Functional in situ assessment of muscle contraction in wild-type and mdx mice

Muscle weakness and mitochondrial stress occur before severe metastasis in a novel mouse model of ovarian cancer cachexia

OBJECTIVES

A high proportion of women with advanced epithelial ovarian cancer (EOC) experience weakness and cachexia. This relationship is associated with increased morbidity and mortality. EOC is the most lethal gynecological cancer, yet no preclinical cachexia model has demonstrated the combined hallmark features of metastasis, ascites development, muscle loss and weakness in adult immunocompetent mice.

METHODS

Here, we evaluated a new model of ovarian cancer-induced cachexia with the advantages of inducing cancer in adult immunocompetent C57BL/6J mice through orthotopic injections of EOC cells in the ovarian bursa. We characterized the development of metastasis, ascites, muscle atrophy, muscle weakness, markers of inflammation, and mitochondrial stress in the tibialis anterior (TA) and diaphragm ∼45, ∼75 and ∼90 days after EOC injection.

RESULTS

Primary ovarian tumour sizes were progressively larger at each time point while severe metastasis, ascites development, and reductions in body, fat and muscle weights occurred by 90 Days. There were no changes in certain inflammatory (TNFα), atrogene (MURF1 and Atrogin) or GDF15 markers within both muscles whereas IL-6 was increased at 45 and 90 Day groups in the diaphragm. TA weakness in 45 Day preceded atrophy and metastasis that were observed later (75 and 90 Day, respectively). The diaphragm demonstrated both weakness and atrophy in 45 Day. In both muscles, this pre-severe-metastatic muscle weakness corresponded with considerable reprogramming of gene pathways related to mitochondrial bioenergetics as well as reduced functional measures of mitochondrial pyruvate oxidation and creatine-dependent ADP/ATP cycling as well as increased reactive oxygen species emission (hydrogen peroxide). Remarkably, muscle force per unit mass at 90 days was partially restored in the TA despite the presence of atrophy and severe metastasis. In contrast, the diaphragm demonstrated progressive weakness. At this advanced stage, mitochondrial pyruvate oxidation in both muscles exceeded control mice suggesting an apparent metabolic super-compensation corresponding with restored indices of creatine-dependent adenylate cycling.

CONCLUSIONS

This mouse model demonstrates the concurrent development of cachexia and metastasis that occurs in women with EOC. The model provides physiologically relevant advantages of inducing tumour development within the ovarian bursa in immunocompetent adult mice. Moreover, the model reveals that muscle weakness in both TA and diaphragm precedes severe metastasis while weakness also precedes atrophy in the TA. An underlying mitochondrial bioenergetic stress corresponded with this early weakness. Collectively, these discoveries can direct new research towards the development of therapies that target pre-atrophy and pre-severe-metastatic weakness during EOC in addition to therapies targeting cachexia.

Muscle weakness and mitochondrial stress occur before metastasis in a novel mouse model of ovarian cancer cachexia

Objectives

A high proportion of women with advanced epithelial ovarian cancer (EOC) experience weakness and cachexia. This relationship is associated with increased morbidity and mortality. EOC is the most lethal gynecological cancer, yet no preclinical cachexia model has demonstrated the combined hallmark features of metastasis, ascites development, muscle loss and weakness in adult immunocompetent mice.

Methods

Here, we evaluated a new model of ovarian cancer-induced cachexia with the advantages of inducing cancer in adult immunocompetent C57BL/6J mice through orthotopic injections of EOC cells in the ovarian bursa. We characterized the development of metastasis, ascites, muscle atrophy, muscle weakness, markers of inflammation, and mitochondrial stress in the tibialis anterior (TA) and diaphragm ~45, ~75 and ~90 days after EOC injection.

Results

Primary ovarian tumour sizes were progressively larger at each time point while robust metastasis, ascites development, and reductions in body, fat and muscle weights occurred by 90 Days. There were no changes in certain inflammatory (TNFα), atrogene (MURF1 and Atrogin) or GDF15 markers within both muscles whereas IL-6 was increased at 45 and 90 Day groups in the diaphragm. TA weakness in 45 Day preceded atrophy and metastasis that were observed later (75 and 90 Day, respectively). The diaphragm demonstrated both weakness and atrophy in 45 Day. In both muscles, this pre-metastatic muscle weakness corresponded with considerable reprogramming of gene pathways related to mitochondrial bioenergetics as well as reduced functional measures of mitochondrial pyruvate oxidation and creatine-dependent ADP/ATP cycling as well as increased reactive oxygen species emission (hydrogen peroxide). Remarkably, muscle force per unit mass at 90 days was partially restored in the TA despite the presence of atrophy and metastasis. In contrast, the diaphragm demonstrated progressive weakness. At this advanced stage, mitochondrial pyruvate oxidation in both muscles exceeded control mice suggesting an apparent metabolic super-compensation corresponding with restored indices of creatine-dependent adenylate cycling.

