Molecular characterisation of the synovial fluid microbiome in rheumatoid arthritis patients and healthy control subjects

From Skin and Gut to the Brain: The Infectious Journey of the Human Commensal Fungus Malassezia and Its Neurological Consequences

The human mycobiome encompasses diverse communities of fungal organisms residing within the body and has emerged as a critical player in shaping health and disease. While extensive research has focused on the skin and gut mycobiome, recent investigations have pointed toward the potential role of fungal organisms in neurological disorders. Among those fungal organisms, the presence of the commensal fungus Malassezia in the brain has created curiosity because of its commensal nature and primary association with the human skin and gut. This budding yeast is responsible for several diseases, such as Seborrheic dermatitis, Atopic dermatitis, Pityriasis versicolor, Malassezia folliculitis, dandruff, and others. However recent findings surprisingly show the presence of Malassezia DNA in the brain and have been linked to diseases like Alzheimer's disease, Parkinson's disease, Multiple sclerosis, and Amyotrophic lateral sclerosis. The exact role of Malassezia in these disorders is unknown, but its ability to infect human cells, travel through the bloodstream, cross the blood-brain barrier, and reside along with the lipid-rich neuronal cells are potential mechanisms responsible for pathogenesis. This also includes the induction of pro-inflammatory cytokines, disruption of the blood-brain barrier, gut-microbe interaction, and accumulation of metabolic changes in the brain environment. In this review, we discuss these key findings from studies linking Malassezia to neurological disorders, emphasizing the complex and multifaceted nature of these cases. Furthermore, we discuss potential mechanisms through which Malassezia might contribute to the development of neurological conditions. Future investigations will open up new avenues for our understanding of the fungal gut-brain axis and how it influences human behavior. Collaborative research efforts among microbiologists, neuroscientists, immunologists, and clinicians hold promise for unraveling the enigmatic connections between human commensal Malassezia and neurological disorders.

Murine cartilage microbial DNA deposition occurs rapidly following the introduction of a gut microbiome and changes with obesity, aging, and knee osteoarthritis

Cartilage microbial DNA patterns have been recently characterized in osteoarthritis (OA). The objectives of this study were to evaluate the gut origins of cartilage microbial DNA, to characterize cartilage microbial changes with age, obesity, and OA in mice, and correlate these to gut microbiome changes. We used 16S rRNA sequencing performed longitudinally on articular knee cartilage from germ-free (GF) mice following oral microbiome inoculation and cartilage and cecal samples from young and old wild-type mice with/without high-fat diet-induced obesity (HFD) and with/without OA induced by destabilization of the medial meniscus (DMM) to evaluate gut and cartilage microbiota. Microbial diversity was assessed, groups compared, and functional metagenomic profiles reconstructed. Findings were confirmed in an independent cohort by clade-specific qPCR. We found that cartilage microbial patterns developed at 48 h and later timepoints following oral microbiome inoculation of GF mice. Alpha diversity was increased in SPF mouse cartilage samples with age (P = 0.013), HFD (P = 5.6E-4), and OA (P = 0.029) but decreased in cecal samples with age (P = 0.014) and HFD (P = 1.5E-9). Numerous clades were altered with aging, HFD, and OA, including increases in Verrucomicrobia in both cartilage and cecal samples. Functional analysis suggested changes in dihydroorotase, glutamate-5-semialdehyde dehydrogenase, glutamate-5-kinase, and phosphoribosylamine-glycine ligase, in both cecum and cartilage, with aging, HFD, and OA. In conclusion, cartilage microbial DNA patterns develop rapidly after the introduction of a gut microbiome and change in concert with the gut microbiome during aging, HFD, and OA in mice. DMM-induced OA causes shifts in both cartilage and cecal microbiome patterns independent of other factors.

The Microbiome of Osteoarthritic Hip and Knee Joints: A Prospective Multicenter Investigation

BACKGROUND

Recent advances in high-throughput DNA sequencing technologies have made it possible to characterize the microbial profile in anatomical sites previously assumed to be sterile. We used this approach to explore the microbial composition within joints of osteoarthritic patients.

METHODS

This prospective multicenter study recruited 113 patients undergoing hip or knee arthroplasty between 2017 and 2019. Demographics and prior intra-articular injections were noted. Matched synovial fluid, tissue, and swab specimens were obtained and shipped to a centralized laboratory for testing. Following DNA extraction, microbial 16S-rRNA sequencing was performed.

