RESUMO
Previous studies have shown that catecholamines in vivo and in vitro inhibit the activity of Ca2+-dependent proteolysis in skeletal muscles under basal conditions. In the present study we sought to investigate the role of catecholamines in regulating the Ca2+-dependent proteolysis in soleus and extensor digitorum longus (EDL) muscles from rats acutely exposed to cold. Overall proteolysis, the activity of proteolytic systems, protein levels and gene expression of different components of the calpain system were investigated in rats submitted to adrenodemedullation (ADMX) and exposed to cold for 24 h. ADMX drastically reduced plasma epinephrine and promoted an additional increase in the overall proteolysis, which was already increased by cold exposure. The rise in the rate of protein degradation in soleus muscles from adrenodemedullated cold-exposed rats was caused by the high activity of the Ca2+-dependent proteolysis, which was associated with the generation of a 145-kDa cleaved α-fodrin fragment, a typical calpain substrate, and lower protein levels and mRNA expression of calpastatin, the endogenous calpain inhibitor. Unlike that observed for soleus muscles, the cold-induced muscle proteolysis in EDL was not affected by ADMX. In isolated soleus muscle, clenbuterol, a selective ß2-adrenoceptor agonist, reduced the basal Ca2+-dependent proteolysis and completely abolished the activation of this pathway by the cholinergic agonist carbachol. These data suggest that catecholamines released from the adrenal medulla inhibit cold-induced protein breakdown in soleus, and this antiproteolytic effect on the Ca2+-dependent proteolytic system is apparently mediated through expression of calpastatin, which leads to suppression of calpain activation.NEW & NOTEWORTHY Although many effects of the sympathetic nervous system on muscle physiology are known, the role of catecholamines in skeletal muscle protein metabolism has been scarcely studied. We suggest that catecholamines released from adrenal medulla may be of particular importance for restraining the activation of the Ca2+-dependent proteolysis in soleus muscles during acute cold exposure. This finding helps us to understand the adaptive changes that occur in skeletal muscle protein metabolism during cold stress.
Assuntos
Medula Suprarrenal/metabolismo , Medula Suprarrenal/fisiologia , Cálcio/metabolismo , Músculo Esquelético/metabolismo , Músculo Esquelético/fisiologia , Animais , Proteínas de Ligação ao Cálcio/metabolismo , Calpaína/metabolismo , Proteínas de Transporte/metabolismo , Catecolaminas/metabolismo , Temperatura Baixa , Epinefrina/metabolismo , Masculino , Proteínas dos Microfilamentos/metabolismo , Proteínas Musculares/metabolismo , Proteólise , RNA Mensageiro/metabolismo , Ratos , Ratos Wistar , Transdução de Sinais/fisiologiaRESUMO
Although it is well established that carbohydrate and lipid metabolism are profoundly altered by cold stress, the effects of short-term cold exposure on protein metabolism in skeletal muscle are still poorly understood. Because cold acclimation requires that an organism adjust its metabolic flux, and muscle amino acids may be an important energy source for heat production, we hypothesize that muscle proteolysis is increased and protein synthesis is decreased under such a stress condition. Herein, cold exposure for 24 h decreased rates of protein synthesis and increased overall proteolysis in both soleus and extensor digitorum longus (EDL) muscles, but it did not affect muscle weight. An increase in proteolysis was accompanied by hyperactivity of the ubiquitin-proteasome system (UPS) in both soleus and EDL, and Ca(2+)-dependent proteolysis in EDL. Furthermore, muscles of rats exposed to cold showed increased mRNA and protein levels of atrogin-1 and muscle RING finger enzyme-1 (MuRF1). Additionally, cold stress reduced phosphorylation of Akt and Forkhead box class O1 (FoxO1), a well-known effect that increases FoxO translocation to the nucleus and leads to activation of proteolysis. Plasma insulin levels were lower, whereas catecholamines, corticosterone, and thyroid hormones were higher in cold-exposed rats compared with control rats. The present data provide the first direct evidence that short-term cold exposure for 24 h decreases rates of protein synthesis and increases the UPS and Ca(2+)-dependent proteolytic processes, and increases expression of atrogin-1 and MuRF1 in skeletal muscles of young rats. The activation of atrophy induced by acute cold stress seems to be mediated at least in part through the inactivation of Akt/FoxO signaling and activation of AMP-activated protein kinase.
