Rehabilitative activity can improve injury repair, but it risks additional damage and reduces the functional recovery of regenerating muscle. This study tested the hypothesis that moderate electrically evoked contractions would slow restoration of neuromuscular function after cardiotoxin-induced injury; however exogenous mitochondrial transplantation (MT) would enhance recovery of contractile function after injury. Cardiotoxin was injected into the tibialis anterior of C57BL/6 mice (10-12 weeks of age) to induce muscle necrosis. Exogenous mitochondria or phosphate-buffered saline (PBS) were injected into the mouse tail vein after cardiotoxin injury. Injured muscles were either rested or given 40 Hz submaximal electrically evoked contractions to cardiotoxin-injured muscles during the recovery period. Relative to intra-animal non-damaged control muscles restoration of peak tetanic torque after both rested and evoked contractions during recovery and twitch torque was greater, and the difference between control and injured muscle twitch one-half relaxation time was lower in injured muscles that were rested for 10 days after injury and received MT compared to PBS-treated muscles. Neuromuscular junction efficiency in cardiotoxin-injured muscles was ∼70% of control undamaged muscles, but MT improved the recovery of neuromuscular junction efficiency to produce torque by 14 days after cardiotoxin injury in muscles that received additional damage induced by evoked contractions during the recovery period. These data suggest that MT enhances the recovery of neuromuscular function when the muscle is rested after injury, but it provides limited improvement in muscle function when the muscle is challenged with electrically evoked contractions in the recovery period after injury. KEY POINTS: Mitochondrial transplantation by systemically infusing healthy donor mitochondria into injured mice improved the recovery of maximal torque production of injured muscles when evoked contractions were provided to the regenerating muscle during the recovery period after injury. Mitochondrial transplantation improved the restoration of neuromuscular junction efficiency after muscle injury. The recovery of maximal torque capabilities function following cardiotoxin-induced tibialis anterior muscle injury was attenuated by electrically evoked muscle contractions conducted every other day during the recovery period in young adult mice.

PURPOSE OF REVIEW:The purpose of this review is to highlight recently published research that can provide insight into how either sex or chemotherapeutics can impact cancer regulation of muscle anabolic resistance. Critical knowledge gaps are emphasized that are linked to cancer and treatment disruptions to muscle anabolic signaling. We speculate and propose a rationale for estrogen's protective effect against cancer-induced muscle anabolic resistance in females. Furthermore, there is growing evidence that many cancer treatments have the potential to exacerbate muscle anabolic resistance in both males and females. We present current evidence and speculate on how nutritional interventions could serve as key modulators of cancer-induced anabolic resistance in these conditions. RECENT FINDINGS:Recently published studies have reinforced that sex impacts the regulation of cancer cachexia in several established preclinical models, with males often developing more severe cachexia when compared to females. Importantly, recent research has established these sex differences at the transcriptomic level. Recent research has also strengthened the link between hypogonadism as a driver of cancer cachexia in preclinical models. Furthermore, chemotherapy has the potential to exacerbate muscle anabolic resistance. SUMMARY:There is a growing body of literature that provides a strong rationale for further investigation into the impact of sex and chemotherapy on the cancer regulation of muscle anabolic resistance.

Electrically evoked muscle contractions conducted every other day after muscle injury caused additional damage and slowed recovery of muscle regeneration; however, mitochondria transplantation attenuated the negative regenerative effects of rehabilitative contractions on muscle fiber regeneration. This suggests that optimizing mitochondrially regulated repair may improve muscle regeneration. Furthermore, injured muscles treated by mitochondrial transplantation had lower collagen content/fibrosis than those treated with PBS after injury. Mitochondrial transplantation blunts fibrosis and improves muscle fiber repair after injury.

