Overexpression of Lrp5 enhanced the anti-breast cancer effects of osteocytes in bone

Shengzhi Liu,Jing Liu,Joseph Rispoli,Nicole Vike,Bai-Yan Li,Akihiro Sudo,Xun Sun,Tomohiko Sano,Yan Feng,Alexander Robling,Yao Fan,Di Wu,Rongrong Zha,Fangjia Li,Harikrishna Nakshatri,Hiroki Yokota,Kexin Li,Aydin Jalali

doi:10.1038/s41413-021-00152-2

Abstract

Osteocytes are the most abundant cells in bone, which is a frequent site of breast cancer metastasis. Here, we focused on Wnt signaling and evaluated tumor-osteocyte interactions. In animal experiments, mammary tumor cells were inoculated into the mammary fat pad and tibia. The role of Lrp5-mediated Wnt signaling was examined by overexpressing and silencing Lrp5 in osteocytes and establishing a conditional knockout mouse model. The results revealed that administration of osteocytes or their conditioned medium (CM) inhibited tumor progression and osteolysis. Osteocytes overexpressing Lrp5 or β-catenin displayed strikingly elevated tumor-suppressive activity, accompanied by downregulation of tumor-promoting chemokines and upregulation of apoptosis-inducing and tumor-suppressing proteins such as p53. The antitumor effect was also observed with osteocyte-derived CM that was pretreated with a Wnt-activating compound. Notably, silencing Lrp5 in tumors inhibited tumor progression, while silencing Lrp5 in osteocytes in conditional knockout mice promoted tumor progression. Osteocytes exhibited elevated Lrp5 expression in response to tumor cells, implying that osteocytes protect bone through canonical Wnt signaling. Thus, our results suggest that the Lrp5/β-catenin axis activates tumor-promoting signaling in tumor cells but tumor-suppressive signaling in osteocytes. We envision that osteocytes with Wnt activation potentially offer a novel cell-based therapy for breast cancer and osteolytic bone metastasis.

Highlights

Primary bone cancer is relatively rare, but bone is a frequent site of cancer metastases.[1,2] Estrogen receptor (ER)-positive cancers preferentially metastasize to bone,[3] but bone is a common site of metastasis of ER-negative breast cancers, including triplenegative breast cancer.[4]
The western blot results Using a proof-of-principle model with C57BL6 mice, we showed that in EO771 cells, A5 conditioned medium (CM) downregulated tumorpromoting genes such as Sclerostin, Lrp[5], β-catenin, MMP9, Runx[2], TGFβ, and Snail and elevated the level of an apoptosis evaluated the effect of osteocytes on mammary tumors, which provided preclinical proof of principle of osteocytes’ antitumor efficacy
In this study, we showed that osteocytes or their CM acted as antitumor agents against mammary tumors and suppressed tumor growth in bone in a mouse model. μCT images showed the protection of trabecular bone, and MR images and histological results indicated a reduction in the tumor-invaded region

Summary

Introduction

Primary bone cancer is relatively rare, but bone is a frequent site of cancer metastases.[1,2] Estrogen receptor (ER)-positive cancers preferentially metastasize to bone,[3] but bone is a common site of metastasis of ER-negative breast cancers, including triplenegative breast cancer.[4]. Wnt signaling, which is required for load-driven bone homeostasis, we evaluated the interactions of tumor cells with mechanosensitive osteocytes. The extracellular matrix in bone is remodeled by bone-forming osteoblasts and bone-resorbing osteoclasts.[7] Osteocytes are matrix-laden, differentiated osteoblasts, and mature osteocytes have an elevated level of Sclerostin.[8] In response to mechanical stimulation, these cells activate Wnt signaling and orchestrate bone remodeling.[9] With their extensive dendritic architecture, osteocytes act as mechanosensors.[10] Low-density lipoprotein receptor-related protein 5 (Lrp5) is a Wnt coreceptor[11] that promotes loading-driven bone formation by downregulating Sclerostin.[7] In the canonical Wnt signaling pathway, β-catenin acts as an epicenter of intracellular signal transduction.[12] In contrast to its beneficial role in osteocytes, Wnt signaling plays a detrimental role in cancer, and strategies to inhibit Wnt signaling have been sought.[13] This study aimed to examine the role of Lrp5- and β-catenin-mediated Wnt signaling in tumorosteocyte interactions in order to develop a novel therapeutic strategy based on Wnt regulation. To the best of our knowledge, the effect of osteocytic Wnt activation on tumor-osteocyte interactions has not been investigated

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