A loss-of-function mutation in the Lrp5 gene in mice leads to a low bone mass disorder due to the inhibition of the canonical Wnt signaling pathway; however, the role of bone marrow microenvironment in mice with this mutation remains unclear. In this study, we evaluated proliferation and osteogenic potential of mouse osteoblasts using the MTT assay and Alizarin red staining. The levels of alkaline phosphatase, tartrate-resistant acid phosphatase, and adiponectin in culture supernatants were measured using the enzyme-linked immunosorbent assay. Osteoclast bone resorbing activity was evaluated by toluidine staining and the number and area of bone resorption pits were determined. We observed increased osteogenesis in osteoblasts co-cultured with the BM-derived myeloid cells compared to the osteoblasts cultured alone. Mice with global Lrp5 deletion had a relatively higher bone density compared to the mice carrying osteoblast/osteocyte-specific Lrp5 deletion. An increased frequency of M2 macrophages and reduced expression of inflammatory cytokines were detected in the myeloid cells derived from the bone marrow of mice with global Lrp5 deletion. Higher adipogenic potential and elevated levels of adiponectin in the global Lrp5 deletion mice contributed to the preferential M2 macrophage polarization. Here, we identified a novel systemic regulatory mechanism of bone formation and degradation in mice with global Lrp5 deletion. This mechanism depends on a crosstalk between the adipocytes and M2 macrophages in the bone marrow and is responsible for partly rescuing osteopenia developed as a result of decreased Wnt signaling.

Lrp5中的功能丧失突变由于经典 Wnt 信号通路的抑制，小鼠中的基因导致低骨量疾病；然而，骨髓微环境在具有这种突变的小鼠中的作用仍不清楚。在这项研究中，我们使用 MTT 测定和茜素红染色评估了小鼠成骨细胞的增殖和成骨潜力。使用酶联免疫吸附法测定培养上清液中碱性磷酸酶、抗酒石酸酸性磷酸酶和脂联素的水平。通过甲苯胺染色评估破骨细胞的骨吸收活性，并确定骨吸收坑的数量和面积。我们观察到与单独培养的成骨细胞相比，与 BM 衍生的骨髓细胞共培养的成骨细胞中的成骨增加。具有全局Lrp5的小鼠与携带成骨细胞/骨细胞特异性Lrp5缺失的小鼠相比，缺失的骨密度相对较高。在来自具有全局Lrp5缺失的小鼠骨髓的骨髓细胞中检测到 M2 巨噬细胞的频率增加和炎性细胞因子的表达减少。全球Lrp5缺失小鼠中更高的脂肪生成潜力和升高的脂联素水平促成了优先的 M2 巨噬细胞极化。在这里，我们确定了一种新的全身Lrp5小鼠骨形成和降解的系统调节机制删除。这种机制依赖于骨髓中脂肪细胞和 M2 巨噬细胞之间的串扰，并负责部分挽救由于 Wnt 信号减少而导致的骨质减少。