mTORC1 and BMP-Smad1/5 Regulation of Serum-Stimulated Myotube Hypertrophy: A Role for Autophagy

Protein synthesis regulation is critical for skeletal muscle hypertrophy; yet, other established cellular processes are necessary for growth-related cellular remodeling. Autophagy has a well-acknowledged role in muscle quality control, but evidence for its role in myofiber hypertrophy remains equivocal. Both mTORC1 and BMP-Smad1/5 signaling are reported regulators of myofiber hypertrophy; however, gaps remain in our understanding of how this regulation is integrated with the growth processes and autophagy regulation. Therefore, we investigated the mTORC1 and Smad1/5 regulation of protein synthesis and autophagy flux during serum-stimulated myotube growth. Chronic serum stimulation experiments were performed on day-5 differentiated C2C12 myotubes incubated in differentiation media (2%HS) or growth media (5%FBS) for 48 hours. Rapamycin or LDN193189 were dosed for 48 hours to inhibit mTORC1 and BMP-Smad1/5 signaling, respectively. Acute serum stimulation was examined in day-7 differentiated myotubes. Protein synthesis was measured by puromycin incorporation. Bafilomycin A1 and immunoblotting for LC3B were used to assess autophagy flux. Chronic serum stimulation increased myotube diameter 22%, total protein 21%, total RNA 100%, Smad1/5 phosphorylation 404%, and suppressed autophagy flux. Rapamycin, but not LDN193189, blocked serum-induced myotube hypertrophy and the increase in total RNA. Acute serum stimulation increased protein synthesis 111%, Smad1/5 phosphorylation 559%, rpS6 phosphorylation 117%, and suppressed autophagy flux. Rapamycin increased autophagy flux during acute serum stimulation. These results provide evidence for mTORC1, but not BMP-Smad1/5 signaling, being required for serum-induced myotube hypertrophy and autophagy flux by measuring LC3BII/I expression. Further investigation is warranted to examine the role of autophagy flux in myotube hypertrophy.

Mouse skeletal muscle adaptations to different durations of treadmill exercise after the cessation of FOLFOX chemotherapy

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

Recovery from FOLFOX Chemotherapy-induced Systemic and Skeletal Muscle Metabolic Dysfunction in Mice

FOLFOX (5-fluorouracil, leucovorin, oxaliplatin) chemotherapy is used to treat colorectal cancer and can acutely induce metabolic dysfunction. However, the lasting effects on systemic and skeletal muscle metabolism after treatment cessation are poorly understood. Therefore, we investigated the acute and lasting effects of FOLFOX chemotherapy on systemic and skeletal muscle metabolism in mice. Direct effects of FOLFOX in cultured myotubes were also investigated. Male C57BL/6J mice completed four cycles (acute) of FOLFOX or PBS. Subsets were allowed to recover for 4-wks or 10-wks. CLAMS metabolic measurements were performed for 5-days prior to study endpoint. C2C12 myotubes were treated with FOLFOX for 24-hrs. Acute FOLFOX attenuated body mass and body fat accretion independent of food intake or cage activity. Acute FOLFOX decreased blood glucose, oxygen consumption (VO2), carbon dioxide production (VCO2), energy expenditure, and carbohydrate (CHO) oxidation. Deficits in VO2 and energy expenditure remained at 10-wks. CHO oxidation remained disrupted at 4-wks but returned to control levels after 10-wks. Acute FOLFOX reduced muscle COXIV enzyme activity, AMPK(T172), ULK1(S555), and LC3BII protein expression. Muscle LC3BII/I ratio was associated with altered CHO oxidation (r=0.75, p=0.03). In vitro, FOLFOX suppressed myotube AMPK(T172), ULK1(S555), and autophagy flux. Recovery for 4-wks normalized skeletal muscle AMPK and ULK1 phosphorylation. Our results provide evidence that FOLFOX disrupts systemic metabolism, which is not readily recoverable after treatment cessation. FOLFOX effects on skeletal muscle metabolic signaling did recover. Further investigations are warranted to prevent and treat FOLFOX-induced metabolic toxicities that negatively impact cancer patient survival and life quality.

Abstract 360: Changes in adipose tissue microenvironment occurs early in murine models of pancreatic cancer cachexia

Cachexia is the unintentional loss of skeletal muscle and adipose tissue. Over 80% of patients with pancreatic adenocarcinoma cancer (PDAC) suffer from cachexia, resulting in reduced survival and quality of life. The magnitude of adipose loss is often greater than muscle loss in patients and animal models. Our prior work in a mouse model of orthotopic PDAC cachexia revealed alterations of multiple pathways in adipose, predominantly inflammation, cytokine signaling, and metabolism. Deconvolution analysis predicts immune cell infiltration and activation. Inflammation-stimulated lipolysis results in fat pad wasting, while the resulting myosteatosis promotes skeletal muscle catabolism. Given this essential role for fat loss in the pathophysiology of cancer cachexia, we aimed to characterize the adipose tissue microenvironment in early and late PDAC cachexia.

Methods: Male C57BL/6J (N=30) mice underwent orthotopic injection of KPC32098 pancreatic cancer cells derived from the LSL-KrasG12D:LSL-Trp53R172H:Pdx1-Cre mouse model or sham surgery. Body composition was determined by serial EchoMRI. Tissues were harvested every three days starting on day 6 after injection until euthanasia on day 18. Bulk RNA sequencing of the entire epididymal fat pad was performed. Single nucleus RNA sequencing of pooled sham (n=4) and pooled day 12 KPC (n=4) epididymal WAT nuclei was performed to identify changes in the adipose tissue microenvironment during cachexia development.

