PDGF-BB May Improve BM-MSC Integration with β-TCP Scaffolds

Objective: Reconstructing craniofacial defects using bone-marrow derived mesenchymal stem cells (BM-MSCs) and osteoconductive scaffolds is a promising treatment approach. For its success, efficient cell-scaffold integration before transplantation is critical. Beta-tricalcium phosphate (β-TCP), a commonly used scaffold material, only has moderate cell-integration efficiency. Potentially, this limitation can be overcome by using chemotactic agents, e.g., platelet-derived growth factor-BB (PDGF-BB). This study was to 1) confirm that PDGF-BB does not compromise BM-MSC proliferation and osteogenic differentiation and 2) test whether PDGF-BB improve the integration between MSCs and β-TCP scaffolds.

Method: For Objective-1, monolayer pig BM-MSCs were treated with PDGF-BB of varied concentration (0/5/10/20ng/ml) and duration (1/3days), followed by trypan blue exclusion and RT-qPCR assays. For Objective-2, cytotoxicity staining was performed on MSC-β-TCP constructs seeded with varied density (0.2/1/2x10⁶ cells) to determine an optimal seeding density. Subsequently, 50mg β-TCP granules (1000-2000µm, Cerasorb), pretreated with PDGF-BB (10ng/ml, 24hr) or with medium only were incubated with 0.2x10⁶ BM-MSCs on non-attaching culturing plates for 1/3days. DNA content of cell-TCP constructs was then assayed and normalized to that of 0.2x10⁶ monolayer BM-MSCs. Based on the relative DNA content, the effects of PDGF-BB on MSC seeding and proliferating efficiency for β-TCP were examined statistically. 

Result: Compared to control cells, the effect of PDGF-BB on monolayer BM-MSC proliferation and osteogenic differentiation was weakly stimulatory (overall 1.1-2.1 fold differences, 10ng/mL PDGF-BB being the strongest). Qualitatively, 0.2x10⁶ cells seeded on 50mg β-TCP exhibited better cell distribution with substantially fewer cell aggregates or death than 1-2x10⁶ seeding densities. PDGF-treated cell-β-TCP constructs had a significantly higher relative DNA content than non-PDGF-treated cell-β-TCP constructs (ANOVA, p=0.007), while the length of cell-β-TCP incubation time did not affect the relative DNA content on the constructs (p=0.511). 

Conclusion: PDGF-BB may improve the integration efficiency between MSCs and β-TCP granules without posing risks to MSC proliferation and osteogenic differentiation.