High-fat Diet Induces Nr4a3-dependent Decrease In Respiratory Capacity Of Mouse Soleus Muscle

Abstract

The Nuclear Hormone Receptor 4A family of genes have been observed to play a role in proper metabolic function in various tissues, including skeletal muscle. PURPOSE: To analyze the effect of the Nr4a3 gene on respiratory capacity of mitochondria in skeletal muscle of mice on a normal or high fat diet. METHODS: Nr4a3-/- and WT mice were fed a normal chow (NC) or high fat diet (HF) for at least 20 weeks. After euthanasia, soleus muscle was harvested and wet weight was measured. Muscle fibers were teased apart and permeabilized with saponin in preparation for respirometry. Mitochondrial respiration was evaluated using an Oroboros Oxygraph Respirometer. Respiratory capacity comparisons were made with a two-way ANOVA and Tukey multiple comparison test. RESULTS: Oxygen consumption is reported as pmol/(s*mg wet tissue) and statistics are represented as mean ± SEM. In the WT male mice there was a decrease in coupled complex I supported respiration in HF vs. NC diet (25.9 ± 7.3 vs. 64.5 ± 5.0, p=0.004). In the HF WT group there was also a decrease in coupled complex I and II supported respiration (57.2 ± 13.4 vs. 102.5 ± 7.0, p=0.0005) and uncoupled respiration (61.4 ± 15.0 vs. 107.8 ± 7.1, p=0.0004) compared to NC WT. In female mice there was also a decrease between HF WT and NC WT in complex I (28.2 ± 3.7 vs. 57.4 ± 5.7, p=0.0005) and complex I and II (78.2 ± 6.1 vs. 108.8 ± 6.7, p=0.0003) supported respiration as well as in uncoupled respiration (87.1 ± 7.1 vs. 119.4 ± 8.9, p=0.0001). However, there was no significant difference between the WT NC mice and either of the Nr4a3-/- groups. Coupled complex I, complex I and II and uncoupled respiration states in both Nr4a3-/- groups were not significantly different from WT. CONCLUSIONS: The Nr4a3 gene plays a role in mitochondrial function in mouse skeletal muscle. Feeding mice a high fat diet impairs proper mitochondrial function in muscle when compared to a normal chow diet. The decrease in respiration from the HF diet is dependent upon the function of the Nr4a3 gene, as no decrease was observed in Nr4a3-/- mice. A limitation of this study is that this effect could be due to the lack of Nr4a3 in the skeletal muscle, or a secondary effect of lacking the gene in other parts of the body.