Regulation of dental pulp stem cell's anti-apoptotic ability and proliferation through over-expression of Bcl-2

Abstract

The pulp organ is retained in the pulp chamber of teeth and maintains the biological and physiological vitality of the surrounding dentin. It works as a biosensor and generates secondary dentine and tertiary dentine to resist tooth abrasion and pathogenic stimuli (Zhang and Yelick, 2010). However, dental pulp is vulnerable to injury (Smulson and Sieraski, 1989). Most people experience some irreversible pulpal diseases during their lifetime. Hence, pulp regeneration is one of the research tasks in dentistry that attracts much attention.

Stem cell transplantation is a plausible strategy for the regeneration of dental pulp organ. Dental pulp stem cells (DPSCs)derived from heavy or inflamed dental pulps have the natural advantage in pulp regeneration due to its dentinogenic potentiality (Huang et al., 2009). DPSCs are delivered into prepared root canal, which then differentiate into odontoblasts, fibroblasts, and other kinds of cells. It was shown that these transplanted DPSCs were able to produce dentin and formed a dentin-pulp like tissue both in vitro and in vivo(Huang, 2009).However, low survival rate of the transplanted cells is a common problem in pulp regeneration. Overexpression of Bcl-2 could enhance cell anti-apoptotic ability. Studies of many kinds of cell transplantation showed that a large number of cells died upon grafting and a large proportion of cell death seemed to have occurred due to apoptosis (Liu et al., 2013; Zhang et al., 2001).The aim of this study was to improve cell survival through making DPSCs overexpress lymphoma 2 (Bcl-2) protein.Bcl-2 is a proto-oncogene which playsa significant role in (anti) apoptosis. Former studies in the literature have provided evidences that overexpressing Bcl-2 could reduce cell apoptosis. However, this strategy has not been studied in the modification of DPSCs.

In this study, DPSCs were isolated from discarded third molars of adults and manipulated to overexpressing Bcl-2. Proliferation of modified DPSCs was analyzed by static batch culture, CCK-8 test and BrdU based proliferation test. Apoptosis of modified DPSCs was analyzed by measuring DNA fragments in the cells. Modified DPSCs generated a higher maximum cell population during static batch culture and showed higher viability (the ratio of live cells to total cells). CCK-8 test showed that the population of modified DPSCs increased faster than control group cells and wild type cells. Modified DPSCs were not better than the other cells in proliferative ability, but had lower apoptosis level when culturing in serum free medium. Hence, overexpressing Bcl-2 could increase cell population, the mechanism is to help DPSCs survival rather than promote the proliferative ability of cells.