Transcriptomic analysis of the development of skeletal muscle atrophy in cancer-cachexia in tumor-bearing mice

Coculture with Colon-26 cancer cells decreases the protein synthesis rate and shifts energy metabolism toward glycolysis dominance in C2C12 myotubes

Cancer cachexia is the result of complex interorgan interactions initiated by cancer cells and changes in patient behavior such as decreased physical activity and energy intake. Therefore, it is crucial to distinguish between the direct and indirect effects of cancer cells on muscle mass regulation and bioenergetics to identify novel therapeutic targets. In this study, we investigated the direct effects of Colon-26 cancer cells on the molecular regulating machinery of muscle mass and its bioenergetics using a coculture system with C2C12 myotubes. Our results demonstrated that coculture with Colon-26 cells induced myotube atrophy and reduced skeletal muscle protein synthesis and its regulating mechanistic target of rapamycin complex 1 signal transduction. However, we did not observe any activating effects on protein degradation pathways including ubiquitin-proteasome and autophagy-lysosome systems. From a bioenergetic perspective, coculture with Colon-26 cells decreased the complex I-driven, but not complex II-driven, mitochondrial ATP production capacity, while increasing glycolytic enzyme activity and glycolytic metabolites, suggesting a shift in energy metabolism toward glycolysis dominance. Gene expression profiling by RNA sequencing showed that the increased activity of glycolytic enzymes was consistent with changes in gene expression. However, the decreased ATP production capacity of mitochondria was not in line with the gene expression. The potential direct interaction between cancer cells and skeletal muscle cells revealed in this study may contribute to a better fundamental understanding of the complex pathophysiology of cancer cachexia.NEW & NOTEWORTHY We explored the potential direct interplay between colon cancer cells (Colon-26) and skeletal muscle cells (C2C12 myotubes) employing a noncontact coculture experimental model. Our findings reveal that coculturing with Colon-26 cells substantially impairs the protein synthesis rate, concurrently instigating a metabolic shift toward glycolytic dominance in C2C12 myotubes. This research unveils critical insights into the intricate cellular cross talk underpinning the complex pathophysiology of cancer cachexia.

Transcriptomic signature of cancer cachexia by integration of machine learning, literature mining and meta-analysis

BACKGROUND

Cancer cachexia is a severe metabolic syndrome marked by skeletal muscle atrophy. A successful clinical intervention for cancer cachexia is currently lacking. The study of cachexia mechanisms is largely based on preclinical animal models and the availability of high-throughput transcriptomic datasets of cachectic mouse muscles is increasing through the extensive use of next generation sequencing technologies.

METHODS

Cachectic mouse muscle transcriptomic datasets of ten different studies were combined and mined by seven attribute weighting models, which analysed both categorical variables and numerical variables. The transcriptomic signature of cancer cachexia was identified by attribute weighting algorithms and was used to evaluate the performance of eleven pattern discovery models. The signature was employed to find the best combination of drugs (drug repurposing) for developing cancer cachexia treatment strategies, as well as to evaluate currently used cachexia drugs by literature mining.

RESULTS

Attribute weighting algorithms ranked 26 genes as the transcriptomic signature of muscle from mice with cancer cachexia. Deep Learning and Random Forest models performed better in differentiating cancer cachexia cases based on muscle transcriptomic data. Literature mining revealed that a combination of melatonin and infliximab has negative interactions with 2 key genes (Rorc and Fbxo32) upregulated in the transcriptomic signature of cancer cachexia in muscle.

CONCLUSIONS

The integration of machine learning, meta-analysis and literature mining was found to be an efficient approach to identifying a robust transcriptomic signature for cancer cachexia, with implications for improving clinical diagnosis and management of this condition.

Diet-induced obesity does not exacerbate cachexia in male mice bearing Lewis-lung carcinoma tumors

Cachexia is a muscle-wasting syndrome commonly observed in patients with cancer, which can significantly worsen clinical outcomes. Because of a global rise in obesity, the coexistence of cachexia in obese individuals poses unique challenges, with the impact of excessive adiposity on cachexia severity and underlying pathophysiology not well defined. Understanding the interplay between cachexia and obesity is crucial for improving diagnosis and treatment strategies for these patients; therefore, the present study examined differences in cachexia between lean and obese mice bearing Lewis lung carcinoma (LLC) tumors. Nine-week-old, male C57Bl6J mice were placed on either a chow or a high-fat diet (HFD) for 9 wk. After the diet intervention, mice were inoculated with LLC or vehicle. Markers of cachexia, such as body and muscle loss, were noted in both chow and HFD groups with tumors. Tumor weight of HFD animals was greater than that of chow. LLC tumors reduced gastrocnemius, plantaris, and soleus mass, regardless of diet. The tibialis anterior and plantaris mass and cross-sectional area of type IIb/x fibers in the gastrocnemius were not different between HFD-chow, HFD-tumor, and chow-tumor. Using RNA sequencing (RNA-seq) of the plantaris muscle from chow-tumor and HFD-tumor groups, we identified ∼400 differentially expressed genes. Bioinformatic analysis identified changes in lipid metabolism, mitochondria, bioenergetics, and proteasome degradation. Atrophy was not greater despite larger tumor burden in animals fed an HFD, and RNA-seq data suggests that partial protection is mediated through differences in mitochondrial function and protein degradation, which may serve as future mechanistic targets.NEW & NOTEWORTHY This study provides timely information on the interaction between obesity and cancer cachexia. Lean and obese animals show signs of cachexia with reduced body weight, adipose tissue, and gastrocnemius muscle mass. There was not significant wasting in the tibialis anterior, plantaris, or fast twitch fibers in the gastrocnemius muscle of obese animals with tumors. RNA-seq analysis reveals that obese tumor bearing animals had differential expression of mitochondria- and degradation-related genes, which may direct future studies in mechanistic research.

