A peroxisomal disorder of severe intellectual disability, epilepsy, and cataracts due to fatty acyl-CoA reductase 1 deficiency

An alternative membrane topology permits lipid droplet localization of peroxisomal fatty acyl-CoA reductase 1

Fatty acyl-CoA reductase 1 (Far1) is a ubiquitously expressed peroxisomal membrane protein that generates the fatty alcohols required for the biosynthesis of ether lipids. Lipid droplet localization of exogenously expressed and endogenous human Far1 was observed by fluorescence microscopy under conditions of increased triglyceride synthesis in tissue culture cells. This unexpected finding was supported further by correlative light electron microscopy and subcellular fractionation. Selective permeabilization, protease sensitivity and N-glycosylation tagging suggested that Far1 is able to assume two different membrane topologies, differing in the orientation of the short hydrophilic C-terminus towards the lumen or the cytosol, respectively. Two closely spaced hydrophobic domains are contained within the C-terminal region. When analyzed separately, the second domain was sufficient for the localization of a fluorescent reporter to lipid droplets. Targeting of Far1 to lipid droplets was not impaired in either Pex19 or ASNA1 (also known as TRC40) CRISPR/Cas9 knockout cells. In conclusion, our data suggest that Far1 is a novel member of the rather exclusive group of dual topology membrane proteins. At the same time, Far1 shows lipid metabolism-dependent differential subcellular localizations to peroxisomes and lipid droplets.

Leukodystrophy caused by plasmalogen deficiency rescued by glyceryl 1-myristyl ether treatment

Plasmalogens are the most abundant form of ether phospholipids in myelin and their deficiency causes Rhizomelic Chondrodysplasia Punctata (RCDP), a severe developmental disorder. Using the Gnpat-knockout (KO) mouse as a model of RCDP, we determined the consequences of a plasmalogen deficiency during myelination and myelin homeostasis in the central nervous system (CNS). We unraveled that the lack of plasmalogens causes a generalized hypomyelination in several CNS regions including the optic nerve, corpus callosum and spinal cord. The defect in myelin content evolved to a progressive demyelination concomitant with generalized astrocytosis and white matter-selective microgliosis. Oligodendrocyte precursor cells (OPC) and mature oligodendrocytes were abundant in the CNS of Gnpat KO mice during the active period of demyelination. Axonal loss was minimal in plasmalogen-deficient mice, although axonal damage was observed in spinal cords from aged Gnpat KO mice. Characterization of the plasmalogen-deficient myelin identified myelin basic protein and septin 7 as early markers of dysmyelination, whereas myelin-associated glycoprotein was associated with the active demyelination phase. Using in vitro myelination assays, we unraveled that the intrinsic capacity of oligodendrocytes to ensheath and initiate membrane wrapping requires plasmalogens. The defect in plasmalogens was rescued with glyceryl 1-myristyl ether [1-O-tetradecyl glycerol (1-O-TDG)], a novel alternative precursor in the plasmalogen biosynthesis pathway. 1-O-TDG treatment rescued myelination in plasmalogen-deficient oligodendrocytes and in mutant mice. Our results demonstrate the importance of plasmalogens for oligodendrocyte function and myelin assembly, and identified a novel strategy to promote myelination in nervous tissue.

The many faces of peroxisomal disorders: Lessons from a large Arab cohort

Defects in the peroxisomes biogenesis and/or function result in peroxisomal disorders. In this study, we describe the largest Arab cohort to date (72 families) of clinically, biochemically and molecularly characterized patients with peroxisomal disorders. At the molecular level, we identified 43 disease-causing variants, half of which are novel. The founder nature of many of the variants allowed us to calculate the minimum disease burden for these disorders in our population ~1:30 000, which is much higher than previous estimates in other populations. Clinically, we found an interesting trend toward genotype/phenotype correlation in terms of long-term survival. Nearly half (40/75) of our peroxisomal disorders patients had documented survival beyond 1 year of age. Most unusual among the long-term survivors was a multiplex family in which the affected members presented as adults with non-specific intellectual disability and epilepsy. Other unusual presentations included the very recently described peroxisomal fatty acyl-CoA reductase 1 disorder as well as CRD, spastic paraparesis, white matter (CRSPW) syndrome. We conclude that peroxisomal disorders are highly heterogeneous in their clinical presentation. Our data also confirm the demonstration that milder forms of Zellweger spectrum disorders cannot be ruled out by the "gold standard" very long chain fatty acids assay, which highlights the value of a genomics-first approach in these cases.

Clinical and Neuroimaging Spectrum of Peroxisomal Disorders

Peroxisomes play vital roles in a broad spectrum of cellular metabolic pathways. Defects in genes encoding peroxisomal proteins can result in a wide array of disorders, depending upon the metabolic pathways affected. These disorders can be broadly classified into 2 main groups; peroxisome biogenesis disorders (PBDs) and single peroxisomal enzyme deficiencies. Peroxisomal enzyme deficiencies are result of dysfunction of a specific metabolic pathway, while PBDs are due to generalized peroxisomal dysfunction. Mutations in PEX1 gene are the most common cause of PBDs, accounting for two-thirds of cases. Peroxisomal fission defects is a recently recognized entity, included under the subgroup of PBDs. The aim of this article is to provide a comprehensive review on the clinical and neuroimaging spectrum of peroxisomal disorders.

