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Dysfunction of the endothelium is proposed as the primary initiator of atherosclerotic peripheral artery disease, which occurs mainly in medium- to large-sized conduit arteries of the lower extremities (e.g., iliac, femoral, popliteal arteries). In this review article, we propose the novel concept that conduit artery endothelial cell phenotype is determined, in part, by microvascular tone in skeletal muscle resistance arteries through both changes in arterial blood pressure as well as upstream conduit artery shear stress patterns. First, we summarize the literature supporting the involvement of sympathetic nerve activity (SNA) and nitric oxide (NO) in the modulation of microvascular tone and arterial blood pressure. We then focus on the role of elevated blood pressure and shear stress profiles in modulating conduit artery endothelial cell phenotype. Last, we discuss findings from classic and emerging studies indicating that increased vascular resistance, as it occurs in the context of increased SNA and/or reduced NO bioavailability, is associated with greater oscillatory shear stress (e.g., increased retrograde shear) in upstream conduit arteries. The ideas put forth in this review set the stage for a new paradigm concerning the mechanistic link between increased microvascular tone and development of conduit artery endothelial dysfunction and thus increased risk for peripheral artery disease. Indeed, a vast amount of evidence supports the notion that excessive blood pressure and oscillatory shear stress are potent pro-atherogenic signals to the endothelium.

New Findings: What is the central question of this study? Does endurance exercise training cause anti-atherogenic effects on the endothelium in a swine model of familial hypercholesterolaemia (FH), and how are these effects distributed across veins, arteries and multiple vascular territories within each system? What is the main finding and its importance? Coronary artery endothelium-dependent vasomotor function was depressed in sedentary FH pigs compared with sedentary control animals, and exercise training did not change vasomotor function within FH. In systemic conduit arteries and veins, few effects of FH on endothelial cell protein expression were noted, including both pro- and anti-atherogenic changes. These findings suggest that exercise training does not produce a consistently improved endothelial cell phenotype in either coronary or systemic conduit vessels in this swine model of FH. Exercise training has emerged as an intervention for the primary and secondary prevention of coronary artery disease, but the mechanisms through which training reduces relative risk are not completely understood. The goal of this study was to investigate the impact of endurance exercise training on vasomotor function and vascular cell phenotype in coronary arteries and systemic conduit arteries and veins against a background of advanced atherosclerosis. We tested the hypothesis that exercise training restores endothelial vasomotor function and produces an anti-atherogenic endothelial and smooth muscle cell phenotype in familial hypercholesterolaemic (FH) swine. The study included 30 FH (15 exercised and 15 sedentary) and 13 non-FH control male castrated swine. The exercise-training intervention consisted of treadmill running 5 days per week for 16-20 weeks. Tissues sampled at sacrifice included vascular rings from the coronary circulation for vasomotor function experiments (dose-dependent bradykinin-induced vasorelaxation) and endothelial cells (ECs) from isolated segments of the thoracic aorta, the carotid, brachial, femoral and renal arteries, as well as each corresponding regionally associated vein, and from the abdominal vena cava, the right coronary and internal mammary arteries. Smooth muscle cells were sampled from the right coronary artery only. Vascular cell phenotype was assessed by immunoblotting for a host of both pro- and anti-atherogenic markers [e.g. endothelial nitric oxide synthase, p67phox, superoxide dismutase 1 (SOD1)]. Coronary artery endothelium-dependent vasomotor function was depressed in sedentary FH pigs compared with sedentary control pigs, and exercise training did not change vasomotor function within FH. In contrast, only scattered effects of FH on EC phenotype were noted across the vasculature, which included both pro- and anti-atherogenic changes in EC protein expression (e.g. increased endothelial nitric oxide synthase in carotid artery ECs, decreased p67phox in brachial artery ECs, but decreased expression of the antioxidant protein SOD1 in thoracic vena cava; all P < 0.05). In thoracic vena cava ECs, this deficit was corrected by exercise training, while no other effects of exercise were observed in conduit vessel EC phenotype. Thus, while exercise training abrogated the adverse effect of hypercholesterolaemia on thoracic vena cava SOD1 expression, it appears that exercise training does not produce a consistently improved EC phenotype in either coronary or systemic conduit vessels in this FH swine model.

