Osteolytic Breast Cancer Causes Skeletal Muscle Weakness in an Immunocompetent Syngeneic Mouse Model.

Jenna N Regan,Khalid S Mohammad,Theresa A Guise,David L Waning,Carter Mikesell,Haifang Xu,Andrew R Marks,Steven Reiken

doi:10.3389/fendo.2017.00358

Abstract

Muscle weakness and cachexia are significant paraneoplastic syndromes of many advanced cancers. Osteolytic bone metastases are common in advanced breast cancer and are a major contributor to decreased survival, performance, and quality of life for patients. Pathologic fracture caused by osteolytic cancer in bone (OCIB) leads to a significant (32%) increased risk of death compared to patients without fracture. Since muscle weakness is linked to risk of falls which are a major cause of fracture, we have investigated skeletal muscle response to OCIB. Here, we show that a syngeneic mouse model of OCIB (4T1 mammary tumor cells) leads to cachexia and skeletal muscle weakness associated with oxidation of the ryanodine receptor and calcium (Ca2+) release channel (RyR1). Muscle atrophy follows known pathways via both myostatin signaling and expression of muscle-specific ubiquitin ligases, atrogin-1 and MuRF1. We have identified a mechanism for skeletal muscle weakness due to increased oxidative stress on RyR1 via NAPDH oxidases [NADPH oxidase 2 (Nox2) and NADPH oxidase 4 (Nox4)]. In addition, SMAD3 phosphorylation is higher in muscle from tumor-bearing mice, a critical step in the intracellular signaling pathway that transmits TGFβ signaling to the nucleus. This is the first time that skeletal muscle weakness has been described in a syngeneic model of OCIB and represents a unique model system in which to study cachexia and changes in skeletal muscle.

Highlights

Breast cancer is the most common cancer in women [1] and frequently metastasizes to bone in advanced disease [2]
We found that mice with 4T1 osteolytic cancer in bone (OCIB) had progressive weight loss starting at approximately 14-day postinoculation (Figure 1B)
The extensor digitorum longus (EDL), tibialis anterior (TA), soleus (SOL), and gastrocnemius (Gastroc) muscles were dissected from hindlimb contralateral to the site of inoculation and weighed intact (Figure 1C)

Summary

INTRODUCTION

Breast cancer is the most common cancer in women [1] and frequently metastasizes to bone in advanced disease [2]. Muscle is one of the organ systems responsive to bone-derived signals Conditions such as osteolytic cancer in bone (OCIB) that disrupt the balance of normal bone resorption [7, 8] may have detrimental effects on skeletal muscle. We have previously shown that RyR1 oxidation and loss of its stabilizing subunit, calstabin ( known as FKBP12), is a biochemical signature of RyR1 channel Ca2+ leak in OCIB [9] This biochemical signature was present in skeletal muscle samples taken from patients with breast cancer that had metastasized to bone, validating the clinical importance of our model systems. NADPH oxidase 4 (Nox4), a constitutively active oxidase and TGFβ target gene, is the source of reactive oxygen species in our models of OCIB that lead to skeletal muscle weakness. These data indicate that a syngeneic model of OCIB shows both muscle weakness due to Ca2+ mishandling and activation of a muscle atrophy program

RESULTS

DISCUSSION

MATERIALS AND METHODS

Ethics Statement

ETHICS STATEMENT