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.

Leucine Supplementation Exacerbates Morbidity in Male but Not Female Mice with Colorectal Cancer-Induced Cachexia

Cancer cachexia (CC) is a multifactorial wasting syndrome characterized by a significant loss in lean and/or fat mass and represents a leading cause of mortality in cancer patients. Nutraceutical treatments have been proposed as a potential treatment strategy to mitigate cachexia-induced muscle wasting. However, contradictory findings warrant further investigation. The purpose of this study was to determine the effects of leucine supplementation on skeletal muscle in male and female ApcMin/+ mice (APC). APC mice and their wild-type (WT) littermates were given normal drinking water or 1.5% leucine-supplemented water (n = 4-10/group/sex). We measured the gene expression of regulators of inflammation, protein balance, and myogenesis. Leucine treatment lowered survival rates, body mass, and muscle mass in males, while in females, it had no effect on body or muscle mass. Leucine treatment altered inflammatory gene expression by lowering Il1b 87% in the APC group and decreasing Tnfa 92% in both WT and APC males, while it had no effect in females (p < 0.05). Leucine had no effect on regulators of protein balance and myogenesis in either sex. We demonstrated that leucine exacerbates moribundity in males and is not sufficient for mitigating muscle or fat loss during CC in either sex in the ApcMin/+ mouse.

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.

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.

Development of skeletal muscle fibrosis in a rodent model of cancer cachexia

Cachexia is characterized by losses in lean body mass and its progression results in worsened quality of life and exacerbated outcomes in cancer patients. However, the role and impact of fibrosis during the early stages and development of cachexia in under-investigated. The purpose of this study was to determine if fibrosis occurs during cachexia development, and to evaluate this in both sexes. Female and male C57BL6/J mice were injected with phosphate-buffered saline or Lewis Lung Carcinoma (LLC) at 8-week of age, and tumors were allowed to develop for 1, 2, 3, or 4 weeks. 3wk and 4wk female tumor-bearing mice displayed a dichotomy in tumor growth and were reassigned to high tumor (HT) and low tumor (LT) groups. In vitro analyses were also performed on cocultured C2C12 and 3T3 cells exposed to LLC conditioned media. Immunohistochemistry and quantitative polymerase chain reaction (qPCR) analysis were used to investigate fibrosis and fibrosis-related signaling in skeletal muscle. Collagen deposition in skeletal muscle was increased in the 1wk, LT, and HT groups in female mice. However, collagen deposition was only increased in the 4wk group in male mice. In general, female mice displayed earlier alterations in extracellular matrix (ECM)-related genes beginning at 1wk post-LLC injection. Whereas this was not seen in males. While overall tumor burden is tightly correlated to cachexia development in both sexes, fibrotic development is not. Male mice did not exhibit early-stage alterations in ECM-related genes contrary to what was noted in female mice.

Effects of PGC-1α overexpression on the myogenic response during skeletal muscle regeneration

The ability of skeletal muscle to regenerate from injury is crucial for locomotion, metabolic health, and quality of life. Peroxisome proliferator-activated receptor-γ coactivator-1α (PGC1A) is a transcriptional coactivator required for mitochondrial biogenesis. Increased mitochondrial biogenesis is associated with improved muscle cell differentiation, however PGC1A's role in skeletal muscle regeneration following damage requires further investigation. The purpose of this study was to investigate the role of skeletal muscle-specific PGC1A overexpression during regeneration following damage. 22 C57BL/6J (WT) and 26 PGC1A muscle transgenic (A1) mice were injected with either phosphate-buffered saline (PBS, uninjured control) or Bupivacaine (MAR, injured) into their tibialis anterior (TA) muscle to induce skeletal muscle damage. TA muscles were extracted 3- or 28-days post-injury and analyzed for markers of regenerative myogenesis and protein turnover. Pgc1a mRNA was ∼10–20 fold greater in A1 mice. Markers of protein synthesis, AKT and 4EBP1, displayed decreases in A1 mice compared to WT at both timepoints indicating a decreased protein synthetic response. Myod mRNA was ∼75% lower compared to WT 3 days post-injection. WT mice exhibited decreased cross-sectional area of the TA muscle at 28 days post-injection with bupivacaine compared to all other groups. PGC1A overexpression modifies the myogenic response during regeneration.