Biological sex divergence in transcriptomic profiles during the onset of hindlimb unloading-induced atrophy

Disuse-induced muscle atrophy is a common clinical problem observed mainly in older adults, intensive care units patients, or astronauts. Previous studies presented biological sex divergence in progression of disuse-induced atrophy along with differential changes in molecular mechanisms possibly underlying muscle atrophy. The aim of this study was to perform transcriptomic profiling of male and female mice during the onset and progression of unloading disuse-induced atrophy. Male and female mice underwent hindlimb unloading (HU) for 24, 48, 72, and 168 h (n = 8/group). Muscles were weighed for each cohort and gastrocnemius was used for RNA-sequencing analysis. Females exhibited muscle loss as early as 24 h of HU, whereas males after 168 h of HU. In males, pathways related to proteasome degradation were upregulated throughout 168 h of HU, whereas in females these pathways were upregulated up to 72 h of HU. Lcn2, a gene contributing to regulation of myogenesis, was upregulated by 6.46- to 19.86-fold across all time points in females only. A reverse expression of Fosb, a gene related to muscle degeneration, was observed between males (4.27-fold up) and females (4.57-fold down) at 24-h HU. Mitochondrial pathways related to tricarboxylic acid (TCA) cycle were highly downregulated at 168 h of HU in males, whereas in females this downregulation was less pronounced. Collagen-related pathways were consistently downregulated throughout 168 h of HU only in females, suggesting a potential biological sex-specific protective mechanism against disuse-induced fibrosis. In conclusion, females may have protection against HU-induced skeletal muscle mitochondrial degeneration and fibrosis through transcriptional mechanisms, although they may be more vulnerable to HU-induced muscle wasting compared with males.NEW & NOTEWORTHY Herein, we have assessed the transcriptomic response across biological sexes during the onset and progression of unloading disuse-induced atrophy in mice. We have demonstrated an inverse expression of Fosb between males and females, as well as differentially timed patterns of expressing atrophy-related pathways between sexes that are concomitant to the accelerated atrophy in females. We also identified in females signs of mechanisms to combat disuse-induced mitochondrial degeneration and fibrosis.

Cancer Cachexia: Underlying Mechanisms and Potential Therapeutic Interventions

Cancer cachexia, a multifactorial metabolic syndrome developed during malignant tumor growth, is characterized by an accelerated loss of body weight accompanied by the depletion of skeletal muscle mass. This debilitating condition is associated with muscle degradation, impaired immune function, reduced functional capacity, compromised quality of life, and diminished survival in cancer patients. Despite the lack of the known capability of fully reversing or ameliorating this condition, ongoing research is shedding light on promising preclinical approaches that target the disrupted mechanisms in the pathophysiology of cancer cachexia. This comprehensive review delves into critical aspects of cancer cachexia, including its underlying pathophysiological mechanisms, preclinical models for studying the progression of cancer cachexia, methods for clinical assessment, relevant biomarkers, and potential therapeutic strategies. These discussions collectively aim to contribute to the evolving foundation for effective, multifaceted counteractive strategies against this challenging condition.

Females display relatively preserved muscle quality compared with males during the onset and early stages of C26-induced cancer cachexia

Cancer cachexia is clinically defined by involuntary weight loss >5% in <6 mo, primarily affecting skeletal muscle. Here, we aimed to identify sex differences in the onset of colorectal cancer cachexia with specific consideration to skeletal muscle contractile and metabolic functions. Eight-weeks old BALB/c mice (69 males, 59 females) received subcutaneous C26 allografts or PBS vehicle. Tumors were developed for 10-, 15-, 20-, or 25 days. Muscles and organs were collected, in vivo muscle contractility, protein synthesis rate, mitochondrial function, and protein turnover markers were assessed. One-way ANOVA within sex and trend analysis between sexes were performed, P < 0.05. Gastrocnemius and tibialis anterior (TA) muscles became atrophic in male mice at 25 days, whereas female mice exhibited no significant differences in muscle weights at endpoints despite presenting hallmarks of cancer cachexia (fat loss, hepatosplenomegaly). We observed lowered muscle contractility and protein synthesis concomitantly to muscle mass decay in males, with higher proteolytic markers in muscles of both sexes. mRNA of Opa1 was lower in TA, whereas Bnip3 was higher in gastrocnemius after 25 days in male mice, with no significant effect in female mice. Our data suggest relative protections to skeletal muscle in females compared with males despite other canonical signs of cancer cachexia and increased protein degradation markers; suggesting we should place onus upon nonmuscle tissues during early stages of cancer cachexia in females. We noted potential protective mechanisms relating to skeletal muscle contractile and mitochondrial functions. Our findings underline possible heterogeneity in onset of cancer cachexia between biological sexes, suggesting the need for sex-specific approaches to treat cancer cachexia.NEW & NOTEWORTHY Our study demonstrates biological-sex differences in phenotypic characteristics of cancer cachexia between male and female mice, whereby females display many common characteristics of cachexia (gonadal fat loss and hepatosplenomegaly), protein synthesis markers alterations, and common catabolic markers in skeletal muscle despite relatively preserved muscle mass in early-stage cachexia compared with males. Mechanisms of cancer cachexia appear to differ between sexes. Data suggest need to place onus of early cancer cachexia detection and treatment on nonmuscle tissues in females.

