Unilateral maxillary molar extraction influences AQP5 expression and distribution in the rat submandibular salivary gland

P2X7R and P2X4R expression of mice submandibular gland in high-fat diet/streptozotocin-induced type 2 diabetes

Type 2 diabetes mellitus (T2DM) is a chronic inflammatory disease that can compromise the functioning of various organs, including the salivary glands (SG). The purinergic system is one of the most important inflammatory pathways in T2DM condition, and P2X7R and P2X4R are the primary purinergic receptors in SG that regulate inflammatory homeostasis. This study aimed to evaluate P2X7R and P2X4R expression, and morphological changes in the submandibular gland (SMG) in T2DM. Twenty-four 5-week-old mice were randomly assigned to control (CON) and diabetes mellitus (DM) groups (n = 12 each). Body weight, diet, and blood glucose levels were monitored weekly. The histomorphology of the SMG and the expression of the P2X7R, and P2X7R was evaluated by immunohistochemistry (IHC) staining and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) at 11 and 13 weeks of age. Our findings indicate a significant increase in food consumption, body weight, and blood glucose levels in the DM group. Although a significant increase in P2X7R and P2X4R expression was observed in the DM groups, the receptor location remained unchanged. We also observed a significant increase in the acinar area in the DM13w group, and a significant decrease in the ductal area in the DM11w and DM13w groups. Targeting purinergic receptors may offer novel therapeutic methods for diabetic complications.

Characterizations of alveolar repair after mandibular second molar extraction: an experimental study in rats

BACKGROUND

Characterizations of rat mandibular second molar extraction socket with significantly different buccal and lingual alveolar ridge width remain unclear.

OBJECTIVE

To observe alterations in the alveolar ridge after extraction of mandibular second molars, and to examine processes of alveolar socket healing in an experimental model of alveolar ridge absorption and preservation.

METHODOLOGY

Eighteen Wistar rats were included and divided into six groups regarding healing time in the study. Bilateral mandibular second molars were extracted. The rats with tooth extraction sockets took 0, 1.5, 2, 3, 4 and 8 weeks of healing. Histological observation, tartrate-resistant acidic phosphatase (TRAP) staining, Masson's trichrome staining, immunohistochemical staining and micro-computed tomography (micro-CT) were applied to estimate alterations in the alveolar ridge.

RESULTS

Different buccal and lingual alveolar ridge width led to different height loss. Lingual wall height (LH) decreased significantly two weeks after tooth extraction. Buccal wall height rarely reduced its higher ridge width. From two to eight weeks after extraction, bone volume (BV/TV), density (BMD), and trabecular thickness (Tb.Th) progressively increased in the alveolar socket, which gradually decreased in Tb.Sp and Tb.N. LH showed no significant change during the same period. Osteogenic marker OCN and OPN increased during bone repair from two to eight weeks. The reduced height of the lingual wall of the tooth extraction socket was rarely repaired in the later repair stage. Osteoclast activity led to absorption of the alveolar ridge of the alveolar bone wall within two weeks after operation. We observed positive expression of EMMPRIN and MMP-9 in osteoclasts that participated in the absorption of the spire region.

CONCLUSION

Extraction of rat mandibular second molars may help the study of alveolar ridge absorption and preservation. The EMMPRIN-MMP-9 pathway may be a candidate for further study on attenuating bone resorption after tooth extraction.

Molar extraction alters gastric mucosa and ghrelin expression in rat stomach: A preliminary study

Objectives:

Ghrelin is a key regulator of food intake and is considered a hunger hormone that affects cognition, memory, glucose metabolism, and antidepressant effects. Altered occlusion, such as a loss of molars, has been thought to retard digestive function. However, the association between occlusion and digestive function remains poorly understood. Here, we aimed to explore the effect of bilateral maxillary molar extraction on the gastrointestinal mucosa of growing rats and the expression of ghrelin and its receptor, growth hormone secretagogue receptor (GHSR).

