Radiation induces long-term muscle fibrosis and promotes a fibrotic phenotype in fibro-adipogenic progenitors.

BACKGROUND: Radiation-induced muscle pathology, characterized by muscle atrophy and fibrotic tissue accumulation, is the most common debilitating late effect of therapeutic radiation exposure particularly in juvenile cancer survivors. In healthy muscle, fibro/adipogenic progenitors (FAPs) are required for muscle maintenance and regeneration, while in muscle pathology FAPs are precursors for exacerbated extracellular matrix deposition. However, the role of FAPs in radiation-induced muscle pathology has not previously been explored. METHODS: Four-week-old Male CBA or C57Bl/6J mice received a single dose (16 Gy) of irradiation (IR) to a single hindlimb with the shielded contralateral limb (CLTR) serving as a non-IR control. Mice were sacrificed 3, 7, 14 (acute IR response), and 56 days post-IR (long-term IR response). Changes in skeletal muscle morphology, myofibre composition, muscle niche cellular dynamics, DNA damage, proliferation, mitochondrial respiration, and metabolism and changes in progenitor cell fate where assessed. RESULTS: Juvenile radiation exposure resulted in smaller myofibre cross-sectional area, particularly in type I and IIA myofibres (P < 0.05) and reduced the proportion of type I myofibres (P < 0.05). Skeletal muscle fibrosis (P < 0.05) was evident at 56 days post-IR. The IR-limb had fewer endothelial cells (P < 0.05) and fibro-adipogenic progenitors (FAPs) (P < 0.05) at 56 days post-IR. Fewer muscle satellite (stem) cells were detected at 3 and 56 days in the IR-limb (P < 0.05). IR induced FAP senescence (P < 0.05), increased their fibrogenic differentiation (P < 0.01), and promoted their glycolytic metabolism. Further, IR altered the FAP secretome in a manner that impaired muscle satellite (stem) cell differentiation (P < 0.05) and fusion (P < 0.05). CONCLUSIONS: Our study suggests that following juvenile radiation exposure, FAPs contribute to long-term skeletal muscle atrophy and fibrosis. These findings provide rationale for investigating FAP-targeted therapies to ameliorate the negative late effects of radiation exposure in skeletal muscle.

Kinesiologists in Clinical Exercise Interventional Research for Stroke and Coronary Artery Disease: A Scoping Review.

Background: Kinesiology contributions to research and implementation of programs for cardiovascular disease have not been documented. This scoping review assesses kinesiology affiliates participation in exercise interventional research. Methods: The review followed the Preferred Reporting Items for Systematic review and Meta-Analyses Extension for Scoping Reviews (PRISMA-ScR) Checklist. Eligible studies included individuals diagnosed with coronary artery (CAD) or heart disease (CHD) or stroke participating in exercise interventions supervised or designed by a kinesiologist affiliate (exercise physiologist, kinesiologist, exercise trainer, exercise therapist). Results: The search in MEDLINE, Embase, Scopus, PsychINFO, SPORTDiscus, and CINAHL yielded 219 studies, including 13,874 participants (5,242 CAD, 4,526 CHD, and 4,106 post-stroke). Randomized controlled trials were the most common study design (52%). Kinesiologists were involved in 70% of the studies and supervised 23%. Forty percent did not specify the supervisor. Kinesiologists are involved in prevention and rehabilitation exercise studies that look to improve feasibility of practice, aerobic fitness, muscle and body composition, functional capacity, gait, neurological, psychosocial, and cardiovascular outcomes. Conclusions: Documentation of kinesiology contributions to research for patients with cardiovascular disease may enhance their acceptance in research and care for people with impaired cardiovascular health.

Kinesiology affiliates frequently implement and supervise clinical exercise interventions in stroke, CAD, and CHD populationsKinesiology affiliates make contributions to high-quality evidence generating research and patient careClinical exercise intervention supervisors are often kinesiology affiliates but are not identified in 40% of research reports.

