A study on erythrocyte membrane plasmalogen in myotonic dystrophy

Delineating the role of alterations in lipid metabolism to the pathogenesis of inherited skeletal and cardiac muscle disorders: Thematic Review Series: Genetics of Human Lipid Diseases

As the specific composition of lipids is essential for the maintenance of membrane integrity, enzyme function, ion channels, and membrane receptors, an alteration in lipid composition or metabolism may be one of the crucial changes occurring during skeletal and cardiac myopathies. Although the inheritance (autosomal dominant, autosomal recessive, and X-linked traits) and underlying/defining mutations causing these myopathies are known, the contribution of lipid homeostasis in the progression of these diseases needs to be established. The purpose of this review is to present the current knowledge relating to lipid changes in inherited skeletal muscle disorders, such as Duchenne/Becker muscular dystrophy, myotonic muscular dystrophy, limb-girdle myopathic dystrophies, desminopathies, rostrocaudal muscular dystrophy, and Dunnigan-type familial lipodystrophy. The lipid modifications in familial hypertrophic and dilated cardiomyopathies, as well as Barth syndrome and several other cardiac disorders associated with abnormal lipid storage, are discussed. Information on lipid alterations occurring in these myopathies will aid in the design of improved methods of screening and therapy in children and young adults with or without a family history of genetic diseases.

Human and great ape red blood cells differ in plasmalogen levels and composition

Background

Plasmalogens are ether phospholipids required for normal mammalian developmental, physiological, and cognitive functions. They have been proposed to act as membrane antioxidants and reservoirs of polyunsaturated fatty acids as well as influence intracellular signaling and membrane dynamics. Plasmalogens are particularly enriched in cells and tissues of the human nervous, immune, and cardiovascular systems. Humans with severely reduced plasmalogen levels have reduced life spans, abnormal neurological development, skeletal dysplasia, impaired respiration, and cataracts. Plasmalogen deficiency is also found in the brain tissue of individuals with Alzheimer disease.

Results

In a human and great ape cohort, we measured the red blood cell (RBC) levels of the most abundant types of plasmalogens. Total RBC plasmalogen levels were lower in humans than bonobos, chimpanzees, and gorillas, but higher than orangutans. There were especially pronounced cross-species differences in the levels of plasmalogens with a C16:0 moiety at the sn-1 position. Humans on Western or vegan diets had comparable total RBC plasmalogen levels, but the latter group showed moderately higher levels of plasmalogens with a C18:1 moiety at the sn-1 position. We did not find robust sex-specific differences in human or chimpanzee RBC plasmalogen levels or composition. Furthermore, human and great ape skin fibroblasts showed only modest differences in peroxisomal plasmalogen biosynthetic activity. Human and chimpanzee microarray data indicated that genes involved in plasmalogen biosynthesis show cross-species differential expression in multiple tissues.

Conclusion

We propose that the observed differences in human and great ape RBC plasmalogens are primarily caused by their rates of biosynthesis and/or turnover. Gene expression data raise the possibility that other human and great ape cells and tissues differ in plasmalogen levels. Based on the phenotypes of humans and rodents with plasmalogen disorders, we propose that cross-species differences in tissue plasmalogen levels could influence organ functions and processes ranging from cognition to reproduction to aging.

Plasmalogens, phospholipases A2 and signal transduction

Several lines of evidence indicate that the breakdown of plasmalogens in neural membranes during neurodegenerative diseases is a receptor-mediated process catalyzed by a plasmalogen-selective phospholipase A2. This enzyme has recently been purified from bovine brain. It does not require Ca2+ and is localized in cytosol. It has a molecular mass of 39 kDa and is strongly inhibited by glycosaminoglycans, with the pattern of inhibition being heparan sulfate > hyaluronic acid > chondroitin sulfate > heparin. This plasmalogen-selective phospholipase A2 is also inhibited by gangliosides and sialoglycoproteins. Substrate specificity and the effects of metal ions, detergents and inhibitors suggest that this phospholipase A2 is different from the well-known 85 kDa Ca(2+)-dependent cytosolic phospholipase A2 that has recently been cloned and is not plasmalogen-selective. The plasmalogen-selective phospholipase A2 may be regulated by glycosaminoglycans and sialoglycoconjugates and may be involved in the regulation of K+ channels. This enzyme, which plays a major role in the release of fatty acids during ischemic injury and reperfusion, shows promise as a major target for drug therapy.

