The Energy Crisis in CPT II Variant Fibroblasts

Carnitine palmitoyltransferase II (CPT II) deficiency is one of the most common causes of fatty acid oxidation metabolism disorders. However, the molecular mechanism between CPT2 gene polymorphisms and metabolic stress has not been fully clarified. We previously reported that a number of patients show a thermal instable phenotype of compound hetero/homozygous variants of CPT II. To understand the mechanism of the metabolic disorder resulting from CPT II deficiency, the present study investigated CPT II variants in patient fibroblasts, [c.1102 G>A (p.V368I)] (heterozygous), [c.1102 G>A (p.V368I)] (homozygous), and [c.1055 T>G (p.F352C)] (heterozygous) + [c.1102 G>A (p.V368I)] (homozygous) compared with fibroblasts from healthy controls. CPT II variants exerted an effect of dominant negative on the homotetrameric proteins that showed thermal instability, reduced residual enzyme activities and a short half-life. Moreover, CPT II variant fibroblasts showed a significant decrease in fatty acid β-oxidation and adenosine triphosphate generation, combined with a reduced mitochondrial membrane potential, resulting in cellular apoptosis. Collectively, our data indicate that the CPT II deficiency induces an energy crisis of the fatty acid metabolic pathway. These findings may contribute to the elucidation of the genetic factors involved in metabolic disorder encephalopathy caused by the CPT II deficiency

Characterization of compound missense mutation and deletion of carnitine palmitoyltransferase II in a patient with adenovirus-associated encephalopathy

Background : In mammals, carnitine palmitoyltransferase (CPT) system is a pivotal component of energy metabolism through mitochondrial fatty acid oxidation. The majority of patients with fatal or handicapped influenza-associated encephalopathy exhibit thermolabile compound homo/heterozygous mutations of CPT II. Objective : Compound CPT II mutations, [c.647A G (p.Q216R)], [c.1102G A (p.V368I)], [c.1939A G (p.M647V)] and [c.745delG (p.G249EfsX16)], were found in a patient with adenovirus-associated encephalopathy and his family. The properties of these CPT II mutations were analyzed in COS-7 cells. Methods : CPT II mutations in the patient and his family were expressed in COS-7 cells and their molecular masses, enzyme activities, thermal instabilities and halflives were analyzed. Results : We identified two novel CPT II mutations in the patient, [c.647A G (p.Q216R)] and [c.745delG (p.G249EfsX16)]. The CPT II Q216R mutation showed mild reduction of activity, thermal instability and short half-life but compound mutations with Q216R+V368I+M647V showed further enhancement of these disabilities, although mutations V368I and M647V had no such effects. CPT II mutation [c.745delG (p.G249 EfsX16)] abolished enzyme activity and showed short half-life. Conclusion : The thermal instability and short half-life of the novel CPT II mutations, [c.647A G (p.Q216R)] and [c.745delG (p.G249EfsX16)], could play important roles in energy crisis in the pathogenesis of virus-associated encephalopathy

Abbreviated half-lives and impaired fuel utilization in carnitine palmitoyltransferase II variant fibroblasts.

Carnitine palmitoyltransferase II (CPT II) deficiency is one of the most common causes of fatty acid oxidation metabolism disorders. However, the molecular mechanism between CPT2 gene polymorphisms and metabolic stress has not been fully clarified. We previously reported that a number of patients show a thermal instable phenotype of compound hetero/homozygous variants of CPT II. To understand the mechanism of the metabolic disorder resulting from CPT II deficiency, the present study investigated CPT II variants in patient fibroblasts, [c.1102 G>A (p.V368I)] (heterozygous), [c.1102 G>A (p.V368I)] (homozygous), and [c.1055 T>G (p.F352C)] (heterozygous) + [c.1102 G>A (p.V368I)] (homozygous) compared with fibroblasts from healthy controls. CPT II variants exerted an effect of dominant negative on the homotetrameric proteins that showed thermal instability, reduced residual enzyme activities and a short half-life. Moreover, CPT II variant fibroblasts showed a significant decrease in fatty acid β-oxidation and adenosine triphosphate generation, combined with a reduced mitochondrial membrane potential, resulting in cellular apoptosis. Collectively, our data indicate that the CPT II deficiency induces an energy crisis of the fatty acid metabolic pathway. These findings may contribute to the elucidation of the genetic factors involved in metabolic disorder encephalopathy caused by the CPT II deficiency

