Skeletal development and the hematopoietic niche

描述（由申请人提供）：某些免疫骨骼和造血疾病可能是由造血生态位受损引起的，而造血生态位受损又可能是由软骨内成骨（EO）缺陷引起的，其中软骨骨骼蓝图被小梁骨和骨髓所取代。该建议将验证我们的假设，即EO衍生的软骨-骨连接处（COJ）由肥大软骨和小梁骨组成，是骨髓内关键的造血生态位。这一假设来自于我们的转基因（Tg）小鼠和X胶原小鼠，X胶原是在EO之前在肥大软骨中表达的基质蛋白。X胶原蛋白功能被破坏的小鼠表现出骨骼造血缺陷，包括COJ软骨肥大和骨小梁改变、骨髓发育不全、淋巴生成减少和免疫功能受损。我们提出这些缺陷源于COJ内造血生态位的改变，这些小鼠提供了一种创新的系统来识别生态位介导的疾病的机制基础。本研究的目的是通过：1)通过骨髓移植评估X胶原小鼠的所有造血缺陷是否可归因于生态位损伤，以及移植的造血干细胞是否可以通过双光子显微镜观察到COJ生态位的归巢；2)检测来自对照和X胶原小鼠的eo祖细胞在移植后重建异位COJ和HSC生态位的能力；3)确定eo来源的骨祖细胞是否需要X胶原来建立和/或维持生态位。

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.