Elastin‑derived peptides are involved in the processes of human temporomandibular disorder by inducing inflammatory responses in synovial cells

Temporomandibular joint disc responses to installation and removal of the experimental malocclusion

BACKGROUND

Aberrant occlusion and aging are two main risks for temporomandibular joint (TMJ) degeneration.

OBJECTIVE

To assess the combined impact of occlusion and age on TMJ disc.

METHODS

To avoid the confounding impact of gender, presently, 126 female C57BL/6J mice, 63 youngsters, 6-week old and 63 adults, 28-week old, were used. An experimental bilateral anterior crossbite (BAC) relation was created by installing metal tubes onto the mandibular incisors. Mice were sacrificed at 3, 7 and 11 weeks (n = 9). Additionally, the installed tubes were removed at 7 weeks in removal groups and the TMJs were sampled after another 4 weeks (n = 9). Disc changes were detected by histomorphology, immunohistochemistry, and western blot assays.

RESULTS

Disc deformation was obvious in BAC groups. The typical change was hyperplasia at the posterior region of the disc where there was significant infiltration of inflammatory cells. Expressions of the inflammatory markers, including tumour necrosis factor-α and interleukin-1β, and the catabolic markers, including fibronectin (FN), FN N-terminal fragments, and vascular endothelial growth factor-A, were all increased. The changes were more obvious in adults than in youngsters. Removal of BAC attenuated inflammatory and catabolic changes in the youngsters, but the inflammatory markers recovered little in the adults.

CONCLUSION

TMJ disc responds to BAC by degeneration and inflammation, and respond to BAC removal by rehabilitation. Adult discs show severer degeneration responses to BAC and a lower level of anti-inflammatory capability to BAC removal than the youngster's discs. Animals cannot be equated with humans. The human disc response to occlusion changes worth further exploration.

Synovial microenvironment in temporomandibular joint osteoarthritis: crosstalk with chondrocytes and potential therapeutic targets

Temporomandibular joint osteoarthritis (TMJOA) is considered to be a low-grade inflammatory disease involving multiple joint tissues. The crosstalk between synovium and cartilage plays an important role in TMJOA. Synovial cells are a group of heterogeneous cells and synovial microenvironment is mainly composed of synovial fibroblasts (SF) and synovial macrophages. In TMJOA, SF and synovial macrophages release a large number of inflammatory cytokines and extracellular vesicles and promote cartilage destruction. Cartilage wear particles stimulate SF proliferation and macrophages activation and exacerbate synovitis. In TMJOA, chondrocytes and synovial cells exhibit increased glycolytic activity and lactate secretion, leading to impaired chondrocyte matrix synthesis. Additionally, the synovium contains mesenchymal stem cells, which are the seed cells for cartilage repair in TMJOA. Co-culture of chondrocytes and synovial mesenchymal stem cells enhances the chondrogenic differentiation of stem cells. This review discusses the pathological changes of synovium in TMJOA, the means of crosstalk between synovium and cartilage, and their influence on each other. Based on the crosstalk between synovium and cartilage in TMJOA, we illustrate the treatment strategies for improving synovial microenvironment, including reducing cell adhesion, utilizing extracellular vesicles to deliver biomolecules, regulating cellular metabolism and targeting inflammatory cytokines.

Elastin-derived peptides (EDPs) as a potential pro-malignancy factor in human leukemia cell lines