Chorea-acanthocytosis: abnormal composition of covalently bound fatty acids of erythrocyte membrane proteins

Phospholipid class, peak profile of each phospholipid class, loosely bound fatty acids, covalently (tightly) bound fatty acids of the erythrocyte membranes, and plasma fatty acids were investigated using high-performance liquid chromatography in six patients with chorea-acanthocytosis and 14 age- and sex-matched normal control subjects. Additionally, six patients with Huntington's disease were included as disease control subjects in the study of covalently bound fatty acids. Study of covalently (tightly) bound fatty acids in erythrocyte membrane proteins after alkaline hydrolysis, hitherto undescribed in chorea-acanthocytosis, revealed that palmitic acid (C16:0) was significantly increased and stearic acid (C18:0) was decreased in the patients with chorea-acanthocytosis. Analyses for total covalently bound fatty acids disclosed that palmitic and docosahexaenoic (C22:6) acids were increased and stearic acid was decreased in chorea-acanthocytosis. Phospholipid class (phosphatidylcholine, phosphatidylethanolamine, sphingomyelin, and phosphatidylserine) and peak profile of each phospholipid class from the erythrocyte membranes did not differ between the patients with chorea-acanthocytosis and the control subjects. Of the loosely bound fatty acids, linoleic acid (C18:2) was significantly decreased in those with chorea-acanthocytosis, which seemed to be nonspecific.

Increased plasma membrane fluidity and decreased receptor availability of nonmuscle cells in myotonic dystrophy

Plasma membrane fluidity of intact nonmuscle cells from patients with myotonic dystrophy (MyD) was determined by fluorescence anisotropy measurements. Anisotropy values of the probe diphenylhexatriene were decreased in patient mononuclear cells (0.163 +/- 0.017, n = 13) versus controls (0.181 +/- 0.013, n = 13, P less than 0.01) and in patient platelets (0.087 +/- 0.017, n = 9) versus controls (0.137 +/- 0.015, n = 9, P less than 0.001) indicating increased plasma membrane fluidity in patient nonmuscle cells. Vasopressin plasma concentrations were increased in patients (7.4 +/- 2.1 pg/ml, n = 12) versus controls (4.5 +/- 1.4 pg/ml, n = 22, P less than 0.0005), whereas serum osmolality was normal. These data are compatible with a decreased vasopressin sensitivity in MyD patients. Specific binding of 125I-labelled vasoactive intestinal peptide (VIP) was decreased in patient mononuclear cells (2.9 +/- 0.9%/10(6) cells, n = 8) versus controls (5.2 +/- 1.6%/10(6) cells, n = 9, P less than 0.005) and receptor affinity for VIP was decreased in patient mononuclear cells (Kd = 0.26 +/- 0.05 nM, n = 8) versus controls (Kd = 0.19 +/- 0.02 nM, n = 9, P less than 0.005). In nonmuscle cells of MyD patients, increased membrane fluidity correlated with decreased receptor availability. This might explain the various endocrine defects described in MyD patients.

Decreased plasmalogen ratios in cultured skin fibroblasts from myotonic dystrophy

It has become known that hypolipidemic agents, which can induce experimental myotonia in humans and animals, may alter the lipid metabolisms of intracellular organelles, peroxisomes. However, there has been no reported study on peroxisomal lipid metabolisms in myotonic dystrophy showing myotonia as well as experimental myotonia. We investigated one of the peroxisomal lipid metabolisms, i.e., plasmalogen metabolism in cultured skin fibroblasts from myotonic dystrophy, and found plasmalogen ratios to be significantly reduced.

Plasmalogen deficiency in cultured skin fibroblasts from neonatal adrenoleukodystrophy

The plasmalogen ratio (defined as area ratio of lysophosphatidylethanolamine to the diacyl form of phosphatidylethanolamine) was investigated in cultured skin fibroblasts from neonatal adrenoleukodystrophy (N = 4) and X-linked recessive (N = 3) in addition to Zellweger syndrome (N = 3) because plasmalogen was reported to be reduced in Zellweger syndrome. The ratio was markedly decreased in all cases of Zellweger syndrome studied and in three of the four cases of neonatal adrenoleukodystrophy, whereas it was normal in the X-linked cases. This is the first documentation of a plasmalogen deficiency in neonatal adrenoleukodystrophy.

Fatty acid compositions of erythrocytes, mononuclear cells and blood plasma of patients with myotonic dystrophy

Fatty acid compositions of erythrocyte membrane phospholipids including phosphatidylethanolamine subclasses, blood plasma and mononuclear cells of 8 patients with myotonic dystrophy (MyD) and 8 normal controls were analyzed by high performance liquid chromatography. Slight changes (decreased C18:2 and increased C16:0) in the fatty acid compositions of erythrocyte membrane glycerophospholipids and blood plasma lipids were observed in MyD. There was no significant difference in the fatty acid composition of mononuclear cells between MyD and normal controls. It seems that no essential defect exists in either the erythrocyte membrane fatty acid composition or the fatty acid metabolism itself in MyD.