Assuntos
Aclimatação , Temperatura Baixa , Resposta ao Choque Frio , Proteínas Musculares/metabolismo , Músculo Esquelético/metabolismo , Proteínas Quinases Ativadas por AMP/metabolismo , Animais , Proteínas de Ligação ao Cálcio/metabolismo , Calpaína/metabolismo , Proteínas de Transporte/metabolismo , Fatores de Transcrição Forkhead/metabolismo , Hormônios/sangue , Cinética , Lisossomos/metabolismo , Masculino , Proteínas dos Microfilamentos/metabolismo , Proteínas Musculares/genética , Proteínas do Tecido Nervoso/metabolismo , Fosforilação , Complexo de Endopeptidases do Proteassoma/metabolismo , Proteólise , Proteínas Proto-Oncogênicas c-akt/metabolismo , RNA Mensageiro/metabolismo , Ratos , Ratos Wistar , Proteínas Ligases SKP Culina F-Box/genética , Proteínas Ligases SKP Culina F-Box/metabolismo , Transdução de Sinais , Proteínas com Motivo Tripartido , Complexos Ubiquitina-Proteína Ligase/metabolismo , Ubiquitina-Proteína Ligases/genética , Ubiquitina-Proteína Ligases/metabolismoRESUMO
Insulin is an important regulator of the ubiquitin-proteasome system (UPS) and of lysosomal proteolysis in cardiac muscle. However, the role of insulin in the regulation of the muscle atrophy-related Ub-ligases atrogin-1 and MuRF1 as well as in autophagy, a major adaptive response to nutritional stress, in the heart has not been characterized. We report here that acute insulin deficiency in the cardiac muscle of rats induced by streptozotocin increased the expression of atrogin-1 and MuRF1 as well as LC3 and Gabarapl1, 2 autophagy-related genes. These effects were associated with decreased phosphorylation levels of Akt and its downstream target Foxo3a; this phenomenon is a well-known effect that permits the maintenance of Foxo in the nucleus to activate protein degradation by proteasomal and autophagic processes. The administration of insulin increased Akt and Foxo3a phosphorylation and suppressed the diabetes-induced expression of Ub-ligases and autophagy-related genes. In cultured neonatal rat cardiomyocytes, nutritional stress induced by serum/glucose deprivation strongly increased the expression of Ub-ligases and autophagy-related genes; this effect was inhibited by insulin. Furthermore, the addition of insulin in vitro prevented the decrease in Akt/Foxo signaling induced by nutritional stress. These findings demonstrate that insulin suppresses atrophy- and autophagy-related genes in heart tissue and cardiomyocytes, most likely through the phosphorylation of Akt and the inactivation of Foxo3a.
Assuntos
Autofagia/genética , Fatores de Transcrição Forkhead/metabolismo , Regulação da Expressão Gênica/efeitos dos fármacos , Insulina/farmacologia , Miocárdio/patologia , Miócitos Cardíacos/metabolismo , Proteínas Proto-Oncogênicas c-akt/metabolismo , Animais , Atrofia/genética , Autofagia/efeitos dos fármacos , Glicemia/metabolismo , Peso Corporal/efeitos dos fármacos , Diabetes Mellitus Experimental/genética , Diabetes Mellitus Experimental/patologia , Jejum/metabolismo , Lisossomos/efeitos dos fármacos , Lisossomos/metabolismo , Masculino , Miocárdio/metabolismo , Miócitos Cardíacos/efeitos dos fármacos , Miócitos Cardíacos/patologia , Tamanho do Órgão/efeitos dos fármacos , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Ratos , Ratos Wistar , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/genética , Ubiquitina-Proteína Ligases/genética , Ubiquitina-Proteína Ligases/metabolismoRESUMO
Mammalian cells contain several proteolytic systems to carry out the degradative processes and complex regulatory mechanisms to prevent excessive protein breakdown. Among these systems, the Ca2+-activated proteolytic system involves the cysteine proteases denoted calpains, and their inhibitor, calpastatin. Despite the rapid progress in molecular research on calpains and calpastatin, the physiological role and regulatory mechanisms of these proteins remain obscure. Interest in the adrenergic effect on Ca2+-dependent proteolysis has been stimulated by the finding that the administration of beta2-agonists induces muscle hypertrophy and prevents the loss of muscle mass in a variety of pathologic conditions in which calpains are activated. This review summarizes evidence indicating that the sympathetic nervous system produces anabolic, protein-sparing effects on skeletal muscle protein metabolism. Studies are reviewed, which indicate that epinephrine secreted by the adrenal medulla and norepinephrine released from adrenergic terminals have inhibitory effects on Ca2+-dependent protein degradation, mainly in oxidative muscles, by increasing calpastatin levels. Evidence is also presented that this antiproteolytic effect, which occurs under both basal conditions and in stress situations, seems to be mediated by beta2- and beta3-adrenoceptors and cAMP-dependent pathways. The understanding of the precise mechanisms by which catecholamines promote muscle anabolic effects may have therapeutic value for the treatment of muscle-wasting conditions and may enhance muscle growth in farm species for economic and nutritional purposes.
