Expression and Significance of High-Mobility Group Protein B1 (HMGB1) and the Receptor for Advanced Glycation End-Product (RAGE) in Knee Osteoarthritis

The Role of Alarmins in the Pathogenesis of Rheumatoid Arthritis, Osteoarthritis, and Psoriasis

Alarmins are immune-activating factors released after cellular injury or death. By secreting alarmins, cells can interact with immune cells and induce a variety of inflammatory responses. The broad family of alarmins involves several members, such as high-mobility group box 1, S100 proteins, interleukin-33, and heat shock proteins, among others. Studies have found that the concentrations and expression profiles of alarmins are altered in immune-mediated diseases. Furthermore, they are involved in the pathogenesis of inflammatory conditions. The aim of this narrative review is to present the current evidence on the role of alarmins in rheumatoid arthritis, osteoarthritis, and psoriasis. We discuss their potential involvement in mechanisms underlying the progression of these diseases and whether they could become therapeutic targets. Moreover, we summarize the impact of pharmacological agents used in the treatment of these diseases on the expression of alarmins.

IRF1 governs the expression of SMARCC1 via the GCN5-SETD2 axis and actively engages in the advancement of osteoarthritis

Background

Osteoarthritis (OA) is a degenerative joint disease characterized by the breakdown of joint cartilage and underlying bone. Macrophages are a type of white blood cell that plays a critical role in the immune system and can be found in various tissues, including joints. Research on the relationship between OA and macrophages is essential to understand the mechanisms underlying the development and progression of OA.

Objective

This study was performed to analyze the functions of the IRF1-GCN5-SETD2-SMARCC1 axis in osteoarthritis (OA) development.

Methods

A single-cell RNA sequencing (scRNA-seq) dataset, was subjected to a comprehensive analysis aiming to identify potential regulators implicated in the progression of osteoarthritis (OA). In order to investigate the role of IRF1 and SMARCC1, knockdown experiments were conducted in both OA-induced rats and interleukin (IL)-1β-stimulated chondrocytes, followed by the assessment of OA-like symptoms, secretion of inflammatory cytokines, and polarization of macrophages. Furthermore, the study delved into the identification of aberrant epigenetic modifications and functional enzymes responsible for the regulation of SMARCC1 by IRF1. To evaluate the clinical significance of the factors under scrutiny, a cohort comprising 13 patients diagnosed with OA and 7 fracture patients without OA was included in the analysis.

Results

IRF1 was found to exert regulatory control over the expression of SMARCC1, thus playing a significant role in the development of osteoarthritis (OA). The knockdown of either IRF1 or SMARCC1 disrupted the pro-inflammatory effects induced by IL-1β in chondrocytes, leading to a mitigation of OA-like symptoms, including inflammatory infiltration, cartilage degradation, and tissue injury, in rat models. Additionally, this intervention resulted in a reduction in the predominance of M1 macrophages both in vitro and in vivo. Significant epigenetic modifications, such as abundant H3K27ac and H3K4me3 marks, were observed near the SMARCC1 promoter and 10 kb upstream region. These modifications were attributed to the recruitment of GCN5 and SETD2, which are functional enzymes responsible for these modifications. Remarkably, the overexpression of either GCN5 or SETD2 restored SMARCC1 expression in rat cartilages or chondrocytes, consequently exacerbating the OA-like symptoms.

Conclusion

This research postulates that the transcriptional activity of SMARCC1 can be influenced by IRF1 through the recruitment of GCN5 and SETD2, consequently regulating the H3K27ac and H3K4me3 modifications in close proximity to the SMARCC1 promoter and 10 kb upstream region. These modifications, in turn, facilitate the M1 skewing of macrophages and contribute to the progression of osteoarthritis (OA).

The Translational Potential of this Article

The study demonstrated that the regulation of SMARCC1 by IRF1 plays a crucial role in the development of OA. Knocking down either IRF1 or SMARCC1 disrupted the pro-inflammatory effects induced by IL-1β in chondrocytes, leading to a mitigation of OA-like symptoms in rat models. These symptoms included inflammatory infiltration, cartilage degradation, and tissue injury. These findings suggest that targeting the IRF1-SMARCC1 regulatory axis, as well as the associated epigenetic modifications, could potentially be a novel approach in the development of OA therapies, offering new opportunities for disease management and improved patient outcomes.