Results: Tumors were palpable on day 9 and increased in size from day 12 (0.612 ± 0.092g) to day 18 (1.79 ± 0.309g, P<0.05). Total body fat loss was evident as early as day 9 (P < 0.001), although epididymal and inguinal white adipose tissues (WAT) were consistently reduced only at days 15 (P=0 and 18. Intrascapular brown adipose tissue (BAT) was reduced by day 18. Histology of skin biopsies showed subcutaneous adipose was reduced by day 12 and absent by day 18, with no difference in epidermis, dermis, or muscle layer thickness. Bulk RNAseq of epididymal WAT in late PDAC cachexia suggested de-differentiation but not browning, including reduced expression of pro-WAT genes Sfrp5, Slc2a4, and Fasn as well as increased expression of the anti-WAT marker Vdr. PPARg targets and other pro-BAT markers trended lower in expression. Early analysis of the snRNAseq data revealed cells positive for Krt18 and Pdx1 in KPC but not sham samples, suggesting that tumor cells are present in the epididymal WAT.

Conclusions: Loss of percentage body fat precedes detectable wasting of individual fat pads in this model of PDAC cachexia. Subcutaneous adipose wasting contributes to this generalized loss of adiposity. Gene expression in late cachexia in orthotopic PDAC suggests de-differentiation but not browning of WAT. Visceral WAT represents a site of tumor micrometastasis, whether as an artifact of the experimental system or as a genuine pathophysiological mechanism.

Citation Format: Sephora Jean, Brittany R. Counts, Anne E. Gowan, Samuel A. Philleo, Sha Cao, Leonidas Koniaris, Teresa A. Zimmers. Changes in adipose tissue microenvironment occurs early in murine models of pancreatic cancer cachexia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 360.

Abstract A062: Skeletal Muscle Selective Autophagy Receptors are induced PDAC Cachexia

Cancer-induced cachexia is a hypermetabolic condition characterized by the unintentional wasting of muscle and adipose tissue, affecting over 80% of patients with pancreatic ductal adenocarcinoma (PDAC). Muscle wasting during cachexia is due to increased skeletal muscle protein degradation via ubiquitin-proteasome and autophagy-lysosome pathways. Autophagy-lysosome degradation requires delivery of cargo to the lysosome for destruction and recycling. Macroautophagy is the most prevalent component of autophagy, encompassing bulk and selective autophagy, and it requires the de novo synthesis of an autophagosome. Bulk autophagy randomly engulfs portions of the cytoplasm. Selective autophagy is mediated through selective autophagy receptors (SAR), which bind and couple cargo to the autophagosome via the general autophagy ligands LC3B and GABARAP. While an increase in the general autophagy machinery is well described in cachectic muscle, much less is known about how complexes and organelles are selectively targeted for degradation. Methods: Here, 12-week-old male C57BL/6J mice were orthotopically implanted with 1x105 KPC cells; controls underwent sham surgery. Half of the tumor-bearing mice were treated with 120 mg/kg gemcitabine and 10 mg/kg nab-paclitaxel (GemNP) at 4 and 10 days. For endpoint analysis, mice were euthanized at 14 days when KPC mice had significant body weight, muscle mass and muscle protein loss compared to SHAM controls. In our in vitro model of PDAC cachexia, KPC-conditioned media (CM) induces C2C12 myotube wasting; thus, myotubes were treated with 50% KPC-CM or control for 48hrs. Results: GemNP reduced end tumor mass by nearly 25% and prevented body weight and muscle loss. mRNAseq of gastrocnemius muscle demonstrated induction of ribosomal component gene expression, while deep proteomics revealed reduction of 30 ribosomal component proteins in KPC mice, consistent with ongoing destruction of ribosomes. Gene expression of general autophagy ligands, LC3B (2.9-fold) and GABARAP (1.6-fold), were increased in KPC mice. Gene expression for SARs associated with ribophagy (NUFIP1, 2.6-fold) and reticulophagy (Fam134b, 11.3-fold) were increased in KPC. FAM134b protein (1.8-fold) was also increased in KPC mice. SARs for lipophagy (PNPLA2, 3.2- and PNPLA8, 1.8-fold) and mitophagy (BNIP3, 4.5-fold) were induced in KPC versus SHAM, while SARs for glycophagy and ferritinophagy were similar. SQSTM1 (3.9-fold) and NBR1 (1.9-fold), general SARs for multiple organelles including aggrephagy, lysophagy, proteaphagy and pexophagy, were increased in KPC. This activation of SARs was due to tumor-induced wasting and not chemotherapy as SAR gene expression in KPC-GemNP mice was similar to SHAM controls. Finally, we also observe markers of SAR-mediated autophagy in our in vitro model of PDAC cachexia. Conclusion: These data indicate that muscle wasting in PDAC cachexia is through activation of selective autophagy of ribosomes, mitochondria, lipid droplets, endoplasmic reticulum, protein aggregates, lysosomes, peroxisomes, and proteasomes.

Citation Format: Brittany R. Counts, Ashok Narasimhan, Tara S. Umberger, Emma H. Doud, Amber L. Mosley, Teresa A. Zimmers. Skeletal Muscle Selective Autophagy Receptors are induced PDAC Cachexia [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr A062.