Assuntos
Cálcio/metabolismo , Inibidores de Cisteína Proteinase/metabolismo , Proteínas Musculares/metabolismo , Músculo Esquelético/metabolismo , Sistema Nervoso Simpático/metabolismo , Medula Suprarrenal/metabolismo , Cálcio/antagonistas & inibidores , Proteínas de Ligação ao Cálcio/metabolismo , Epinefrina/metabolismo , Humanos , Músculo Esquelético/química , Norepinefrina/metabolismoRESUMO
Mammalian cells contain several proteolytic systems to carry out the degradative processes and complex regulatory mechanisms to prevent excessive protein breakdown. Among these systems, the Ca2+-activated proteolytic system involves the cysteine proteases denoted calpains, and their inhibitor, calpastatin. Despite the rapid progress in molecular research on calpains and calpastatin, the physiological role and regulatory mechanisms of these proteins remain obscure. Interest in the adrenergic effect on Ca2+-dependent proteolysis has been stimulated by the finding that the administration of β2-agonists induces muscle hypertrophy and prevents the loss of muscle mass in a variety of pathologic conditions in which calpains are activated. This review summarizes evidence indicating that the sympathetic nervous system produces anabolic, protein-sparing effects on skeletal muscle protein metabolism. Studies are reviewed, which indicate that epinephrine secreted by the adrenal medulla and norepinephrine released from adrenergic terminals have inhibitory effects on Ca2+-dependent protein degradation, mainly in oxidative muscles, by increasing calpastatin levels. Evidence is also presented that this antiproteolytic effect, which occurs under both basal conditions and in stress situations, seems to be mediated by β2- and β3-adrenoceptors and cAMP-dependent pathways. The understanding of the precise mechanisms by which catecholamines promote muscle anabolic effects may have therapeutic value for the treatment of muscle-wasting conditions and may enhance muscle growth in farm species for economic and nutritional purposes.
Assuntos
Humanos , Cálcio/metabolismo , Inibidores de Cisteína Proteinase/metabolismo , Proteínas Musculares/metabolismo , Músculo Esquelético/metabolismo , Sistema Nervoso Simpático/metabolismo , Medula Suprarrenal , Proteínas de Ligação ao Cálcio/metabolismo , Cálcio/antagonistas & inibidores , Epinefrina , Músculo Esquelético/química , NorepinefrinaRESUMO
1. The role of beta2-agonist and of cAMP in chick skeletal muscle proteolytic pathways and protein synthesis was investigated using an in vitro preparation that maintains tissue glycogen stores and metabolic activity for several hours. 2. In extensor digitorum longus (EDL) muscle total proteolysis decreased by 15 to 20% in the presence of equimolar concentrations of epinephrine, clenbuterol, a selective hbetaagonist, or dibutyryl-cAMP. Rates of protein synthesis were not altered by clenbuterol or dibutyryl-cAMP. 3. The decrease in the rate of total protein degradation induced by 10(-5)M clenbuterol was paralleled by a 44% reduction in Ca2+-dependent proteolysis, which was prevented by 10(-5)M ICI 118.551, a selective fbeta2antagonist. 4. No change was observed in the activity of the lysosomal, ATP-dependent, and ATP-independent proteolytic systems. Ca2+-dependent proteolytic activity was also reduced by 58% in the presence of 10(-4)M dibutyryl-cAMP or isobutylmethylxanthine. 5. The data suggest that catecholamines exert an inhibitory control of Ca2+-dependent proteolysis in chick skeletal muscle, probably mediated by fbeta2adrenoceptors, with the participation of a cAMP-dependent pathway.
