Boon Chin Heng1, Xin Ye2, Yuan Liu3, Waruna Lakmal Dissanayaka3, Gary Shun Pan Cheung1, Chengfei Zhang4. 1. Comprehensive Dental Care, Endodontics, Faculty of Dentistry, The University of Hong Kong, Pokfulam, Hong Kong. 2. Comprehensive Dental Care, Endodontics, Faculty of Dentistry, The University of Hong Kong, Pokfulam, Hong Kong; School of Stomatology, Shandong University, Jinan, Shandong, China; Shandong Provincial Key Laboratory of Oral Tissue Regeneration, Shandong University, Jinan, Shandong, China. 3. Comprehensive Dental Care, Endodontics, Faculty of Dentistry, The University of Hong Kong, Pokfulam, Hong Kong; Shenzhen Institute of Research and Innovation, The University of Hong Kong, Pokfulam, Hong Kong. 4. Comprehensive Dental Care, Endodontics, Faculty of Dentistry, The University of Hong Kong, Pokfulam, Hong Kong; Shenzhen Institute of Research and Innovation, The University of Hong Kong, Pokfulam, Hong Kong. Electronic address: zhangcf@hku.hk.
Abstract
INTRODUCTION: The therapeutic usefulness of dental pulp stem cells (DPSCs) is severely limited by low survivability upon transplantation in situ because of the presence of various proapoptotic factors within damaged/diseased tissues (ie, hypoxia and inflammation). One strategy to enhance the survivability of grafted DPSCs could be recombinant overexpression of antiapoptotic genes, such as the B-cell lymphoma 2 gene (Bcl2). METHODS: DPSCs were transfected with the Bcl2 and/or GFP gene. Cell density and mitotic activity of transfected DPSCs within in vitro culture were evaluated with the water soluble tetrazolium salt-8 (WST-8) and bromodeoxyuridine assay, respectively, whereas apoptosis was evaluated through the detection of cytoplasmic histone-associated DNA fragments. The osteogenic/odontogenic differentiation potential of these cells was evaluated with quantitative real-time polymerase chain reaction, alkaline phosphatase, and alizarin red staining. RESULTS: Bcl2-transfected DPSCs exhibited consistently higher cell densities than the GFP-transfected control within in vitro culture, and this was not because of the higher mitotic rate but was instead attributed to enhanced cell survivability because of the inhibition of apoptosis by Bcl2. Recombinant overexpression of Bcl2 inhibited the osteogenic/odontogenic potential of DPSCs, as indicated by lower levels of alkaline phosphatase activity and mineralized calcium deposition, together with the down-regulated expression of several key osteogenic/odontogenic gene markers including collagen I, osteocalcin, dentin matrix protein-1, bone sialoprotein, and alkaline phosphatase. CONCLUSIONS: The results place a "caveat" or limitation on the use of recombinant Bcl2 overexpression as a therapeutic strategy for improving the survivability of grafted DPSCs in that the osteogenic/odontogenic potential of these cells may be compromised despite enhanced survival within the host.
INTRODUCTION: The therapeutic usefulness of dental pulp stem cells (DPSCs) is severely limited by low survivability upon transplantation in situ because of the presence of various proapoptotic factors within damaged/diseased tissues (ie, hypoxia and inflammation). One strategy to enhance the survivability of grafted DPSCs could be recombinant overexpression of antiapoptotic genes, such as the B-cell lymphoma 2 gene (Bcl2). METHODS: DPSCs were transfected with the Bcl2 and/or GFP gene. Cell density and mitotic activity of transfected DPSCs within in vitro culture were evaluated with the water soluble tetrazolium salt-8 (WST-8) and bromodeoxyuridine assay, respectively, whereas apoptosis was evaluated through the detection of cytoplasmic histone-associated DNA fragments. The osteogenic/odontogenic differentiation potential of these cells was evaluated with quantitative real-time polymerase chain reaction, alkaline phosphatase, and alizarin red staining. RESULTS:Bcl2-transfected DPSCs exhibited consistently higher cell densities than the GFP-transfected control within in vitro culture, and this was not because of the higher mitotic rate but was instead attributed to enhanced cell survivability because of the inhibition of apoptosis by Bcl2. Recombinant overexpression of Bcl2 inhibited the osteogenic/odontogenic potential of DPSCs, as indicated by lower levels of alkaline phosphatase activity and mineralized calcium deposition, together with the down-regulated expression of several key osteogenic/odontogenic gene markers including collagen I, osteocalcin, dentin matrix protein-1, bone sialoprotein, and alkaline phosphatase. CONCLUSIONS: The results place a "caveat" or limitation on the use of recombinant Bcl2 overexpression as a therapeutic strategy for improving the survivability of grafted DPSCs in that the osteogenic/odontogenic potential of these cells may be compromised despite enhanced survival within the host.