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Mechanisms underlying mechanical overload-induced skeletal muscle hypertrophy have been extensively researched since the landmark report by Morpurgo (1897) of "work-induced hypertrophy" in dogs that were treadmill trained. Much of the preclinical rodent and human resistance training research to date supports that involved mechanisms include enhanced mammalian/mechanistic target of rapamycin complex 1 (mTORC1) signaling, an expansion in translational capacity through ribosome biogenesis, increased satellite cell abundance and myonuclear accretion, and postexercise elevations in muscle protein synthesis rates. However, several lines of past and emerging evidence suggest that additional mechanisms that feed into or are independent of these processes are also involved. This review first provides a historical account of how mechanistic research into skeletal muscle hypertrophy has progressed. A comprehensive list of mechanisms associated with skeletal muscle hypertrophy is then outlined, and areas of disagreement involving these mechanisms are presented. Finally, future research directions involving many of the discussed mechanisms are proposed.
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Músculo Esquelético , Transducción de Señal , Humanos , Animales , Perros , Músculo Esquelético/metabolismo , Diana Mecanicista del Complejo 1 de la Rapamicina/metabolismo , Biosíntesis de Proteínas , Hipertrofia/metabolismo , Mamíferos/metabolismoRESUMEN
Circadian rhythms in physiology and behavior are ≈24-hour biological cycles regulated by internal biological clocks (ie, circadian clocks) that optimize organismal homeostasis in response to predictable environmental changes. These clocks are present in virtually all cells in the body, including cardiomyocytes. Many decades ago, clinicians and researchers became interested in studying daily patterns of triggers for sudden cardiac death, the incidence of sudden cardiac death, and cardiac arrhythmias. This review highlights historical and contemporary studies examining the role of day/night rhythms in the timing of cardiovascular events, delves into changes in the timing of these events over the last few decades, and discusses cardiovascular disease-specific differences in the timing of cardiovascular events. The current understanding of the environmental, behavioral, and circadian mechanisms that regulate cardiac electrophysiology is examined with a focus on the circadian regulation of cardiac ion channels and ion channel regulatory genes. Understanding the contribution of environmental, behavioral, and circadian rhythms on arrhythmia susceptibility and the incidence of sudden cardiac death will be essential in developing future chronotherapies.
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Arritmias Cardíacas , Relojes Circadianos , Humanos , Ritmo Circadiano , Miocitos Cardíacos , Muerte Súbita Cardíaca/etiología , Electrofisiología CardíacaRESUMEN
Numerous molecular and physiological processes in the skeletal muscle undergo circadian time-dependent oscillations in accordance with daily activity/rest cycles. The circadian regulatory mechanisms underlying these cyclic processes, especially at the post-transcriptional level, are not well defined. Previously, we reported that the circadian E3 ligase FBXL21 mediates rhythmic degradation of the sarcomere protein TCAP in conjunction with GSK-3ß, and Psttm mice harboring an Fbxl21 hypomorph allele show reduced muscle fiber diameter and impaired muscle function. To further elucidate the regulatory function of FBXL21 in skeletal muscle, we investigated another sarcomere protein, Myozenin1 (MYOZ1), that we identified as an FBXL21-binding protein from yeast 2-hybrid screening. We show that FBXL21 binding to MYOZ1 led to ubiquitination-mediated proteasomal degradation. GSK-3ß co-expression and inhibition were found to accelerate and decelerate FBXL21-mediated MYOZ1 degradation, respectively. Previously, MYOZ1 has been shown to inhibit calcineurin/NFAT signaling important for muscle differentiation. In accordance, Fbxl21 KO and MyoZ1 KO in C2C12 cells impaired and enhanced myogenic differentiation respectively compared with control C2C12 cells, concomitant with distinct effects on NFAT nuclear localization and NFAT target gene expression. Importantly, in Psttm mice, both the levels and diurnal rhythm of NFAT2 nuclear localization were significantly diminished relative to wild-type mice, and circadian expression of NFAT target genes associated with muscle differentiation was also markedly dampened. Furthermore, Psttm mice exhibited significant disruption of sarcomere structure with a considerable excess of MYOZ1 accumulation in the Z-line. Taken together, our study illustrates a pivotal role of FBXL21 in sarcomere structure and muscle differentiation by regulating MYOZ1 degradation and NFAT2 signaling.