PGC-1α overexpression is not sufficient to mitigate cancer cachexia in either male or female mice

Cancer-cachexia accounts for 20-40% of cancer-related deaths. Mitochondrial aberrations have been shown to precede muscle atrophy in different atrophy models, including cancer. Therefore, this study investigated potential protection from the cachectic phenotype through overexpression of PGC-1α. First, to establish potential of mitochondria-based approaches we showed that the mitochondrial antioxidant mitoTEMPO attenuates myotube atrophy induced by Lewis Lung Carcinoma (LLC) cell conditioned media. Next, cachexia was induced in muscle specific PGC-1α overexpressing (MCK-PCG1α) or wildtype (WT) littermate mice by LLC implantation. MCK-PCG1α did not protect LLC-induced muscle mass loss. In plantaris, Atrogin mRNA content was 6.2-fold and ~11-fold greater in WT-LLC vs. WT-PBS for males and females, respectively (p<0.05). MitoTimer red:green ratio for male PGC was ~65% higher than WT groups (p<0.05), with ~3-fold more red puncta in LLC than PBS (p<0.05). Red:green ratio was ~56% lower in females WT-LLC vs. PGC-LLC (p<0.05). In females, no change in red puncta was noted across conditions. Lc3 mRNA content was ~ 73% and 2-fold higher in male and female LLC mice respectively vs. PBS (p<0.05). While MitoTEMPO could mitigate cancer-induced atrophy in vitro, PGC1α overexpression was insufficient to protect muscle mass and mitochondrial health in vivo despite mitigation of cachexia-associated signaling pathways.

Muscle miR-16 deletion results in impaired insulin sensitivity and contractile function in a sex-dependent manner

microRNAs (miRs) are linked to various human diseases including type 2 diabetes mellitus (T2DM) and emerging evidence suggests that miRs may serve as potential therapeutic targets. Lower miR-16 content is consistent across different models of T2DM; however, the role of miR-16 in muscle metabolic health is still elusive. Therefore, the purpose of this study was to investigate how deletion of miR-16 in mice affects skeletal muscle metabolic health and contractile function in both sexes. This study was conducted using both 1) in vitro and 2) in vivo experiments. In in vitro experiments, we used C2C12 myoblasts to test if inhibition or overexpression of miR-16 affected insulin-mediated glucose handling. In in vivo experiments, we generated muscle-specific miR-16 knockout (KO) mice fed a high-fat diet (HFD) to assess how miR-16 content impacts metabolic and contractile properties including glucose tolerance, insulin sensitivity, muscle contractile function, protein anabolism, and mitochondrial network health. In in vitro experiments, although inhibition of miR-16 induced impaired insulin signaling (P = 0.002) and glucose uptake (P = 0.014), overexpression of miR-16 did not attenuate lipid overload-induced insulin resistance using the diacylglycerol analog 1-oleoyl-2-acetyl-sn-glycerol. In in vivo experiments, miR-16 deletion induced both impaired muscle contractility (P = 0.031-0.033), and mitochondrial network health (P = 0.008-0.018) in both sexes. However, although males specifically exhibited impaired insulin sensitivity following miR-16 deletion (P = 0.030), female KO mice showed pronounced glucose intolerance (P = 0.046), corresponding with lower muscle weights (P = 0.015), and protein hyperanabolism (P = 0.023). Our findings suggest distinct sex differences in muscle adaptation in response to miR-16 deletion and miR-16 may serve as a key regulator for metabolic dysregulation in T2DM.NEW & NOTEWORTHY We set to investigate the role of miR-16 in skeletal muscle during diet-induced insulin resistance. Our data provide novel evidence that the lack of miR-16 induced multiple aberrations in insulin sensitivity, muscle contractility, mitochondrial network health, and protein turnover in a sex-dependent manner. Interestingly, miR-16 deletion leads to insulin resistance in males and exacerbated glucose intolerance in females, suggesting different mechanisms of metabolic dysregulation with a lack of miR-16 between sexes.

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.

Mitochondrial aberrations during the progression of disuse atrophy differentially affect male and female mice

BACKGROUND

Disuse decreases muscle size and is predictive of mortality across multiple pathologies. Detriments to mitochondrial function are hypothesized to underlie disuse-induced muscle atrophy. Little data exist on early mechanisms contributing to onset of these pathologies, nor is it known how they differ between sexes. The purpose of this study was to examine differential and conserved responses to mitochondrial quality control in male and female mice during the development and progression of disuse-induced atrophy.

METHODS

One hundred C57BL/6J mice (50 male and 50 female) were hindlimb unloaded to induce disuse atrophy for 0 (con), 24, 48, 72, or 168 h. At designated time-points, extensor digitorum longus, gastrocnemius, and soleus muscles were collected for analysis of mitochondrial quality control markers.