Role of transforming growth factor-β in peripheral nerve regeneration

Injuries caused by trauma and neurodegenerative diseases can damage the peripheral nervous system and cause functional deficits. Unlike in the central nervous system, damaged axons in peripheral nerves can be induced to regenerate in response to intrinsic cues after reprogramming or in a growth-promoting microenvironment created by Schwann cells. However, axon regeneration and repair do not automatically result in the restoration of function, which is the ultimate therapeutic goal but also a major clinical challenge. Transforming growth factor (TGF) is a multifunctional cytokine that regulates various biological processes including tissue repair, embryo development, and cell growth and differentiation. There is accumulating evidence that TGF-β family proteins participate in peripheral nerve repair through various factors and signaling pathways by regulating the growth and transformation of Schwann cells; recruiting specific immune cells; controlling the permeability of the blood-nerve barrier, thereby stimulating axon growth; and inhibiting remyelination of regenerated axons. TGF-β has been applied to the treatment of peripheral nerve injury in animal models. In this context, we review the functions of TGF-β in peripheral nerve regeneration and potential clinical applications

Fas Ligand Gene (Faslg) Plays an Important Role in Nerve Degeneration and Regeneration After Rat Sciatic Nerve Injury

Wallerian degeneration (WD) is associated with changes in the expression levels of a large number of genes. However, the effects of these up- or down-regulated genes are poorly understood. We have reported some key factors that are differentially regulated during WD in our previous research. Here, we explored the roles of Fas ligand gene (Faslg) in WD after rat sciatic nerve injury. The data showed that Faslg was up-regulated in injured nerves. Expression changed of Faslg in Schwann cells (SCs) resulted in alterations in the release of related factors. Silencing or overexpression of Faslg affected SC proliferation, migration, and apoptosis through β-catenin, nuclear factor-κB (NF-κB), and caspase-3 pathways in vivo and in vitro. Our data suggest that Faslg is a key regulatory gene that affects nerve repair and regeneration in peripheral nerve injury. This study sheds new light on the effects of Faslg on peripheral nerve degeneration and/or regeneration

Reduction of mitochondrial membrane potential of control and variant CPT IIs in cultured fibroblasts.

<p>Control (A, D), V368I (homozygous) (B, E), and F352C (heterozygous) + V368I (homozygous) (C, F) fibroblasts were cultured at 37°C and 41°C. Mitochondrial depolarization was monitored by 15 min treatment with 10 μM of JC-1 in the dark and visualized under a fluorescence microscope. Scale bars, 100 μm.</p

A proposed energy crisis pathway induced by CPT II deficiency.

<p>A proposed energy crisis pathway induced by CPT II deficiency.</p

CPT II expression and the dominant—negative effect of <i>CPT II</i> variants on substrate-dependent kinetics.

<p>(A) CPT II expression was analyzed by Western Blotting with an anti-CPT II antibody. (B) Dominant—negative effect of <i>CPT II</i> variants was analyzed by substrate-dependent kinetics. (C) Relative protein expression of control and variant CPT II. (D) Real-time PCR analysis of control and variant <i>CPT II</i> expression. Lane 1, control fibroblasts; lane 2, V368I (heterozygous); lane 3, V368I (homozygous); lane 4, F352C (heterozygous) + V368I (homozygous). CPT II protein was expressed relative to β-actin. <i>V</i>_max and <i>K</i>_m values were obtained from kinetic analysis (1/V versus 1/[S] plots) by varying the concentrations of L-[methyl-³H] carnitine between 0–300 μM at a fixed 50 μM palmitoyl-CoA concentration. (●) control, (▲) V368I (Homo), (◆) F352C (Hetero) + V368I (Homo). Data are means of three separate experiments. The average of three independent experiments is shown ± SEM (*P<0.05)</p

CPT II activities and thermal instability in CPT II-deficient fibroblasts.

<p>Fibroblast lysates were preincubated at 37°C or 41°C. Enzymatic reactions commenced by the addition of substrates at 37°C. Data are the means of five separate experiments. The average of three independent experiments is shown ± SEM (*P<0.05).</p

Pulse-chase (left) and half-lives (right) of control and variant CPT II in fibroblasts.

<p>Cultured fibroblasts were pulse-labeled with L-[³⁵S] methionine for 2 h and chased for 0, 6, 12, and 18 h. CPT II from fibroblast lysates was immunoprecipitated with anti-CPT II antibodies, then subjected to SDS-PAGE followed by autoradiography. (●) control, (■) V368I (homozygous), (▲) F352C (heterozygous) + V368I (homozygous). The average of three independent experiments is shown ± SEM.</p