Inflammation o'clock: interactions of circadian rhythms with inflammation-induced skeletal muscle atrophy

Circadian rhythms are ∼24 h cycles evident in behaviour, physiology and metabolism. The molecular mechanism directing circadian rhythms is the circadian clock, which is composed of an interactive network of transcription-translation feedback loops. The core clock genes include Bmal1, Clock, Rev-erbα/β, Per and Cry. In addition to keeping time, the core clock regulates a daily programme of gene expression that is important for overall cell homeostasis. The circadian clock mechanism is present in all cells, including skeletal muscle fibres, and disruption of the muscle clock is associated with changes in muscle phenotype and function. Skeletal muscle atrophy is largely associated with a lower quality of life, frailty and reduced lifespan. Physiological and genetic modification of the core clock mechanism yields immune dysfunction, alters inflammatory factor expression and secretion and is associated with skeletal muscle atrophy in multiple conditions, such as ageing and cancer cachexia. Here, we summarize the possible interplay between the circadian clock modulation of immune cells, systemic inflammatory status and skeletal muscle atrophy in chronic inflammatory conditions. Although there is a clear disruption of circadian clocks in various models of atrophy, the mechanism behind such alterations remains unknown. Understanding the modulatory potential of muscle and immune circadian clocks in inflammation and skeletal muscle health is essential for the development of therapeutic strategies to protect skeletal muscle mass and function of patients with chronic inflammation.

The time-course of cancer cachexia onset reveals biphasic transcriptional disruptions in female skeletal muscle distinct from males

BACKGROUND

Cancer-cachexia (CC) is a debilitating condition affecting up to 80% of cancer patients and contributing to 40% of cancer-related deaths. While evidence suggests biological sex differences in the development of CC, assessments of the female transcriptome in CC are lacking, and direct comparisons between sexes are scarce. This study aimed to define the time course of Lewis lung carcinoma (LLC)-induced CC in females using transcriptomics, while directly comparing biological sex differences.

RESULTS

We found the global gene expression of the gastrocnemius muscle of female mice revealed biphasic transcriptomic alterations, with one at 1 week following tumor allograft and another during the later stages of cachexia development. The early phase was associated with the upregulation of extracellular-matrix pathways, while the later phase was characterized by the downregulation of oxidative phosphorylation, electron transport chain, and TCA cycle. When DEGs were compared to a known list of mitochondrial genes (MitoCarta), ~ 47% of these genes were differently expressed in females exhibiting global cachexia, suggesting transcriptional changes to mitochondrial gene expression happens concomitantly to functional impairments previously published. In contrast, the JAK-STAT pathway was upregulated in both the early and late stages of CC. Additionally, we observed a consistent downregulation of Type-II Interferon signaling genes in females, which was associated with protection in skeletal muscle atrophy despite systemic cachexia. Upregulation of Interferon signaling was noted in the gastrocnemius muscle of cachectic and atrophic male mice. Comparison of female tumor-bearing mice with males revealed ~ 70% of DEGs were distinct between sexes in cachectic animals, demonstrating dimorphic mechanisms of CC.

CONCLUSION

Our findings suggest biphasic disruptions in the transcriptome of female LLC tumor-bearing mice: an early phase associated with ECM remodeling and a late phase, accompanied by the onset of systemic cachexia, affecting overall muscle energy metabolism. Notably, ~ 2/3 of DEGs in CC are biologically sex-specific, providing evidence of dimorphic mechanisms of cachexia between sexes. Downregulation of Type-II Interferon signaling genes appears specific to CC development in females, suggesting a new biological sex-specific marker of CC not reliant on the loss of muscle mass, that might represent a protective mechanism against muscle loss in CC in female mice.

Zfp697 is an RNA-binding protein that regulates skeletal muscle inflammation and regeneration

Muscular atrophy is a mortality risk factor that happens with disuse, chronic disease, and aging. Recovery from atrophy requires changes in several cell types including muscle fibers, and satellite and immune cells. Here we show that Zfp697/ZNF697 is a damage-induced regulator of muscle regeneration, during which its expression is transiently elevated. Conversely, sustained Zfp697 expression in mouse muscle leads to a gene expression signature of chemokine secretion, immune cell recruitment, and extracellular matrix remodeling. Myofiber-specific Zfp697 ablation hinders the inflammatory and regenerative response to muscle injury, compromising functional recovery. We uncover Zfp697 as an essential interferon gamma mediator in muscle cells, interacting primarily with ncRNAs such as the pro-regenerative miR-206. In sum, we identify Zfp697 as an integrator of cell-cell communication necessary for tissue regeneration.

Skeletal muscle omics signatures in cancer cachexia: perspectives and opportunities

Cachexia is a life-threatening complication of cancer that occurs in up to 80% of patients with advanced cancer. Cachexia reflects the systemic consequences of cancer and prominently features unintended weight loss and skeletal muscle wasting. Cachexia impairs cancer treatment tolerance, lowers quality of life, and contributes to cancer-related mortality. Effective treatments for cancer cachexia are lacking despite decades of research. High-throughput omics technologies are increasingly implemented in many fields including cancer cachexia to stimulate discovery of disease biology and inform therapy choice. In this paper, we present selected applications of omics technologies as tools to study skeletal muscle alterations in cancer cachexia. We discuss how comprehensive, omics-derived molecular profiles were used to discern muscle loss in cancer cachexia compared with other muscle-wasting conditions, to distinguish cancer cachexia from treatment-related muscle alterations, and to reveal severity-specific mechanisms during the progression of cancer cachexia from early toward severe disease.

