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Background This study focused on the aging mechanism and degradation of mechanical and structural features of elastodontic appliances (EA) under artificial and intraoral aging to achieve oral myofunctional therapy with particular removable silicone elastomer devices. Materials and methods EAs artificially aged in saliva with different pH values were investigated through cyclic compression testing along with characterization techniques (Scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy), and characterization analysis was also performed on clinically retrieved EAs. Results Artificial aging was found to have minimal effect on the structural properties of EAs, and intraorally aged samples showed perceptible micro-morphology. The Mullins index and peak stress decreased ( P <0.01), while the compression set increased with prolonged aging time. Samples in alkaline saliva showed the largest Mullins effect ( P <0.05). Conclusions The aging mechanism of the elastomer was found to be the crosslinking of main chains and scission of side chains. The presence of OH- enhanced the rupture degree of side bonds. The decline in viscoelastic properties was shown to be more severe with longer service durations. Clinical relevance Research on how the salivary environment and pH affect the aging characteristics of EAs is vital for guiding clinical applications and future modifications to extend their clinical lifetime.

Aging-related salivary dysfunction commonly induces the poor oral health, including decreased saliva flow and dental caries. Although the clinical significance of the salivary glands is well-known, the complex metabolic pathways contributing to the aging-dysfunction process are only beginning to be uncovered. Here, we provide a comprehensive overview of the metabolic changes in aging-mediated salivary gland dysfunction as a key aspect of oral physiology. Several metabolic neuropeptides or hormones are involved in causing or contributing to salivary gland dysfunction, including hyposalivation and age-related diseases. Thus, aging-related metabolism holds promise for early diagnosis, increased choice of therapy and the identification of new metabolic pathways that could potentially be targeted in salivary gland dysfunction.

Age‐related dysfunction of salivary glands (SGs) leading to xerostomia or dry mouth is typically associated with increased dental caries and difficulties in mastication, deglutition or speech. Inflammaging‐induced hyposalivation plays a significant role in aged SGs; however, the mechanisms by which ageing shapes the inflammatory microenvironment of SGs remain unclear. Here, we show that reduced salivary secretion flow rate in aged human and mice SGs is associated with impaired autophagy and increased M1 polarization of macrophages. Our study reveals the crucial roles of SIRT6 in regulating macrophage autophagy and polarization through the PI3K/AKT/mTOR pathway, as demonstrated by generating two conditional knock out mice. Furthermore, triptolide (TP) effectively rejuvenates macrophage autophagy and polarization via targeting this pathway. We also design a local delivery of TP‐loaded apoptotic extracellular vesicles (ApoEVs) to improve age‐related SGs dysfunction therapeutically. Collectively, our findings uncover a previously unknown link between SIRT6‐regulated autophagy and macrophage polarization in age‐mediated hyposalivation, while our locally therapeutic strategy exhibits potential preventive effects for age‐related hyposalivation. In this study, we demonstrated impaired autophagy and polarization of macrophage in aged mouse and human salivary gland with age‐related changes. Furthermore, we further validate the in vivo role of SIRT6‐mediated PI3K/AKT/mTOR signal pathway in controlling salivary gland function.

Women experience several systemic changes over all stages of life, many due to hormonal fluctuations. The sensation of dry mouth is the most common oral clinical symptom in women from climacteric period onwards, suggesting that sex hormones are important in maintaining salivary glands and oral homeostasis. Although the oral cavity is not conventional considered a target tissue for oestrogen, the extent to which salivary glands morphology and function are impacted by ageing and hormonal variations remain unknown. Due to the clinical demand for understanding oral changes related to the ageing process, this study aimed to portray the glandular morphological aspects in female during the different stages of life. To achieve this, 85 post-mortem specimens of labial minor salivary glands were obtained from females; they were distributed into three groups: group I (reproductive phase: up to 44 years, n = 18); group II (climateric phase: 45–55 years, n = 21) and group III (post-menopausal phase: over 56 years, n = 46). The most significant changes observed included degenerative parenchymal aspects including the replacement of parenchymal structures by fibrous tissue, inflammatory infiltrate as well as vascular and endothelial changes. Ageing was associated with acinar serous metaplasia ( p  = 0.011), acinar fibrosis ( p  = 0.042) and ductal ectasia ( p  = 0.003). The process of acinar atrophy was observed in all groups, with an increase in severity in group III. These degenerative aspects appear to be age-dependent.

