title: Thermal instability of compound variants of carnitine palmitoyltransferase II and impaired mitochondrial fuel utilization in influenza-associated encephalopathy.
abstract: Influenza-associated encephalopathy (IAE) is characterized by persistent high fever, febrile convulsions, severe brain edema, and high mortality in otherwise apparently healthy individuals. We have reported that a large proportion of patients suffering from disabling or fatal IAE, with transiently elevated serum acylcarnitine during high fever, exhibit a thermolabile phenotype of compound homo-/heterozygous variants of carnitine palmitoyltransferase II (CPT II, gene symbol CPT2). We characterized the enzymatic properties of five single and three compound CPT II variants in patients with IAE. The kinetic characteristics of WT and variant CPT IIs, expressed in COS-7 cells, indicated that the variants exert a dominant-negative effect on the homotetrameric protein of the enzyme. Among the variants, three compound variations found in patients with severe encephalopathy; [c.1055T>G (p.Phe352Cys); c.1102G>A (p.Val368Ile)], [c.1511C>T (p.Pro504Leu); c.1813G>C (p.Val605Leu)], and [c.1055T>G (p.Phe352Cys); c.1102G>A (p.Val368Ile); c.1813G>C (p.Val605Leu)], showed reduced activities, thermal instability, and short half-lives compared with the WT. Like other disease-causing mutant proteins, these variant proteins were poly-ubiquitinated and rapidly degraded by a lactacystin-sensitive proteasome pathway. COS-7 cells transfected with the compound variants had their fatty acid beta-oxidation decreased to 30-59% and intracellular ATP levels to 48-79%, and a marked reduction of mitochondrial membrane potential at 41 degrees C, compared with control cells transfected with WT at 37 degrees C. The unstable CPT II variants with decreased enzymatic activities may bring mitochondrial fuel utilization below the phenotypic threshold during high fever, and thus may play an important etiopathological role in the development of brain edema of IAE.
authors.affiliation: Division of Enzyme Chemistry, Institute for Enzyme Research, The University of Tokushima, Tokushima, Japan.
authors.forename: Dengbing
authors.initials: D
authors.lastname: Yao
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Mizuguchi
authors.forename: Miyoko
authors.initials: M
authors.lastname: Yamaguchi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yamada
authors.forename: Junji
authors.initials: J
authors.lastname: Chida
authors.forename: Koji
authors.initials: K
authors.lastname: Shikata
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kido
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D019556:COS Cells; D002334:Carnitine O-Palmitoyltransferase / Q000235:genetics / Q000378:metabolism*; D002522:Chlorocebus aethiops; D018792:Encephalitis, Viral / Q000201:enzymology / Q000209:etiology*; D004795:Enzyme Stability; D006358:Hot Temperature; D006801:Humans; D007251:Influenza, Human / Q000150:complications*; D008564:Membrane Potentials; D008928:Mitochondria / Q000378:metabolism*; D011110:Polymorphism, Genetic; D012333:RNA, Messenger / Q000235:genetics
chemical_list: D012333:RNA, Messenger; D000255:Adenosine Triphosphate; D002334:Carnitine O-Palmitoyltransferase