Knee Osteoarthritis: Epidemiology, Pathogenesis, and Mesenchymal Stem Cells: What Else Is New? An Update

Osteoarthritis (OA) is a chronic disease and the most common orthopedic disorder. A vast majority of the social OA burden is related to hips and knees. The prevalence of knee OA varied across studies and such differences are reflected by the heterogeneity of data reported by studies conducted worldwide. A complete understanding of the pathogenetic mechanisms underlying this pathology is essential. The OA inflammatory process starts in the synovial membrane with the activation of the immune system, involving both humoral and cellular mediators. A crucial role in this process is played by the so-called “damage-associated molecular patterns” (DAMPs). Mesenchymal stem cells (MSCs) may be a promising option among all possible therapeutic options. However, many issues are still debated, such as the best cell source, their nature, and the right amount. Further studies are needed to clarify the remaining doubts. This review provides an overview of the most recent and relevant data on the molecular mechanism of cartilage damage in knee OA, including current therapeutic approaches in regenerative medicine.

Mitochondrial reactivity following acute exposure to experimental pain testing in people with HIV and chronic pain

Background: Physical stressors can cause a physiological response that can contribute to an increase in mitochondrial dysfunction and Mitochondrial DNA damage (mtDNA damage). People living with HIV (PWH) are more likely to suffer from chronic pain and may be more susceptible to mitochondrial dysfunction following exposure to a stressor. We used Quantitative Sensory Testing (QST) as an acute painful stressor in order to investigate whether PWH with/without chronic pain show differential mitochondrial physiological responses. Methods: The current study included PWH with (n = 26), and without (n = 29), chronic pain. Participants completed a single session that lasted approximately 180 min, including QST. Blood was taken prior to and following the QST battery for assays measuring mtDNA damage, mtDNA copy number, and mtDNA damage-associated molecular pattern (DAMP) levels (i.e., ND1 and ND6). Results: We examined differences between those with and without pain on various indicators of mitochondrial reactivity following exposure to QST. However, only ND6 and mtDNA damage were shown to be statistically significant between pain groups. Conclusion: PWH with chronic pain showed greater mitochondrial reactivity to laboratory stressors. Consequently, PWH and chronic pain may be more susceptible to conditions in which mitochondrial damage/dysfunction play a central role, such as cognitive decline.

Necroptosis in pathogenesis of osteoarthritis and its therapeutic implications

Osteoarthritis is a progressive degenerative joint disease induced by many causes, for which there is no radical cure currently. Necroptosis is a newly reported programmed cell death, and its related factors are also inseparable from the progress of osteoarthritis. For examples, damage-associated molecular pattern promotes the release of various inflammatory factors, so as to recruit macrophages and promote local inflammation of the joint; inhibition of receptor-interacting protein kinase can reduce the death of cell and the expression of inflammatory factors, so as to reduce cartilage damage. Therefore, in-depth study of the regulatory mechanism of necroptosis in osteoarthritis will help to further reveal the pathogenesis of osteoarthritis, so as to provide potential targets for the treatment of osteoarthritis.

AGE/Non-AGE Glycation: An Important Event in Rheumatoid Arthritis Pathophysiology

Rheumatoid arthritis (RA) is a chronic inflammatory, autoimmune disease that gradually affects the synovial membrane and joints. Many intrinsic and/or extrinsic factors are crucial in making RA pathology challenging throughout the disease. Substantial enzymatic or non-enzymatic modification of proteins driving inflammation has gained a lot of interest in recent years. Endogenously modified glycated protein influences disease development linked with AGEs/non-AGEs and is reported as a disease marker. In this review, we summarized current knowledge of the differential abundance of glycated proteins by compiling and analyzing a variety of AGE and non-AGE ligands that bind with RAGE to activate multi-faceted inflammatory and oxidative stress pathways that are pathobiologically associated with RA-fibroblast-like synoviocytes (RA-FLS). It is critical to comprehend the connection between oxidative stress and inflammation generation, mediated by glycated protein, which may bind to the receptor RAGE, activate downstream pathways, and impart immunogenicity in RA. It is worth noting that AGEs and non-AGEs ligands play a variety of functions, and their functionality is likely to be more reliant on pathogenic states and severity that may serve as biomarkers for RA. Screening and monitoring of these differentially glycated proteins, as well as their stability in circulation, in combination with established pre-clinical characteristics, may aid or predict the onset of RA.