Sebaceous gland abnormalities in fatty acyl CoA reductase 2 (Far2) null mice result in primary cicatricial alopecia

In a large scale screen for skin, hair, and nail abnormalities in null mice generated by The Jackson Laboratory’s KOMP center, homozygous mutant Far2^{tm2b(KOMP)Wtsi}/2J (hereafter referrred to as Far2^-/-) mice were found to develop focal areas of alopecia as they aged. As sebocytes matured in wildtype C57BL/NJ mice they became pale with fine, uniformly sized clear lipid containing vacuoles that were released when sebocytes disintegrated in the duct. By contrast, the Far2^-/- null mice had sebocytes that were similar within the gland but become brightly eosinophilic when the cells entered the sebaceous gland duct. As sebocytes disintegrated, their contents did not readily dissipate. Scattered throughout the dermis, and often at the dermal hypodermal fat junction, were dystrophic hair follicles or ruptured follicles with a foreign body granulomatous reaction surrounding free hair shafts (trichogranuloma). The Meibomian and clitoral glands (modified sebaceous glands) of Far2^-/- mice showed ducts dilated to various degrees that were associated with mild changes in the sebocytes as seen in the truncal skin. Skin surface lipidomic analysis revealed a lower level of wax esters, cholesterol esters, ceramides, and diacylglycerols compared to wildtype control mice. Similar changes were described in a number of other mouse mutations that affected the sebaceous glands resulting in primary cicatricial alopecia.

Expanding the concept of peroxisomal diseases and efficient diagnostic system in Japan

The concept of peroxisomal diseases is expanding because of improvements in diagnostic technology based on advanced biochemical analysis and development of next-generation sequencing. For quicker and more accurate diagnosis of as many patients as possible, we developed a new diagnostic system combining the conventional diagnostic system and comprehensive mutational analysis by whole-exome sequencing in Japan. Adrenoleukodystrophy (ALD) is the most common peroxisomal disease. In the cerebral type of ALD, hematopoietic stem cell transplantation is the only treatment in the early stage, and thus prompt diagnosis will improve the prognosis of affected patients. Furthermore, it is also important to identify pre-symptomatic patients by family analysis of probands by providing appropriate disease information and genetic counseling, which will also lead to early intervention. Here, we summarize current information related to peroxisomal diseases and ALD and introduce our efficient diagnostic system for use in Japan, which resulted in the diagnosis of 73 Japanese patients with peroxisome biogenesis disorders, 16 with impaired β-oxidation of fatty acids, three with impaired etherphospholipid biosynthesis, and 191 Japanese families with ALD so far.

Tissue-selective alteration of ethanolamine plasmalogen metabolism in dedifferentiated colon mucosa

Human colon lipid analysis by imaging mass spectrometry (IMS) demonstrates that the lipid fingerprint is highly sensitive to a cell's pathophysiological state. Along the colon crypt axis, and concomitant to the differentiation process, certain lipid species tightly linked to signaling (phosphatidylinositols and arachidonic acid (AA)-containing diacylglycerophospholipids), change following a rather simple mathematical expression. We extend here our observations to ethanolamine plasmalogens (PlsEtn), a unique type of glycerophospholipid presenting a vinyl ether linkage at sn-1 position. PlsEtn distribution was studied in healthy, adenomatous, and carcinomatous colon mucosa sections by IMS. In epithelium, 75% of PlsEtn changed in a highly regular manner along the crypt axis, in clear contrast with diacyl species (67% of which remained constant). Consistently, AA-containing PlsEtn species were more abundant at the base, where stem cells reside, and decreased while ascending the crypt. In turn, mono-/diunsaturated species experienced the opposite change. These gradients were accompanied by a gradual expression of ether lipid synthesis enzymes. In lamina propria, 90% of stromal PlsEtn remained unchanged despite the high content of AA and the gradient in AA-containing diacylglycerophospholipids. Finally, both lipid and protein gradients were severely affected in polyps and carcinoma. These results link PlsEtn species regulation to cell differentiation for the first time and confirm that diacyl and ether species are differently regulated. Furthermore, they reaffirm the observations on cell lipid fingerprint image sensitivity to predict cell pathophysiological status, reinforcing the translational impact both lipidome and IMS might have in clinical research.

Structural and functional roles of ether lipids

Ether lipids, such as plasmalogens, are peroxisome-derived glycerophospholipids in which the hydrocarbon chain at the sn-1 position of the glycerol backbone is attached by an ether bond, as opposed to an ester bond in the more common diacyl phospholipids. This seemingly simple biochemical change has profound structural and functional implications. Notably, the tendency of ether lipids to form non-lamellar inverted hexagonal structures in model membranes suggests that they have a role in facilitating membrane fusion processes. Ether lipids are also important for the organization and stability of lipid raft microdomains, cholesterol-rich membrane regions involved in cellular signaling. In addition to their structural roles, a subset of ether lipids are thought to function as endogenous antioxidants, and emerging studies suggest that they are involved in cell differentiation and signaling pathways. Here, we review the biology of ether lipids and their potential significance in human disorders, including neurological diseases, cancer, and metabolic disorders.

