Effect of melatonin on human dental papilla cells

Therapeutic applications of melatonin in disorders related to the gastrointestinal tract and control of appetite

Most animals have large amounts of the special substance melatonin, which is controlled by the light/dark cycle in the suprachiasmatic nucleus. According to what is now understood, the gastrointestinal tract (GIT) and other areas of the body are sites of melatonin production. According to recent studies, the GIT and adjacent organs depend critically on a massive amount of melatonin. Not unexpectedly, melatonin's many biological properties, such as its antioxidant, anti-inflammatory, pro-apoptotic, anti-proliferative, anti-metastasis, and antiangiogenic properties, have drawn the attention of researchers more and more. Because melatonin is an antioxidant, it produces a lot of secretions in the GIT's mucus and saliva, which shields cells from damage and promotes the development of certain GIT-related disorders. Melatonin's ability to alter cellular behavior in the GIT and other associated organs, such as the liver and pancreas, is another way that it functions. This behavior alters the secretory and metabolic activities of these cells. In this review, we attempted to shed fresh light on the many roles that melatonin plays in the various regions of the gastrointestinal tract by focusing on its activities for the first time.

Hypothalamic-pituitary-gonadal axis response to photoperiod changes in female guanacos (Lama guanicoe)

The guanaco, a wild South American camelid, is renowned for its remarkable resilience to extreme conditions. Despite this, little is known about how reproductive hormones in female camelids are influenced during their seasonal breeding period, which occurs during long photoperiod. To explore this, the study investigated the response of the hypothalamic-pituitary-gonadal axis in female guanacos during short days (10L:14D; July) and long days (16L:8D; December) in the Mediterranean ecosystem (33°38'28″S, 70°34'27″W). Blood samples from 14 adult animals were collected, and measurements of melatonin, 17β-estradiol, FSH, and LH concentrations were taken. The results showed that melatonin concentration was lower (P < 0.05) during long days than short days, whereas 17β-estradiol, FSH, and LH concentrations were higher (P < 0.05) during long days compared to short days. Furthermore, the study detected the expression of the melatonin receptor 1A and kisspeptin in the hypothalamus and pituitary, suggesting that the pineal gland of female guanacos is sensitive to seasonal changes in day length. These findings also indicate a seasonal variation in the concentration of reproductive hormones, likely linked to the distinct modulation of the hypothalamic-pituitary-gonadal axis of female guanacos during short and long days.

The effects of melatonin on the viability and osteogenic/odontogenic differentiation of human stem cells from the apical papilla

BACKGROUND

An experimental study was conducted to examine whether melatonin influences osteogenic/odontogenic differentiation of human stem cells derived from the apical papilla (hSCAPs).

MATERIALS AND METHODS

In order to isolate hSCAPs, the undeveloped root of a third molar of a human tooth was used. Melatonin was administered to the experimental groups in an osteogenic medium. No treatment was administered to the control group. The methyl thiazolyl tetrazolium (MTT) assay was performed on days 1, 2, and 3 to assess cell viability (n = 8). A determination of odontogenic/osteogenic differentiation was accomplished using alkaline phosphatase (ALP) activity alizarin red staining (ARS) (n = 6), and the expression of osteogenic genes by real-time polymerase chain reaction (RT-PCR) (n = 3) on days 1, 2, and 7. Evaluation of the data was conducted using SPSS version 18. All experiments were conducted at least three times. The Mann Whitney U test, the ANOVA analysis, Tukey's test, and t-test was implemented to analyze the data (α = 0.05).

RESULTS

After 24 h, 48 h, and 72 h, No significant difference was observed between the control group and the melatonin treatment group in terms of viability of hSCAPs. (from 1 up to 10 µg/ml) (P > 0.05). The assessment of ARS and ALP activity showed that melatonin treatment enhanced osteogenic differentiation of hSCAPs (P < 0.001). Melatonin treatment caused hSCAPs to show an increase of genes related to osteogenic/odontogenic differentiation. These genes included ALP, dentin sialophosphoprotein (DSPP), dentin matrix protein 1 (DMP-1), and bone sialoprotein (BSP) (P < 0.001).

CONCLUSIONS

Melatonin treatment enhanced osteogenic/odontogenic differentiation of hSCAPs with a dose dependent effect on cell viability.

