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It has become clear that circadian clocks in peripheral tissues play important functions. Disruption of the circadian clock in skeletal muscle, for example, results in insulin resistance, sarcomere disorganization, and muscle weakness1. Interestingly, cavefish, which exhibit a disrupted central clock, exhibit similar muscle phenotypes2,3,4, raising the question of whether they are caused by alterations to central or peripheral clocks. Here, we demonstrate a loss in clock function in the skeletal muscle of the Mexican Cavefish Astyanax mexicanus that is associated with reduced rhythmicity of a large number of genes and disrupted nocturnal protein catabolism. Some of the identified genes are associated with metabolic dysfunction in humans.
Assuntos
Characidae , Relógios Circadianos , Animais , Humanos , Ritmo Circadiano/fisiologia , Relógios Circadianos/genética , Músculo Esquelético/fisiologia , MéxicoRESUMO
Circadian control of physiology and metabolism is pervasive throughout nature, with circadian disruption contributing to premature aging, neurodegenerative disease, and type 2 diabetes (Musiek et al. 2016; Panda, 2016). It has become increasingly clear that peripheral tissues, such as skeletal muscle, possess cell-autonomous clocks crucial for metabolic homeostasis (Gabriel et al. 2021). In fact, disruption of the skeletal muscle circadian rhythm results in insulin resistance, sarcomere disorganization, and muscle weakness in both vertebrates and non-vertebrates - indicating that maintenance of a functional muscle circadian rhythm provides an adaptive advantage. We and others have found that cavefish possess a disrupted central circadian rhythm and, interestingly, a skeletal muscle phenotype strikingly similar to circadian knock-out mutants; namely, muscle loss, muscle weakness, and insulin resistance (Olsen et al. 2022; Riddle et al. 2018; Mack et al. 2021). However, whether the cavefish muscle phenotype results from muscle-specific circadian disruption remains untested. To this point, we investigated genome-wide, circadian-regulated gene expression within the skeletal muscle of the Astyanax mexicanus - comprised of the river-dwelling surface fish and troglobitic cavefish - providing novel insights into the evolutionary consequence of circadian disruption on skeletal muscle physiology.
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Physical injury and tissue damage is prevalent throughout the animal kingdom, with the ability to quickly and efficiently regenerate providing a selective advantage. The skeletal muscle possesses a uniquely large regenerative capacity within most vertebrates, and has thus become an important model for investigating cellular processes underpinning tissue regeneration. Following damage, the skeletal muscle mounts a complex regenerative cascade centered around dedicated muscle stem cells termed satellite cells. In non-injured muscle, satellite cells remain in a quiescent state, expressing the canonical marker Pax7 (Chen et al. 2020). However, following injury, satellite cells exit quiescence, enter the cell cycle to initiate proliferation, asymmetrically divide, and in many cases terminally differentiate into myoblasts, ultimately fusing with surrounding myoblasts and pre-existing muscle fibers to resolve the regenerative process (Chen et al. 2020).
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Physical inactivity is a scourge to human health, promoting metabolic disease and muscle wasting. Interestingly, multiple ecological niches have relaxed investment into physical activity, providing an evolutionary perspective into the effect of adaptive physical inactivity on tissue homeostasis. One such example, the Mexican cavefish Astyanax mexicanus, has lost moderate-to-vigorous activity following cave colonization, reaching basal swim speeds ~3.7-fold slower than their river-dwelling counterpart. This change in behavior is accompanied by a marked shift in body composition, decreasing total muscle mass and increasing fat mass. This shift persisted at the single muscle fiber level via increased lipid and sugar accumulation at the expense of myofibrillar volume. Transcriptomic analysis of laboratory-reared and wild-caught cavefish indicated that this shift is driven by increased expression of pparγ-the master regulator of adipogenesis-with a simultaneous decrease in fast myosin heavy chain expression. Ex vivo and in vivo analysis confirmed that these investment strategies come with a functional trade-off, decreasing cavefish muscle fiber shortening velocity, time to maximal force, and ultimately maximal swimming speed. Despite this, cavefish displayed a striking degree of muscular endurance, reaching maximal swim speeds ~3.5-fold faster than their basal swim speeds. Multi-omic analysis suggested metabolic reprogramming, specifically phosphorylation of Pgm1-Threonine 19, as a key component enhancing cavefish glycogen metabolism and sustained muscle contraction. Collectively, we reveal broad skeletal muscle changes following cave colonization, displaying an adaptive skeletal muscle phenotype reminiscent to mammalian disuse and high-fat models while simultaneously maintaining a unique capacity for sustained muscle contraction via enhanced glycogen metabolism.