Peroxisomes and Their Central Role in Metabolic Interaction Networks in Humans

Peroxisomes catalyze a number of essential metabolic functions and impairments in any of these are usually associated with major clinical signs and symptoms. In contrast to mitochondria which are autonomous organelles that can catalyze the degradation of fatty acids, certain amino acids and other compounds all by themselves, peroxisomes are non-autonomous organelles which are highly dependent on the interaction with other organelles and compartments to fulfill their role in metabolism. This includes mitochondria, the endoplasmic reticulum, lysosomes, and the cytosol. In this paper we will discuss the central role of peroxisomes in different metabolic interaction networks in humans, including fatty acid oxidation, ether phospholipid biosynthesis, bile acid synthesis, fatty acid alpha-oxidation and glyoxylate metabolism.

The landscape of human mutually exclusive splicing

Mutually exclusive splicing of exons is a mechanism of functional gene and protein diversification with pivotal roles in organismal development and diseases such as Timothy syndrome, cardiomyopathy and cancer in humans. In order to obtain a first genomewide estimate of the extent and biological role of mutually exclusive splicing in humans, we predicted and subsequently validated mutually exclusive exons (MXEs) using 515 publically available RNA‐Seq datasets. Here, we provide evidence for the expression of over 855 MXEs, 42% of which represent novel exons, increasing the annotated human mutually exclusive exome more than fivefold. The data provide strong evidence for the existence of large and multi‐cluster MXEs in higher vertebrates and offer new insights into MXE evolution. More than 82% of the MXE clusters are conserved in mammals, and five clusters have homologous clusters in Drosophila. Finally, MXEs are significantly enriched in pathogenic mutations and their spatio‐temporal expression might predict human disease pathology.

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.

Plasmalogen homeostasis - regulation of plasmalogen biosynthesis and its physiological consequence in mammals

Plasmalogens, mostly ethanolamine-containing alkenyl ether phospholipids, are a major subclass of glycerophospholipids. Plasmalogen synthesis is initiated in peroxisomes and completed in the endoplasmic reticulum. The absence of plasmalogens in several organs of peroxisome biogenesis-defective patients suggests that the de novo synthesis of plasmalogens plays a pivotal role in its homeostasis in tissues. Plasmalogen synthesis is regulated by modulating the stability of fatty acyl-CoA reductase 1 on peroxisomal membranes, a rate-limiting enzyme in plasmalogen synthesis, by sensing plasmalogens in the inner leaflet of plasma membranes. Dysregulation of plasmalogen homeostasis impairs cholesterol biosynthesis by altering the stability of squalene monooxygenase, a key enzyme in cholesterol biosynthesis, implying physiological consequences of plasmalogen homeostasis with respect to cholesterol metabolism in cells, as well as in organs such as the liver.

Systematic screening for skin, hair, and nail abnormalities in a large-scale knockout mouse program

The International Knockout Mouse Consortium was formed in 2007 to inactivate (“knockout”) all protein-coding genes in the mouse genome in embryonic stem cells. Production and characterization of these mice, now underway, has generated and phenotyped 3,100 strains with knockout alleles. Skin and adnexa diseases are best defined at the gross clinical level and by histopathology. Representative retired breeders had skin collected from the back, abdomen, eyelids, muzzle, ears, tail, and lower limbs including the nails. To date, 169 novel mutant lines were reviewed and of these, only one was found to have a relatively minor sebaceous gland abnormality associated with follicular dystrophy. The B6N(Cg)-Far2^{tm2b(KOMP)Wtsi}/2J strain, had lesions affecting sebaceous glands with what appeared to be a secondary follicular dystrophy. A second line, B6N(Cg)-Ppp1r9b^{tm1.1(KOMP)Vlcg}/J, had follicular dystrophy limited to many but not all mystacial vibrissae in heterozygous but not homozygous mutant mice, suggesting that this was a nonspecific background lesion. We discuss potential reasons for the low frequency of skin and adnexal phenotypes in mice from this project in comparison to those seen in human Mendelian diseases, and suggest alternative approaches to identification of human disease-relevant models.

Effects of Lucilia sericata on wound healing in streptozotocin-induced diabetic rats and analysis of its secretome at the proteome level

The use of Lucilia sericata larvae on the healing of wounds in diabetics has been reported. However, the role of the excretion/secretion (ES) products of the larvae in treatment of diabetic wounds remains unknown. This study investigated whether application of the ES products of L. sericata on the wound surface could improve the impaired wound healing in streptozotocin-induced diabetic rats. Additional analysis was performed to understand proteome content of L. sericata secretome to understand ES contribution at the molecular level. For this purpose, full-thickness skin wounds were created on the backs of diabetic and control rats. A study was conducted to assess the levels of the ES-induced collagen I/III expression and to assay nuclear factor κB (NF-κB) (p65) activity in wound biopsies and ES-treated wounds of diabetic rat skin in comparison to the controls. The expression levels of collagen I/III and NF-κB (p65) activity were determined at days 3, 7, and 14 after wounding using immunohistological analyses and enzyme-linked immunosorbent assay technique. The results indicated that treatment with the ES extract increased collagen I expressions of the wound control and diabetic tissue. But the increase in collagen I expression in the controls was higher than the one in the diabetics. NF-κB (p65) activity was also increased in diabetic wounds compared to the controls, whereas it was decreased in third and seventh days upon ES treatment. The results indicated that ES products of L. sericata may enhance the process of wound healing by influencing phases such as inflammation, NF-κB (p65) activity, collagen synthesis, and wound contraction. These findings may provide new insights into understanding of therapeutic potential of ES in wound healing in diabetics.

