Abstract
BackgroundThe intervertebral disc (IVD) has limited self-healing potential and disc repair strategies require an appropriate cell source such as progenitor cells that could regenerate the damaged cells and tissues. The objective of this study was to identify nucleus pulposus-derived progenitor cells (NPPC) and examine their potential in regenerative medicine in vitro.MethodsNucleus pulposus cells (NPC) were obtained from 1-year-old bovine coccygeal discs by enzymatic digestion and were sorted for the angiopoietin-1 receptor Tie2. The obtained Tie2– and Tie2+ fractions of cells were differentiated into osteogenic, adipogenic, and chondrogenic lineages in vitro. Colony-forming units were prepared from both cell populations and the colonies formed were analyzed and quantified after 8 days of culture. In order to improve the preservation of the Tie2+ phenotype of NPPC in monolayer cultures, we tested a selection of growth factors known to have stimulating effects, cocultured NPPC with IVD tissue, and exposed them to hypoxic conditions (2 % O2).ResultsAfter 3 weeks of differentiation culture, only the NPC that were positive for Tie2 were able to differentiate into osteocytes, adipocytes, and chondrocytes as characterized by calcium deposition (p < 0.0001), fat droplet formation (p < 0.0001), and glycosaminoglycan content (p = 0.0095 vs. Tie2– NPC), respectively. Sorted Tie2– and Tie2+ subpopulations of cells both formed colonies; however, the colonies formed from Tie2+ cells were spheroid in shape, whereas those from Tie2– cells were spread and fibroblastic. In addition, Tie2+ cells formed more colonies in 3D culture (p = 0.011) than Tie2– cells. During expansion, a fast decline in the fraction of Tie2+ cells was observed (p < 0.0001), which was partially reversed by low oxygen concentration (p = 0.0068) and supplementation of the culture with fibroblast growth factor 2 (FGF2) (p < 0.0001).ConclusionsOur results showed that the bovine nucleus pulposus contains NPPC that are Tie2+. These cells fulfilled formally progenitor criteria that were maintained in subsequent monolayer culture for up to 7 days by addition of FGF2 or hypoxic conditions. We propose that the nucleus pulposus represents a niche of precursor cells for regeneration of the IVD.
Highlights
The intervertebral disc (IVD) has limited self-healing potential and disc repair strategies require an appropriate cell source such as progenitor cells that could regenerate the damaged cells and tissues
Sorting of angiopoietin-1 receptor (Tie2)+ cells from isolated Nucleus pulposus cells (NPC) The fraction of sorted Tie2+ cells after isolation of NPC accounted for 8.66 ± 3.94 % of the entire NPC population (N = 10 animals)
Differentiation of NPC in vitro For the differentiation assays of NPC into osteogenic, adipogenic, and chondrogenic lineages, we considered the sorted Tie2– cells, the sorted Tie2+ cells, and a mixed nucleus pulposus (NP) population of cells for comparison
Summary
The intervertebral disc (IVD) has limited self-healing potential and disc repair strategies require an appropriate cell source such as progenitor cells that could regenerate the damaged cells and tissues. The intervertebral disc (IVD) has limited regenerative potential and disc degeneration is a major cause of chronic low back pain. This represents a leading cause of disability with significant economic and social burdens [1,2,3]. The gelatinous NP is an avascular tissue containing a highly organized extracellular matrix rich in proteoglycans and collagens with few dispersed cells [4]. In this respect, the NP cells reside within hypoxic conditions, since no vasculature enters the NP [5]. Members of the transforming growth factor (TGF) superfamily, including TGFβ1, growth and differentiation factor, fibroblast growth factor 2 (FGF2), and vascular endothelial growth factor (VEGF) were identified previously as anabolic regulators within the IVD [6]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
