Reduced muscle strength in ether lipid-deficient mice is accompanied by altered development and function of the neuromuscular junction

Ether-lipids and cellular signaling: A differential role of alkyl- and alkenyl-ether-lipids?

Ether-lipids (EL) are specific lipids bearing a characteristic sn-1 ether bond. Depending on the ether or vinyl-ether nature of this bond, they are present as alkyl- or alkenyl-EL, respectively. Among EL, alkenyl-EL, also referred as plasmalogens in the literature, attract most of the scientific interest as they are the predominant EL species in eukaryotic cells, thus less is known about alkyl-EL. EL have been implicated in various signaling pathways and alterations in their quantity are frequently observed in pathologies such as neurodegenerative and cardiovascular diseases or cancer. However, it remains unknown whether both alkyl- and alkenyl-EL play the same roles in these processes. This review summarizes the roles and mechanisms of action of EL in cellular signaling and tries to discriminate between alkyl- and alkenyl-EL. We also focus on the involvement of EL-mediated alterations of cellular signaling in diseases and discuss the potential interest for EL in therapy.

Determination and Comparison of Soybean Lecithin and Bovine Brain Plasmalogens Effects in Healthy Male Wistar Rats

The aim of this study was to investigate the effects of soybean lecithin and plasmalogens concentrating on a variety of physiological tests and biochemical analyses in healthy Wistar rats. For six weeks, male Wistar rats were given a standard diet that included plasmalogens or soybean lecithin. We measured anxiety levels, overall exploratory activity, short- and long-term memory, cognitive abilities, and grip strength. Lecithin increased significantly anxiety and enhanced memory and cognitive functions. Plasmalogens significantly improved appetite and increased grip strength. When compared to plasmalogens, lecithin significantly raised HDL levels while lowering LDL levels. The plasmalogens group showed a significant increase in the C16:0DMA/C16:0 ratio, which led us to assume that plasmalogen consumption could increase their synthesis in neural tissue. The study's findings imply that, despite their various modes of action, soy lecithin and plasmalogens may both be significant nutritional components for enhancing cognitive functions.

Overlapping and Distinct Features of Cardiac Pathology in Inherited Human and Murine Ether Lipid Deficiency

Inherited deficiency in ether lipids, a subgroup of glycerophospholipids with unique biochemical and biophysical properties, evokes severe symptoms in humans resulting in a multi-organ syndrome. Mouse models with defects in ether lipid biosynthesis have widely been used to understand the pathophysiology of human disease and to study the roles of ether lipids in various cell types and tissues. However, little is known about the function of these lipids in cardiac tissue. Previous studies included case reports of cardiac defects in ether-lipid-deficient patients, but a systematic analysis of the impact of ether lipid deficiency on the mammalian heart is still missing. Here, we utilize a mouse model of complete ether lipid deficiency (Gnpat KO) to accomplish this task. Similar to a subgroup of human patients with rhizomelic chondrodysplasia punctata (RCDP), a fraction of Gnpat KO fetuses present with defects in ventricular septation, presumably evoked by a developmental delay. We did not detect any signs of cardiomyopathy but identified increased left ventricular end-systolic and end-diastolic pressure in middle-aged ether-lipid-deficient mice. By comprehensive electrocardiographic characterization, we consistently found reduced ventricular conduction velocity, as indicated by a prolonged QRS complex, as well as increased QRS and QT dispersion in the Gnpat KO group. Furthermore, a shift of the Wenckebach point to longer cycle lengths indicated depressed atrioventricular nodal function. To complement our findings in mice, we analyzed medical records and performed electrocardiography in ether-lipid-deficient human patients, which, in contrast to the murine phenotype, indicated a trend towards shortened QT intervals. Taken together, our findings demonstrate that the cardiac phenotype upon ether lipid deficiency is highly heterogeneous, and although the manifestations in the mouse model only partially match the abnormalities in human patients, the results add to our understanding of the physiological role of ether lipids and emphasize their importance for proper cardiac development and function.

