Systemic sclerosis (SSc) is characterized by vascular alterations, activation of the immune system and tissue fibrosis. Vascular insufficiency manifests early in the disease, and although there is evidence of an active repair process, capillaries deteriorate and regress. Factors that contribute to the failure of vascular regeneration might include persistent injury, an imbalance between proangiogenic and antiangiogenic mediators, intrinsic abnormal properties of the cellular components of the vessels, and the presence of fibroblast-derived antiangiogenic factors. In addition, circulating dysfunctional endothelial progenitor cells might further exacerbate vessel deterioration. Abnormal expression of transcription factors, including Fra2 and Fli1, has been proposed to contribute to SSc vasculopathy. Fli1 regulates genes that are involved in vessel maturation and stabilization, suggesting that reduced levels of Fli1 in SSc vasculature could contribute to the development of unstable vessels that are prone to regression. Conversely, proliferating endothelial cells and pericytes, in the presence of an appropriate stimulus, might transdifferentiate into collagen-producing cells, and thus contribute to the initiation of fibrosis. Despite progress in treating the symptoms of vascular disease in SSc, the underlying mechanisms remain poorly understood. An improved knowledge of the molecular and cellular pathways that contribute to SSc vasculopathy could help in the design of effective therapies in the future.
Recent studies have highlighted a potentially important role for Wnts as profibrotic mediators, and implicated increased Wnt activity in systemic sclerosis and other fibrotic diseases. Strikingly, new data indicates that Wnts have a central role in the profibrotic activity of TGF-β.
Rapid-onset cardiovascular disease is a major concern for many patients suffering from SLE. Cardiovascular events are more frequent and occur much earlier in SLE patients compared to healthy controls. Traditional risk factors such as altered lipid levels, older age and smoking do not fully explain the increased risk of cardiovascular disease, strongly suggesting that autoimmunity contributes to accelerated atherosclerosis. Altered immune system function is recognized as the primary contributor to both the initiation and progression of atherosclerosis. Multiple manifestations of autoimmunity, including autoantibodies, altered cytokine levels and innate immunity response, adipokines, dysfunctional lipids, and oxidative stress appear to contribute to atherosclerotic risk. In addition, multiple SLE therapeutics appear to affect the development and progression of atherosclerosis both positively and negatively. SLE-specific biomarkers for identifying patients at risk of developing accelerated atherosclerosis are starting to be identified by multiple groups, and a comprehensive, clinically testable biomarker panel could be invaluable for identifying and treating these patients.
Aging and a sedentary lifestyle conspire to reduce bone quantity and quality, decrease muscle mass and strength, and undermine postural stability, culminating in an elevated risk of skeletal fracture. Concurrently, a marked reduction in the available bone-marrow-derived population of mesenchymal stem cells (MSCs) jeopardizes the regenerative potential that is critical to recovery from musculoskeletal injury and disease. A potential way to combat the deterioration involves harnessing the sensitivity of bone to mechanical signals, which is crucial in defining, maintaining and recovering bone mass. To effectively utilize mechanical signals in the clinic as a non-drug-based intervention for osteoporosis, it is essential to identify the components of the mechanical challenge that are critical to the anabolic process. Large, intense challenges to the skeleton are generally presumed to be the most osteogenic, but brief exposure to mechanical signals of high frequency and extremely low intensity, several orders of magnitude below those that arise during strenuous activity, have been shown to provide a significant anabolic stimulus to bone. Along with positively influencing osteoblast and osteocyte activity, these low-magnitude mechanical signals bias MSC differentiation towards osteoblastogenesis and away from adipogenesis. Mechanical targeting of the bone marrow stem-cell pool might, therefore, represent a novel, drug-free means of slowing the age-related decline of the musculoskeletal system.
Genome-wide association studies of human diseases have uncovered large numbers of common genetic variants with low effect sizes; however, rare genetic variants with large effect sizes may have greater relevance with respect to disease heritability. The identification and characterization of rare variants such as SIAE is, therefore, likely to be a major endeavor in the field in the coming years.
A number of studies published over the past 10 years have examined the long-term health, functional and quality of life outcomes of adults with childhood-onset rheumatic diseases such as juvenile idiopathic arthritis, systemic lupus erythematosus, juvenile dermatomyositis and localized scleroderma. As increasing numbers of patients with these conditions survive into adulthood, understanding the adult outcomes of these pediatric conditions has become ever-more important. Identifying modifiable risk factors for poor outcomes is vital to improving care for these patients. In addition, as these conditions and their treatments can affect cardiovascular health, bone health and fertility, particular attention needs to be paid to these outcomes. Preparing patients and their families for a successful transition from pediatric to adult rheumatology care is an important first-step in the long-term management strategy for this expanding patient population.
