Cigarette Smoke Exposure in Mice Impairs Force Development of Injured Fast‐Twitch Skeletal Muscles

Abstract

The use of tobacco cigarettes is known to impair muscle contractile function and decrease muscle mass. Smokers also show a slower recovery following overuse‐induced muscle injury, but the effects of cigarette smoke exposure on muscle repair are not known. We tested whether a short‐term cigarette smoke exposure would affect the regeneration of locomotor muscles following injury by lengthening contractions. Wild‐type C57Bl/6J mice were nose‐only exposed to the smoke of 10 tobacco research cigarettes (1R6F) a day (CS, n=12 mice), or air‐exposed (Air, n=10 mice), for 5 days per week, lasting 8 weeks. CS mice gained less weight than their Air counterparts over the 8‐week period (2.0 ± 0.5 g vs 3.0 ± 0.4 g, respectively). On the seventh week of the exposure, the mice underwent an in vivo lengthening contraction procedure (LCP) to injure the tibialis anterior (TA) and the extensor digitorum longus (EDL) muscles of the right hindlimb (LCP leg), while the left hindlimb was used as a contralateral control (Control leg). During the LCP, the peroneal nerve of the right hindlimb from each mouse was electrically stimulated to evoke contractions of the anterior crural muscles and the foot was actively moved to produce plantar flexion (150 contractions with 20 s intervals). One week after the LCP, mice were euthanized and the EDL and TA muscles were harvested from both legs to test ex‐vivo contractility and to perform histochemistry of cross‐sections of the muscles. Force development in EDL muscles from the LCP legs were significantly smaller than the control legs for both groups (7 ± 4 % and 14 ± 6 % decrease, for CS Air and CS groups; P<0.01 vs control leg). Air and CS groups did not show differences in force in EDL muscles from the control legs (473 ± 25 vs 469 ± 13 kPa, respectively), but in muscles from the LCP legs, force in the CS group (398 ± 24 kPa) was significantly smaller than the Air group (444 ± 24 kPa; P<0.05). These data suggest that tobacco smoking impairs muscle regeneration when muscles are injured by lengthening contractions.Support or Funding InformationTobacco‐Related Disease Research Program