Alteration of epidermal lipid composition as a result of deficiency in the magnesium transporter Nipal4.

Lipids in the stratum corneum play an important role in the formation of the skin permeability barrier. The causative gene for congenital ichthyosis, NIPAL4, encodes a Mg2+ transporter and is involved in increases in intracellular Mg2+ concentrations that depend on keratinocyte differentiation. However, the role of this increased Mg2+ concentration in skin barrier formation and its effect on the lipid composition of the stratum corneum has remained largely unknown. Therefore, in the present study, we performed a detailed analysis of epidermal lipids in Nipal4 KO mice via TLC and MS. Compared with WT mice, the Nipal4 KO mice showed compositional changes in many ceramide classes (including decreases in ω-O-acylceramides and increases in ω-hydroxy ceramides), together with increases in ω-hydroxy glucosylceramides, triglycerides, and free fatty acids and decreases in ω-O-acyl hydroxy fatty acids containing a linoleic acid. We also found increases in unusual ω-O-acylceramides containing oleic acid or palmitic acid in the KO mice. However, there was little change in levels of cholesterol or protein-bound ceramides. The TLC analysis showed that some unidentified lipids were increased, and the MS analysis showed that these were special ceramides called 1-O-acylceramides. These results suggest that elevated Mg2+ concentrations in differentiated keratinocytes affect the production of various lipids, resulting in the lipid composition necessary for skin barrier formation.

ω-O-Acylceramides but not ω-hydroxy ceramides are required for healthy lamellar phase architecture of skin barrier lipids.

Epidermal omega-O-acylceramides (ω-O-acylCers) are essential components of a competent skin barrier. These unusual sphingolipids with ultralong N-acyl chains contain linoleic acid esterified to the terminal hydroxyl of the N-acyl, the formation of which requires the transacylase activity of patatin-like phospholipase domain containing 1 (PNPLA1). In ichthyosis with dysfunctional PNPLA1, ω-O-acylCer levels are significantly decreased, and ω-hydroxylated Cers (ω-OHCers) accumulate. Here, we explore the role of the linoleate moiety in ω-O-acylCers in the assembly of the skin lipid barrier. Ultrastructural studies of skin samples from neonatal Pnpla1+/+ and Pnpla1-/- mice showed that the linoleate moiety in ω-O-acylCers is essential for lamellar pairing in lamellar bodies, as well as for stratum corneum lipid assembly into the long periodicity lamellar phase. To further study the molecular details of ω-O-acylCer deficiency on skin barrier lipid assembly, we built in vitro lipid models composed of major stratum corneum lipid subclasses containing either ω-O-acylCer (healthy skin model), ω-OHCer (Pnpla1-/- model), or combination of the two. X-ray diffraction, infrared spectroscopy, and permeability studies indicated that ω-OHCers could not substitute for ω-O-acylCers, although in favorable conditions, they form a medium lamellar phase with a 10.8 nm-repeat distance and permeability barrier properties similar to long periodicity lamellar phase. In the absence of ω-O-acylCers, skin lipids were prone to separation into two phases with diminished barrier properties. The models combining ω-OHCers with ω-O-acylCers indicated that accumulation of ω-OHCers does not prevent ω-O-acylCer-driven lamellar stacking. These data suggest that ω-O-acylCer supplementation may be a viable therapeutic option in patients with PNPLA1 deficiency.

Endogenous levels of 1-O-acylceramides increase upon acidic ceramidase deficiency and decrease due to loss of Dgat1 in a tissue-dependent manner.

Except for epidermis and liver, little is known about endogenous expression of 1-O-acylceramides (1-OACs) in mammalian tissue. Therefore, we screened several organs (brain, lung, liver, spleen, lymph nodes, heart, kidney, thymus, small intestine, and colon) from mice for the presence of 1-OACs by LC-MS2. In most organs, low levels of about 0.25-1.3 pmol 1-OACs/mg wet weight were recorded. Higher levels were detected in liver, small and large intestines, with about 4-13 pmol 1-OACs/mg wet weight. 1-OACs were esterified mainly with palmitic, stearic, or oleic acids. Esterification with saturated very long-chain fatty acids, as in epidermis, was not observed. Western-type diet induced 3-fold increased 1-OAC levels in mice livers while ceramides were unaltered. In a mouse model of Farber disease with a decrease of acid ceramidase activity, we observed a strong, up to 50-fold increase of 1-OACs in lung, thymus, and spleen. In contrast, 1-OAC levels were reduced 0.54-fold in liver. Only in lung 1-OAC levels correlated to changes in ceramide levels - indicating tissue-specific mechanisms of regulation. Glucosylceramide synthase deficiency in liver did not cause changes in 1-OAC or ceramide levels, whereas increased ceramide levels in glucosylceramide synthase-deficient small intestine caused an increase in 1-OAC levels. Deficiency of Dgat1 in mice resulted in a reduction of 1-OACs to 30% in colon, but not in small intestine and liver, going along with constant free ceramides levels. From these data, we conclude that Dgat1 as well as lysosomal lipid metabolism contribute in vivo to homeostatic 1-OAC levels in an organ-specific manner.