Drosophila Courtship Conditioning As a Measure of Learning and Memory

Many insights into the molecular mechanisms underlying learning and memory have been elucidated through the use of simple behavioral assays in model organisms such as the fruit fly, Drosophila melanogaster. Drosophila is useful for understanding the basic neurobiology underlying cognitive deficits resulting from mutations in genes associated with human cognitive disorders, such as intellectual disability (ID) and autism. This work describes a methodology for testing learning and memory using a classic paradigm in Drosophila known as courtship conditioning. Male flies court females using a distinct pattern of easily recognizable behaviors. Premated females are not receptive to mating and will reject the male's copulation attempts. In response to this rejection, male flies reduce their courtship behavior. This learned reduction in courtship behavior is measured over time, serving as an indicator of learning and memory. The basic numerical output of this assay is the courtship index (CI), which is defined as the percentage of time that a male spends courting during a 10 min interval. The learning index (LI) is the relative reduction of CI in flies that have been exposed to a premated female compared to naïve flies with no previous social encounters. For the statistical comparison of LIs between genotypes, a randomization test with bootstrapping is used. To illustrate how the assay can be used to address the role of a gene relating to learning and memory, the pan-neuronal knockdown of Dihydroxyacetone phosphate acyltransferase (Dhap-at) was characterized here. The human ortholog of Dhap-at, glyceronephosphate O-acyltransferase (GNPT), is involved in rhizomelic chondrodysplasia punctata type 2, an autosomal-recessive syndrome characterized by severe ID. Using the courtship conditioning assay, it was determined that Dhap-at is required for long-term memory, but not for short-term memory. This result serves as a basis for further investigation of the underlying molecular mechanisms.

Plasmalogen biosynthesis is spatiotemporally regulated by sensing plasmalogens in the inner leaflet of plasma membranes

Alkenyl ether phospholipids are a major sub-class of ethanolamine- and choline-phospholipids in which a long chain fatty alcohol is attached at the sn-1 position through a vinyl ether bond. Biosynthesis of ethanolamine-containing alkenyl ether phospholipids, plasmalogens, is regulated by modulating the stability of fatty acyl-CoA reductase 1 (Far1) in a manner dependent on the level of cellular plasmalogens. However, precise molecular mechanisms underlying the regulation of plasmalogen synthesis remain poorly understood. Here we show that degradation of Far1 is accelerated by inhibiting dynamin-, Src kinase-, or flotillin-1-mediated endocytosis without increasing the cellular level of plasmalogens. By contrast, Far1 is stabilized by sequestering cholesterol with nystatin. Moreover, abrogation of the asymmetric distribution of plasmalogens in the plasma membrane by reducing the expression of CDC50A encoding a β-subunit of flippase elevates the expression level of Far1 and plasmalogen synthesis without reducing the total cellular level of plasmalogens. Together, these results support a model that plasmalogens localised in the inner leaflet of the plasma membranes are sensed for plasmalogen homeostasis in cells, thereby suggesting that plasmalogen synthesis is spatiotemporally regulated by monitoring cellular level of plasmalogens.

Detection of unusual very-long-chain fatty acid and ether lipid derivatives in the fibroblasts and plasma of patients with peroxisomal diseases using liquid chromatography-mass spectrometry

Metabolic changes occur in patients with peroxisomal diseases owing to impairments in the genes involved in peroxisome function. For diagnostic purposes, saturated very-long-chain fatty acids (VLCFAs) such as C24:0 and C26:0, phytanic acid, pristanic acid, and plasmalogens are often measured as metabolic hallmarks. As the direct pathology of peroxisomal disease is yet to be fully elucidated, we sought to explore the fatty acid species that accumulate in patients with peroxisomal diseases. We developed a method for detecting a range of fatty acids implicated in peroxisomal diseases such as Zellweger syndrome (ZS) and X-linked adrenoleukodystrophy (X-ALD). To this end, we employed an ultra-performance liquid chromatography-mass spectrometry (LC-MS) coupled with negatively charged electrospray ionization. Fatty acids from patients and control subjects were extracted from total lipids by acid-hydrolysis and compared. In accordance with previous results, the amounts of VLCFAs, phytanic acid, and pristanic acid differed between the two groups. We identified extremely long and highly polyunsaturated VLCFAs (ultra-VLC-PUFAs) such as C44:12 in ZS samples. Moreover, three unknown molecules were prominent in control samples but scarcely detectable in ZS samples. LC-MS/MS analysis identified these as 1-alkyl-sn-glycerol 3-phosphates derived from ether lipids containing fatty alcohols such as C16:0, C18:0, or C18:1. Our method provides an approach to observing a wide range of lipid-derived fatty acids and related molecules in order to understand the metabolic changes involved in peroxisomal diseases. This technique can therefore be used in identifying metabolic markers and potential clinical targets for future treatment.

Analysis of Plasmalogen Synthesis in Cultured Cells

Plasmalogen synthesis can be analyzed by metabolic labeling, followed by the separation of ethanolamine plasmalogens from glycerophospholipids on one-dimensional thin-layer chromatography. The vinyl-ether bond of plasmalogens is acid-labile, which allows separating plasmalogens as 2-acyl-glycerophospholipids from diacyl-glycerophospholipids.