Cancer-induced inflammation has been widely investigated as a driver of cachexia, and sex can affect the inflammatory response to cancer. We have an incomplete understanding of how anticancer treatments and sex impact the relationship between inflammatory responses and changes to body composition and physical function during cancer treatment. We investigated the effect of FOLFOX chemotherapy (5-fluorouracil, leucovorin, oxaliplatin) on circulating inflammatory cytokines, body composition, and physical function in CT26 tumor-bearing male and female mice. BALB/c mice were injected with CT26 tumor cells, and after the tumor was palpable, underwent three cycles of FOLFOX. FOLFOX reduced tumor mass in both sexes. CT26 induced plasma interleukin-6 (IL-6), leukemia inhibitory factor (LIF), and tumor necrosis factor-alpha (TNF-α) in males and females. FOLFOX attenuated the CT26-induced IL-6 and LIF levels in males, but in females FOLFOX alone induced IL-6 and TNF-α, and did not attenuate their CT26 induction. In CT26 males, but not females, total lean and hindlimb mass were negatively associated with IL-6, and FOLFOX disrupted this association. The CT26-induced muscle p-STAT3 was inversely associated with muscle mass in males only and disrupted by FOLFOX. Circulating inflammatory cytokines were associated with body composition changes and functional deficits in CT26 males, but FOLFOX and female sex altered this relationship. Our results provide evidence that the female response to circulating inflammatory cytokines in the CT26 tumor environment, following FOLFOX chemotherapy, differs from that of males, and the physiological ramifications of this regulation warrant further investigation.NEW & NOTEWORTHY The present study demonstrates that in colon tumor-bearing mice, the administration of FOLFOX chemotherapy alters plasma inflammatory cytokines' relationship to tumor mass, body composition, and physical function. Furthermore, sex influences these responses. These findings have implications for mechanistically understanding sex-specific muscle wasting and metabolic complications experienced by patients with colorectal cancer undergoing chemotherapy treatment.

BACKGROUND:Cancer promotes muscle wasting through an imbalance in the tightly regulated protein synthesis and degradation processes. An array of intracellular signalling pathways, including mTORC1 and AMPK, regulate protein synthesis, and these pathways are responsive to the muscle's microenvironment and systemic stimuli. Although feeding and fasting are established systemic regulators of muscle mTORC1 and protein synthesis, the cancer environment's impact on these responses during cachexia development is poorly understood. Although the IL-6 cytokine family has been widely investigated as a driver of cachexia with several cancers, how this signalling regulates muscle responses to feeding and fasting requires further study. We investigated if the cancer environment alters the feeding and fasting regulation of skeletal muscle protein synthesis and if the IL-6 family of cytokines signalling through muscle glycoprotein 130 could regulate this response. METHODS:Male C57BL/6J mice were subcutaneously injected with 1 × 106 LLC cells or PBS. Mice were euthanized 25-30 days post-injection after a 12-h dark cycle fast, followed by access to food pellets for 1 h (fed) or immediately sacrificed. To determine AMPK and gp13's regulation of protein synthesis and anabolic signalling, we injected tamoxifen-inducible skeletal muscle AMPKa1a2 or gp130 knockout and floxed control mice with LLC cells or PBS. The gastrocnemius muscle was analysed for protein expression. RESULTS:Feeding increased p-rpS6 and protein synthesis in PBS (2.2- and 0.4-fold, p < 0.001) and LLC mice (1.7- and 0.9-fold, p < 0.001), but overall, LLC significantly reduced p-rpS6 and protein synthesis. Feeding only increased p-AKT in PBS mice (1.5-fold, p < 0.001). In vitro LLC-conditioned media did not inhibit the insulin induction of myotube p-AKT (p < 0.001) and p-rpS6 (p < 0.001). Muscle gp130 loss reduced the fasting p-AMPK induction in LLC mice but did not alter suppression of p-AKT and p-rpS6 and protein synthesis. Muscle AMPK loss increased p-rpS6 (2.1-fold, p < 0.001) and protein synthesis (0.7-fold, p < 0.001) in PBS mice but did not restore LLC-suppressed protein synthesis. CONCLUSIONS:Our study provides novel insight into muscle responsiveness to feeding and fasting in a cancer environment. We find the acute anabolic response to feeding is maintained during LLC-induced cachexia, whereas the fasting catabolic response is exacerbated. Muscle-specific gp130 loss prevented disrupted fasting AMPK activation but not protein synthesis. There is a need to understand the aberrant upstream and downstream regulation of muscle AMPK activity that is disrupted with cancer and leads to aberrant protein turnover regulation.