Exploring the role of lipids in protein modification and amyotrophic lateral sclerosis / Explorando o papel dos lipídeos na modificação de proteínas e esclerose lateral amiotrófica

Lipids are a diverse and ubiquitous group of compounds, which have several biological functions such as structural components of cell membranes, energy storage, and participation in signaling pathways. Free radicals or reactive oxygen species could attack polyunsaturated fatty acid esterified to phospholipids generating oxidized products. Once oxidized, lipids are able to modify amino acids residues in proteins leading to modulation signaling pathways and cellular redox balance. Furthermore, alteration of lipid homeostasis is also linked to development and progression of neurodegenerative diseases. The purposes of this study were (i) to investigate the role of lipids in protein aggregation, (ii) to investigate the plasma lipidome of an ALS rat model (SOD1G93A rats), and (iii) to investigate the effect of high-fat diet in plasma lipidome of an ALS rat model. In chapters 1 and 2, the interaction between cytochrome c (cytc) and cardiolipin hydroperoxide (CLOOH), as well as cholesterol hydroperoxide (ChOOH) promoted protein aggregation. Mass spectrometry analysis of tryptic peptides from CLOOH-containing reaction revealed K72 and H26 consistently modified by 4- hydroxynonenal (4-HNE). Further, adduction of K27, K73 and K88 were detected with 4- oxynonenal (4-ONE). For the first time, we characterized the dityrosine cross-linked peptides at Y48-Y74, Y48-97 and Y74-Y97 in oligomeric cytc. Similarly, ChOOH-containing reaction showed dityrosine cross-linked peptides at Y48-Y48, Y48-Y74 and Y48-Y97 in dimeric cytc. In accordance to previous studies, the proposed mechanism under covalent protein oligomerization mediated by lipid hydroperoxide could be related to modification of lysine and tyrosine residues. In chapter 3, we characterized the lipid composition of blood plasma in amyotrophic lateral sclerosis (ALS), since dysregulation of lipid metabolism is increasingly associated with neuropathology. Using untargeted lipidomics approach based on liquid chromatography coupled to mass spectrometry, we found main alterations in triglycerides, phospholipids and sphingolipids in symptomatic ALS rats relative to controls. Additionally, for the first time we reported acylceramides species in the plasma. In order to investigate the source of these lipid alterations, we analyzed the lipid content of fractioned lipoproteins. Triglycerides and phospholipids were found in very low-density lipoprotein (VLDL), while acylceramides and hexosylceramides were found enriched in high-density lipoprotein (HDL). In chapter 4, high-fat diet containing lard or high-fish oil as much as 60% of total lipids has both the largest change on plasma lipid composition. Overall survival was not statistically different when compared to control diet. Increased levels of acylceramides, hexosylceramides and acylcarnitines were observed in ALS rats fed a control diet or high-fat diet in comparison to WT controls. Importantly, untargeted lipidomic analysis of blood plasma highlighted acylceramide d18:1/24:1+20:4 as potential biomarkers of ALS progression. Thus, our lipidomic analysis provides a novel insight into the molecular level event driving molecular dysregulation in ALS. Additional research is needed to determine the effect of plasma lipid alteration on motor neuron process and energetic metabolism. Collectively, our findings reinforce the idea that lipids play a relevant role in modulating cellular processes linked to protein aggregation and neurodegeneration

