Prediction of Erosive Disease Development by Antimitochondrial Antibodies in Rheumatoid Arthritis

Anti-HSP90α IgG may protect against antiphospholipid syndrome in systemic lupus erythematosus by reducing platelet activation

Natural autoantibodies (NAAbs) are immunoglobulins generated in the absence of antigen provocation, with no inherent pathogenic effect, but instead involved in maintaining immune homeostasis. We aimed to evaluate the implication of immunoglobulin G (IgG) antibodies against heat shock protein 90α (HSP90α) in systemic lupus erythematosus (SLE) patients, focusing on how those NAAbs may interfere with the immunothrombosis process. Anti-HSP90α IgG was measured by an enzyme-linked immunosorbent assay in the plasma of 308 SLE individuals, paired with 308 healthy controls (HC). Validation was performed in another cohort, comprised of serum from 125 SLE and 77 HC. In an in vitro experiment, platelets were cultured with mitochondria (abundant sources of HSP90α) treated with anti-HSP90α IgG, and the activation markers thrombospondin-1 and platelet factor 4 were measured in the supernatant. Levels of anti-HSP90α IgG were comparable in SLE and HC, but decreased in the SLE patients with secondary antiphospholipid syndrome (APS), both in the exploratory and the validation cohort (p = 0.0265, and p = 0.0472 respectively). Mitochondria triggered platelet activation in a TLR2- and HSP90α-dependent manner (p = 0.0152 and p < 0.001 respectively). Anti-HSP90α IgG emerges as a prominent NAAb-modulating immunothrombosis in SLE and holds promise as a biomarker of APS risk in these patients.

Precision Medicine in Rheumatology: The Role of Biomarkers in Diagnosis and Treatment Optimization

Rheumatic diseases encompass a wide range of autoimmune and inflammatory disorders, including rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), psoriatic arthritis (PsA), and systemic sclerosis (SSc). These conditions often result in chronic pain, disability, and reduced quality of life, with unpredictable disease courses that may lead to joint destruction, organ damage, or systemic complications. Biomarkers, defined as measurable indicators of biological processes or conditions, have the potential to transform clinical practice by improving disease diagnosis, monitoring, prognosis, and treatment decisions. While significant strides have been made in identifying and validating biomarkers in rheumatic diseases, challenges remain in their standardization, clinical utility, and integration into routine practice. This review provides an overview of the current state of biomarkers in rheumatic diseases, their roles in clinical settings, and the emerging advancements in the field.

Mitochondrial-Mediated Platelet Activation in Polymyalgia Rheumatica

OBJECTIVE

Platelet activation is thought to participate in polymyalgia rheumatica (PMR) pathogenesis. Upon platelet activation, mitochondria are expelled into the extracellular space. However, whether extracellular mitochondria are present in patients with PMR and whether they can induce platelet activation is not known.

METHODS

To investigate this, we measured markers of platelet activation (thrombospondin-1 [TSP-1]), mitochondrial-derived N-formyl methionine peptide (fMET), and autoantibodies directed toward specific mitochondrial antigen mitofusin-1 (MFN1) by enzyme-linked immunosorbent assay in plasma of healthy controls (HCs, n = 30) and patients with PMR without giant cell arteritis (GCA) (n = 45) and patients with PMR with GCA (n = 9) before and after treatment with glucocorticoid therapy. Ultrapure mitochondria were opsonized with plasma from patients with PMR without GCA (n = 45) or HCs (n = 10) and were subsequently incubated with HC platelets. Platelet activation was assessed by P-selectin levels using flow cytometry.

RESULTS

Plasma levels of anti-MFN1 IgG were elevated in patients with PMR with and without GCA before glucocorticoid therapy when compared with HCs (P < 0.01 for both groups). Levels of anti-MFN1 IgG significantly reduced after treatment with glucocorticoids in both groups (P < 0.01). Levels of fMET were also significantly higher in patients with PMR with and without GCA before glucocorticoid therapy in comparison with HCs (P < 0.001 and P < 0.01, respectively). However, the levels of fMET only dropped significantly after therapy in patients with PMR without GCA (P < 0.001). Plasma levels of TSP-1 were elevated in patients with PMR with and without GCA before glucocorticoid therapy when compared to HC (P < 0.001 for both groups). After glucocorticoid therapy, plasma levels of TSP-1 decreased significantly only in patients with PMR without GCA (P = 0.023). Mitochondria opsonized with plasma from patients with PMR without GCA induced higher platelet activation regardless of treatment status as compared with plasma from HCs (P < 0.0001 and P < 0.01 for pretreatment and posttreatment).

CONCLUSION

Our results indicate increased platelet activation and the presence of mitochondrial antigens and antibodies in the circulation of patients with PMR. Blocking mitochondrial-mediated platelet activation may reduce inflammation in patients with PMR, with potential therapeutic implications.

Mitochondria in skeletal system-related diseases

Skeletal system-related diseases, such as osteoporosis, arthritis, osteosarcoma and sarcopenia, are becoming major public health concerns. These diseases are characterized by insidious progression, which seriously threatens patients' health and quality of life. Early diagnosis and prevention in high-risk populations can effectively prevent the deterioration of these patients. Mitochondria are essential organelles for maintaining the physiological activity of the skeletal system. Mitochondrial functions include contributing to the energy supply, modulating the Ca2+ concentration, maintaining redox balance and resisting the inflammatory response. They participate in the regulation of cellular behaviors and the responses of osteoblasts, osteoclasts, chondrocytes and myocytes to external stimuli. In this review, we describe the pathogenesis of skeletal system diseases, focusing on mitochondrial function. In addition to osteosarcoma, a characteristic of which is active mitochondrial metabolism, mitochondrial damage occurs during the development of other diseases. Impairment of mitochondria leads to an imbalance in osteogenesis and osteoclastogenesis in osteoporosis, cartilage degeneration and inflammatory infiltration in arthritis, and muscle atrophy and excitationcontraction coupling blockade in sarcopenia. Overactive mitochondrial metabolism promotes the proliferation and migration of osteosarcoma cells. The copy number of mitochondrial DNA and mitochondria-derived peptides can be potential biomarkers for the diagnosis of these disorders. High-risk factor detection combined with mitochondrial component detection contributes to the early detection of these diseases. Targeted mitochondrial intervention is an effective method for treating these patients. We analyzed skeletal system-related diseases from the perspective of mitochondria and provided new insights for their diagnosis, prevention and treatment by demonstrating the relationship between mitochondria and the skeletal system.

Clinical Phenotypes, Serological Biomarkers, and Synovial Features Defining Seropositive and Seronegative Rheumatoid Arthritis: A Literature Review

Rheumatoid arthritis (RA) is a chronic autoimmune disorder which can lead to long-term joint damage and significantly reduced quality of life if not promptly diagnosed and adequately treated. Despite significant advances in treatment, about 40% of patients with RA do not respond to individual pharmacological agents and up to 20% do not respond to any of the available medications. To address this large unmet clinical need, several recent studies have focussed on an in-depth histological and molecular characterisation of the synovial tissue to drive the application of precision medicine to RA. Currently, RA patients are clinically divided into "seropositive" or "seronegative" RA, depending on the presence of routinely checked antibodies. Recent work has suggested that over the last two decades, long-term outcomes have improved significantly in seropositive RA but not in seronegative RA. Here, we present up-to-date differences in epidemiology, clinical features, and serological biomarkers in seronegative versus seropositive RA and discuss how histological and molecular synovial signatures, revealed by recent large synovial biopsy-based clinical trials, may be exploited to refine the classification of RA patients, especially in the seronegative group.