Department of Anatomy, University of California, San Francisco, CA 94143, USA.
Dis Model Mech. 2010 Mar-Apr;3(3-4):224-35. doi: 10.1242/dmm.004226. Epub 2010 Feb 8.
Long bone development depends on endochondral bone formation, a complex process requiring exquisite balance between hypertrophic cartilage (HC) formation and its ossification. Dysregulation of this process may result in skeletal dysplasias and heterotopic ossification. Endochondral ossification requires the precise orchestration of HC vascularization, extracellular matrix remodeling, and the recruitment of osteoclasts and osteoblasts. Matrix metalloproteinase-9 (MMP-9), vascular endothelial growth factor (VEGF) and osteoclasts have all been shown to regulate endochondral ossification, but how their function interrelates is not known. We have investigated the functional relationship among these regulators of endochondral ossification, demonstrating that they have complementary but non-overlapping functions. MMP-9, VEGF and osteoclast deficiency all cause impaired growth plate ossification resulting in the accumulation of HC. VEGF mRNA and protein expression are increased at the MMP-9-/- growth plate, and VEGF activity contributes to endochondral ossification since sequestration of VEGF by soluble receptors results in further inhibition of growth plate vascularization and ossification. However, VEGF bioavailability is still limited in MMP-9 deficiency, as exogenous VEGF is able to rescue the MMP-9-/- phenotype, demonstrating that MMP-9 may partially, but not fully, regulate VEGF bioavailability. The organization of the HC extracellular matrix at the MMP-9-/- growth plate is altered, supporting a role for MMP-9 in HC remodeling. Inhibition of VEGF impairs osteoclast recruitment, whereas MMP-9 deficiency leads to an accumulation of osteoclasts at the chondro-osseous junction. Growth plate ossification in osteoclast-deficient mice is impaired in the presence of normal MMP-9 expression, indicating that other osteoclastic functions are also necessary. Our data delineate the complementary interplay between MMP-9, VEGF and osteoclast function that is necessary for normal endochondral bone formation and provide a molecular framework for investigating the molecular defects contributing to disorders of endochondral bone formation.
长骨发育依赖于软骨内骨形成，这是一个复杂的过程，需要精细地平衡肥大软骨（HC）形成和其矿化。这个过程的失调可能导致骨骼发育不良和异位骨化。软骨内骨化需要精确地协调 HC 血管生成、细胞外基质重塑以及破骨细胞和成骨细胞的募集。基质金属蛋白酶-9（MMP-9）、血管内皮生长因子（VEGF）和成骨细胞都被证明可以调节软骨内骨化，但它们的功能如何相互关联尚不清楚。我们已经研究了这些软骨内骨化调节剂之间的功能关系，证明它们具有互补但不重叠的功能。MMP-9、VEGF 和破骨细胞缺陷都会导致生长板矿化受损，导致 HC 积累。在 MMP-9-/-生长板上，VEGF mRNA 和蛋白表达增加，并且 VEGF 活性有助于软骨内骨化，因为通过可溶性受体隔离 VEGF 会导致生长板血管生成和矿化进一步抑制。然而，在 MMP-9 缺乏的情况下，VEGF 的生物利用度仍然有限，因为外源性 VEGF 能够挽救 MMP-9-/-表型，表明 MMP-9 可能部分但不完全调节 VEGF 的生物利用度。在 MMP-9-/-生长板上，HC 细胞外基质的组织发生改变，支持 MMP-9 在 HC 重塑中的作用。VEGF 抑制会损害破骨细胞募集，而 MMP-9 缺乏则导致软骨骨交界处破骨细胞堆积。在正常 MMP-9 表达的情况下，破骨细胞缺陷小鼠的生长板矿化受损，表明其他破骨细胞功能也是必要的。我们的数据描绘了 MMP-9、VEGF 和破骨细胞功能之间的互补相互作用，这对于正常的软骨内骨形成是必要的，并为研究导致软骨内骨形成障碍的分子缺陷提供了一个分子框架。
