RESUMEN
Patients receiving mechanical ventilation in the intensive care unit (ICU) frequently develop contractile weakness of the diaphragm. Consequently, they may experience difficulty weaning from mechanical ventilation, which increases mortality and poses a high economic burden. Because of a lack of knowledge regarding the molecular changes in the diaphragm, no treatment is currently available to improve diaphragm contractility. We compared diaphragm biopsies from ventilated ICU patients (N = 54) to those of non-ICU patients undergoing thoracic surgery (N = 27). By integrating data from myofiber force measurements, x-ray diffraction experiments, and biochemical assays with clinical data, we found that in myofibers isolated from the diaphragm of ventilated ICU patients, myosin is trapped in an energy-sparing, super-relaxed state, which impairs the binding of myosin to actin during diaphragm contraction. Studies on quadriceps biopsies of ICU patients and on the diaphragm of previously healthy mechanically ventilated rats suggested that the super-relaxed myosins are specific to the diaphragm and not a result of critical illness. Exposing slow- and fast-twitch myofibers isolated from the diaphragm biopsies to small-molecule compounds activating troponin restored contractile force in vitro. These findings support the continued development of drugs that target sarcomere proteins to increase the calcium sensitivity of myofibers for the treatment of ICU-acquired diaphragm weakness.
Asunto(s)
Diafragma , Contracción Muscular , Miosinas , Respiración Artificial , Músculos Respiratorios , Humanos , Animales , Miosinas/metabolismo , Diafragma/metabolismo , Diafragma/fisiopatología , Músculos Respiratorios/metabolismo , Ratas , Masculino , Unidades de Cuidados Intensivos , Persona de Mediana Edad , Femenino , Anciano , Hibernación/fisiología , Actinas/metabolismoRESUMEN
Diaphragm weakness frequently develops in mechanically ventilated critically ill patients and is associated with increased morbidity, including ventilator weaning failure, mortality, and health care costs. The mechanisms underlying diaphragm weakness are incompletely understood but may include the elastic properties of titin, a giant protein whose layout in the muscle's sarcomeres makes it an ideal candidate to sense ventilation-induced diaphragm unloading, resulting in downstream signaling through titin-binding proteins. In the current study, we investigated whether modulating titin stiffness affects the development of diaphragm weakness during mechanical ventilation. To this end, we ventilated genetically engineered mice with reduced titin stiffness (Rbm20ΔRRM), and robust (TtnΔIAjxn) or severely (TtnΔ112-158) increased titin stiffness for 8 h, and assessed diaphragm contractility and protein expression of titin-binding proteins. Mechanical ventilation reduced the maximum active tension of the diaphragm in WT, TtnΔIAjxn and TtnΔ112-158 mice. However, in Rbm20ΔRRM mice maximum active tension was preserved after ventilation. Analyses of titin binding proteins suggest that muscle ankyrin repeat proteins (MARPs) 1 and 2 may play a role in the adaptation of the diaphragm to mechanical ventilation, and the preservation of diaphragm contractility in Rbm20ΔRRM mice. Thus, Rbm20ΔRRM mice, expressing titin isoforms with lower stiffness, are protected from mechanical ventilation-induced diaphragm weakness, suggesting that titin elasticity may modulate the diaphragm's response to unloading during mechanical ventilation.
Asunto(s)
Trastornos Respiratorios , Respiración Artificial , Ratones , Animales , Conectina/metabolismo , Respiración Artificial/efectos adversos , Diafragma/metabolismo , Debilidad Muscular/genética , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Proteínas Quinasas/metabolismo , Proteínas de Unión al ARNRESUMEN
Hyperventilation is common in pulmonary arterial hypertension and may be related to autonomic imbalance. Patients underwent exercise testing and hyperoxic breathing before and after bisoprolol treatment. We found that neither beta blocker treatment nor hyperoxic breathing in patients reduced hyperventilation at rest and during exercise, although it reduced heart rate.
RESUMEN
Pulmonary hypertension is a fatal condition of elevated pulmonary pressures, complicated by right heart failure. Pulmonary hypertension appears in various forms; one of those is pulmonary arterial hypertension (PAH) and is particularly characterised by progressive remodelling and obstruction of the smaller pulmonary vessels. Neurohormonal imbalance in PAH patients is associated with worse prognosis and survival. In this back-to-basics article on neurohormonal modulation in PAH, we provide an overview of the pharmacological and nonpharmacological strategies that have been tested pre-clinically and clinically. The benefit of neurohormonal modulation strategies in PAH patients has been limited by lack of insight into how the neurohormonal system is changed throughout the disease and difficulties in translation from animal models to human trials. We propose that longitudinal and individual assessments of neurohormonal status are required to improve the timing and specificity of neurohormonal modulation strategies. Ongoing developments in imaging techniques such as positron emission tomography may become helpful to determine neurohormonal status in PAH patients in different disease stages and optimise individual treatment responses.