Short duration treadmill exercise improves physical function and skeletal muscle mitochondria protein expression after recovery from FOLFOX chemotherapy in male mice

FOLFOX (5-FU, leucovorin, oxaliplatin) is a chemotherapy treatment for colorectal cancer which induces toxic side effects involving fatigue, weakness, and skeletal muscle dysfunction. There is a limited understanding of the recovery from these toxicities after treatment cessation. Exercise training can improve chemotherapy-related toxicities. However, how exercise accelerates recovery and the dose required for these benefits are not well examined. The purpose of this study was to examine the effect of exercise duration on physical function, muscle mass, and mitochondria protein expression during the recovery from FOLFOX chemotherapy. 12-week-old male mice were administered four cycles of either PBS or FOLFOX over 8-weeks. Outcomes were assessed after the fourth cycle and after either 4 (short-term; STR) or 10 weeks (long-term; LTR) recovery. Subsets of mice performed 14 sessions (6 d/wk, 18 m/min, 5% grade) of 60 min/d (long) or 15 min/d (short duration) treadmill exercise during STR. Red and white gastrocnemius mRNA and protein expression were examined. FOLFOX treatment decreased run time (RT) (-53%) and grip strength (GS) (-9%) compared to PBS. FOLFOX also reduced muscle OXPHOS complexes, COXIV, and VDAC protein expression. At LTR, FOLFOX RT (-36%) and GS (-16%) remained reduced. Long- and short-duration treadmill exercise improved RT (+58% and +56%) without restoring GS in FOLFOX mice. Both exercise durations increased muscle VDAC and COXIV expression in FOLFOX mice. These data provide evidence that FOLFOX chemotherapy induces persistent deficits in physical function that can be partially reversed by short-duration aerobic exercise.

Response to immune checkpoint blockade improved in pre-clinical model of breast cancer after bariatric surgery

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

As the number of people classified as obese rises globally, so do obesity-related health risks. Studies show that people diagnosed with obesity have inflammation that contributes to tumor growth and their immune system is worse at detecting cancer cells. But weight loss is not currently used as a strategy for preventing or treating cancer.

Surgical procedures for weight loss, also known as ‘bariatric surgeries’, are becoming increasingly popular. Recent studies have shown that individuals who lose weight after these treatments have a reduced risk of developing tumors. But how bariatric surgery directly impacts cancer progression has not been well studied: does it slow tumor growth or boost the anti-tumor immune response?

To answer these questions, Sipe et al. compared breast tumor growth in groups of laboratory mice that were obese due to being fed a high fat diet. The first group of mice lost weight after undergoing a bariatric surgery in which part of their stomach was removed. The second lost the same amount of weight but after receiving a restricted diet, and the third underwent a fake surgery and did not lose any weight. The experiments found that surgical weight loss cuts breast cancer tumor growth in half compared with obese mice. But mice who lost the same amount of weight through dietary restrictions had even less tumor growth than surgically treated mice.

The surgically treated mice who lost weight had more inflammation than mice in the two other groups, and had increased amounts of proteins and cells that block the immune response to tumors. Giving the surgically treated mice a drug that enhances the immune system’s ability to detect and destroy cancer cells reduced inflammation and helped shrink the mice’s tumors. Finally, Sipe et al. identified 54 genes which were turned on or off after bariatric surgery in both mice and humans, 11 of which were linked with tumor size.

These findings provide crucial new information about how bariatric surgery can impact cancer progression. Future studies could potentially use the conserved genes identified by Sipe et al. to develop new ways to stimulate the anti-cancer benefits of weight loss without surgery.

PKC agonism restricts innate immune suppression, promotes antigen cross-presentation and synergizes with agonistic CD40 antibody therapy to activate CD8+ T cells in breast cancer

Myeloid-derived suppressor cells (MDSCs) are an immature innate cell population that expands in pathological conditions such as cancer and suppresses T cells via production of immunosuppressive factors. Conversely, efficient cytotoxic T cell priming is dependent on the ability of antigen-presenting cells (APCs) to cross-present tumor antigens to CD8⁺ T cells, a process that requires a specific subtype of dendritic cells (DCs) called conventional DC1 (cDC1) which are often dysfunctional in cancer. One way to activate cDC1 is ligation of CD40 which is abundantly expressed by myeloid cells and its agonism leads to myeloid cell activation. Thus, targeting MDSCs while simultaneously expanding cross-presenting DCs represents a promising strategy that, when combined with agonistic CD40, may result in long-lasting protective immunity. In this study, we investigated the effect of PKC agonists PEP005 and prostratin on MDSC expansion, differentiation, and recruitment to the tumor microenvironment. Our findings demonstrate that PKC agonists decreased MDSC expansion from hematopoietic progenitors and induced M-MDSC differentiation to an APC-like phenotype that expresses cDC1-related markers via activation of the p38 mitogen-activated protein kinase (MAPK) pathway. Simultaneously, PKC agonists favored cDC1 expansion at the expense of cDC2 and plasmacytoid DCs (pDC). Functionally, PKC agonists blunted MDSC suppressive activity and enhanced MDSC cross-priming capacity both in vitro and in vivo. Finally, combination of PKC agonism with agonistic CD40 mAb resulted in a marked reduction in tumor growth with a significant increase in intratumoral activated CD8⁺ T cells and tissue-resident memory CD8⁺ T cells in a syngeneic breast cancer mouse model. In sum, this work proposes a novel promising strategy to simultaneously target MDSCs and promote APC function that may have highly impactful clinical relevance in cancer patients.