The physiological functions of human peroxisomes

Peroxisomes are subcellular organelles that play a central role in human physiology by catalyzing a range of unique metabolic functions. The importance of peroxisomes for human health is exemplified by the existence of a group of usually severe diseases caused by an impairment in one or more peroxisomal functions. Among others these include the Zellweger spectrum disorders, X-linked adrenoleukodystrophy, and Refsum disease. To fulfill their role in metabolism, peroxisomes require continued interaction with other subcellular organelles including lipid droplets, lysosomes, the endoplasmic reticulum, and mitochondria. In recent years it has become clear that the metabolic alliance between peroxisomes and other organelles requires the active participation of tethering proteins to bring the organelles physically closer together, thereby achieving efficient transfer of metabolites. This review intends to describe the current state of knowledge about the metabolic role of peroxisomes in humans, with particular emphasis on the metabolic partnership between peroxisomes and other organelles and the consequences of genetic defects in these processes. We also describe the biogenesis of peroxisomes and the consequences of the multiple genetic defects therein. In addition, we discuss the functional role of peroxisomes in different organs and tissues and include relevant information derived from model systems, notably peroxisomal mouse models. Finally, we pay particular attention to a hitherto underrated role of peroxisomes in viral infections.

A Pex7 Deficient Mouse Series Correlates Biochemical and Neurobehavioral Markers to Genotype Severity—Implications for the Disease Spectrum of Rhizomelic Chondrodysplasia Punctata Type 1

Rhizomelic chondrodysplasia punctata type 1 (RCDP1) is a peroxisome biogenesis disorder caused by defects in PEX7 leading to impairment in plasmalogen (Pls) biosynthesis and phytanic acid (PA) oxidation. Pls deficiency is the main pathogenic factor that determines the severity of RCDP. Severe (classic) RCDP patients have negligible Pls levels, congenital cataracts, skeletal dysplasia, growth and neurodevelopmental deficits, and cerebral hypomyelination and cerebellar atrophy on brain MRI. Individuals with milder or nonclassic RCDP have higher Pls levels, better growth and cognitive outcomes. To better understand the pathophysiology of RCDP disorders, we generated an allelic series of Pex7 mice either homozygous for the hypomorphic allele, compound heterozygous for the hypomorphic and null alleles or homozygous for the null allele. Pex7 transcript and protein were almost undetectable in the hypomorphic model, and negligible in the compound heterozygous and null mice. Pex7 deficient mice showed a graded reduction in Pls and increases in C26:0-LPC and PA in plasma and brain according to genotype. Neuropathological evaluation showed significant loss of cerebellar Purkinje cells over time and a decrease in brain myelin basic protein (MBP) content in Pex7 deficient models, with more severe effects correlating with Pex7 genotype. All Pex7 deficient mice exhibited a hyperactive behavior in the open field environment. Brain neurotransmitters analysis of Pex7 deficient mice showed a significant reduction in levels of dopamine, norepinephrine, serotonin and GABA. Also, a significant correlation was found between brain neurotransmitter levels, the hyperactivity phenotype, Pls level and the severity of Pex7 genotype. In conclusion, our study showed evidence of a genotype-phenotype correlation between the severity of Pex7 deficiency and several clinical and neurobiochemical phenotypes in RCDP1 mouse models. We propose that PA accumulation may underlie the cerebellar atrophy seen in older RCDP1 patients, as even relatively low tissue levels were strongly associated with Purkinje cells loss over time in the murine models. Also, our data demonstrate the interrelation between Pls, brain neurotransmitter deficiencies and the neurobehavioral phenotype, which could be further used as a valuable clinical endpoint for therapeutic interventions. Finally, these models show that incremental increases in Pex7 levels result in dramatic improvements in phenotype.

Targeted Plasmalogen Supplementation: Effects on Blood Plasmalogens, Oxidative Stress Biomarkers, Cognition, and Mobility in Cognitively Impaired Persons