Asunto(s)
Insuficiencia Cardíaca , Hipertensión Pulmonar , Hipertensión Arterial Pulmonar , Animales , Hipertensión Pulmonar Primaria Familiar , Humanos , Hipertensión Pulmonar/tratamiento farmacológico , PronósticoRESUMEN
Monoamine oxidases (MAOs), a class of enzymes bound to the outer mitochondrial membrane, are important sources of reactive oxygen species. Increased MAO-A activity in endothelial cells and cardiomyocytes contributes to vascular dysfunction and progression of left heart failure. We hypothesized that inhibition of MAO-A can be used to treat pulmonary arterial hypertension (PAH) and right ventricular (RV) failure. MAO-A levels in lung and RV samples from patients with PAH were compared with levels in samples from donors without PAH. Experimental PAH was induced in male Sprague-Dawley rats by using Sugen 5416 and hypoxia (SuHx), and RV failure was induced in male Wistar rats by using pulmonary trunk banding (PTB). Animals were randomized to receive either saline or the MAO-A inhibitor clorgyline at 10 mg/kg. Echocardiography and RV catheterization were performed, and heart and lung tissues were collected for further analysis. We found increased MAO-A expression in the pulmonary vasculature of patients with PAH and in experimental experimental PAH induced by SuHx. Cardiac MAO-A expression and activity was increased in SuHx- and PTB-induced RV failure. Clorgyline treatment reduced RV afterload and pulmonary vascular remodeling in SuHx rats through reduced pulmonary vascular proliferation and oxidative stress. Moreover, clorgyline improved RV stiffness and relaxation and reversed RV hypertrophy in SuHx rats. In PTB rats, clorgyline had no direct clorgyline had no direct effect on the right ventricle effect. Our study reveals the role of MAO-A in the progression of PAH. Collectively, these findings indicated that MAO-A may be involved in pulmonary vascular remodeling and consecutive RV failure.
Asunto(s)
Progresión de la Enfermedad , Monoaminooxidasa/metabolismo , Hipertensión Arterial Pulmonar/enzimología , Animales , Clorgilina/farmacología , Clorgilina/uso terapéutico , Modelos Animales de Enfermedad , Ventrículos Cardíacos/efectos de los fármacos , Ventrículos Cardíacos/enzimología , Ventrículos Cardíacos/patología , Ventrículos Cardíacos/fisiopatología , Humanos , Hipertrofia Ventricular Derecha/complicaciones , Hipertrofia Ventricular Derecha/fisiopatología , Indoles , Estrés Oxidativo/efectos de los fármacos , Hipertensión Arterial Pulmonar/inducido químicamente , Hipertensión Arterial Pulmonar/tratamiento farmacológico , Hipertensión Arterial Pulmonar/fisiopatología , Arteria Pulmonar/efectos de los fármacos , Arteria Pulmonar/enzimología , Arteria Pulmonar/patología , Arteria Pulmonar/fisiopatología , Pirroles , Ratas , Remodelación Vascular/efectos de los fármacos , Rigidez Vascular/efectos de los fármacos , Vasodilatación/efectos de los fármacosRESUMEN
Uncoupling of mitochondrial proton pumping and adenosine triphosphate (ATP) production lowers mitochondrial efficiency. Current methods to determine mitochondrial efficiency require substantial amounts of tissue and permeabilization or isolation procedures. A simple histochemical method has been described by Meijer and Vloedman (Histochemistry 69:217-232, 1980, https://doi.org/10.1007/BF00489769 ), but this was not quantitative. We found linear correlations between (1) absorbance and sections thickness and (2) absorbance and incubation time. Because the method obeys Lambert-Beer's law, we can estimate ATP/O2 ratios for healthy and overloaded right-sided rat myocardium. We related mitochondrial efficiency to the ratio between cardiolipin and its precursor phosphatidylglycerol. We found a non-linear relationship between mitochondrial efficiency and this ratio, indicating that lower mitochondrial efficiency as found in experimental pulmonary hypertension may be due to altered composition of the mitochondrial inner membrane. We conclude that the histochemical method of Meijer and Vloedman can be applied to quantify mitochondrial efficiency.
