RESUMO
The major glycerophospholipid phosphatidylethanolamine (PE) in the nervous system is essential for neural development and function. There are two major PE synthesis pathways, the CDP-ethanolamine pathway in the endoplasmic reticulum (ER) and the phosphatidylserine decarboxylase (PSD) pathway in mitochondria. However, the role played by mitochondrial PE synthesis in maintaining cellular PE homeostasis is unknown. Here, we show that Drosophila pect (phosphoethanolamine cytidylyltransferase) mutants lacking the CDP-ethanolamine pathway, exhibited alterations in phospholipid composition, defective phototransduction, and retinal degeneration. Induction of the PSD pathway fully restored levels and composition of cellular PE, thus rescued the retinal degeneration and defective visual responses in pect mutants. Disrupting lipid exchange between mitochondria and ER blocked the ability of PSD to rescue pect mutant phenotypes. These findings provide direct evidence that the synthesis of PE in mitochondria contributes to cellular PE homeostasis, and suggest the induction of mitochondrial PE synthesis as a promising therapeutic approach for disorders associated with PE deficiency.
Assuntos
Carboxiliases/genética , Cistina Difosfato/análogos & derivados , Retículo Endoplasmático/genética , Degeneração Retiniana/genética , Animais , Carboxiliases/metabolismo , Cistina Difosfato/deficiência , Cistina Difosfato/genética , Cistina Difosfato/metabolismo , Modelos Animais de Doenças , Drosophila melanogaster/genética , Retículo Endoplasmático/metabolismo , Etanolaminas/metabolismo , Homeostase/genética , Humanos , Metabolismo dos Lipídeos/genética , Mitocôndrias/genética , Mitocôndrias/metabolismo , Fosfatidilserinas/genética , Fosfatidilserinas/metabolismo , Degeneração Retiniana/metabolismo , Degeneração Retiniana/patologia , Transdução de Sinais/genéticaRESUMO
Phosphatidylethanolamine (PE) is an important inner membrane phospholipid mostly synthesized de novo via the PE-Kennedy pathway and by the decarboxylation of phosphatidylserine. CTP:phosphoethanolamine cytidylyltransferase (Pcyt2) catalyzes the formation of CDP-ethanolamine, which is often the rate regulatory step in the PE-Kennedy pathway. In the current investigation, we show that the reduced CDP-ethanolamine formation in Pcyt2(+/-) mice limits the rate of PE synthesis and increases the availability of diacylglycerol. This results in the increased formation of triglycerides, which is facilitated by stimulated de novo fatty acid synthesis and increased uptake of pre-existing fatty acids. Pcyt2(+/-) mice progressively accumulate more diacylglycerol and triglycerides with age and have modified fatty acid composition, predominantly in PE and triglycerides. Pcyt2(+/-) additionally have an inherent blockage in fatty acid utilization as energy substrate and develop impaired tolerance to glucose and insulin at an older age. Accordingly, gene expression analyses demonstrated the up-regulation of the main lipogenic genes and down-regulation of mitochondrial fatty acid beta-oxidation genes. These data demonstrate for the first time that to preserve membrane PE phospholipids, Pcyt2 deficiency generates compensatory changes in triglyceride and energy substrate metabolism, resulting in a progressive development of liver steatosis, hypertriglyceridemia, obesity, and insulin resistance, the main features of the metabolic syndrome.
Assuntos
Cistina Difosfato/análogos & derivados , Etanolaminas/metabolismo , Erros Inatos do Metabolismo Lipídico/enzimologia , Fosfatidiletanolaminas/biossíntese , RNA Nucleotidiltransferases , Animais , Cistina Difosfato/genética , Cistina Difosfato/metabolismo , Diglicerídeos/genética , Diglicerídeos/metabolismo , Fígado Gorduroso/enzimologia , Fígado Gorduroso/genética , Feminino , Regulação da Expressão Gênica/genética , Hipertrigliceridemia/enzimologia , Hipertrigliceridemia/genética , Resistência à Insulina/genética , Erros Inatos do Metabolismo Lipídico/genética , Masculino , Síndrome Metabólica/enzimologia , Síndrome Metabólica/genética , Camundongos , Camundongos Knockout , Fosfatidiletanolaminas/genética , Fosfatidilserinas/genética , Fosfatidilserinas/metabolismo , Triglicerídeos/genética , Triglicerídeos/metabolismoRESUMO
Myogenic factor 5 (myf-5) is the product of the MYF5 gene, belonging to the MyoD family. This transcription factor participates in the control of myogenesis. We identified 3 new mutations in the promoter region of the gene: A65C, C580T and C613T. The aim of this study was to evaluate the influence of the A65C transversion on gene expression. The analysis was conducted on 15 Polish Large White gilts. The relative content of MYF5 mRNA in m. longissimus dorsi did not differ significantly across MYF5 genotypes (AA, AC, CC). This result suggests that the A65C transversion may not play an important role in the expression of the MYF5 gene in analysed adult muscle but it abolishes a putative binding site for two transcription factors (CDP and HSF1) and creates such a site for Sp1.