The Preventive Effect of Melatonin on Radiation-Induced Oral Mucositis

Melatonin exerts various physiological effects through melatonin receptors and their ability to scavenge free radicals. Radiotherapy is a common treatment for head and neck tumors, but stomatitis, a side effect affecting irradiated oral mucosa, can impact treatment outcomes. This study investigated the preventive effect of melatonin, a potent free radical scavenger, on radiation-induced oral mucositis. Mice were irradiated with 15 Gy of X-ray radiation to the head and neck, and the oral mucosa was histologically compared between a melatonin-administered group and a control group. The results showed that radiation-induced oral mucositis was suppressed in mice administered melatonin before and after irradiation. It was suggested that the mechanism involved the inhibition of apoptosis and the inhibition of DNA damage. From these findings, we confirmed that melatonin has a protective effect against radiation-induced oral mucositis.

Melatonin-mediated malic enzyme 2 orchestrates mitochondrial fusion and respiratory functions to promote odontoblastic differentiation during tooth development

Tooth development is a complex process that is tightly controlled by circadian rhythm. Melatonin (MT) is a major hormonal regulator of the circadian rhythm, and influences dentin formation and odontoblastic differentiation during tooth development; however, the underlying mechanism remains elusive. This study investigated how MT regulates odontoblastic differentiation, with a special focus on its regulation of mitochondrial dynamics. In rat dental papilla cells (DPCs), we found that MT promotes odontoblastic differentiation concurrently with enhanced mitochondrial fusion, while disruption of mitochondrial fusion by depleting optic atrophy 1 (OPA1) impairs MT-mediated differentiation and mitochondrial respiratory functions. Through RNA sequencing, we discovered that MT significantly upregulated malic enzyme 2 (ME2), a mitochondrial NAD(P)⁺ -dependent enzyme, and identified ME2 as a critical MT downstream effector that orchestrates odontoblastic differentiation, mitochondrial fusion, and respiration functions. By detecting the spatiotemporal expression of ME2 in developing tooth germs, and using tooth germ reconstituted organoids, we also provided in vivo and ex vivo evidence that ME2 promotes dentin formation, indicating a possible involvement of ME2 in MT-modulated tooth development. Collectively, our findings offer novel understandings regarding the molecular mechanism by which MT affects cell differentiation and organogenesis, meanwhile, the critical role of ME2 in MT-regulated mitochondrial functions is also highlighted.

Neural Regulations in Tooth Development and Tooth-Periodontium Complex Homeostasis: A Literature Review

The tooth-periodontium complex and its nerves have active reciprocal regulation during development and homeostasis. These effects are predominantly mediated by a range of molecules secreted from either the nervous system or the tooth-periodontium complex. Different strategies mimicking tooth development or physiological reparation have been applied to tooth regeneration studies, where the application of these nerve- or tooth-derived molecules has been proven effective. However, to date, basic studies in this field leave many vacancies to be filled. This literature review summarizes the recent advances in the basic studies on neural responses and regulation during tooth-periodontium development and homeostasis and points out some research gaps to instruct future studies. Deepening our understanding of the underlying mechanisms of tooth development and diseases will provide more clues for tooth regeneration.

The effect of melatonin on the mouse ameloblast-lineage cell line ALCs

Melatonin plays a critical role in promoting the proliferation of osteoblasts and the growth and development of dental papilla cells. However, the effect and mechanism of melatonin on the growth and development of ALCs still need to be explored. CCK8 assay was used for the evaluation of cell numbers. qRT-PCR was used to identify the differentially expressed genes in ALCs after melatonin treatment. The number and morphology of ALCs were investigated by confocal microscopy. Alkaline phosphatase assay and Alizarin red S staining were used for measuring mineralization. Then, we focused on observing the crucial factors of the signaling pathway by RNA-seq and qRT-PCR. Melatonin limited the cell number of ALCs in a dose-dependent manner and promoted the production of actin fibers. A high concentration of melatonin significantly promoted the mRNA levels of enamel matrix proteins and the formation of mineralized nodules. RNA-seq data showed that Wnt signaling pathway may be involved in the differentiation of ALCs under the influence of melatonin. This study suggests that melatonin plays a regulatory role in the cell number, differentiation, and mineralization of the ALCs, and then shows the relationship between the Wnt signaling pathway with the ALCs under melatonin.

Melatonin enhances osteogenic differentiation of dental pulp mesenchymal stem cells by regulating MAPK pathways and promotes the efficiency of bone regeneration in calvarial bone defects

Background

Mesenchymal stem cell (MSC)-based tissue engineering plays a major role in regenerative medicine. However, the efficiency of MSC transplantation and survival of engrafted stem cells remain challenging. Melatonin can regulate MSC biology. However, its function in the osteogenic differentiation of dental pulp-derived MSCs (DPSCs) remains unclear. We investigated the effects and mechanisms of melatonin on the osteogenic differentiation and bone regeneration capacities of DPSCs.