The use of biomarkers is becoming increasingly intrinsic to the practice of medicine and holds great promise for transforming the practice of rheumatology. Biomarkers have the potential to aid clinical diagnosis when symptoms are present or to provide a means of detecting early signs of disease when they are not. Some biomarkers can serve as early surrogates of eventual clinical outcomes or guide therapeutic decision making by enabling identification of individuals likely to respond to a specific therapy. Using biomarkers might reduce the costs of drug development by enabling individuals most likely to respond to be enrolled in clinical trials, thereby minimizing the number of participants required. In this Review, we discuss the current use and the potential of biomarkers in rheumatology and in select fields at the forefront of biomarker research. We emphasize the value of different types of biomarkers, addressing the concept of ‘actionable’ biomarkers, which can be used to guide clinical decision making, and ‘mechanistic’ biomarkers, a subtype of actionable biomarker that is embedded in disease pathogenesis and, therefore, represents a superior biomarker. We provide examples of actionable and mechanistic biomarkers currently available, and discuss how development of such biomarkers could revolutionize clinical practice and drug development.
Rheumatoid arthritis (Ra) is partly heritable; genetic and serological markers are known to confer risk of developing pathology. But given clinical heterogeneity in Ra, can we predict who will develop severe disease? Substantial heritability of erosive progression rates has now been identified, but better prognostic biomarkers remain wanting.
Emerging evidence points to a critical role for the skeleton in several homeostatic processes including energy balance. The connection between fuel utilization and skeletal remodeling begins in the bone marrow with lineage allocation of mesenchymal stromal cells into adipocytes or osteoblasts. Mature bone cells secrete factors that influence insulin sensitivity and fat cells synthesize cytokines that regulate osteoblast differentiation. The emerging importance of the bone-fat interaction suggests that novel molecules could be used as targets to enhance bone formation and possibly prevent fractures. In this review, we discuss three pathways that could favor pharmacologic intervention with the ultimate goal of enhancing bone mass and reducing osteoporotic fracture risk. Not surprisingly, because of the complex interactions across homeostatic networks, other pathways will likely be activated by this targeting and these could prove to be beneficial or detrimental for the organism. Hence a more complete picture of energy utilization and skeletal remodeling will be required to bring these potential agents into any future clinical armamentarium.
Uric acid is a waste product of purine catabolism. This molecule comes to clinical attention when it nucleates to form crystals of monosodium urate (MSU) in joints or other tissues and thereby causes the inflammatory disease of gout. Patients with gout also frequently suffer from a number of co-morbid conditions including hypertension, diabetes mellitus and cardiovascular disease. Why MSU crystals trigger inflammation and are associated with comorbidities of gout has been unclear, but recent studies provide new insights these issues. Rather than simply being a waste product, uric acid could serve a pathophysiological role as a local alarm signal that alerts the immune system to cell injury and helps to trigger both innate and adaptive immune responses. The inflammatory component of these immune responses is caused when urate crystals trigger both inflammasome-dependent and independent pathways to generate the proinflammatory cytokine IL-1. The resulting bioactive IL-1 stimulates the inflammation of gout and might contribute to the development of other comorbidities. Surprisingly, the same mechanisms underlie the inflammatory response to a number of irritant particles, many of which also cause disease. These new insights help to explain the pathogenesis of gout and point to potential new therapeutic targets for this and other sterile inflammatory diseases.
A significant body of data implicates the type I interferon (IFN) pathway in the pathogenesis of autoimmune rheumatic diseases. In these disorders, a reinforcing cycle of IFN production can contribute to immunopathology through multiple mechanisms. The type I IFN cytokines are pleiotropic in their effects, mediating anti-viral and anti-tumor activities, and possessing numerous immunomodulatory functions for both the innate and adaptive immune responses. A key principle of the type I IFN system is rapid induction and amplification of the signaling pathway, which generates a feed-forward loop of IFN production, ensuring that a vigorous anti-viral immune response is mounted. While such feed-forward pathways are highly adaptive when it comes to rapid and effective virus eradication, this amplification can be maladaptive in immune responses directed against host tissues. Such feed-forward loops, however, create special opportunities for therapy.