Material and Methods:

Twenty-four male 5-week-old Wistar rats were divided into control (CON) and experimental (EXP) groups (n = 12/group). The rats in the EXP group underwent extraction of the bilateral maxillary first, second, and third molars under general anesthesia. Rats in the CON group underwent a sham operation. All rats in both the CON and EXP groups were fed a powder diet and water ad libitum. The body weight of all rats was monitored throughout the EXP period. Rats in both the CON and EXP groups were euthanized on days 14 and 28, and the stomachs were isolated and subjected to histological analysis. Paraffin serial sections were prepared using a microtome for hematoxylin-eosin and immunohistochemical staining using anti-ghrelin and anti-GHSR antibodies. The distribution and expression of ghrelin-immunopositive and GHSR cells were detected and observed under a light microscope. Data were statistically analyzed using t-tests (P < 0.05).

Results:

There were no significant differences in body weight between the CON and EXP groups throughout the EXP period. Histological analysis showed that the area of the submucosa (ASM), and the number of ghrelinimmunopositive cells were significantly decreased in the EXP group compared with the CON group on day 14. Alternatively, there was no significant difference in the ASM and the number of ghrelin-immunopositive cells between the CON and EXP groups on day 28, whereas the number of ghrelin receptors showed no differences across groups. Furthermore, the number of eosinophilic blood cells significantly increased in the EXP group on days 14 and 28.

Conclusion:

Our findings suggest that bilateral maxillary molar extraction may trigger stomach mucosal changes and alter digestive function through ghrelin expression in rats. This is the first report that occlusal deficiency could alter ghrelin expression in the mucosa of the rat stomach, thus raising concerns about the consequential role of ghrelin.

Changes of the condylar cartilage and subchondral bone in the temporomandibular joints of rats under unilateral mastication and expression of Insulin-like Growth Factor-1

OBJECTIVES

This study aimed to define changes in the rat condylar cartilage and subchondral bone using the unilateral mastication model.

MATERIALS AND METHODS

In this study, forty 4-week-old Wistar rats were randomly divided into experimental (n = 20) and control group (n = 20). In the experimental group, unilateral dental splints were placed on the occlusal surface of left maxillary molars. The rats were sacrificed at 1, 2, 3, and 4 weeks after placement of the splint. Micro-CT scanning and histological staining were performed to observe the changes in the mandibular condylar cartilage and subchondral bone. Levels of insulin-like growth factor-1 (IGF-1) were determined via immunohistochemistry to analyse the occurrence of osteogenic changes.

RESULTS

Micro-CT scanning findings demonstrated the occurrence of asymmetric growth of condyle in the experimental group. The condylar cartilage and subchondral bone exhibited degradation on the chewing side of the experimental group and showed decreased bone mineral density, thinner cartilage thickness, and increased degree of degeneration and osteoclast activity. Compared with the control group, the expression of IGF-1 was remarkably higher on the non-chewing side.

CONCLUSION

Long-term unilateral mastication can lead to the occurrence of degenerative changes in the condylar cartilage and subchondral bone during growth and development. IGF-1 may play a role in promoting the process of osteogenesis.

Occlusional Modifications Reversibly Alter Aquaporin 5 Expression and Localization in Rat Salivary Glands

Background

Aquaporin 5 (AQP5) is a water channel–forming protein that plays a key role in saliva secretion. A decrease in masticatory function associated with the molar extraction adversely affects the submandibular salivary gland (SMG) in rats, inducing hypertrophic changes in the acinar cells and the expression of AQP5 in acinar cells or intercalated duct of the SMG. However, changes in AQP5 expression and localization in the SMG in association with occlusal modification have not been fully characterized.

Methods

We examined the influence of the decline and recovery of masticatory function on expression and localization of AQP5 in the rat SMG by inserting and removing an incisor bite plate (IBP). Thirty 5-week-old male Wistar rats were randomly divided into IBP (n = 12), recovery (REC) (n = 6), and control (CON) (n = 12) groups. Each rat in both the IBP and REC groups was fitted with the IBP on its maxillary incisors. Rats without the IBPs served as controls. All rats were fed powder diet and water ad libitum. Rats in the IBP and CON groups were sacrificed after 14 (n = 6) and 28 (n = 6) days after the IBP attachment. In the REC group, the IBP was detached on the 14th day and sacrificed on 28th day after the IBP attachment. AQP5 mRNA expression was quantified by reverse transcription–polymerase chain reaction. Changes in the localization of AQP5 were tracked by immunohistochemical staining.