RESULTS

One hundred sixty-eight hours of disuse resulted in ~25% lower oxidative muscle fibre CSA in both male (P = 0.003) and female (P = 0.02) mice without any differences due to disuse in glycolytic fibres. In male mice, 48 h of unloading was sufficient to result in ~67% greater mitochondrial oxidative stress as assessed by the reporter gene pMitoTimer compared with 0 h (P = 0.002), this mitochondrial stress preceded detectable muscle loss. However in female mice, mitochondrial oxidative stress did not occur until 168 h of disuse (~40% greater mitochondrial oxidative stress in 168 h compared with 0 h of disuse, P < 0.0001). Blunted oxidative stress in female mice appeared to coincide with greater inductions of autophagy and mitophagy in female mice (~3-fold greater BNIP3 and ~6-fold greater LC3II/I ratio P < 0.0001 and P = 0.038 respectively). Male mice overall had greater reactive oxygen species (ROS) production compared with female mice. Female mice had a greater induction of ROS within 24 h of disuse (~4-fold greater compared with 0 h, P < 0.0001); whereas male mice did not have greater ROS production until 168 h of disuse (~2-fold greater, P < 0.0001). Although all muscle types exhibited some alterations to mitochondrial quality control, such as increased markers of mitophagy and fission, the soleus muscle in both male and female mice exhibited consistent alterations to various markers of mitochondrial quality. Markers of mitochondrial translation were approximately 30-50% lower within 24 h of unloading in both male and female soleus muscle (P value ranges: <0.0001-0.03).

CONCLUSIONS

Disuse negatively affects mitochondria differentially between sexes during development of muscle wasting. Acutely, female mice may forgo muscle mass to maintain mitochondrial quality compared with male mice. These differences may contribute to divergent clinical manifestations of atrophy.

The effect of diet-induced obesity on extracellular matrix remodeling during skeletal muscle regeneration

Diet-induced obesity has previously been shown to occur with the concomitant rise in the expression of proinflammatory cytokines and increases in collagen deposition. While it has been known that the regenerative process of skeletal muscle is altered in obese mice following an acute muscle injury, we sought to examine differences in the expression of various markers of extracellular matrix remodeling and repair. Our laboratory has previously reported an impaired inflammatory and protein synthetic signaling in these mice that may contribute negatively to the muscle regenerative process. To expand upon this previous investigation, tissues from these animals underwent further analysis to determine the extent of changes to the regenerative response within the extracellular matrix, including transcriptional changes in Collagen I, Collagen III, and Fibronectin. Here, we show that the expression of Collagen III:I is significantly increased at 3-days post-injury in obese injured animals compared to lean injured animals (p ​= ​0.0338), and by 28-days the obese injured animals exhibit a significantly lower Collagen III:I than their lean injured counterparts (p ​= ​0.0035). We demonstrate an impaired response to an acute muscle injury in obese mice when compared with lean counterparts. However, further studies are required to elucidate translational consequences of these changes, as well as to determine any causative mechanisms that may be driving this effect.

Female mice may have exacerbated catabolic signalling response compared to male mice during development and progression of disuse atrophy

BACKGROUND

Muscle atrophy is a common pathology associated with disuse, such as prolonged bed rest or spaceflight, and is associated with detrimental health outcomes. There is emerging evidence that disuse atrophy may differentially affect males and females. Cellular mechanisms contributing to the development and progression of disuse remain elusive, particularly protein turnover cascades. The purpose of this study was to investigate the initial development and progression of disuse muscle atrophy in male and female mice using the well-established model of hindlimb unloading (HU).

METHODS

One hundred C57BL/6J mice (50 male and 50 female) were hindlimb suspended for 0 (control), 24, 48, 72, or 168 h to induce disuse atrophy (10 animals per group). At designated time points, animals were euthanized, and tissues (extensor digitorum longus, gastrocnemius, and soleus for mRNA analysis, gastrocnemius and extensor digitorum longus for protein synthesis rates, and tibialis anterior for histology) were collected for analysis of protein turnover mechanisms (protein anabolism and catabolism).

RESULTS

Both males and females lost ~30% of tibialis anterior cross-sectional area after 168 h of disuse. Males had no statistical difference in MHCIIB fibre area, whereas unloaded females had ~33% lower MHCIIB cross-sectional area by 168 h of unloading. Both males and females had lower fractional protein synthesis rates (FSRs) within 24-48 h of HU, and females appeared to have a greater reduction compared with males within 24 h of HU (~23% lower FSRs in males vs. 40% lower FSRs in females). Males and females exhibited differential patterns and responses in multiple markers of protein anabolism, catabolism, and myogenic capacity during the development and progression of disuse atrophy. Specifically, females had greater mRNA inductions of catabolic factors Ubc and Gadd45a (~4-fold greater content in females compared with ~2-fold greater content in males) and greater inductions of anabolic inhibitors Redd1 and Deptor with disuse across multiple muscle tissues exhibiting different fibre phenotypes.

CONCLUSIONS

These results suggest that the aetiology of disuse muscle atrophy is more complicated and nuanced than previously thought, with different responses based on muscle phenotypes and between males and females, with females having greater inductions of atrophic markers early in the development of disuse atrophy.

The effect of autologous repair and voluntary wheel running on force recovery in a rat model of volumetric muscle loss

NEW FINDINGS

What is the central question of this study? Following large traumatic loss of muscle tissue (volumetric muscle loss; VML), permanent functional and cosmetic deficits present themselves and regenerative therapies alone have not been able to generate a robust regenerative response: how does the addition of rehabilitative therapies affects the regenerative response? What is the main finding and its importance? Using exercise along with autologous muscle repair, we demonstrated accelerated muscle force recovery response post-VML. The accentuated force recovery 2 weeks post-VML would allow patients to return home sooner than allowed with current therapies.