Assuntos
Characidae , Animais , Humanos , Characidae/genética , Evolução Biológica , Glicogênio , Músculos , México , Cavernas , MamíferosRESUMO
Insights from organisms, which have evolved natural strategies for promoting survivability under extreme environmental pressures, may help guide future research into novel approaches for enhancing human longevity. The cave-adapted Mexican tetra, Astyanax mexicanus, has attracted interest as a model system for metabolic resilience, a term we use to denote the property of maintaining health and longevity under conditions that would be highly deleterious in other organisms (Figure 1). Cave-dwelling populations of Mexican tetra exhibit elevated blood glucose, insulin resistance and hypertrophic visceral adipocytes compared to surface-dwelling counterparts. However, cavefish appear to avoid pathologies typically associated with these conditions, such as accumulation of advanced-glycation-end-products (AGEs) and chronic tissue inflammation. The metabolic strategies underlying the resilience properties of A. mexicanus cavefish, and how they relate to environmental challenges of the cave environment, are poorly understood. Here, we provide an untargeted metabolomics study of long- and short-term fasting in two A. mexicanus cave populations and one surface population. We find that, although the metabolome of cavefish bears many similarities with pathological conditions such as metabolic syndrome, cavefish also exhibit features not commonly associated with a pathological condition, and in some cases considered indicative of an overall robust metabolic condition. These include a reduction in cholesteryl esters and intermediates of protein glycation, and an increase in antioxidants and metabolites associated with hypoxia and longevity. This work suggests that certain metabolic features associated with human pathologies are either not intrinsically harmful, or can be counteracted by reciprocal adaptations. We provide a transparent pipeline for reproducing our analysis and a Shiny app for other researchers to explore and visualize our dataset.
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Antioxidantes , Characidae , Envelhecimento , Animais , Evolução Biológica , Humanos , Metaboloma , AçúcaresRESUMO
Cell lines have become an integral resource and tool for conducting biological experiments ever since the Hela cell line was first developed (Scherer et al. in J Exp Med 97:695-710, 1953). They not only allow detailed investigation of molecular pathways but are faster and more cost-effective than most in vivo approaches. The last decade saw many emerging model systems strengthening basic science research. However, lack of genetic and molecular tools in these newer systems pose many obstacles. Astyanax mexicanus is proving to be an interesting new model system for understanding metabolic adaptation. To further enhance the utility of this system, we developed liver-derived cell lines from both surface-dwelling and cave-dwelling morphotypes. In this study, we provide detailed methodology of the derivation process along with comprehensive biochemical and molecular characterization of the cell lines, which reflect key metabolic traits of cavefish adaptation. We anticipate these cell lines to become a useful resource for the Astyanax community as well as researchers investigating fish biology, comparative physiology, and metabolism.
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Characidae , Adaptação Fisiológica/genética , Animais , Evolução Biológica , Cavernas , Characidae/fisiologia , Células HeLa , Humanos , FígadoRESUMO
Studying how different genotypes respond to environmental variation is essential to understand the genetic basis of adaptation. The Mexican tetra, Astyanax mexicanus, has cave and surface-dwelling morphotypes that have adapted to entirely different environments in the wild, and are now successfully maintained in lab conditions. While this has enabled the identification of genetic adaptations underlying a variety of physiological processes, few studies have directly compared morphotypes between lab-reared and natural populations. Such comparative approaches could help dissect the varying effects of environment and morphotype, and determine the extent to which phenomena observed in the lab are generalizable to conditions in the field. To this end, we take a transcriptomic approach to compare the Pachón cavefish and their surface fish counterparts in their natural habitats and the lab environment. We identify key changes in expression of genes implicated in metabolism and physiology between groups of fish, suggesting that morphotype (surface or cave) and environment (natural or lab) both alter gene expression. We find gene expression differences between cave and surface fish in their natural habitats are much larger than differences in expression between morphotypes in the lab environment. However, lab-raised cave and surface fish still exhibit numerous gene expression changes, supporting genetically encoded changes in livers of this species. From this, we conclude that a controlled laboratory environment may serve as an ideal setting to study the genetic underpinnings of metabolic and physiological differences between the cavefish and surface fish.