Assuntos
Agonistas Adrenérgicos beta/farmacologia , Epinefrina/farmacologia , Proteínas Musculares/metabolismo , Músculo Esquelético/metabolismo , Receptores Adrenérgicos beta 2/fisiologia , Antagonistas Adrenérgicos beta/farmacologia , Animais , Bucladesina/farmacologia , Galinhas , Clembuterol/farmacologia , Cinética , Proteínas Musculares/efeitos dos fármacos , Propanolaminas/farmacologia , Receptores Adrenérgicos beta 2/efeitos dos fármacosRESUMO
Overall proteolysis and the activity of skeletal muscle proteolytic systems were investigated in rats 1, 2, or 4 days after adrenodemedullation. Adrenodemedullation reduced plasma epinephrine by 95% and norepinephrine by 35% but did not affect muscle norepinephrine content. In soleus and extensor digitorum longus (EDL) muscles, rates of overall proteolysis increased by 15-20% by 2 days after surgery but returned to normal levels after 4 days. The rise in rates of protein degradation was accompanied by an increased activity of Ca(2+)-dependent proteolysis in both muscles, with no significant change in the activity of lysosomal and ATP-dependent proteolytic systems. In vitro rates of Ca(2+)-dependent proteolysis in soleus and EDL from normal rats decreased by ~35% in the presence of either 10(-5) M clenbuterol, a beta(2)-adrenergic agonist, or epinephrine or norepinephrine. In the presence of dibutyryl cAMP, proteolysis was reduced by 62% in soleus and 34% in EDL. The data suggest that catecholamines secreted by the adrenal medulla exert an inhibitory control of Ca(2+)-dependent proteolysis in rat skeletal muscle, mediated by beta(2)-adrenoceptors, with the participation of a cAMP-dependent pathway.
Assuntos
Cálcio/farmacologia , Catecolaminas/farmacologia , AMP Cíclico/fisiologia , Proteínas Musculares/metabolismo , Músculo Esquelético/efeitos dos fármacos , Receptores Adrenérgicos beta 2/fisiologia , Medula Suprarrenal/fisiologia , Medula Suprarrenal/cirurgia , Agonistas de Receptores Adrenérgicos beta 2 , Animais , Bucladesina/farmacologia , Catecolaminas/fisiologia , Clembuterol/farmacologia , Endopeptidases/metabolismo , Epinefrina/análise , Epinefrina/sangue , Lisossomos/enzimologia , Masculino , Músculo Esquelético/química , Músculo Esquelético/metabolismo , Norepinefrina/análise , Norepinefrina/sangue , Ratos , Ratos Wistar , Receptores Adrenérgicos beta 2/efeitos dos fármacosRESUMO
The role of adrenoceptor subtypes and of cAMP on rat skeletal muscle proteolysis was investigated using a preparation that maintains tissue glycogen stores and metabolic activity for several hours. In both soleus and extensor digitorum longus (EDL) muscles, proteolysis decreased by 15-20% in the presence of equimolar concentrations of epinephrine, isoproterenol, a nonselective beta-agonist, or clenbuterol, a selective beta(2)-agonist. Norepinephrine also reduced proteolysis but less markedly than epinephrine. No change in proteolysis was observed when muscles were incubated with phenylephrine, a nonselective alpha-agonist. The decrease in the rate of protein degradation induced by 10(-4) M epinephrine was prevented by 10(-5) M propranolol, a nonselective beta-antagonist, and by 10(-5) M ICI 118.551, a selective beta(2)-antagonist. The antiproteolytic effect of epinephrine was not inhibited by prazosin or yohimbine (selective alpha(1)-and alpha(2)-antagonists, respectively) or by atenolol, a selective beta(1)-antagonist. Dibutyryl cAMP and isobutylmethylxanthine reduced proteolysis in both soleus and EDL muscles. The data suggest that catecholamines exert an inhibitory control of skeletal muscle proteolysis, probably mediated by beta(2)-adrenoceptors, with the participation of a cAMP-dependent pathway.
