Breast cancer-associated skeletal muscle mitochondrial dysfunction and lipid accumulation is reversed by PPARG

Abstract

The peroxisome-proliferator activated receptors (PPARs) have been previously implicated in the pathophysiology of skeletal muscle dysfunction in women with breast cancer (BC) and in animal models of BC. Here, we sought to describe the metabolic alterations induced in skeletal muscle by BC-derived factors in an in vitro conditioned media (CM) system and hypothesized that BC cells secrete a factor that represses PPARgamma (PPARG) expression and its transcriptional activity, leading to downregulation of PPARG target genes involved in mitochondrial function and other metabolic pathways.We found that BC-derived factors repress PPAR-mediated transcriptional activity without altering protein expression of PPARG. Further, we show that BC-derived factors induce significant alterations in skeletal muscle mitochondrial function and lipid metabolism, which are rescued with exogenous expression of PPARG. The PPARG agonist drug rosiglitazone was able to rescue BC-induced lipid accumulation, but did not rescue effects of BC-derived factors on PPAR-mediated transcription or mitochondrial function. These data suggest that BC-derived factors induce deficits in lipid metabolism and mitochondrial function via different mechanisms that are both related to PPARG signaling, with mitochondrial dysfunction likely being altered via repression of PPARmediated transcription, and lipid accumulation being altered via transcriptionindependent functions of PPARG. PPARG agonist rosiglitazone rescues BC-CM-induced lipid accumulation but fails to rescue BC-CM-induced mitochondrial dysfunction and PPAR repressionFinally, we pharmacologically targeted PPARG to overcome BC-induced mitochondrial dysfunction and lipid accumulation, using the potent PPARG agonist rosiglitazone (rosi) of the thiazolidinedione (TZD) drug class. Rosiglitazone did induce PPAR-mediated transcription in the absence of BC-CM (Figure 4A), but it was unable to rescue BC-CM's repression of PPAR-mediated transcription (Figure 4B). Unsurprisingly then, this agonist did not rescue BC-induced mitochondrial dysfunction (Figure 4C). However,

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

“…Skeletal muscle biopsy (e.g., using Bergström needle) is the only technique allowing full investigation of the cellular mechanisms of muscle deconditioning (Bergstrom, 1975;Tarnopolsky et al, 2011). To date, only six clinical studies, published in seven different publications, used muscle biopsies in early breast cancer patients (stage I-III) to decipher mechanisms of muscle deconditioning (Lønbro et al, 2017;Bohlen et al, 2018;Guigni et al, 2018;Mijwel et al, 2018b;Møller et al, 2019;Toth et al, 2020;Wilson et al, 2020). Altogether, these studies highlighted several important aspects of muscle deconditioning detailed below and outlined in Figure 1.…”

“…If a large number of excellent reviews have already documented the critical role of protein turnover homeostasis in the mechanisms related to skeletal muscle atrophy (Sandri, 2008;Chopard et al, 2009;Bodine, 2013;Bonaldo and Sandri, 2013;Schiaffino et al, 2013;Brioche et al, 2016;Larsson et al, 2019;Vainshtein and Sandri, 2020;Sartori et al, 2021) including in cancer cachexia (Argilés et al, 2014;Bowen et al, 2015;Petruzzelli and Wagner, 2016;Baracos et al, 2018;Dolly et al, 2020;Silva et al, 2020), little is known in the unique context of breast cancer. Indeed, only four studies investigated the mechanisms related to protein turnover homeostasis in breast cancer patients (Bohlen et al, 2018;Mijwel et al, 2018b;Møller et al, 2019;Wilson et al, 2020). Two publications from the same research team showed, through RNAseq analysis on pectoralis muscle, an increased expression of genes related to ubiquitinmediated proteolysis and a decreased expression of genes related to ribosomes (Bohlen et al, 2018;Wilson et al, 2020).…”

“…Indeed, only four studies investigated the mechanisms related to protein turnover homeostasis in breast cancer patients (Bohlen et al, 2018;Mijwel et al, 2018b;Møller et al, 2019;Wilson et al, 2020). Two publications from the same research team showed, through RNAseq analysis on pectoralis muscle, an increased expression of genes related to ubiquitinmediated proteolysis and a decreased expression of genes related to ribosomes (Bohlen et al, 2018;Wilson et al, 2020). These results potentially indicate an altered protein turnover balance, with a reduced protein synthesis and an increased protein breakdown.…”

“…Mitochondrial alterations represent, to date, one of the most investigated aspect of muscle deconditioning in breast cancer, especially in response to chemotherapeutic agents. In clinical studies, the RNAseq analysis used by both Bohlen et al (2018) and Wilson et al (2020) showed a clear dysregulation of genes implicated in mitochondrial function and oxidative phosphorylation. Interestingly, the authors showed a decrease in multiple genes implicated in the electron transport chain, antioxidant capacity, and altered PPAR signaling (including PGC-1α), emphasizing that mitochondria and overall energy homeostasis may be perturbed in breast cancer patients treated with chemotherapeutic agents.…”

“…Aside from studies presented in the section of this review dedicated to breast cancer clinical studies (Lønbro et al, 2017;Bohlen et al, 2018;Guigni et al, 2018;Mijwel et al, 2018b;Møller et al, 2019;Wilson et al, 2020), no preclinical study has been done in order to explore protein breakdown in breast cancer models. However, some pre-clinical studies explored the effect of doxorubicin on skeletal muscle and an increase in both UPS and autophagy pathways was suggested as MAFbx, beclin1, Atg12, Atg7, and LC3B-II/I ratio increased with doxorubicin treatment in mice and rats (Smuder et al, 2011;Kavazis et al, 2014;Hulmi et al, 2018;Montalvo et al, 2020).…”