Physiological and molecular responses in the pulp associated with early inflammatory process

Abstract

Therapies to promote pulp repair and regeneration after injury should be underpinned by a deep understanding of normal tissue behaviour, cellular cross-talk and regulation. The objectives of this study were to investigate the expression of cyclooxygenases (COX1 and COX2), prostanoid receptors (EP1 and EP2) and nitric oxide synthase 1 (NOS1) within the normal dental pulp. The effect of experimental inflammatory conditions on these elements at mRNA level (both normal and experimentally inflamed) were investigated to explore the possibility of a nitric oxide (NO)/prostaglandin (PG) signalling pathway interaction in the rat mandibular incisor (normal and experimentally inflamed). Rodent mandibular incisors were utilised as a model throughout this thesis with structural and functional investigations on demineralised teeth, non-demineralised freshly extracted pulp tissues and tissue explants. The work described in this thesis used immunohistochemical, ELISA and quantitative reverse transcription polymerase chain reaction (q-RT-PCR) techniques. Cellular heterogeneity was observed both in the odontoblasts population and in the interstitial cells forming the bulk of the pulp. Cellular processes were also observed in addition to the observation of cellular processes extending from interstitial cells in the cell-rich zone to odontoblasts. The presence and localisation of immunoreactivity to the above mentioned targets (COX1, COX2, NOS1 and prostanoid receptors) are novel and confirmed with q-RT-PCR. Isolated pulp tissues exposed to LPS were found to release an increased amount of PGE2, which was found to be inhibited by other factors like the presence of NO and ATP. Functional cross-talk between PG and NO was investigated by the ELISA technique, with experimentally-induced inflammation increasing PG release, whereas NO and ATP caused inhibition of PGE2 release. The effects of carefully selected pro-inflammatory agents (LPS, NO and ATP) on PG pathway were examined at the mRNA level by q-RT-PCR. Exposure to LPS was found to cause upregulation of all target genes, whereas variable reactions were observed in response to incubation with NO, ATP and PGE2.