Clinical and Laboratory Diagnosis of Peroxisomal Disorders

The peroxisomal disorders (PDs) are a heterogeneous group of genetic diseases in man caused by an impairment in peroxisome biogenesis or one of the metabolic functions of peroxisomes. Thanks to the revolutionary technical developments in gene sequencing methods and their increased use in patient diagnosis, the field of genetic diseases in general and peroxisomal disorders in particular has dramatically changed in the last few years. Indeed, several novel peroxisomal disorders have been identified recently and in addition it has been realized that the phenotypic spectrum of patients affected by a PD keeps widening, which makes clinical recognition of peroxisomal patients increasingly difficult. Here, we describe these new developments and provide guidelines for the clinical and laboratory diagnosis of peroxisomal patients.

ACBD5 deficiency causes a defect in peroxisomal very long-chain fatty acid metabolism

BACKGROUND

Acyl-CoA binding domain containing protein 5 (ACBD5) is a peroxisomal membrane protein with a cytosolic acyl-CoA binding domain. Because of its acyl-CoA binding domain, ACBD5 has been assumed to function as an intracellular carrier of acyl-CoA esters. In addition, a role for ACBD5 in pexophagy has been suggested. However, the precise role of ACBD5 in peroxisomal metabolism and/or functioning has not yet been established. Previously, a genetic ACBD5 deficiency was identified in three siblings with retinal dystrophy and white matter disease. We identified a pathogenic mutation in ACBD5 in another patient and studied the consequences of the ACBD5 defect in patient material and in ACBD5-deficient HeLa cells to uncover this role.

METHODS

We studied a girl who presented with progressive leukodystrophy, syndromic cleft palate, ataxia and retinal dystrophy. We performed biochemical, cell biological and molecular studies in patient material and in ACBD5-deficient HeLa cells generated by CRISPR-Cas9 genome editing.

RESULTS

We identified a homozygous deleterious indel mutation in ACBD5, leading to complete loss of ACBD5 protein in the patient. Our studies showed that ACBD5 deficiency leads to accumulation of very long-chain fatty acids (VLCFAs) due to impaired peroxisomal β-oxidation. No effect on pexophagy was found.

CONCLUSIONS

Our investigations strongly suggest that ACBD5 plays an important role in sequestering C26-CoA in the cytosol and thereby facilitates transport into the peroxisome and subsequent β-oxidation. Accordingly, ACBD5 deficiency is a novel single peroxisomal enzyme deficiency caused by impaired VLCFA metabolism, leading to retinal dystrophy and white matter disease.

Growth charts for individuals with rhizomelic chondrodysplasia punctata

Rhizomelic chondrodysplasia punctata (RCDP) is a class of peroxisomal disorders characterized by defective plasmalogen biosynthesis. There are multiple recognized types of RCDP, all of which have autosomal recessive inheritance, and their associated genes are known: RCDP type 1 with PEX7, RCDP type 2 with GNPAT, RCDP type 3 with AGPS, RCDP type 4 with FAR1, and RCDP type 5 with PEX5. Among other medical/developmental issues, plasmalogen deficiency has a direct effect on bone growth and results in postnatal growth failure, the severity of which corresponds to the degree of plasmalogen deficiency. In order to document growth in patients with RCDP, we present detailed growth curves for length, weight, and head circumference derived from retrospective data from 23 individuals with RCDP types 1 and 2 confirmed by molecular and/or biochemical studies. We stratified growth curves by age as well as by plasmalogen level, with those with higher plasmalogens grouped as "non-classic." The growth charts presented here provide guidance to families and physician caretakers on the natural course of growth in individuals with RCDP during infancy into early childhood, and thus will have particular utility in setting expectations and guiding optimal feeding interventions in this population.© 2016 Wiley Periodicals, Inc.

Antenatal manifestations of inborn errors of metabolism: biological diagnosis

Inborn errors of metabolism (IEMs) that present with abnormal imaging findings in the second half of pregnancy are mainly lysosomal storage disorders (LSDs), cholesterol synthesis disorders (CSDs), glycogen storage disorder type IV (GSD IV), peroxisomal disorders, mitochondrial fatty acid oxidation defects (FAODs), organic acidurias, aminoacidopathies, congenital disorders of glycosylation (CDGs), and transaldolase deficiency. Their biological investigation requires fetal material. The supernatant of amniotic fluid (AF) is useful for the analysis of mucopolysaccharides, oligosaccharides, sialic acid, lysosphingolipids and some enzyme activities for LSDs, 7- and 8-dehydrocholesterol, desmosterol and lathosterol for CSDs, acylcarnitines for FAODs, organic acids for organic acidurias, and polyols for transaldolase deficiency. Cultured AF or fetal cells allow the measurement of enzyme activities for most IEMs, whole-cell assays, or metabolite measurements. The cultured cells or tissue samples taken after fetal death can be used for metabolic profiling, enzyme activities, and DNA extraction. Fetal blood can also be helpful. The identification of vacuolated cells orients toward an LSD, and plasma is useful for diagnosing peroxisomal disorders, FAODs, CSDs, some LSDs, and possibly CDGs and aminoacidopathies. We investigated AF of 1700 pregnancies after exclusion of frequent etiologies of nonimmune hydrops fetalis and identified 108 fetuses affected with LSDs (6.3 %), 29 of them with mucopolysaccharidosis type VII (MPS VII), and six with GSD IV (0.3 %). In the AF of 873 pregnancies, investigated because of intrauterine growth restriction and/or abnormal genitalia, we diagnosed 32 fetuses affected with Smith-Lemli-Opitz syndrome (3.7 %).