Early-Onset Physical Inactivity and Metabolic Dysfunction in Tumor-bearing Mice Is Associated with Accelerated Cachexia

METHODS

Male C57BL/6J mice (12 wk of age) were injected with 1 × 106 LLC cells or phosphate-buffered saline (PBS) subcutaneously in the right flank, and tissue was collected 26-28 d after cell injection. Tumor volume was measured every 5 d throughout the study to calculate the tumor growth rate. Fifteen days after tumor inoculation, a subset of PBS (n = 11) and LLC (n = 16) mice were individually housed in metabolic Comprehensive Laboratory Animal Monitoring System cages for 5 d.

RESULTS

LLC mice exhibited greater body weight loss (-5.1%), decreased muscle mass (-7%), decreased fat mass (-22%), and increased plasma interleukin-6 (212%) compared with PBS mice. Before the onset of cachexia, total cage activity was decreased in tumor-bearing mice. Cage activity was negatively associated with tumor mass and positively associated with hindlimb muscle mass. In addition, LLC mice had greater lipid oxidation than PBS mice.

CONCLUSIONS

LLC mice exhibit early-onset physical inactivity and altered systemic lipid oxidation, which are associated with the eventual development of cachexia.

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.

The Effect of Wheel Exercise on Functional Indices of Cachexia in Tumor-bearing Mice

INTRODUCTION

Cancer-related fatigue and muscle wasting have received significant attention over the last few decades with the goal of establishing interventions that can improve cancer patient life quality and survival. Increased physical activity has shown to reduce cancer-associated fatigue and has been proposed as a promising therapeutic to attenuate cancer-induced wasting. However, significant gaps remain in our understanding of how physical activity affects the compositional and functional changes that initiate muscle wasting. The purpose of the current study was to determine the effect of wheel exercise on body composition and functional indices of cancer cachexia before the development of significant wasting.

METHODS

Thirteen-week-old male Apc (MIN) and C57BL/6 (B6) mice were given free wheel access (W) or a locked wheel (Sed) for 5 wk.

RESULTS

Wheel activity was reduced in the MIN compared with B6; however, wheel access increased complex II expression in isolated skeletal muscle mitochondria regardless of genotype. Wheel access had no effect on tumor burden or plasma interleukin-6 in the MIN. MIN-W increased body weight and lean mass compared with MIN-Sed, and there was a direct correlation between wheel distance and lean mass change. MIN-W increased grip strength and treadmill time to fatigue compared with MIN-Sed. Within MIN-W mice, skeletal muscle fatigability was only improved in high runners (>60 min·d).

CONCLUSIONS

Our results suggest that there were therapeutic benefits of increased activity related to body composition, behavior, and whole-body function that were not dependent on exercise duration; however, there was an exercise threshold needed to improve skeletal muscle fatigability in tumor-bearing mice. Interestingly, wheel access was able to improve compositional and functional outcomes without mitigating tumor number or size.

Validity of the Handheld Doppler to Determine Lower-Limb Blood Flow Restriction Pressure for Exercise Protocols

Laurentino, GC, Loenneke, JP, Mouser, JG, Buckner, SL, Counts, BR, Dankel, SJ, Jessee, MB, Mattocks, KT, Iared, W, Tavares, LD, Teixeira, EL, and Tricoli, V. Validity of the handheld Doppler to determine lower-limb blood flow restriction pressure for exercise protocols. J Strength Cond Res 34(9): 2693-2696, 2020-Handheld (HH) Doppler is frequently used for determining the arterial occlusion pressure during blood flow restriction exercises; however, it is unknown whether the blood flow is occluded when the auscultatory signal is no longer present. The purpose of this study was to assess the validity between the HH Doppler and the Doppler ultrasound (US) measurements for determining the arterial occlusion pressure in healthy men. Thirty-five participants underwent 2 arterial occlusion pressure measurements. In the first measure, a pressure cuff (17.5 cm wide) was placed at the most proximal region of the thigh and the pulse of posterior tibial artery was detected using an HH Doppler probe. The cuff was inflated until the auscultatory pulse was no longer detected. After 10 minutes of rest, the procedure was repeated with the Doppler US probe placed on the superficial femoral artery. The cuff was inflated up to the point at which the femoral arterial blood flow was interrupted. The point at which the auscultatory pulse and blood flow were no longer detected was deemed the arterial occlusion pressure. There were no significant differences in arterial occlusion pressure level between the HH Doppler and the Doppler US (133 [±18] vs. 135 [±17] mm Hg, p = 0.168). There was a significant correlation (r = 0.938, p = 0.168), reasonable agreement, and a total error of the estimate of 6.0 mm Hg between measurements. Arterial occlusion pressure level determined by the HH Doppler and the Doppler US was similar, providing evidence that the HH Doppler is a valid and practical method.

Cachexia Disrupts Diurnal Regulation of Activity, Feeding, and Muscle Mechanistic Target of Rapamycin Complex 1 in Mice

INTRODUCTION

Cancer cachexia is characterized by severe skeletal muscle mass loss, which is driven by decreased muscle protein synthesis and increased protein degradation. Daily physical activity and feeding behaviors exhibit diurnal fluctuations in mice that can impact the systemic environment and skeletal muscle signaling.

PURPOSE

We investigated the effect of cancer cachexia on the diurnal regulation of feeding, physical activity, and skeletal muscle mechanistic target of rapamycin complex 1 (mTORC1) signaling in tumor-bearing mice. We also examined the impact of increased physical activity on diurnal behaviors and skeletal muscle mTROC1 signaling in the cancer environment.