Skeletal muscle is a primary tissue of dysfunction during both aging and obesity. Recently, the coincidence of obesity and aging has gained attention due to the intersection of the obesity epidemic with an aging demographic. Both aging and obesity are associated with marked defects in skeletal muscle metabolic health. Despite these findings, we have a poor understanding of how obesity and aging may interact to impact skeletal muscle mass and metabolic health. Therefore, we investigated the impact of high-fat diet (HFD)-induced obesity on skeletal muscle mass, mitochondrial function, transcriptomics, and whole-body metabolism in young and aged mice. We observed main effects of diet and age on several measures of whole-body metabolic function (VO 2 , VCO 2 , and RER). Complex I-driven mitochondrial proton leak was significantly elevated by HFD-induced obesity across both age groups; however, a main effect of aging for reduced complex I leak was detected in the soleus muscle. Interestingly, aged animals fed a HFD did not exhibit lower muscle mass than chow-fed young animals, but did present with stark increases in muscle triglyceride content and a unique transcriptional response to HFD. HFD-induced obesity impacted the muscle transcriptome differently in the muscles of young and aged mice, indicating that obesity can change altered gene expression with age. Our findings suggest that the presence of obesity can both compound and counteract age-associated changes to muscle mass, gene expression, and mitochondrial function.

The present study demonstrates that myotube hypertrophy caused by chronic serum stimulation requires mammalian target of rapamycin complex 1 (mTORC1) signaling but not bone morphogenetic protein (BMP)-Smad1/5 signaling. The suppression of autophagy flux was associated with serum-induced myotube hypertrophy and mTORC1 regulation of autophagy flux by measuring LC3BII/I expression. Rapamycin is widely investigated for beneficial effects in aging skeletal muscle and sarcopenia; our results provide evidence that rapamycin can regulate autophagy-related signaling during myotube growth, which could benefit skeletal muscle functional and metabolic health.

Cancer cachexia, the unintentional loss of lean mass, contributes to functional dependency, poor treatment outcomes, and decreased survival. Although its pathogenicity is multifactorial, metabolic dysfunction remains a hallmark of cachexia. However, significant knowledge gaps exist in understanding the role of skeletal muscle lipid metabolism and dynamics in this condition. We examined skeletal muscle metabolic dysfunction, intramyocellular lipid droplet (LD) content, LD morphology and subcellular distribution, and LD-mitochondrial interactions using the Lewis lung carcinoma (LLC) murine model of cachexia. C57/BL6 male mice (n = 20) were implanted with LLC cells (106) in the right flank or underwent PBS sham injections. Skeletal muscle was excised for transmission electron microscopy (TEM; soleus), oil red O/lipid staining [tibialis anterior (TA)], and protein (gastrocnemius). LLC mice had a greater number (232%; P = 0.006) and size (130%; P = 0.023) of intramyocellular LDs further supported by increased oil-red O positive (87%; P = 0.0109) and "very high" oil-red O positive (178%; P = 0.0002) fibers compared with controls and this was inversely correlated with fiber size (R-2 = 0.5294; P < 0.0001). Morphological analyses of LDs show increased elongation and complexity [aspect ratio: intermyofibrillar (IMF) = 9%, P = 0.046) with decreases in circularity [circularity: subsarcolemmal (SS) = 6%, P = 0.042] or roundness (roundness: whole = 10%, P = 0.033; IMF = 8%, P = 0.038) as well as decreased LD-mitochondria touch (-15%; P = 0.006), contact length (-38%; P = 0.036), and relative contact (86%; P = 0.004). Furthermore, dysregulation in lipid metabolism (adiponectin, CPT1b) and LD-associated proteins, perilipin-2 and perilipin-5, in cachectic muscle (P < 0.05) were observed. Collectively, we provide evidence that skeletal muscle myosteatosis, altered LD morphology, and decreased LD-mitochondrial interactions occur in a preclinical model of cancer cachexia. NEW & NOTEWORTHY We sought to advance our understanding of skeletal muscle lipid metabolism and dynamics in cancer cachexia. Cachexia increased the number and size of intramyocellular lipid droplets (LDs). Furthermore, decreases in LD-mitochondrial touch, contact length, and relative contact along with increased LD shape complexity with decreases in circularity and roundness. Dysregulation in lipid metabolism and LD-associated proteins was also documented. Collectively, we show that myosteatosis, altered LD morphology, and decreased LD-mitochondrial interactions occur in cancer cachexia.

