Search

Background: In response to seasonal cold and food shortage, the Xizang plateau frogs, Nanorana parkeri (Anura: Dicroglossidae), enter a reversible hypometabolic state where heart rate and oxygen consumption in skeletal muscle are strongly suppressed. However, the effect of winter hibernation on gene expression and metabolic profiling in these two tissues remains unknown. In the present study, we conducted transcriptomic and metabolomic analyses of heart and skeletal muscle from summer- and winter-collected N. parkeri to explore mechanisms involved in seasonal hibernation. Results: We identified 2407 differentially expressed genes (DEGs) in heart and 2938 DEGs in skeletal muscle. Enrichment analysis showed that shared DEGs in both tissues were enriched mainly in translation and metabolic processes. Of these, the expression of genes functionally categorized as "response to stress", "defense mechanisms", or "muscle contraction" were particularly associated with hibernation. Metabolomic analysis identified 24 and 22 differentially expressed metabolites (DEMs) in myocardium and skeletal muscle, respectively. In particular, pathway analysis showed that DEMs in myocardium were involved in the pentose phosphate pathway, glycerolipid metabolism, pyruvate metabolism, citrate cycle (TCA cycle), and glycolysis/gluconeogenesis. By contrast, DEMs in skeletal muscle were mainly involved in amino acid metabolism. Conclusions: In summary, natural adaptations of myocardium and skeletal muscle in hibernating N. parkeri involved transcriptional alterations in translation, stress response, protective mechanisms, and muscle contraction processes as well as metabolic remodeling. This study provides new insights into the transcriptional and metabolic adjustments that aid winter survival of high-altitude frogs N. parkeri. [ABSTRACT FROM AUTHOR]

The frog Nanorana parkeri (Dicroglossidae) is endemic to the Tibetan Plateau, and overwinters shallow pond within damp caves for up to 6 months. Herein, we investigate the freeze tolerance of this species and profile changes in liver and skeletal muscle metabolite levels using an untargeted LC–MS-based metabolomic approach to investigate molecular mechanisms that may contribute to freezing survival. We found that three of seven specimens of N. parkeri could survive after being frozen for 12 h at − 2.0 °C with 39.91% ± 5.4% (n = 7) of total body water converted to ice. Freezing exposure induced partial dehydration of the muscle, which contributed to decreasing the amount of freezable water within the muscle and could be protective for the myocytes themselves. A comparative metabolomic analysis showed that freezing elicited significant responses, and a total of 33 and 36 differentially expressed metabolites were identified in the liver and muscle, respectively. These metabolites mainly participate in alanine, aspartic acid and glutamic acid metabolism, arginine and proline metabolism, and D-glutamine and D-glutamate metabolism. After freezing exposure, the contents of ornithine, melezitose, and maltotriose rose significantly; these may act as cryoprotectants. Additionally, the content of 8-hydroxy-2-deoxyguanine, 7-Ketocholesterol and hypoxanthine showed a marked increase, suggesting that freezing induced oxidative stress in the frogs. In summary, N. parkeri can tolerate a brief and partial freezing of their body, which was accompanied by substantial changes in metabolomic profiles after freezing exposure. [ABSTRACT FROM AUTHOR]

The Xizang plateau frog, Nanorana parkeri, has the highest altitudinal distribution of all frogs in the world and survives the cold of winter without feeding by entering into a hibernating state. However, little attention has been paid to its physiological and biochemical characteristics that support overwintering underwater in small ponds. Here, we measured metabolic rate and heart rate, and collected liver and muscle samples from N. parkeri in summer and winter for analysis of mitochondrial respiration rate, and activities and relative mRNA transcript expression of metabolic enzymes. Compared with summer-collected frogs, both resting metabolic rate and heart rate were significantly reduced in winter-collected frogs. Both state 3 and state 4 respiration of liver mitochondria were also significantly reduced in winter but muscle mitochondria showed a decline only in state 3 respiration in winter. The activities and corresponding mRNA expression of cytochrome c oxidase showed a marked decline in winter, whereas the activities and corresponding mRNA expression of lactate dehydrogenase increased in winter-collected frogs, compared to summer. The thermal sensitivity (Q10 values) for state 3 respiration rate by liver mitochondria, and activities of lactate dehydrogenase, and cytochrome c oxidase all increased in winter-collected frogs, compared with summer frogs, suggesting that overwintering frogs were more sensitive to changes in external temperature. Enzyme changes mainly result from lower overall quantities of these enzymes as well as post-translational modifications. We conclude that overwintering N. parkeri exhibit a seasonal, temperature-independent suppression of metabolism that is mediated at multiple levels: physiological, mitochondrial, gene expression and enzyme activity levels. [ABSTRACT FROM AUTHOR]