Host-Derived Cytotoxic Agents in Chronic Inflammation and Disease Progression

At inflammatory sites, cytotoxic agents are released and generated from invading immune cells and damaged tissue cells. The further fate of the inflammation highly depends on the presence of antagonizing principles that are able to inactivate these host-derived cytotoxic agents. As long as the affected tissues are well equipped with ready-to-use protective mechanisms, no damage by cytotoxic agents occurs and resolution of inflammation is initiated. However, long-lasting and severe immune responses can be associated with the decline, exhaustion, or inactivation of selected antagonizing principles. Hence, cytotoxic agents are only partially inactivated and contribute to damage of yet-unperturbed cells. Consequently, a chronic inflammatory process results. In this vicious circle of permanent cell destruction, not only novel cytotoxic elements but also novel alarmins and antigens are liberated from affected cells. In severe cases, very low protection leads to organ failure, sepsis, and septic shock. In this review, the major classes of host-derived cytotoxic agents (reactive species, oxidized heme proteins and free heme, transition metal ions, serine proteases, matrix metalloproteases, and pro-inflammatory peptides), their corresponding protective principles, and resulting implications on the pathogenesis of diseases are highlighted.

LP07 and LLC preclinical models of lung cancer induce divergent anabolic deficits and expression of pro-inflammatory effectors of muscle wasting

Preclinical models have been instrumental to elucidate the mechanisms underlying muscle wasting in lung cancer (LC). We investigated anabolic deficits and the expression of proinflammatory effectors of muscle wasting in the LP07 and Lewis lung carcinoma (LLC) tumor models. Tumor growth resulted in significant weakness in LP07 but not in LLC mice despite similar reductions in gastrocnemius muscle mass in both models. The LP07 tumors caused a reduction in ribosomal (r)RNA and a decrease in rRNA gene (rDNA) transcription elongation, whereas no changes in ribosomal capacity were evident in LLC tumor-bearing mice. Expression of RNA Polymerase I (Pol I) elongation-associated subunits Polr2f, PAF53, and Znrd1 mRNAs was significantly elevated in the LP07 model, whereas Pol I elongation-related factors FACT and Spt4/5 mRNAs were elevated in the LLC mice. Reductions in RPS6 and 4E-BP1 phosphorylation were similar in both models but were independent of mTOR phosphorylation in LP07 mice. Muscle inflammation was also tumor-specific, IL-6 and TNF-α mRNA increased with LLC tumors, and upregulation of NLRP3 mRNA was independent of tumor type. In summary, although both models caused muscle wasting, only the LP07 model displayed muscle weakness with reductions in ribosomal capacity. Intracellular signaling diverged at the mTOR level with similar reductions in RPS6 and 4E-BP1 phosphorylation regardless of tumor type. The increase in proinflammatory factors was more pronounced in the LLC model. Our results demonstrate novel divergent anabolic deficits and expression of proinflammatory effectors of muscle wasting in the LP07 and LLC preclinical models of lung cancer.NEW & NOTEWORTHY We provide novel data demonstrating significant divergence in anabolic deficits and the expression of proinflammatory effectors of muscle wasting consequent to different lung-derived tumors.

Muscle metabolic stress determines cancer cachexia severity in mice

Objectives: To determine the metabolic effects of cancer-conditioned media on myotube metabolism and to understand whether the variability of these effects is associated with cancer cachexia progression. Materials and methods: We established single-cell clones from murine Lewis lung carcinoma (LLC) cells and generated conditioned media from each clonal line. Differentiated primary mouse myotubes were incubated with conditioned media derived from each individual clonal cell line. After initial analysis, we selected a specific LLC clonal cell line that failed to induce metabolic stress in myotubes for further investigation in vitro and in vivo. Results: Short-term incubation with conditioned media from 10/34 LLC clonal cells failed to affect oxygen consumption rate (OCR) in myotubes. Incubation with parental LLC-conditioned media decreased protein content and changed the expression of key regulators of muscle function in myotubes, but the incubation of conditioned media from a selected clone that failed to affect OCR in myotubes also did not affect protein content and expression of muscle regulators. Mice injected with parental LLC cells had a significantly reduced body mass and muscle wasting compared to the mice injected with cells derived from this selected LLC clone. Conclusion: Factors secreted by LLC cells induce metabolic stress in primary myotubes and induce cancer cachexia in mice. However, a selected clonal LLC cell line that failed to induce metabolic stress in myotubes also promoted weaker catabolism in mice. These novel findings establish that early disruption of muscle oxidative metabolism is associated with cancer cachexia progression.

Integrated Analyses of DNA Methylation and Gene Expression of Rainbow Trout Muscle under Variable Ploidy and Muscle Atrophy Conditions

Rainbow trout, Oncorhynchus mykiss, is an important cool, freshwater aquaculture species used as a model for biological research. However, its genome reference has not been annotated for epigenetic markers affecting various biological processes, including muscle growth/atrophy. Increased energetic demands during gonadogenesis/reproduction provoke muscle atrophy in rainbow trout. We described DNA methylation and its associated gene expression in atrophying muscle by comparing gravid, diploid females to sterile, triploid females. Methyl Mini-seq and RNA-Seq were simultaneously used to characterize genome-wide DNA methylation and its association with gene expression in rainbow trout muscle. Genome-wide enrichment in the number of CpGs, accompanied by depleted methylation levels, was noticed around the gene transcription start site (TSS). Hypermethylation of CpG sites within ±1 kb on both sides of TSS (promoter and gene body) was weakly/moderately associated with reduced gene expression. Conversely, hypermethylation of the CpG sites in downstream regions of the gene body +2 to +10 kb was weakly associated with increased gene expression. Unlike mammalian genomes, rainbow trout gene promotors are poor in CpG islands, at <1% compared to 60%. No signs of genome-wide, differentially methylated (DM) CpGs were observed due to the polyploidy effect; only 1206 CpGs (0.03%) were differentially methylated, and these were primarily associated with muscle atrophy. Twenty-eight genes exhibited differential gene expression consistent with methylation levels of 31 DM CpGs. These 31 DM CpGs represent potential epigenetic markers of muscle atrophy in rainbow trout. The DM CpG-harboring genes are involved in apoptosis, epigenetic regulation, autophagy, collagen metabolism, cell membrane functions, and Homeobox proteins. Our study also identified genes explaining higher water content and modulated glycolysis previously shown as characteristic biochemical signs of rainbow trout muscle atrophy associated with sexual maturation. This study characterized DNA methylation in the rainbow trout genome and its correlation with gene expression. This work also identified novel epigenetic markers associated with muscle atrophy in fish/lower vertebrates.