Results

Attachment of IBP resulted in a decrease in the expression of AQP5 in the IBP group. Changes in the localization of AQP5 were observed between 14 and 28 days in the IBP group. In contrast, changes in the expression and localization of AQP5 were not observed in the REC group.

Conclusion

Findings suggested that a loss of molar occlusion, due to the IBP attachment, altered AQP5 expression and localization in the rat SMG. However, removal of the bite plate allowed the recovery of both AQP5 expression and its normal localization in the SMGs.

Orthognathic surgery induces genomewide changes longitudinally in DNA methylation in saliva

OBJECTIVE

Orthognathic surgery dramatically changes morphology of the maxillofacial deformity and improves the malocclusion morphologically and functionally. We investigated the influence of orthognathic surgery on genomewide DNA methylation in saliva.

METHODS

Saliva was obtained from nine patients undergoing orthognathic surgery and two healthy reference individuals before and 3 months after orthognathic surgery. Genomewide DNA methylation profiling of saliva (341,482 CpG dinucleotides) was conducted using Infinium HumanMethylation450 BeadChips.

RESULTS

Comparison between pre- and postsurgery saliva samples revealed significant changes in DNA methylation patterns at 2,381 CpG sites (p < 0.01) with suggestive significance. The differentially methylated probe sets were significantly associated with the cancer pathway (p = 2.8 × 10^-7 ; a false discovery rate q-value = 3.7 × 10^-4 ) and PI3K-Akt signalling pathway (p = 2.4 × 10^-5 ; a false discovery rate q-value = 3.1 × 10^-2 ).

CONCLUSION

Pathway enrichment analysis of genes with suggestive significance demonstrated that altered DNA methylation in saliva of patients undergoing orthognathic surgery, possibly as a response to surgical stress or bone injury. Further studies with a large sample size and long-term observation are needed to validate the phenomena identified in this study.

Proteomic analysis reveals an impaired Ca2+/AQP5 pathway in the submandibular gland in hypertension

Hypertension is a systemic disorder that affects numerous physiological processes throughout the body. Improper sodium transport is a common comorbidity of hypertension, and sodium transport is also critical for maintaining the secretion of submandibular glands, whether the function of submandibular glands is affected by hypertension remains unclear. To determine whether hypertension induces changes in the protein expression of submandibular glands, we compared the proteome of submandibular glands from 14-week-old spontaneously hypertensive rats (SHR) and Wistar Kyoto (WKY) rats using LC-MS/MS. The results revealed that 95 proteins displayed different levels of expression between the submandibular glands from the SHRs and WKYs. Among these, 35 proteins were more abundant, and 60 proteins were less abundant in the SHR compared with the WKY rats. Specifically, aquaporin 5 and parvalbumin, which are correlated with water transport and intracellular Ca²⁺ signal transduction, were verified to exhibit differences in protein abundance. Impaired Ca²⁺ response to carbachol was confirmed in the acinar cells from SHRs, and hyposecretion by the submandibular glands was further confirmed by in vivo saliva collection. In conclusion, the proteomic analysis of the submandibular glands of SHRs revealed novel changes in protein abundance that provides possible mechanisms connecting hypertension and hyposecretion in submandibular glands.

Degeneration of fungiform and circumvallate papillae following molar extraction in rats

OBJECTIVE

Proper occlusion facilitates food intake and gustatory function is indispensable for the enjoyment of food. Although an interaction between dentoalveolar and gustatory afferent neurons has been suggested by previous studies, the relationship between occlusion and gustation remains unclear. This study investigated the effect of upper molar extraction which diminished occlusal support on peripheral gustatory receptors in rats.