High Mobility Group Box 1 Protein in Osteoarthritic Knee Tissue and Chondrogenic Progenitor Cells: An Ex Vivo and In Vitro Study

OBJECTIVE

In osteoarthritis (OA), a loss of healthy cartilage extracellular matrix (ECM) results in cartilage degeneration. Attracting chondrogenic progenitor cells (CPCs) to injury sites and stimulating them toward chondrogenic expression profiles is a regenerative approach in OA therapy. High mobility group box 1 protein (HMGB1) is associated with chemoattractant and proinflammatory effects in various pathological processes. Here, we investigate the migratory effects of HMGB1 in knee OA and CPCs for the first time.

DESIGN

Immunohistochemistry, immunoblotting, and immunocytochemistry were performed to identify HMGB1 and its receptors, receptor for advanced glycation end products (RAGE) and toll-like receptor 4 (TLR4) in OA knee tissue, chondrocytes, and CPCs. In situ hybridization for HMGB1 mRNA was performed in CPCs ex vivo. The chemoattractant effects of HMGB1 on CPCs were analyzed in cell migration assays.

RESULTS

HMGB1 expression in OA tissue and OA chondrocytes was higher than in healthy specimens and cells. HMGB1, RAGE, and TLR4 were expressed in CPCs and chondrocytes. In situ hybridization revealed HMGB1 mRNA in CPCs after migration into OA knee tissue, and immunohistochemistry confirmed HMGB1 expression at the protein level. Stimulation via HMGB1 significantly increased the migration of CPCs.

CONCLUSIONS

Our results show the chemoattractant role of HMGB1 in knee OA. HMGB1 is released by chondrocytes and has migratory effects on CPCs. These effects might be mediated via RAGE and TLR4. The in vitro and ex vivo results of this study need to be confirmed in vivo.

Sex- and cell-dependent contribution of peripheral high mobility group box 1 and TLR4 in arthritis-induced pain

ABSTRACT

Spinal high mobility group box 1 protein (HMGB1) plays crucial roles in arthritis-induced pain; however, the involvement of peripheral HMGB1 has not been examined previously. In this study, we addressed the role of peripheral HMGB1 and explored if sex contributes differentially to nociception in arthritis. We found Hmgb1 expression to be elevated in the ankle joints of male and female mice subjected to collagen antibody-induced arthritis. Blocking the action of peripheral HMGB1, however, only reversed collagen antibody-induced arthritis-mediated hypersensitivity in males. Intra-articular injection of the toll-like receptor (TLR)4-activating, partially reduced disulfide, but not the fully reduced all-thiol, HMGB1 evoked mechanical hypersensitivity in both sexes. A sex-dependent temporal profile in expression of inflammatory factors in the ankle joint was observed in response to intra-articular injection of disulfide HMGB1, with male mice showing a delayed, yet longer-lasting increase in mRNA levels for several of the investigated factors. Intra-articular HMGB1 did not induce cellular infiltration in the ankle joint suggesting its action on tissue resident cells. To further explore possible sex differences in cellular involvement, we used the macrophage inhibitor, minocycline, and mice with specific TLR4 depletion in myeloid cells or nociceptors. We found that inhibition of resident macrophages attenuated HMGB1-induced pain-like behavior only in male mice. Interestingly, although the contribution of TLR4 on myeloid cells to nociception was minimal in females compared to males, TLR4 on nociceptors are important for HMGB1-induced pain in both sexes. Collectively, our work highlights sex- and cellular location-dependent roles of HMGB1 and TLR4 in peripheral pain mechanisms.