Skeletal muscle proteome expression differentiates severity of cancer cachexia in mice and identifies loss of fragile X mental retardation syndrome-related protein 1

TMT-based quantitative proteomics was used to examine protein expression in skeletal muscle from mice with moderate and severe cancer cachexia to study mechanisms underlying varied cachexia severity. Weight loss of 10% (moderate) and 20% (severe) was induced by injection of colon-26 cancer cells in 10-week old Balb/c mice. In moderate cachexia, enriched pathways reflected fibrin formation, integrin/MAPK signaling, and innate immune system, suggesting an acute phase response and fibrosis. These pathways remained enriched in severe cachexia, however, energy-yielding pathways housed in mitochondria were prominent additions to the severe state. These enrichments suggest distinct muscle proteome expression patterns that differentiate cachexia severity. When analyzed with two other mouse models, eight differentially expressed targets were shared including Serpina3n, Sypl2, Idh3a, Acox1, Col6a1, Myoz3, Ugp2, and Slc41a3. Acox1 and Idh3a control lipid oxidation and NADH generation in the TCA cycle, respectively, and Col6a1 comprises part of type VI collagen with reported profibrotic functions, suggesting influential roles in cachexia. A potential target was identified in FXR1, an RNA-binding protein not previously implicated in cancer cachexia. FXR1 decreased in cachexia and related linearly with weight change and myofiber size. These findings suggest distinct mechanisms associated with cachexia severity and potential biomarkers and therapeutic targets. This article is protected by copyright. All rights reserved.

Development of metabolic and contractile alterations in development of cancer cachexia in female tumor-bearing mice

Cancer cachexia (CC) results in impaired muscle function and quality of life and is the primary cause of death for ∼20%-30% of patients with cancer. We demonstrated mitochondrial degeneration as a precursor to CC in male mice; however, whether such alterations occur in females is currently unknown. The purpose of this study was to elucidate muscle alterations in CC development in female tumor-bearing mice. Sixty female C57BL/6J mice were injected with PBS or Lewis lung carcinoma at 8 wk of age, and tumors developed for 1, 2, 3, or 4 wk to assess the time course of cachectic development. In vivo muscle contractile function, protein fractional synthetic rate (FSR), protein turnover, and mitochondrial health were assessed. Three- and four-week tumor-bearing mice displayed a dichotomy in tumor growth and were reassigned to high tumor (HT) and low tumor (LT) groups. HT mice exhibited lower soleus, tibialis anterior, and fat weights than PBS mice. HT mice showed lower peak isometric torque and slower one-half relaxation time than PBS mice. HT mice had lower FSR than PBS mice, whereas E3 ubiquitin ligases were greater in HT than in other groups. Bnip3 (mitophagy) and pMitoTimer red puncta (mitochondrial degeneration) were greater in HT mice, whereas Pgc1α1 and Tfam (mitochondrial biogenesis) were lower in HT mice than in PBS mice. We demonstrate alterations in female tumor-bearing mice where HT exhibited greater protein degradation, impaired muscle contractility, and mitochondrial degeneration compared with other groups. Our data provide novel evidence for a distinct cachectic development in tumor-bearing female mice compared with previous male studies.NEW & NOTEWORTHY Our study demonstrates divergent tumor development and tissue wasting within 3- and 4-wk mice, where approximately half the mice developed large tumors and subsequent cachexia. Unlike previous male studies, where metabolic perturbations precede the onset of cachexia, females appear to exhibit protections from the metabolic perturbations and cachexia development. Our data provide novel evidence for divergent cachectic development in tumor-bearing female mice compared with previous male CC studies, suggesting different mechanisms of CC between sexes.

REDD1 deletion attenuates cancer cachexia in mice

Cancer cachexia is a wasting disorder associated with advanced cancer that contributes to mortality. Cachexia is characterized by involuntary loss of body weight and muscle weakness that affects physical function. Regulated in DNA damage and development 1 (REDD1) is a stress-response protein that is transcriptionally upregulated in muscle during wasting conditions and inhibits mechanistic target of rapamycin complex 1 (mTORC1). C2C12 myotubes treated with Lewis lung carcinoma (LLC)-conditioned media increased REDD1 mRNA expression and decreased myotube diameter. To investigate the role of REDD1 in cancer cachexia, we inoculated 12-week old male wild-type or global REDD1 knockout (REDD1 KO) mice with LLC cells and euthanized 28-days later. Wild-type mice had increased skeletal muscle REDD1 expression, and REDD1 deletion prevented loss of body weight and lean tissue mass, but not fat mass. We found that REDD1 deletion attenuated loss of individual muscle weights and loss of myofiber cross sectional area. We measured markers of the Akt/mTORC1 pathway and found that, unlike wild-type mice, phosphorylation of both Akt and 4E-BP1 was maintained in the muscle of REDD1 KO mice after LLC inoculation, suggesting that loss of REDD1 is beneficial in maintaining mTORC1 activity in mice with cancer cachexia. We measured Foxo3a phosphorylation as a marker of the ubiquitin proteasome pathway and autophagy and found that REDD1 deletion prevented dephosphorylation of Foxo3a in muscles from cachectic mice. Our data provides evidence that REDD1 plays an important role in cancer cachexia through the regulation of both protein synthesis and protein degradation pathways.