The extracellular matrix (ECM) is currently considered to be an important factor influencing the migration and progression of cancer cells. Therefore, the aim of our study was to investigate the mechanism of action of elastin-derived peptides in cancerous cells derived from the immunological system, i.e., HL-60, K562, and MEG-A2 cell lines. Moreover, an attempt to clarify the involvement of c-SRC kinase in EDP mechanism of action was also undertaken. Our data show that the VGVAPG and VVGPGA peptides are not toxic in the studied cell lines. Moreover, due to the involvement of KI67 and PCNA proteins in the cell cycle and proliferation, we can assume that neither peptide stimulates cell proliferation. Our data suggest that both peptides could initiate the differentiation process in all the studied cell lines. However, due to the different origins (HL-60 and K562-leukemic cell line vs. MEG-A2-megakaryoblastic origin) of the cell lines, the mechanism may differ. The increase in the ELANE mRNA expression noted in our experiments may also suggest enhancement of the migration of the tested cells. However, more research is needed to fully explain the mechanism of action of the VGVAPG and VVGPGA peptides in the HL-60, K562, and MEG-A2 cell lines. HIGHLIGHTS: • VGVAPG and VVGPGA peptides do not affect the metabolic activity of HL-60, K562, and MEG-A2 cells. • mTOR and PPARγ proteins are involved in the mechanism of action of VGVAPG and VVGPGA peptides. • Both peptides may initiate differentiation in HL-60, K562, and MEG-A2 cell lines.

Temporomandibular Joint Disorder: An integrated study of the pathophysiology, neural mechanisms, and therapeutic strategies

OBJECTIVE

The study aims to investigate Temporomandibular Joint Disorder (TMJD) through a interdisciplinary lens, integrating insights from neuroscience, dentistry, and psychology to dissect its complex pathophysiology and neural mechanisms. It focuses on exploring the neurobiological underpinnings of TMJD, emphasizing the role of pain perception, modulation, and the impact of neurophysiological changes on the disorder.

DESIGN

This is a comprehensive narrative review of the literature.

RESULTS

Research findings pinpoint altered pain perception and modulation processes as central neural mechanisms contributing to TMJD, highlighting the importance of personalized treatment approaches due to the disorder's complexity and patient variability. The study recognizes advances in neuroscience offering new treatment avenues, such as neuromodulation and biofeedback, which provide non-invasive and personalized options. However, it also addresses the challenges in TMJD research, such as the multifaceted nature of the disorder and the need for more comprehensive, interdisciplinary strategies in research and clinical practice.

CONCLUSIONS

TMJD is a multifaceted disorder requiring an interdisciplinary approach for effective management. The study stresses the crucial role of neuroscience in understanding and treating TMJD, facilitating the development of innovative treatment strategies. It emphasizes the need for further research, advocating an integrated approach that combines neuroscience, dentistry, and psychology to address TMJD's complexities comprehensively and improve patient care, thereby enhancing the quality of life for affected individuals.

Critical signaling molecules in the temporomandibular joint osteoarthritis under different magnitudes of mechanical stimulation

The mechanical stress environment in the temporomandibular joint (TMJ) is constantly changing due to daily mandibular movements. Therefore, TMJ tissues, such as condylar cartilage, the synovial membrane and discs, are influenced by different magnitudes of mechanical stimulation. Moderate mechanical stimulation is beneficial for maintaining homeostasis, whereas abnormal mechanical stimulation leads to degeneration and ultimately contributes to the development of temporomandibular joint osteoarthritis (TMJOA), which involves changes in critical signaling molecules. Under abnormal mechanical stimulation, compensatory molecules may prevent degenerative changes while decompensatory molecules aggravate. In this review, we summarize the critical signaling molecules that are stimulated by moderate or abnormal mechanical loading in TMJ tissues, mainly in condylar cartilage. Furthermore, we classify abnormal mechanical stimulation-induced molecules into compensatory or decompensatory molecules. Our aim is to understand the pathophysiological mechanism of TMJ dysfunction more deeply in the ever-changing mechanical environment, and then provide new ideas for discovering effective diagnostic and therapeutic targets in TMJOA.

Design and Synthesis of Novel Ultralong-Acting Peptides as EDP-EBP Interaction Inhibitors for Pulmonary Fibrosis Treatment

The increased remodeling of the extracellular matrix (ECM) in pulmonary fibrosis (PF) generates bioactive ECM fragments called matricryptins, which include elastin-derived peptides (EDPs). The interaction between EDPs and their receptors, including elastin-binding protein (EBP), plays a crucial role in exacerbating fibrosis. Here, we present LXJ-02 for the first time, a novel ultralong-acting inhibitor that disrupts the EDPs/EBP peptide-protein interaction, promoting macrophages to secrete matrix metalloproteinase-12 (MMP-12), and showing great promise as a stable peptide. MMP-12 has traditionally been implicated in promoting inflammation and fibrosis in various acute and chronic diseases. However, we reveal a novel role of LXJ-02 that activates the macrophage-MMP-12 axis to increase MMP-12 expression and degrade ECM components like elastin. This leads to the preventing of PF while also improving EDP-EBP interaction. LXJ-02 effectively reverses PF in mouse models with minimal side effects, holding great promise as an excellent therapeutic agent for lung fibrosis.