Physical Activity Level and Perspectives of Participants Transitioning from Onsite to Virtual Cardiac Rehabilitation during the Early COVID-19 Pandemic: A Mixed-Method Study.

This mixed-method study aimed to compare physical activity (PA) patterns of a cross-over cardiac rehabilitation (CR) cohort with a center-based CR cohort and to explore barriers and facilitators of participants transitioning and engaging in virtual CR. It included the retrospective self-reported PA of a cross-over CR cohort (n = 75) and a matched center-based CR cohort (n = 75). Some of the participants included in the cross-over cohort (n = 12) attended semi-structured focus group sessions and results were interpreted in the context of the PRECEDE-PROCEED model. Differences between groups were not observed (p > 0.05). The center-based CR cohort increased exercise frequency (p = 0.002), duration (p = 0.007), and MET/minutes (p = 0.007) over time. The cross-over cohort increased exercise duration (p = 0.04) with no significant change in any other parameters. Analysis from focus groups revealed six overarching themes classified under predisposing factors (knowledge), enabling factors (external support, COVID-19 restrictions, mental health, personal reasons/preferences), and reinforcing factors (recommendations). These findings suggest an improvement of the PA levels of center-based CR cohort participants pre-pandemic and mitigated improvement in those who transitioned to a virtual CR early in the pandemic. Improving patients' exercise-related knowledge, provider endorsements, and the implementation of group videoconferencing sessions could help overcome barriers to participation in virtual CR.

Breast cancer survivors' physical activity and experiences while transitioning to a virtual cardiovascular rehabilitation program during a pandemic (COVID-19).

Breast cancer accounts for 25% of all cancers among Canadian females. Despite successes of decreased mortality, adverse treatment effects, such as cardiotoxicity, contribute to a sedentary lifestyle and decreased quality of life. Physical activity (PA) is a possible therapy for the late effects; however, COVID-19 restricted access to in-person cardiovascular rehabilitation (CR) programs. The purposes are as follows: (1) compare PA of breast cancer survivors' in-person CR to virtual CR following a transition during COVID-19 and (2) compare the PA of the pandemic cohort to a matched cohort who had completed the program in 2018/2019; (3) explore survivors' experiences of transitioning to and engaging in virtual CR. Mixed methods included analysis of CR PA data from a pandemic cohort (n = 18) and a 2018/2019 cohort (n = 18) and semi-structured focus group interviews with the pandemic cohort (n = 9) in the context of the PRECEDE-PROCEED model. After the transition, there were no significant differences in mean activity duration, frequency, and cumulative activity (expressed as MET-minutes) (p > 0.05). However, variation of PA duration doubled following the transition from in-person to virtual (p = 0.029), while for the 2018/2019 cohort, variation remained unchanged. Focus groups revealed that women valued their CR experiences pre-COVID-19 and had feelings of anxiety during the transition. Perceived factors affecting participation were environmental, personal, and behavioural. Recommendations for virtual programs were to increase comradery, technology, and professional guidance. PA experiences during a transition to virtual care prompted by a pandemic vary among breast cancer survivors. Targeting individualised strategies and exercise prescriptions are important for improving PA programs and patient outcomes.

Exercise Improves Cancer-free Survival and Health Span in a Model of Radiation-induced Cancer.