Methods

The biological effects and signaling mechanisms of melatonin with different concentrations on DPSCs were evaluated using a proliferation assay, the quantitative alkaline phosphatase (ALP) activity, Alizarin red staining, a real-time polymerase chain reaction, and a western blot in vitro cell culture model. The in vivo bone regeneration capacities were assessed among empty control, MBCP, MBCP + DPSCs, and MBCP + DPSCs + melatonin preconditioning in four-created calvarial bone defects by using micro-computed tomographic, histological, histomorphometric, and immunohistochemical analyses after 4 and 8 weeks of healing.

Results

In vitro experiments revealed that melatonin (1, 10, and 100 μM) significantly and concentration-dependently promoted proliferation, surface marker expression (CD 146), ALP activity and extracellular calcium deposition, and osteogenic gene expression of DPSCs (p < 0.05). Melatonin activated the protein expression of ALP, OCN, and RUNX-2 and inhibited COX-2/NF-κB expression. Furthermore, the phosphorylation of mitogen-activated protein kinase (MAPK) p38/ERK signaling was significantly increased in DPSCs treated with 100 μM melatonin, and their inhibitors significantly decreased osteogenic differentiation. In vivo experiments demonstrated that bone defects implanted with MBCP bone-grafting materials and melatonin-preconditioned DPSCs exhibited significantly greater bone volume fraction, trabecular bone structural modeling, new bone formation, and osteogenesis-related protein expression than the other three groups at 4 and 8 weeks postoperatively (p < 0.05).

Conclusions

These results suggest that melatonin promotes the proliferation and osteogenic differentiation of DPSCs by regulating COX-2/NF-κB and p38/ERK MAPK signaling pathways. Preconditioning DPSCs with melatonin before transplantation can efficiently enhance MSCs function and regenerative capacities.

Genome-Wide Association Study on Reproduction-Related Body-Shape Traits of Chinese Holstein Cows

Reproduction is an important production activity for dairy cows, and their reproductive performance can directly affect the level of farmers' income. To better understand the genomic regions and biological pathways of reproduction-related traits of dairy cows, in the present study, three body shape traits-Loin Strength (LS), Rump Angle (RA), and Pin Width (PW)-were selected as indicators of the reproductive ability of cows, and we conducted genome-wide association analyses on them. The heritability of these three traits was medium, ranging from 0.20 to 0.38. A total of 11 significant single-nucleotide polymorphisms (SNPs) were detected associated with these three traits. Bioinformatics analysis was performed on genes close to the significant SNPs (within 200 Kb) of LS, RA, and PW, and we found that these genes were totally enriched in 20 gene ontology terms and six KEGG signaling pathways. Finally, the five genes CDH12, TARP, PCDH9, DTHD1, and ARAP2 were selected as candidate genes that might affect LS. The six genes LOC781835, FSTL4, ATG4C, SH3BP4, DMP1, and DSPP were selected as candidate genes that might affect RA. The five genes USP6NL, CNTN3, LOC101907665, UPF2, and ECHDC3 were selected as candidate genes that might affect the PW of Chinese Holstein cows. Our results could provide useful biological information for the improvement of body shape traits and contribute to the genomic selection of Chinese Holstein cows.

The effect of melatonin on Hippo signaling pathway in dental pulp stem cells

Dental pulp stem cells (DPSCs) have a high capacity to differentiate into the neuronal cell lineage. Meanwhile, both Hippo signaling and melatonin are key regulators in neuronal differentiation of neuronal progenitor cells. Recently emerging evidences suggest the possible interaction between melatonin and Hippo signaling in different cell lines. But underlying mechanisms involved in the initiation or progression of neurogenic differentiation in DPSCs through this connection need to be explored. Therefore, the scope of this study is to investigate the effect of melatonin on Hippo signaling pathway through the expression of its downstream effector (YAP/p-YAP^Y357) after the neuronal differentiation of DPSCs. In regard with this, DPSCs were incubated with growth and dopaminergic neuronal differentiation medium with or without melatonin (10 μM) for 21 days. The morphological changes were followed by phase contrast microscopy and differentiation of DPSCs was evaluated by immunofluorescence labelling with NeuN, GFAP, and tyrosine hydroxylase. Furthermore, we evaluated the presence of neural progenitor cells by nestin immunoreactivity. Hippo signaling pathway was investigated by evaluating the immunoreactivity of YAP and p-YAP^Y357. Our results were also supported by western-blot analysis and SOX2, PCNA and caspase-3 were also evaluated. The positive immunoreactivity for NeuN, tyrosine hydroxylase and negative immunoreactivity for GFAP showed the successful differentiation of DPSCs to neurons, not glial cells. Melatonin addition to dopaminergic media induced tyrosine hydroxylase and decreased significantly nestin expression. The expressions of PCNA and caspase-3 were also decreased significantly with melatonin addition into growth media. Melatonin treatment induced phosphorylation of YAP^Y357 and reduced YAP expression. In conclusion, melatonin has potential to induce neuronal differentiation and reduce the proliferation of DPSCs by increasing phosphorylation of YAP^Y357 and eliminating the activity of YAP, which indicates the active state of Hippo signaling pathway.

