Aging‐associated skeletal muscle defects in HER2/Neu transgenic mammary tumour model

Abstract

Background Loss of skeletal muscle volume and functional limitations are poor prognostic markers in breast cancer patients. Several molecular defects in skeletal muscle including reduced myoblast determination protein 1 (MyoD) levels and increased protein turn over due to enhanced proteosomal activity have been suggested as causes of skeletal muscle loss in cancer patients. However, it is unknown whether molecular defects in skeletal muscle are dependent on tumour aetiology. Methods We characterized functional and molecular defects of skeletal muscle in mouse mammary tumour virus (MMTV)-Neu (Neu+) mice (n = 6-12), an animal model that represents HER2 + human breast cancer, and compared the results with well-characterized luminal B breast cancer model MMTV-PyMT (PyMT+). Functional studies such as grip strength, rotarod performance, and ex vivo muscle contraction were performed to measure the effects of cancer on skeletal muscle. Expression of muscle-enriched genes and microRNAs as well as circulating cytokines/chemokines were measured. Because nuclear factor-kappaB (NF-κB) pathway plays a significant role in skeletal muscle defects, the ability of NF-κB inhibitor dimethylaminoparthenolide (DMAPT) to reverse skeletal muscle defects was examined. Results Neu+ mice showed skeletal muscle defects similar to accelerated aging. Compared with age and sex-matched wild type mice, Neu+ tumour-bearing mice had lower grip strength (202 ± 6.9 vs. 179 ± 6.8 g grip force, P = 0.0069) and impaired rotarod performance (108 ± 12.1 vs. 30 ± 3.9 s, P < 0.0001), which was consistent with reduced muscle contractibility (P < 0.0001). Skeletal muscle of Neu+ mice (n = 6) contained lower levels of CD82 + (16.2 ± 2.9 vs. 9.0 ± 1.6) and CD54 + (3.8 ± 0.5 vs. 2.4 ± 0.4) muscle stem and progenitor cells (P < 0.05), suggesting impaired capacity of muscle regeneration, which was accompanied by decreased MyoD, p53, and miR-486 expression in muscles (P < 0.05). Unlike PyMT+ mice, which showed skeletal muscle mitochondrial defects including reduced mitochondria levels and peroxisome proliferator-activated receptor gamma co-activator 1 (beta), Neu + mice displayed accelerated aging-associated changes including muscle fibre shrinkage and increased extracellular matrix deposition. Circulating 'aging factor' and cachexia and fibromyalgia-associated chemokine CC motif chemokine ligand 11 (Ccl11) was elevated in Neu+ mice (1439.56 ± 514 vs. 1950 ± 345 pg/mL, P < 0.05). Treatment of Neu+ mice with DMAPT significantly restored grip strength (205 ± 6 g force), rotarod performance (74 ± 8.5 s), reversed molecular alterations associated with skeletal muscle aging, reduced circulating Ccl11 (1083.26 ± 478 pg/mL), and improved animal survival. Conclusions These results suggest that breast cancer subtype has a specific impact on the type of molecular and structural changes in skeletal muscle, which needs to be taken into consideration while designing therapies to reduce breast cancer-induced skeletal muscle loss and functional limitations.

Skeletal muscle-specific overexpression of miR-486 limits mammary tumor-induced skeletal muscle functional limitations

“…Transgenic MMTV-Neu and MMTV-PyMT female mice in FVB/N background were used to characterize systemic impacts of mammary tumors in mouse model of breast cancer as described in previous studies. 9 , 10 Double-transgenic mice of miR-486+/Neu+ and miR-486+/PyMT+ in FVB/N background were generated to test the role of functional biomarker miR-486 in overcoming cancer-induced systemic effects. First, we backcrossed MCK-miR-486 transgenic mice in C57BL/6 background to FVB/N background for six generations ( Figure 1 A).…”

“… 6 In breast cancer patients, lower circulating levels of miR-486 have been reported by us and others, 1 , 7 , 8 which is consistent with the findings in animal models of mammary tumors. 9 , 10 Recently, we demonstrated that miR-486 is an estradiol-regulated microRNA, and decrease in its level in circulation is more severe in men with cancer compared with women with the same cancer type. 11 We further showed that the NF-κB inhibitor dimethylaminoparthenolide could restore circulating and skeletal muscle levels of miR-486, depending on the model system, and ameliorate cancer-induced functional limitations.…”

“… 11 We further showed that the NF-κB inhibitor dimethylaminoparthenolide could restore circulating and skeletal muscle levels of miR-486, depending on the model system, and ameliorate cancer-induced functional limitations. 9 , 10 On the basis of these observations, we had proposed that circulating microRNAs, particularly those whose levels are reduced in cancer compared with healthy controls, likely reflect the systemic effects of cancer on microRNA biosynthesis and release from other organs such as skeletal muscle, and these microRNAs could be used as biomarkers of cancer-induced systemic effects. 9 …”

“…The MMTV-Neu (hereafter Neu+) model is a tumor model that represents a HER2-amplified intrinsic subtype of breast cancer, and animals with tumors survive to ∼220 days. 10 In contrast, MMTV-PyMT model (hereafter PyMT+) is an aggressive mammary tumor model with tumors resembling luminal B intrinsic subtype of breast cancer, and animals need to be sacrificed by ∼110 days. Although only 25% of breast cancer patients demonstrate classic cachexia-like symptoms, skeletal muscle defects leading to functional limitations and toxicity to chemotherapy are frequently observed in breast cancer patients.…”

Skeletal Muscle Deconditioning in Breast Cancer Patients Undergoing Chemotherapy: Current Knowledge and Insights From Other Cancers

“…However, in these studies, the second muscle biopsy was performed after ∼5 weeks and might explain the lack of atrophy as the effects of chemotherapeutic agents on skeletal muscle are strongly suggested to be cumulative. It is important to note that in vitro and in vivo studies also demonstrated the negative impact of both chemotherapeutic agents (McLoon et al, 1998;Gouspillou et al, 2015;Min et al, 2015;Barreto et al, 2016;Guigni et al, 2018) and breast cancer-bearing mice models (Hesse et al, 2019;Wang et al, 2021) on skeletal muscle structure, strengthening the results obtained in clinical studies.…”