Exercise induces expression of leukaemia inhibitory factor in human skeletal muscle

Abstract

The leukaemia inhibitory factor (LIF) belongs to the interleukin (IL)-6 cytokine superfamily and is constitutively expressed in skeletal muscle. We tested the hypothesis that LIF expression in human skeletal muscle is regulated by exercise. Fifteen healthy young male volunteers performed either 3 h of cycle ergometer exercise at approximately 60% of VO2,max(n = 8) or rested (n = 7). Muscle biopsies were obtained from the vastus lateralis prior to exercise, immediately after exercise, and at 1.5, 3, 6 and 24 h post exercise. Control subjects had biopsy samples taken at the same time points as during the exercise trial. Skeletal muscle LIF mRNA increased immediately after the exercise and declined gradually during recovery. However, LIF protein was unchanged at the investigated time points. Moreover, we tested the hypothesis that LIF mRNA and protein expressions are modulated by calcium (Ca(2+)) in primary human skeletal myocytes. Treatment of myocytes with the Ca(2+) ionophore, ionomycin, for 6 h resulted in an increase in both LIF mRNA and LIF protein levels. This finding suggests that Ca(2+) may be involved in the regulation of LIF in endurance-exercised skeletal muscle. In conclusion, primary human skeletal myocytes have the capability to produce LIF in response to ionomycin stimulation and LIF mRNA levels increase in skeletal muscle following concentric exercise. The finding that the increase in LIF mRNA levels is not followed by a similar increase in skeletal muscle LIF protein suggests that other exercise stimuli or repetitive stimuli are necessary in order to induce a detectable accumulation of LIF protein.

Figure 1. LIF mRNA levels in skeletal muscle in response to exercise or rest

LIF mRNA levels were examined in biopsies taken from m. vastus lateralis before (Pre) 3 h of ergometer bicycle exercise, immediately after (Post) and at time points 1.5 h, 3 h, 6 h and 24 h after exercise. Data are expressed as geometric means ±s.e.m. (n = 8, exercise; and n = 7, control). Effect of time area under the curve, P = 0.002; *post hoc analysis (Bonferroni-adjusted paired t tests), P < 0.05.

Figure 2. LIF protein expression in skeletal muscle in response to exercise

LIF protein expression was examined in biopsies taken from m. vastus lateralis before (Pre) 3 h ergometer bicycle exercise, immediately after (Post) and at time points 1.5 h, 3 h, 6 h and 24 h after exercise. Data are expressed as means ±s.e.m. (n = 8). A representative immunoblot is shown.

Figure 3. LIF mRNA levels in primary human skeletal myocytes in response to ionomycin stimulation

Primary human skeletal myocytes were incubated with the Ca²⁺ ionophore ionomycin for 6 h. Data are expressed as geometric means ±s.e.m. (n = 4). *P < 0.01.

Figure 4. LIF protein expression in primary human skeletal myocytes in response to ionomycin stimulation

Primary human skeletal myocytes were incubated with the Ca²⁺ ionophore ionomycin for 6 h. Representative immunoblots are shown. Data are expressed as means ±s.e.m. (n = 3). *P < 0.05.