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Proteínas F-Box , Ubiquitina-Proteína Ligasas , Ratones , Animales , Glucógeno Sintasa Quinasa 3 beta/genética , Glucógeno Sintasa Quinasa 3 beta/metabolismo , Ubiquitina-Proteína Ligasas/genética , Ubiquitina-Proteína Ligasas/metabolismo , Sarcómeros/metabolismo , Diferenciación Celular/genética , Ubiquitinación , Músculo Esquelético/metabolismo , Mioblastos/metabolismo , Factores de Transcripción NFATC/genética , Factores de Transcripción NFATC/metabolismo , Proteínas F-Box/genética , Proteínas F-Box/metabolismoRESUMEN
Rhythmic feeding behavior is critical for regulating phase and amplitude in the ≈24-h variation of heart rate (RR intervals), ventricular repolarization (QT intervals), and core body temperature in mice. We hypothesized changes in cardiac electrophysiology associated with feeding behavior were secondary to changes in core body temperature. Telemetry was used to record electrocardiograms and core body temperature in mice during ad libitum-fed conditions and after inverting normal feeding behavior by restricting food access to the light cycle. Light cycle-restricted feeding modified the phase and amplitude of 24-h rhythms in RR and QT intervals, and core body temperature to realign with the new feeding time. Changes in core body temperature alone could not account for changes in phase and amplitude in the ≈24-h variation of the RR intervals. Heart rate variability analysis and inhibiting ß-adrenergic and muscarinic receptors suggested that changes in the phase and amplitude of 24-h rhythms in RR intervals were secondary to changes in autonomic signaling. In contrast, changes in QT intervals closely mirrored changes in core body temperature. Studies at thermoneutrality confirmed that the daily variation in QT interval, but not RR interval, primarily reflected daily changes in core body temperature (even in ad libitum-fed conditions). Correcting the QT interval for differences in core body temperature helped unmask QT interval prolongation after starting light cycle-restricted feeding and in a mouse model of long QT syndrome. We conclude feeding behavior alters autonomic signaling and core body temperature to regulate phase and amplitude in RR and QT intervals, respectively.NEW & NOTEWORTHY We used time-restricted feeding and thermoneutrality to demonstrate that different mechanisms regulate the 24-h rhythms in heart rate and ventricular repolarization. The daily rhythm in heart rate reflects changes in autonomic input, whereas daily rhythms in ventricular repolarization reflect changes in core body temperature. This novel finding has major implications for understanding 24-h rhythms in mouse cardiac electrophysiology, arrhythmia susceptibility in transgenic mouse models, and interpretability of cardiac electrophysiological data acquired in thermoneutrality.
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Temperatura Corporal , Ritmo Circadiano , Conducta Alimentaria , Frecuencia Cardíaca , Ratones Endogámicos C57BL , Animales , Ritmo Circadiano/fisiología , Frecuencia Cardíaca/fisiología , Conducta Alimentaria/fisiología , Masculino , Temperatura Corporal/fisiología , Ratones , Electrocardiografía , Fotoperiodo , Factores de Tiempo , Sistema Nervioso Autónomo/fisiologíaRESUMEN
Circadian rhythms are â¼24 h cycles evident in behaviour, physiology and metabolism. The molecular mechanism directing circadian rhythms is the circadian clock, which is composed of an interactive network of transcription-translation feedback loops. The core clock genes include Bmal1, Clock, Rev-erbα/ß, Per and Cry. In addition to keeping time, the core clock regulates a daily programme of gene expression that is important for overall cell homeostasis. The circadian clock mechanism is present in all cells, including skeletal muscle fibres, and disruption of the muscle clock is associated with changes in muscle phenotype and function. Skeletal muscle atrophy is largely associated with a lower quality of life, frailty and reduced lifespan. Physiological and genetic modification of the core clock mechanism yields immune dysfunction, alters inflammatory factor expression and secretion and is associated with skeletal muscle atrophy in multiple conditions, such as ageing and cancer cachexia. Here, we summarize the possible interplay between the circadian clock modulation of immune cells, systemic inflammatory status and skeletal muscle atrophy in chronic inflammatory conditions. Although there is a clear disruption of circadian clocks in various models of atrophy, the mechanism behind such alterations remains unknown. Understanding the modulatory potential of muscle and immune circadian clocks in inflammation and skeletal muscle health is essential for the development of therapeutic strategies to protect skeletal muscle mass and function of patients with chronic inflammation.