Plasmalogens are a specific type of glycerophospholipid found in especially high levels in neuronal membranes. Decreased blood and brain levels of docosahexaenoic acid (DHA) containing plasmalogens are associated with decreased cognition and neuromuscular function in humans. Administration of 1-O-alkyl-2-acylglycerol (AAG) plasmalogen precursors containing DHA at the sn-2 position dose-dependently increase blood DHA plasmalogens and are neuroprotective in animal models of neurodegeneration at doses between 10 and 50 mg/kg. We conducted an investigational clinical trial in 22 cognitively impaired persons to evaluate the effects of an escalating oral dosing regimen of DHA-AAG from 900 to 3,600 mg/day over a 4-month period on blood serum plasmalogen and non-plasmalogen phospholipids and oxidative stress biomarkers. Safety, tolerability and therapeutic effects on cognition and mobility were also evaluated. DHA plasmalogen levels increased with increasing dose and remained significantly elevated at all treatment doses and durations. DHA plasmalogen levels were positively associated with catalase activity and negatively associated with malondialdehyde (MDA) levels. DHA-AAG supplementation normalized catalase activity in persons with low baseline catalase activity, normalized MDA levels in persons with high baseline MDA levels, and normalized superoxide dismutase activity in persons with high baseline SOD activity. Cognition improved in nine participants, was unchanged in nine, and declined in four. Mobility improved in twelve, was unchanged in five and declined in four participants. Changes in cognition and mobility were statistically significant versus a random outcome. Baseline DHA-plasmalogen levels were not predictive of clinical response. DHA-AAG was well tolerated at all dosages and no adverse reactions were observed.

Pharmacokinetics, Mass Balance, Excretion, and Tissue Distribution of Plasmalogen Precursor PPI-1011

PPI-1011 is a synthetic plasmalogen precursor in development as a treatment for multiple plasmalogen-deficiency disorders. Previous work has demonstrated the ability of PPI-1011 to augment plasmalogens and its effects in vitro and in vivo, however, the precise uptake and distribution across tissues in vivo has not been investigated. The purpose of this study was to evaluate the pharmacokinetics, mass balance, and excretion of [¹⁴C]PPI-1011 following a single oral administration at 100 mg/kg in Sprague-Dawley rats. Further tissue distribution was examined using quantitative whole-body autoradiography after both single and repeat daily doses at 100 mg/kg/day. Non-compartmental analysis showed that following a single dose, PPI-1011 exhibited peak levels between 6 and 12 h but also a long half-life with mean t_1/2 of 40 h. Mass balance showed that over 50% of the compound-associated radioactivity was absorbed by the body, while approximately 40% was excreted in the feces, 2.5% in the urine, and 10% in expired air within the first 24 h. Quantitative whole-body autoradiography following a single dose showed uptake to nearly all tissues, with the greatest initial uptake in the intestines, liver, and adipose tissue, which decreased time-dependently throughout 168 h post-dose. Following 15 consecutive daily doses, uptake was significantly higher across the entire body at 24 h compared to single dose and remained high out to 96 h where 75% of the initially-absorbed compound-associated radioactivity was still present. The adipose tissue remained particularly high, suggesting a possible reserve of either plasmalogens or alkyl diacylglycerols that the body can pull from for plasmalogen biosynthesis. Uptake to the brain was also definitively confirmed, proving PPI-1011’s ability to cross the blood-brain barrier. In conclusion, our results suggest that oral administration of PPI-1011 results in high uptake across the body, and that repeated dosing over time represents a viable therapeutic strategy for treating plasmalogen deficiencies.

Studies on the Manner of Collateral Regeneration From Nerve Stem to Motor Endplate

Despite recent evidence suggesting that nerve transfer techniques help improve clinical outcomes, the underlying manner by which collateral-regenerated nerve enters skeletal muscles to restore an organized pattern of the neuromuscular junction (NMJ) is unclear. To construct the animal models of collateral regeneration, the proximal peroneal nerve was fixed to the distal tibial nerve stump. Three months after surgery, the spatial distribution of motor endplates (MEPs) and corresponding in-muscle nerve branches in long flexor digitorum muscles were observed with tissue optical clearing combined with light-sheet microscopy in transgenic fluorescent mice. The results showed that the number of fibers in the proximal donor peroneal nerve was 415 ± 11, while regenerated nerve fibers in the distal tibial stump were 781 ± 43, which indicates a collateral regeneration ratio of 1.88. The spatial distribution of MEPs was restored to an organized pattern of the lamella, and the corresponding in-muscle nerve branches reverted to the normal manner such as after collateral regeneration. Beyond this, the numbers of MEPs dominated by the single distal nerve fiber were 25.58 ± 0.50 and 26.42 ± 0.94, respectively (n = 6, p > 0.05, collateral regeneration group vs. normal group). However, the numbers of distal-regenerated nerve fibers were less than those in normal control groups (781 ± 43 vs. 914 ± 55, n = 6, p < 0.05), and the number and perforations of MEPs were lower than those in normal control groups as such. In summary, this is the first study to show the manner of collateral regeneration of the peripheral nerve that the smaller proximal donor nerve can sprout more axonal buds to connect distal larger nerves and finally restore to an organized pattern of lamella dominated by corresponding in-muscle nerve branches.