Follicular helper T (TFH) cells are essential for B-cell maturation and immunoglobulin production after immunization with thymus-dependent antigens. Nevertheless, the development and function of TFH cells have been less clearly defined than classic CD4+ effector T-cell subsets, including T-helper-1 (TH1), TH2 and TH17 cells. As such, our understanding of the genesis of TFH cells in humans and their role in the development of autoimmunity remains incomplete. However, evidence from animal models of systemic lupus erythematosus (SLE) and patients with systemic autoimmune diseases suggests that these cells are necessary for pathogenic autoantibody production, in a manner analogous to their role in promotion of B-cell maturation during normal immune responses. In this Review, I discuss the findings that have increased our knowledge of TFH-cell development and function in normal and aberrant immune responses. Such information might improve our understanding of autoimmune diseases, such as SLE, and highlights the potential of TFH cells as therapeutic targets in these diseases.
Osteoarthritis (OA) is the most common musculoskeletal disorder. It is a complex and multifaceted disease, characterized by the degradation of articular cartilage and joint inflammation. Although few pathogenesis pathways have been characterized, current knowledge is incomplete and has not led to effective approaches for prevention or treatment. These limitations can be overcome by advances in the understanding of molecular mechanisms that are involved in the maintenance and destruction of articular cartilage. Understanding extracellular regulators and intracellular signaling mechanisms in joint cells that control cartilage homeostasis has the potential to lead to the identification of new therapeutic targets for OA. Recently, non-coding RNAs, miRNAs, was noted to act as novel regulatory molecules that regulated the expression of several target genes. The major role of miRNAs is to control development and tissue homeostasis through the ‘fine-tuning’ of the gene expression. Several miRNAs exhibit a tissue- or developmental stage-specific expression pattern and have been associated with diseases such as cancer and cardiovascular disorders. This review is based on our observations that miRNAs play an important role in cartilage homeostasis, and is to summarize the information on miRNA involved in OA pathogenesis, and its clinical approach.
Osteoarthritis; Cartilage; Chondrocytes; microRNA; miR-140
Human disorders of hereditary and nonhereditary heterotopic ossification are conditions in which osteogenesis occurs outside of the skeleton, within soft tissues of the body. The resulting extraskeletal bone is normal. The aberration lies within the mechanisms that regulate cell-fate determination, directing the inappropriate formation of cartilage or bone, or both, in tissues such as skeletal muscle and adipose tissue. Specific gene mutations have been identified in two rare inherited disorders that are clinically characterized by extensive and progressive extraskeletal bone formation—fibrodysplasia ossificans progressiva and progressive osseous heteroplasia. In fibrodysplasia ossificans progressiva, activating mutations in activin receptor type-1, a bone morphogenetic protein type I receptor, induce heterotopic endochondral ossification, which results in the development of a functional bone organ system that includes skeletal-like bone and bone marrow. In progressive osseous heteroplasia, the heterotopic ossification leads to the formation of mainly intramembranous bone tissue in response to inactivating mutations in the GNAS gene. Patients with these diseases variably show malformation of normal skeletal elements, identifying the causative genes and their associated signaling pathways as key mediators of skeletal development in addition to regulating cell-fate decisions by adult stem cells.
Systemic sclerosis is associated with a high level of patient mortality. A promising prognostic model that could enable more effective management and improve survival was recently validated; however, the results demonstrate that choosing the best cohorts for development and validation of predictors of mortality is essential.
Systemic lupus erythematosus (SLE) is an autoimmune disease of unclear etiology that affects mostly women of childbearing age. Profound abnormalities in both innate and adaptive immunity triggered by genetic and environmental factors are well documented to play an important part in the pathogenesis of SLE. Nonetheless, the role of neutrophils—the most abundant immune cell type—in the pathology of this disease has been unclear. Over the past decade, compelling evidence has emerged that implicates neutrophils in the initiation and perpetuation of SLE and also in the resultant organ damage frequently observed in patients with this disease. SLE-derived low-density granulocytes (LDGs) induce vascular damage and synthesize increased amounts of type I interferons and, as such, could play a prominent part in the pathogenesis of SLE. Furthermore, increased cell death and enhanced extracellular trap formation observed in SLE-derived neutrophils might have key roles in the induction of autoimmunity and the development of organ damage in patients with SLE. Together, these events could have significant deleterious effects and promote aberrant immune responses in this disease. This Review highlights the role of neutrophils in the pathogenesis of SLE, with a particular focus on the putative deleterious effects of LDGs and neutrophil extracellular trap formation.
