Contribution of the Non-Canonical BMP Receptor Signaling Pathway Osteogenesis on Bioinspired Nanoparticulate Mineralized Collagen Scaffolds
Qi Zhou, MD1, Xiaoyan Ren, MD, PhD1, David Bischoff, PhD2, Daniel Weisgerber, PhD3, Dean Yamaguchi, MD, PhD2, Timothy Miller, MD1, Brendan Harley, ScD3, Justine C. Lee, MD, PhD1.
1UCLA Division of Plastic and Reconstructive Surgery, Los Angeles, CA, USA, 2Greater Los Angeles VA Healthcare System, Los Angeles, CA, USA, 3University of Illinois Urbana Champaign, Urbana, IL, USA.
PURPOSE:We recently described a bioinspired material composed of nanoparticulate mineralized collagen glycosaminoglycan (MC-GAG) that induces efficient osteogenic differentiation of human mesenchymal stem cells (hMSCs) without the addition of exogenous growth factors, thereby suggestive of a promising, growth factor-free, materials-based method for clinically utilizable bone regeneration. We have previously reported that MC-GAG scaffolds autogenously induce BMP receptor signaling via the canonical (Smad1/5) pathway. However, the necessary and sufficient components of this mechanism remain unknown. Our current study evaluates the contribution of the non-canonical (MAP kinase) pathway in MC-GAG induced osteogenesis.
METHODS:hMSCs were cultured in osteogenic media on non-mineralized (Col-GAG) and nanoparticulate mineralized (MC-GAG) collagen glycosaminoglycan scaffolds. Scaffolds were untreated or treated with the MAP kinase inhibitor PD98059 at 20 μM and 50 μM for 4 days, 14 days, 24 days, 4 weeks, and 8 weeks. Gene and protein expression were measured using quantitative RT-PCR and western blot analysis. Scaffolds were subjected to histochemical and micro-computed tomographic analyses.
RESULTS:Inhibition of the non-canonical BMP receptor signaling pathway resulted in a decrease in expression of early osteogenic genes. Western blot analysis demonstrated that PD98059 inhibited phosphorylation of ERK1/2 and JNK without affecting Smad1/5, p38, and Akt phosphorylation. At 4 and 8 weeks of culture, Runx2 protein expression and mineralization on μCT scans were decreased in the presence of PD98059.
CONCLUSION:Activation of the non-canonical BMP receptor signaling pathway is essential for osteogenic differentiation of hMSCs on MC-GAG scaffolds.
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