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Circadian rhythmicity in transcriptomic profiles has been shown in many physiological processes, and the disruption of circadian patterns has been found to associate with several diseases. In this paper, we developed a series of likelihood-based methods to detect (i) circadian rhythmicity (denoted as LR_rhythmicity) and (ii) differential circadian patterns comparing two experimental conditions (denoted as LR_diff). In terms of circadian rhythmicity detection, we demonstrated that our proposed LR_rhythmicity could better control the type I error rate compared to existing methods under a wide variety of simulation settings. In terms of differential circadian patterns, we developed methods in detecting differential amplitude, differential phase, differential basal level and differential fit, which also successfully controlled the type I error rate. In addition, we demonstrated that the proposed LR_diff could achieve higher statistical power in detecting differential fit, compared to existing methods. The superior performance of LR_rhythmicity and LR_diff was demonstrated in four real data applications, including a brain aging data (gene expression microarray data of human postmortem brain), a time-restricted feeding data (RNA sequencing data of human skeletal muscles) and a scRNAseq data (single cell RNA sequencing data of mouse suprachiasmatic nucleus). An R package for our methods is publicly available on GitHub https://github.com/diffCircadian/diffCircadian.
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Ritmo Circadiano/genética , Biología Computacional/métodos , Perfilación de la Expresión Génica/métodos , Regulación de la Expresión Génica , Funciones de Verosimilitud , Programas Informáticos , Transcriptoma , Factores de Edad , Algoritmos , Animales , Biomarcadores , Encéfalo/fisiología , Humanos , Ratones , Reproducibilidad de los ResultadosRESUMEN
Circadian clocks are 24-h endogenous oscillators in physiological and behavioral processes. Though recent transcriptomic studies have been successful in revealing the circadian rhythmicity in gene expression, the power calculation for omics circadian analysis have not been fully explored. In this paper, we develop a statistical method, namely CircaPower, to perform power calculation for circadian pattern detection. Our theoretical framework is determined by three key factors in circadian gene detection: sample size, intrinsic effect size and sampling design. Via simulations, we systematically investigate the impact of these key factors on circadian power calculation. We not only demonstrate that CircaPower is fast and accurate, but also show its underlying cosinor model is robust against variety of violations of model assumptions. In real applications, we demonstrate the performance of CircaPower using mouse pan-tissue data and human post-mortem brain data, and illustrate how to perform circadian power calculation using mouse skeleton muscle RNA-Seq pilot as case study. Our method CircaPower has been implemented in an R package, which is made publicly available on GitHub ( https://github.com/circaPower/circaPower).
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Ritmo Circadiano , Proyectos de Investigación , Humanos , Animales , Ratones , Ritmo Circadiano/genética , Perfilación de la Expresión Génica , Transcriptoma , Tamaño de la MuestraRESUMEN
Daily variations in cardiac electrophysiology and the incidence for different types of arrhythmias reflect ≈24 h changes in the environment, behaviour and internal circadian rhythms. This article focuses on studies that use animal models to separate the impact that circadian rhythms, as well as changes in the environment and behaviour, have on 24 h rhythms in heart rate and ventricular repolarization. Circadian rhythms are initiated at the cellular level by circadian clocks, transcription-translation feedback loops that cycle with a periodicity of 24 h. Several studies now show that the circadian clock in cardiomyocytes regulates the expression of cardiac ion channels by multiple mechanisms; underlies time-of-day changes in sinoatrial node excitability/intrinsic heart rate; and limits the duration of the ventricular action potential waveform. However, the 24 h rhythms in heart rate and ventricular repolarization are primarily driven by autonomic signalling. A functional role for the cardiomyocyte circadian clock appears to buffer the heart against perturbations. For example, the cardiomyocyte circadian clock limits QT-interval prolongation (especially at slower heart rates), and it may facilitate the realignment of the 24 h rhythm in heart rate to abrupt changes in the light cycle. Additional studies show that modifying rhythmic behaviours (including feeding behaviour) can dramatically impact the 24 h rhythms in heart rate and ventricular repolarization. If these mechanisms are conserved, these studies suggest that targeting endogenous circadian mechanisms in the heart, as well as modifying the timing of certain rhythmic behaviours, could emerge as therapeutic strategies to support heart function against perturbations and regulate 24 h rhythms in cardiac electrophysiology.