FOLFOX (5-fluorouracil, leucovorin, oxaliplatin) chemotherapy is used to treat colorectal cancer and can acutely induce metabolic dysfunction. However, the lasting effects on systemic and skeletal muscle metabolism after treatment cessation are poorly understood. Therefore, we investigated the acute and lasting effects of FOLFOX chemotherapy on systemic and skeletal muscle metabolism in mice. Direct effects of FOLFOX in cultured myotubes were also investigated. Male C57BL/6J mice completed four cycles (acute) of FOLFOX or PBS. Subsets were allowed to recover for 4 wk or 10 wk. Comprehensive Laboratory Animal Monitoring System (CLAMS) metabolic measurements were performed for 5 days before study endpoint. C2C12 myotubes were treated with FOLFOX for 24 hr. Acute FOLFOX attenuated body mass and body fat accretion independent of food intake or cage activity. Acute FOLFOX decreased blood glucose, oxygen consumption (V̇o2), carbon dioxide production (V̇co2), energy expenditure, and carbohydrate (CHO) oxidation. Deficits in V̇o2 and energy expenditure remained at 10 wk. CHO oxidation remained disrupted at 4 wk but returned to control levels after 10 wk. Acute FOLFOX reduced muscle COXIV enzyme activity, AMPK(T172), ULK1(S555), and LC3BII protein expression. Muscle LC3BII/I ratio was associated with altered CHO oxidation (r = 0.75, P = 0.03). In vitro, FOLFOX suppressed myotube AMPK(T172), ULK1(S555), and autophagy flux. Recovery for 4 wk normalized skeletal muscle AMPK and ULK1 phosphorylation. Our results provide evidence that FOLFOX disrupts systemic metabolism, which is not readily recoverable after treatment cessation. FOLFOX effects on skeletal muscle metabolic signaling did recover. Further investigations are warranted to prevent and treat FOLFOX-induced metabolic toxicities that negatively impact survival and life quality of patients with cancer.NEW & NOTEWORTHY The present study demonstrates that FOLFOX chemotherapy induces long-lasting deficits in systemic metabolism. Interestingly, FOLFOX modestly suppressed skeletal muscle AMPK and autophagy signaling in vivo and in vitro. The FOLFOX-induced suppression of muscle metabolic signaling recovered after treatment cessation, independent of systemic metabolic dysfunction. Future research should investigate if activating AMPK during treatment can prevent long-term toxicities to improve health and quality of life of patients with cancer and survivors.

FOLFOX (5-fluorouracil, leucovorin, oxaliplatin) chemotherapy is a treatment for colorectal cancer that can induce persistent fatigue and metabolic dysfunction. Regular exercise after chemotherapy cessation is widely recommended for cancer patients and has been shown to improve fatigue resistance in mice. However, gaps remain in understanding whether the early systemic and skeletal muscle adaptations to regular exercise are altered by prior FOLFOX chemotherapy treatment. Furthermore, the effects of exercise duration on early metabolic and skeletal muscle transcriptional adaptations are not fully established.Purpose: Investigate the effects of prior FOLFOX chemotherapy treatment on the early adaptations to repeated short- or long-duration treadmill exercise, including the fasting regulation of circulating metabolic regulators, skeletal muscle COXIV activity and myokine/exerkine gene expression in male mice.Methods: Male C57BL6/J mice completed 4 cycles of FOLFOX or PBS and were allowed to recover for 4-weeks. Subsets of mice performed 14 sessions (6 d/wk, 18 m/min, 5% grade) of short- (10 min/d) or long-duration (55 min/d) treadmill exercise. Blood plasma and muscle tissues were collected 48–72 h after the last exercise bout for biochemical analyses.Results: Long-duration exercise increased fasting plasma osteocalcin, LIF, and IL-6 in healthy PBS mice, and these changes were ablated by prior FOLFOX treatment. Slow-oxidative soleus muscle COXIV activity increased in response to long-duration exercise in PBS mice, which was blocked by prior FOLFOX treatment. Fast-glycolytic plantaris muscle COXIV activity increased with short-duration exercise independent of FOLFOX administration. There was a main effect for long-duration exercise to increase fasting muscle IL-6 and COXIV mRNA expression independent of FOLFOX. FOLFOX administration reduced muscle IL-6, LIF, and BDNF mRNA expression irrespective of long-duration exercise. Interestingly, short-duration exercise suppressed the FOLXOX induction of muscle myostatin mRNA expression.Conclusion: FOLFOX attenuated early exercise adaptations related to fasting circulating osteocalcin, LIF, and IL-6. However, prior FOLFOX treatment did not alter the exercise adaptations of plantaris muscle COXIV activity and plasma adiponectin. An improved understanding of mechanisms underlying exercise adaptations after chemotherapy will provide the basis for successfully treating fatigue and metabolic dysfunction in cancer survivors.

