Cigarette smoke exposure accelerates locomotor myofiber injury and delays regeneration after lengthening contractions

Mice exposed to tobacco cigarette smoke (CS) show impaired recovery of myofiber cross-sectional area and reduced satellite cell differentiation during early muscle recovery from lengthening contractions. However, it remains unclear whether CS exposure results in a higher number of injured myofibers, which could influence regeneration. We examined whether chronic CS exposure affects the timeline of myofiber injury and force changes during the injury phase (first three days post-injury) and the regeneration phase (7 to 14 days post-injury) in locomotor muscles following lengthening contractions. We hypothesize that smoke exposure increases myofiber vulnerability to injury and delays recovery. Adult male (8-week-old) wild-type (C57Bl/6J, n=48) mice were used to study injury development. Age-matched male mice expressing TdTomato (TdT) fluorescent protein in satellite cells (Pax7CreER-Ai9, n=24) were utilized to investigate muscle regeneration. All mice were exposed daily to smoke from 10 research cigarettes (1R6F) or to air as controls, five times per week for 8 consecutive weeks. In C57Bl/6J mice, after exposure, animals were treated with Evans Blue Dye (EBD), and 24 hours later, the anterior crural muscles from one hindlimb underwent a peroneal nerve-stimulated lengthening contractions protocol (LCP). Torque was measured, followed by dissection of the extensor digitorum longus (EDL) and tibialis anterior (TA) muscles at 30 min, 24 hours, or 72 hours post-LCP. Pax7CreER-Ai9 mice were treated with tamoxifen (once daily for 5 days) during week 6 of exposure. In week 7, one hind limb was subjected to LCP and allowed to recover for 7 or 14 days, then TA and EDL were dissected. For all mice, EDL contractility was assessed ex vivo, and TA was used for immunohistochemistry. EBD-stained myofibers indicated injury, and TdT expression marked regenerating fibers. Data are expressed as mean ± standard deviation. In C57Bl/6J mice, the maximum force of the leg after 24 hours of recovery was 72 ± 20 % (P=0.028) of the uninjured leg in CS-exposed mice, but not in air-exposed mice (110 ± 27 %, P=0.94). EBD-stained fibers were only observed 24 hours post-LCP. Pax7CreER-Ai9 mice exhibited significantly lower EDL force at day-7 recovery in CS vs. air-exposed mice (P=0.033), with no difference at day-14 (P >0.05). On day 14, CS-exposed mice showed a higher number of TdT-expressing myofibers (P=0.0024) and a greater percentage of myofibers with smaller cross-sectional areas (interaction P=0.02; exposure P=0.013) compared to air controls. These findings demonstrate that CS exposure increases myofiber susceptibility to injury, contributing to delayed force recovery after eccentric exercise. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.