Circulating Endothelial and Progenitor Cells in Healthy Children and Children with Juvenile Idiopathic Arthritis: Role of Fitness, Physical Activity, and Acute Exercise

Abstract

Circulating endothelial cells (CECs) and endothelial progenitor cells (EPCs) are sensitive markers of cardiovascular damage and repair, respectively. The aim of this thesis was to advance the state of knowledge regarding CECs and EPCs, and the factors affecting their concentrations, in children and adolescents. The first and second studies demonstrated that CECs and EPCs were similar when participants were split by sex, chronological age (8-10 vs. 14-16 years), and biological age (≤ -1 vs. ≥ +1 year from peak height velocity). Moreover, CECs, but not EPCs, were positively associated with aerobic fitness and negatively related to daily moderate-to-vigorous physical activity. Neither CECs nor EPCs were related to level of adiposity. Although there was a large degree of inter-individual variability in both cell types, most of our data were clustered towards one end of the reported range. These observations highlighted the need to examine these cells in children with chronic conditions associated with an increased risk of poor cardiovascular health. Therefore, CECs and EPCs were examined at rest and in response to acute exercise in juvenile idiopathic arthritis (JIA) and healthy controls. Resting levels of CECs and EPCs were similar in both groups, which may be attributable to the low disease activity in the participants with JIA. High intensity, intermittent exercise (HIIE) and moderate intensity, continuous exercise (MICE) had no effect on CECs in both groups. Conversely, MICE led to a robust increase in EPCs in healthy controls; no such change was observed in youth with JIA. This thesis represents the first comprehensive assessment of CECs and EPCs in the context of fitness, physical activity, and acute exercise in children and adolescents. Future research should examine the function and fate of these cells in youth, as well as the potential mechanisms underlying the blunted EPC response to exercise in JIA.