Skeletal development and the hematopoietic niche

描述（由申请人提供）：某些免疫骨性和造血疾病可能由造血生态位受损引起，而造血生态位受损又可能由软骨内骨化（EO）缺陷引起，其中软骨骨骼蓝图被小梁骨和骨髓取代。该提议将检验我们的假设，即EO衍生的软骨-骨连接（COJ），由肥大软骨和骨小梁组成，是骨髓内关键的造血生态位。这一假设源于我们的转基因（Tg）和裸小鼠的胶原蛋白X，一种基质蛋白表达在肥大的软骨前EO。X型胶原蛋白功能受损的小鼠表现出骨骼造血缺陷，包括COJ中的肥大软骨和骨小梁改变、骨髓发育不全、淋巴细胞生成减少和免疫功能受损。我们认为这些缺陷源于COJ内造血生态位的改变，这些小鼠提供了一个创新的系统来识别生态位介导的疾病的机制基础。该建议的目标是通过以下方式暗示COJ祖细胞和胶原X的亚群作为造血生态位的关键调节剂：1）通过骨髓移植评估胶原X小鼠中的所有造血缺陷是否可归因于生态位损伤，以及移植的HSC归巢到COJ生态位是否可通过双光子显微镜观察到; 2）测试来自对照和胶原X小鼠的EO-祖细胞在移植后重建异位COJ和HSC小生境的能力;和3）确定EO-衍生的骨祖细胞是否需要胶原X用于小生境建立和/或小生境维持。 公共卫生相关性：这项提议将测试骨髓中形成血细胞的环境或“生态位”是否是由骨骼发育过程产生的。我们将使用具有生态位缺陷的基因工程小鼠来识别血细胞生态位的正确形成和功能所需的骨骼成分。数据应该产生对基本干细胞生物学的见解，以及对小生境介导疾病的诊断和治疗的帮助。

DESCRIPTION (provided by applicant): Certain immuno-osseous and hematopoietic disorders likely result from an impaired hematopoietic niche, which in turn may ensue from defective endochondral ossification (EO), where a cartilage skeletal blueprint is replaced by trabecular bone and marrow. This proposal will test our hypothesis that the EO- derived chondro-osseous junction (COJ), comprised of hypertrophic cartilage and trabecular bone, is a key hematopoietic niche within the marrow. This hypothesis stems from our transgenic (Tg) and null mice for collagen X, a matrix protein expressed in hypertrophic cartilage prior to EO. Mice with disrupted collagen X function display skeleto-hematopoietic defects including altered hypertrophic cartilage and trabecular bone in the COJ, marrow hypoplasia, diminished lymphopoiesis, and impaired immune function. We propose that these defects stem from an altered hematopoietic niche within the COJ, and that these mice provide an innovative system to identify the mechanistic basis for niche-mediated disorders. The goals of this proposal are to implicate a subset of COJ progenitors and collagen X as key regulators of the hematopoietic niche by: 1) Assessing by bone marrow transplantation if all hematopoietic defects in the collagen X mice could be attributed to niche impairment and whether homing of transplanted HSCs to the COJ niche could be visualized via two-photon microscopy; 2) Testing the ability of EO-progenitors from control and collagen X mice to reconstitute an ectopic COJ and HSC niche upon transplantation; and 3) Determining if EO-derived osteoprogenitors require collagen X for niche establishment and/or niche maintenance. PUBLIC HEALTH RELEVANCE: This proposal will test if the environment or "niche" in the marrow where blood cells form, is generated by a skeletal development process. We will use genetically engineered mice that have a niche defect to identify the skeletal components needed for proper formation and function of the blood cell niche. Data should yield insights into basic stem cell biology, as well as aid in diagnosis and treatment of niche-mediated diseases.