Asunto(s)
Mitocondrias/metabolismo , Miocardio/metabolismo , Absorción Fisiológica , Animales , Biomarcadores/metabolismo , Cardiolipinas/metabolismo , Histocitoquímica , Hipertensión Pulmonar/metabolismo , Masculino , Protones , Ratas , Ratas WistarRESUMEN
Chronic hypoxia is associated with muscle wasting and decreased oxidative capacity. By contrast, training under hypoxia may enhance hypertrophy and increase oxidative capacity as well as oxygen transport to the mitochondria, by increasing myoglobin (Mb) expression. The latter may be a feasible strategy to prevent atrophy under hypoxia and enhance an eventual hypertrophic response to anabolic stimulation. Mb expression may be further enhanced by lipid supplementation. We investigated individual and combined effects of hypoxia, insulin-like growth factor (IGF)-1 and lipids, in mouse skeletal muscle C2C12 myotubes. Differentiated C2C12 myotubes were cultured for 24 h under 20%, 5% and 2% oxygen with or without IGF-1 and/or lipid treatment. In culture under 20% oxygen, IGF-1 induced 51% hypertrophy. Hypertrophy was only 32% under 5% and abrogated under 2% oxygen. This was not explained by changes in expression of genes involved in contractile protein synthesis or degradation, suggesting a reduced rate of translation rather than of transcription. Myoglobin mRNA expression increased by 75% under 5% O2 but decreased by 50% upon IGF-1 treatment under 20% O2, compared to control. Inhibition of mammalian target of rapamycin (mTOR) activation using rapamycin restored Mb mRNA expression to control levels. Lipid supplementation had no effect on Mb gene expression. Thus, IGF-1-induced anabolic signaling can be a strategy to improve muscle size under mild hypoxia, but lowers Mb gene expression.
Asunto(s)
Factor I del Crecimiento Similar a la Insulina/genética , Atrofia Muscular/genética , Mioglobina/genética , Animales , Regulación de la Expresión Génica/genética , Humanos , Hipoxia/genética , Hipoxia/patología , Ratones , Mitocondrias/genética , Mitocondrias/metabolismo , Contracción Muscular/efectos de los fármacos , Fibras Musculares Esqueléticas/metabolismo , Fibras Musculares Esqueléticas/patología , Músculo Esquelético/metabolismo , Músculo Esquelético/patología , Atrofia Muscular/patología , Factores Reguladores Miogénicos , Mioglobina/metabolismo , Oxígeno/metabolismo , Transducción de Señal/efectos de los fármacos , Succinato Deshidrogenasa/genética , Serina-Treonina Quinasas TOR/genética , Congéneres de la Testosterona/metabolismoRESUMEN
BACKGROUND: Sarcopenia contributes to the decreased quality of life in the older person. While resistance exercise is an effective measure to increase muscle mass and strength, the hypertrophic response may be blunted in old age. OBJECTIVES: To determine 1) whether hypertrophy in the m. plantaris of old mice was blunted compared to adult and 2) whether this was related to a reduced satellite cell (SC) density and 3) how resveratrol affects hypertrophy in old mice. METHODS: In adult (7.5 months, n=11), old (23.5 months, n=10) and old-resveratrol-treated (n=10) male C57BL/6J mice, hypertrophy of the left m. plantaris was induced by denervation of its synergists. The contralateral leg served as control. RESULTS: After six weeks, overload-induced myofiber hypertrophy and IIB-IIA shift in myofiber type composition were less pronounced in old than adult mice (P=0.03), irrespective of resveratrol treatment. Muscles from old mice had a lower SC density than adult muscles (P=0.002). Overload-induced SC proliferation (P<0.05) resulted in an increased SC density in old, but not adult muscles (P=0.02), while a decrease occurred after resveratrol supplementation (P=0.044). Id2 and myogenin protein expression levels were higher in old than adult muscles (P<0.05). Caspase-3 was expressed more in hypertrophied than control muscles and was reduced with resveratrol (P<0.05). CONCLUSION: The blunted hypertrophic response in old mice was associated with a lower SC density, but there was no evidence for a lower capacity for proliferation. Resveratrol did not rescue the hypertrophic response and even reduced, rather than increased, the number of SCs in hypertrophied muscles.