The Damage-Associated Molecular Patterns (DAMPs) as Potential Targets to Treat Osteoarthritis: Perspectives From a Review of the Literature

During the osteoarthritis (OA) process, activation of immune systems, whether innate or adaptive, is strongly associated with low-grade systemic inflammation. This process is initiated and driven in the synovial membrane, especially by synovium cells, themselves previously activated by damage-associated molecular patterns (DAMPs) released during cartilage degradation. These fragments exert their biological activities through pattern recognition receptors (PRRs) that, as a consequence, induce the activation of signaling pathways and beyond the release of inflammatory mediators, the latter contributing to the vicious cycle between cartilage and synovial membrane. The primary endpoint of this review is to provide the reader with an overview of these many molecules categorized as DAMPs and the contribution of the latter to the pathophysiology of OA. We will also discuss the different strategies to control their effects. We are convinced that a better understanding of DAMPs, their receptors, and associated pathological mechanisms represents a decisive issue for degenerative joint diseases such as OA.

The Role of Chronic Inflammatory Bone and Joint Disorders in the Pathogenesis and Progression of Alzheimer's Disease

Late-onset Alzheimer's Disease (LOAD) is a devastating neurodegenerative disorder that causes significant cognitive debilitation in tens of millions of patients worldwide. Throughout disease progression, abnormal secretase activity results in the aberrant cleavage and subsequent aggregation of neurotoxic Aβ plaques in the cerebral extracellular space and hyperphosphorylation and destabilization of structural tau proteins surrounding neuronal microtubules. Both pathologies ultimately incite the propagation of a disease-associated subset of microglia-the principle immune cells of the brain-characterized by preferentially pro-inflammatory cytokine secretion and inhibited AD substrate uptake capacity, which further contribute to neuronal degeneration. For decades, chronic neuroinflammation has been identified as one of the cardinal pathophysiological driving features of AD; however, despite a number of works postulating the underlying mechanisms of inflammation-mediated neurodegeneration, its pathogenesis and relation to the inception of cognitive impairment remain obscure. Moreover, the limited clinical success of treatments targeting specific pathological features in the central nervous system (CNS) illustrates the need to investigate alternative, more holistic approaches for ameliorating AD outcomes. Accumulating evidence suggests significant interplay between peripheral immune activity and blood-brain barrier permeability, microglial activation and proliferation, and AD-related cognitive decline. In this work, we review a narrow but significant subset of chronic peripheral inflammatory conditions, describe how these pathologies are associated with the preponderance of neuroinflammation, and posit that we may exploit peripheral immune processes to design interventional, preventative therapies for LOAD. We then provide a comprehensive overview of notable treatment paradigms that have demonstrated considerable merit toward treating these disorders.

RAGE-dependent NF-kB inflammation processes in the capsule of frozen shoulders

BACKGROUND

The etiology of frozen shoulder (FS) remains uncertain. Advanced glycation end-products (AGEs) cause the cross-linking and stabilization of collagen and are increased in FS. The purpose of this study was to elucidate the pathogenesis of FS by evaluating the receptor of AGE (RAGE)-dependent pathways.

METHODS

Tissue samples of the coracohumeral ligament (CHL) and anterior inferior glenohumeral ligament (IGHL) were collected from 33 patients with FS, with severe stiffness, and 25 with rotator cuff tears (RCTs) as controls. Gene expression levels of RAGE, high-mobility group box 1 (HMGB1), Toll-like receptor 2 (TLR2), TLR4, nuclear factor-kappa B (NF-kB), and cytokines were evaluated using a quantitative real-time polymerase chain reaction. The immunoreactivities of carboxymethyllysine (CML), pentosidine, and RAGE were also evaluated. CML and pentosidine were further evaluated using high-performance liquid chromatography.

RESULTS

Gene expression levels of RAGE, HMGB1, TLR2, TLR4, and NF-kB were significantly greater in the CHLs and IGHLs from the FS group than in those from the RCT group. Immunoreactivities of RAGE and CML were stronger in the CHLs and IGHLs from the FS group than in those from the RCT group. Pentosidine was weakly immunostained in the CHLs and IGHLs from the FS group. CML using high-performance liquid chromatography was significantly greater in the CHLs and IGHLs from the FS group than in those from the RCT group.

CONCLUSIONS

AGEs and HMGB1 might play important roles in the pathogenesis of FS by binding to RAGE and activating NF-kB signaling pathways. Suppression of these pathways could be a treatment option for FS.

