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.

Fatal Encephalopathy Associated with Influenza in a Health Care Professional

“…Although the use of nonsteroidal anti-inflammatory drugs, such as aspirin and diclofenac sodium, is associated with a significant increase in the mortality rate of influenzaassociated encephalopathy (7,8), acetaminophen, which was used in the present case, may have had little effect on the development of encephalopathy. Furthermore, although the patient had a history of hypersensitive pneumonitis, we doubt that an allergic reaction affected the development of encephalopathy.…”

Carnitine palmitoyltransferase 2 gene polymorphism is a genetic risk factor for sudden unexpected death in infancy

“…While CPT2 gene polymorphisms do not decrease CPT II activity in normal physiological situations, the F352C variant alone has been reported to reduce CPT II activity by about 50% under certain conditions such as heat stress, fasting, acidosis, and seizures [9][10][11]17]. Shinohara et al has reported that the F352C variant is a statistically significant risk factor in patients with acute encephalopathy [12].…”

“…A congenital or acquired abnormality of mitochondrial fatty acid oxidation causes the accumulation of mini-plasmin in the cerebral capillaries and the proteolytical destruction of the blood-brain barrier in mice after influenza virus infection [9,18]. Intracellular ATP production is reduced by about 50% for the F352C variant compared to the wild type under severe conditions [9][10][11]17]. The suppression of intracellular ATP production weakens interactions between tight junction proteins of cerebral microvascular endothelial cells, leading to the destruction of brain homeostasis and brain edema [10].…”

“…Intracellular ATP production is reduced by about 50% for the F352C variant compared to the wild type under severe conditions [9][10][11]17]. The suppression of intracellular ATP production weakens interactions between tight junction proteins of cerebral microvascular endothelial cells, leading to the destruction of brain homeostasis and brain edema [10]. Thus, under severe conditions such as high fever and respiratory or metabolic acidosis, decreased CPT II activity with the F352C variant might lead to energy crisis, acute brain edema, and sudden death.…”

“…Carnitine palmitoyltransferase 2 gene polymorphisms have not been reported to affect enzyme activity, although a thermolabile phenotype of the CPT2 polymorphism (F352C) has been recently reported to reduce enzyme activity at high temperature [9][10][11]. Shinohara et al have reported that the F352C variant causes energy crisis at high temperature and is associated with acute encephalopathy [12].…”