RORα Regulates Odontoblastic Differentiation and Mediates the Pro-Odontogenic Effect of Melatonin on Dental Papilla Cells

Dental papilla cells (DPCs), precursors of odontoblasts, are considered promising seed cells for tissue engineering. Emerging evidence suggests that melatonin promotes odontoblastic differentiation of DPCs and affects tooth development, although the precise mechanisms remain unknown. Retinoid acid receptor-related orphan receptor α (RORα) is a nuclear receptor for melatonin that plays a critical role in cell differentiation and embryonic development. This study aimed to explore the role of RORα in odontoblastic differentiation and determine whether melatonin exerts its pro-odontogenic effect via RORα. Herein, we observed that RORα was expressed in DPCs and was significantly increased during odontoblastic differentiation in vitro and in vivo. The overexpression of RORα upregulated the expression of odontogenic markers, alkaline phosphatase (ALP) activity and mineralized nodules formation (p < 0.05). In contrast, odontoblastic differentiation of DPCs was suppressed by RORα knockdown. Moreover, we found that melatonin elevated the expression of odontogenic markers, which was accompanied by the upregulation of RORα (p < 0.001). Utilising small interfering RNA, we further demonstrated that RORα inhibition attenuated melatonin-induced odontogenic gene expression, ALP activity and matrix mineralisation (p < 0.01). Collectively, these results provide the first evidence that RORα can promote odontoblastic differentiation of DPCs and mediate the pro-odontogenic effect of melatonin.

Melatonin antagonizes lipopolysaccharide-induced pulpal fibroblast responses

Background

Pulpal inflammation is known to be mediated by multiple signaling pathways. However, whether melatonin plays regulatory roles in pulpal inflammation remains unclear. This study aimed at elucidating an in situ expression of melatonin and its receptors in human pulpal tissues, and the contribution of melatonin on the antagonism of lipopolysaccharide (LPS)-infected pulpal fibroblasts.

Methods

Melatonin expression in pulpal tissues harvested from healthy teeth was investigated by immunohistochemical staining. Its receptors, melatonin receptor 1 (MT1) and melatonin receptor 2 (MT2), were also immunostained in pulpal tissues isolated from healthy teeth and inflamed teeth diagnosed with irreversible pulpitis. Morphometric analysis was subsequently performed. After LPS infection of cultured pulpal fibroblasts, cyclo-oxygenase (COX) and interleukin-1 β (IL-1 β) transcripts were examined by using reverse transcription-polymerase chain reaction (RT-PCR). Analysis of mRNA expression was performed to investigate an antagonism of LPS stimulation by melatonin via COX and IL-1 β induction. Mann-Whitney U test and One-way ANOVA were used for statistical analysis to determine a significance level.

Results

Melatonin was expressed in healthy pulpal tissue within the odontoblastic zone, cell-rich zone, and in the pulpal connective tissue. Furthermore, in health, strong MT1 and MT2 expression was distributed similarly in all 3 pulpal zones. In contrast, during disease, expression of MT2 was reduced in inflamed pulpal tissues (P-value< 0.001), but not MT1 (P-value = 0.559). Co-culturing of melatonin with LPS resulted in the reduction of COX-2 and IL-1 β expression in primary pulpal fibroblasts, indicating that melatonin may play an antagonistic role to LPS infection in pulpal fibroblasts.

Conclusions

Human dental pulp abundantly expressed melatonin and its receptors MT1 and MT2 in the odontoblastic layers and pulpal connective tissue layers. Melatonin exerted antagonistic activity against LPS-mediated COX-2 and IL-1 β induction in pulpal fibroblasts, suggesting its therapeutic potential for pulpal inflammation and a possible role of pulpal melatonin in an immunomodulation via functional melatonin receptors expressed in dental pulp.