The important role of biochemical and functional studies in the diagnostics of peroxisomal disorders

Peroxisomes are dynamic organelles that play an essential role in a variety of metabolic pathways. Peroxisomal dysfunction can lead to various biochemical abnormalities and result in abnormal metabolite levels, such as increased very long-chain fatty acid or reduced plasmalogen levels. The metabolite abnormalities in peroxisomal disorders are used in the diagnostics of these disorders. In this paper we discuss in detail the different diagnostic tests available for peroxisomal disorders and focus specifically on the important role of biochemical and functional studies in cultured skin fibroblasts in reaching the right diagnosis. Several examples are shown to underline the power of such studies.

Genome-wide association study of periweaning failure-to-thrive syndrome (PFTS) in pigs

Porcine periweaning-failure-to-thrive syndrome (PFTS) is a condition that affects newly weaned piglets. It is characterised by a progressive debilitation leading to death, in the absence of infectious, nutritional, management or environmental factors. In this study, we present the first report of PFTS in South America and the results of a genome-wide association study to identify the genetic markers associated with the appearance of this condition in a crossbred swine population. Four chromosomal regions were associated with PFTS predisposition, one located on SSCX, one on SSC8, and the two other regions on SSC14. Regions on SSC8 and SSC14 harbour important functional candidate genes involved in human depression and might have an important role in PFTS. Our findings contribute to the increasing knowledge about this syndrome, which has been investigated since 2007, and to the identification of the aetiology of this disease.

Small molecules, both dietary and endogenous, influence the onset of lens cataracts

How the lens ages successfully is a lesson in biological adaption and the emergent properties of its complement of cells and proteins. This living tissue contains some of the oldest proteins in our bodies and yet they remain functional for decades, despite exposure to UV light, to reactive oxygen species and all the other hazards to protein function. This remarkable feat is achieved by a shrewd investment in very stable proteins as lens crystallins, by providing a reservoir of ATP-independent protein chaperones unequalled by any other tissue and by an oxidation-resistant environment. In addition, glutathione, a free radical scavenger, is present in mM concentrations and the plasma membranes contain oxidation-resistant sphingolipids what compromises lens function as it ages? In this review, we examine the role of small molecules in the prevention or causation of cataracts, including those associated with diet, metabolic pathways and drug therapy (steroids).

Genetics and prospective therapeutic targets for Sjögren-Larsson Syndrome

INTRODUCTION

Sjögren-Larsson syndrome (SLS) is a rare neurocutaneous disease characterized by ichthyosis, spasticity, intellectual disability and a distinctive retinopathy. It is caused by inactivating mutations in ALDH3A2, which codes for fatty aldehyde dehydrogenase (FALDH) and results in abnormal metabolism of long-chain aliphatic aldehydes and alcohols. The potential disease mechanisms leading to symptoms include 1) accumulation of toxic fatty aldehydes that form covalent adducts with lipids and membrane proteins; 2) physical disruption of multi-lamellar membranes in skin and brain; 3) abnormal activation of the JNK cell signaling pathway; and 4) defective farnesol metabolism resulting in abnormal PPAR-α dependent gene expression. Currently, no effective pathogenesis-based therapy is available.

AREAS COVERED

The clinical, pathologic and genetic features of SLS are summarized. The biochemical abnormalities caused by deficient activity of FALDH are reviewed in the context of proposed pathogenic mechanisms and potential therapeutic interventions.

EXPERT OPINION

The most promising pharmacologic approach to SLS involves blocking the formation of potentially harmful fatty aldehyde adducts using aldehyde scavenging drugs, currently in phase 2 clinical trials. Other approaches needing further investigation include: 1) ALDH-specific activator drugs and PPAR-α agonists to increase mutant FALDH activity; 2) inhibitors of the JNK phosphorylation cascade; 3) antioxidants to decrease aldehyde load; 4) dietary lipid modification; and 5) gene therapy.

Fatty Acyl-CoA Reductase 1 Deficiency

Investigators from Erlangen, Germany; Calgary, CA; and Kafranbel, Syria, identified mutations in the gene, fatty acyl-CoA reductase 1 (FAR1) deficiency, adding to three other genes involved in plasmalogen biosynthesis, in two families affected by severe intellectual disability, early-onset epilepsy, microcephaly, congenital cataracts, growth retardation, and spasticity.

Peroxisome biogenesis disorders in the Zellweger spectrum: An overview of current diagnosis, clinical manifestations, and treatment guidelines

Peroxisome biogenesis disorders in the Zellweger spectrum (PBD-ZSD) are a heterogeneous group of genetic disorders caused by mutations in PEX genes responsible for normal peroxisome assembly and functions. As a result of impaired peroxisomal activities, individuals with PBD-ZSD can manifest a complex spectrum of clinical phenotypes that typically result in shortened life spans. The extreme variability in disease manifestation ranging from onset of profound neurologic symptoms in newborns to progressive degenerative disease in adults presents practical challenges in disease diagnosis and medical management. Recent advances in biochemical methods for newborn screening and genetic testing have provided unprecedented opportunities for identifying patients at the earliest possible time and defining the molecular bases for their diseases. Here, we provide an overview of current clinical approaches for the diagnosis of PBD-ZSD and provide broad guidelines for the treatment of disease in its wide variety of forms. Although we anticipate future progress in the development of more effective targeted interventions, the current guidelines are meant to provide a starting point for the management of these complex conditions in the context of personalized health care.

