Rheumatoid arthritis CD14⁺ monocytes display metabolic and inflammatory dysfunction, a phenotype that precedes clinical manifestation of disease

Abstract

IntroductionThis study investigates the metabolic activity of circulating monocytes and their impact on pro‐inflammatory responses in RA and explores whether this phenotype is already primed for inflammation before clinical manifestations of disease.MethodsBlood was collected and CD14+ monocytes isolated from healthy control donors (HC), individuals at‐risk (IAR) and RA patients. Monocyte frequency in blood and synovial tissue was assessed by flow cytometry. Inflammatory responses and metabolic analysis ± specific inhibitors were quantified by RT‐PCR, Western blot, migration assays, Seahorse‐XFe‐technology, mitotracker assays and transmission electron microscopy. Transcriptomic analysis was performed on HC, IAR and RA synovial tissue.ResultsCD14+ monocytes from RA patients are hyper‐inflammatory following stimulation, with significantly higher expression of cytokines/chemokines than those from HC. LPS‐induced RA monocyte migratory capacity is consistent with increased monocyte frequency in RA synovial tissue. RA CD14+ monocytes show enhanced mitochondrial respiration, biogenesis and alterations in mitochondrial morphology. Furthermore, RA monocytes display increased levels of key glycolytic enzymes HIF1α, HK2 and PFKFB3 and demonstrate a reliance on glucose consumption, blockade of which abrogates pro‐inflammatory mediator responses. Blockade of STAT3 activation inhibits this forced glycolytic flux resulting in metabolic reprogramming and resolution of inflammation. Interestingly, this highly activated monocytic phenotype is evident in IAR of developing disease, in addition to an enhanced monocyte gene signature observed in synovial tissue from IAR.ConclusionRA CD14+ monocytes are metabolically re‐programmed for sustained induction of pro‐inflammatory responses, with STAT3 identified as a molecular regulator of metabolic dysfunction. This phenotype precedes clinical disease onset and may represent a potential pathway for therapeutic targeting early in disease.

The Effects of Trained Innate Immunity on T Cell Responses; Clinical Implications and Knowledge Gaps for Future Research

“…McGarry and Hanlon et al reported that CD14 + monocytes in the peripheral blood of RA patients are metabolically reprogrammed towards glycolysis ( 82 ), a key feature of trained immunity ( 48 , 65 ). Furthermore, when compared with healthy controls, monocytes from the blood of RA patients produced more TNF, IL-6 and IL-1β in response to LPS stimulation in vitro ( 82 ). These are key cytokines that are enhanced in cells that have undergone pro-inflammatory innate immune training with BCG or β-glucan ( 5 , 6 ).…”

“…In the setting of established RA disease, the enhanced inflammatory function of monocytes may not be indicative of trained immunity, but it could also reflect chronic inflammation. To determine if these hyperinflammatory monocytes were a precipitating factor for inappropriate inflammation in people with RA, the study examined monocytes in people who were identified as being at increased risk of developing RA ( 82 ). The hyperinflammatory CD14 + cell phenotype was present in these individuals at risk of developing RA, suggesting that this trained immunity phenotype may precede clinical signs of disease and may therefore be implicated in pathology ( 82 ).…”

“…To determine if these hyperinflammatory monocytes were a precipitating factor for inappropriate inflammation in people with RA, the study examined monocytes in people who were identified as being at increased risk of developing RA ( 82 ). The hyperinflammatory CD14 + cell phenotype was present in these individuals at risk of developing RA, suggesting that this trained immunity phenotype may precede clinical signs of disease and may therefore be implicated in pathology ( 82 ). This study provides empirical evidence that monocytes in the circulation of people with established RA and in those at risk of developing RA are “primed” towards a hyper-inflammatory and hyper-metabolic state, akin to that observed in monocytes that have undergone innate immune training.…”

“…Since Th17 cell plasticity is directed by innate cytokines, trained immunity may have a key role in promoting pathological ex-Th17 cells. Interestingly both pathological Th17 lineage cells and monocytes displaying the features of trained immunity in RA patients are dependent on STAT3 signalling ( 82 , 83 ). There is evidence that activated monocytes from the joints of patients with RA specifically promote Th17 cell responses, and this is mediated by elevated production TNF and IL-1β in the RA monocytes ( 84 ).…”

“…There is emerging evidence to suggest that trained immunity may be an underlying feature that promotes the pathogenic phenotype of the hyperinflammatory myeloid cells found in RA patients, and precedes the clinical diagnosis of RA ( 82 ). These innate immune responses may subsequently drive a pathogenic T cell response.…”