The emerging role of fibroblast-like synoviocytes-mediated synovitis in osteoarthritis: An update

Osteoarthritis (OA), the most ubiquitous degenerative disease affecting the entire joint, is characterized by cartilage degradation and synovial inflammation. Although the pathogenesis of OA remains poorly understood, synovial inflammation is known to play an important role in OA development. However, studies on OA pathophysiology have focused more on cartilage degeneration and osteophytes, rather than on the inflamed and thickened synovium. Fibroblast-like synoviocytes (FLS) produce a series of pro-inflammatory regulators, such as inflammatory cytokines, nitric oxide (NO) and prostaglandin E₂ (PGE₂ ). These regulators are positively associated with the clinical symptoms of OA, such as inflammatory pain, joint swelling and disease development. A better understanding of the inflammatory immune response in OA-FLS could provide a novel approach to comprehensive treatment strategies for OA. Here, we have summarized recently published literatures referring to epigenetic modifications, activated signalling pathways and inflammation-associated factors that are involved in OA-FLS-mediated inflammation. In addition, the current related clinical trials and future perspectives were also summarized.

Downregulation of HMGB1 by miR-103a-3p Promotes Cell Proliferation, Alleviates Apoptosis and in Flammation in a Cell Model of Osteoarthritis

Background

MiR-103a-3p is a small non-coding RNA and has been reported to be involved in osteogenic proliferation and differentiation, but the role of miR-103a-3p in human osteoarthritis (OA) remains unclear.

Objectives

In this study, we aimed to explore its function and molecular target in chondrocytes during OA pathogenesis.

Materials and Methods

Total 12 experimental OA rat models, together with 12 rats without knee OA lesions were established and cartilage samples were collected. Chondrocytes were treated with LPS in vitro. MiR-103a-3p expression was detected in articular cartilage tissues and chondrocytes using quantitative real-time PCR. Knee OA chondrocytes were transfected with miR-103a-3p mimics, and siHMGB1, respectively. Then cellular proliferation, apoptosis, apoptosis related factors and inflammatory cytokines were analyzed by MTT, flow cytometry, western blot, caspase-3 activity and ELISA, respectively. Potential targets of miR-103a-3p were predicted using series of bioinformatics analysis, then confirmed by luciferase reporter assay.

Results

We first found miR-103a-3p was significantly down-regulated in the articular cartilage tissues from experimental OA rats, as well as in chondrocytes treated with LPS in vitro. The gain-of-function assay further demonstrated that up-regulation of miR-103a-3p significantly promoted cell proliferation, inhibited apoptosis and inflammation, which was accompanied with elevated expression of PCNA, and reduced expression of caspase-3, PARP, IL-1β, IL-6, IL-10 and TNF-α. Furthermore, high mobility group box 1 (HMGB1), an important inflammatory mediator of OA, was a target of miR-103a-3p. Moreover, knockdown of HMGB1 mimicked the effects of miR-103a-3p on chondrocytes treated with LPS.

Conclusions

Taken together, our study suggests that miR-103a-3p inhibits chondrocyte apoptosis and inflammation in OA, which appears to be an attractive approach to OA treatment.

NOV/CCN3 induces cartilage protection by inhibiting PI3K/AKT/mTOR pathway

Osteoarthritis (OA), an age‐related degenerative joint disease, is pathologically characterized by articular cartilage degeneration and synovial inflammation. Nephroblastoma overexpressed (NOV or CCN3), a matricellular protein, is a primary member of the CCN family (Cyr61, Ctgf, NOV) of proteins and is involved in various inflammatory disorders. Previous studies reported that CCN3 might play a therapeutic role in OA. However, the underlying mechanism remains unclear. In this study, we confirmed the expression of CCN3 was decreased in human and rat OA articular cartilage. Recombinant CCN3 ameliorated the IL‐1β‐induced matrix catabolism, as demonstrated by MMP1, MMP3, MMP13, ADAMTS5 and iNOS expression, in vitro. In addition, the degradation of cartilage matrix such as collagen 2 and aggrecan could be reversed by CCN3. Furthermore, we found CCN3 promoted autophagy as Atg5, Beclin1 and LC3‐II expression were increased. High‐mobility group box 1 was negatively correlated with CCN3 in IL‐1β‐induced osteoarthritis responses, and HMGB1 is involved in the protective effect of CCN3 in OA. Moreover, CCN3 overexpression decreased the expression of HMGB1 and reversed the IL‐1β induced MMPs production. Additionally, recombinant CCN3 or CCN3 overexpression attenuated the activation of PI3K/AKT/mTOR pathway induced by IL‐1β. Our study presents new mechanisms of CCN3 in osteoarthritis and indicates that CCN3 can serve as a novel potential therapeutic target for osteoarthritis.