METHODS

Physical activity and feeding behaviors were measured for four consecutive days before sacrifice in male C57BL/6 (B6; n = 24) and Apc (MIN; n = 22) mice at 7:00 AM and 7:00 PM under ad libitum condition. A subset of B6 (n = 16) and MIN (n = 19) mice were given wheel access for 2 wk before diurnal behavior measurements. Gastrocnemius muscle protein expression was examined.

RESULTS

The MIN mice demonstrated altered diurnal fluctuations in feeding and activity compared with the B6. Interestingly, cachexia did not alter MIN total food intake, but dramatically reduced cage physical activity. As a measurement of mTORC1 activity, 4E-BP1 phosphorylation increased after the dark cycle in B6 and precachectic MIN mice, whereas rpS6 phosphorylation was only increased after the dark cycle in MIN mice. MIN 4E-BP1 phosphorylation at the end of the light cycle was significantly correlated with cachexia progression and reduced physical activity. Voluntary wheel running increased light cycle MIN 4E-BP1 phosphorylation and attenuated muscle mass loss.

CONCLUSIONS

The cancer environment can alter diurnal feeding and physical activity behaviors in tumor-bearing mice, which are linked to the progression of cachexia and muscle wasting. Furthermore, suppressed physical activity during cachexia is associated with decreased skeletal muscle mTORC1 signaling.

Regulation of Skeletal Muscle DRP-1 and FIS-1 Protein Expression by IL-6 Signaling

IL-6 signals through the ubiquitously expressed glycoprotein 130 (gp130) transmembrane protein to activate intracellular signaling that includes signal transducer and activator of transcription 3 (STAT3) and extracellular signal-regulated kinase 1/2 (ERK1/2). Dynamin-1-like protein (DRP-1) and mitochondrial fission 1 protein (FIS-1) are key proteins in the process of mitochondrial fission and have emerged as IL-6-sensitive targets. The purpose of this study was to examine the regulation of DRP-1 and FIS-1 expression by IL-6 and gp130 signaling in myotubes and skeletal muscle. Fully differentiated C2C12 myotubes were treated with 100 ng of IL-6 for 24 hours in the presence of gp130siRNA, C188-9 (STAT3 inhibitor), or PD98059 (ERK1/2 inhibitor). Male C57BL/6 (B6) and muscle-specific gp130 knockout mice (KO) had IL-6 systemically overexpressed for 2 weeks by transient transfection with 50 ng of an IL-6-expressing or control plasmid in the quadriceps muscles, and the tibialis anterior muscle was analyzed to determine systemic effects of IL-6. IL-6 induced DRP-1 and FIS-1 expression in myotubes 124% and 82% (p = .001) and in skeletal muscle 97% and 187% (p = .001). Myotube gp130 knockdown suppressed the IL-6 induction of DRP-1 68% (p = .002) and FIS-1 65% (p = .001). Muscle KO suppressed the IL-6 induction of DRP-1 220% (p = .001) and FIS-1 121% (p = .001). ERK1/2 inhibition suppressed the IL-6 induction of DRP-1 59% (p = .0003) and FIS-1 102% (p = .0001) in myotubes, while there was no effect of STAT3 inhibition. We report that chronically elevated IL-6 can directly induce DRP-1 and FIS-1 expression through gp130 signaling in cultured myotubes and skeletal muscle. Furthermore, ERK 1/2 signaling is necessary for the IL-6 induction of DRP-1 and FIS-1 expression in myotubes.

The regulation of skeletal muscle fatigability and mitochondrial function by chronically elevated interleukin-6

NEW FINDINGS

What is the central question of this study? Interleukin-6 has been associated with muscle mass and metabolism in both physiological and pathological conditions. A causal role for interleukin-6 in the induction of fatigue and disruption of mitochondrial function has not been determined. What is the main finding and its importance? We demonstrate that chronically elevated interleukin-6 increased skeletal muscle fatigability and disrupted mitochondrial content and function independent of changes in fibre type and mass.

ABSTRACT

Interleukin-6 (IL-6) can initiate intracellular signalling in skeletal muscle by binding to the IL-6-receptor and interacting with the transmembrane gp130 protein. Circulating IL-6 has established effects on skeletal muscle mass and metabolism in both physiological and pathological conditions. However, the effects of circulating IL-6 on skeletal muscle function are not well understood. The purpose of this study was to determine whether chronically elevated systemic IL-6 was sufficient to disrupt skeletal muscle force, fatigue and mitochondrial function. Additionally, we examined the role of muscle gp130 signalling during overexpression of IL-6. Systemic IL-6 overexpression for 2 weeks was achieved by electroporation of an IL-6 overexpression plasmid or empty vector into the quadriceps of either C57BL/6 (WT) or skeletal muscle gp130 knockout (KO) male mice. Tibialis anterior muscle in situ functional properties and mitochondrial respiration were determined. Interleukin-6 accelerated in situ skeletal muscle fatigue in the WT, with a 18.5% reduction in force within 90 s of repeated submaximal contractions and a 7% reduction in maximal tetanic force after 5 min. There was no difference between fatigue in the KO and KO+IL-6. Interleukin-6 reduced WT muscle mitochondrial respiratory control ratio by 36% and cytochrome c oxidase activity by 42%. Interleukin-6 had no effect on either KO respiratory control ratio or cytochrome c oxidase activity. Interleukin-6 also had no effect on body weight, muscle mass or tetanic force in either genotype. These results provide evidence that 2 weeks of elevated systemic IL-6 is sufficient to increase skeletal muscle fatigability and decrease muscle mitochondrial content and function, and these effects require muscle gp130 signalling.