Identification of Lipid Heterogeneity and Diversity in the Developing Human Brain

The lipidome is currently understudied but fundamental to life. Within the brain, little is known about cell-type lipid heterogeneity, and even less is known about cell-to-cell lipid diversity because it is difficult to study the lipids within individual cells. Here, we used single-cell mass spectrometry-based protocols to profile the lipidomes of 154 910 single cells across ten individuals consisting of five developmental ages and five brain regions, resulting in a unique lipid atlas available via a web browser of the developing human brain. From these data, we identify differentially expressed lipids across brain structures, cortical areas, and developmental ages. We inferred lipid profiles of several major cell types from this data set and additionally detected putative cell-type specific lipids. This data set will enable further interrogation of the developing human brain lipidome.

Differences in phosphatidylcholine profiles and identification of characteristic phosphatidylcholine molecules in meat animal species and meat cut locations

Phosphatidylcholine (PC) is an essential component of the plasma membrane. Its profile varies with species and tissues. However, the PC profiles in meat have not been explored in depth. This study aimed to investigate the differences in PC profiles between various meat animal species and meat cut sites, along with the identification of characteristic PC molecules. The results demonstrated that the PC profiles of chicken meat differed from those of other species. Significant differences were also observed between the PC profiles of pork meat and the meat obtained from other species. The amount of PCs containing ether bonds was high in pork meat. PCs containing an odd number of carbon atoms were characteristic of beef and lamb meats. Furthermore, PC profiles differed based on the muscle location in chicken and pork. These results suggest that the PC profiles of skeletal muscles are indicators of animal species and muscle location.

Plasmalogen-Based Liquid Crystalline Multiphase Structures Involving Docosapentaenoyl Derivatives Inspired by Biological Cubic Membranes

Structural properties of plasmenyl-glycerophospholipids (plasmalogens) have been scarcely studied for plasmalogens with long polyunsaturated fatty acid (PUFA) chains, despite of their significance for the organization and functions of the cellular membranes. Elaboration of supramolecular assemblies involving PUFA-chain plasmalogens in nanostructured mixtures with lyotropic lipids may accelerate the development of nanomedicines for certain severe pathologies (e.g., peroxisomal disorders, cardiometabolic impairments, and neurodegenerative Alzheimer's and Parkinson's diseases). Here, we investigate the spontaneous self-assembly of bioinspired, custom-produced docosapentaenoyl (DPA) plasmenyl (ether) and ester phospholipids in aqueous environment (pH 7) by synchrotron small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM). A coexistence of a liquid crystalline primitive cubic Im3m phase and an inverted hexagonal (H_II) phase is observed for the DPA-ethanolamine plasmalogen (C16:1p-22:5n6 PE) derivative. A double-diamond cubic Pn3m phase is formed in mixed assemblies of the phosphoethanolamine plasmalogen (C16:1p-22:5n6 PE) and monoolein (MO), whereas a coexistence of cubic and lamellar liquid crystalline phases is established for the DPA-plasmenyl phosphocholine (C16:1p-22:5n6 PC)/MO mixture at ambient temperature. The DPA-diacyl phosphoinositol (22:5n6-22:5n6 PI) ester lipid displays a propensity for a lamellar phase formation. Double membrane vesicles and multilamellar onion topologies with inhomogeneous distribution of interfacial curvature are formed upon incorporation of the phosphoethanolamine plasmalogen (C16:1p-22:5n6 PE) into dioleoylphosphocholine (DOPC) bilayers. Nanoparticulate formulations of plasmalogen-loaded cubosomes, hexosomes, and various multiphase cubosome- and hexosome-derived architectures and mixed type nano-objects (e.g., oil droplet-embedding vesicles or core-shell particles with soft corona) are produced with PUFA-chain phospholipids and lipophilic antioxidant-containing membrane compositions that are characterized by synchrotron SAXS and cryo-TEM imaging. The obtained multiphase nanostructures reflect the changes in the membrane curvature induced by the inclusion of DPA-based PE and PC plasmalogens, as well as DPA-PI ester derivative, and open new opportunities for exploration of these bioinspired nanoassemblies.

