Temperal and spatial expression of CCN1, CCN3, CCN4, CCN5 and CCN6 proteins in the developing postnatal teeth

CCN proteins are matricellular proteins and are important modulators of development and function of adult organs. However, there is no literature reporting the localization of CCN proteins during postnatal tooth development and the formation of periodontium. Therefore, the aim of our study was to investigate the expression of CCN1, CCN3, CCN4, CCN5 and CCN6 in the developing postnatal teeth. Wistar rats were used at postnatal (PN) 3.5, 7, 16 and 21 days and maxillas were processed for immunohistochemistry. At PN3.5 and PN7, preameloblasts (PA), secretory ameloblasts (SA), odontoblasts (OD) and dental pulp (DP) showed moderate to strong staining for CCN1, CCN4 and CCN6 respectively. CCN5 was intensely expressed in predentin, whereas CCN5 was undetectable in PA, SA, OD and DP. At PN16 and PN21, moderate to strong reaction with CCN1, CCN4 and CCN6 was evident in OD, DP, reduced enamel epithelium (REE), osteoblasts (OB) and periodontal ligament (PDL) respectively, while CCN5 was negative to weakly expressed in REE, OD, DP, OB, PDL and osteocytes (OC). Interestingly, the expression of CCN1, CCN4 and CCN6 was initially negative at PN16 but strong at PN21 in OC. Furthermore, there was no staining for CCN3 in the tissues studied. These results demonstrated that the expression pattern of CCN1, CCN4 and CCN6 is similar and inversely correlated with that of CCN3. CCN5 exhibits a unique distribution pattern. These data indicate that CCN proteins might play regulatory roles in amelogenesis, dentinogenesis, osteogenesis and PDL homeostasis.