Abstract Background Injection of exogenous mitochondria has been shown to improve the ischaemia‐damaged myocardium, but the effect of mitochondrial transplant therapy (MTT) to restore skeletal muscle mass and function has not been tested following neuromuscular injury. Therefore, we tested the hypothesis that MTT would improve the restoration of muscle function after injury. Methods BaCl2 was injected into the gastrocnemius muscle of one limb of 8–12‐week‐old C57BL/6 mice to induce damage without injury to the resident stem cells. The contralateral gastrocnemius muscle was injected with phosphate‐buffered saline (PBS) and served as the non‐injured intra‐animal control. Mitochondria were isolated from donor mice. Donor mitochondria were suspended in PBS or PBS without mitochondria (sham treatment) and injected into the tail vein of BaCl2 injured mice 24 h after the initial injury. Muscle repair was examined 7, 14 and 21 days after injury. Results MTT did not increase systemic inflammation in mice. Muscle mass 7 days following injury was 21.9 ± 2.1% and 17.4 ± 1.9% lower (P < 0.05) in injured as compared with non‐injured intra‐animal control muscles in phosphate‐buffered saline (PBS)‐ and MTT‐treated animals, respectively. Maximal plantar flexor muscle force was significantly lower in injured as compared with uninjured muscles of PBS‐treated (−43.4 ± 4.2%, P < 0.05) and MTT‐treated mice (−47.7 ± 7.3%, P < 0.05), but the reduction in force was not different between the experimental groups. The percentage of collagen and other non‐contractile tissue in histological muscle cross sections, was significantly greater in injured muscles of PBS‐treated mice (33.2 ± 0.2%) compared with MTT‐treated mice (26.5 ± 0.2%) 7 days after injury. Muscle wet weight and maximal muscle force from injured MTT‐treated mice had recovered to control levels by 14 days after the injury. However, muscle mass and force had not improved in PBS‐treated animals by 14 days after injury. The non‐contractile composition of the gastrocnemius muscle tissue cross sections was not different between control, repaired PBS‐treated and repaired MTT‐treated mice 14 days after injury. By 21 days following injury, PBS‐treated mice had fully restored gastrocnemius muscle mass of the injured muscle to that of the uninjured muscle, although maximal plantar flexion force was still 19.4 ± 3.7% (P < 0.05) lower in injured/repaired gastrocnemius as compared with uninjured intra‐animal control muscles. Conclusions Our results suggest that systemic mitochondria delivery can enhance the rate of muscle regeneration and restoration of muscle function following injury.

BACKGROUND:Cancer and its treatment can adversely affect skeletal muscle, impacting physical function, treatment response and survival. No studies, however, have comprehensively characterized these muscle adaptations longitudinally in human patients at the cellular level.METHODS:We examined skeletal muscle size and function from the whole body to the sub-cellular level in 11 patients with non-small cell lung cancer (NSCLC; 6 male/5 female, mean age 58 ± 3 years) studied over a 2-month observation period starting during their first cycle of standard of care cancer treatment and in 11 age- and sex-matched healthy controls (HC) without a current or past history of cancer. Biopsies of the vastus lateralis were performed to assess muscle fibre size, contractility and mitochondrial content, along with assessments of physical function, whole muscle size and function, and circulating cytokines.RESULTS:Body weight, composition and thigh muscle area and density were unaltered over time in patients with NSCLC, while muscle density was lower in patients with NSCLC versus HC (P = 0.03). Skeletal muscle fibre size decreased by 18% over time in patients (all P = 0.02) and was lower than HC (P = 0.02). Mitochondrial fractional area and density did not change over time in patients, but fractional area was lower in patients with NSCLC compared with HC (subsarcolemmal, P = 0.04; intermyofibrillar, P = 0.03). Patients with NSCLC had higher plasma concentrations of IL-6 (HC 1.40 ± 0.50; NSCLC 4.71 ± 4.22; P < 0.01), GDF-15 (HC 569 ± 166; NSCLC 2071 ± 1168; P < 0.01) and IL-8/CXCL8 (HC 4.9 ± 1.8; NSCLC 10.1 ± 6.0; P = 0.02) compared with HC, but there were no changes in inflammatory markers in patients with NSCLC over time. No changes were observed in markers of satellite cell activation or DNA damage in patients and no group differences were noted with HC. Whole-muscle strength was preserved over time in patients with NSCLC coincident with improved single fibre contractility.CONCLUSIONS:This study is the first to comprehensively examine longitudinal alterations in skeletal muscle fibre size and function in patients with NSCLC and suggests that muscle fibre atrophy occurs during cancer treatment despite weight stability and no changes in conventional clinical measurements of whole body or thigh muscle size over this period.