Conclusion

This mouse model demonstrates the concurrent development of cachexia and metastasis that occurs in women with EOC. The model provides physiologically relevant advantages of inducing tumour development within the ovarian bursa in immunocompetent adult mice. Moreover, the model reveals that muscle weakness in both TA and diaphragm precedes metastasis while weakness also precedes atrophy in the TA. An underlying mitochondrial bioenergetic stress corresponded with this early weakness. Collectively, these discoveries can direct new research towards the development of therapies that target pre-atrophy and pre-metastatic weakness during EOC in addition to therapies targeting cachexia.

Microsurgical Transplantation of Pedicled Muscles in an Isolation Chamber—A Novel Approach to Engineering Muscle Constructs via Perfusion-Decellularization

Decellularized whole muscle constructs represent an ideal scaffold for muscle tissue engineering means as they retain the network and proteins of the extracellular matrix of skeletal muscle tissue. The presence of a vascular pedicle enables a more efficient perfusion-based decellularization protocol and allows for subsequent recellularization and transplantation of the muscle construct in vivo. The goal of this study was to create a baseline for transplantation of decellularized whole muscle constructs by establishing an animal model for investigating a complete native muscle isolated on its pedicle in terms of vascularization and functionality. The left medial gastrocnemius muscles of 5 male Lewis rats were prepared and raised from their beds for in situ muscle stimulation. The stimulation protocol included twitches, tetanic stimulation, fatigue testing, and stretching of the muscles. Peak force, maximum rate of contraction and relaxation, time to maximum contraction and relaxation, and maximum contraction and relaxation rate were determined. Afterwards, muscles were explanted and transplanted heterotopically in syngeneic rats in an isolation chamber by microvascular anastomosis. After 2 weeks, transplanted gastrocnemius muscles were exposed and stimulated again followed by intravascular perfusion with a contrast agent for µCT analysis. Muscle constructs were then paraffin embedded for immunohistological staining. Peak twitch and tetanic force values all decreased significantly after muscle transplantation while fatigue index and passive stretch properties did not differ between the two groups. Vascular analysis revealed retained perfused vessels most of which were in a smaller radius range of up to 20 µm and 45 µm. In this study, a novel rat model of heterotopic microvascular muscle transplantation in an isolation chamber was established. With the assessment of in situ muscle contraction properties as well as vessel distribution after 2 weeks of transplantation, this model serves as a base for future studies including the transplantation of perfusion-decellularized muscle constructs.

Transplantation of Dystrophin Expressing Chimeric Human Cells of Myoblast/Mesenchymal Stem Cell Origin Improves Function in Duchenne Muscular Dystrophy Model

Duchenne muscular dystrophy (DMD) is a lethal X-linked disorder caused by mutations in dystrophin gene. Currently, there is no cure for DMD. Cell therapies are challenged by limited engraftment and rejection. Thus, more effective and safer therapeutic approaches are needed for DMD. We previously reported increased dystrophin expression correlating with improved function after transplantation of dystrophin expressing chimeric (DEC) cells of myoblast origin in the mdx mouse models of DMD. This study established new DEC cell line of myoblasts and mesenchymal stem cells (MSC) origin and tested its efficacy and therapeutic potential in mdx/scid mouse model of DMD. Fifteen ex vivo cell fusions of allogenic human myoblast [normal myoblasts (MBN)] and normal human bone marrow-derived MSC (MSCN) from normal donors were performed using polyethylene glycol. Flow cytometry, confocal microscopy, polymerase chain reaction (PCR)-short tandem repeats, polymerase chain reaction-reverse sequence-specific oligonucleotide probe assessed chimeric state of fused MBN/MSCN DEC cells, whereas Comet assay assessed fusion procedure safety testing genotoxicity. Immunofluorescence and real-time PCR assessed dystrophin expression and myogenic differentiation. Mixed lymphocyte reaction (MLR) evaluated DEC's immunogenicity. To test MBN/MSCN DEC efficacy in vivo, gastrocnemius muscle of mdx/scid mice were injected with vehicle (n = 12), nonfused MBN and MSCN (n = 9, 0.25 × 106/each) or MBN/MSCN DEC (n = 9, 0.5 × 106). Animals were evaluated for 90 days using ex vivo and in vivo muscle strength tests. Histology and immunofluorescence staining assessed dystrophin expression, centrally nucleated fibers and scar tissue formation. Post-fusion, MBN/MSCN DEC chimeric state, myogenic differentiation, and dystrophin expression were confirmed. MLR reveled reduced DEC's immune response compared with controls (P < 0.05). At 90 days post-DEC transplant, increase in dystrophin expression (20.26% ± 2.5%, P < 0.05) correlated with improved muscle strength and function in mdx/scid mice. The created human MBN/MSCN DEC cell line introduces novel therapeutic approach combining myogenic and immunomodulatory properties of MB and MSC, and as such may open a universal approach for muscle regeneration in DMD.

