Background: Rheumatoid arthritis (RA) has long been associated with a significantly increased risk of cardiovascular (CV) mortality, only partially explained by traditional CV risk factors, highlighting a pivotal role of chronic systemic inflammation in the pathogenesis of CV disease (CVD)[1]. Inflammation-adapted hematopoietic stem and myeloid progenitor cells have been proposed as a common denominator for different myeloid cell-driven inflammatory diseases by acquiring a long-term pro-inflammatory phenotype [2]. Of note, extramedullary sites may supplement the hematopoietic function of the bone marrow (BM) by producing circulating myeloid cells that infiltrate inflamed tissues, such as the arterial wall [3] and joints [4]. Despite the similarities in pathophysiological mechanisms between synovial and arterial wall inflammation, research focused on the specific mechanisms of RA-associated atherosclerosis is limited.

Objectives: Our hypothesis is that chronic inflammatory pressure in RA alters hematopoiesis to generate circulating myeloid cells with an increased pro-atherogenic potential.

Methods: To promote atherosclerosis, antisense oligonucleotides (ASOs) directed to Ldlr mRNA in combination with a high cholesterol diet (HCD) were administered for 12 weeks to K/BxAg7 mice (atherosclerosis-prone model of spontaneous chronic inflammatory arthritis) as well as to control mice, while scrambled control ASOs were given to chow-fed mice (both arthritic and control). Plasma cholesterol levels were monitored monthly in mice. The degree of atherosclerosis was calculated according to histological and morphometric analysis of atherosclerotic plaques in the aortic root (lipid and collagen content, CD68 and aSMA immunostaining). Additionally, deep immunophenotyping of progenitor cells, mature myeloid and lymphoid cell subsets derived from BM, spleen, synovium and blood was performed to assess for changes in medullary and extramedullary hematopoiesis. Finally, macrophages were generated from the BM (BMDMs) of arthritic and control mice to measure their inflammatory response to oxidized LDL (oxLDL), a crucial driver in atherosclerosis development.

Results: Administration of HCD/ Ldlr ASOs induced hypercholesterolemia in both control and arthritic mice, without significant differences between groups. Nevertheless, atherosclerosis was accelerated in arthritic mice, as lesions exhibited a less stable phenotype demonstrated by increased lipid accumulation and infiltration by macrophages and vascular smooth muscle cells. Immunophenotypic analysis of the BM highlighted an expansion of multipotent progenitor cells and granulocyte-monocyte progenitors (GMPs) in arthritic mice compared to control mice, which was enhanced under hyperlipidemic conditions. Additionally, an increased infiltration of the spleen and joints by GMPs accompanied by elevated numbers of monocytes were observed in dyslipidemic arthritic mice, suggesting a possible contribution of extramedullary hematopoiesis to the progression of atherosclerosis. Last but not least, treatment of BMDMs from arthritic mice with oxLDL induced the expression of Il1b mRNA compared to control mice, indicating a possible inflammatory preparedness of macrophages derived from the chronic inflammatory milieu of arthritic mice.

Conclusions: These findings show that systemic inflammation in RA enhances medullary and extramedullary hematopoiesis to generate monocytes with increased atherogenic potential. Our ongoing experiments focused on the identification of the proatherogenic molecular fingerprint of monocytes and their progenitors will provide novel insights into the pathogenesis of RA-associated atherosclerosis.

REFERENCES: [1] Semb, A.G., et al. Atherosclerotic cardiovascular disease prevention in rheumatoid arthritis. Nat Rev Rheumatol. 2020;16(7):361-379.

[2] Li X, et al. Maladaptive innate immune training of myelopoiesis links inflammatory comorbidities. Cell. 2022;185(10):1709-1727.e18.

[3] Robbins CS, et al. Extramedullary hematopoiesis generates Ly-6C(high) monocytes that infiltrate atherosclerotic lesions. Circulation. 2012;125(2):364-74.

[4] Dragoljevic D, et al. Defective cholesterol metabolism in haematopoietic stem cells promotes monocyte-driven atherosclerosis in rheumatoid arthritis. Eur Heart J. 2018;39(23):2158-2167.

Acknowledgments: NIL.

Disclosure of Interests: None declared.