Acute high-caffeine exposure increases autophagic flux and reduces protein synthesis in C2C12 skeletal myotubes.

Caffeine is a highly catabolic dietary stimulant. High caffeine concentrations (1-10 mM) have previously been shown to inhibit protein synthesis and increase protein degradation in various mammalian cell lines. The purpose of this study was to examine the effect of short-term caffeine exposure on cell signaling pathways that regulate protein metabolism in mammalian skeletal muscle cells. Fully differentiated C2C12 skeletal myotubes either received vehicle (DMSO) or 5 mM caffeine for 6 h. Our analysis revealed that caffeine promoted a 40% increase in autolysosome formation and a 25% increase in autophagic flux. In contrast, caffeine treatment did not significantly increase the expression of the skeletal muscle specific ubiquitin ligases MAFbx and MuRF1 or 20S proteasome activity. Caffeine treatment significantly reduced mTORC1 signaling, total protein synthesis and myotube diameter in a CaMKKß/AMPK-dependent manner. Further, caffeine promoted a CaMKII-dependent increase in myostatin mRNA expression that did not significantly contribute to the caffeine-dependent reduction in protein synthesis. Our results indicate that short-term caffeine exposure significantly reduced skeletal myotube diameter by increasing autophagic flux and promoting a CaMKKß/AMPK-dependent reduction in protein synthesis.

Inhibiting c-Jun N-terminal kinase partially attenuates caffeine-dependent cell death without alleviating the caffeine-induced reduction in mitochondrial respiration in C2C12 skeletal myotubes.

Caffeine is a widely consumed stimulant that has previously been shown to promote cytotoxic stress and even cell death in numerous mammalian cell lines. Thus far there is little information available regarding the toxicity of caffeine in skeletal muscle cells. Our preliminary data revealed that treating C2C12 myotubes with 5 mM caffeine for 6 h increased nuclear fragmentation and reduced basal and maximal oxygen consumption rate (OCR) in skeletal myotubes. The purpose of this study was to further elucidate the pathways by which caffeine increased cell death and reduced mitochondrial respiration. We specifically examined the role of c-Jun N-terminal kinase (JNK), which has previously been shown to simultaneously increase caspase-dependent cell death and reduce mitochondrial respiration in other mammalian cell lines. We found that caffeine promoted a dose-dependent increase in cell death in multinucleated myotubes but did not in mononucleated myoblasts. The addition of 10 µM Z-DEVD-FMK, a specific inhibitor of executioner caspases, completely inhibited caffeine-dependent cell death. Further, the addition of 400 µM dantrolene, a specific ryanodine receptor (RYR) inhibitor, prevented the caffeine-dependent increase in cell death and the reduction in basal and maximal OCR. We also discovered that caffeine treatment significantly increased the phosphorylation of JNK and that the addition of 30 µM SP600125 (JNKi), a specific JNK inhibitor, partially attenuated caffeine-induced cell death without preventing the caffeine-dependent reduction in basal and maximal OCR. Our results suggest that JNK partially mediates the increase in caspase-dependent cell death but does not contribute to reduced mitochondrial respiration in caffeine-treated skeletal muscle cells. We conclude that caffeine increased cell death and reduced mitochondrial respiration in a calcium-dependent manner by activating the RYR and promoting reticular calcium release.

Caffeine promotes autophagy in skeletal muscle cells by increasing the calcium-dependent activation of AMP-activated protein kinase.

Caffeine has been shown to promote calcium-dependent activation of AMP-activated protein kinase (AMPK) and AMPK-dependent glucose and fatty acid uptake in mammalian skeletal muscle. Though caffeine has been shown to promote autophagy in various mammalian cell lines it is unclear if caffeine-induced autophagy is related to the calcium-dependent activation of AMPK. The purpose of this study was to examine the role of calcium-dependent AMPK activation in regulating caffeine-induced autophagy in mammalian skeletal muscle cells. We discovered that the addition of the AMPK inhibitor Compound C could significantly reduce the expression of the autophagy marker microtubule-associated protein 1 light chain 3b-II (LC3b-II) and autophagic vesicle accumulation in caffeine treated skeletal muscle cells. Additional experiments using pharmacological inhibitors and RNA interference (RNAi) demonstrated that the calcium/calmodulin-activated protein kinases CaMKKß and CaMKII contributed to the AMPK-dependent expression of LC3b-II and autophagic vesicle accumulation in a caffeine dose-dependent manner. Our results indicate that in skeletal muscle cells caffeine increases autophagy by promoting the calcium-dependent activation of AMPK.

Understanding maps as symbols: the development of map concepts in children.

We expect that many readers encountered this article with the beliefs that maps are highly specialized devices primarily used for wayfinding; that they represent the spatial world in a single, correct form; that they are readily transparent; and that their sole contribution to psychology is their role in externalizing environmental cognition. By discussing the myriad functions and forms of maps, by highlighting their symbolic nature, and by considering some of the misconceptions about maps, we have attempted to demonstrate the value of maps for addressing a wide range of developmental questions. Our review of past research literature suggests that research conducted within individual disciplines has both strengths and limitations. Work in the psychological tradition is characterized by attention to important subject characteristics and to carefully described and implemented research designs, procedures, coding, and analyses. At the same time, this work reveals, at best, highly restricted views about maps, and at worst, fundamental misconceptions about maps. Work in the geographic and environmental traditions, in contrast, samples a broader range of map forms and functions, but it suffers from inattention to procedural details that makes the conclusions less compelling than they might otherwise be. A conventional wisdom is emerging from the work in both traditions: That children's map understanding occurs extremely early and extremely easily. The limitations of both research traditions, however, suggest the need for caution in accepting this view. Developmental and cartographic theories provide a compelling reason to reexamine the early and easy view and suggest the need for alternative conceptual and empirical approaches. We have argued that future work should integrate the traditions of psychology and geography. Illustrative data from an interdisciplinary program of research were presented. We described work demonstrating the gradual and difficult process of mastering the representational and geometric correspondences that link the map to its referent in the world. Our data suggest that there are significant achievements in map conceptualization (the understanding of the concept of a map), map identification (understanding the formal components of a map), and map utilization (the ability to use maps). Our data support the view that maps are not transparent and that children's abilities to understand, use, and create maps are linked to their developing representational and spatial skills. In concluding, we should acknowledge that we have deliberately pushed interpretations about understanding maps as symbolic representations to the extreme. The reason for this strategy is simple: We believe that work on maps--both in the public schools and in academia--is assumed to be an expendable and irrelevant luxury.(ABSTRACT TRUNCATED AT 400 WORDS)