Dystrophin Expressing Chimeric (DEC) Human Cells Provide a Potential Therapy for Duchenne Muscular Dystrophy

Duchenne Muscular Dystrophy (DMD) is a progressive and lethal disease caused by mutations of the dystrophin gene. Currently no cure exists. Stem cell therapies targeting DMD are challenged by limited engraftment and rejection despite the use of immunosuppression. There is an urgent need to introduce new stem cell-based therapies that exhibit low allogenic profiles and improved cell engraftment. In this proof-of-concept study, we develop and test a new human stem cell-based approach to increase engraftment, limit rejection, and restore dystrophin expression in the mdx/scid mouse model of DMD. We introduce two Dystrophin Expressing Chimeric (DEC) cell lines created by ex vivo fusion of human myoblasts (MB) derived from two normal donors (MB^N1/MB^N2), and normal and DMD donors (MB^N/MB^DMD). The efficacy of fusion was confirmed by flow cytometry and confocal microscopy based on donor cell fluorescent labeling (PKH26/PKH67). In vitro, DEC displayed phenotype and genotype of donor parent cells, expressed dystrophin, and maintained proliferation and myogenic differentiation. In vivo, local delivery of both DEC lines (0.5 × 10⁶) restored dystrophin expression (17.27%±8.05—MB^N1/MB^N2 and 23.79%±3.82—MB^N/MB^DMD) which correlated with significant improvement of muscle force, contraction and tolerance to fatigue at 90 days after DEC transplant to the gastrocnemius muscles (GM) of dystrophin-deficient mdx/scid mice. This study establishes DEC as a potential therapy for DMD and other types of muscular dystrophies.

Curcumin improves exercise performance of mice with coronary artery ligation-induced HFrEF: Nrf2 and antioxidant mechanisms in skeletal muscle

A hallmark of chronic heart failure (HF) with low ejection fraction (HFrEF) is exercise intolerance. We hypothesized that reduced expression of nuclear factor E2-related factor 2 (Nrf2) in skeletal muscle contributes to impaired exercise performance. We further hypothesized that curcumin, a Nrf2 activator, would preserve or increase exercise capacity in HF. Experiments were carried out in mice with coronary artery ligation-induced HFrEF. Curcumin was deliveried by a subcutaneous osmotic minipump at a dose of 50 mg·kg^-1·day^-1 for 8 weeks. In vivo, in situ, and in vitro experiments were employed to evaluate exercise capacity, muscle function, and molecular mechanisms. We found that: 1) the maximal speed, running distance to exhaustion, and limb grip force were significantly lower in HFrEF mice compared with sham. Curcumin-treated HF mice displayed enhanced exercise performance compared with vehicle-treated HF mice; 2) both soleus (Sol) and extensor digitorum longus (EDL) muscles of HFrEF mice exhibited reduced force and rapid fatigue, which were ameliorated by curcumin; and 3) protein expression of Nrf2, hemeoxygenase-1, SOD2, myogenin, and MyoD were significantly lower, but total ubiquitinated proteins, MURF1, and atrogen-1 were higher in Sol and EDL of HFrEF compared with sham mice, whereas these alterations in Nrf2 signaling and antioxidant defenses in HFrEF were attenuated by curcumin, which had no effect on cardiac function per se in mice with severe HFrEF. These data suggest that impaired Nrf2 signaling intrinsic to skeletal muscle contributes to exercise intolerance in HFrEF. Skeletal muscle Nrf2 should be considered as a novel therapeutic target in severe HF. NEW & NOTEWORTHY These studies suggest that impaired nuclear factor E2-related factor 2 (Nrf2) signaling is a critical mechanism underlying the enhanced oxidative stress in skeletal muscle in heart failure with low ejection fraction (HFrEF). Curcumin prevents the decline in running performance in HFrEF mice by upregulating antioxidant defenses in skeletal muscle, likely mediated by activating Nrf2 signaling. These findings suggest a novel therapeutic target for the improvement of exercise capacity and quality of life in HFrEF patients.