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J Physiol ; 591(2): 571-92, 2013 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-23129796

RESUMO

Creatine (Cr) plays an important role in muscle energy homeostasis by its participation in the ATP-phosphocreatine phosphoryl exchange reaction mediated by creatine kinase. Given that the consequences of Cr depletion are incompletely understood, we assessed the morphological, metabolic and functional consequences of systemic depletion on skeletal muscle in a mouse model with deficiency of l-arginine:glycine amidinotransferase (AGAT(-/-)), which catalyses the first step of Cr biosynthesis. In vivo magnetic resonance spectroscopy showed a near-complete absence of Cr and phosphocreatine in resting hindlimb muscle of AGAT(-/-) mice. Compared with wild-type, the inorganic phosphate/ß-ATP ratio was increased fourfold, while ATP levels were reduced by nearly half. Activities of proton-pumping respiratory chain enzymes were reduced, whereas F(1)F(0)-ATPase activity and overall mitochondrial content were increased. The Cr-deficient AGAT(-/-) mice had a reduced grip strength and suffered from severe muscle atrophy. Electron microscopy revealed increased amounts of intramyocellular lipid droplets and crystal formation within mitochondria of AGAT(-/-) muscle fibres. Ischaemia resulted in exacerbation of the decrease of pH and increased glycolytic ATP synthesis. Oral Cr administration led to rapid accumulation in skeletal muscle (faster than in brain) and reversed all the muscle abnormalities, revealing that the condition of the AGAT(-/-) mice can be switched between Cr deficient and normal simply by dietary manipulation. Systemic creatine depletion results in mitochondrial dysfunction and intracellular energy deficiency, as well as structural and physiological abnormalities. The consequences of AGAT deficiency are more pronounced than those of muscle-specific creatine kinase deficiency, which suggests a multifaceted involvement of creatine in muscle energy homeostasis in addition to its role in the phosphocreatine-creatine kinase system.


Assuntos
Erros Inatos do Metabolismo dos Aminoácidos/fisiopatologia , Creatina/deficiência , Metabolismo Energético , Deficiência Intelectual/fisiopatologia , Atrofia Muscular/genética , Distúrbios da Fala/fisiopatologia , Trifosfato de Adenosina/metabolismo , Amidinotransferases/deficiência , Amidinotransferases/genética , Amidinotransferases/metabolismo , Erros Inatos do Metabolismo dos Aminoácidos/dietoterapia , Erros Inatos do Metabolismo dos Aminoácidos/metabolismo , Erros Inatos do Metabolismo dos Aminoácidos/patologia , Animais , Creatina/uso terapêutico , Creatina Quinase/metabolismo , Deficiências do Desenvolvimento/dietoterapia , Deficiências do Desenvolvimento/metabolismo , Deficiências do Desenvolvimento/patologia , Deficiências do Desenvolvimento/fisiopatologia , Força da Mão , Membro Posterior/patologia , Concentração de Íons de Hidrogênio , Deficiência Intelectual/dietoterapia , Deficiência Intelectual/metabolismo , Deficiência Intelectual/patologia , Isquemia/metabolismo , Metabolismo dos Lipídeos , Espectroscopia de Ressonância Magnética , Camundongos , Camundongos Knockout , Mitocôndrias/metabolismo , Mitocôndrias/ultraestrutura , Fibras Musculares Esqueléticas/metabolismo , Fibras Musculares Esqueléticas/patologia , Músculo Esquelético/metabolismo , Músculo Esquelético/patologia , Músculo Esquelético/fisiopatologia , Fosfatos/metabolismo , ATPases Translocadoras de Prótons/metabolismo , Distúrbios da Fala/dietoterapia , Distúrbios da Fala/metabolismo , Distúrbios da Fala/patologia
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