The current study aimed to investigate the effects of ageing on oral immunity using β-defensin (DEFB) 1/2 as a marker and evaluate the effects of curcumin (CUR) on these processes. The study sample included thirty male C57BL/6J mice divided into three groups based on the treatment method used. The young control (YC) and old control (OC) groups received 0·5 % methylcellulose-400 (CUR vehicle) orally for 5 days, whereas the CUR group of older mice received a CUR solution suspended in 0·5 % methylcellulose-400 (dose: 3·0 mg/kg body). DEFB1/2 and immune indicator levels were measured in the saliva and salivary glands post-treatment. The saliva volume and protein content were significantly reduced in the OC group compared with the YC group. CUR administration restored these parameters, decreased DEFB1 expression in the salivary gland and increased DEFB1/2 secretion and DEFB2 expression. These findings were supported by epigenetic gene regulation and partial cytokine activation from changes in WD40 repeat protein 5, TNF alpha and IL-1beta. CUR can partially restore age-related changes in oral immune responses and promote oral health, thereby preventing frailty in the older population through a nutritional therapeutic pathway.

Salivary gland branching morphogenesis is regulated by the functional integration of neuronal signaling, but the underlying mechanisms are not fully understood in aging accelerated klotho‐deficient (Kl−/−) mice. Here, we investigated whether the neuropeptides substance P (SP) and neuropeptide Y (NPY) affect the branching morphogenesis of embryonic salivary glands in aging Kl−/− mice. In the salivary glands of embryonic Kl−/− mice, morphological analysis and immunostaining revealed that epithelial bud formation, neuronal cell proliferation/differentiation, and the expression of the salivary gland functional marker ZO‐1 were decreased in embryonic ductal cells. Incubation with SP/NPY at E12‐E13d promoted branching morphogenesis, parasympathetic innervation, and epithelial proliferation in salivary glands of embryonic Kl−/− mice. The ERK inhibitor U0126 specifically inhibited neuronal substance‐induced epithelial bud formation in the embryonic salivary gland. RNA‐seq profiling analysis revealed that the expression of fibroblast growth factors/fibroblast growth factors (FGFs/FGFRs) and their receptors was significantly regulated by SP/NPY treatment in the embryonic salivary gland (E15). The FGFR inhibitor BGJ389 inhibited new branching formation induced by SP and NPY treatment and ERK1/2 expression. These results showed that aging may affect virtually the development of salivary gland by neuronal dysfunction. The neuropeptides SP/NPY induced embryonic salivary gland development through FGF/FGFR/ERK1/2‐mediated signaling. Schematic representation of Neuropeptide SP/NPY pathways regulating sallvary gland morphogenesis/development. SP/NPY induced ambryonic sallvary gland development through FGF/FGFR/ERK1/2‐mediated signalling.

Previous studies have evaluated the roles of T and B cells in the pathogenesis of Sjögren’s syndrome (SS); however, their relationships with age-dependent and metabolic abnormalities remain unclear. We examined the impacts of changes associated with aging or metabolic abnormalities on populations of T and B cells and SS disease severity. We detected increased populations of IL-17-producing T and B cells, which regulate inflammation, in the salivary glands of NOD/ShiLtJ mice. Inflammation-induced human submandibular gland cell death, determined based on p-MLKL and RIPK3 expression levels, was significantly increased by IL-17 treatment. Among IL-17-expressing cells in the salivary gland, peripheral blood, and spleen, the α4β7 (gut-homing integrin)-negative population was significantly increased in aged NOD/ShiLtJ mice. The α4β7-positive population markedly increased in the intestines of aged NOD/ShiLtJ mice following retinoic acid (RA) treatment. A significant increase in α4β7-negative IL-17-expressing cells in salivary glands may be involved in the onset and progression of SS. These results suggest the potential therapeutic utility of RA in SS treatment.