Mononuclear phagocytes (MPs) play a crucial role in tissue homeostasis; however, MPs also contribute to tumor progression and resistance to immune checkpoint blockade (ICB). Targeting MPs could be an effective strategy to enhance ICB efficacy. We report that protein kinase C delta (PKCδ), a serine/threonine kinase, is abundantly expressed by MPs in human and mouse tumors. PKCδ −/− mice displayed reduced tumor progression compared to wild types, with increased response to anti–PD-1. Tumors from PKCδ −/− mice demonstrated T H 1-skewed immune response including increased antigen presentation and T cell activation. Depletion of MPs in vivo altered tumor growth in control but not PKCδ −/− mice. Coinjection of PKCδ −/− M2-like macrophages with cancer cells into wild-type mice markedly delayed tumor growth and significantly increased intratumoral T cell activation compared to PKCδ +/+ controls. PKCδ deficiency reprogrammed MPs by activating type I and type II interferon signaling. Thus, PKCδ might be targeted to reprogram MPs to augment ICB efficacy.

Background: Cancer patients treated with FOLFOX are burdened by an array of side effects which can lead to early cessation of treatment. Specifically, FOLFOX is associated with increases in arterial stiffness, LV-stunning/weakness, both of which can lead to acute or chronic risk of developing heart failure and cardiovascular disease. To increase cardiovascular fitness and prevent FOLFOX cardiotoxicity exercise interventions have been proposed; however, a dearth of information exists on the timing and type of exercise that should be performed. Therefore, the purpose of this study was to investigate FOLFOX-induced alterations in circulating markers associated with cardiovascular damage 4-weeks post cessation of treatment, and to determine whether exercise can be utilized to mitigate increases in risk associated markers of cardiovascular disease. Methods: Male C57BL/6J mice (3 months) received 4 cycles (1 injection every 2 weeks) of FOLFOX (5-fluorouracil 30mg/kg, oxaliplatin 6mg/kg, leucovorin 90mg/kg), and were randomized to subgroups of sedentary (FOX, n=12), exercise trained (EXFOX, n=10), or PBS shams (CON n=11, EXCON n=9). Exercise training consisted of 14 sessions of treadmill exercise (18m/min, 5%grade, 15 minutes) during weeks 2-4 of the recovery period. Following completion of the treatment/exercise training, mice were sacrificed after a 12h overnight fast and a minimum of 48h after the last bout of exercise. Circulating markers were evaluated using Luminex Magpix® multiplex analyzer (MILLIPLEX Mouse CVD1&CVD2 Bead Panel, Millipore Sigma, Burlington, MA, USA). Results: There was a significant effect of FOLFOX (p<0.05) for soluble endothelium selectin (sE-selectin), soluble platelet selectin (sP-selectin) and thrombomodulin. Significant effects of exercise (p<0.05) were found for soluble intercellular adhesion molecule-1 (sICAM-1), platelet endothelial cell adhesion molecule-1 (Pecam-1) and thrombomodulin. Conclusion: This preliminary investigation suggests there are systemic alterations in markers associated with cardiovascular disease following FOLFOX regimen occurring weeks after cessation of treatment. Low intensity exercise was unable to show any benefits in terms of preventing increases in these cardiovascular disease risk markers. These results promote further investigation into the impact these alterations may have on cardiac or vascular tissue following FOLFOX treatment. National Cancer Institue: R21-CA231131 & National Institutes of Health: R01HL14458 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Skeletal muscle atrophy and dysfunction contribute to morbidity and mortality in patients with cancer. Cachexia pathophysiology is highly complex, given that perturbations to the systemic cancer environment and the interaction with diverse tissues can contribute to wasting processes. Systemic interleukin 6 (IL-6) and glycoprotein 130 (gp130) receptors signaling have established roles in some types of cancer-induced muscle wasting through disruptions to protein turnover and oxidative capacity. Although exercise has documented benefits for cancer prevention and patient survival, there are significant gaps in our understanding of muscle adaptation and plasticity during severe cachexia. Preclinical models have provided valuable insight into the adaptive potential of muscle contraction within the cancer environment. We summarize the current understanding of how resistance-type exercise impacts mechanisms involved in cancer-induced muscle atrophy and dysfunction. Specifically, the role of IL-6 and gp130 receptors in the pathophysiology of muscle wasting and the adaptive response to exercise is explained. The discussion includes current knowledge gaps and future research directions needed to improve preclinical research and accelerate clinical translation in human patients with cancer.