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Relojes Circadianos , Animales , Relojes Circadianos/fisiología , Ritmo Circadiano/fisiología , Técnicas Electrofisiológicas Cardíacas , Canales Iónicos/metabolismo , Miocitos Cardíacos/fisiologíaRESUMEN
Ammonia is a cytotoxic molecule generated during normal cellular functions. Dysregulated ammonia metabolism, which is evident in many chronic diseases such as liver cirrhosis, heart failure, and chronic obstructive pulmonary disease, initiates a hyperammonemic stress response in tissues including skeletal muscle and in myotubes. Perturbations in levels of specific regulatory molecules have been reported, but the global responses to hyperammonemia are unclear. In this study, we used a multiomics approach to vertically integrate unbiased data generated using an assay for transposase-accessible chromatin with high-throughput sequencing, RNA-Seq, and proteomics. We then horizontally integrated these data across different models of hyperammonemia, including myotubes and mouse and human muscle tissues. Changes in chromatin accessibility and/or expression of genes resulted in distinct clusters of temporal molecular changes including transient, persistent, and delayed responses during hyperammonemia in myotubes. Known responses to hyperammonemia, including mitochondrial and oxidative dysfunction, protein homeostasis disruption, and oxidative stress pathway activation, were enriched in our datasets. During hyperammonemia, pathways that impact skeletal muscle structure and function that were consistently enriched were those that contribute to mitochondrial dysfunction, oxidative stress, and senescence. We made several novel observations, including an enrichment in antiapoptotic B-cell leukemia/lymphoma 2 family protein expression, increased calcium flux, and increased protein glycosylation in myotubes and muscle tissue upon hyperammonemia. Critical molecules in these pathways were validated experimentally. Human skeletal muscle from patients with cirrhosis displayed similar responses, establishing translational relevance. These data demonstrate complex molecular interactions during adaptive and maladaptive responses during the cellular stress response to hyperammonemia.
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Genómica , Hiperamonemia/metabolismo , Fibras Musculares Esqueléticas/metabolismo , Músculo Esquelético/metabolismo , Proteómica , Transcriptoma , Animales , Citometría de Flujo , Humanos , Hiperamonemia/genética , Immunoblotting/métodos , Ratones , Reacción en Cadena en Tiempo Real de la Polimerasa , Reproducibilidad de los ResultadosRESUMEN
For more than 20 years, physiologists have observed a morning-to-evening increase in human muscle strength. Recent data suggest that time-of-day differences are the result of intrinsic, nonneural, muscle factors. We evaluate circadian clock data sets from human and mouse circadian studies and highlight possible mechanisms through which the muscle circadian clock may contribute to time-of-day muscle strength outcomes.
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Relojes Circadianos , Ritmo Circadiano , Animales , Ratones , Fuerza MuscularRESUMEN
An often overlooked element of pulmonary vascular disease is time. Cellular responses to time, which are regulated directly by the core circadian clock, have only recently been elucidated. Despite an extensive collection of data regarding the role of rhythmic contribution to disease pathogenesis (such as systemic hypertension, coronary artery, and renal disease), the roles of key circadian transcription factors in pulmonary hypertension remain understudied. This is despite a large degree of overlap in the pulmonary hypertension and circadian rhythm fields, not only including shared signaling pathways, but also cell-specific effects of the core clock that are known to result in both protective and adverse lung vessel changes. Therefore, the goal of this review is to summarize the current dialogue regarding common pathways in circadian biology, with a specific emphasis on its implications in the progression of pulmonary hypertension. In this work, we emphasize specific proteins involved in the regulation of the core molecular clock while noting the circadian cell-specific changes relevant to vascular remodeling. Finally, we apply this knowledge to the optimization of medical therapy, with a focus on sleep hygiene and the role of chronopharmacology in patients with this disease. In dissecting the unique relationship between time and cellular biology, we aim to provide valuable insight into the practical implications of considering time as a therapeutic variable. Armed with this information, physicians will be positioned to more efficiently use the full four dimensions of patient care, resulting in improved morbidity and mortality of pulmonary hypertension patients.
