Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA188

Poster Communications

Role of Xin (Xirp1) in microdamage and repair after moderate eccentric exercise in human m. vastus lateralis

R. Billeter1, L. Deller1, J. Odogwu1, K. Owen1, B. Parmar1, J. Mallinson1, T. Taylor1, K. Tsintzas1

1. School of Life Science, University of Nottingham, Nottingham, Nottinghamshire, United Kingdom.

  • Figure 1: Median values for bound αB crystallin, Hsp27, Xin and p70S6K p421/424 in ~100 fibres per biopsy before and after eccentric exercise. The lines connect biopsies from individual subjects (A-F). * indicates significant differences (p<0.05, Wilcoxon).

Exercise involving repeated high strain contractions results in muscle micro-damage. Adaptations to eccentric exercise reduce susceptibility to micro-damage even after a single bout (Paulsen et al., 2009), presumably due to repair and improvement of susceptible structures. Xin (Xirp1) is an adapter protein involved in the growth of actin filaments. A constituent of adult muscle fibres, it is found at high levels in nascent and regenerating fibres. Focal spots with high signals for Xin have been linked to constitutive local repair in rat muscle fibres (Eulitz et al., 2013). However, no studies have examined Xin during repair of exercise-induced micro-damage in human muscle. We monitored structure bound Xin in a series of vastus lateralis biopsies from six male subjects (age 25.0 ±10.7) after 3 sets of 25 repetitions (5 min rest in between) of single-leg maximal eccentric contractions. Biopsies were obtained before, immediately, 3h and 48 h after exercise. With indirect immunohistochemistry, binding of Xin and other marker proteins to insoluble structures (myofibrils, cytoskeleton) was monitored in each biopsy, in ~100 muscle fibres that were followed through 3 consecutive sections stained with different combinations of antibodies, to αB crystallin, Hsp27 (small chaperones that bind to unfolded proteins), p70S6K phosphorylated at Thr-421/Ser-424 (linked to increasing protein synthesis), the myofibrillar proteins type II myosin, actinin and desmin and to Xin. The sections were scanned on an Axioscan Z1 (Zeiss) at 20 x and selected fibres photographed at 63x. Median bound Xin, αB crystallin and Hsp27 and were significantly increased (p<0.05, Wilcoxon) immediately after exercise and decreased again by 48h (Figure 1). There was considerable inter-individual variability, as expected in an eccentric exercise study. No consistent differences were found between type I and II fibres. In all immediate and 3h post exercise biopsies, significant correlations were found between Xin, αB crystallin and p70S6K-p421/424 bound per fibre (p<0.001, Spearman); αB crystallin and Hsp27 correlated significantly in 11 out of the 12 biopsies. A minority of fibres in the immediate and 3h post exercise biopsies had small areas with very strong staining which we interpret as damage/repair "hot spots". Pixel by pixel analysis of αB crystallin-hot spots in 45 fibres showed that they all had significantly enhanced signals for the other 3 markers (p<0.001, t-test). In longitudinally cut fibres, analysis of larger magnification (63x) images indicated disturbed myofibrillar structures at hot spots. Our results indicate for the first time in humans that Xin is involved in the microdamage/repair cycle following a bout of eccentric exercise. Damage is largely in the sub-microscopic range and repaired locally within a few hours.

Where applicable, experiments conform with Society ethical requirements