A Caenorhabditis elegans model for ether lipid biosynthesis and function

Ether lipids are widespread in nature, and they are structurally and functionally important components of membranes. The roundworm, Caenorhabditis elegans, synthesizes numerous lipid species containing alkyl and alkenyl ether bonds. We isolated C. elegans strains carrying loss-of-function mutations in three genes encoding the proteins required for the initial three steps in the ether lipid biosynthetic pathway, FARD-1/FAR1, ACL-7/GNPAT, and ADS-1/AGPS. Analysis of the mutant strains show that they lack ether lipids, but possess the ability to alter their lipid composition in response to lack of ether lipids. We found that increases in de novo fatty acid synthesis and reduction of stearoyl- and palmitoyl-CoA desaturase activity, processes that are at least partially regulated transcriptionally, mediate the altered lipid composition in ether lipid-deficient mutants. Phenotypic analysis demonstrated the importance of ether lipids for optimal fertility, lifespan, survival at cold temperatures, and resistance to oxidative stress.Caenorhabditis.

Metabolic Interplay between Peroxisomes and Other Subcellular Organelles Including Mitochondria and the Endoplasmic Reticulum

Peroxisomes are unique subcellular organelles which play an indispensable role in several key metabolic pathways which include: (1.) etherphospholipid biosynthesis; (2.) fatty acid beta-oxidation; (3.) bile acid synthesis; (4.) docosahexaenoic acid (DHA) synthesis; (5.) fatty acid alpha-oxidation; (6.) glyoxylate metabolism; (7.) amino acid degradation, and (8.) ROS/RNS metabolism. The importance of peroxisomes for human health and development is exemplified by the existence of a large number of inborn errors of peroxisome metabolism in which there is an impairment in one or more of the metabolic functions of peroxisomes. Although the clinical signs and symptoms of affected patients differ depending upon the enzyme which is deficient and the extent of the deficiency, the disorders involved are usually (very) severe diseases with neurological dysfunction and early death in many of them. With respect to the role of peroxisomes in metabolism it is clear that peroxisomes are dependent on the functional interplay with other subcellular organelles to sustain their role in metabolism. Indeed, whereas mitochondria can oxidize fatty acids all the way to CO₂ and H₂O, peroxisomes are only able to chain-shorten fatty acids and the end products of peroxisomal beta-oxidation need to be shuttled to mitochondria for full oxidation to CO₂ and H₂O. Furthermore, NADH is generated during beta-oxidation in peroxisomes and beta-oxidation can only continue if peroxisomes are equipped with a mechanism to reoxidize NADH back to NAD⁺, which is now known to be mediated by specific NAD(H)-redox shuttles. In this paper we describe the current state of knowledge about the functional interplay between peroxisomes and other subcellular compartments notably the mitochondria and endoplasmic reticulum for each of the metabolic pathways in which peroxisomes are involved.

Peroxisome biogenesis and human peroxisome-deficiency disorders

Peroxisome is a single-membrane-bounded ubiquitous organelle containing a hundred different enzymes that catalyze various metabolic pathways such as β-oxidation of very long-chain fatty acids and synthesis of plasmalogens. To investigate peroxisome biogenesis and human peroxisome biogenesis disorders (PBDs) including Zellweger syndrome, more than a dozen different complementation groups of Chinese hamster ovary (CHO) cell mutants impaired in peroxisome biogenesis are isolated as a model experimental system. By taking advantage of rapid functional complementation assay of the CHO cell mutants, successful cloning of PEX genes encoding peroxins required for peroxisome assembly invaluably contributed to the accomplishment of cloning of pathogenic genes responsible for PBDs. Peroxins are divided into three groups: 1) peroxins including Pex3p, Pex16p and Pex19p, are responsible for peroxisome membrane biogenesis via Pex19p- and Pex3p-dependent class I and Pex19p- and Pex16p-dependent class II pathways; 2) peroxins that function in matrix protein import; 3) those such as Pex11pβ are involved in peroxisome division where DLP1, Mff, and Fis1 coordinately function.

Peroxisomes in brain development and function

Peroxisomes contain numerous enzymatic activities that are important for mammalian physiology. Patients lacking either all peroxisomal functions or a single enzyme or transporter function typically develop severe neurological deficits, which originate from aberrant development of the brain, demyelination and loss of axonal integrity, neuroinflammation or other neurodegenerative processes. Whilst correlating peroxisomal properties with a compilation of pathologies observed in human patients and mouse models lacking all or individual peroxisomal functions, we discuss the importance of peroxisomal metabolites and tissue- and cell type-specific contributions to the observed brain pathologies. This enables us to deconstruct the local and systemic contribution of individual metabolic pathways to specific brain functions. We also review the recently discovered variability of pathological symptoms in cases with unexpectedly mild presentation of peroxisome biogenesis disorders. Finally, we explore the emerging evidence linking peroxisomes to more common neurological disorders such as Alzheimer’s disease, autism and amyotrophic lateral sclerosis. This article is part of a Special Issue entitled: Peroxisomes edited by Ralf Erdmann.