Assuntos
Catecolaminas/farmacologia , AMP Cíclico/fisiologia , Proteínas Musculares/metabolismo , Músculo Esquelético/metabolismo , Receptores Adrenérgicos/fisiologia , 1-Metil-3-Isobutilxantina/farmacologia , Trifosfato de Adenosina/metabolismo , Agonistas alfa-Adrenérgicos/farmacologia , Antagonistas Adrenérgicos alfa/farmacologia , Agonistas Adrenérgicos beta/farmacologia , Antagonistas Adrenérgicos beta/farmacologia , Animais , Bucladesina/farmacologia , Glicogênio/metabolismo , Técnicas In Vitro , Masculino , Contração Muscular/efeitos dos fármacos , Músculo Esquelético/efeitos dos fármacos , Fosfocreatina/metabolismo , Inibidores de Fosfodiesterase/farmacologia , Ratos , Ratos Wistar , Receptores Adrenérgicos/efeitos dos fármacosRESUMO
Overall proteolysis and the activity of skeletal muscle proteolytic systems were investigated in rats submitted to guanethidine-induced adrenergic blockade for 4 days. In soleus, overall proteolysis increased by 15-20% during the first 2 days of guanethidine treatment but decreased to levels below control values after 4 days. Extensor digitorum longus (EDL) did not show the initial increase in total proteolysis, which was already reduced after 2 days of guanethidine treatment. The initial rise in the rate of protein degradation in soleus was accompanied by an increased activity of the Ca(2+)-dependent proteolytic pathway. In both soleus and EDL, the reduction in overall proteolysis was paralleled by decreased activities of the Ca(2+)-dependent and ATP-dependent proteolytic processes. No change was observed in the activity of the lysosomal proteolytic system. Overall proteolysis in soleus and EDL from nontreated rats was partially inhibited by isoproterenol, in vitro. The data suggest an acute inhibitory control of skeletal muscle proteolysis by the adrenergic system, well evident in the oxidative muscle, with an important participation of the Ca(2+)-dependent pathway.
Assuntos
Adrenérgicos/farmacologia , Guanetidina/farmacologia , Músculo Esquelético/efeitos dos fármacos , Músculo Esquelético/enzimologia , Trifosfato de Adenosina/metabolismo , Medula Suprarrenal/química , Agonistas Adrenérgicos beta/farmacologia , Animais , Cálcio/metabolismo , Corticosterona/sangue , Dopamina/análise , Dopamina/sangue , Endopeptidases/metabolismo , Epinefrina/análise , Epinefrina/sangue , Insulina/sangue , Isoproterenol/farmacologia , Lisossomos/enzimologia , Masculino , Músculo Esquelético/química , Norepinefrina/análise , Norepinefrina/sangue , Ratos , Ratos Wistar , Testosterona/sangueRESUMO
The effect of congenital hypothyroidism on the visual system of Wistar rats was studied by determining neuron density in the retinal ganglion cell layer. Retinae of adult rats from mothers treated with propylthiouracil, 50 mg/day, starting on the 15th day of pregnancy (PTU group), and of adult rats from untreated mothers (control group) were examined. Retinae were prepared, and the neurons in the nasotemporal region located above the optic disc were counted. Hypothyroid rats showed a significant reduction in the retinal area (about 6.8%), when compared to controls. The cell density in the retinal ganglion cell layer was significantly decreased in 6 PTU-treated compared to 5 control retinae in total (2,793 +/- 330 vs 3,704 +/- 662 neurons/mm2), nasal (3,031 +/- 580 vs 3,853 +/- 699 neurons/mm2) and temporal (2,555 +/- 155 vs 3,555 +/- 827 neurons/mm2) regions. These alterations in a region considered to be one of the most specialized in the visual process suggest a structural deficiency induced by congenital hypothyroidism, with a possible decrease in the visual acuity of the rat.