Aging elicits quantitative and qualitative changes in different immune components, leading to disruption of tolerogenic circuits and development of autoimmune disorders. Galectin-1 (Gal1), an endogenous glycan-binding protein, has emerged as a regulator of immune cell homeostasis by shaping the fate of myeloid and lymphoid cells. Here, we demonstrate that aged Gal1-null mutant (Lgals1−/−) mice develop a spontaneous inflammatory process in salivary glands that resembles Sjögren’s syndrome. This spontaneous autoimmune phenotype was recapitulated in mice lacking β1,6N-acetylglucosaminyltransferase V (Mgat5), an enzyme responsible for generating β1,6-branched complex N-glycans, which serve as a major ligand for this lectin. Lack of Gal1 resulted in CD11c⁺ dendritic cells (DCs) with higher immunogenic potential, lower frequency of Foxp3⁺ regulatory T cells (Tregs), and increased number of CD8⁺ T cells with greater effector capacity. Supporting its tolerogenic activity, Gal1 expression decreased with age in autoimmunity-prone nonobese diabetic (NOD) mice. Treatment with recombinant Gal1 restored tolerogenic mechanisms and reduced salivary gland inflammation. Accordingly, labial biopsies from primary Sjögren’s syndrome patients showed reduced Gal1 expression concomitant with higher number of infiltrating CD8⁺ T cells. Thus, endogenous Gal1 serves as a homeostatic rheostat that safeguards immune tolerance and prevents age-dependent development of spontaneous autoimmunity.

Salivary gland dysfunction induces salivary flow reduction and a dry mouth, and commonly involves oral dysfunction, tooth structure deterioration, and infection through reduced salivation. This study aimed to investigate the impact of aging on the salivary gland by a metabolomics approach in an extensive aging mouse model, SAMP1/Klotho -/- mice. We found that the salivary secretion of SAMP1/Klotho -/- mice was dramatically decreased compared with that of SAMP1/Klotho WT (+/+) mice. Metabolomics profiling analysis showed that the level of acetylcholine was significantly decreased in SAMP1/Klotho -/- mice, although the corresponding levels of acetylcholine precursors, acetyl-CoA and choline, increased. Interestingly, the mRNA and protein expression of choline acetyltransferase (ChAT), which is responsible for catalyzing acetylcholine synthesis, was significantly decreased in SAMP1/Klotho -/- mice. The overexpression of ChAT induced the expression of salivary gland functional markers (α–amylase, ZO-1, and Aqua5) in primary cultured salivary gland cells from SAMP1/Klotho +/+ and -/- mice. In an in vivo study, adeno-associated virus (AAV)-ChAT transduction significantly increased saliva secretion compared with the control in SAMP1/Klotho -/- mice. These results suggest that the dysfunction in acetylcholine biosynthesis induced by ChAT reduction may cause impaired salivary gland function

Radiation therapy of head and neck cancers frequently leads to irreversible dry mouth that severely compromises the quality of life and is difficult to remedy. Mesenchymal stem cells (MSCs) could ameliorate this adverse effect, but their application is limited by high variations of conventional tissue-derived MSCs and many practical challenges of cell therapies. This study investigated the potential of extracellular vesicles (EVs) from standardized MSCs derived from iPS cells (iMSCs) in ameliorating radiation-caused dry mouth. In a mouse model, locally injected young but not aging iMSC-EVs after radiation preserved saliva secretion and acinar structures. Mechanistically, young iMSC-EVs reversed the acute inhibition of physiological inflammation and chronic increase of pathogenic inflammation in radiated salivary glands, which is related to the preservation of tissue-resident macrophages and polarization of infiltrated macrophages. At both acute and chronic phase after radiation, iMSC-EVs enhanced mitochondria-related cell metabolism pathways such as Oxidative Phosphorylation that modulate cell survival and macrophage polarization. OXPHOS-promoting protein eIF5A and spermidine required for functional eIF5A hypusination are much richer in effective young iMSC-EVs compared with inert aging EVs. Moreover, young iMSC-EV treatment increased hypusinated eIF5A in radiated salivary glands, especially in macrophages. These findings together indicated that iMSC-EVs are a promising cell-free product to restore salivary gland function impaired by radiation, which is mediated by maintaining immune balance and mitochondria-related cell metabolism at both acute and chronic phases. Highlights Locally injected mesenchymal stem cell extracellular vesicles ameliorated long-term dry mouth, a common side effect of radiation therapy for head and neck cancer. This treatment reversed the acute inhibition of physiological inflammation and the chronic increase of pathogenic inflammation by radiation. Therapeutic effects of extracellular vesicles are related to immunomodulatory metabolic changes such as OXPHOS in recipient cells, especially macrophages. Spermidine and eIF5A proteins delivered by extracellular vesicles contribute to their therapeutic effects.