The role of interleukin-6 trans-signalling on cardiovascular dysfunction in inflammatory arthritis

Objectives

Cardiovascular (CV) mortality in RA patients is 50% higher than in the general population. There is increasing recognition that systemic inflammation is a major driver of this. IL-6 is implicated in cardiovascular disease (CVD) in the general population but its role in CVD in RA is undefined. Of the two modes of IL-6 signalling, trans-signalling is pro-inflammatory whereas classical signalling is linked with inflammation resolution. This study examines the role of IL-6 trans-signalling in CVD in a mouse model and patients with RA.

Methods

Myography determined the effect of IL-6 trans-signalling blockade, using sgp130Fc, on aortic constriction in murine collagen-induced arthritis. Serum CCL2 and sVCAM-1 as soluble biomarkers of sIL-6R trans-signalling were investigated in a human cross-sectional study. An observational longitudinal study investigated the association between these biomarkers and progression of subclinical atherosclerosis in early RA by measuring carotid intima-media thickness (CIMT).

Results

sgp130Fc reduced arthritis severity, serum CCL2 and sVCAM-1 and restored vascular function in collagen-induced arthritis (CIA). In established RA, sVCAM-1 correlated with the 28-joint DAS (DAS28) and CV risk. In early RA, baseline DAS28 was associated with CIMT change at 6 months. CIMT ‘rapid progressors’ at 12 months had higher baseline sVCAM-1, haemoglobin A1c, cholesterol:high-density lipoprotein cholesterol ratio and LDL cholesterol.

Conclusions

IL-6 trans-signalling plays a pivotal role in vascular dysfunction in CIA. In early RA, sVCAM-1 was associated with progression of subclinical atherosclerosis. Inflammation from RA onset in CVD-susceptible individuals may accelerate atherosclerosis. IL-6 trans-signalling blockade may be beneficial to RA patients and perhaps for atherosclerosis in the general population.

In Vivo Models for Inflammatory Arthritis

In vivo mouse models of inflammatory arthritis are extensively used to investigate pathogenic mechanisms governing inflammation-driven joint damage. Two commonly utilized models include collagen-induced arthritis (CIA) and methylated bovine serum albumin (mBSA) antigen-induced arthritis (AIA). These offer unique advantages for modeling different aspects of human disease. CIA involves breach of immunological tolerance resulting in systemic autoantibody-driven arthritis, while AIA results in local resolving inflammatory flares and articular T cell-mediated damage. Despite limitations that apply to all animal models of human disease, CIA and AIA have been instrumental in identifying pathogenic mediators, immune cell subsets and stromal cell responses that determine disease onset, progression, and severity. Moreover, these models have enabled investigation of disease phases not easily studied in patients and have served as testing beds for novel biological therapies, including cytokine blockers and small molecule inhibitors of intracellular signaling that have revolutionized rheumatoid arthritis treatment.

Alterations to adipose tissue morphology during inflammatory arthritis is indicative of vasculopathology in DBA/1 mice

The physiologic function of adipose tissue is altered by the host's inflammatory response; the implications for maintaining human health and regulating inflammation-associated disease progression are ill defined. However, this cannot be investigated in humans, therefore the use of animal models is required. With the aim to determine morphological and molecular alterations to perivascular and organ-associated adipose tissues during inflammatory arthritis, collagen-induced arthritis (CIA) was established in male DBA/1 mice. Emerging evidence from this study signposts CIA in the DBA/1 mouse as a model that is relevant to study the development and treatment of early cardiovascular pathology associated with inflammatory arthritis. Here, we show global morphological changes in adipose tissue and the thoracic aorta in animals induced with CIA compared with the non-immunized controls. In CIA, we concluded that the increased cell count in PVAT was, at least in part, caused by an ingress and/or expansion of macrophages that had a mixed phenotype. A substantial increase of galectin-3 was expressed in PVAT from mice with CIA. Galectin-3 is elevated in the blood of patients with CVDs, however, it has never before been measured in PVAT in rodents or humans. Here, PVAT-associated galectin-3 is identified as a potential biomarker for detecting early vascular pathology in CIA and a promising candidate for translation to RA.