ABSTRACT

Skeletal muscle can regenerate from damage but is overwhelmed with extreme tissue loss, known as volumetric muscle loss (VML). Patients suffering from VML do not fully recover force output in the affected limb. Recent studies show that replacement tissue (i.e., autograph) into the VML defect site plus physical activity show promise for optimizing force recovery post-VML. The purpose of this study was to measure the effects of autologous repair and voluntary wheel running on force recovery post-VML. Thirty-two male Sprague-Dawley rats had 20% of their left tibialis anterior (LTA) excised then replaced and sutured into the intact muscle (autologous repair). The right tibialis anterior (RTA) acted as the contralateral control. Sixteen rats were given free access to a running wheel (Wheel) whereas the other 16 remained in a cage with the running wheel locked (Sed). At 2 and 8 weeks post-VML, the LTA underwent force testing; then the muscle was removed and morphological and gene expression analysis was conducted. At 2 weeks post-injury, normalized LTA force was 58% greater in the Wheel group compared to the Sed group. At 8 weeks post-VML, LTA force was similar between the Wheel and Sed groups but was still lower than the uninjured RTA. Gene expression analysis at 2 weeks post-VML showed the wheel groups had lower mRNA content of interleukin (IL)-1β, IL-6 and tumour necrosis factor α compared to the Sed group. Overall, voluntary wheel running promoted early force recovery, but was not sufficient to fully restore force. The accentuated early force recovery is possibly due to a more pro-regenerative microenvironment.

Moderators of skeletal muscle maintenance are compromised in sarcopenic obese mice

The purpose of this study was to determine whether sarcopenic obesity accelerates impairments in muscle maintenance through the investigation of cell cycle progression and myogenic, inflammatory, catabolic and protein synthetic signaling in mouse gastrocnemius muscles. At 4 weeks old, 24 male C57BL/6 mice were fed either a high fat diet (HFD, 60 % fat) or normal chow (NC, 17 % fat) for either 8-12 weeks or 21-23 months. At 3-4 months or 22-24 months the gastrocnemius muscles were excised. In addition, plasma was taken for C2C12 differentiation experiments. Mean cross-sectional area (CSA) was reduced by 29 % in aged HFD fed mice compared to the aged NC mice. MyoD was roughly 50 % greater in the aged mice compared to young mice, whereas TNF-α and IGF-1 gene expression in aged HFD fed mice were reduced by 52 % and 65 % in comparison to aged NC fed mice, respectively. Myotubes pretreated with plasma from aged NC fed mice had 14 % smaller myotube diameter than their aged HFD counterparts. Aged obese mice had greater impairments to mediators of muscle maintenance as evident by reductions in muscle mass, CSA, along with alterations in cell cycle regulation and inflammatory and insulin signaling.

Cancer-induced Cardiac Atrophy Adversely Affects Myocardial Redox State and Mitochondrial Oxidative Characteristics

Cachexia presents in 80% of advanced cancer patients; however, cardiac atrophy in cachectic patients receives little attention. This cardiomyopathy contributes to increased occurrence of adverse cardiac events compared to age-matched population norms. Research on cardiac atrophy has focused on remodeling; however, alterations in metabolic properties may be a primary contributor.

PURPOSE

Determine how cancer-induced cardiac atrophy alters mitochondrial turnover, mitochondrial mRNA translation machinery and in-vitro oxidative characteristics.

METHODS

Lewis lung carcinoma (LLC) tumors were implanted in C57BL6/J mice and grown for 28days to induce cardiac atrophy. Endogenous metabolic species, and markers of mitochondrial function were assessed. H9c2 cardiomyocytes were cultured in LLC-conditioned media with(out) the antioxidant MitoTempo. Cells were analyzed for ROS, oxidative capacity, and hypoxic resistance.

RESULTS

LLC heart weights were ~10% lower than controls. LLC hearts demonstrated ~15% lower optical redox ratio (FAD/FAD+NADH) compared to PBS controls. When compared to PBS, LLC hearts showed ~50% greater COX-IV and VDAC, attributed to ~50% lower mitophagy markers. mt-mRNA translation machinery was elevated similarly to markers of mitochondrial content. mitochondrial DNA-encoded Cytb was ~30% lower in LLC hearts. ROS scavengers GPx-3 and GPx-7 were ~50% lower in LLC hearts. Treatment of cardiomyocytes with LLC-conditioned media resulted in higher ROS (25%), lower oxygen consumption rates (10% at basal, 75% at maximal), and greater susceptibility to hypoxia (~25%) -- which was reversed by MitoTempo.