Nestlet Shredding and Nest Building Tests to Assess Features of Psychiatric Disorders in Mice

Mimicking the various facets of human psychiatric and neurodevelopmental disorders in animal models is a challenging task. Nevertheless, mice have emerged as a widely used model system to study pathophysiology and treatment strategies for these diseases. However, the corresponding behavioral tests are often elaborate and require extensive experience in behavioral testing. Here, we present protocols for two simple assays, nest building and nestlet shredding, that can serve as a starting point for the behavioral phenotyping of mouse models with (potential) features of psychiatric disorders. Both tests have been reported previously and we extend prior descriptions by including adaptations and refinements derived from our practical experience, like the use of the home cage instead of a fresh cage for nestlet shredding. Summarized, we provide ready-to-use protocols for two behavioral assays that allow the generation of robust data with minimal time and cost expenditure and enable an initial assessment of features of psychiatric or neurodevelopmental disorders in mouse models of these diseases.

Oral batyl alcohol supplementation rescues decreased cardiac conduction in ether phospholipid-deficient mice

Plasmalogens (Pls) are a class of membrane phospholipids which serve a number of essential biological functions. Deficiency of Pls is associated with common disorders such as Alzheimer's disease or ischemic heart disease. A complete lack of Pls due to genetically determined defective biosynthesis gives rise to rhizomelic chondrodysplasia punctata (RCDP), characterized by a number of severe disabling pathologic features and death in early childhood. Frequent cardiac manifestations of RCDP include septal defects, mitral valve prolapse, and patent ductus arteriosus. In a mouse model of RCDP, reduced nerve conduction velocity was partially rescued by dietary oral supplementation of the Pls precursor batyl alcohol (BA). Here, we examine the impact of Pls deficiency on cardiac impulse conduction in a similar mouse model (Gnpat KO). In-vivo electrocardiographic recordings showed that the duration of the QRS complex was significantly longer in Gnpat KO mice than in age- and sex-matched wild-type animals, indicative of reduced cardiac conduction velocity. Oral supplementation of BA for 2 months resulted in normalization of cardiac Pls levels and of the QRS duration in Gnpat KO mice but not in untreated animals. BA treatment had no effect on the QRS duration in age-matched wild-type mice. These data suggest that Pls deficiency is associated with increased ventricular conduction time which can be rescued by oral BA supplementation.

Plasmalogens, platelet-activating factor and beyond - Ether lipids in signaling and neurodegeneration

Glycerol-based ether lipids including ether phospholipids form a specialized branch of lipids that in mammals require peroxisomes for their biosynthesis. They are major components of biological membranes and one particular subgroup, the plasmalogens, is widely regarded as a cellular antioxidant. Their vast potential to influence signal transduction pathways is less well known. Here, we summarize the literature showing associations with essential signaling cascades for a wide variety of ether lipids, including platelet-activating factor, alkylglycerols, ether-linked lysophosphatidic acid and plasmalogen-derived polyunsaturated fatty acids. The available experimental evidence demonstrates links to several common players like protein kinase C, peroxisome proliferator-activated receptors or mitogen-activated protein kinases. Furthermore, ether lipid levels have repeatedly been connected to some of the most abundant neurological diseases, particularly Alzheimer’s disease and more recently also neurodevelopmental disorders like autism. Thus, we critically discuss the potential role of these compounds in the etiology and pathophysiology of these diseases with an emphasis on signaling processes. Finally, we review the emerging interest in plasmalogens as treatment target in neurological diseases, assessing available data and highlighting future perspectives. Although many aspects of ether lipid involvement in cellular signaling identified in vitro still have to be confirmed in vivo, the compiled data show many intriguing properties and contributions of these lipids to health and disease that will trigger further research.

