A potential role of p75NTR in the regulation of circadian rhythm and incremental growth lines during tooth development

Abstract

Objective: Tooth morphogenesis and the formation of hard tissues have been reported to be closely related to circadian rhythms. This study investigates the spatiotemporal expression and relationship of p75NTR with core clock genes, mineralization-related or odontogenesis-related genes, and aims to derive the potential role of p75NTR in regulating circadian rhythm and incrementality growth line formation during tooth development.Materials and methods: The dynamic morphology of the rat dental germ was observed at seven stages (E14.5 d, E16.5 d, E18.5 d, P.N. 4 d, P.N. 7 d, P.N. 10 d, and P.N. 15 d). Next, the expressions of p75NTR and other target factors were traced. The ectomesenchymal stem cells (EMSCs) were isolated from the E18.5d rat dental germs and synchronized using 50% of fetal bovine serum. Then, they were cultured in light/light (L.L.), dark/dark (D.D.), and light/dark (L.D.) conditions for 48 h. The total RNA was collected every 4 h, and the circadian rhythm dynamics of target factors were observed. To reveal the mechanism further, p75NTR was down-regulated in p75NTRExIII−/− mice and up-regulated in immortalized mouse dental apical papilla progenitor cells. The change tendencies of other target factors were also detected.Results: The clock genes Bmal1, Clock, Per1, and Per2 were all expressed in tooth germs before the formation of dental hard tissues and demonstrated a regular oscillating expression pattern in EMSCs from dental germs. Their expression was affected by the L.D. stimulus, and most of them were promoted by D.D. conditions. p75NTR presented a similar expression pattern and a positive or negative relationship with most clock genes, mineralization-related and odontogenesis-related factors, such as brain and muscle ARNT-like protein-1 (Bmal1), runt-related transcription factor 2 (Runx2), alkaline phosphatase (ALP), MSH-like 1 (MSX1), dentin matrix acidic phosphoprotein 1 (Dmp1), and dentin sialophosphoprotein (Dspp). Moreover, the arrangement, morphology, and even boundary in pre-odontoblast/pre-ameloblast layers were disordered in the p75NTRExIII−/− mice.Conclusion: Circadian rhythm was found to affect tooth development. p75NTR might play a crucial role in regulating clock genes in the mineralization and formation of the dental hard tissues. p75NTR is actively involved in the odontoblast-ameloblast junction and cell polarity establishment during tooth morphogenesis.

Circadian clock—A promising scientific target in oral science

“…In odontoblasts, collagen synthetic and secretion activities showed a circadian rhythm, and collagen secreted during the day is twice the amount secreted at night, which is likely to control the circadian incremental lines of dentin ( Papakyrikos et al, 2020 ; Zheng et al, 2014 ) The clock proteins BMAL1, CLOCK, CRY1, PER1 and REV-ERBs are strongly expressed in odontoblasts, and the expression patterns are different in the crown and root dentin; the root is obviously strong ( Zheng et al, 2011 ; Fu et al, 2022 ). Bmal1 promotes cementoblast differentiation and cementum mineralization via Wnt/β-catenin signaling ( Yuan et al, 2022 ). Data obtained from in vivo studies of clock gene Bmal1 did not participate in the dentinogenesis process because the incremental lines persisted in both Bmal1 KO and wild-type mice housed in continuous darkness ( Kondratov et al, 2006 ).…”

Effect and potential mechanism of p75NTR in the regulation of the circadian rhythm and daily mineralization during tooth development

“…Moreover, several odontogenesis-related factors (e.g., ameloblastin, amelogenin, and lysosomeassociated membrane protein) have been reported to exhibit regular oscillating expression patterns in rat tooth germs at postnatal day 1 (PN1) 5,21,22 . In our previous studies 23 , the clock genes Bmal1, Clock, Per1, and Per2 were detected in both antenatal and postnatal tooth germs. Moreover, several mineralization-related and odontogenesis-related factors (e.g., runt-related transcription factor 2 (Runx2), alkaline phosphatase (ALP), collagen type I (Col1), distal-less homeobox 1 (Dlx1), Msh Homeobox 1 (Msx1), dentin sialophosphoprotein (Dspp), and dentin matrix acidic phosphoprotein 1 (DMP1)) were found to display similar oscillating expression patterns to the clock genes in ectomesenchymal stem cells (EMSCs) isolated from tooth germs.…”

“…These data con rm that tooth development, especially dental hard tissue formation, exhibits a characteristic circadian rhythm and is tightly controlled by clock genes. Interestingly, in our previous study, p75 neurotrophin receptor (p75NTR) was found to exhibit a close relationship with the circadian rhythm during tooth development 23,24 .…”

“…Genotyping of tail DNA was performed to distinguish p75NTRE xIII−/− from p75NTRE xIII+/+ and p75NTRE xIII+/− progenies by PCR, as previously described 23 . The gene identi cational primer sequences are shown in Table S3.…”

“…p75NTR, an important marker of cells derived from the cranial neural crest, has been found to participate in the regulation of mineralization during tooth development [28][29][30] . Notably, p75NTR was found to exhibit a characteristic 24hour oscillation in EMSCs 23,31 , and p75NTR-knockout mice displayed a signi cantly lower daily mineralization speed and incremental growth line width of the incisors compared with wild-type mice. This suggests that p75NTR potentially plays a role in periodic mineralization and circadian rhythm regulation during tooth development 10 .…”