Effects of Aerobic Exercise Training on C1q Tumor Necrosis Factor α-Related Protein Isoform 5 (Myonectin): Association with Insulin Resistance and Mitochondrial DNA Density in Women

Context:

The C1q TNFα-related protein (C1QTNF) families exhibit a C-terminal complement factor C1q globular domain similar to that of TNF. However, their clinical implications are largely unknown. We recently found that the C1q TNFα-related protein isoform 5 (C1QTNF5 or myonectin) level was increased in insulin-resistant rodents and mitochondrial DNA (mtDNA)-depleted myocytes.

Objective:

We aimed to determine the effects of aerobic exercise training on C1QTNF5 level and its association with insulin resistance and mtDNA density in young and old healthy women.

Design and Setting:

Fourteen healthy young women aged 22.5 ± 2.7 yr and 14 healthy older women aged 60.3 ± 5.2 yr performed aerobic exercise at 60–80% of maximal oxygen consumption (VO₂max) over three 1-h sessions per week for 10 wk. Insulin resistance was assessed by homeostasis model assessment of insulin resistance and adiponectin concentration. Serum C1QTNF5 level was estimated by immunoblotting. The mtDNA/28S rRNA ratio was used to determine mtDNA density.

Results:

VO₂max increased significantly after the exercise training from 33.1 ± 6.2 to 35.3 ± 5.3 ml/kg · min in younger women and from 23.2 ± 3.1 to 27.2 ± 4.8 ml/kg · min in older women (P < 0.05). The C1QTNF5 level and homeostasis model assessment of insulin resistance decreased significantly after exercise training and were correlated positively (r = 0.462; P < 0.01). There were negative correlations between the changes in C1QTNF5 level and the changes in VO₂max, mtDNA density, and adiponectin level (r = −0.495, −0.672, and −0.569, respectively; all P < 0.01).

Conclusion:

These findings suggest a physiological function for C1QTNF5 (myonectin) in linking insulin resistance with quantitative changes in mtDNA. Further research exploring the role of C1QTNF5 in the development of insulin resistance is warranted.