Understanding the Role of Exercise in Cancer Cachexia Therapy

Cachexia, the unintentional loss of body weight, is prevalent in many cancer types, and the associated skeletal muscle mass depletion increases patient morbidity and mortality. While anorexia can be present, cachexia is not reversible with nutritional therapies alone. Pharmacological agents have been proposed to treat this condition, but there are currently no approved treatments. Nonetheless, the hallmark characteristics associated with cancer cachexia remain viable foundations for future therapies. Regular physical activity holds a promising future as a nonpharmacological alternative to improve patient survival through cachexia prevention. Evidence suggests exercise training is beneficial during cancer treatment and survival. However, the mechanistic examination of cachectic skeletal muscle's response to exercise is both needed and justified. The primary objective of this review is to discuss the role of exercise for the prevention and treatment of cancer-associated muscle wasting. Initially, we provide an overview of systemic alterations induced by cancer and their role in the regulation of wasting processes during cachexia progression. We then discuss how exercise could alter disrupted regulatory pathways related to growth and metabolism during cancer-induced muscle atrophy. Last, we outline current exercise prescription guidelines and how exercise could be a potential behavioral therapy to curtail cachexia development in cancer patients.

The Effect of Estradiol Administration on Muscle Mass Loss and Cachexia Progression in Female Apc Min/+ Mice

Cancer cachexia is a multifactorial muscle wasting condition characterized by severe body weight and muscle mass loss which is secondary to chronic disease. The mechanistic examination of cachexia has predominately focused on the male phenotype and created significant gaps in understanding cachexia progression in the female. Female hypogonadism can accompany cancer cachexia and is characterized by reduced circulating 17ß-estradiol and uterine atrophy. Estrogen has known functions in skeletal muscle homeostasis involving the regulation of muscle protein turnover, cellular stressors, and oxidative metabolism. However, 17ß-estradiol's ability to regulate cachexia progression in the female is not known. The purpose of this study was to determine the effect of gonadal function and estradiol administration on muscle mass loss and cachexia progression in female Apc ^Min/+ mice. Methods: Female C57BL/6 (B6; N = 82) and Apc ^Min/+ (MIN; N = 88) mice were used in two separate experiments. In experiment 1, mice were sacrificed at either 12 (N = 20) or 20 (N = 41) weeks of age. Body weight and estrous cycle presence was determined weekly. In experiment 2, B6 and MIN mice were randomly allocated to: Control (N = 17), received E2 pellet (E2, N = 18), ovariectomy surgery (OVX; N = 19) or ovariectomy surgery with E2 pellet (OVX + E2; N = 21). 17ß-estradiol was administered through an implanted slow-releasing pellet (0.1 mg). In estrogen and ovariectomy experiments, food intake, and functional outcomes were recorded 1 week prior to sacrifice. Results: We report that E2 administration prevented body weight loss, muscle mass loss, cage inactivity, and grip strength loss associated with cachexia. In skeletal muscle, E2 reduced skeletal muscle AMPK phosphorylation, improved mTORC1 signaling, and prevented mitochondrial dysfunction. Conclusion: Our results demonstrate a role for 17ß-estradiol for the prevention of skeletal muscle mass loss in female tumor bearing mice. Furthermore, 17ß-estradiol prevented cachexia's disruption in skeletal muscle signaling involving AMPK and mTORC1, in addition to improving mitochondrial function in female tumor bearing mice.

Understanding sex differences in the regulation of cancer-induced muscle wasting

PURPOSE OF REVIEW

We highlight evidence for sexual dimorphism in preclinical and clinical studies investigating the cause and treatment of cancer cachexia.

RECENT FINDINGS

Cancer cachexia is unintended bodyweight loss occurring with cancer, and skeletal muscle wasting is a critical predictor of negative outcomes in the cancer patient. Skeletal muscle exhibits sexual dimorphism in fiber type, function, and regeneration capacity. Sex differences have been implicated in skeletal muscle metabolism, mitochondrial function, immune response to injury, and myogenic stem cell regulation. All of these processes have the potential to be involved in cancer-induced muscle wasting. Unfortunately, the vast majority of published studies examining cancer cachexia in preclinical models or cancer patients either have not accounted for sex in their design or have exclusively studied males. Preclinical studies have established that ovarian function and estradiol can affect skeletal muscle function, metabolism and mass; ovarian function has also been implicated in the sensitivity of circulating inflammatory cytokines and the progression of cachexia.

SUMMARY

Females and males have unique characteristics that effect skeletal muscle's microenvironment and intrinsic signaling. These differences provide a strong rationale for distinct causes for cancer cachexia development and treatment in males and females.

Determining Strength: A Case for Multiple Methods of Measurement

Muscle strength is often measured through the performance of a one-repetition maximum (1RM). However, we that feel a true measurement of 'strength' remains elusive. For example, low-load alternatives to traditional resistance training result in muscle hypertrophic changes similar to those resulting from traditional high-load resistance training, with less robust changes observed with maximal strength measured by the 1RM. However, when strength is measured using a test to which both groups are 'naive', differences in strength become less apparent. We suggest that the 1RM is a specific skill, which will improve most when training incorporates its practice or when a lift is completed at a near-maximal load. Thus, if we only recognize increases in the 1RM as indicative of strength, we will overlook many effective and diverse alternatives to traditional high-load resistance training. We wish to suggest that multiple measurements of strength assessment be utilized in order to capture a more complete picture of the adaptation to resistance training.