Melatonin ameliorates brain oxidative stress and upregulates senescence marker protein-30 and osteopontin in a rat model of vascular dementia

The aim of this study was to investigate the effect of melatonin on oxidative stress and senescence marker protein-30 (SMP30) as well as osteopontin (OPN) expression in the hippocampus of rats subjected to vascular dementia (VD). A total of 72 male rats were divided into six groups (n = 12 each) as follows: (i) untreated control (CON), (ii) sham-operated group, (iii) sham-operated + melatonin, (iv) rats exposed to VD induced by permanent bilateral occlusion of the common carotid arteries (BCCAO) leading to chronic cerebral hypoperfusion, (v) rats exposed to VD + melatonin, and (vi) rats exposed to VD + donepezil (DON). At the end of experiment, the hippocampal levels of acetylcholine (ACh), norepinephrine (NE), and dopamine (Dop) were measured. Expression of OPN was determined using immunohistochemistry, and SMP30 expression was determined using real-time PCR in the hippocampus. Hippocampal thiobarbituric acid reactive substances (TBARS) and total antioxidant capacity (TAC) were evaluated. The BCCAO group showed significantly decreased TAC (p < 0.05) and significantly increased in TBARS levels compared with the CON group. In addition, BCCAO significantly decreased (p < 0.05) the expression of both OPN and SMP30 and the levels of ACh, NE, and Dop in the hippocampus compared with CON treatment. Treatment with melatonin significantly increased OPN and SMP30 expression and ACh, NE, and Dop levels in the hippocampus with amelioration of the oxidative stress compared with BCCAO rats. Melatonin might produce a neuroprotective effect through its antioxidant action and by increasing the expression of SMP30 and OPN that is not comparable with that of DON.

Diabetic Status Influences the Storage of Melatonin in Human Salivary Glands

Recently we reported on the detailed localization of melatonin (and its receptors) in human salivary glands, revealing that serous cells are able to store and secrete melatonin into saliva. Since we found that type 2 diabetic patients display reduced melatonin content in saliva, our next step was to examine the presence of melatonin in salivary glands removed from type 2 diabetic subjects. The resulting data were compared with those previously obtained by identical procedures in non-diabetics, to establish if the diabetic status may affect melatonin distribution. Bioptic samples of diabetic parotid and submandibular glands were fixed, dehydrated, embedded in Epon Resin and processed to demonstrate melatonin reactivity by the immunogold staining method. The labeling density (expressed as the number of gold particles per μm² /granule) and the percentage of melatonin-positive granules were assessed in diabetic samples. These values were compared with those in non-diabetic samples and differences were evaluated. In parotid and submandibular diabetic glands the reactivity for melatonin was specifically associated with secretory granules and small vesicles in serous cells. Melatonin reactivity was higher in parotid than in submandibular glands. Our data were in line with those obtained in our previous study on non-diabetic glands. Diabetic salivary glands showed a higher labeling density and a lower number of melatonin-positive granules compared to non-diabetic glands. Taken together, these data might explain the decreased salivary melatonin content and the associated oral problems observed in diabetics. Anat Rec, 301:711-716, 2018. © 2017 Wiley Periodicals, Inc.

Circadian Rhythm Regulates Development of Enamel in Mouse Mandibular First Molar

Rhythmic incremental growth lines and the presence of melatonin receptors were discovered in tooth enamel, suggesting possible role of circadian rhythm. We therefore hypothesized that circadian rhythm may regulate enamel formation through melatonin receptors. To test this hypothesis, we examined expression of melatonin receptors (MTs) and amelogenin (AMELX), a maker of enamel formation, during tooth germ development in mouse. Using qRT-PCR and immunocytochemistry, we found that mRNA and protein levels of both MTs and AMELX in normal mandibular first molar tooth germs increased gradually after birth, peaked at 3 or 4 day postnatal, and then decreased. Expression of MTs and AMELX by immunocytochemistry was significantly delayed in neonatal mice raised in all-dark or all-light environment as well as the enamel development. Furthermore, development of tooth enamel was also delayed showing significant immature histology in those animals, especially for newborn mice raised in all daylight condition. Interestingly, disruption in circadian rhythm in pregnant mice also resulted in delayed enamel development in their babies. Treatment with melatonin receptor antagonist 4P-PDOT in pregnant mice caused underexpression of MTs and AMELX associated with long-lasting deficiency in baby enamel tissue. Electromicroscopic evidence demonstrated increased necrosis and poor enamel mineralization in ameloblasts. The above results suggest that circadian rhythm is important for normal enamel development at both pre- and postnatal stages. Melatonin receptors were partly responsible for the regulation.