall rates of metabolism were retained. E310D and E310Q substitutions having longer side chains exhibit lower overall rates, likely due to higher conformational entropy for these residues, but they retained high preferences for octane -hydroxylation. Sequence comparisons indicated that active-site residues constraining octane for -hydroxylation are conserved in family 4 P450s. Moreover, the heme 7-propionate is positioned in the active site and provides additional restraints on substrate binding. In conclusion, P450 4B1 exhibits structural adaptations for -hydroxylation that include changes in the conformation of the heme and changes in a highly conserved helix I motif that is associated with selective oxygenation of unactivated primary C-H bonds.Cytochrome P450 family 4 fatty acid -hydroxylases are heme-containing monooxygenases that provide pathways for the reduction of potentially toxic non-esterified fatty acids and for the elimination of excess nutritive and non-nutritive lipids by catalyzing the addition of oxygen to a C-H bond of the terminal -carbon of fatty acids (1, 2). The resulting -alcohols are generally oxidized further to produce dicarboxylic acids, but they also may be transformed to glucuronides or esterified to glycerolipids. Urinary dicarboxylic fatty acids are elevated in humans by fasting or in uncontrolled diabetes, which are conditions where adipocyte lipolysis increases the availability of non-esterified fatty acids to fuel metabolism (3). It is estimated that roughly 15% of fatty acids undergo -hydroxylation during peak periods of fatty acid catabolism (4), whereas this fraction is much smaller under conditions where concentrations of nonesterified fatty acids are low (5). Collectively, these enzymes provide pathways for the metabolic clearance of branched chain fatty acids, eicosanoids, and xenobiotic substrates such as dietary phytanic acid, drugs, toxins, and vitamins E and K (1, 2, 6).Similar to other P450 2 gene families encoding multipurpose enzymes for the elimination of xenobiotic compounds, family 4 exhibits genetic diversi...