Dysregulation of Plasmalogen Homeostasis Impairs Cholesterol Biosynthesis

Plasmalogen biosynthesis is regulated by modulating fatty acyl-CoA reductase 1 stability in a manner dependent on cellular plasmalogen level. However, physiological significance of the regulation of plasmalogen biosynthesis remains unknown. Here we show that elevation of the cellular plasmalogen level reduces cholesterol biosynthesis without affecting the isoprenylation of proteins such as Rab and Pex19p. Analysis of intermediate metabolites in cholesterol biosynthesis suggests that the first oxidative step in cholesterol biosynthesis catalyzed by squalene monooxygenase (SQLE), an important regulator downstream HMG-CoA reductase in cholesterol synthesis, is reduced by degradation of SQLE upon elevation of cellular plasmalogen level. By contrast, the defect of plasmalogen synthesis causes elevation of SQLE expression, resulting in the reduction of 2,3-epoxysqualene required for cholesterol synthesis, hence implying a novel physiological consequence of the regulation of plasmalogen biosynthesis.

Peroxisomal Disorders: A Review on Cerebellar Pathologies

Peroxisomes are organelles with diverse metabolic tasks including essential roles in lipid metabolism. They are of utmost importance for the normal functioning of the nervous system as most peroxisomal disorders are accompanied with neurological symptoms. Remarkably, the cerebellum exquisitely depends on intact peroxisomal function both during development and adulthood. In this review, we cover all aspects of cerebellar pathology that were reported in peroxisome biogenesis disorders and in diseases caused by dysfunction of the peroxisomal α-oxidation, β-oxidation or ether lipid synthesis pathways. We also discuss the phenotypes of mouse models in which cerebellar pathologies were recapitulated and search for connections with the metabolic abnormalities. It becomes increasingly clear that besides the most severe forms of peroxisome dysfunction that are associated with developmental cerebellar defects, milder impairments can give rise to ataxia later in life.

"Role of peroxisomes in human lipid metabolism and its importance for neurological development"

Peroxisomes play a crucial role in normal neurological development as exemplified by the devastating neurological consequences of a defect in the biogenesis of peroxisomes as in Zellweger syndrome. The underlying basis for the important role of peroxisomes in neurological development resides in the fact that peroxisomes catalyze a number of physiological functions, notably involving the metabolism of different lipids. Indeed, peroxisomes catalyse the beta-oxidative breakdown of certain fatty acids including: (1.) the very long-chain fatty acids C22:0, C24:0, and C26:0; (2.) pristanic acid and (3.) the bile acid intermediates di- and trihydroxycholestanoic acid which cannot be oxidized in mitochondria. Furthermore, peroxisomes catalyze the synthesis of a particular type of lipids, i.e. ether-linked phospholipids, which are highly abundant in brain, especially in myelin. The current state of knowledge with respect to the metabolic role of peroxisomes will be described in this paper with particular emphasis on the role of peroxisomes in brain.

Rhizomelic Chondrodysplasia Punctata Type 1 Caused by a Novel Mutation in the PEX7 Gene

Peroxisomes are involved in various metabolic reactions. Rhizomelic chondrodysplasia punctata (RCDP) type 1 is one of the peroxisomal biogenesis disorders caused by mutations in the PEX7 gene and is inherited in an autosomal recessive manner. We present a nine-year-old boy with skeletal abnormalities and dysmorphic facial appearance. The patient was born to parents who were first cousins. Very-long-chain fatty acids and pristanic acid levels were in the normal range, but an elevated phytanic acid level was detected by gas chromatography/mass spectrometry. The PEX7 gene was sequenced in the patient and his parents. A novel homozygous mutation, c.192delT (p.F64Lfs*10), was identified in the patient and was present in heterozygosity in both parents. In conclusion, the clinical presentation and peroxisome profile of the patient suggest that this novel mutation leads to RCDP type 1.

Plasma/Serum Plasmalogens: Methods of Analysis and Clinical Significance

Age-related diseases, such as atherosclerosis and dementia, are associated with oxidative stress and chronic inflammation. Peroxisome dysfunction may be related to aging and age-related pathologies, possibly through the derangement of redox homeostasis. The biosyntheses of plasmalogens (Pls), a subclass of glycerophospholipids, are primarily regulated by peroxisomes. Thus, plasma Pls may reflect the systemic functional activity of peroxisomes and serve as potential biomarkers for diseases related to oxidative stress and aging. Recently, we have established three promising analytical methods for plasma/serum Pls using high-performance liquid chromatography with radioactive iodine, liquid chromatography-tandem mass spectrometry, and enzymatic assay. These methods were validated and used to obtain detailed molecular information regarding these molecules. In cross-sectional studies on asymptomatic, coronary artery disease, and elderly dementia individuals, we found that serum choline Pls, particularly those containing oleic and linoleic acid in the sn-2 position of the glycerol backbone, may serve as reliable antiatherogenic biomarkers. Furthermore, we also found that serum ethanolamine Pls were effective in discriminating cognitive impairment. These results support our hypothesis and further studies are clearly needed to elucidate Pls pathophysiologic significance.