Aim: Gastrointestinal disturbances are common in athletes following intense exercise. Variations in apoptotic protein expression and cell death may contribute to acute exercise-induced intestinal inflammation. The effect of age on apoptotic protein response in the intestinal compartment in response to exercise is not known. Using a mouse model, we examined the effects of a single bout of treadmill running in young and old mice on intestinal lymphocyte (IL) expression of the apoptosis-inducing cytokine TNF-α, the pro-apoptotic proteins caspase-3 and 7, the anti-apoptotic protein Bcl-2, and IL apoptotic status (% AnnexinV+).
Methods: Young (3-4 months, N.=44) and old (13-14 months, N.=45) female C57Bl/6 mice were randomized to treadmill exercise (10 min warm-up, 20 min at 22 m min-1, 30 min at 25 m min-1, 30 min at 28 m min-1, 2º slope) with sacrifice immediately (IMM) or 2hr after (2Hr), or to a non-exercised control (SED). IL were removed and prepared for analysis of % apoptosis (flow cytometry) and determination of apoptotic protein and cytokine expression (Western blotting). Plasma corticosterone and 8-iso-PGF2α were measured by EIA.
Results: Exercise was associated with a higher IL expression of caspase-3 in IMM and 2Hr groups vs. SED (P<0.001), a higher expression of TNF-α in the IMM group vs. SED (P<0.001), and a lower Bcl-2 expression in the IMM and 2Hr groups vs. SED (P<0.01). There was a trend (P=0.07) for increased caspase-7 expression after exercise. IL caspase-3 and 7 and TNF-α expression did not differ by age whereas Bcl-2 expression was lower (P<0.001) and % Annexin V+ IL was higher (P<0.05) in old vs. young mice. Plasma corticosterone and 8-iso-PGF2α were higher (P<0.001 and P<0.05) in IMM vs. SED mice but did not differ by age.
Conclusion: The expression of the pro-apoptotic proteins, caspase-3 and caspase-7, and the apoptosis-inducing cytokine, TNF-α, in IL did not differ by age in this animal model in response to a single intense exercise challenge. However, Old mice had lower expression of the 'protective' anti-apoptotic protein Bcl-2 and a higher percentage of early apoptotic IL. Whether repeated exercise results in less IL resiliency in elderly individuals remains to be determined.