Cancer-induced muscle atrophy is determined by intrinsic muscle oxidative capacity

We tested the hypothesis that cancer cachexia progression would induce oxidative post-translational modifications (Ox-PTMs) associated with skeletal muscle wasting, with different responses in muscles with the prevalence of glycolytic and oxidative fibers. We used cysteine-specific isotopic coded affinity tags (OxICAT) and gel-free mass spectrometry analysis to investigate the cysteine Ox-PTMs profile in the proteome of both plantaris (glycolytic) and soleus (oxidative) muscles in tumor-bearing and control rats. Histological analysis revealed muscle atrophy in type II fibers in plantaris muscle, with no changes in plantaris type I fibers and no differences in both soleus type I and II fibers in tumor-bearing rats when compared to healthy controls. Tumor progression altered the Ox-PTMs profile in both plantaris and soleus. However, pathway analysis including the differentially oxidized proteins revealed tricarboxylic acid cycle and oxidative phosphorylation as main affected pathways in plantaris muscle from tumor-bearing rats, while the same analysis did not show main metabolic pathways affected in the soleus muscle. In addition, cancer progression affected several metabolic parameters such as ATP levels and markers of oxidative stress associated with muscle atrophy in plantaris muscle, but not in soleus. However, isolated soleus from tumor-bearing rats had a reduced force production capacity when compared to controls. These novel findings demonstrate that tumor-bearing rats have severe muscle atrophy exclusively in glycolytic fibers. Cancer progression is associated with cysteine Ox-PTMs in the skeletal muscle, but these modifications affect different pathways in a glycolytic muscle compared to an oxidative muscle, indicating that intrinsic muscle oxidative capacity determines the response to cancer cachectic effects.

Wheel running improves fasting-induced AMPK signaling in skeletal muscle from tumor-bearing mice

Disruptions to muscle protein turnover and metabolic regulation contribute to muscle wasting during the progression of cancer cachexia. The initiation of cachexia is also associated with decreased physical activity. While chronic muscle AMPK activation occurs during cachexia progression in ApcMin/+ (MIN) mice, a preclinical cachexia model, the understanding of muscle AMPK's role during cachexia initiation is incomplete. Therefore, we examined if voluntary wheel exercise could improve skeletal muscle AMPK signaling in pre-cachectic MIN mice. Next, we examined muscle AMPK's role in aberrant catabolic signaling in response to a 12-h fast in mice initiating cachexia. Male C57BL/6 (B6: N = 26) and MIN (N = 29) mice were subjected to ad libitum feeding, 12-h fast, or 4 wks. of wheel access and then a 12-h fast during the initiation of cachexia. Male tamoxifen-inducible skeletal muscle AMPKα1 α2 (KO) knockout mice crossed with ApcMin/+ and floxed controls were examined (WT: N = 8, KO: N = 8, MIN: N = 10, MIN KO: N = 6). Male mice underwent a 12-h fast and the gastrocnemius muscle was analyzed. MIN gastrocnemius mass was reduced compared to B6 mice. A 12-h fast induced MIN muscle AMPKT172 , FOXOS413 , and ULK-1S555 phosphorylation compared to B6. Wheel running attenuated these inductions. A 12-h fast induced MIN muscle MuRF-1 protein expression compared to B6 and was suppressed by wheel running. Additionally, fasting induced muscle autophagy signaling and disrupted mitochondrial quality protein expression in the MIN, which was prevented in the MIN KO. We provide evidence that increased skeletal muscle AMPK sensitivity to a 12-h fast is an adverse event in pre-cachectic MIN mice, and exercise can improve this regulation.

Methylarginine metabolites are associated with attenuated muscle protein synthesis in cancer-associated muscle wasting

Cancer cachexia is characterized by reductions in peripheral lean muscle mass. Prior studies have primarily focused on increased protein breakdown as the driver of cancer-associated muscle wasting. Therapeutic interventions targeting catabolic pathways have, however, largely failed to preserve muscle mass in cachexia, suggesting that other mechanisms might be involved. In pursuit of novel pathways, we used untargeted metabolomics to search for metabolite signatures that may be linked with muscle atrophy. We injected 7-week-old C57/BL6 mice with LLC1 tumor cells or vehicle. After 21 days, tumor-bearing mice exhibited reduced body and muscle mass and impaired grip strength compared with controls, which was accompanied by lower synthesis rates of mixed muscle protein and the myofibrillar and sarcoplasmic muscle fractions. Reductions in protein synthesis were accompanied by mitochondrial enlargement and reduced coupling efficiency in tumor-bearing mice. To generate mechanistic insights into impaired protein synthesis, we performed untargeted metabolomic analyses of plasma and muscle and found increased concentrations of two methylarginines, asymmetric dimethylarginine (ADMA) and N^G-monomethyl-l-arginine, in tumor-bearing mice compared with control mice. Compared with healthy controls, human cancer patients were also found to have higher levels of ADMA in the skeletal muscle. Treatment of C2C12 myotubes with ADMA impaired protein synthesis and reduced mitochondrial protein quality. These results suggest that increased levels of ADMA and mitochondrial changes may contribute to impaired muscle protein synthesis in cancer cachexia and could point to novel therapeutic targets by which to mitigate cancer cachexia.

