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

Abstract

Actively steering the chondrogenic differentiation of mesenchymal stromal cells (MSCs) into either permanent cartilage or hypertrophic cartilage destined to be replaced by bone has not yet been possible. During limb development, the developing long bone is exposed to a concentration gradient of oxygen, with lower oxygen tension in the region destined to become articular cartilage and higher oxygen tension in transient hypertrophic cartilage. Here, we prove that metabolic programming of MSCs by oxygen tension directs chondrogenesis into either permanent or transient hyaline cartilage. Human MSCs chondrogenically differentiated in vitro under hypoxia (2.5% O 2 ) produced more hyaline cartilage, which expressed typical articular cartilage biomarkers, including established inhibitors of hypertrophic differentiation. In contrast, normoxia (21% O 2 ) prevented the expression of these inhibitors and was associated with increased hypertrophic differentiation. Interestingly, gene network analysis revealed that oxygen tension resulted in metabolic programming of the MSCs directing chondrogenesis into articular-or epiphyseal cartilage-like tissue. This differentiation program resembled the embryological development of these distinct types of hyaline cartilage. Remarkably, the distinct cartilage phenotypes were preserved upon implantation in mice. Hypoxia-preconditioned implants remained cartilaginous, whereas normoxia-preconditioned implants readily underwent calcification, vascular invasion, and subsequent endochondral ossification. In conclusion, metabolic programming of MSCs by oxygen tension provides a simple yet effective mechanism by which to direct the chondrogenic differentiation program into either permanent articular-like cartilage or hypertrophic cartilage that is destined to become endochondral bone.tissue engineering | chondral defects | skeletogenesis | cell therapy | regenerative medicine

Recapitulation of physiological spatiotemporal signals promotes in vitro formation of phenotypically stable human articular cartilage

“…Instead, discs formed in isotropic cultures underwent uncontrolled mineralization and endochondral ossification in vivo, in agreement with previous studies (4,15,30). The stratification was evidenced by superficialzone expression of lubricin and deep-zone expression of osteopontin.…”

A computational model to explore the role of angiogenic impairment on endochondral ossification during fracture healing

“…The initialisation step began when the newly differentiated CCs transformed into HCs. Based on the literature, this was assumed to occur when the local oxygen tension increased beyond a threshold value (O 2 hypertrophy ) (Sheehy et al, 2012;Leijten et al, 2014). The ossification step then characterised the process by which the newly transformed HCs recruit blood vessels and osteoprogenitor cells before undergoing apoptosis (Mackie et al 2008) or transdifferentiating into OBs (Bahney et al, 2014).…”

“…This computational model did not however propose a specific hypothesis for how environmental factors regulate the initiation and progression of chondrocyte hypertrophy and endochondral ossification, which is central to successful secondary fracture healing. This is clearly a potential limitation of such models, as a number of recent studies have demonstrated that low oxygen conditions can supress hypertrophy and endochondral ossification of chondrogenically primed MSCs (Zhu et al, 2014;Sheehy et al, 2012;Gawlitta et al, 2012;Leijten et al, 2012Leijten et al, , 2014.…”

“…Motivated by in-vitro observations (Zhu et al, 2014;Sheehy et al, 2012;Gawlitta et al, 2012;Leijten et al, 2012Leijten et al, , 2014 our previous in-silico model of MSC differentiation (Burke and Kelly, 2012) was updated to include specific rules for how oxygen levels regulate hypertrophy of chondrocytes. The model was then tested by attempting to simulate fracture healing within a murine tibia in both normal and ischemic limbs, where experimental data was generated to quantify the proportion of hypertrophic cartilage within the calluses of such bones at specific time-points after the initiation of injury.…”

Unravelling the Role of Mechanical Stimuli in Regulating Cell Fate During Osteochondral Defect Repair

“…Based on the literature, it was assumed that the first step occurred in regions where the oxygen tension increased beyond a threshold value (O2 hypertrophic ) [48][49][50] . Following this, the second step depicted the ossification process whereby HCs either transdifferentiate into, or are replaced by invading OBs 47,51,52 .…”