Magnesium-Based Whitlockite Bone Mineral Promotes Neural and Osteogenic Activities

Nerves spread throughout human bone minerals and play an important role in regulating osteogenic homeostasis. However, whether the distributive nerves can sense bone minerals and the role of bone minerals in nerve outgrowth are still unclear. We hypothesized that a natural magnesium-containing bone mineral, whitlockite (WH), the second most abundant bone mineral in the human body, could simultaneously promote both osteogenic and neural activities. To verify the hypothesis, both WH and hydroxyapatite (HAP) nanoparticles were synthesized, and their characterization was completed by Fourier-transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The effect of WH on neural differentiation of mesenchymal stem cells (MSCs) and neural progenitor cells (NPCs) in 2D and 3D culture was examined by immunostaining and quantitative real-time polymerase chain reaction (qRT-PCR). The secretion of calcitonin gene-related polypeptide (CGRP) was examined by enzyme-linked immunosorbent assay (ELISA). The neural and osteogenic differentiation in a preosteoblasts and NPCs coculture system was examined by immunostaining and qRT-PCR. The results showed that WH promotes the gene and protein expression of neuronal specific marker (MAP-2 and βIII-tubulin) in 2D and 3D culture systems. In addition, the neurite length in the WH group was significantly longer than in other groups. Furthermore, both neural differentiation and osteogenic differentiation were simultaneously enhanced in the WH group in the coculture system. Thus, this study demonstrated the simultaneous stimulatory effect of WH bone mineral on neural and osteogenic activities, which provided WH as a valuable material for bone regeneration.