MATERIALS AND METHODS

Thirty-six 7-week-old male Wistar rats were randomly assigned to either the experimental or the control group. All maxillary molars were extracted from rats in the experimental group under anesthesia, while a sham operation was conducted in the control group. The rats were euthanized 7, 14 or 28 days after the procedure. The morphology of the circumvallate papillae and taste buds using immunohistochemical methods and the fungiform papillae were visualized with 1% methylene blue.

RESULTS

Defects in the gustatory epithelium were observed after maxillary molar extraction. Rats in the experimental group had significantly fewer fungiform papillae, narrower circumvallate papillae, shallower trench depth, smaller trench area, smaller taste bud area, lower ratios of taste bud area to trench area and fewer taste buds than those in the control group.

CONCLUSIONS

The findings indicate that molar extraction would affect peripheral gustatory receptors. This is the first study to characterize changes in rat fungiform and circumvallate papillae after maxillary molar extraction. This study suggests a possible synergic relationship between dentoalveolar perception and gustatory function, which has clinical implications that occlusion is closely correlated with gustatory perception.

Expression of glucose-dependent insulinotropic polypeptide and its receptor in the rat major salivary glands

Glucose-dependent insulinotropic polypeptide receptors (GIPR) are expressed throughout the body. The expression of its ligand, glucose-dependent insulinotropic polypeptide (GIP) however, has only been reported in a limited numbers of organs. Although the rat submandibular salivary gland (SMG) has been found to express GIP, its biological role is still not understood. Moreover, nothing is known about the expression of GIP in other types of salivary glands, i.e. the parotid (PG) and sublingual (SLG) glands. We detected the expression of GIP mRNA in the rat PG, SMG and SLG. Immunohistochemical analyses revealed that GIP and GIPR were expressed only in the ductal area of all types of major salivary glands, and no immunostaining was found in the acini area. We also found GIP expression in the rat SMG to be age dependent, with 8-week-old rats showing 2-3-fold higher than those of 9- and 11-week-old rats, respectively. This is the first study to indicate both GIP and GIPR expression in the rat major salivary glands, as well as its variation in the rat SMG during the growth period. These findings are crucial for a better understanding of the physiological function of GIP in rat major salivary gland.

Adiponectin increases secretion of rat submandibular gland via adiponectin receptors-mediated AMPK signaling

Adiponectin and adiponectin receptors (AdipoR1/2) are expressed in various tissues and are involved in the regulation of multiple functions such as energy metabolism and inflammatory responses. However, the effect of adiponectin and AdipoRs in submandibular glands has not been fully evaluated. In the present study, we found that mRNA and protein of both adiponectin and AdipoR1/2 were expressed in rat submandibular glands and in the SMG-C6 cell line, as evidenced by RT-PCR and Western blot analysis. Immunofluorescence staining showed that adiponectin was diffused in the cytoplasm, while AdipoR1/2 was concentrated in the membrane of acinar cells. Saliva flow was significantly increased by full length adiponectin (fAd) or globular adiponectin (gAd) perfusion in isolated rat submandibular glands. 5-Aminoimidazole-4-carboxamide-1-4-ribofuranoside (AICAR), an adenosine monophosphate activated protein kinase (AMPK) activator, also increased saliva secretion. fAd, gAd, and AICAR all increased the average width of apical tight junctions in perfused submandibular glands, and decreased transepithelial electrical resistance (TER) in SMG-C6 cells, suggesting that adiponectin promoted secretion by modulating paracellular permeability. fAd and gAd increased p-AMPK levels, while AraA, an AMPK antagonist, abolished fAd- and gAd-induced changes in secretion, tight junction ultrastructure, and TER. Moreover, both AdipoR1 and AdipoR2 were required for fAd- or gAd-induced p-AMPK and TER responses, suggesting from their inhibition following AdipoR1 or AdipoR2 knockdown, and co-knockdown of AdipoRs by RNA interference. Our results suggest that adiponectin functions as a promoter of salivary secretion in rat submandibular glands via activation of AdipoRs, AMPK, and paracellular permeability.