Dual regulatory roles of HMGB1 in inflammatory reaction of chondrocyte cells and mice

Osteoarthritis (OA) is one of the most common bone diseasesas it is reported that the impact of knee osteoarthritis symptomatic form is estimated at 240/100,000 people per year. The inflammation of articular cartilageis thought to be the pathologic drive for development of this disease. HMGB1(high mobility group box-1), a regulatory factor for gene transcription, could stimulate inflammation response. However, theexact regulatory role of HMGB1 in the inflammation of articular cartilage still need to be elucidated. In the current study, we used Quantitative Real-Time PCR(Q-PCR) to detect them RNA levels of Collagen Type II Alpha 1(Col2a1), Aggrecan, MMP3(Matrix Metallopeptidase 3), MMP13, ADAMTs4 and ADAMTs5; Enzyme-Linked Immunosorbent Assay(ELISA) was used to detect the content of IL-1β and calpain protein; Cell apoptosis was evaluated by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling(TUNEL) assay and flow cytometryanalysis; Western blot and immunofluorescence assays were applied to assess the expression of HMGB1; Lastly autophagic activity was mainly verified by monodansylcadaverine (MDC) staining. Our data revealed that in the early stage of chondrocyte inflammation(3 and 6 h of LPS stimulation), cytosolic HMGB1 attenuated inflammation response by facilitating cell autophagy and preventing cell apoptosis. While in the late stage (24 and 48 h of LPS stimulation), the extracellular HMGB1 stimulated inflammation reaction and contributed to the cartilage destruction in OA.

Effects of knockout of the receptor for advanced glycation end-products on bone mineral density and synovitis in mice with intra-articular fractures

Our group employed the mouse closed intra-articular fracture (IAF) model to test the hypothesis that the innate immune system plays a role in initiating synovitis and post-traumatic osteoarthritis (PTOA) in fractured joints. A transgenic strategy featuring knockout of the receptor for advanced glycation end-products (RAGE ^-/- ) was pursued. The 42 and 84 mJ impacts used to create fractures were in the range previously reported to cause PTOA at 60 days post-fracture. MicroCT (μCT) was used to assess fracture patterns and epiphyseal and metaphyseal bone loss at 30 and 60 days post-fracture. Cartilage degeneration, synovitis, and matrix metalloproteinase (MMP-3, -13) expression were evaluated by histologic analyses. In wild-type mice, μCT imaging showed that 84 mJ impacts led to significant bone loss at 30 days (p < 0.05), but recovered to normal at 60 days. Bone losses did not occur in RAGE^-/- mice. Synovitis was significantly elevated in 84 mJ impact wild-type mice at both endpoints (30 day, p = 0.001; 60 day, p = 0.05), whereas in RAGE^-/- mice synovitis was elevated only at 30 days (p = 0.02). Mankin scores were slightly elevated in both mouse strains at 30 days, but not at 60 days. Immunohistochemistry revealed significant fracture-related increases in MMP-3 and -13 expression at 30 days (p < 0.05), with no significant difference between genotypes. These findings indicated that while RAGE ^-/- accelerated recovery from fracture and diminished synovitis, arthritic changes were temporary and too modest to detect an effect on the pathogenesis of PTOA. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2439-2449, 2018.

