Evaluating the role of Thrombospondin-1-CD47 mediated nitric oxide signaling in t

描述（由申请人提供）：癌症转移到骨是许多晚期癌症的常见现象，包括乳腺癌、前列腺癌和肺癌，引起剧烈疼痛、危及生命的高钙血症和神经压迫综合征。在稳态条件下，骨吸收破骨细胞受到严格调节，以维持健康的骨转换。然而，在骨骼转移中，肿瘤细胞分泌促进破骨细胞活性的可溶性因子，从而释放刺激局部肿瘤生长的生长因子。这导致破骨细胞活化和肿瘤细胞增殖的“恶性循环”，导致肿瘤负荷增加和骨病变。血小板反应蛋白-1 （TSP1）是一种分泌蛋白，主要以其抑制血管生成的作用而闻名。有证据表明，TSP1通过其两种配体CD36和CD47调节一氧化氮（NO）信号。补益水平的NO对细胞存活至关重要。病理状态下，NO信号通过iNOS上调。iNOS的具体调控途径尚未确定。TSP1调控NO是治疗原发性和转移性癌症的一个有希望的新靶点。我们建议在健康和骨转移状态下评估tsp1介导的NO信号在骨重塑中的作用。我们发现TSP1缺陷巨噬细胞iNOS转录水平升高，NO活性增加。TSP1缺失的破骨细胞分化缺陷与NO信号失调一致。TSP1-/-小鼠骨体积显著增加，骨转换减少，这一缺陷在给予pan-NOS抑制剂后得以修复。我们已经发表了CD47-/-小鼠也有骨量增加和相关的破骨细胞缺陷。重要的是，我们发现，与它们在抗血管生成中的作用相反，骨转移细胞系C42b和B16F10增加了TSP1的表达。我们假设TSP1连接CD47通过抑制破骨细胞中的iNOS来调节NO信号，并且肿瘤来源的TSP1有助于骨转移中肿瘤相关的骨溶解增加。通过小鼠模型、模拟物和抑制剂调节TSP1/CD47相互作用和NOS活性来评估健康和转移性骨重塑中的TSP1/CD47/NO信号轴。

DESCRIPTION (provided by applicant): Cancer metastasis to bone is common to many advanced cancers including breast, prostate, and lung cancers, causing severe pain, life-threatening hypercalcemia, and nerve compression syndromes. Under homeostatic conditions, bone-resorbing osteoclasts are tightly regulated for healthy bone turnover. In skeletal metastasis, however, tumor cells secrete soluble factors that promote osteoclast activity, resulting in the release of growth factors that stimulate local tumor growth. This leads to a "vicious cycle" of osteoclast activation and tumor cell proliferation, causing increased tumor burden and bone lesions. Thrombospondin-1 (TSP1) is a secreted protein that is known primarily for its role in inhibiting angiogenesis. There is evidence that TSP1 regulates nitric oxie (NO) signaling via two of its ligands, CD36 and CD47. Tonic levels of NO are critical for cell survival. Under pathological conditions, NO signaling is upregulated through iNOS. Specific regulatory pathways of iNOS have not been identified. TSP1 regulation of NO represents a promising novel therapeutic target for the treatment of primary and metastatic cancer. We propose to evaluate TSP1-mediated NO signaling in bone remodeling, both in healthy and bone metastatic states. We found that TSP1 deficient macrophages showed elevated iNOS transcript levels and increased NO activity. TSP1 depleted osteoclasts had differentiation defects consistent with misregulated NO signaling. TSP1-/- mice had significantly increased bone volume and reduced bone turnover, a defect rescued upon administration of a pan-NOS inhibitor. We have published that CD47-/- mice also have increased bone mass with associated osteoclast defects. Importantly, we found that, contrary to their roles in anti-angiogenesis, bone metastatic cell lines C42b and B16F10 have increased TSP1 expression. We hypothesize that TSP1 ligation of CD47 regulates NO signaling via inhibition of iNOS in osteoclasts and that tumor-derived TSP1 contributes to increased tumor-associated osteolysis in bone metastasis. The TSP1/CD47/NO signaling axis in healthy and metastatic bone remodeling will be evaluated using mouse models and mimetics and inhibitors to modulate TSP1/CD47 interaction and NOS activity. Significance: The research proposed in this research training plan will further the understanding of bone remodeling and elucidate the role of TSP1 regulation of NO signaling. Importantly, we will characterize the TSP1/CD47/NO signaling in bone under pathological conditions and provide valuable insight into the off-target effects of cancer therapeutics in trialto modulate this signaling pathway.