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 Phrynocephaluserythrurus (Lacertilia: Agamidae), which inhabits high altitudes (4500 m) and Phrynocephalusprzewalskii (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.

Figure 1. Mitochondrial respiratory rate and the uncoupling of liver and skeletal muscle in Phrynocephalus erythrurus and Phrynocephalus przewalskii , respectively.

Values are means ± s.e.m.

Figure 2. Activities of lactate dehydrogenase (LDH), citrate synthase (CS) and β-hydroxyacyl coenzyme A dehydrogenase (HOAD) at 20 and 30°C in the liver of Phrynocephalus erythrurus (Open columns) and Phrynocephalus przewalskii (Twill columns).

Values are means ± s.e.m.

Figure 3. Activities of lactate dehydrogenase (LDH), citrate synthase (CS) and β-hydroxyacyl coenzyme A dehydrogenase (HOAD) at 20 and 30°C in the skeletal muscle of Phrynocephalus erythrurus (Open columns) and Phrynocephalus przewalskii (Twill columns).

Values are means ± s.e.m.

Figure 4. Real-time PCR analysis of PGC-1α and PPAR-γ mRNA levels in liver and skeletal muscle from Phrynocephalus erythrurus and Phrynocephalus przewalskii .

Values are means ± s.e.m. in each group.