RESULTS

Comparisons of paired specimens indicated that each was a comparable measure for microbiological sampling of the joint. Swab specimens were modestly different in bacterial composition from synovial fluid and tissue. The 5 most abundant genera were Escherichia, Cutibacterium, Staphylococcus, Acinetobacter, and Pseudomonas. Although sample size varied, the hospital of origin explained a significant portion (18.5%) of the variance in the microbial composition of the joint, and corticosteroid injection within 6 months before arthroplasty was associated with elevated abundance of several lineages.

CONCLUSIONS

The findings revealed that prior intra-articular injection and the operative hospital environment may influence the microbial composition of the joint. Furthermore, the most common species observed in this study were not among the most common in previous skin microbiome studies, suggesting that the microbial profiles detected are not likely explained solely by skin contamination. Further research is needed to determine the relationship between the hospital and a "closed" microbiome environment. These findings contribute to establishing the baseline microbial signal and identifying contributing variables in the osteoarthritic joint, which will be valuable as a comparator in the contexts of infection and long-term arthroplasty success.

LEVEL OF EVIDENCE

Diagnostic Level II. See Instructions for Authors for a complete description of levels of evidence.

Gut bacteriome, mycobiome and virome alterations in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic destructive autoimmune disease of the joints which causes significant pain, functional disability, and mortality. Although aberrant immune cell activation induced by the imbalance between T helper Th1/Th17 and Treg cells is implicated in the RA development, its etiopathogenesis remains unclear. The presence of mucosal inflammation and systemic IgA-isotype-autoantibodies (anti-citrullinated peptide antibodies and rheumatoid factor) in pre-clinical RA supports the mucosal origin hypothesis involving altered microbiota in disease development. The gut microbiota comprises diverse bacteria, fungal and viral components, which are critical in developing host immunity. Alterations in microbial abundance are known to exacerbate or attenuate immune responses in the gut microenvironment subsequently affecting the joints. Further, these changes can provide biomarkers for disease activity and outcome in RA. Most of the research till date has been focused on describing gut bacterial components in RA. Studies on gut mycobiome and virome components in RA are relatively new and burgeoning field. Given the paucity of mycobiome or virome specific studies in RA, this review, discusses the recent findings on alterations in gut bacterial, fungal, and viral components as well as their role in regulating the spectrum of immune-pathogenic events occurring in RA which might be explored in future as a potential therapeutic target. Further, we provide an overview on inter-kingdom interactions between bacteria, fungi, and viruses in RA. The current understanding on gut microbiota modulation for managing RA is also summarised.

Yields of mesenchymal stromal cells from synovial fluid reflect those from synovium in patients with rheumatoid arthritis

The yield of primary synovial mesenchymal stromal cells (MSCs) from synovium of patients with rheumatoid arthritis (RA) is highly variable, but cell transplantation therapy with autologous synovial MSCs requires accurate prediction of the synovial MSC yield per synovium weight. Here, we determined whether the yield of synovial fluid MSCs might predict the ultimate yield of primary MSCs from the synovium of RA knees. Synovial fluid and synovium were harvested during total knee arthroplasty from the knee joints of 10 patients with RA. Synovial fluid (1.5 mL) was diluted fourfold and plated equally into six 60 cm² dishes. Nucleated cells from digested synovium were similarly plated at 1 × 10⁴ cells in 6 dishes. All dishes were cultured for 14 days and analyzed for MSC yields and properties, including in vitro chondrogenesis. The cultured synovial cell number was correlated with the cultured synovial fluid cell number (n = 10, R² = 0.64, p < 0.01). Synovial fluid cells formed cell colonies and showed MSC-like surface epitopes and multi-differentiation potential. However, the cartilage pellet weight indicated a greater chondrogenic potential of the synovial MSCs (n = 8). The primary MSC yields from synovial fluid and synovium were correlated, indicating that the synovial fluid MSC yield can predict the ultimate synovial MSC yield.

Alterations of gut fungal microbiota in patients with rheumatoid arthritis

BACKGROUND

Rheumatoid arthritis (RA) is a systemic autoimmune disease, in addition, gut microbiota plays an important role in the etiology of RA. However, our understanding of alterations to the gut fungal microbiota in Chinese population with RA is still limited.

METHODS

Serum samples were obtained from 62 patients with RA, and 39 age- and gender-matched healthy controls (HCs). Fecal samples were obtained from 42 RA patients and 39 HCs. Fecal fungal microbiota targeting internal transcribed spacer region 2 (ITS2) rRNA genes was investigated using MiSeq sequencing, as well as their associations with some diagnostic biomarkers for RA.