Biomarkers have an important influence on the clinical decision-making processes involved in diagnosis, assessment of disease activity, allocation of treatment, and determining prognosis. The clinical usefulness of a biomarker is dependant on demonstration of its validity. Ideally, biomarkers should provide information not available from currently available tests and should be tested as they would be used in clinical practice; however, potential biomarkers could be affected by many different clinical or patient variables—such as disease activity, therapeutic intervention, or the presence of comorbidities—and validation studies might not include all the design features that are required to ensure that the biomarker is a true measure of the clinical process it is intended to reflect. In this Review, we appraise studies that have been conducted to validate six promising new biomarkers for diagnosis, disease activity assessment, or prognosis in patients with systemic autoimmune diseases. We discuss the validity of these six biomarkers with particular reference to the features of the studies that lend weight to or distract from their findings. The intent of this discussion is to draw attention to elements of validation study design that should be considered when evaluating the robustness of a biomarker, which differ according to the marker's intended use.
Gene transfer technologies enable the controlled, targeted and sustained expression of gene products at precise anatomical locations, such as the joint. In this way, they offer the potential for more-effective, less-expensive treatments of joint diseases with fewer extra-articular adverse effects. A large body of preclinical data confirms the utility of intra-articular gene therapy in animal models of rheumatoid arthritis and osteoarthritis. However, relatively few clinical trials have been conducted, only one of which has completed phase II. This article summarizes the status in 2010 of the clinical development of gene therapy for arthritis, identifies certain constraints to progress and suggests possible solutions.
Programmed Cell Death (PCD) is a key process regulating immune cell development and peripheral immune homeostasis. Caspase-dependent apoptosis as well as a number of alternative cell death mechanisms account for immune cell PCD induced by cell-intrinsic as well as extrinsic pathways. In animal models, compelling evidence has emerged that genetic defects in programmed cell death can result in autoimmune disease. Autoimmune disease can arise from single-gene mutations affecting PCD, and defective PCD has been observed in some tissues and cells from patients with rheumatic disease. Selectively inducing PCD in autoreactive B and T cells is very attractive as a therapeutic strategy because it offers the possibility of permanently eliminating these cells. In addition, the anti-inflammatory effects of apoptotic cells may add to the therapeutic benefit of inducing apoptosis. Immune cell subsets vary widely in their sensitivity to specific inducers of cell death, and understanding these differences is key to predicting the outcome of inducing apoptosis for therapeutic means. Here we review approaches that have been taken to induce programmed cell death in the therapy of autoimmune disease and prospects for bringing these experimental strategies into clinical practice.
Rheumatologists see patients with a range of autoimmune diseases. Phenotyping these diseases for diagnosis, prognosis and selection of therapies is an ever increasing problem. Advances in multiplexed assay technology at the gene, protein, and cellular level have enabled the identification of `actionable biomarkers'; that is, biological metrics that can inform clinical practice. Not only will such biomarkers yield insight into the development, remission, and exacerbation of a disease, they will undoubtedly improve diagnostic sensitivity and accuracy of classification, and ultimately guide treatment. This Review provides an introduction to these powerful technologies that could promote the identification of actionable biomarkers, including mass cytometry, protein arrays, and immunoglobulin and T-cell receptor high-throughput sequencing. In our opinion, these technologies should become part of routine clinical practice for the management of autoimmune diseases. The use of analytical tools to deconvolve the data obtained from use of these technologies is also presented here. These analyses are revealing a more comprehensive and interconnected view of the immune system than ever before and should have an important role in directing future treatment approaches for autoimmune diseases.
As critical regulators of numerous cell signaling pathways, tyrosine kinases are implicated in the pathogenesis of several diseases, including rheumatoid arthritis (RA). In the absence of disease, synoviocytes produce factors that provide nutrition and lubrication for the surrounding cartilage tissue; few cellular infiltrates are seen in the synovium. In RA, however, macrophages, neutrophils, T cells and B cells infiltrate the synovium and produce cytokines, chemokines and degradative enzymes that promote inflammation and joint destruction. In addition, the synovial lining expands owing to the proliferation of synoviocytes and infiltration of inflammatory cells to form a pannus, which invades the surrounding bone and cartilage. Many of these cell responses are regulated by tyrosine kinases that operate in specific signaling pathways, and inhibition of a number of these kinases might be expected to provide benefit in RA.
In 2010, important research into the systemic autoinflammatory diseases has confirmed and extended the role of IL-1 inhibition in hereditary autoinflammatory disorders, demonstrated a novel treatment for a dangerous complication, and expanded the spectrum of systemic autoinflammatory diseases while further implicating autoinflammation in the pathophysiology of the metabolic syndrome.
A new single cell detection technology allows simultaneous measurement of up to 100 surface markers and signaling proteins of immune cells. This method provides the opportunity to make great advances into the scientific understanding of rheumatic disease and the provision of individualized patient care.