Biodegradable zinc (Zn) metals, a new generation of biomaterials, have attracted much attention due to their excellent biodegradability, bioabsorbability, and adaptability to tissue regeneration. Compared with magnesium (Mg) and iron (Fe), Zn exhibits better corrosion and mechanical behaviors in orthopedic and stent applications. After implantation, Zn containing material will slowly degrade, and Zn ions (Zn2+) will be released to the surrounding tissue. For stent applications, the local Zn2+concentration near endothelial tissue/cells could be high. However, it is unclear how endothelia will respond to such high concentrations of Zn2+, which is pivotal to vascular remodeling and regeneration. Here, we evaluated the short-term cellular behaviors of primary human coronary artery endothelial cells (HCECs) exposed to a concentration gradient (0−140 μM) of extracellular Zn2+. Zn2+ had an interesting biphasic effect on cell viability, proliferation, spreading, and migration. Generally, low concentrations of Zn2+ promoted viability, proliferation, adhesion, and migration, while high concentrations of Zn2+ had opposite effects. For gene expression profiles, the most affected functional genes were related to cell adhesion, cell injury, cell growth, angiogenesis, inflammation, vessel tone, and coagulation. These results provide helpful information and guidance for Zn-based alloy design as well as the controlled release of Zn2+in stent and other related medical applications.

Zn biomaterials attract strong attentions recently for load-bearing medical implants because of their mechanical properties similar to bone, biocompatibility, and degradability at a more matched rate to tissue healing. It has been shown previously that Zn alloys are beneficial for bone regeneration, but the supporting mechanisms have not been explored in detail. Here, we studied the biological responses of human bone marrow mesenchymal stem cells (hMSC) to Zn and the underlying cellular signaling mechanisms. Typical Mg material AZ31 was used as a comparative benchmark control. Direct culture of cells on the materials revealed that cell adhesion, proliferation, and motility were higher on Zn than on AZ31. Significant cytoskeletal reorganizations induced by Zn or AZ31 were also observed. Mineralization of extracellular matrix (ECM) and hMSC osteogenic differentiation, measured by Alizarin red and ALP staining and activities, were significantly enhanced when cells were cultured with Zn or AZ31. Quantitative PCR also showed the increased expression of bone-related genes including ALP, collagen I, and osteopontin. Using small RNA interference to knockdown related key molecules, we illustrated the mechanisms of Zn-induced cellular signaling. TRPM7 and GPR39 appear to be the major cellular receptors facilitating Zn-entry into hMSC. The intracellular Zn then activates the cAMP-PKA pathway and triggers intracellular Ca responses, leading to activation of MAPK. In addition, Zn activates the Gαq-PLC-AKT pathway as well. Eventually, all of this signaling would lead to enhanced differential regulation of genes, cell survival/growth and differentiation, ECM mineralization, osteogenesis, and other cellular activities.

Mesenchymal stem cells (MSC) which have self-renewal and multiple differentiation potential in vitro play important roles in regenerative medicine and tissue engineering. However, long-term culture in vitro leads to senescence which results in the growth arrest and reduction of differentiation. In this study, MSC derived from human bone-marrow (BM-MSC) and umbilical cord (UC-MSC) were cultured in vitro lasted to senescence. Senescence and apoptosis detection showed that the senescent cells increased significantly but the increase of apoptosis was not significant in the long term culture. Senescence related genes p16, p21 and p53 increased gradually in BM-MSC. However, p16 and p53 reduced and then increased but with the gradual increase of p21 in UC-MSC. Adipogenic differentiation decreased whereas the propensity for osteogenic differentiation increased in senescent MSC. Real time RT-PCR demonstrated that both C/EBPα and PPARγ decreased in senescent BM-MSC. However, in UC-MSC, PPARγ decreased but C/EBPα increased in late phase compared to early phase. The study demonstrated p21 was important in the senescence of BM-MSC and UC-MSC. C/EBPα and PPARγ could regulate the balance of adipogenic differentiation in BM-MSC but only PPARγ not C/EBPα was involved in the adipogenic differentiation in UC-MSC.

Bioabsorbable metal zinc (Zn) is a promising new generation of implantable scaffold for cardiovascular and orthopedic applications. In cardiovascular stent applications, zinc ion (Zn2+) will be gradually released into the surrounding vascular tissues from such Zn-containing scaffolds after implantation. However, the interactions between vascular cells and Zn2+ are still largely unknown. We explored the short-term effects of extracellular Zn2+ on human smooth muscle cells (SMCs) up to 24 h, and an interesting biphasic effect of Zn2+ was observed. Lower concentrations (<80 μM) of Zn2+ had no adverse effects on cell viability but promoted cell adhesion, cell spreading, cell proliferation, cell migration, and enhanced the expression of F-actin and vinculin. Cells treated with such lower concentrations of Zn2+ displayed an elongated shape compared to controls without any treatment. In contrast, cells treated with higher Zn2+ concentrations (80–120 μM) had opposite cellular responses and behaviors. Gene expression profiles revealed that the most affected functional genes were related to angiogenesis, inflammation, cell adhesion, vessel tone, and platelet aggregation. Results indicated that Zn has interesting concentration-dependent biphasic effects on SMCs with low concentrations being beneficial to cellular functions.