Osteocalcin expression confers divergent roles of endothelial progenitor cells in cumulative inflammation-induced coronary calcification development

Abstract

Background: Osteogenic circulating endothelial progenitor cells (EPC) that carry the osteoblastic marker osteocalcin (OCN) may implicate in vascular calcification. However, its role in relation to EPC phenotypic characterization in coronary calcification promulgated by inflammatory stress remained unknown. Purpose: To investigate the effect of cumulative inflammation load on incident coronary calcification and mechanistic relations with EPC OCN phenotypic expression. Methods: We conducted a retrospective clinical-pathophysiological cohort analysis of patients with rheumatoid arthritis (n=145). Data on serum C-reactive protein (CRP) was retrieved from each quarterly measurements in the past 60 months immediately preceding the date of CT coronary angiography and EPC measurements. Raised CRP was defined as >0.35mg/dL. A dichotomous score of 1 was assigned to each biomarker encounter with any raised CRP >0.35mg/dL, whereas each CRP ≤0.35mg/dL was conferred a score of 0. A time-adjusted CRP aggregate score as estimate of cumulative inflammation load over the preceding 60 months was composed conglomerating all biomarkers encounters. Flow cytometry was performed to measure the OCN-positive (OCN+) CD34+KDR+ and OCN+CD34+ circulating EPC. Conventional early circulating EPC CD34+CD133+KDR+ was determined. Presence of CT-detected coronary calcification was defined as any Agatston score >0. Results: 50% patients (n=72/145) had CT-detected coronary calcification. CRP burden score was associated with presence of coronary calcification (P=0.004), which remained independent after multivariable adjustment for age, gender, history of hypertension, diabetes mellitus, hyperlipidemia, fasting levels of LDL-/HDL-cholesterol, triglycerides and glucose, creatinine, systolic/diastolic blood pressure, smoking status, use of statins and disease-modifying anti-rheumatic agents, and duration of rheumatoid arthritis (highest versus lowest quartile OR=4.8, 95% CI 1.2–19.2, P=0.026, Figure 1A). Furthermore, CRP score was significantly associated with increased OCN+CD34+KDR+ (Pearson R=0.27, P=0.002) and OCN+CD34+ EPC (R=0.22, P=0.010), but not CD34+CD133+KDR+ EPC (P=0.2). Strikingly, ROC curve analyses revealed divergent effects of osteogenic EPC (Figure 1B, OCN+CD34+ EPC: AUC=0.60, P=0.034; OCN+CD34+KDR+ EPC: AUC=0.59, P=0.053) versus conventional early CD34+CD133+KDR+ EPC (AUC=0.40, P=0.034) on coronary calcification. Conclusions: OCN expression confers a detrimental pathophysiological role to circulating EPC in cumulative inflammation-induced coronary calcification, exemplified in rheumatoid arthritis.