Biomarker-based assessment of the muscle maintenance and energy status of anurans from an extremely seasonal semi-arid environment, the Brazillian Caatinga

Abstract

We studied seasonal variation of key metabolic regulators in the muscles of anurans that 21 experience drastic variation in environmental conditions and differ in the seasonal 22 activity patterns. 23 2 24 Abstract 25 Strongly seasonal environments pose challenges for performance and survival of 26 animals, especially when resource abundance seasonally fluctuates. We investigated the 27 seasonal variation of expression of key metabolic biomarkers in the muscles of three 28 species of anurans from the drastically seasonal Brazilian semi-arid area, Caatinga. The 29 three studied anuran species (Rhinella jimi, R. granulosa and Pleurodema diplolister) 30 differ in their seasonal activity patterns. We examined the expression of proteins 31 regulating energy turnover (AMP-activated protein kinase [AMPK] and protein kinase 32 B [AKT]), protein synthesis and homeostasis (total and phosphorylated eukaryotic 33 initiation factor 2α [eIF2α and p-eIF2α] and chaperone proteins [HSP 60, 70, and 90]) 34 in muscles related to reproduction and locomotion. Cytochrome c oxidase (COX) 35 activity was also assessed as an index of the muscle aerobic capacity. Our results point 36 to the importance of metabolic regulators mediating the muscular function during the 37 drastic seasonal variation. The toads that remain active during the drought appear to 38 maintain muscles through more energy extensive pathways including elevated protein 39 synthesis, while the aestivating species employs energy conservation strategy 40 suppressing protein synthesis, decreasing chaperone expression and increasing 41 expression of AMPK. All three studied species activate cell survival pathways during 42 the drought likely to prevent muscle atrophy, and maintain the muscle capacity 43 throughout the year, despite the resource limitation. These strategies are important 44 considering the unpredictability of the reproductive event and high demand on muscular 45 activity during the reproductive season in these amphibians. 3 47 Introduction 48 Strongly seasonal environments characterized by large changes in conditions 49 such as temperature and food availability, pose challenges to the organisms that need to 50 adjust their functions to survive and complete their life cycles [1, 2]. These 51 physiological adjustments are dependent on biochemical regulators and cell signaling 52 pathways that mediate cell survival, ensure cell and organ integrity and prioritize the use 53 of energy to meet the (often conflicting) needs of survival, growth and reproduction 54 [1,3]. In vertebrate ectotherms, the skeletal muscle physiology and performance are 55 directly related to the overall fitness due to the muscles' involvement in courtship, 56 territorial defense, foraging, escape from predators, mating interactions and migration 57 [4]. In seasonally fluctuating environments, skeletal muscles can display phenotypic 58 changes such as atrophy and changes in the fiber number and type during extreme 59 environmental stress and/or resource limitation [5]. Nevertheless, anuran ...

Biomarker-based assessment of the muscle maintenance and energy status of anurans from an extremely seasonal semi-arid environment, the Brazilian Caatinga

“…Furthermore, the expression of phosphorylated and total AMPK might not always be in the same direction which limits our conclusions on the potential changes in the active form of this protein (since the phosphorylated form of AMPK could not be measured in our present study due to the lack of antibody cross-reactivity with the anuran protein). Different responses regarding AMPK activation in anuran species submitted to the same freezing condition has been reported in Rana perezi and Rana sylvatica [45,46]. Additionally, during reproductive period, AMPK expression was particularly elevated in trunk of P. diplolister compared to other muscle types, which might indicate a metabolic stress due to high energy demand of the trunk muscles due to calling activity [48,49,50].…”

“…The copyright holder for this preprint (which was this version posted August 17, 2018. ; https://doi.org/10.1101/394544 doi: bioRxiv preprint resource-and energy-limited periods in many organisms including hibernating mammals [43,44] and frogs exposed to hypothermia, hypoxia, freezing, dehydration or anoxia [45,46,44]. Furthermore, AMPK suppresses energy-demanding metabolic processes [47,22] and induces cell cycle arrest [12,22,44], which also contributes to energy savings.…”

“…During periods that animals need to save energy, AMPK is activated to regulate catabolic versus anabolic metabolism increasing ATP synthesis and suppressing ATP consumption [21,22]. Protein kinase B (AKT) plays a central role in metabolism and cell survival stimulating glucose uptake, glycogen synthesis, lipogenesis and protein synthesis, and regulating the cell cycle and apoptosis [23]. Eukaryotic initiation factor 2α regulates protein synthesis and plays a key role in the stress response and suppression of the ATP-consuming protein synthesis under low energetic budget scenarios [24].…”