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MITOCHONDRIAL ENERGETIC DEFECTS IN MUSCLE AND BRAIN OF A
HMBS-/- MOUSE MODEL OF ACUTE INTERMITTENT PORPHYRIA
Chadi Homedan1,2,†, Caroline Schmitt3,4,5,†, Jihane Laafi1,†, Naïg Gueguen2,6, Valérie
Desquiret-Dumas2,6, Hugo Lenglet4,5, Zoubida Karim4,5, Laurent Gouya3,4,5, JeanCharles Deybach3,4,5, Gilles Simard1,2, Hervé Puy3,4,5, Yves Malthièry1,2, Pascal
Reynier2,6,* 1UMR INSERM 1063, Centre Hospitalier Universitaire, 4 rue Larrey, 49933 Angers, France 2Département de Biochimie et Génétique, Centre Hospitalier Universitaire, 4 rue Larrey, 49933 Angers, France 3Assistance Publique Hôpitaux de Paris, Centre Français des Porphyries, Hôpital Louis
Mourier AP-HP, 178 rue des Renouillers, 92701, Colombes, France 4INSERM U1149, CNRS ERL 8252, Center for Research on Inflammation (CRI), Université
Paris Diderot, site Bichat, Sorbonne Paris Cité, 16 rue Henri Huchard, 75018, Paris, France 5Laboratory of Excellence, GR-Ex, Sorbonne Paris Cité, 16 rue Henri Huchard, 75018, Paris,
France 6UMR CNRS 6214 - INSERM 1083, Centre Hospitalier Universitaire, 4 rue Larrey, 49933
Angers, France *To whom correspondence should be addressed at: Département de Biochimie et Génétique,
CHU d'Angers - 4 rue Larrey, F-49933 Angers, France, Tel : +33 241355542, Fax : +33 241354017, Email : firstname.lastname@example.org †Authors contributed equally to this work
HMG Advance Access published June 12, 2015 at U niversity of N ebraska-Lincoln Libraries on Septem ber 10, 2015 http://hm g.oxfordjournals.org/
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Acute intermittent porphyria (AIP), an autosomal dominant metabolic disease (MIM #176000), is due to a deficiency of hydroxymethylbilane synthase (HMBS), which catalyzes the third step of the heme biosynthetic pathway. The clinical expression of the disease is mainly neurological, involving the autonomous, central and peripheral nervous systems. We explored mitochondrial oxidative phosphorylation (OXPHOS) in the brain and skeletal muscle of the Hmbs-/- mouse model first in the basal state, and then after induction of the disease with phenobarbital and treatment with heme arginate. The modification of the respiratory parameters, determined in mice in the basal state, reflected a spontaneous metabolic energetic adaptation to HMBS deficiency. Phenobarbital induced a sharp alteration of the oxidative metabolism with a significant decrease of ATP production in skeletal muscle that was restored by treatment with heme arginate. This OXPHOS defect was due to deficiencies in complexes I and II in the skeletal muscle whereas all four respiratory chain complexes were affected in the brain. To date, the pathogenesis of AIP has been mainly attributed to the neurotoxicity of aminolevulinic acid and heme deficiency. Our results show that mitochondrial energetic failure also plays an important role in the expression of the disease. at U niversity of N ebraska-Lincoln Libraries on Septem ber 10, 2015 http://hm g.oxfordjournals.org/
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Acute intermittent porphyria (AIP) is characterized by episodic neurovisceral attacks involving severe abdominal pain, peripheral neuropathy and psychiatric disturbances (1,2).
Diffuse abdominal pain, mimicking the acute abdomen syndrome, is accompanied by other neurovisceral symptoms such as nausea, vomiting, constipation, or diarrhoea. These symptoms, together with tachycardia, cardiac arrhythmia and high blood pressure, are thought to be due to the dysfunction of the sympathetic autonomic nervous system (3). The central nervous system is also involved in AIP. Porphyric attacks are often preceded by a prodromic phase with behavioural changes such as anxiety, restlessness and insomnia (4). In 20-30% of patients, signs of mental disturbance such as anxiety, insomnia, depression, disorientation, hallucinations, paranoia, agitation or confusion have been reported (5). Encephalopathy may also develop with altered consciousness and cortical lesions detected by brain MRI (6). Acute attacks can be life-threatening because of complications such as paralysis of the respiratory muscles. Indeed, unrecognized or untreated AIP is associated with a significant mortality of up to 10% (7). Muscle pain, weakness and paresis, beginning proximally in the arms and legs, also often develop during the crisis (5,8) as a consequence of peripheral neuropathy (3,2).
Electromyography and muscle biopsies show features of denervation together with muscle atrophy (9,10). Pathological studies have shown widespread peripheral nerve degeneration and chromatolysis of the anterior horn cells (10). These neurophysiological features may resolve after the crisis, but the partial improvement and persistence of irreversible nerve damage and muscle atrophy may accompany the evolution of the disease especially after recurrent AIP attacks (11). Subtle anomalies of nerve conduction have also been identified in patients not in the acute phase of the disease, reflecting subclinical neuropathy between acute attacks (12). at U niversity of N ebraska-Lincoln Libraries on Septem ber 10, 2015 http://hm g.oxfordjournals.org/
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The causes of this constellation of neurological features in AIP are far from being understood.
AIP, an autosomal dominant metabolic disease (MIM #176000), is caused by the deficiency of hydroxymethylbilane synthase (HMBS, EC 184.108.40.206), which catalyzes the third step of heme biosynthetic pathway (13). Acute attacks are provoked by endocrine or environmental factors including malnutrition (14) and drugs such as phenobarbital that induce the gene expression of cytochrome P450 enzymes in the liver (15). AIP patients are unable to respond satisfactorily to the increased demand for heme. In addition, the relative lack of heme greatly activates hepatic aminolevulinate synthase-1 (ALAS-1), the first step of the heme biosynthetic pathway that catalyzes the synthesis of aminolevulinic acid (ALA). The increased hepatic