5-Fluorouracil (5FU) remains a first-line chemotherapeutic for several cancers despite its established adverse side effects. Reduced blood counts with cytotoxic chemotherapies not only expose patients to infection and fatigue, but can disrupt tissue repair and remodeling, leading to lasting functional deficits. We sought to characterize the impact of 5FU-induced leukopenia on skeletal muscle in the context of remodeling. First, C57BL/6 mice were subjected to multiple dosing cycles of 5FU and skeletal muscle immune cells were assessed. Second, mice given 1 cycle of 5FU were subjected to 1.2% BaCl2 intramuscularly to induce muscle damage. One cycle of 5FU induced significant body weight loss, but only three dosing cycles of 5FU induced skeletal muscle mass loss. One cycle of 5FU reduced skeletal muscle CD45+ immune cells with a particular loss of infiltrating CD11b+Ly6cHi monocytes. Although CD45+ cells returned following three cycles, CD11b+CD68+ macrophages were reduced with three cycles and remained suppressed at 1 mo following 5FU administration. One cycle of 5FU blocked the increase in CD45+ immune cells 4 days following BaCl2; however, there was a dramatic increase in CD11b+Ly6g+ neutrophils and a loss of CD11b+Ly6cHi monocytes in damaged muscle with 5FU compared with PBS. These perturbations resulted in increased collagen production 14 and 28 days following BaCl2 and a reduction in centralized nuclei and myofibrillar cross-sectional area compared with PBS. Together, these results demonstrate that cytotoxic 5FU impairs muscle damage repair and remodeling concomitant with a loss of immune cells that persists beyond the cessation of treatment.NEW & NOTEWORTHY We examined the common chemotherapeutic 5-fluorouracil's (5FU) impact on skeletal muscle immune cells and skeletal muscle repair. 5FU monotherapy decreased body weight and muscle mass, and perturbed skeletal muscle immune cells. In addition, 5FU decreased skeletal muscle immune cells and impaired infiltration following damage contributing to disrupted muscle repair. Our results demonstrate 5FU's impact on skeletal muscle and provide a potential explanation for why some patients may be unable to properly repair damaged tissue.

ABSTRACT Cancer-induced skeletal muscle mass loss is a critical characteristic of cachexia. Although physical inactivity and systemic metabolic dysfunction can precede cachexia development, how these early-onset disruptions are related to cachexia’s eventual severity is not well understood. The well-established Lewis lung carcinoma (LLC) preclinical cachexia model exhibits a varying degree of cachexia. Therefore, we examined if the early-onset of physical inactivity and metabolic dysfunction were associated with accelerated cachexia development in LLC tumor-bearing mice. Methods Male C57BL/6J mice (12 wk of age) were injected with 1 × 10 6 LLC cells or phosphate-buffered saline (PBS) subcutaneously in the right flank, and tissue was collected 26–28 d after cell injection. Tumor volume was measured every 5 d throughout the study to calculate the tumor growth rate. Fifteen days after tumor inoculation, a subset of PBS ( n = 11) and LLC ( n = 16) mice were individually housed in metabolic Comprehensive Laboratory Animal Monitoring System cages for 5 d. Results LLC mice exhibited greater body weight loss (−5.1%), decreased muscle mass (−7%), decreased fat mass (−22%), and increased plasma interleukin-6 (212%) compared with PBS mice. Before the onset of cachexia, total cage activity was decreased in tumor-bearing mice. Cage activity was negatively associated with tumor mass and positively associated with hindlimb muscle mass. In addition, LLC mice had greater lipid oxidation than PBS mice. Conclusions LLC mice exhibit early-onset physical inactivity and altered systemic lipid oxidation, which are associated with the eventual development of cachexia.