The Emerging Role of MMP12 in the Oral Environment

Matrix metalloproteinase-12 (MMP12), or macrophage metalloelastase, plays important roles in extracellular matrix (ECM) component degradation. Recent reports show MMP12 has been implicated in the pathogenesis of periodontal diseases. To date, this review represents the latest comprehensive overview of MMP12 in various oral diseases, such as periodontitis, temporomandibular joint dysfunction (TMD), orthodontic tooth movement (OTM), and oral squamous cell carcinoma (OSCC). Furthermore, the current knowledge regarding the distribution of MMP12 in different tissues is also illustrated in this review. Studies have implicated the association of MMP12 expression with the pathogenesis of several representative oral diseases, including periodontitis, TMD, OSCC, OTM, and bone remodelling. Although there may be a potential role of MMP12 in oral diseases, the exact pathophysiological role of MMP12 remains to be elucidated. Understanding the cellular and molecular biology of MMP12 is essential, as MMP12 could be a potential target for developing therapeutic strategies targeting inflammatory and immunologically related oral diseases.

Immunohistochemical Markers of Temporomandibular Disorders: A Review of the Literature

Temporomandibular disorders (TMD) are a group of internal derangements encompassing dysfunction, displacement, degeneration of the temporomandibular joints and surroundings muscles of mastication, often accompanied by pain. Relationships between TMD and various chemical biomarkers have been examined throughout the years. This paper aims to gather evidence from the literature regarding other biomarkers and presenting them as one systematic review to investigate the potential links between TMD and different biochemical activity. To identify relevant papers, a comprehensive literature search was carried out in MEDLINE/PubMED, EMBASE, Web of Science and a manual search was performed in the International Journal of Oral and Maxillofacial Surgery, Journal of Oral and Maxillofacial surgery, and Journal of Cranio-Maxillo-Facial Surgery. The literature review produced extensive results relating to the biochemical and immunohistochemical markers of TMD. Many enzymes, inflammatory markers, proteoglycans, and hormones were identified and organized in tables, along with a brief description, study design, and conclusion of each study. Through this review, recurring evidence provides confidence in suggesting involvement of certain biomarkers that may be involved in this complex pathogenesis, in addition to pointing to differences in gender prevalence of TMD. However, more organized research on large human samples needs to be conducted to delve deeper into the understanding of how this disease develops and progresses.

Identification of crucial salivary proteins/genes and pathways involved in pathogenesis of temporomandibular disorders

Temporomandibular disorder (TMD) is a collective term for a group of conditions that lead to impairment of the function of the temporomandibular joint. The proteins/genes and signaling pathways associated with TMD are still poorly understood. The aim of this study was to identify key differentially expressed salivary proteins/genes (DEGs) associated with TMD progression using LC-MS/MS coupled with a bioinformatics approach. The protein–protein interaction network was obtained from the STRING database and the hub genes were identified using Cytoscape including cytoHubba and MCODE plug-ins. In addition, enrichment of gene ontology functions and the Reactome signaling pathway was performed. A total of 140 proteins/genes were differentially expressed. From cluster analysis, a set of 20 hub genes were significantly modulated: ALB, APOA1, B2M, C3, CAT, CLU, CTSD, ENO1, GSN, HBB, HP, HSPA8, LTF, LYZ, MMP9, S100A9, SERPINA1, TF, TPI1, and TXN. Two enriched signaling pathways, glycolysis and gluconeogenesis, and tryptophan signaling pathway involving the hub genes CAT, ENO1, and TPI1 have been identified. The rest of the hub genes were mainly enriched in the innate immune system and antimicrobial peptides signaling pathways. In summary, hub DEGs and the signaling pathways identified here have elucidated the molecular mechanisms of TMD pathogenesis.

