The remarkable hypoxia tolerance in Brandt's voles ( Lasiopodomys brandtii )

Physiological indices and liver gene expression related to glucose supply in Brandt's vole (Lasiopodomys brandtii) exhibit species- and oxygen concentration-specific responses to hypoxia

Brandt's vole (Lasiopodomys brandtii) is a species with hypoxia tolerance, and glucose serves as the primary energy substrate under hypoxia. However, the glucose supply in Brandt's voles under hypoxia has not been studied. This study aimed to investigate characteristics in physiological indices and liver gene expression associated with glucose supply in Brandt's voles under hypoxia. Serum glucose of Brandt's voles remained stable under 10% O2, increased under 7.5% O2, and decreased under 5% O2. Serum lactate increased under 10% O2, decreased under 7.5% O2, increased at 6 h and decreased at 12 h under 5% O2. Liver glycogen increased under 10% O2, remained constant under 7.5% O2, and reduced under 5% O2. Pepck and G6pase expression associated with gluconeogenesis decreased under 10% O2, while Pepck expression decreased and G6pase expression increased under 7.5% and 5% O2. Regarding genes related to glycogen metabolism, Gys expression decreased at all oxygen concentrations, Phk expression increased under 5% O2, and Gp expression increased under 7.5% and 5% O2. The alterations in glucose, lactate, liver glycogen, and gene expression related to glycogenolysis in Kunming mice (Mus musculus, control species) are similar to discovery of Brandt's voles under 7.5% O2, but gene expression involved in gluconeogenesis and glycogen synthesis increased. The findings suggest that Brandt's voles are more tolerant to hypoxia than Kunming mice, and their physiological indices and liver gene expression related to glucose supply exhibit species- and oxygen concentration-specific responses to hypoxia. This research offers novel insights for studying hypoxia tolerance of Brandt's voles.

Changes in gene expression and enzyme activity related to glucose metabolism in the livers of Brandt's voles (Lasiopodomys brandtii) exposed to hypoxia

Brandt's vole (Lasiopodomys brandtii) is a hypoxia-tolerant species, and the metabolic characteristics of hypoxia-tolerant species have become a focus of recent research. However, insights into the anaerobic and aerobic metabolism of the livers of Brandt's voles under hypoxia remain limited. In this study, Brandt's voles and hypoxia-intolerant Kunming mice (Mus musculus, control species) were exposed to hypoxia conditions (Brandt's voles, 10% and 7.5% O₂; Kunming mice, 10% O₂) for 24 h, and changes in gene expression and enzyme activity related to anaerobic and aerobic metabolism in the livers were evaluated. Phosphofructokinase 1 (PFK1), phosphofructokinase 2 (PFK2), pyruvate kinase muscle (PKM), hexokinase 2 (HK2), and lactate dehydrogenase (LDH) related to anaerobic metabolism in the livers of Brandt's voles were increased under 7.5% O₂. Regarding gene expression and enzyme activity for aerobic metabolism in Brandt's voles under 7.5% and 10% O₂, pyruvate dehydrogenase kinase 1 (PDK1) expression was up-regulated, and succinate dehydrogenase (SDH) activity was decreased. In the livers of Kunming mice, gene expression related to anaerobic and aerobic metabolism was increased at the late stage of 10% O₂, and SDH activity was enhanced at 6 h and reduced at 18 h. In addition, PFK1,PKM, PDK1 expression and SDH activity in Brandt's voles were significantly correlated with HIF-1a expression. PFK1, PKM, LDHand PDK1 expression in Kunming mice were significantly correlated with HIF-1a expression. These findings indicate that the livers of Brandt's voles have a certain tolerance to hypoxia, and metabolic changes play important roles in hypoxia tolerance.

Antioxidant response to severe hypoxia in Brandt's vole Lasiopodomys brandtii

The antioxidant defense system is essential for animals to cope with homeostasis disruption and overcome oxidative stress caused by adverse environmental conditions such as hypoxia. However, our understanding of how this system works in subterranean rodents remains limited. In this study, Brandt's vole Lasiopodomys brandtii was exposed to normoxia (21% O₂ ) or hypoxia (mild or severe hypoxia: 10% or 5% O₂ ) for 6 h. Changes in key enzymes of the classic enzymatic antioxidant system at both mRNA and enzyme activity levels, and tissue antioxidant levels of the low-molecular-weight antioxidant system were determined in brain, liver, and kidney. Transcript levels of the upstream regulator NF-E2-related factor 2 (Nrf2) were also measured. We found that the mRNA expression of Nrf2 and its downstream antioxidant enzyme genes in L. brandtii were relatively conserved in response to hypoxia in most tissues and genes tested, except in the liver. Hepatic Nrf2, Cu/Zn SOD, GPx1, and GPx3 levels were significantly upregulated in response to mild hypoxia, whereas Mn SOD level decreased significantly in severe hypoxia. Unmatched with changes at the RNA level, constitutively high and relatively stable antioxidant enzyme activities were maintained throughout. For the low-molecular-weight antioxidant system, an abrupt increase of cerebral ascorbic acid (AA) levels in hypoxia indicated a tissue-specific antioxidant response. Although hypoxia did not cause significant oxidative damage in most tissues tested, the significant decrease in antioxidant enzyme activities (GPX and GR) and increase in lipid peroxidation in the kidney suggest that prolonged hypoxia may pose a critical threat to this species.

Diverse energy metabolism patterns in females in Neodon fuscus, Lasiopodomys brandtii, and Mus musculus revealed by comparative transcriptomics under hypoxic conditions

The effects of global warming and anthropogenic disturbance force animals to migrate from lower to higher elevations to find suitable new habitats. As such migrations increase hypoxic stress on the animals, it is important to understand how plateau- and plain-dwelling animals respond to low-oxygen environments. We used comparative transcriptomics to explore the response of Neodon fuscus, Lasiopodomys brandtii, and Mus musculus skeletal muscle tissues to hypoxic conditions. Results indicate that these species have adopted different oxygen transport and energy metabolism strategies for dealing with a hypoxic environment. N. fuscus promotes oxygen transport by increasing hemoglobin synthesis and reduces the risk of thrombosis through cooperative regulation of genes, including Fga, Fgb, Alb, and Ttr; genes such as Acs16, Gpat4, and Ndufb7 are involved in regulating lipid synthesis, fatty acid β-oxidation, hemoglobin synthesis, and electron-linked transmission, thereby maintaining a normal energy supply in hypoxic conditions. In contrast, the oxygen-carrying capacity and angiogenesis of red blood cells in L. brandtii are promoted by genes in the CYP and COL families; this species maintains its bodily energy supply by enhancing the pentose phosphate pathway and mitochondrial fatty acid synthesis pathway. However, under hypoxia, M. musculus cannot effectively transport additional oxygen; thus, its cell cycle, proliferation, and migration are somewhat affected. Given its lack of hypoxic tolerance experience, M. musculus also shows significantly reduced oxidative phosphorylation levels under hypoxic conditions. Our results suggest that the glucose capacity of M. musculus skeletal muscle does not provide sufficient energy during hypoxia; thus, we hypothesize that it supplements its bodily energy by synthesizing ketone bodies. For the first time, we describe the energy metabolism pathways of N. fuscus and L. brandtii skeletal muscle tissues under hypoxic conditions. Our findings, therefore, improve our understanding of how vertebrates thrive in high altitude and plain habitats when faced with hypoxic conditions.