Engineering of a functional bone organ through endochondral ossification

Abstract

Embryonic development, lengthening, and repair of most bones proceed by endochondral ossification, namely through formation of a cartilage intermediate. It was previously demonstrated that adult human bone marrow-derived mesenchymal stem/stromal cells (hMSCs) can execute an endochondral program and ectopically generate mature bone. Here we hypothesized that hMSCs pushed through endochondral ossification can engineer a scaled-up ossicle with features of a "bone organ," including physiologically remodeled bone, mature vasculature, and a fully functional hematopoietic compartment. Engineered hypertrophic cartilage required IL-1β to be efficiently remodeled into bone and bone marrow upon subcutaneous implantation. This model allowed distinguishing, by analogy with bone development and repair, an outer, cortical-like perichondral bone, generated mainly by host cells and laid over a premineralized area, and an inner, trabecular-like, endochondral bone, generated mainly by the human cells and formed over the cartilaginous template. Hypertrophic cartilage remodeling was paralleled by ingrowth of blood vessels, displaying sinusoid-like structures and stabilized by pericytic cells. Marrow cavities of the ossicles contained phenotypically defined hematopoietic stem cells and progenitor cells at similar frequencies as native bones, and marrow from ossicles reconstituted multilineage long-term hematopoiesis in lethally irradiated mice. This study, by invoking a "developmental engineering" paradigm, reports the generation by appropriately instructed hMSC of an ectopic "bone organ" with a size, structure, and functionality comparable to native bones. The work thus provides a model useful for fundamental and translational studies of bone morphogenesis and regeneration, as well as for the controlled manipulation of hematopoietic stem cell niches in physiology and pathology.

Engineering cartilage or endochondral bone: A comparison of different naturally derived hydrogels

“…An endochondral approach to bone tissue engineering may circumvent many of the issues associated with the intramembranous method, as cells progressing down the endochondral route are equipped to survive hypoxic conditions and release pro-angiogenic factors for the conversion of avascular tissue to vascularized tissue [8]. Indeed, it has been demonstrated that MSC-based cartilaginous grafts can be used to generate bone in vivo in both ectopic and orthotopic sites by executing such an endochondral program [8][9][10][11][12][13][14][15].…”

Bone marrow–on–a–chip replicates hematopoietic niche physiology in vitro

“…Therefore, studies on hematopoiesis commonly rely on animal models to ensure the presence of an intact bone marrow microenvironment that enables normal physiologic marrow responses [12][13][14][15] . Furthermore, although it has been reported that bone marrow can be engineered in vivo [16][17][18][19] , no method exists to culture engineered bone marrow in vitro. To bridge the functional gap between in vivo and in vitro systems, we developed a method to produce a "bone marrow-on-a-chip" culture system that contains artificial bone and a living marrow, which is first generated in mice, and then explanted whole and maintained in vitro within a microfluidic device.…”

Metabolic programming of mesenchymal stromal cells by oxygen tension directs chondrogenic cell fate

“…Instead, the present protocols for chondrogenically differentiating MSCs result in the production of neocartilage that is characterized by hypertrophic differentiation (6)(7)(8)(9). Consequently, the newly formed cartilage undergoes endochondral ossification upon implantation (8,(10)(11)(12). In fact, it has been reported that, currently, the most efficient way to engineer new bone from multipotent progenitor cells is via implantation of in vitro-generated neocartilage (6).…”