Elastin-Derived Peptides in the Central Nervous System: Friend or Foe

Elastin is one of the main structural matrix proteins of the arteries, lung, cartilage, elastic ligaments, brain vessels, and skin. These elastin fibers display incredible resilience and structural stability with long half-life. However, during some physiological and pathophysiological conditions, elastin is prone to proteolytic degradation and, due to the extremely low turnover rate, its degradation is practically an irreversible and irreparable phenomenon. As a result of elastin degradation, new peptides called elastin-derived peptides (EDPs) are formed. A growing body of evidence suggests that these peptides play an important role in the development of age-related vascular disease. They are also detected in the cerebrospinal fluid of healthy people, and their amount increases in patients after ischemic stroke. Recently, elastin-like polypeptides have been reported to induce overproduction of beta-amyloid in a model of Alzheimer's disease. Nevertheless, the role and mechanism of action of EDPs in the nervous system is largely unknown and limited to only a few studies. The article summarizes the current state of knowledge on the role of EDPs in the nervous system.

Metalloelastase-12 is involved in the temporomandibular joint inflammatory response as well as cartilage degradation by aggrecanases in STR/Ort mice

Temporomandibular joint dysfunction (TMJD) is characterised by clinical symptoms involving both the masticatory muscles and the temporomandibular joint (TMJ). Disc internal derangement and osteoarthritis (OA) are the most common forms of TMJD. Currently, the molecular process associated with degenerative changes in the TMJ is unclear. Our previous study showed that elastin-digested peptides act on human TMJ synovial cells and lead to upregulation of interleukin-6 (IL-6) and metalloelastase-12 (MMP-12; an elastin-degrading enzyme) in vitro. However, there is limited information regarding the involvement of elastin-degradation by MMP-12 in the processes of inflammatory responses and cartilage degradation in vivo. STR/Ort mice were used as a model of TMJ OA in the present study. Significant articular cartilage degeneration was observed starting at 20 weeks of age in the STR/Ort mice and this progressed gradually until 40 weeks, compared with the age-matched CBA mice. Immunostaining analysis showed that MMP-12 and IL-6 were expressed in the chondrocytes in the superficial zones of the cartilage. Immunostaining also showed that aggrecanases [a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-4 and ADAMTS-5] were expressed in the chondrocytes in the superficial zones of the cartilage. These findings suggest that an inflammatory and degradative process was initiated in the TMJ. Harmful mechanical stimuli, particularly pressure, may cause damage to the elastin fibres in the most elastin-rich superficial layer of the articular cartilage. Elastin-digested peptides are then generated as endogenous warning signals and they initiate a pro-inflammatory cascade. This leads to upregulation of pro-inflammatory mediators, such as IL-6 and MMP-12, which further trigger tissue damage resulting in elevated levels of elastin-digested peptides. IL-6 increases expression of the aggrecanases ADAMTS-4 and ADAMTS-5, following cartilage degradation. This leads to the establishment of a positive feedback loop and may result in chronic inflammation and cartilage degradation of the TMJ in vivo.

Elastin-derived peptide VGVAPG decreases differentiation of mouse embryo fibroblast (3T3-L1) cells into adipocytes

Elastin is a highly elastic protein present in connective tissue. As a result of protease activity, elastin hydrolysis occurs, and during this process, elastin-derived peptides (EDPs) are released. One of the constitutively repeating elastin and EDP building sequences is the hexapeptide VGVAPG. Therefore, the aim of our research was to define the effect of VGVAPG peptide on adipogenesis in a mouse 3T3-L1 cell line. 3T3-L1 cells were differentiated according to a previously described protocol and exposed to increasing concentrations of VGVAPG or VVGPGA peptide. The obtained results showed that VGVAPG peptide does not stimulate reactive oxygen species (ROS) production, caspase-1 activation, and 3T3-L1 cell proliferation. In the second part of the experiments, it was proved that VGVAPG peptide decreased lipid accumulation as measured by oil red O staining, which was confirmed by the profile of increased expression markers of undifferentiated preadipocytes. In our experiments, 10 nM VGVAPG added for differentiating to adipocytes increased the expression of Pref-1, serpin E1, and adiponectin as compared to rosiglitazone (PPARγ agonist)-treated group and simultaneously decreased the expression of VEGF and resistin as compared to the rosiglitazone-treated group. The obtained results show that VGVAPG peptide sustains 3T3 cells in undifferentiated state.