CONCLUSION

These results substantiate metabolic cardiotoxic effects attributable to tumor-associated factors and provide insight into interactions between mitochondrial mRNA translation, ROS mitigation, oxidative capacity and hypoxia resistance.

Mitochondrial Function and Protein Turnover in the Diaphragm are Altered in LLC Tumor Model of Cancer Cachexia

It is established that cancer cachexia causes limb muscle atrophy and is strongly associated with morbidity and mortality; less is known about how the development of cachexia impacts the diaphragm. The purpose of this study was to investigate cellular signaling mechanisms related to mitochondrial function, reactive oxygen species (ROS) production, and protein synthesis during the development of cancer cachexia. C57BL/J6 mice developed Lewis Lung Carcinoma for either 0 weeks (Control), 1 week, 2 weeks, 3 weeks, or 4 weeks. At designated time points, diaphragms were harvested and analyzed. Mitochondrial respiratory control ratio was ~50% lower in experimental groups, which was significant by 2 weeks of cancer development, with no difference in mitochondrial content markers COXIV or VDAC. Compared to the controls, ROS was 4-fold elevated in 2-week animals but then was not different at later time points. Only one antioxidant protein, GPX3, was altered by cancer development (~70% lower in experimental groups). Protein synthesis, measured by a fractional synthesis rate, appeared to become progressively lower with the cancer duration, but the mean difference was not significant. The development and progression of cancer cachexia induces marked alterations to mitochondrial function and ROS production in the diaphragm and may contribute to increased cachexia-associated morbidity and mortality.

Comparative plasma proteomics in muscle atrophy during cancer-cachexia and disuse: The search for atrokines

Skeletal muscle atrophy is common across a variety of pathologies. Underlying mechanisms of atrophy differ between pathologies, and in many conditions, circulating factors are tied to muscle atrophy. Therefore, we sought to identify alterations to the plasma proteome across divergent forms of muscle atrophy, disuse and cancer cachexia, as potential mediators of atrophy. C57BL6/J mice were assigned to Lewis Lung Carcinoma (LLC)-induced cachexia, disuse by hindlimb unloading (HU), or control (CON). Plasma samples were submitted for discovery proteomics and targets of interest confirmed by immunoblot. Considerably more peptides were altered in plasma from LLC (91) than HU (9) as compared to CON. Five total proteins were similarly modulated in HU and LLC compared to CON, none reached criteria for differential expression. Serum Amyloid A1 (SAA) was 4 and 6 Log2 FC greater in LLC than CON or HU, respectively, confirmed by immunoblot. Recent reports suggest SAA is sufficient to induce atrophy via TLR. Therefore, we assessed TLR2,4, and IL-6 mRNAs in hindlimb muscles. TLR mRNAs were not altered, suggesting SAA effects on atrophy during LLC are independent of TLR signaling. However, we noted > 6-fold induction of IL-6 in soleus of HU mice, despite minimal shift in the plasma proteome, indicating potential localized inflammation in atrophying muscle. Furthermore, paraoxonase 1 (PON1) was highly repressed in LLC mice and largely undetectable by immunoblot in this group. Our data suggest SAA and PON1 as potential novel atrokines for cancer cachexia and indicate localized inflammation in atrophying muscles independent of the plasma proteome.

Altering aspects of mitochondrial quality to improve musculoskeletal outcomes in disuse atrophy

Muscle atrophy is a significant moderator for disease prognosis; as such, interventions to mitigate disuse-induced muscle loss are imperative to improve clinical interventions. Mitochondrial deteriorations may underlie disuse-induced myopathies; therefore, improving mitochondrial quality may be an enticing therapeutic intervention. However, different mitochondria-based treatments may have divergent impacts on the prognosis of disuse atrophy. Therefore, the purpose of this study was to investigate different mitochondria-centered interventions during disuse atrophy in hindlimb unloaded male and female mice. Male and female mice overexpressing peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) or mitochondrially targeted catalase (MCAT) and their respective wild-type (WT) littermate controls were hindlimb unloaded for 7 days to induce disuse atrophy or allowed normal ambulatory activity (cage control; CON). After designated interventions, animals were euthanized, and tissues were collected for measures of mitochondrial quality control and protein turnover. Although PGC-1α overexpression mitigated ubiquitin-proteasome activation (MuRF1 and Atrogin mRNA content), this did not correspond to phenotypic protections from disuse-induced atrophy. Rather, PGC-1α mice appeared to have a greater reliance on autophagic protein breakdown compared with WT mice. In MCAT mice, females exhibited a mitigated response to disuse atrophy; however, this effect was not noted in males. Despite these phenotypic differences, there were no clear cellular signaling differences between MCAT hindlimb unloaded females and MCAT fully loaded females. PGC-1α overexpression does not protect against phenotypic alterations during disuse atrophy but appears to shift catabolic pathways moderating atrophy. However, increased mitochondrially targeted catalase activity appears to blunt disuse atrophy within highly oxidative muscles specifically in female mice.NEW & NOTEWORTHY We present data suggesting that mitochondria-based interventions may mitigate disuse atrophy. However, the efficacy of mitochondria-based interventions may vary depending on the specific target of the intervention and the sex of the organism. Females appear to be more responsive to increased mitochondrial catalase as a potential therapeutic for mitigating disuse atrophy.