Development and progression of cancer cachexia: Perspectives from bench to bedside

Cancer cachexia (CC) is a devastating syndrome characterized by weight loss, reduced fat mass and muscle mass that affects approximately 80% of cancer patients and is responsible for 22%–30% of cancer-associated deaths. Understanding underlying mechanisms for the development of CC are crucial to advance therapies to treat CC and improve cancer outcomes. CC is a multi-organ syndrome that results in extensive skeletal muscle and adipose tissue wasting; however, CC can impair other organs such as the liver, heart, brain, and bone as well. A considerable amount of CC research focuses on changes that occur within the muscle, but cancer-related impairments in other organ systems are understudied. Furthermore, metabolic changes in organ systems other than muscle may contribute to CC. Therefore, the purpose of this review is to address degenerative mechanisms which occur during CC from a whole-body perspective. Outlining the information known about metabolic changes that occur in response to cancer is necessary to develop and enhance therapies to treat CC. As much of the current evidences in CC are from pre-clinical models we should note the majority of the data reviewed here are from pre-clinical models.

Sex Differences in Cancer Cachexia

PURPOSE OF REVIEW

Cachexia, a feature of cancer and other chronic diseases, is marked by progressive weight loss and skeletal muscle wasting. This review aims to highlight the sex differences in manifestations of cancer cachexia in patients, rodent models, and our current understanding of the potential mechanisms accounting for these differences.

RECENT FINDINGS

Male cancer patients generally have higher prevalence of cachexia, greater weight loss or muscle wasting, and worse outcomes compared with female cancer patients. Knowledge is increasing about sex differences in muscle fiber type and function, mitochondrial metabolism, global gene expression and signaling pathways, and regulatory mechanisms at the levels of sex chromosomes vs. sex hormones; however, it is largely undetermined how such sex differences directly affect the susceptibility to stressors leading to muscle wasting in cancer cachexia. Few studies have investigated basic mechanisms underlying sex differences in cancer cachexia. A better understanding of sex differences would improve cachexia treatment in both sexes.

Molecular mechanisms of cancer cachexia‑induced muscle atrophy (Review)

Muscle atrophy is a severe clinical problem involving the loss of muscle mass and strength that frequently accompanies the development of numerous types of cancer, including pancreatic, lung and gastric cancers. Cancer cachexia is a multifactorial syndrome characterized by a continuous decline in skeletal muscle mass that cannot be reversed by conventional nutritional therapy. The pathophysiological characteristic of cancer cachexia is a negative protein and energy balance caused by a combination of factors, including reduced food intake and metabolic abnormalities. Numerous necessary cellular processes are disrupted by the presence of abnormal metabolites, which mediate several intracellular signaling pathways and result in the net loss of cytoplasm and organelles in atrophic skeletal muscle during various states of cancer cachexia. Currently, the clinical morbidity and mortality rates of patients with cancer cachexia are high. Once a patient enters the cachexia phase, the consequences are difficult to reverse and the treatment methods for cancer cachexia are very limited. The present review aimed to summarize the recent discoveries regarding the pathogenesis of cancer cachexia-induced muscle atrophy and provided novel ideas for the comprehensive treatment to improve the prognosis of affected patients.

Exercise training reverses cancer-induced oxidative stress and decrease in muscle COPS2/TRIP15/ALIEN

OBJECTIVE

We tested the hypothesis that exercise training would attenuate metabolic impairment in a model of severe cancer cachexia.

METHODS

We used multiple in vivo and in vitro methods to explore the mechanisms underlying the beneficial effects induced by exercise training in tumor-bearing rats.

RESULTS

Exercise training improved running capacity, prolonged lifespan, reduced oxidative stress, and normalized muscle mass and contractile function in tumor-bearing rats. An unbiased proteomic screening revealed COP9 signalosome complex subunit 2 (COPS2) as one of the most downregulated proteins in skeletal muscle at the early stage of cancer cachexia. Exercise training normalized muscle COPS2 protein expression in tumor-bearing rats and mice. Lung cancer patients with low endurance capacity had low muscle COPS2 protein expression as compared to age-matched control subjects. To test whether decrease in COPS2 protein levels could aggravate or be an intrinsic compensatory mechanism to protect myotubes from cancer effects, we performed experiments in vitro using primary myotubes. COPS2 knockdown in human myotubes affected multiple cellular pathways, including regulation of actin cytoskeleton. Incubation of cancer-conditioned media in mouse myotubes decreased F-actin expression, which was partially restored by COPS2 knockdown. Direct repeat 4 (DR4) response elements have been shown to positively regulate gene expression. COPS2 overexpression decreased the DR4 activity in mouse myoblasts, and COPS2 knockdown inhibited the effects of cancer-conditioned media on DR4 activity.

CONCLUSIONS

These studies demonstrated that exercise training may be an important adjuvant therapy to counteract cancer cachexia and uncovered novel mechanisms involving COPS2 to regulate myotube homeostasis in cancer cachexia.

