Women have higher protein content of beta-oxidation enzymes in skeletal muscle than men

Abstract

It is well recognized that compared with men, women have better ultra-endurance capacity, oxidize more fat during endurance exercise, and are more resistant to fat oxidation defects i.e. diet-induced insulin resistance. Several groups have shown that the mRNA and protein transcribed and translated from genes related to transport of fatty acids into the muscle are greater in women than men; however, the mechanism(s) for the observed sex differences in fat oxidation remains to be determined. Muscle biopsies from the vastus lateralis were obtained from moderately active men (N=12) and women (N=11) at rest to examine mRNA and protein content of genes involved in lipid oxidation. Our results show that women have significantly higher protein content for tri-functional protein alpha (TFPalpha), very long chain acyl-CoA dehydrogenase (VLCAD), and medium chain acyl-CoA dehydrogenase (MCAD) (P<0.05). There was no significant sex difference in the expression of short-chain hydroxyacyl-CoA dehydrogenase (SCHAD), or peroxisome proliferator activated receptor alpha (PPARalpha), or PPARgamma, genes potentially involved in the transcriptional regulation of lipid metabolism. In conclusion, women have more protein content of the major enzymes involved in long and medium chain fatty acid oxidation which could account for the observed differences in fat oxidation during exercise.

Figure 1. VLCAD protein content is higher in women than men.

Differences in VLCAD mRNA content between men and women shown by Real time RT-PCR, adjusted to β2-M mRNA (A). Protein content of VLCAD in skeletal muscle of men and women, adjusted to CS (B,C). Representative western blot (B) Lanes 1–4 are men, lanes 5–8 women. N = 12 men and 11 women. *P≤0.05.

Figure 2. MCAD protein content is higher in women than men.

Differences in MCAD mRNA content between men and women shown by Real time RT-PCR, adjusted to β2-M mRNA (A). Protein content of MCAD in skeletal muscle of men and women, adjusted to CS (B,C). Representative western blot (B) Lanes 1–4 are men, lanes 5–8 women. N = 12 men and 11 women. *P≤0.05.

Figure 3. TFPα protein content is higher in women than men.

Differences in TFPα mRNA content between men and women shown by Real time RT-PCR, adjusted to β2-M mRNA (A). Protein content of TFPα in skeletal muscle of men and women, adjusted to CS (B,C). Representative western blot (B) Lanes 1–5 are men, lanes 6–10 are women. N = 12 men and 11 women. *P≤0.05.

Figure 4. SCHAD protein content is equal in women and men.

SCHAD mRNA content between men and women shown by Real time RT-PCR, adjusted to β2-M mRNA (A). Protein content of SCHAD in skeletal muscle of men and women, adjusted to CS (B,C). Representative western blot (B) Lanes 1–4 are men, lanes 5–8 women. N = 12 men and 11 women.

Figure 5. No sex differences in PPARα or PPARγ protein content.

Protein content of PPARα (A) and PPARγ (B) in skeletal muscle of men and women, adjusted to actin. Representative western blots; lanes 1–4 are men, lanes 5–8 women. N = 12 men and 11 women.