Neither autophagy nor exercise training mode affect exercise-induced beneficial adaptations in high fat-fed mice

Purpose

Methods

Results

Conclusions

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.

Hepatic alterations during the development and progression of cancer cachexia

Cancer-associated bodyweight loss (cachexia) is a hallmark of many cancers and is associated with decreased quality of life and increased mortality. Hepatic function can dramatically influence whole-body energy expenditure and may therefore significantly influence whole-body health during cancer progression. The purpose of this study was to examine alterations in markers of hepatic metabolism and physiology during cachexia progression. Male C57BL/6J mice were injected with 1 × 10⁶ Lewis Lung Carcinoma cells dissolved in 100 μL PBS and cancer was allowed to develop for 1, 2, 3, or 4 weeks. Control animals were injected with an equal volume of phosphate-buffered saline. Livers were analyzed for measures of metabolism, collagen deposition, protein turnover, and mitochondrial quality. Animals at 4 weeks had ∼30% larger livers compared with all other groups. Cancer progression was associated with altered regulators of fat metabolism. Additionally, longer duration of cancer development was associated with ∼3-fold increased regulators of collagen deposition as well as phenotypic collagen content, suggesting increased liver fibrosis. Mitochondrial quality control regulators appeared to be altered before any phenotypic alterations to collagen deposition. While induction of Akt was noted, downstream markers of protein synthesis were not altered. In conclusions, cancer cachexia progression is associated with hepatic pathologies, specifically liver fibrosis. Alterations to mitochondrial quality control mechanisms appear to precede this fibrotic phenotype, potentially suggesting mitochondrial mechanisms for the development of hepatic pathologies during the development and progression of cancer cachexia. Novelty Cachexia progression results in liver collagen deposition and fibrosis. Alterations in mitochondrial quality control may precede liver pathologies during cachexia.

Regulation of mitochondrial quality following repeated bouts of hindlimb unloading

Muscle disuse impairs muscle quality and is associated with increased mortality. Little is known regarding additive effects of multiple bouts of disuse, which is a common occurrence in patients experiencing multiple surgeries. Mitochondrial quality is vital to muscle health and quality; however, to date mitochondrial quality control has not been investigated following multiple bouts of disuse. Therefore, the purpose of this study was to investigate mitochondrial quality controllers during multiple bouts of disuse by hindlimb unloading. Male rats (n ∼ 8/group) were assigned to the following groups: hindlimb unloading for 28 days, hindlimb unloading with 56 days of reloading, 2 bouts of hindlimb unloading separated by a recovery phase of 56 days of reloading, 2 bouts of hindlimb unloading and recovery after each disuse, or control animals with no unloading. At designated time points, tissues were collected for messenger RNA and protein analysis of mitochondrial quality. Measures of mitochondrial biogenesis, such as proliferator-activated receptor gamma coactivator 1 alpha, decreased 30%-40% with unloading with no differences noted between unloading conditions. Measures of mitochondrial translation were 40%-50% lower in unloading conditions, with no differences noted between bouts of unloading. Measures of mitophagy were 40%-50% lower with reloading, with no differences noted between reloading conditions. In conclusion, disuse causes alterations in measures of mitochondrial quality; however, multiple bouts of disuse does not appear to have additive effects. Novelty Disuse atrophy causes multiple alterations to mitochondrial quality control. With sufficient recovery most detriments to mitochondrial quality control are fixed. In general, multiple bouts of disuse do not produce additive effects.

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

Cancer-cachexia (CC) is a wasting condition directly responsible for 20-40% of cancer-related deaths. The mechanisms controlling development of CC-induced muscle wasting are not fully elucidated. Most investigations focus on the postcachectic state and do not examine progression of the condition. We recently demonstrated mitochondrial degenerations precede muscle wasting in time course progression of CC. However, the extent of muscle perturbations before wasting in CC is unknown. Therefore, we performed global gene expression analysis in CC-induced muscle wasting to enhance understanding of intramuscular perturbations across the development of CC. Lewis lung carcinoma (LLC) was injected into the hind-flank of C57BL6/J mice at 8 wk of age with tumor allowed to develop for 1, 2, 3, or 4 wk and compared with PBS-injected control. Muscle wasting was evident at 4 wk LLC. RNA sequencing of gastrocnemius muscle samples showed widespread alterations in LLC compared with PBS animals with largest differences seen in 4 wk LLC, suggesting extensive transcriptomic alterations concurrent to muscle wasting. Commonly altered pathways included: mitochondrial dysfunction and protein ubiquitination, along with other less studied processes in this condition regulating transcription/translation and cytoskeletal structure. Current findings present novel evidence of transcriptomic shifts and altered cellular pathways in CC-induced muscle wasting.

