Turnover of muscle lipids and response to exercise differs between neutral and polar fractions in a model songbird, the Zebra Finch

Abstract

The turnover rates of tissues and their constituent molecules give us insights into animals’ physiological demands and their functional flexibility over time. Thus far, most studies of this kind have focused on protein turnover, and few have considered lipid turnover despite an increasing appreciation of the functional diversity of this class of molecules. We measured the turnover rates of neutral and polar lipids from the pectoralis muscles of a model songbird, the Zebra Finch (Taeniopygia guttata, N=65), in a 256 day C3 / C4 diet shift experiment, with tissue samples taken at ten time points. We also manipulated the physiological state of a subset of these birds with a 10-week flight training regimen to test the effect of exercise on lipid turnover. We measured lipid δ13C values via IRMS and estimated turnover in different fractions and treatment groups with nonlinear mixed effect regression. We found a significant difference between the mean retention times of neutral and polar lipids (t119=-2.22, P=0.028), with polar lipids τ=11.80±1.28 days) having shorter retention times than neutral lipids τ=19.47±3.22 days). When all birds were considered, we also found a significant decrease in the mean retention time of polar lipids in exercised birds relative to control birds (difference=-2.2±1.83 days, t56=-2.37, P=0.021), but not neutral lipids (difference=4.2±7.41 days, t56=0.57, P=0.57). A larger, more variable neutral lipid pool and the exposure of polar lipids in mitochondrial membranes to oxidative damage and increased turnover provide mechanisms consistent with our results.