Inflammatory signalling regulates eccentric contraction-induced protein synthesis in cachectic skeletal muscle

BACKGROUND

Skeletal muscle responds to eccentric contractions (ECC) with an anabolic response that involves the induction of protein synthesis through the mechanistic target of rapamycin complex 1. While we have reported that repeated ECC bouts after cachexia initiation attenuated muscle mass loss and inflammatory signalling, cachectic muscle's capacity to induce protein synthesis in response to ECC has not been determined. Therefore, we examined cachectic muscle's ability to induce mechano-sensitive pathways and protein synthesis in response to an anabolic stimulus involving ECC and determined the role of muscle signal transducer and activator of transcription 3 (STAT3)/nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) signalling on ECC-induced anabolic signalling.

METHODS

Mechano-sensitive pathways and anabolic signalling were examined immediately post or 3 h after a single ECC bout in cachectic male Apc^Min/+ mice (n = 17; 16 ± 1% body weight loss). Muscle STAT3/NFκB regulation of basal and ECC-induced anabolic signalling was also examined in an additional cohort of Apc^Min/+ mice (n = 10; 16 ± 1% body weight loss) that received pyrrolidine dithiocarbamate 24 h prior to a single ECC bout. In all experiments, the left tibialis anterior performed ECC while the right tibialis anterior served as intra-animal control. Data were analysed by Student's t-test or two-way repeated measures analysis of variance with Student-Newman-Keuls post-hoc when appropriate. The accepted level of significance was set at P < 0.05 for all analysis.

RESULTS

Apc^Min/+ mice exhibited a cachectic muscle signature demonstrated by perturbed proteostasis (Ribosomal Protein S6 (RPS6), P70S6K, Atrogin-1, and Muscle RING-finger protein-1 (MuRF1)), metabolic (adenosine monophosphate-activated protein kinase, Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), and Cytochrome c oxidase subunit IV (COXIV)), and inflammatory (STAT3, NFκB, extracellular signal-regulated kinases 1 and 2, and P38) signalling pathway regulation. Nonetheless, mechano-sensitive signalling pathways (P38, extracellular signal-regulated kinases 1 and 2, and Protein kinase B (AKT)) were activated immediately post-ECC irrespective of cachexia. While cachexia did not attenuate ECC-induced P70S6K activation, the protein synthesis induction remained suppressed compared with healthy controls. However, muscle STAT3/NFκB inhibition increased basal and ECC-induced protein synthesis in cachectic Apc^Min/+ mice.

CONCLUSIONS

These studies demonstrate that mechano-sensitive signalling is maintained in cachectic skeletal muscle, but chronic STAT3/NFκB signalling serves to attenuate basal and ECC-induced protein synthesis.

Blood flow in humans following low-load exercise with and without blood flow restriction

Blood flow restriction (BFR) in combination with exercise has been used to increase muscle size and strength using relatively low loads (20%–30% 1-repetition maximum (1RM)). In research, the range of applied pressures based on a percentage of arterial occlusion pressure (AOP), is wide. The purpose of the study is to measure the blood flow response before exercise, following each set of exercise, and postexercise to low-load elbow flexion combined with no restriction (NOBFR), 40% of AOP (40BFR), and 80% of AOP (80BFR). One hundred and fifty-two participants volunteered; 140 completed the protocol (women = 75, men = 65). Participants were counter-balanced into 1 of 3 conditions. Following AOP and 1RM measurement, ultrasound was used to measure standing blood flow at rest in the right brachial artery. Participants performed 4 sets of elbow flexion at 30% 1RM. Blood flow was measured between sets and at 1 and 5 min postexercise. Blood flow decreased following inflation, with no difference between conditions (p < 0.001). Men had greater blood flow than women in all conditions at all time points (p < 0.001). Resting hyperemia decreased with pressure (NOBFR > 40BFR > 80BFR, p < 0.001). Blood flow increased from rest to after set 1 regardless of condition. Following cuff deflation, blood flow increased in both the 80BFR and 40BFR conditions. The reduction in hyperemia during BFR is pressure-dependent. Contrary to previous investigations, blood flow was increased above baseline following exercise.

The acute muscular response to two distinct blood flow restriction protocols

The purpose of this study was to determine acute physiological and perceptual responses to two commonly implemented blood flow restriction protocols. Using a within-subject design, 15 participants (age ∼25) performed four sets of unilateral elbow flexion with each arm. One arm exercised using a 3-cm elastic cuff inflated to 160 mmHg, whereas the other arm exercised using a 5-cm nylon cuff inflated to 40% of the individual's arterial occlusion pressure. While both protocols elicited increases in acute muscle thickness [pre: 4.5 (0.2) cm, post: 5.0 (0.2) cm; p < 0.001] and electromyography amplitude [first 3 reps: 55 ( 5 ) %MVC; last 3 reps: 87 ( 10 ) %MVC], there were no differences between conditions. Both protocols produced decreases in post-exercise strength (pre: 70 Nm, post: 51 Nm; p < 0.001) with no difference between conditions. The nylon protocol resulted in more repetitions during sets 2 [13 ( 2 ) vs. 9 ( 4 ); p = 0.001] and 3 [10 ( 2 ) vs. 7 ( 4 ); p = 0.05], while producing lower levels of discomfort following each set (average 3 vs. 4; p < 0.05). In conclusion, both protocols produced similar acute responses thought to be important for promoting muscle growth. However, the use of arbitrary pressures may place some individuals under complete arterial occlusion which may increase the potential risk of an adverse event.