Protein imbalance in the development of skeletal muscle wasting in tumour-bearing mice

BACKGROUND

Cancer cachexia occurs in approximately 80% of cancer patients and is a key contributor to cancer-related death. The mechanisms controlling development of tumour-induced muscle wasting are not fully elucidated. Specifically, the progression and development of cancer cachexia are underexplored. Therefore, we examined skeletal muscle protein turnover throughout the development of cancer cachexia in tumour-bearing mice.

METHODS

Lewis lung carcinoma (LLC) was injected into the hind flank of C57BL6/J mice at 8 weeks age with tumour allowed to develop for 1, 2, 3, or 4 weeks and compared with PBS injected control. Muscle size was measured by cross-sectional area analysis of haematoxylin and eosin stained tibialis anterior muscle. ² H₂ O was used to assess protein synthesis throughout the development of cancer cachexia. Immunoblot and RT-qPCR were used to measure regulators of protein turnover. TUNEL staining was utilized to measure apoptotic nuclei. LLC conditioned media (LCM) treatment of C2C12 myotubes was used to analyse cancer cachexia in vitro.

RESULTS

Muscle cross-sectional area decreased ~40% 4 weeks following tumour implantation. Myogenic signalling was suppressed in tumour-bearing mice as soon as 1 week following tumour implantation, including lower mRNA contents of Pax7, MyoD, CyclinD1, and Myogenin, when compared with control animals. AchRδ and AchRε mRNA contents were down-regulated by ~50% 3 weeks following tumour implantation. Mixed fractional synthesis rate protein synthesis was ~40% lower in 4 week tumour-bearing mice when compared with PBS controls. Protein ubiquitination was elevated by ~50% 4 weeks after tumour implantation. Moreover, there was an increase in autophagy machinery after 4 weeks of tumour growth. Finally, ERK and p38 MAPK phosphorylations were fourfold and threefold greater than control muscle 4 weeks following tumour implantation, respectively. Inhibition of p38 MAPK, but not ERK MAPK, in vitro partially rescued LCM-induced loss of myotube diameter.

CONCLUSIONS

Our findings work towards understanding the pathophysiological signalling in skeletal muscle in the initial development of cancer cachexia. Shortly following the onset of the tumour-bearing state alterations in myogenic regulatory factors are apparent, suggesting early onset alterations in the capacity for myogenic induction. Cancer cachexia presents with a combination of a loss of protein synthesis and increased markers of protein breakdown, specifically in the ubiquitin-proteasome system. Also, p38 MAPK may be a potential therapeutic target to combat cancer cachexia via a p38-FOX01-atrogene-ubiquitin-proteasome mechanism.

Skeletal Muscle Insulin Resistance as a Precursor to Diabetes: Beyond Glucoregulation

BACKGROUND

Prevalence of Type 2 Diabetes Mellitus (T2DM) has reached pandemic levels in the Western societies. T2DM begins with the development of peripheral insulin resistance which prior research suggests may commonly originate within the skeletal muscle. A number of mechanisms have been proposed for the development of muscle insulin resistance including those of classical glucose handling, and also other cellular derangements observed in this disease which include mitochondrial degeneration, alterations in muscle protein turnover and early evidences for dysregulation of the microRNAs. The purpose of the current review is to examine the current findings on these latter aspects of mitochondrial maintenance, protein turnover and microRNA dysregulation along with the potential implications for these derangements in the development of insulin resistance and hence T2DM. We summarize multiple evidences for the degeneration of mitochondria and known elements of the processes regulating mitochondrial quality. Subsequently, we examine current findings of the alterations in muscle protein synthesis and autophagic protein degradation in T2DM and potential feedback of these systems onto canonical insulin signaling. Finally, evidences have emerged for the dysregulation of microRNAs in muscle insulin resistance. Of note early data point to several microRNAs altered by the insulin resistant state which exhibit relations to classic insulin signaling and the other processes discussed here.

CONCLUSION

Considering that T2DM may be initiated with muscle insulin resistance, improved understanding of the dysregulation of these metabolic parameters of skeletal muscle in the pathogenesis of T2DM may be key to developing efficacious therapeutic modalities to prevent and treat this condition.

Mitochondrial degeneration precedes the development of muscle atrophy in progression of cancer cachexia in tumour-bearing mice

BACKGROUND

Cancer cachexia is largely irreversible, at least via nutritional means, and responsible for 20-40% of cancer-related deaths. Therefore, preventive measures are of primary importance; however, little is known about muscle perturbations prior to onset of cachexia. Cancer cachexia is associated with mitochondrial degeneration; yet, it remains to be determined if mitochondrial degeneration precedes muscle wasting in cancer cachexia. Therefore, our purpose was to determine if mitochondrial degeneration precedes cancer-induced muscle wasting in tumour-bearing mice.