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Ritmo Circadiano/fisiología , Salud , Enfermedades Pulmonares/fisiopatología , Pulmón/irrigación sanguínea , Animales , Restricción Calórica , Relojes Circadianos , HumanosRESUMEN
Chromatin accessibility is a key factor influencing gene expression. We optimized the Omni-ATAC-seq protocol and used it together with RNA-seq to investigate cis-regulatory elements in rat white adipose and skeletal muscle, two tissues with contrasting metabolic functions. While promoter accessibility correlated with RNA expression, integration of the two datasets identified tissue-specific differentially accessible regions (DARs) that predominantly localized in intergenic and intron regions. DARs were mapped to differentially expressed (DE) genes enriched in distinct biological processes in each tissue. Randomly selected DE genes were validated by qPCR. Top enriched motifs in DARs predicted binding sites for transcription factors (TFs) showing tissue-specific up-regulation. The correlation between differential chromatin accessibility at a given TF binding motif and differential expression of target genes further supported the functional relevance of that motif. Our study identified cis-regulatory regions that likely play a major role in the regulation of tissue-specific gene expression in adipose and muscle.
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Cromatina , Transcriptoma , Animales , Cromatina/genética , Secuenciación de Inmunoprecipitación de Cromatina , Músculos , Ratas , Secuencias Reguladoras de Ácidos NucleicosRESUMEN
Circadian rhythms are central to optimal physiological function, as disruption contributes to the development of several chronic diseases. Alcohol (EtOH) intoxication disrupts circadian rhythms within liver, brain, and intestines, but it is unknown whether alcohol also disrupts components of the core clock in skeletal muscle. Female C57BL/6Hsd mice were randomized to receive either saline (control) or alcohol (EtOH) (5 g/kg) via intraperitoneal injection at the start of the dark cycle [Zeitgeber time (ZT12)], and gastrocnemius was collected every 4 h from control and EtOH-treated mice for the next 48 h following isoflurane anesthetization. In addition, metyrapone was administered before alcohol intoxication in separate mice to determine whether the alcohol-induced increase in serum corticosterone contributed to circadian gene regulation. Finally, synchronized C2C12 myotubes were treated with alcohol (100 mM) to assess the influence of centrally or peripherally mediated effects of alcohol on the muscle clock. Alcohol significantly disrupted mRNA expression of Bmal1, Per1/2, and Cry1/2 in addition to perturbing the circadian pattern of clock-controlled genes, Myod1, Dbp, Tef, and Bhlhe40 (P < 0.05), in muscle. Alcohol increased serum corticosterone levels and glucocorticoid target gene, Redd1, in muscle. Metyrapone prevented the EtOH-mediated increase in serum corticosterone but did not normalize the EtOH-induced change in Per1, Cry1 and Cry2, and Myod1 mRNA expression. Core clock gene expression (Bmal, Per1/2, and Cry1/2) was not changed following 4, 8, or 12 h of alcohol treatment on synchronized C2C12 myotubes. Therefore, binge alcohol disrupted genes of the core molecular clock independently of elevated serum corticosterone or direct effects of EtOH on the muscle.NEW & NOTEWORTHY Alcohol is a myotoxin that impairs skeletal muscle metabolism and function following either chronic consumption or acute binge drinking; however, mechanisms underlying alcohol-related myotoxicity have not been fully elucidated. Herein, we demonstrate that alcohol acutely interrupts oscillation of skeletal muscle core clock genes, and this is neither a direct effect of ethanol on the skeletal muscle, nor an effect of elevated serum corticosterone, a major clock regulator.
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Consumo Excesivo de Bebidas Alcohólicas/metabolismo , Péptidos y Proteínas de Señalización del Ritmo Circadiano/genética , Ritmo Circadiano/efectos de los fármacos , Glucocorticoides/metabolismo , Músculo Esquelético/metabolismo , Intoxicación Alcohólica/sangre , Animales , Ritmo Circadiano/genética , Femenino , Regulación de la Expresión Génica/efectos de los fármacos , Metirapona/farmacología , Ratones , Ratones Endogámicos C57BL , Fibras Musculares Esqueléticas/efectos de los fármacos , Fibras Musculares Esqueléticas/metabolismo , ARN Mensajero/biosíntesis , ARN Mensajero/genéticaRESUMEN
Disruption of the skeletal muscle circadian clock leads to a preferential shift toward lipid oxidation while reducing carbohydrate oxidation. These effects are apparent at the whole-body level, including glucose intolerance, increased energy expenditure, and fasting hyperglycemia. We hypothesize that exercise counters these metabolic disturbances by modifying the skeletal muscle clock and reverting substrate metabolism back toward an optimal substrate balance.