Obtaining a precise velocity field of the Earth's surface is critical for probing Earth's tectonic movements. In this contribution we construct a precise vertical velocity field with high-spatial resolution for the Tibetan Plateau (TP) and its surrounding areas using both 113 continuous and 969 campaign GPS time series over the period 2008 to 2019. Specifically, we compared the statistical distribution of residual continuous GPS time series to find the optimal regional surface mass loading (SML) models. The optimal modeled nontectonic displacements were used to correct these campaign GPS time series to reduce their scatter and accordingly improve the precision of the uplift rate estimates. The results showed that we could reduce the root mean square (RMS) on the vertical coordinate time series by more than 75% of the campaign GPS stations. We computed and removed vertical deformation due to horizontal strain rates obtained from GPS time series, and discussed dynamic sources (mantle dynamic topography, isostatic adjustment, and flexural loading) that drive the residual vertical tectonic motion. The study presents the most recent surface kinematic constraints for comprehending the dynamic sources of tectonic uplift or subsidence between and within tectonic units. Plain Language Summary : Movements of the Tibetan Plateau (TP) have a profound impact on adjacent areas. We collected all available GPS data to determine a precise vertical velocity field with high-spatial resolution. We make use of optimal surface mass loading (SML) models to improve estimation accuracy of campaign GPS stations, including an estimate of the vertical movement caused by the horizontal tectonic motions. We combine geological and geophysical data with our vertical velocity field to understand the dynamic sources of uplift or subsidence between and within tectonic units of the TP. • We obtain a high spatial resolution vertical velocities over the TP. • Regional optimal surface mass loadings can reduce the scatter of most campaign GPS. • New vertical velocities provide the latest surface kinematic constraint of the TP. [ABSTRACT FROM AUTHOR]

The Xizang plateau frog Nanorana parkeri can tolerate brief and partial freezing of their body. To determine the significant role of antioxidant defense and non-specific immune defense in freezing survival of this species, we assayed parameters of oxidative damage, antioxidant defense and non-specific immune enzymes during freezing exposure (−2 °C for 12 h) in five organs (heart, brain, liver, kidney, and skeletal muscle). The results showed that freezing led to a significant rise in the content of malondialdehyde (MDA) and carbonyl groups (CG) in brain, liver and kidney tissues. The activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) increased significantly in brain and liver tissues with an augmentation of total antioxidant capacity (T-AOC). Apparent increments in muscle SOD activity and liver GST activity were also observed during freezing exposure. Vitamin C content significantly decreased in liver and kidney but a significant increase occurred in brain. Activities of non-specific immune enzymes, acid phosphatase (ACP) and alkaline phosphatase (AKP), were also assessed. ACP activity was significantly reduced in all five tissues tested whereas AKP activity decreased significantly in four tissues but rose in brain. In summary, freezing is accompanied by oxidative stress in the high-altitude frog, N. parkeri , as documented by increases in the content of MDA and CG in tissues. Freezing exposure also induced tissue-specific changes in the antioxidant defenses showing that activation of antioxidant systems is a part of the survival strategy of this in a high-altitude frog during freezing. Such up-regulation of antioxidant enzymes suggests a particularly important role for them in the liver and brain, serving as an anticipatory mechanism to deal with the ROS challenge during freeze/thaw episodes. Our findings contribute to extending the current understanding of the mechanisms of freeze tolerance in high-altitude frogs. • Freezing exposure induced oxidative stress in the high-altitude frog, Nanorana parkeri. • Freezing exposure induced oxidative damage in brain, liver and kidney tissues. • The activities of SOD, CAT and GPX and T-AOC increased significantly in brain and liver tissues after freezing exposure. • ACP and AKP activities reduced significantly in all tissues except brain after freezing exposure. [ABSTRACT FROM AUTHOR]