Roles of endogenous ether lipids and associated PUFAs in the regulation of ion channels and their relevance for disease

Ether lipids (ELs) are lipids characterized by the presence of either an ether linkage (alkyl lipids) or a vinyl ether linkage [i.e., plasmalogens (Pls)] at the sn1 position of the glycerol backbone, and they are enriched in PUFAs at the sn2 position. In this review, we highlight that ELs have various biological functions, act as a reservoir for second messengers (such as PUFAs) and have roles in many diseases. Some of the biological effects of ELs may be associated with their ability to regulate ion channels that control excitation-contraction/secretion/mobility coupling and therefore cell physiology. These channels are embedded in lipid membranes, and lipids can regulate their activities directly or indirectly as second messengers or by incorporating into membranes. Interestingly, ELs and EL-derived PUFAs have been reported to play a key role in several pathologies, including neurological disorders, cardiovascular diseases, and cancers. Investigations leading to a better understanding of their mechanisms of action in pathologies have opened a new field in cancer research. In summary, newly identified lipid regulators of ion channels, such as ELs and PUFAs, may represent valuable targets to improve disease diagnosis and advance the development of new therapeutic strategies for managing a range of diseases and conditions.

Gnpat does not play an essential role in systemic iron homeostasis in murine model

The GNPAT variant rs11558492 (p.D519G) was identified as a novel genetic factor that modifies the iron‐overload phenotype in homozygous carriers of the HFE p.C282Y variant. However, the reported effects of the GNPAT p.D519G variant vary among study populations. Here, we investigated the role of GNPAT in iron metabolism using Gnpat‐knockout (Gnpat^−/−), Gnpat/Hfe double‐knockout (Gnpat^−/−Hfe^−/− or DKO) mice and hepatocyte‐specific Gnpat‐knockout mice (Gnpat^fl/fl;Alb‐Cre). Our analysis revealed no significant difference between wild‐type (Gnpat^+/+) and Gnpat^−/− mice, between Hfe^−/− and DKO mice, or between Gnpat^fl/fl and Gnpat^fl/fl;Alb‐Cre with respect to serum iron and tissue iron. In addition, the expression of hepcidin was not affected by deleting Gnpat expression in the presence or absence of Hfe. Feeding Gnpat^−/− and DKO mice a high‐iron diet had no effect on tissue iron levels compared with wild‐type and Hfe^−/− mice, respectively. Gnpat knockdown in primary hepatocytes from wild‐type or Hfe^−/− mice did not alter hepcidin expression, but it repressed BMP6‐induced hepcidin expression. Taken together, these results support the hypothesis that deleting Gnpat expression has no effect on either systemic iron metabolism or the iron‐overload phenotype that develops in Hfe^−/− mice, suggesting that GNPAT does not directly mediate iron homeostasis under normal or high‐iron dietary conditions.

Disturbed neurotransmitter homeostasis in ether lipid deficiency

Plasmalogens, the most prominent ether (phospho)lipids in mammals, are structural components of most cellular membranes. Due to their physicochemical properties and abundance in the central nervous system, a role of plasmalogens in neurotransmission has been proposed, but conclusive data are lacking. Here, we targeted this issue in the glyceronephosphate O-acyltransferase (Gnpat) KO mouse, a model of complete deficiency in ether lipid biosynthesis. Throughout the study, focusing on adult male animals, we found reduced brain levels of various neurotransmitters. In the dopaminergic nigrostriatal tract, synaptic endings but not neuronal cell bodies were affected. Neurotransmitter turnover was altered in ether lipid-deficient murine as well as human post-mortem brain tissue. A generalized loss of synapses did not account for the neurotransmitter deficits, since the levels of several presynaptic proteins appeared unchanged. However, reduced amounts of vesicular monoamine transporter indicate a compromised vesicular uptake of neurotransmitters. As exemplified by norepinephrine, the release of neurotransmitters from Gnpat KO brain slices was diminished in response to strong electrical and chemical stimuli. Finally, addressing potential phenotypic correlates of the disturbed neurotransmitter homeostasis, we show that ether lipid deficiency manifests as hyperactivity and impaired social interaction. We propose that the lack of ether lipids alters the properties of synaptic vesicles leading to reduced amounts and release of neurotransmitters. These features likely contribute to the behavioral phenotype of Gnpat KO mice, potentially modeling some human neurodevelopmental disorders like autism or attention deficit hyperactivity disorder.

