Faculty Bibliography

Psoriatic arthritis (PsA) is an inflammatory arthritis associated with psoriasis. About a quarter of patients with psoriasis of the skin will develop PsA, although it is currently challenging-if not impossible-to determine a priori which individuals will progress. Identification of biomarkers for screening, disease activity, joint damage, treatment response and comorbidities are therefore perceived as important clinical needs in the field. Over the last few years, several lines of investigation have advanced our knowledge of new markers for PsA and its outcomes, including genomic, proteomic, cellular and tissue studies. Imaging studies utilizing ultrasonography have been applied to better understand the natural history of the disease. Novel biomarkers, such as soluble proteins and microbiomics, are also being described. Although no biomarker has yet been validated for use in clinical practice, discovery studies are in progress and validation cohorts are being designed. In this report, we review the latest progress in biomarker research in PsA and its potential implications in pathogenesis, diagnosis and therapy.

PURPOSE OF REVIEW: Since the early 1900s, the role of periodontal disease in the pathogenesis of rheumatoid arthritis has been a matter of intense research. The last decade has witnessed many advances supporting a link between periodontitis, the presence of specific bacterial species (i.e. Porphyromonas gingivalis) and their effects in immune response. This review will examine available evidence on the individuals. RECENT FINDINGS: Epidemiological studies have stressed the commonalities shared by periodontal disease and rheumatoid arthritis. Many groups have focused their attention toward understanding the periodontal microbiota and its alterations in states of health and disease. The presence of circulating antibodies against periodontopathic bacteria and associated inflammatory response has been found in both rheumatoid arthritis (RA) patients and individuals at-risk for disease development. Most recently, the periodontal microbiota of smokers and patients with RA has been elucidated, revealing profound changes in the bacterial communities compared with those of healthy controls. This has led to several small clinical trials of progressive disease treatment as adjuvant for disease-modifying therapy in RA. SUMMARY: Smoking and periodontal disease are emerging risk factors for the development of RA. Epidemiological, clinical, and basic research has further strengthened this association, pointing toward changes in the oral microbiota as possible contributors to systemic inflammation and arthritis.

Targeting pro-inflammatory cytokines is a promising approach to the treatment of certain autoimmune diseases. However, the signaling mechanisms involved in the initiation and effector phases of auto-aggressive pathways are still an enigma. Rho-associated kinase 2 (ROCK2) regulates the secretion of inflammatory cytokines interleukin (IL)-21 and IL-17 and the development of autoimmunity in mice. Our data from a phase 1 clinical trial demonstrates that oral administration of KD025, a selective ROCK2 inhibitor, to healthy human subjects significantly down-regulates the ability of T cells to secrete IL-21 and IL-17, but not interferon (IFN)-g in response to TCR stimulation in vitro. Pharmacological inhibition with KD025 or siRNA-mediated inhibition of ROCK2, but not ROCK1, leads to down-regulation of STAT3 phosphorylation, interferon regulatory factor 4 (IRF4) and steroid receptor-type nuclear receptor RORgt protein levels in T cells derived from healthy subjects or rheumatoid arthritis (RA) patients. Simultaneously, ROCK2 inhibition induces phosphorylation of STAT5 and SMAD2/3, and subsequently increases the percentage of Foxp3+ T cells. Thus, ROCK2 signaling appears to be instrumental in regulating the balance between pro-inflammatory and regulatory T cell subsets in man. Targeted inhibition of ROCK2 may therefore have a role in the treatment of autoimmune disease with disturbed immune homeostasis

PURPOSE OF REVIEW: Despite the progress toward understanding the molecular pathogenesis of rheumatoid arthritis (RA), its cause remains elusive. Genes are important but rather insufficient to explain the majority of RA cases. This review describes the novel data supporting the microbiome and its interactions with the human host as potential en('in')vironmental factors in RA pathogenesis. RECENT FINDINGS: Animal models of inflammatory arthritis have shown that the presence of bacteria in mucosal surfaces is sufficient to alter local and systemic host immune responses and elicit joint inflammation. Human RA studies have focused on three mucosal sites: the gut, the gingiva, and the respiratory tree. The oral microbiome, and specifically Porphyromonas gingivalis, has long been implicated. Novel sequencing technologies have allowed investigations into the role of the gut microbiome in the development of autoimmune arthritis. Most recently, the pulmonary parenchyma has also been described as yet another possible mucosal site of initiation of autoimmunity in RA. SUMMARY: Emerging data implicate the microbiome in RA pathogenesis. Mucosal sites exposed to a high load of bacterial antigens - such as the periodontium, lung, and gut - may represent the initial site of autoimmune generation. If validated, these findings could lead to the discovery of potential biomarkers and therapeutic approaches in the preclinical and clinical phases of RA.

Rheumatoid arthritis (RA) is a prevalent systemic autoimmune disease, caused by a combination of genetic and environmental factors. Animal models suggest a role for intestinal bacteria in supporting the systemic immune response required for joint inflammation. Here we performed 16S sequencing on 114 stool samples from rheumatoid arthritis patients and controls, and shotgun sequencing on a subset of 44 such samples. We identified the presence of Prevotella copri as strongly correlated with disease in new-onset untreated rheumatoid arthritis (NORA) patients. Increases in Prevotella abundance correlated with a reduction in Bacteroides and a loss of reportedly beneficial microbes in NORA subjects. We also identified unique Prevotella genes that correlated with disease. Further, colonization of mice revealed the ability of P. copri to dominate the intestinal microbiota and resulted in an increased sensitivity to chemically induced colitis. This work identifies a potential role for P. copri in the pathogenesis of RA. DOI: http://dx.doi.org/10.7554/eLife.01202.001.

Rheumatoid arthritis, currently regarded as a complex multifactorial disease, was initially characterized as such at the turn of the 19th century. Ever since, multiple lines of investigation have attempted to elucidate the etiological factor(s) involved in disease incidence. Genes - including those risk alleles within HLA-DR4 - have been implicated but are insufficient to explain the vast majority of cases. Several environmental factors, therefore, are being studied. Among them, the role of periodontal disease and Porphyromonas gingivalis in the pathogenesis of rheumatoid arthritis has attracted both clinical and bench interest given supportive epidemiologic and mechanistic data.