Damage-Associated Molecular Patterns in Inflammatory Diseases

Damage-associated molecular patterns (DAMPs) are endogenous danger molecules that are released from damaged or dying cells and activate the innate immune system by interacting with pattern recognition receptors (PRRs). Although DAMPs contribute to the host's defense, they promote pathological inflammatory responses. Recent studies have suggested that various DAMPs, such as high-mobility group box 1 (HMGB1), S100 proteins, and heat shock proteins (HSPs), are increased and considered to have a pathogenic role in inflammatory diseases. Here, we review current research on the role of DAMPs in inflammatory diseases, including rheumatoid arthritis, systemic lupus erythematosus, osteoarthritis, atherosclerosis, Alzheimer's disease, Parkinson's disease, and cancer. We also discuss the possibility of DAMPs as biomarkers and therapeutic targets for these diseases.

The Pathobiology of the Meniscus: A Comparison Between the Human and Dog

Serious knee pain and related disability have an annual prevalence of approximately 25% on those over the age of 55 years. As curative treatments for the common knee problems are not available to date, knee pathologies typically progress and often lead to osteoarthritis (OA). While the roles that the meniscus plays in knee biomechanics are well characterized, biological mechanisms underlying meniscus pathophysiology and roles in knee pain and OA progression are not fully clear. Experimental treatments for knee disorders that are successful in animal models often produce unsatisfactory results in humans due to species differences or the inability to fully replicate disease progression in experimental animals. The use of animals with spontaneous knee pathologies, such as dogs, can significantly help addressing this issue. As microscopic and macroscopic anatomy of the canine and human menisci are similar, spontaneous meniscal pathologies in canine patients are thought to be highly relevant for translational medicine. However, it is not clear whether the biomolecular mechanisms of pain, degradation of extracellular matrix, and inflammatory responses are species dependent. The aims of this review are (1) to provide an overview of the anatomy, physiology, and pathology of the human and canine meniscus, (2) to compare the known signaling pathways involved in spontaneous meniscus pathology between both species, and (3) to assess the relevance of dogs with spontaneous meniscal pathology as a translational model. Understanding these mechanisms in human and canine meniscus can help to advance diagnostic and therapeutic strategies for painful knee disorders and improve clinical decision making.

The Association Between Variants of Receptor for Advanced Glycation End Products (RAGE) Gene Polymorphisms and Age-Related Macular Degeneration

Background

Age-related macular degeneration (AMD) is the leading cause of blindness in people aged 65 years and older in developed countries. The pathogenesis of AMD has been linked to mechanisms involving inflammation, oxidative stress, and basal laminar deposit formation between retinal pigment epithelium (RPE) cells and the basal membrane, caused by advanced glycation end products (AGEs). AGEs are implicated in the pathogenesis of AMD through the AGE-and receptor for AGE (RAGE) interaction, which can be altered by polymorphisms of the RAGE gene. We examined RAGE rs1800624 and rs1800625 gene polymorphisms contributing to AMD development.

Material/Methods

The study enrolled 300 patients with early AMD, 300 patients with exudative AMD, and 800 healthy controls. The genotyping was carried out using the RT-PCR method.

Results

The analysis of two single nucleotide polymorphisms (SNPs) in the RAGE gene showed that rs1800624 was associated with a 1.6-fold decreased risk for exudative AMD under the dominant model after adjustment for age (OR=0.616; 95% CI: 0.394–0.963; p=0.034) and each copy of allele T at rs1800624 was associated with a 1.4-fold decreased risk for exudative AMD development under the additive model after adjustment for age (OR=0.701; 95% CI: 0.510–0.962; p=0.028). Analysis revealed that the rs1800625 allele G at rs1800625 was associated with a 1.5-fold increased risk for exudative AMD after adjustment for age (OR=1.545; 95% CI: 1.003–2.379; p=0.048). These results suggested that the allele G at rs1800625 was a risk-allele for exudative AMD development. In haplotype analysis, A-G haplotype was significantly more frequently observed in exudative AMD patients compared to healthy controls (3.3% versus 1.4%, p=0.035).

Conclusions

We revealed a significant association between RAGE gene rs1800624 and rs1800625 polymorphisms and AMD risk. We considered T allele at rs1800624 to be protective against AMD development, while allele G at rs1800625 was considered to be a marker of poor prognosis in AMD development.