Chemotherapy represents a commonly used treatment strategy to mitigate cancer progression. Studies suggest it can independently induce body weight loss, fatigue, and weakness. Increased physical activity during treatment has beneficial effects, however, given the low adherence to exercise prescriptions, determining if an exercise threshold is required to improve chemotherapy toxicity is necessary. Gaps remain in our understanding of the extent of chemotherapy toxicities after the completion of treatment, and if a low dose of exercise is sufficient to improve chemotherapy-induced dysfunction. PURPOSE: To examine the effects of exercise dose on body composition and physical function in mice during the recovery from Folfox chemotherapy. METHODS: Male C57BL/6 J mice (12wks) were injected with 4 cycles (1 cycle = 1 injection every other wk) of Folfox (FOL; 5FU 30 mg/kg, Oxaliplatin 6 mg/kg, Leucovorin 90 mg/kg) or PBS. Mice were sacrificed 0wks (n = 8) or 4wks (n = 16) after the 4th cycle. Subsets of mice performed 14 sessions (6d/wk, 5% grade) of Low- (15 min/d; n = 10) or High-dose (60 min/d; n = 10) treadmill exercise during recovery. Body composition via MRI, run time to fatigue (RTF), and grip strength tests were performed pre, post, and after 4wks recovery. RESULTS: Four cycles of FOL attenuated body weight gain (PBS 10%, FOL 3%) with no changes in food intake (p = 0.586) or cage activity (p = 0.801). FOL mice had decreased fat mass accumulation (PBS: 56%, FOL: -3%) with no changes in lean mass over the treatment period. During recovery, body mass remained suppressed (-8%; p = 0.02) and RTF (-43%; p < 0.01) and grip strength were reduced (-9%; p = 0.045) in FOL mice compared to PBS. Treadmill exercise improved body weight loss (3%; p = 0.041) independent of fat mass. There was a main effect for increased lean mass in high- compared to low-dose exercisers (p < 0.01). Both high- and low-dose exercise improved RTF (93%; p < 0.01) with no changes in grip strength. CONCLUSION: Folfox chemotherapy can induce persistent deficits in physical function and fat mass. Two weeks of low-dose treadmill exercise was sufficient to reverse chemotherapy induced fatigue without altering deficits in strength. Future studies should examine if the combined effects of aerobic and resistance exercise can improve strength. Acknowledgements: NCI R21-CA231131

Bariatric surgery is a sustainable weight loss approach, including vertical sleeve gastrectomy (VSG). Obesity exacerbates tumor growth, while diet-induced weight loss impairs progression. It remains unknown how bariatric surgery-induced weight loss impacts cancer progression or alters response to therapy. Using a pre-clinical model of obesity followed by VSG or diet-induced weight loss, breast cancer progression and immune checkpoint blockade therapy were investigated. Weight loss by VSG or weight-matched dietary intervention before tumor engraftment protected against obesity-exacerbated tumor progression. However, VSG was not as effective as diet in reducing tumor burden despite achieving similar weight and adiposity loss. Leptin did not associate with changes in tumor burden; however, circulating IL-6 was elevated in VSG mice. Uniquely, VSG tumors displayed elevated inflammation and immune checkpoint ligand PD-L1+ myeloid and non-immune cells. VSG tumors also had reduced T lymphocytes and markers of cytolysis, suggesting an ineffective anti-tumor microenvironment which prompted investigation of immune checkpoint blockade. While obese mice were resistant to immune checkpoint blockade, anti-PD-L1 potently impaired tumor progression after VSG through improved anti-tumor immunity. Thus, in formerly obese mice, surgical weight loss followed by immunotherapy reduced breast cancer burden. Finally, we compared transcriptomic changes in adipose tissue after bariatric surgery from patients and mouse models. A conserved bariatric surgery-associated weight loss signature (BSAS) was identified which significantly associated with decreased tumor volume. Findings demonstrate conserved impacts of obesity and bariatric surgery-induced weight loss pathways associated with breast cancer progression.