Metabolic Characteristics and Response to High Altitude in Phrynocephalus erythrurus (Lacertilia: Agamidae), a Lizard Dwell at Altitudes Higher Than Any Other Living Lizards in the World

Abstract

Metabolic response to high altitude remains poorly explored in reptiles. In the present study, the metabolic characteristics of Phrynocephalus erythrurus (Lacertilia: Agamidae), which inhabits high altitudes (4500 m) and Phrynocephalus przewalskii (Lacertilia: Agamidae), which inhabits low altitudes, were analysed to explore the metabolic regulatory strategies for lizards living at high-altitude environments. The results indicated that the mitochondrial respiratory rates of P . erythrurus were significantly lower than those of P . przewalskii , and that proton leak accounts for 74~79% of state 4 and 7~8% of state3 in P . erythrurus vs. 43~48% of state 4 and 24~26% of state3 in P . przewalskii . Lactate dehydrogenase (LDH) activity in P . erythrurus was lower than in P . przewalskii , indicating that at high altitude the former does not, relatively, have a greater reliance on anaerobic metabolism. A higher activity related to β-hydroxyacyl coenzyme A dehydrogenase (HOAD) and the HOAD/citrate synthase (CS) ratio suggested there was a possible higher utilization of fat in P . erythrurus . The lower expression of PGC-1α and PPAR-γ in P . erythrurus suggested their expression was not influenced by cold and low PO2 at high altitude. These distinct characteristics of P . erythrurus are considered to be necessary strategies in metabolic regulation for living at high altitude and may effectively compensate for the negative influence of cold and low PO2.

Comparison of thermoregulation and metabolic characteristics in Phrynocephalus vlangalii (Lacertilia, Agamidae) from different altitudes

“…Meanwhile, the proton leak of liver mitochondria in the Maduo population accounts for a lower percentage of state III than that of the Golmud population (11.4~14.6% VS. 22.5~25.1%). These results were similar to our previous comparison study on P. erythruru and P. przewalskii (Xiaolong Tang, Ying Xin et al 2013), and indicate that the function of uncoupling protein and adenine nucleotide translocase on mitochondrial proton leak may conservative in lizards. More importantly, the relatively low ratio of proton leak/state III may benefit to a high ATP productivity and turnover rate, as well as help to improve the efficiency of mitochondrial respiration and energy utilization (Rolfe and Brand 1997).…”

“…The results of mitochondrial respiratory in the present study also confirmed this conclusion, the mitochondrial respiratory rates of Maduo population were significantly lower than that in Golmud population. Similar results were also found in another study on the resting metabolic rate of P. vlangalii (Hu, Lu et al 2019), as well as in our previous study on another high-altitude living lizard P. erythrurus (Xiaolong Tang, Ying Xin et al 2013). The depression metabolism of reptile living at high altitudes could be achieved mainly through two aspects of regulation.…”

“…Proton leak control could significantly affect the metabolic level of mitochondria by changing the consumption rate of oxygen and transmembrane potential (Brand, Pakay et al 2005). Invalid loops of proton leak may cause energy loss in the form of heat, but may also help to maintain body temperature and be an important component of the basal metabolic rate (Xiaolong Tang, Ying Xin et al 2013).…”

“…Lactate dehydrogenase (LDH), citrate synthase (CS), and β-hydroxyacyl coenzyme A dehydrogenase (HOAD) are important enzymes in anaerobic, aerobic, and lipid metabolism, respectively (Voet and Voet 1995). The activities of these enzymes are usually changed with seasons or environmental conditions, which is especially important to improve energy and oxygen utilization for high altitude living lizards (Xiaolong Tang, Ying Xin et al 2013).…”

Changes in intestinal microbiota across an altitudinal gradient in the lizard Phrynocephalus vlangalii

“…; Lu et al., ), lung and/or heart mass (Han et al., ; He, Xiu, Tang, Yue, et al. ) as well as by decreasing aerobic respiration (Tang et al., ).…”