Stabilization of FASN by ACAT1-mediated GNPAT acetylation promotes lipid metabolism and hepatocarcinogenesis

Metabolic alteration for adaptation of the local environment has been recognized as a hallmark of cancer. GNPAT dysregulation has been implicated in hepatocellular carcinoma (HCC). However, the precise posttranslational regulation of GNPAT is still undiscovered. Here we show that ACAT1 is upregulated in response to extra palmitic acid (PA). ACAT1 acetylates GNPAT at K128, which represses TRIM21-mediated GNPAT ubiquitination and degradation. Conversely, GNPAT deacetylation by SIRT4 antagonizes ACAT1's function. GNPAT represses TRIM21-mediated FASN degradation and promotes lipid metabolism. Furthermore, shRNA-mediated ACAT1 ablation and acetylation deficiency of GNPAT repress lipid metabolism and tumor progression in xenograft and DEN/CCl₄-induced HCC. Otherwise, ACAT1 inhibitor combination with sorafenib enormously retards tumor formation in mice. Collectively, we demonstrate that stabilization of FASN by ACAT1-mediated GNPAT acetylation plays a critical role in hepatocarcinogenesis.

Snap29 mutant mice recapitulate neurological and ophthalmological abnormalities associated with 22q11 and CEDNIK syndrome

Synaptosomal-associated protein 29 (SNAP29) encodes a member of the SNARE family of proteins implicated in numerous intracellular protein trafficking pathways. SNAP29 maps to the 22q11.2 region and is deleted in 90% of patients with 22q11.2 deletion syndrome (22q11.2DS). Moreover, bi-allelic SNAP29 mutations in patients are responsible for CEDNIK (cerebral dysgenesis, neuropathy, ichthyosis, and keratoderma) syndrome. A mouse model that recapitulates abnormalities found in these syndromes is essential for uncovering the cellular basis of these disorders. In this study, we report that mice with a loss of function mutation of Snap29 on a mixed CD1;FvB genetic background recapitulate skin abnormalities associated with CEDNIK, and also phenocopy neurological and ophthalmological abnormalities found in CEDNIK and a subset of 22q11.2DS patients. Our work also reveals an unanticipated requirement for Snap29 in male fertility and supports contribution of hemizygosity for SNAP29 to the phenotypic spectrum of abnormalities found in 22q11.2DS patients.

Impaired plasmalogen synthesis dysregulates liver X receptor-dependent transcription in cerebellum

Synthesis of ethanolamine plasmalogen (PlsEtn) is regulated by modulating the stability of fatty acyl-CoA reductase 1 (Far1) on peroxisomal membrane, a rate-limiting enzyme in plasmalogen synthesis. Dysregulation of plasmalogen homeostasis impairs cholesterol biosynthesis in cultured cells by altering the stability of squalene epoxidase (SQLE). However, regulation of PlsEtn synthesis and physiological consequences of plasmalogen homeostasis in tissues remain unknown. In the present study, we found that the protein but not the transcription level of Far1 in the cerebellum of the Pex14 mutant mouse expressing Pex14p lacking its C-terminal region (Pex14ΔC/ΔC) is higher than that from wild-type mouse, suggesting that Far1 is stabilized by the lowered level of PlsEtn. The protein level of SQLE was increased, whereas the transcriptional activity of the liver X receptors (LXRs), ligand-activated transcription factors of the nuclear receptor superfamily, is lowered in the cerebellum of Pex14ΔC/ΔC and the mice deficient in dihydroxyacetonephosphate acyltransferase, the initial enzyme for the synthesis of PlsEtn. These results suggest that the reduction of plasmalogens in the cerebellum more likely compromises the cholesterol homeostasis, thereby reducing the transcriptional activities of LXRs, master regulators of cholesterol homeostasis.