High Mobility Group Box-1 (HMGb1): Current Wisdom and Advancement as a Potential Drug Target

High mobility group box-1 (HMGb1) protein, a nuclear non-histone protein that is released or secreted from the cell in response to damage or stress, is a sentinel for the immune system that plays a critical role in cell survival/death pathways. This review highlights key features of the endogenous danger-associated molecular pattern (DAMP) protein, HMGb1 in the innate inflammatory response along with various cofactors and receptors that regulate its downstream effects. The evidence demonstrating increased levels of HMGb1 in human inflammatory diseases and conditions is presented, along with a summary of current small molecule or peptide-like antagonists proven to specifically target HMGb1. Additionally, we delineate the measures needed toward validating this protein as a clinically relevant biomarker or bioindicator and as a relevant drug target.

Characteristics of Plantar Loads During Walking in Patients with Knee Osteoarthritis

BACKGROUND Knee osteoarthritis (KOA) is a common disease that can change the load on lower limbs during walking. Plantar loads in patients with KOA may provide a basis for clinical decisions regarding footwear and foot orthoses. This study aimed to compare plantar loads in females with and without KOA during gait. MATERIAL AND METHODS Plantar pressure during walking was recorded in 23 females with KOA and 23 females without KOA. Maximum force (MF), contact area (CA), and peak pressure (PP) were measured at 7 different regions underneath the foot, named heel (M1), midfoot (M2), first metatarsophalangeal joint (MPJ) (M3), second MPJ (M4), third to fifth MPJ (M5), hallux (M6), and lesser toes (M7). RESULTS PPs for M2 and (M3) in females with KOA were higher than those in females without KOA. High PPs were also found in females with KOA for M2, M3, and M4. CONCLUSIONS Increased plantar loading in females with KOA may lead to foot pronation and gait changes during walking. Plantar loading may be offered to patients with KOA when considering footwear and foot orthoses.

Increased expression of damage-associated molecular patterns (DAMPs) in osteoarthritis of human knee joint compared to hip joint

Osteoarthritis (OA) is a degenerative disease characterized by the destruction of cartilage. The greatest risk factors for the development of OA include age and obesity. Recent studies suggest the role of inflammation in the pathogenesis of OA. The two most common locations for OA to occur are in the knee and hip joints. The knee joint experiences more mechanical stress, cartilage degeneration, and inflammation than the hip joint. This could contribute to the increased incidence of OA in the knee joint. Damage-associated molecular patterns (DAMPs), including high-mobility group box-1, receptor for advanced glycation end products, and alarmins (S100A8 and S100A9), are released in the joint in response to stress-mediated chondrocyte and cartilage damage. This facilitates increased cartilage degradation and inflammation in the joint. Studies have documented the role of DAMPs in the pathogenesis of OA; however, the comparison of DAMPs and its influence on OA has not been discussed. In this study, we compared the DAMPs between OA knee and hip joints and found a significant difference in the levels of DAMPs expressed in the knee joint compared to the hip joint. The increased levels of DAMPs suggest a difference in the underlying pathogenesis of OA in the knee and the hip and highlights DAMPs as potential therapeutic targets for OA in the future.

Prognostic significance of high-mobility group box protein 1 genetic polymorphisms in rheumatoid arthritis disease outcome

Rheumatoid arthritis (RA) is a systemic inflammatory disease that causes chronic inflammation of the joints. Analysis of genetic variants offers promise for guiding treatment and improving outcomes in RA. High-mobility group box protein 1 (HMGB1) is a ubiquitous nuclear protein found in all mammal eukaryotic cells that participates in several biological functions including immune response, cell survival and apoptosis. We investigated the effects of HMGB1 gene polymorphisms on the risk of RA disease progression in a cohort of Chinese Han individuals. Four single nucleotide polymorphisms (SNPs) from the HMGB1 gene were selected and genotyped in 232 patients with RA and 353 healthy controls. We found that having one C allele in rs1360485 and one G allele in rs2249825 polymorphisms lowered the risk of RA in females. Moreover, among healthy controls, those who bore the C/G/T haplotype at SNPs rs1360485, rs2249825 and rs1412125 were at reduced risk of developing RA by 0.13-fold (p <0.05). This is the first report to examine the risk factors associated with HMGB1 SNPs in the development of RA disease in the Chinese Han population.