METHODS

First, weight-stable (MinStable) and cachectic (MinCC) Apc^Min/+ mice were compared with C57Bl6/J controls for mRNA contents of mitochondrial quality regulators in quadriceps muscle. Next, Lewis lung carcinoma (LLC) cells or PBS (control) were injected into the hind flank of C57Bl6/J mice at 8 week age, and tumour allowed to develop for 1, 2, 3, or 4 weeks to examine time course of cachectic development. Succinate dehydrogenase stain was used to measure oxidative phenotype in tibialis anterior muscle. Mitochondrial quality and function were assessed using the reporter MitoTimer by transfection to flexor digitorum brevis and mitochondrial function/ROS emission in permeabilized adult myofibres from plantaris. RT-qPCR and immunoblot measured the expression of mitochondrial quality control and antioxidant proteins. Data were analysed by one-way ANOVA with Student-Newman-Kuels post hoc test.

RESULTS

MinStable mice displayed ~50% lower Pgc-1α, Pparα, and Mfn2 compared with C57Bl6/J controls, whereas MinCC exhibited 10-fold greater Bnip3 content compared with C57Bl6/J controls. In LLC, cachectic muscle loss was evident only at 4 weeks post-tumour implantation. Oxidative capacity and mitochondrial content decreased by ~40% 4 weeks post-tumour implantation. Mitochondrial function decreased by ~25% by 3 weeks after tumour implantation. Mitochondrial degeneration was evident by 2 week LLC compared with PBS control, indicated by MitoTimer red/green ratio and number of pure red puncta. Mitochondrial ROS production was elevated by ~50 to ~100% when compared with PBS at 1-3 weeks post-tumour implantation. Mitochondrial quality control was dysregulated throughout the progression of cancer cachexia in tumour-bearing mice. In contrast, antioxidant proteins were not altered in cachectic muscle wasting.

CONCLUSIONS

Functional mitochondrial degeneration is evident in LLC tumour-bearing mice prior to muscle atrophy. Contents of mitochondrial quality regulators across Apc^Min/+ and LLC mice suggest impaired mitochondrial quality control as a commonality among pre-clinical models of cancer cachexia. Our data provide novel evidence for impaired mitochondrial health prior to cachectic muscle loss and provide a potential therapeutic target to prevent cancer cachexia.

Autophagy activation, not peroxisome proliferator-activated receptor γ coactivator 1α, may mediate exercise-induced improvements in glucose handling during diet-induced obesity

NEW FINDINGS

What is the central question of this study? What are the individual and combined effects of muscle-specific peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) overexpression and physical activity during high-fat feeding on glucose and exercise tolerance? What is the main finding and its importance? Our main finding is that muscle-specific PGC-1α overexpression provides no protection against lipid-overload pathologies nor does it enhance exercise adaptations. Instead, physical activity, regardless of PGC-1α content, protects against high-fat diet-induced detriments. Activation of muscle autophagy was correlated with exercise protection, suggesting that autophagy might be a mediating factor for exercise-induced protection from lipid overload. The prevalence of glucose intolerance is alarmingly high. Efforts to promote mitochondrial biogenesis through peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) to mitigate glucose intolerance have been controversial. However, physical activity remains a primary means to alleviate the condition. The aim of this study was to determine the combined effects of muscle-specific overexpression of PGC-1α and physical activity on glucose handling during diet-induced obesity. Wild-type (WT, ∼20) and PGC-1α muscle transgenic (MCK-PGC-1α, ∼20) mice were given a Western diet (WD) at 8 weeks age and allowed to consume food ab libitum throughout the study. At 12 weeks of age, all animals were divided into sedentary (SED) or voluntary wheel running (VWR) interventions. At 7, 11 and 15 weeks of age, animals underwent glucose tolerance tests (GTT) and graded exercise tests (GXT). At 16 weeks of age, tissues were collected. At 11 weeks, the MCK-PGC-1α animals had 50% greater glucose tolerance integrated area under the curve compared with WT. However, at 15 weeks, SED animals also had greater GTT integrated area under the curve compared with VWR, regardless of genotype; furthermore, SED animals demonstrated reduced exercise capacity compared with earlier time points, which was not seen in VWR animals. Voluntary distance run per day was correlated with GTT in VWR-WT, but not VWR-MCK-PGC-1α mice. Voluntary wheel running and genotype independently resulted in a greater LC3II/LC3I ratio, suggesting enhanced autophagosome formation, which was correlated with exercise-induced improvements in GTT. In conclusion, artificially increasing mitochondrial content does not protect from lipid-induced pathologies nor does it augment exercise adaptations. Physical activity ameliorates the effects of lipid overload-induced glucose intolerance, an effect that appears to be related to enhanced activation of autophagy.