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Relojes Circadianos , Ejercicio Físico , Metabolismo Energético , Humanos , Metabolismo de los Lípidos , Músculo Esquelético/metabolismoRESUMEN
KEY POINTS: Disruptions in circadian rhythms across an organism are associated with negative health outcomes, such as cardiometabolic and neurodegenerative diseases. Exercise has been proposed as a time cue for the circadian clock in rodents and humans. In this study, we assessed the effect of a single bout of endurance exercise on the skeletal muscle clock in vivo and a bout of muscle contractions in vitro. Timing of exercise or contractions influences the directional response of the muscle clock phase in vivo and in vitro. Our findings demonstrate that muscle contractions, as a component of exercise, can directly modulate the expression of muscle clock components in a time-of-day dependent manner. ABSTRACT: Exercise has been proposed to be a zeitgeber for the muscle circadian clock mechanism. However, this is not well defined and it is unknown if exercise timing induces directional shifts of the muscle clock. Our purpose herein was to assess the effect of one bout of treadmill exercise on skeletal muscle clock phase changes. We subjected PERIOD2::LUCIFERASE mice (n = 30F) to one 60 min treadmill exercise bout at three times of day. Exercise at ZT5, 5 h after lights on, induced a phase advance (100.2 ± 25.8 min; P = 0.0002), whereas exercise at ZT11, 1 h before lights off, induced a phase delay (62.1 ± 21.1 min; P = 0.0003). Exercise at ZT17, middle of the dark phase, did not alter the muscle clock phase. Exercise induces diverse systemic changes so we developed an in vitro model system to examine the effects of contractile activity on muscle clock phase. Contractions applied at peak or trough Bmal1 expression induced significant phase delays (applied at peak: 27.2 ± 10.2 min; P = 0.0017; applied at trough: 64.6 ± 6.5 min, P < 0.0001). Contractions applied during the transition from peak to trough Bmal1 expression induced a phase advance (49.8 ± 23.1 min; P = 0.0051). Lastly, contractions at different times of day resulted in differential changes of core clock gene expression, demonstrating an exercise and clock interaction, providing insight into potential mechanisms of exercise-induced phase shifts. These data demonstrate that muscle contractions, as part of exercise, are sufficient to shift the muscle circadian clock phase, likely through changes in core clock gene expression. Additionally, our findings that exercise induces directional muscle clock phase changes confirms that exercise is a bona fide environmental time cue for skeletal muscle.
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Relojes Circadianos , Condicionamiento Físico Animal , Animales , Ritmo Circadiano , Ratones , Contracción Muscular , Músculo EsqueléticoRESUMEN
Circadian rhythms are endogenous and entrainable daily patterns of physiology and behavior. Molecular mechanisms underlie circadian rhythms, characterized by an ~24-h pattern of gene expression of core clock genes. Although it has long been known that breathing exhibits circadian rhythms, little is known concerning clock gene expression in any element of the neuromuscular system controlling breathing. Furthermore, we know little concerning gene expression necessary for specific respiratory functions, such as phrenic motor plasticity. Thus, we tested the hypotheses that transcripts for clock genes (Bmal1, Clock, Per1, and Per2) and molecules necessary for phrenic motor plasticity (Htr2a, Htr2b, Bdnf, and Ntrk2) oscillate in regions critical for phrenic/diaphragm motor function via RT-PCR. Tissues were collected from male Sprague-Dawley rats entrained to a 12-h light-dark cycle at 4 zeitgeber times (ZT; n = 8 rats/group): ZT5, ZT11, ZT17, and ZT23; ZT0 = lights on. Here, we demonstrate that 1) circadian clock genes (Bmal1, Clock, Per1, and Per2) oscillate in regions critical for phrenic/diaphragm function, including the caudal medulla, ventral C3-C5 cervical spinal cord, and diaphragm; 2) the clock protein BMAL1 is localized within CtB-labeled phrenic motor neurons; 3) genes necessary for intermittent hypoxia-induced phrenic/diaphragm motor plasticity (Htr2b and Bdnf) oscillate in the caudal medulla and ventral C3-C5 spinal cord; and 4) there is higher intensity of immunofluorescent BDNF protein within phrenic motor neurons at ZT23 compared with ZT11 (n = 11 rats/group). These results suggest local circadian clocks exist in the phrenic motor system and confirm the potential for local circadian regulation of neuroplasticity and other elements of the neural network controlling breathing.
