Cytoskeletal Reorganization in Human Dental Pulp Stem Cells

Cytoskeletal f-actin reorganization is essential in many cellular processes. It has been shown that as stem cells differentiate along various lineages they undergo a unique change in cytoskeletal organization. In dental pulp regeneration, dental pulp stem cells differentiate to replace lost or damaged odontoblasts. Odontoblasts are lineage commited cells found within the tooth whose responsibility is to maintain the mineralized tissue of the tooth. Dental-pulp inflammation is a complex process involving cellular microenvironment and mitogenic signaling. Exposure to inflammatory mediators induces downstream cellular events mediating angiogenic signaling, a process crucial for pulpal inflammation and repair. Further, inflammation has been shown to initiate certain changes in cytoskeletal organization. Also, it has been demonstrated that certain materials commonly used in dentistry may be play a role in the regeneration response of dental pulp stem cells. Several studies have addressed the effects of proinflammatory stimuli on the survival and differentiation of dental-pulp stem cells. However, the mechanisms common to the inflammatory and angiogenic signaling involved in DPSC survival and differentiation remain unknown. Our studies observed that short-term exposure to TNF-α induced apoptosis with an upregulation of NF-κB signaling. In contrast, long-term exposure resulted in an increased proliferation with an associated telomere length shortening. Interestingly, DPSC pretreated with Nemo binding domain peptide, a cell permeable NF-κB inhibitor, significantly ameliorated TNF-α-induced increases in proliferation and the shortening of telomere length. Furthermore, NBD peptide pretreatment significantly ameliorated TNF-α-induced downregulation of proteins essential for differentiation, such as bone morphogenic proteins. Furthermore, inhibition of NF-κB signaling markedly increased the mineralization, abrogated by TNF-α signaling. Thus, our studies demonstrate that chronic inflammation mediates telomere shortening via NF-κB signaling in human DPSC. The resultant chromosomal instability leads to an emergence of angiogenic proliferation of DPSC and negative regulation of differentiation of DPSC, in vitro.