Effects of conditioned media from murine lung cancer cells and human tumor cells on cultured myotubes

Factors secreted from tumors/tumor cells are hypothesized to cause skeletal muscle wasting in cancer patients. We examined whether cancer cells secrete factors to promote atrophy by evaluating the effects of conditioned media (CM) from murine lung cancer cells and primary cultures of human lung tumor cells on cultured myotubes. We evaluated murine Lewis lung carcinoma (LLC) and KRAS^G12D cells, and primary cell lines derived from tumor biopsies from patients with lung cancer (hTCM; n = 6). In all experiments, serum content was matched across treatment groups. We hypothesized that CM from murine and human tumor cells would reduce myotube myosin content, decrease mitochondrial content, and increase mitochondrial reactive oxygen species (ROS) production. Treatment of myotubes differentiated for 7 days with CM from LLC and KRAS^G12D cells did not alter any of these variables. Effects of murine tumor cell CM were observed when myotubes differentiated for 4 days were treated with tumor cell CM and compared with undiluted differentiation media. However, these effects were not apparent if tumor cell CM treatments were compared with control cell CM or dilution controls. Finally, CM from human lung tumor primary cell lines did not modify myosin content or mitochondrial content or ROS production compared with either undiluted differentiated media, control cell CM, or dilution controls. Our results do not support the hypothesis that factors released from cultured lung cancer/tumor cells promote myotube wasting or mitochondrial abnormalities, but we cannot dismiss the possibility that these cells could secrete such factors in vivo within the native tumor microenvironment.

Muscle alterations in the development and progression of cancer-induced muscle atrophy: a review

Cancer cachexia-cancer-associated body weight and muscle loss-is a significant predictor of mortality and morbidity in cancer patients across a variety of cancer types. However, despite the negative prognosis associated with cachexia onset, there are no clinical therapies approved to treat or prevent cachexia. This lack of treatment may be partially due to the relative dearth of literature on mechanisms occurring within the muscle before the onset of muscle wasting. Therefore, the purpose of this review is to compile the current scientific literature on mechanisms contributing to the development and progression of cancer cachexia, including protein turnover, inflammatory signaling, and mitochondrial dysfunction. We define "development" as changes in cell function occurring before the onset of cachexia and "progression" as alterations to cell function that coincide with the exacerbation of muscle wasting. Overall, the current literature suggests that multiple aspects of cellular function, such as protein turnover, inflammatory signaling, and mitochondrial quality, are altered before the onset of muscle loss during cancer cachexia and clearly highlights the need to study more thoroughly the developmental stages of cachexia. The studying of these early aberrations will allow for the development of effective therapeutics to prevent the onset of cachexia and improve health outcomes in cancer patients.

LIM and cysteine-rich domains 1 (LMCD1) regulates skeletal muscle hypertrophy, calcium handling, and force

BACKGROUND

Skeletal muscle mass and strength are crucial determinants of health. Muscle mass loss is associated with weakness, fatigue, and insulin resistance. In fact, it is predicted that controlling muscle atrophy can reduce morbidity and mortality associated with diseases such as cancer cachexia and sarcopenia.

METHODS

We analyzed gene expression data from muscle of mice or human patients with diverse muscle pathologies and identified LMCD1 as a gene strongly associated with skeletal muscle function. We transiently expressed or silenced LMCD1 in mouse gastrocnemius muscle or in mouse primary muscle cells and determined muscle/cell size, targeted gene expression, kinase activity with kinase arrays, protein immunoblotting, and protein synthesis levels. To evaluate force, calcium handling, and fatigue, we transduced the flexor digitorum brevis muscle with a LMCD1-expressing adenovirus and measured specific force and sarcoplasmic reticulum Ca²⁺ release in individual fibers. Finally, to explore the relationship between LMCD1 and calcineurin, we ectopically expressed Lmcd1 in the gastrocnemius muscle and treated those mice with cyclosporine A (calcineurin inhibitor). In addition, we used a luciferase reporter construct containing the myoregulin gene promoter to confirm the role of a LMCD1-calcineurin-myoregulin axis in skeletal muscle mass control and calcium handling.

RESULTS

Here, we identify LIM and cysteine-rich domains 1 (LMCD1) as a positive regulator of muscle mass, that increases muscle protein synthesis and fiber size. LMCD1 expression in vivo was sufficient to increase specific force with lower requirement for calcium handling and to reduce muscle fatigue. Conversely, silencing LMCD1 expression impairs calcium handling and force, and induces muscle fatigue without overt atrophy. The actions of LMCD1 were dependent on calcineurin, as its inhibition using cyclosporine A reverted the observed hypertrophic phenotype. Finally, we determined that LMCD1 represses the expression of myoregulin, a known negative regulator of muscle performance. Interestingly, we observed that skeletal muscle LMCD1 expression is reduced in patients with skeletal muscle disease.

CONCLUSIONS

Our gain- and loss-of-function studies show that LMCD1 controls protein synthesis, muscle fiber size, specific force, Ca²⁺ handling, and fatigue resistance. This work uncovers a novel role for LMCD1 in the regulation of skeletal muscle mass and function with potential therapeutic implications.

Modeling Human Cancer-induced Cachexia

Cachexia is a wasting syndrome characterized by pronounced skeletal muscle loss. In cancer, cachexia is associated with increased morbidity and mortality and decreased treatment tolerance. Although advances have been made in understanding the mechanisms of cachexia, translating these advances to the clinic has been challenging. One reason for this shortcoming may be the current animal models, which fail to fully recapitulate the etiology of human cancer-induced tissue wasting. Because pancreatic ductal adenocarcinoma (PDA) presents with a high incidence of cachexia, we engineered a mouse model of PDA that we named KPP. KPP mice, similar to PDA patients, progressively lose skeletal and adipose mass as a consequence of their tumors. In addition, KPP muscles exhibit a similar gene ontology as cachectic patients. We envision that the KPP model will be a useful resource for advancing our mechanistic understanding and ability to treat cancer cachexia.