RESUMO
Resorbable hydrogels are widely used as scaffolds for tissue engineering. These hydrogels can be modified by grafting dendrimer-linked functionalized molecules (dendrigrafts). Our aim was to develop a tunable poly(L-lysine) dendrigrafts (DGL)/PEG-based hydrogel with an inverse porosity and to investigate its osteogenic potential. DGL/PEG hydrogels were emulsified in a surfactant-containing oil solution to form microspheres. The toxicity was evaluated on Human Vascular Endothelial Cells (HUVECs) and Bone Marrow Mesenchymal Stem Cells (hMSCs) with Live/Dead and MTT assays. The effects on HUVECs were investigated through C5 Complement expression by RT-PCR and C5a/TGF-ß1 secretion by ELISA. Recruitment of hMSCs was investigated using Boyden chambers and their osteogenic differentiation was studied by measuring Alkaline Phosphatase activity (ALP) and BMP-2 secretion by ELISA. Adjusting the stirring speed during the emulsification allowed to obtain spherical microspheres with tunable diameters (10-1600 µm). The cell viability rate with the hydrogel was 95 and 100% with HUVECs and hMSCs, respectively. Incubating HUVECs with the biomaterial induced a 5-fold increase in TGF-ß1 and a 3-fold increase in Complement C5a release. Furthermore, HUVEC supernatants obtained after incubation with the hydrogel induced a 2.5-fold increase in hMSC recruitment. The hydrogel induced a 3-fold increase both in hMSC ALP activity and BMP-2 secretion. Overall, the functionalized hydrogel enhanced the osteogenic potential by interacting with endothelial cells and hMSCs and represents a promising tool for bone tissue engineering.
RESUMO
Upon traumatic injuries or carious lesions, the elimination of bacteria infiltrating the pulp is recognized as a prerequisite for initiating the regeneration process. Complement is a major system involved in initiating the inflammatory reaction and the subsequent bacteria elimination. This plasma system of above 35 proteins is synthesized by the liver and some immune cells. It is activated by 3 pathways: the classical, alternative, and lectin pathways that can be triggered by physical injuries, infection, and biomaterials. Recent data have shown that the pulp fibroblast represents a unique nonimmune cell type able to synthesize Complement proteins. Indeed, after physical injuries/bacteria stimulation, the pulp fibroblast has been shown to synthesize and to activate the complement system leading to the production of biologically active molecules such as C5a, C3b, and the membrane attack complex. This local secretion represents a rapid and efficient mechanism for eliminating bacteria invading the pulp, thus supporting complement activation from the plasma. Pulp fibroblast-secreted Complement proteins allow cariogenic bacteria direct lysis via membrane attack complex formation on their surface, phagocytic cell recruitment by producing C5a and cariogenic bacteria opsonization by C3b fixation on their surface, stimulating cariogenic bacteria phagocytosis. Overall, this review highlights that, in addition to initiating the inflammatory reaction, pulp fibroblasts also provide a powerful control of this inflammation via local Complement activation. The pathogen elimination capacity by fibroblast-produced complement demonstrates that this system is a strong local actor in arresting bacterial progression into the dental pulp.