Objectively-Measured Free-Living Physical Activity and Heart Rate Recovery

The purpose of this study was to examine the association of free-living, objectively-measured physical activity on treadmill-based heart rate recovery (HRR), a parameter known to associate with morbidity and mortality. Data was used from 2003 to 2004 NHANES. Physical activity was assessed via accelerometry, with HRR recovery assessed from a treadmill-based test. Heart rate recovery minute 1 (HRR₁) and minute 2 (HRR₂) were calculated. After adjustment, light and vigorous-intensity free-living physical activity, respectively, were associated with HRR₁ (β_adjusted = 0.69, 95% CI 0.22-1.14; β_adjusted 1.94, 95% CI 0.01-3.9) and HRR₂ (β_adjusted = 0.99, 95% CI 0.35-1.62; β_adjusted = 5.88, 95% CI 2.63-9.12). Moderate physical activity was not associated with HRR₁ (β_adjusted = 0.60, 95% CI -0.41 to 1.62), but was with HRR₂ (β_adjusted = 2.28, 95% CI 1.27-3.28). As free-living physical activity intensity increased, there was a greater association with HRR. This finding may provide mechanistic insight of previous research observations demonstrating intensity-specific effects of physical activity on various health outcomes.

The acute muscular response to blood flow-restricted exercise with very low relative pressure

To investigate the acute responses to blood flow-restricted (BFR) exercise across low, moderate and high relative pressures. Muscle thickness, maximal voluntary contraction (MVC) and electromyography (EMG) amplitude were assessed following exercise with six different BFR pressures: 0%, 10%, 20%, 30%, 50% and 90% of arterial occlusion pressure (AOP). There were differences between each time point within each condition for muscle thickness, which increased postexercise [+0·47 (0·40, 0·54) cm] and then trended towards baseline. For MVC, higher pressures resulted in greater decrements than lower pressures [e.g. 10% AOP: -20·7 (-15·5, -25·8) Nm versus 90% AOP: -24 (-19·1, -28·9) Nm] postexercise. EMG amplitude increased from the first three repetitions to the last three repetitions within each set. When using a common BFR protocol with 30% 1RM, applying BFR does not seem to augment acute responses over that of exercise alone when exercise is taken to failure.

Influence of cuff material on blood flow restriction stimulus in the upper body

The purpose of this study was to examine the acute skeletal muscle and perceptual responses to blood flow restriction (BFR) exercise to failure between narrow nylon and elastic inflatable cuffs at rest and during exercise. Torque and muscle thickness was measured pre, post, and 5, 20, 40, and 60 min post-exercise with muscle activation being measured throughout exercise. Resting arterial occlusion pressure was different between the nylon [139 (14) mmHg] and elastic [246 (71) mmHg, p < 0.001] cuffs. However, when exercising at 40 % of each cuff's respective arterial occlusion pressure [nylon: 57 (7) vs. elastic: 106 (38) mmHg, p < 0.001], there were no differences in repetitions to failure, torque, muscle thickness, or muscle activation between the cuffs. Exercising with cuffs of different material but similar width resulted in the same acute muscular response when the cuffs were inflated to a pressure relative to each individual cuff.

Let's talk about sex: where are the young females in blood flow restriction research?

Low-load resistance exercise with the blood flow restriction (BFR) has been shown to increase muscle size similar to that of traditional high-load resistance training. Throughout the BFR literature, there is a vast difference between the quantity of young females included in the literature compared to young males, older males and older females. Therefore, the purpose of this minireview is to discuss the underrepresentation of young females in the BFR literature and review the potential physiologic reasons as to why they may have been excluded. In conclusion, the female menstrual cycle, a normal physiological occurrence, is presumably the reason as to why majority of young females are excluded from participation in BFR studies. Instead of excluding females, we recommend that BFR studies should include both sexes and plot the results separately to determine whether a sex difference exists.

Do rhythms exist in elbow flexor torque, oral temperature and muscle thickness during normal waking hours?

The purpose of the current study was to examine the influence of "time" on isometric elbow flexion torque, body temperature and muscle size without interrupting the sleep wake cycle in college aged males. Two hours following the participants normal wake time, oral temperature was measured, followed by muscle thickness of the upper and lower body using ultrasound, as well as elbow flexor torque via a maximal voluntary contraction (MVC). Measurements were repeated every 2h for 12h (Time points 1-7). To examine the repeatability of the rhythm, participants returned and completed the same procedures as before within 14days of their first circadian visit (Circadian visit 2). There was no time×day interaction for body temperature (p=0.29), nor were there main effects for time (p=0.15) or day (p=0.74). For MVC, there was no time×day interaction (p=0.93) or main effect for day (p=0.50), however, there was a main effect for time (p=0.01). MVC at time points 1 (86.4±6.4Nm) and 2 (87.1±6.2Nm) was greater than time points 4 (84.2±6.6Nm) and 6 (83.4±6.8Nm, p<0.05). Additionally, time point 5 MVC was greater than time point 4. For upper body muscle thickness, there was no time×day interaction (p=0.34), nor was there a main effect for day (p=0.38), or time (p=0.06). For lower body muscle thickness, there was no time×day interaction (p=0.57), nor was there a main effect for day (p=0.75), or time (p=0.13). Cosinor analyses revealed no group level rhythms for oral temperature, muscle thickness or strength (p>0.05), however, there were some individual rhythms noted for muscle thickness and strength. Results suggest that, when accounting for an individuals normal wake time, circadian rhythms of strength, temperature and muscle thickness are not apparent in most individuals.