ABBREVIATIONS

DMSO: dimethyl sulphoxide; EBP: elastin-binding protein; EDPs: elastin-derived peptides; FBS: foetal bovine serum; Glb1: gene for beta-galactosidase; LDL: low-density-lipoprotein; PAI-1 (Serpin E1): plasminogen activator inhibitor-1; PBS: phosphate-buffered saline; PPARγ: peroxisome proliferator-activated receptor gamma; Pref-1: preadipocyte factor 1; ROS: reactive oxygen species; VEGF-A: vascular endothelial growth factor-A; VGVAPG: Val-Gly-Val-Ala-Pro-Gly; β-Gal: beta-galactosidase; ORO: oil red O; IBMX: 3-isobutyl-1-methylxanthine; H2DCFDA: 2',7'-dichlorodihydrofluorescein diacetate; DMEM: Dulbecco's Modified Eagle's Medium; VVGPGA: Val-Val-Gly-Pro-Gly-Ala.

Regulation of cellular senescence by extracellular matrix during chronic fibrotic diseases

The extracellular matrix (ECM) is a complex network of macromolecules surrounding cells providing structural support and stability to tissues. The understanding of the ECM and the diverse roles it plays in development, homoeostasis and injury have greatly advanced in the last three decades. The ECM is crucial for maintaining tissue homoeostasis but also many pathological conditions arise from aberrant matrix remodelling during ageing. Ageing is characterised as functional decline of tissue over time ultimately leading to tissue dysfunction, and is a risk factor in many diseases including cardiovascular disease, diabetes, cancer, dementia, glaucoma, chronic obstructive pulmonary disease (COPD) and fibrosis. ECM changes are recognised as a major driver of aberrant cell responses. Mesenchymal cells in aged tissue show signs of growth arrest and resistance to apoptosis, which are indicative of cellular senescence. It was recently postulated that cellular senescence contributes to the pathogenesis of chronic fibrotic diseases in the heart, kidney, liver and lung. Senescent cells negatively impact tissue regeneration while creating a pro-inflammatory environment as part of the senescence-associated secretory phenotype (SASP) favouring disease progression. In this review, we explore and summarise the current knowledge around how aberrant ECM potentially influences the senescent phenotype in chronic fibrotic diseases. Lastly, we will explore the possibility for interventions in the ECM-senescence regulatory pathways for therapeutic potential in chronic fibrotic diseases.

LncRNA PVT1 induces chondrocyte apoptosis through upregulation of TNF-α in synoviocytes by sponging miR-211-3p

Temporomandibular joint osteoarthritis (TMJ OA) is an important subtype of temporomandibular disorders (TMD). Articular cartilage destruction is considered a common pathological feature of TMJ OA, which is reported to be mainly induced by chondrocyte apoptosis. Synovial sterile inflammation is an initial factor of TMJ OA-associated articular cartilage destruction. Therefore, determining the mechanism of synovial membrane inflammation-induced articular cartilage destruction in TMJ OA is important for the TMJ OA therapy. In this study, we detected the function of synoviocytes in chondrocyte apoptosis under lipopolysaccharide (LPS)-induced inflammatory conditions and explored the underlying mechanism. We found that synoviocytes in inflammatory conditions facilitated LPS-induced chondrocytes apoptosis by secreting increased Tumor Necrosis Factor α (TNF-α), which was induced by long non-coding RNA plasmacytoma variant translocation 1 (PVT1) upregulation. PVT1 served as a competing endogenous RNA that sponged the microRNA miR-211-3p and prevented the inhibition of TNF-α expression. In conclusion, our in vitro study revealed that PVT1 has a previously unknown role in chondrocyte apoptosis, which may also be a mechanism underlying synoviocyte involvement in TMJ OA.