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Relojes Circadianos/genética , Ritmo Circadiano/fisiología , Neuronas Motoras/metabolismo , Plasticidad Neuronal/genética , Nervio Frénico/metabolismo , Factores de Transcripción ARNTL/genética , Factores de Transcripción ARNTL/metabolismo , Animales , Factor Neurotrófico Derivado del Encéfalo/genética , Factor Neurotrófico Derivado del Encéfalo/metabolismo , Proteínas CLOCK/genética , Proteínas CLOCK/metabolismo , Expresión Génica , Masculino , Proteínas Circadianas Period/genética , Proteínas Circadianas Period/metabolismo , Ratas , Ratas Sprague-Dawley , Médula Espinal/metabolismoRESUMEN
INTRODUCTION: Tobacco use improves mood states and smoking cessation leads to anhedonia, which contributes to relapse. Animal studies have shown that noncontingent nicotine administration enhances brain reward function and leads to dependence. However, little is known about the effects of nicotine self-administration on the state of the reward system. METHODS: To investigate the relationship between nicotine self-administration and reward function, rats were prepared with intracranial self-stimulation electrodes and intravenous catheters. The rats were trained on the intracranial self-stimulation procedure and allowed to self-administer 0.03 mg/kg/infusion of nicotine. All rats self-administered nicotine daily for 10 days (1 hour/day) and were then switched to an intermittent short access (ShA, 1 hour/day) or long access (LgA, 23 hour/day) schedule (2 days/week, 5 weeks). RESULTS: During the first 10 daily, 1-hour sessions, nicotine self-administration decreased the reward thresholds, which indicates that nicotine potentiates reward function. After switching to the intermittent LgA or ShA schedule, nicotine intake was lower in the ShA rats than the LgA rats. The LgA rats increased their nicotine intake over time and they gradually consumed a higher percentage of their nicotine during the light phase. The nicotinic acetylcholine receptor (nAChR) antagonist mecamylamine induced a larger increase in reward thresholds (ie, anhedonia) in the LgA rats than the ShA rats. In the LgA rats, nAChR blockade with mecamylamine decreased nicotine intake for 2 hours and this was followed by a rebound increase in nicotine intake. CONCLUSIONS: A brief period of nicotine self-administration enhances reward function and a high level of nicotine intake leads to dependence. IMPLICATIONS: These animal studies indicate that there is a strong relationship between the level of nicotine intake and brain reward function. A high level of nicotine intake was more rewarding than a low level of nicotine intake and nicotine dependence was observed after long, but not short, access to nicotine. This powerful combination of nicotine reward and withdrawal makes it difficult to quit smoking. Blockade of nAChRs temporarily decreased nicotine intake, but this was followed by a large rebound increase in nicotine intake. Therefore, nAChR blockade might not decrease the use of combustible cigarettes or electronic cigarettes.
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Anhedonia/efectos de los fármacos , Nicotina/administración & dosificación , Recompensa , Autoestimulación/efectos de los fármacos , Anhedonia/fisiología , Animales , Relación Dosis-Respuesta a Droga , Esquema de Medicación , Electrodos Implantados , Masculino , Mecamilamina/administración & dosificación , Agonistas Nicotínicos/administración & dosificación , Antagonistas Nicotínicos/administración & dosificación , Ratas , Ratas Wistar , Receptores Nicotínicos/fisiología , Autoadministración/métodos , Autoestimulación/fisiología , Factores de Tiempo , Tabaquismo/psicologíaRESUMEN
Androgen depletion in humans leads to significant atrophy of the limb muscles. However, the pathways by which androgens regulate limb muscle mass are unclear. Our laboratory previously showed that mitochondrial degradation was related to the induction of autophagy and the degree of muscle atrophy following androgen depletion, implying that decreased mitochondrial quality contributes to muscle atrophy. To increase our understanding of androgen-sensitive pathways regulating decreased mitochondrial quality, total RNA from the tibialis anterior of sham and castrated mice was subjected to microarray analysis. Using this unbiased approach, we identified significant changes in the expression of genes that compose the core molecular clock. To assess the extent to which androgen depletion altered the limb muscle clock, the tibialis anterior muscles from sham and castrated mice were harvested every 4 h throughout a diurnal cycle. The circadian expression patterns of various core clock genes and known clock-controlled genes were disrupted by castration, with most genes exhibiting an overall reduction in phase amplitude. Given that the core clock regulates mitochondrial quality, disruption of the clock coincided with changes in the expression of genes involved with mitochondrial quality control, suggesting a novel mechanism by which androgens may regulate mitochondrial quality. These events coincided with an overall increase in mitochondrial degradation in the muscle of castrated mice and an increase in markers of global autophagy-mediated protein breakdown. In all, these data are consistent with a novel conceptual model linking androgen depletion-induced limb muscle atrophy to reduced mitochondrial quality control via disruption of the molecular clock.