Ether Lipid Deficiency in Mice Produces a Complex Behavioral Phenotype Mimicking Aspects of Human Psychiatric Disorders

Ether lipids form a specialized subgroup of phospholipids that requires peroxisomes to be synthesized. We have previously detected that deficiency in these lipids leads to a severe disturbance of neurotransmitter homeostasis and release as well as behavioral abnormalities, such as hyperactivity, in a mouse model. Here, we focused on a more detailed examination of the behavioral phenotype of ether lipid-deficient mice (Gnpat KO) and describe a set of features related to human psychiatric disorders. Gnpat KO mice show strongly impaired social interaction as well as nestlet shredding and marble burying, indicating disturbed execution of inborn behavioral patterns. Also, compromised contextual and cued fear conditioning in these animals suggests a considerable memory deficit, thus potentially forming a connection to the previously determined ether lipid deficit in human patients with Alzheimer's disease. Nesting behavior and the preference for social novelty proved normal in ether lipid-deficient mice. In addition, we detected task-specific alterations in paradigms assessing depression- and anxiety-related behavior. The reported behavioral changes may be used as easy readout for the success of novel treatment strategies against ether lipid deficiency in ameliorating nervous system-associated symptoms. Furthermore, our findings underline that ether lipids are paramount for brain function and demonstrate their relevance for cognitive, social, and emotional behavior. We hereby substantially extend previous observations suggesting a link between deficiency in ether lipids and human mental illnesses, particularly autism and attention-deficit hyperactivity disorder.

Collagen VI is required for the structural and functional integrity of the neuromuscular junction

The synaptic cleft of the neuromuscular junction (NMJ) consists of a highly specialized extracellular matrix (ECM) involved in synapse maturation, in the juxtaposition of pre- to post-synaptic areas, and in ensuring proper synaptic transmission. Key components of synaptic ECM, such as collagen IV, perlecan and biglycan, are binding partners of one of the most abundant ECM protein of skeletal muscle, collagen VI (ColVI), previously never linked to NMJ. Here, we demonstrate that ColVI is itself a component of this specialized ECM and that it is required for the structural and functional integrity of NMJs. In vivo, ColVI deficiency causes fragmentation of acetylcholine receptor (AChR) clusters, with abnormal expression of NMJ-enriched proteins and re-expression of fetal AChRγ subunit, both in Col6a1 null mice and in patients affected by Ullrich congenital muscular dystrophy (UCMD), the most severe form of ColVI-related myopathies. Ex vivo muscle preparations from ColVI null mice revealed altered neuromuscular transmission, with electrophysiological defects and decreased safety factor (i.e., the excess current generated in response to a nerve impulse over that required to reach the action potential threshold). Moreover, in vitro studies in differentiated C2C12 myotubes showed the ability of ColVI to induce AChR clustering and synaptic gene expression. These findings reveal a novel role for ColVI at the NMJ and point to the involvement of NMJ defects in the etiopathology of ColVI-related myopathies.

Ether lipids and their elusive function in the nervous system: a role for plasmalogens: An Editorial Highlight for 'Reduced muscle strength in ether lipid-deficient mice is accompanied by altered development and function of the neuromuscular junction' on page 569

In this editorial, we highlight the recent work of Dorninger et al. that demonstrates a reduction in plasmalogens in the motor end plate is associated with a reduction in motor end plate function. This reduction in function is illuminated in reduced muscle function in these mice, corresponding with the reduction in acetylcholine release and in its receptor density observed in these mice.

From peroxisomal disorders to common neurodegenerative diseases - the role of ether phospholipids in the nervous system

The emerging diverse roles of ether (phospho)lipids in nervous system development and function in health and disease are currently attracting growing interest. Plasmalogens, a subgroup of ether lipids, are important membrane components involved in vesicle fusion and membrane raft composition. They store polyunsaturated fatty acids and may serve as antioxidants. Ether lipid metabolites act as precursors for the formation of glycosyl-phosphatidyl-inositol anchors; others, like platelet-activating factor, are implicated in signaling functions. Consolidating the available information, we attempt to provide molecular explanations for the dramatic neurological phenotype in ether lipid-deficient human patients and mice by linking individual functional properties of ether lipids with pathological features. Furthermore, recent publications have identified altered ether lipid levels in the context of many acquired neurological disorders including Alzheimer's disease (AD) and autism. Finally, current efforts to restore ether lipids in peroxisomal disorders as well as AD are critically reviewed.