Os lipídeos são moléculas que possuem várias funções biológicas importantes, atuando como componente de membranas celulares, servindo com fonte de reserva de energia e participando de vias de sinalização. Os ácidos graxos poli-insaturados esterificados aos fosfolipídeos, por exemplo, são potenciais alvos para o ataque de radicais livres gerando produtos oxidados que são capazes de modificar resíduos de aminoácidos em proteínas levando a modulação das vias de sinalização e balanço redox. Por outro lado, alteração na homeostase do metabolismo dos lipídeos está relacionada ao desenvolvimento e progressão de doenças neurodegenerativas. Tendo em vista a importância dos lipídeos nos processos biológicos, os objetivos desse estudo foram (i) investigar o papel dos lipídeos na agregação proteica (capítulo 1 e 2), (ii) investigar as alterações na composição lipídica do plasma de rato modelo SOD1G93A de esclerose lateral amiotrófica (ELA) (capítulo 3) e (iii) investigar o efeito da suplementação de dietas hiperlipídicas na composição lipídica do plasma de rato modelo SOD1G93A (capítulo 4). No capítulo 1 e 2, a interação do citocromo c (citc) com hidroperóxido de cardiolipina (CLOOH) e hidroperóxido de colesterol (ChOOH) promove a agregação covalente do citc. Análise por nLC-MS/MS dos peptídeos digeridos identificou resíduos de lisina (K72) e histidina (H26) modificado por 4-hidroxininenal (4-HNE), enquanto os resíduos K27, K73 e K88 foram modificados por 4-oxinonenal (4-ONE). Pela primeira vez, nós caracterizamos ditirosinas (Y48-Y74, Y48-97 e Y74-Y97) na reação do citc com CLOOH. Também foram caracterizadas ditirosinas envolvendo os resíduos Y48-Y48, Y48-Y74 e Y48-Y97 na reação com ChOOH. Esses resultados corroboram com estudos anteriores que sugerem um mecanismo de agregação proteica envolvendo a perda da carga positiva de lisina e formação de ditirosina pela combinação de radicais de tirosil. No capítulo 3, a análise da composição lipídica do plasma de ratos SOD1G93A utilizando LC-MS/MS revelou alterações significativas na composição de triglicérides, glicerofosfolipídeos e esfingolipídeos em ratos sintomáticos comparado com os assintomáticos. É importante destacar que pela primeira vez acilceramidas foram identificadas em plasma de rato modelo para ALS. Análise da composição lipídica de lipoproteínas isoladas, maior fonte de lipídeos circulantes no plasma, mostraram alterações de triglicérides e glicerofosfolipídeos em VLDL. As acilceramidas e as hexosilceramidas, por sua vez, foram encontradas em maior abundância em HDL. No capítulo 4, a suplementação com dietas hiperlipídicas (rica em banha de porco e óleo de peixe) alterou significativamente o perfil lipídico do plasma em relação a doença. Contudo, não foi observado aumento significativo na sobrevida dos ratos ALS comparado com dieta controle. Independente da dieta, a concentração plasmática de acilcarnitina, hexosilceramidas e acilceramidas foram significativamente aumentadas em ratos ALS comparado com WT. A análise do perfil lipídico do plasma mostrou que a acilceramida d18:1/24:1+20:4 pode ser um potencial marcador de progressão da ALS. Dessa forma, os resultados mostrados fornecem uma visão enriquecedora sobre o evento a nível molecular que conduz a desregulação lipídica na ELA. Coletivamente, nossos resultados reforçam a importância dos lipídeos na modulação dos processos celulares ligados a agregação de proteínas e na neurodegeneração

Seasonal changes in epidermal ceramides are linked to impaired barrier function in acne patients.

Acne skin demonstrates increased transepidermal water loss (TEWL) compared with healthy skin, which may be due, in part, to altered ceramide (CER) levels. We analysed ceramides in the stratum corneum of healthy and acne skin, and studied seasonal variation over the course of a year. Using ultraperformance liquid chromatography with electrospray ionisation and tandem mass spectrometry (UPLC/ESI-MS/MS), we identified 283 ceramides. Acne-affected skin demonstrated overall lower levels of ceramides, with notable reductions in CER[NH] and CER[AH] ceramides, as well as the acylceramides CER[EOS] and CER[EOH]; these differences were more apparent in the winter months. Lower ceramide levels reflected an increase in TEWL in acne, compared with healthy skin, which partly resolves in the summer. Individual ceramide species with 18-carbon 6-hydroxysphingosine (H) bases (including CER[N(24)H(18)], CER[N(26)H(18)], CER[A(24)H(18)], CER[A(26)H(18)]) were significantly reduced in acne skin, suggesting that CER[NH] and CER[AH] species may be particularly important in a healthy skin barrier.

Ceramide synthesis in the epidermis.

The epidermis and in particular its outermost layer the stratum corneum provides terrestrial vertebrates with a pivotal defensive barrier against water loss, xenobiotics and harmful pathogens. A vital demand for this epidermal permeability barrier is the lipid-enriched lamellar matrix that embeds the enucleated corneocytes. Ceramides are the major components of these highly ordered intercellular lamellar structures, in which linoleic acid- and protein-esterified ceramides are crucial for structuring and maintaining skin barrier integrity. In this review, we describe the fascinating diversity of epidermal ceramides including 1-O-acylceramides. We focus on epidermal ceramide biosynthesis emphasizing its metabolic and topological requirements and discuss enzymes that may be involved in α- and ω-hydroxylation. Finally, we turn to epidermal ceramide regulation, highlighting transcription factors and liposensors recently described to play crucial roles in modulating skin lipid metabolism and epidermal barrier homeostasis. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier.