Antigen-induced arthritis of the temporomandibular joint via repeated injections of bovine serum albumin in domestic pigs

Programmed cell death-1-modified pig developed using electroporation-mediated gene editing for in vitro fertilized zygotes

Programmed cell death-1 (PD-1) is an immunoinhibitory receptor required to suppress inappropriate immune responses such as autoimmunity. Immune checkpoint antibodies that augment the PD-1 pathway lead to immune-related adverse events (irAEs), organ non-specific side effects due to autoimmune activation in humans. In this study, we generated a PD-1 mutant pig using electroporation-mediated introduction of the CRISPR/Cas9 system into porcine zygotes to evaluate the PD-1 gene deficiency phenotype. We optimized the efficient guide RNAs (gRNAs) targeting PD-1 in zygotes and transferred electroporated embryos with the optimized gRNAs and Cas9 into recipient gilts. One recipient gilt became pregnant and gave birth to two piglets. Sequencing analysis revealed that both piglets were biallelic mutants. At 18 mo of age, one pig showed non-purulent arthritis of the left elbow/knee joint and oligozoospermia, presumably related to PD-1 modification. Although this study has a limitation because of the small number of cases, our phenotypic analysis of PD-1 modification in pigs will provide significant insight into human medicine and PD-1-deficient pigs can be beneficial models for studying human irAEs.

An analysis of the relationship between dietary pattern changes and temporomandibular joint inflammation in diabetic rats

Background

The temporomandibular joint (TMJ) is the most commonly used joint in the human body. Recent studies have shown pathologic relationships between inflammation, diabetes, and musculoskeletal disorders (MSDs). Chewing disorder is a significant sign of dysfunction in the masticatory system. This study investigated dietary pattern changes in response to TMJ inflammation in diabetic rats.

Methods

This experimental study was carried out on 30 male rats. The rats were fed concentrated 20-mg dietary tablets. Complete Freund's adjuvant (CFA) was used to induce TMJ inflammation and streptozotocin (STZ) was used to induce diabetes. The animals were randomly divided into three groups (n=10), including group I (CFA+STZ), group II (healthy rats+CFA), and group III (healthy rats, no injection). Parameters such as overall food intake, food intake duration, food intake frequency, and the interval between meals were recorded in a checklist and analyzed by Mann-Whitney and Kruskal-Wallis tests (P<0.05).

Results

The results showed no significant difference between groups in overall food intake and food intake frequency on days 0 and 1, but this difference was significant from day 2 to day 7. Regarding the time and end of food intake, there was a significant difference between the three groups from day 1 to day 7, but this difference was not significant on day zero.

Conclusion

Dietary pattern changes were similar in the diabetic TMJ inflammation and TMJ inflammation groups. These changes can be used as a behavioral marker for TMJ inflammation in rats.

Animal Models of Temporomandibular Disorder

Temporomandibular disorders (TMD) are a group of diseases in the oral and maxillofacial region that can manifest as acute or chronic persistent pain, affecting millions of people worldwide. Although hundreds of studies have explored mechanisms and treatments underlying TMD, multiple pathogenic factors and diverse clinical manifestations make it still poorly managed. Appropriate animal models are helpful to study the pathogenesis of TMD and explore effective treatment measures. At present, due to the high cost of obtaining large animals, rodents and rabbits are often used to prepare TMD animal models. Over the past decade, various animal models have been intensively developed to understand neurobiological and molecular mechanisms of TMD, and seek effective treatments. Although these models cannot carry out all clinical features, they are valuable in revealing the mechanisms of TMD and creating curative access. Currently, there are multitudinous animal models of TMD research. They can be constructed in different means and summarized into four ways according to the various causes and symptoms, including chemical induction (intra-articular injection of ovalbumin, collagenase, formalin, vascular endothelial growth factor, intramuscular injection of complete Freund’s adjuvant, etc.), mechanical stress stimulation (passive mouth opening, change of chewing load), surgical operation (partial disc resection, joint disc perforation) and psychological stress induction. Here, we summarize and discuss different approaches of animal models for determining neurophysiological and mechanical mechanisms of TMD and assess their advantages and limitations, respectively.

Therapy of antigen-induced arthritis of the temporomandibular joint via platelet-rich plasma injections in domestic pigs

The aim of this animal study was to investigate the effect of platelet-rich plasma (PRP) injections into the temporomandibular joint (TMJ) to treat antigen-induced arthritis AIA. AIA was induced via the application of bovine serum albumin (BSA) into the TMJ. Clear histological signs and protein analysis results indicating inflammation of the TMJ were observed. Afterwards, two PRP injections were performed over an interval of 2 weeks. Concentration levels of the proinflammatory cytokines IL-1β (PRP: 33.7 ± 5.6 pg/mg, untreated: 50.0 ± 2.9 pg/mg; p = 0.04) and TNF-α (PRP: 20.7 ± 2.5 pg/mg, untreated: 31.4 ± 2.7 pg/mg; p = 0.03) were significantly decreased in the PRP-treated joints. A significant reduction in signs of histological inflammation, such as hyperplasia of the synovial membrane, leucocyte infiltration, cartilage surface alterations, and an increase in cartilage-specific glycosaminoglycan content, was observed. This animal study supports the understanding of the underlying effects of PRP treatment in the TMJ, and may enhance novel PRP therapies in the future.

Peripheral mechanisms of arthritic pain: A proposal to leverage large animals for in vitro studies

Pain arising from musculoskeletal disorders such as arthritis is one of the leading causes of disability. Whereas the past 20-years has seen an increase in targeted therapies for rheumatoid arthritis (RA), other arthritis conditions, especially osteoarthritis, remain poorly treated. Although modulation of central pain pathways occurs in chronic arthritis, multiple lines of evidence indicate that peripherally driven pain is important in arthritic pain. To understand the peripheral mechanisms of arthritic pain, various in vitro and in vivo models have been developed, largely in rodents. Although rodent models provide numerous advantages for studying arthritis pathogenesis and treatment, the anatomy and biomechanics of rodent joints differ considerably to those of humans. By contrast, the anatomy and biomechanics of joints in larger animals, such as dogs, show greater similarity to human joints and thus studying them can provide novel insight for arthritis research. The purpose of this article is firstly to review models of arthritis and behavioral outcomes commonly used in large animals. Secondly, we review the existing in vitro models and assays used to study arthritic pain, primarily in rodents, and discuss the potential for adopting these strategies, as well as likely limitations, in large animals. We believe that exploring peripheral mechanisms of arthritic pain in vitro in large animals has the potential to reduce the veterinary burden of arthritis in commonly afflicted species like dogs, as well as to improve translatability of pain research into the clinic.

Temporomandibular joint damage in K/BxN arthritic mice

Rheumatoid arthritis (RA) is an autoimmune disease affecting 1% of the world population and is characterized by chronic inflammation of the joints sometimes accompanied by extra-articular manifestations. K/BxN mice, originally described in 1996 as a model of polyarthritis, exhibit knee joint alterations. The aim of this study was to describe temporomandibular joint (TMJ) inflammation and damage in these mice. We used relevant imaging modalities, such as micro-magnetic resonance imaging (μMRI) and micro-computed tomography (μCT), as well as histology and immunofluorescence techniques to detect TMJ alterations in this mouse model. Histology and immunofluorescence for Col-I, Col-II, and aggrecan showed cartilage damage in the TMJ of K/BxN animals, which was also evidenced by μCT but was less pronounced than that seen in the knee joints. μMRI observations suggested an increased volume of the upper articular cavity, an indicator of an inflammatory process. Fibroblast-like synoviocytes (FLSs) isolated from the TMJ of K/BxN mice secreted inflammatory cytokines (IL-6 and IL-1β) and expressed degradative mediators such as matrix metalloproteinases (MMPs). K/BxN mice represent an attractive model for describing and investigating spontaneous damage to the TMJ, a painful disorder in humans with an etiology that is still poorly understood.