RESULTS

Our results showed that the fungal diversity did not alter in RA patients but taxonomic composition of the fecal fungal microbiota did. The gut mycobiota of RA patients was characterized by decreased abundance of Pholiota, Scedosporium, and Trichosporon. The linear discriminant analysis (LDA) effect size analysis (LEfSe) analysis identified several RA-enriched fungal genera, which were positively correlated with most RA biomarkers. Furthermore, since RA is an age- and gende-related disease, we classified RA patients into subgroups with age and gender and analyzed the sequencing results. Our data demonstrated that Wallemia and Irpex were the most discriminatory against RA patients over 60 years old, while Pseudeurotiaceae was the most discriminatory against female RA patients.

CONCLUSIONS

The case-control study presented here confirmed the alterations of gut fungal microbiota in Chinese patients with RA, and we speculated that the fungal dysbiosis may contribute to RA development.

Another Look at the Contribution of Oral Microbiota to the Pathogenesis of Rheumatoid Arthritis: A Narrative Review

Although autoimmunity contributes to rheumatoid arthritis (RA), several lines of evidence challenge the dogma that it is mainly an autoimmune disorder. As RA-associated human leukocyte antigens shape microbiomes and increase the risk of dysbiosis in mucosae, RA might rather be induced by epigenetic changes in long-lived synovial presenting cells, stressed by excessive translocations into joints of bacteria from the poorly cultivable gut, lung, or oral microbiota (in the same way as more pathogenic bacteria can lead to "reactive arthritis"). This narrative review (i) lists evidence supporting this scenario, including the identification of DNA from oral and gut microbiota in the RA synovium (but in also healthy synovia), and the possibility of translocation through blood, from mucosae to joints, of microbiota, either directly from the oral cavity or from the gut, following an increase of gut permeability worsened by migration within the gut of oral bacteria such as Porphyromonas gingivalis; (ii) suggests other methodologies for future works other than cross-sectional studies of periodontal microbiota in cohorts of patients with RA versus controls, namely, longitudinal studies of oral, gut, blood, and synovial microbiota combined with transcriptomic analyses of immune cells in individual patients at risk of RA, and in overt RA, before, during, and following flares of RA.

Pseudoseptic Arthritis in a Patient With Psoriasis

A 42-year-old male with a history of untreated psoriasis and a previous episode of presumed left knee septic arthritis developed sudden onset of left knee pain, swelling, and a moderate effusion. The pathogen could not be isolated despite extensive inflammation seen in synovial fluid (SF) and synovial tissue biopsy. Whether this is culture-negative septic arthritis or pseudo-septic arthritis is the enigma, given the limited sensitivity of current available SF microbiologic testing. We present a challenging and stimulating case with no current guidelines for an optimal empiric antibiotic regimen or anti-inflammatory therapy.

Identification and Characterization of the Intra-Articular Microbiome in the Osteoarthritic Knee

Osteoarthritis (OA) is the most common joint disorder in the United States, and the gut microbiome has recently emerged as a potential etiologic factor in OA development. Recent studies have shown that a microbiome is present at joint synovia. Therefore, we aimed to characterize the intra-articular microbiome within osteoarthritic synovia and to illustrate its role in OA disease progression. RNA-sequencing data from OA patient synovial tissue was aligned to a library of microbial reference genomes to identify microbial reads indicative of microbial abundance. Microbial abundance data of OA and normal samples was compared to identify differentially abundant microbes. We computationally explored the correlation of differentially abundant microbes to immunological gene signatures, immune signaling pathways, and immune cell infiltration. We found that microbes correlated to OA are related to dysregulation of two main functional pathways: increased inflammation-induced extracellular matrix remodeling and decreased cell signaling pathways crucial for joint and immune function. We also confirmed that the differentially abundant and biologically relevant microbes we had identified were not contaminants. Collectively, our findings contribute to the understanding of the human microbiome, well-known OA risk factors, and the role microbes play in OA pathogenesis. In conclusion, we present previously undiscovered microbes implicated in the OA disease progression that may be useful for future treatment purposes.

Hypoxia-Inducible Factor Is Critical for Pathogenesis and Regulation of Immune Cell Functions in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a common autoimmune disease with characteristics of synovial inflammation, pannus formation, cartilage destruction, and bone erosion. Further, the inflammation is linked to increased oxygen consumption, resulting in hypoxia within the inflammatory area. Hypoxia-inducible factor (HIF) was reported to be associated with adaptation to the hypoxic microenvironment in the RA synovium. Here, we have briefly summarized the structure and expression of HIF. Moreover, the function of HIF in inflammation, angiogenesis, cartilage damage, and immune cells of RA has been discussed.