The Elastin-Derived Peptide VGVAPG Does Not Activate the Inflammatory Process in Mouse Cortical Astrocytes In Vitro

During vascular aging or in pathological conditions in humans, elastin is degraded and its by-products, the elastin-derived peptides (EDPs), enter the blood circulation. EDPs may be detected in the serum of healthy subjects or people who suffered a stroke. Moreover, recent evidence suggests a potential role of inflammatory mechanisms in neurological conditions, which are usually not categorized as inflammatory. Therefore, the present in vitro study was conducted to investigate the impact of the VGVAPG peptide on the activation of inflammatory process in mouse primary astrocytes, which were maintained in phenol red-free DMEM/F12 supplemented with 10% fetal bovine serum. The cells were exposed to VGVAPG or VVGPGA peptides for 24 and 48 h; this was followed by the determination of the activity of caspase-1 and levels of SOD, CAT, PPARγ, NF-κB, IL-1β, and IL-1βR1. Furthermore, rosiglitazone-a PPARγ agonist-was applied. Our study pioneered the finding that the VGVAPG peptide increases caspase-1 activity in astrocytes in vitro. The VGVAPG peptide simultaneously decreases the release of IL-1β into the cell-culture medium from astrocytes. The ELISA method revealed that the VGVAPG peptide increases the protein expression of SOD1 whereas it decreases the expression of IL-1βR1, CAT, and NF-κB. Therefore, the available data suggest that the VGVAPG peptide (concentration 10 nM) synergistically acts with agonists of PPARγ in mouse astrocytes. However, given the lack of sufficient data to explain the molecular mechanism of action of the VGVAPG peptide in the nervous system, more studies in this area are necessary.

A comparative clinical study of arthrogenous versus myogenous temporomandibular disorder in patients presenting with Costen's syndrome

Objective: Costen's syndrome involves otoneurological and sinonasal symptoms associated with temporomandibular disorder (TMD). The current study compared the symptoms related to Costen's syndrome in patients with arthrogenous versus myogenous TMD.Methods: The study involved 294 consecutive patients with TMD, prospectively examined over a period of 6 months. These were stratified into 180 patients with arthrogenous TMD and 114 patients with myogenous TMD. A questionnaire and examination protocol was applied for each patient.Results: Sinonasal symptoms were more common in the arthrogenous group (p = .001), whereas, hearing loss and vertigo were more common in the myogenous group (p = .001).Conclusion: The current study provides support for central nervous system neuroplastic changes in the genesis of Costen's syndrome symptoms.

Altered neural oscillations within and between sensorimotor cortex and parietal cortex in chronic jaw pain

Pain perception is associated with priming of the motor system and the orienting of attention in healthy adults. These processes correspond with decreases in alpha and beta power in the sensorimotor and parietal cortices. The goal of the present study was to determine whether these findings extend to individuals with chronic pain. Individuals with chronic jaw pain and pain-free controls anticipated and experienced a low pain or a moderate pain-eliciting heat stimulus. Although stimuli were calibrated for each subject, stimulus temperature was not different between groups. High-density EEG data were collected during the anticipation and heat stimulation periods and were analyzed using independent component analyses, EEG source localization, and measure projection analyses. Direct directed transfer function was also estimated to identify frequency specific effective connectivity between regions. Between group differences were most evident during the heat stimulation period. We report three novel findings. First, the chronic jaw pain group had a relative increase in alpha and beta power and a relative decrease in theta and gamma power in sensorimotor cortex. Second, the chronic jaw pain group had a relative increase in power in the alpha and beta bands in parietal cortex. Third, the chronic jaw pain group had less connectivity strength in the beta and gamma bands between sensorimotor cortex and parietal cortex. Our findings show that the effect of chronic pain attenuates rather than magnifies neural responses to heat stimuli. We interpret these findings in the context of system-level changes in intrinsic sensorimotor and attentional circuits in chronic pain.