INTRODUCTION: Radiation therapy increases the risk of secondary malignancy and morbidity in cancer survivors. The role of obesity and exercise training in modulating this risk is not well understood. As such, we used a preclinical model of radiation-induced malignancy to investigate whether diet-induced obesity and/or endurance exercise training altered lifelong survival, cancer incidence, and morbidity. METHODS: Male CBA mice were randomly divided into control diet/sedentary group (CTRL/SED), high-fat diet (45% fat)/sedentary group (HFD/SED), control diet/exercise group (2-3 d·wk-1; CTRL/EX), or high-fat diet/exercise group (HFD/EX) groups then exposed to whole-body radiation (3 Gy). End point monitoring and pathology determined mortality and cancer incidence, respectively. Health span index, a measure of morbidity, was determined by a composite measure of 10 anthropometric, metabolic, performance, and behavioral measures. RESULTS: Overall survival was higher in HFD/SED compared with CTRL/SED (P < 0.05). The risk of cancer-related mortality by 18 months postradiation was 1.99 and 1.63 in HFD/SED compared with CTRL/EX (RR = 1.99, 95% confidence interval = 1.20-3.31, P = 0.0081) and CTRL/SED (RR = 1.63, 95% confidence interval = 1.06-2.49, P = 0.0250), respectively. The number of mice at end point with cancer was higher in HFD/SED compared with CTRL/EX and CTRL/SED (P < 0.05). Health span index was highest in CTRL/EX (score = +2.5), followed by HFD/EX (score = +1), and HFD/SED (score = -1) relative to CTRL/SED. CONCLUSION: This work provides the basis for future preclinical studies investigating the dose-response relationship between exercise training and late effects of radiation therapy as well as the mechanisms responsible for these effects.

Weight loss with exercise improves muscle architecture and progenitor cell populations compared with weight loss alone in mice with preneoplastic colorectal lesions.

Weight loss and exercise reduce colorectal cancer (CRC) risk in persons with obesity. Whether weight loss and exercise effect myofiber characteristics and muscle stem/progenitor cell populations in mice with preneoplastic colorectal lesions, a model of CRC risk, is unknown. To address this gap, male C57Bl/6J mice were fed a high-fat diet (HFD) to induce obesity or a control (CON) diet prior to azoxymethane injection to induce preneoplastic colorectal lesions. The HFD group was then randomized to weight loss conditions that included (1) switching to the CON diet only (HFD-SED) or switching to the CON diet with treadmill exercise training (HFD-EX). Average myofiber cross-sectional area was not different between groups. There were more smaller-sized fibres in HFD-EX (p < 0.05 vs. CON), and more fibrosis in HFD-SED (p < 0.05 vs. HFD-EX and CON). There was a trend for more committed (Pax7+MyoD+) myoblasts (p = 0.059) and more fibro-adipogenic progenitors in HFD-EX (p < 0.05 vs. CON). Additionally, the canonical pro-inflammatory marker p-NF-κB was markedly reduced in the interstitium of HFD-EX (p < 0.05 vs. CON and HFD-SED). Our findings suggest that in mice with preneoplastic colorectal lesions, HFD followed by weight loss with exercise reduces muscle fibrosis and results in a higher content of muscle stem/progenitor cells. Novelty: Exercise improves muscle architecture in mice with preneoplastic colorectal lesion Exercise increases fibro/adipogenic progenitors and reduces inflammatory signaling in mice with preneoplastic colorectal lesions.

The Late Effects of Radiation Therapy on Skeletal Muscle Morphology and Progenitor Cell Content are Influenced by Diet-Induced Obesity and Exercise Training in Male Mice.

Radiation exposure during muscle development induces long-term decrements to skeletal muscle health, which contribute to reduced quality of life in childhood cancer survivors. Whether the effects of radiation on skeletal muscle are influenced by relevant physiological factors, such as obesity and exercise training remains unknown. Using skeletal muscle from our previously published work examining the effects of obesity and exercise training on radiation-exposed bone marrow, we evaluated the influence of these physiological host factors on irradiated skeletal muscle morphology and cellular dynamics. Mice were divided into control and high fat diet groups with or without exercise training. All mice were then exposed to radiation and continued in their intervention group for an additional 4 weeks. Diet-induced obesity resulted in increased muscle fibrosis, while obesity and exercise training both increased muscle adiposity. Exercise training enhanced myofibre cross-sectional area and the number of satellite cells committed to the myogenic lineage. High fat groups demonstrated an increase in p-NFĸB expression, a trend for a decline in IL-6, and increase in TGFB1. These findings suggest exercise training improves muscle morphology and satellite cell dynamics compared to diet-induced obesity in irradiated muscle, and have implications for exercise interventions in cancer survivors.