CD169 ⁺ macrophages mediate pathological formation of woven bone in skeletal lesions of prostate cancer

Abstract

Skeletal metastases present a major clinical challenge for prostate cancer patient care, inflicting distinctive mixed osteoblastic and osteolytic lesions that cause morbidity and refractory skeletal complications. Macrophages are abundant in bone and bone marrow and can influence both osteoblast and osteoclast function in physiology and pathology. Herein, we examined the role of macrophages in prostate cancer bone lesions, particularly the osteoblastic response. First, macrophage and lymphocyte distributions were qualitatively assessed in patient's prostate cancer skeletal lesions by immunohistochemistry. Second, macrophage functional contributions to prostate tumour growth in bone were explored using an immune-competent mouse model combined with two independent approaches to achieve in vivo macrophage depletion: liposome encapsulated clodronate that depletes phagocytic cells (including macrophages and osteoclasts); and targeted depletion of CD169(+) macrophages using a suicide gene knock-in model. Immunohistochemistry and histomorphometric analysis were performed to quantitatively assess cancer-induced bone changes. In human bone metastasis specimens, CD68(+) macrophages were consistently located within the tumour mass. Osteal macrophages (osteomacs) were associated with pathological woven bone within the metastatic lesions. In contrast, lymphocytes were inconsistently present in prostate cancer skeletal lesions and when detected, had varied distributions. In the immune-competent mouse model, CD169(+) macrophage ablation significantly inhibited prostate cancer-induced woven bone formation, suggesting that CD169(+) macrophages within pathological woven bone are integral to tumour-induced bone formation. In contrast, pan-phagocytic cell, but not targeted CD169(+) macrophage depletion resulted in increased tumour mass, indicating that CD169(-) macrophage subset(s) and/or osteoclasts influenced tumour growth. In summary, these observations indicate a prominent role for macrophages in prostate cancer bone metastasis that may be therapeutically targetable to reduce the negative skeletal impacts of this malignancy, including tumour-induced bone modelling. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Resting and injury‐induced inflamed periosteum contain multiple macrophage subsets that are located at sites of bone growth and regeneration

“…As we have also previously reported osteomac presence in calvarial osteal tissue, 1 and others have shown macrophage contributions to calvarial injury repair, this cellular mechanism applies to both flat and long bones. Our evidence that osteomacs are present in human osteal tissues 1 , 47 provides support that this biology is not a species‐specific phenomenon. Definitive dissection of the specific roles of macrophages and osteoblasts in bone formation and repair was recently revealed to be more challenging than traditionally appreciated as macrophage can be resistant to lethal doses of irradiation 48 .…”

Role of bone marrow macrophages in controlling homeostasis and repair in bone and bone marrow niches

“…For example, in BM EIM are particularly susceptible to clodronate liposomes [16], but granulocytes [16] and myeloid precursors are preserved. Both osteomacs and osteoclasts are efficiently depleted by clodronate liposomes [26]. An additional nuance of this model is that delivery route and delivery dose/regimen impact on the macrophage depletion specificity and sensitivity including target organ variation [21,23].…”

“…Thus DTR expression is regulated by the endogenous CD169 promoter. CD169 expression is restricted to a subset of tissue macrophages and is expressed by approximately 30% of BM F4/80 + cells which includes HSC niche macrophages [28], EIM [24] and osteomacs [26]. This model avoids many undesired off-macrophage targets, including osteoclasts [26].…”

Overview of RAW264.7 for osteoclastogensis study: Phenotype and stimuli

“…4,19,32 Otherwise, previous study showed the elder RAW264.7 cells could change its morphology and decrease the production of proteins, which lead RAW264.7 cells resistant for differentiation and transduction. [45][46][47] Otherwise, the CD11c and iNOS in subpanel-1 are demonstrated as highly expressed in pro-inflammatory macrophage stage (M1). Therefore, combined with previous excellent and novel studies in these fields, 4,32 in our experiences, it might be a reason for different RAW-OC induction efficacies among various study groups.…”

“…32 However, comparing to RAW264.7, the bone marrow macrophage-M0 (BMM-Mφ) has been reported markedly express CD169. [45][46][47] Otherwise, the CD11c and iNOS in subpanel-1 are demonstrated as highly expressed in pro-inflammatory macrophage stage (M1). 48 Similarly, genes in subpanel-2 and subpanel-3 also associated with macrophage activation including: CD86, HIF-1α, CD11a, CD18, CD206, CD200R, Glut1 (Glucose transporter 1) and Ly6c and TfR2, Arg1 and SCARA-5b (scavenger receptor class A member 5) respectively.…”