Activation of Erk and catalase restores a redox equilibrium in DPSCs grown onto Hydroxyapatatite/ Alginate composite scaffolds for bone tissue engineering

Abstract

Tissue engineering has been widely recognized as a promising strategy for bone repair and reconstruction and scaffolds consisting in biodegradable polymers are very promising constructs. Our group has previously demonstrated that hydroxyapatite/alginate (HAp/Alg)- based composites scaffolds efficiently support biomineralized matrix deposition and osteogenic differentiation of human dental pulp mesenchymal stem cells (DPSCs) [1]. Cells on HAp/Alg scaffolds express proteins related to osteogenesis like the non-collagenous bone sialoprotein II (BSPII) mainly after 7 and 14 days of culture. Most important, the increased matrix deposition is related to redox homeostasis controlled by the activation of catalase which enhances cell sur- vival as an enzymatic antioxidant. Since the redox equilibrium is crucial for cell survival and osteogenic differentiation of DPSCs [2], we afterwards investigated a plausible molecular path- way underlying cell response to oxidative stress during cell commitment to osteogenesis. Acti- vation of mitogen-activated protein kinase/extracellular signal regulated kinase (Erk) pathway is known to be an hallmark for cell proliferation and survival and it has been found activated by reactive oxygen species during inflammation [3]. In our HAp/Alg scaffold/DPSCs experi- mental model, pErk increases in a time-dependent manner, registering a peak after 14 days of culture. In parallel, the expression of the inducible Cox (Cox2) dramatically raises up after 7 days, whereas it starts to be downregulated on day 14. Evidences shown here confirm catalase increased activity in DPSCs cultured onto HAp/Alg scaffolds, being the expression of Cox2 sig- nificantly decreased in parallel with the boost of the antioxidant activity of the enzyme. Fur- thermore it is plausible to assume that cells escape inflammation activating Erk, thus balancing redox homeostasis.

This work was supported by Cataldi and di Giacomo FAR 2017