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Andrógenos/fisiología , Péptidos y Proteínas de Señalización del Ritmo Circadiano/genética , Extremidades/fisiología , Mitocondrias Musculares/efectos de los fármacos , Mitocondrias Musculares/metabolismo , Músculo Esquelético/efectos de los fármacos , Músculo Esquelético/metabolismo , Animales , Atrofia , Autofagia , Peso Corporal , Extremidades/patología , Masculino , Ratones , Ratones Endogámicos C57BL , Mitofagia , Músculo Esquelético/patología , Orquiectomía , Testosterona/fisiología , Tibia/anatomía & histología , Tibia/crecimiento & desarrolloRESUMEN
Autophagy of mitochondria (mitophagy) is essential for maintaining muscle mass and healthy skeletal muscle. Patients with heritable phosphatidic acid phosphatase lipin-1-null mutations present with severe rhabdomyolysis and muscle atrophy in glycolytic muscle fibers, which are accompanied with mitochondrial aggregates and reduced mitochondrial cytochrome c oxidase activity. However, the underlying mechanisms leading to muscle atrophy as a result of lipin-1 deficiency are still not clear. In this study, we found that lipin-1 deficiency in mice is associated with a marked accumulation of abnormal mitochondria and autophagic vacuoles in glycolytic muscle fibers. Our studies using lipin-1-deficient myoblasts suggest that lipin-1 participates in B-cell leukemia (BCL)-2 adenovirus E1B 19 kDa protein-interacting protein 3 (Bnip3)-regulated mitophagy by interacting with microtubule-associated protein 1A/1B-light chain (LC)3, which is an important step in the recruitment of mitochondria to nascent autophagosomes. The requirement of lipin-1 for Bnip3-mediated mitophagy was further verified in vivo in lipin-1-deficient green fluorescent protein-LC3 transgenic mice (lipin-1-/--GFP-LC3). Finally, we showed that lipin-1 deficiency in mice resulted in defective mitochondrial adaptation to starvation-induced metabolic stress and impaired contractile muscle force in glycolytic muscle fibers. In summary, our study suggests that deregulated mitophagy arising from lipin-1 deficiency is associated with impaired muscle function and may contribute to muscle rhabdomyolysis in humans.-Alshudukhi, A. A., Zhu, J., Huang, D., Jama, A., Smith, J. D., Wang, Q. J., Esser, K. A., Ren, H. Lipin-1 regulates Bnip3-mediated mitophagy in glycolytic muscle.
RESUMEN
Collagen VI myopathies are genetic disorders caused by mutations in collagen 6 A1, A2 and A3 genes, ranging from the severe Ullrich congenital muscular dystrophy to the milder Bethlem myopathy, which is recapitulated by collagen-VI-null (Col6a1(-/-)) mice. Abnormalities in mitochondria and autophagic pathway have been proposed as pathogenic causes of collagen VI myopathies, but the link between collagen VI defects and these metabolic circuits remains unknown. To unravel the expression profiling perturbation in muscles with collagen VI myopathies, we performed a deep RNA profiling in both Col6a1(-/-)mice and patients with collagen VI pathology. The interactome map identified common pathways suggesting a previously undetected connection between circadian genes and collagen VI pathology. Intriguingly, Bmal1(-/-)(also known as Arntl) mice, a well-characterized model displaying arrhythmic circadian rhythms, showed profound deregulation of the collagen VI pathway and of autophagy-related genes. The involvement of circadian rhythms in collagen VI myopathies is new and links autophagy and mitochondrial abnormalities. It also opens new avenues for therapies of hereditary myopathies to modulate the molecular clock or potential gene-environment interactions that might modify muscle damage pathogenesis.