Physical inactivity promotes the development of cardiovascular diseases. However, few data exist examining the vascular consequences of short-term reductions in daily physical activity. Thus we tested the hypothesis that popliteal and brachial artery flow-mediated dilation (FMD) would be reduced and concentrations of endothelial microparticles (EMPs) would be elevated following reduced daily physical activity. To examine this, popliteal and brachial artery FMD and plasma levels of EMPs suggestive of apoptotic and activated endothelial cells (CD31(+)/CD42b(-) and CD62E(+) EMPs, respectively) were measured at baseline and during days 1, 3, and 5 of reduced daily physical activity in 11 recreationally active men (25 ± 2 yr). Subjects were instructed to reduce daily physical activity by taking <5,000 steps/day and refraining from planned exercise. Popliteal artery FMD decreased with reduced activity (baseline: 4.7 ± 0.98%, reduced activity day 5: 1.72 ± 0.68%, P < 0.05), whereas brachial artery FMD was unchanged. In contrast, baseline (pre-FMD) popliteal artery diameter did not change, whereas brachial artery diameter decreased (baseline: 4.35 ± 0.12, reduced activity day 5: 4.12 ± 0.11 P < 0.05) following 5 days of reduced daily physical activity. CD31(+)/CD42b(-) EMPs were significantly elevated with reduced activity (baseline: 17.6 ± 9.4, reduced activity day 5: 104.1 ± 43.1 per μl plasma, P < 0.05), whereas CD62E(+) EMPs were unaltered. Collectively, our results provide evidence for the early and robust deleterious impact of reduced daily activity on vascular function and highlight the vulnerability of the vasculature to a sedentary lifestyle.

The discovery of circulating angiogenic cells (CAC) with cardiovascular regenerative potential has transformed our understanding of the health and maintenance of cardiovascular tissues. We will describe the influence of acute exercise and exercise training on CAC characteristics and evidence for mechanisms that may be important in the optimization of CAC potential.

Acute exercise and exercise training may influence putative endothelial progenitor cell (EPC) number and colony forming units (CFU-ECs), although the mechanisms remain unclear. This study examined the effects of in vitro thrombin supplementation and acute exercise on CFU-EC gene expression, associated with cellular proliferation and differentiation. The effect of habitual physical activity was evaluated through analysis of EPCs from chronically high- and low-active men. Participants were healthy high- and low-active men (n=23), aged 55-80 yr. Circulating CD34+/VEGFR2+ number, CFU-ECs, plasma prothrombin fragment (F1+2), and thrombin-antithrombin III were measured at rest and after 30 min of exercise. Gene expression of cyclin A2, cyclin D1, p27, VE-cadherin, and VEGFR2 was assessed in postexercise CFU-ECs and resting CFU-ECs treated with 0, 1, 5, or 10 U/ml of thrombin. Outcomes were compared between high- and low-active participants. F1+2 and thrombin-antithrombin III, but not CD34+/VEGFR2+ number and CFU-ECs, increased with exercise. Exercise-induced changes in F1+2 correlated with changes in CD34+/VEGFR2+ number in both groups. Thrombin treatments and acute exercise increased cyclin A2 and cyclin D1 expression and decreased p27 expression. One unit per milliliter thrombin increased VEGFR2 and VE-cadherin expression, whereas 5 U/ml, 10 U/ml, and acute exercise did not elicit any changes. An exercise training effect was observed with greater decreases in p27 expression with 5 and 10 U/ml thrombin and greater increases in VEGFR2 and VE-cadherin expression with 1 U/ml thrombin in high-active men. Exercise-induced changes in putative EPC gene expression are associated with thrombin production and may be modulated by long-term exercise training.

We sought to delineate the effects of acute and chronic exercise on the regulation of intracellular nitric oxide (NO(i)) production in putative endothelial progenitor cells (EPCs). Putative EPC colony-forming units (CFU-EC) were cultured from blood drawn before and after 30 min of treadmill exercise at 75% of maximal oxygen uptake in active (n = 8) and inactive (n = 8) men. CFU-EC were similar between groups at baseline, but increased after exercise in active men only (P = 0.04). CFU-EC expressed lower NADPH oxidase subunit gp91(phox) mRNA and elevated endothelial nitric oxide synthase mRNA in active relative to inactive men at baseline (P < 0.05). Acute exercise reduced gp91(phox) mRNA in CFU-EC of both groups (P < 0.05), whereas p47(phox) mRNA levels were reduced in the inactive group only (P = 0.02). There were no differences between groups or with acute exercise in xanthine oxidase, superoxide dismutase isoforms, or gluthathione peroxidase-1 mRNA levels. NO(i) was significantly greater in CFU-EC of active men at baseline (P = 0.004). NO(i) increased in CFU-EC of inactive men with acute exercise, and in vitro experiments with apocynin indicated the increased NO(i) production was caused by suppression of NADPH oxidase. However, the increases in NO(i) with the different treatments in the inactive group did not reach the baseline levels in the active group (P < 0.05). We conclude that acute exercise increases NO(i) in cells generated by the CFU-EC assay through an NADPH oxidase-inhibition mechanism in sedentary men. However, differences due to chronic exercise must involve additional factors. Our findings support exercise as a means to improve putative EPC function and suggest a novel mechanism that may explain this effect.

Subpopulations of peripheral blood mononuclear cells (PMBCs), known as circulating angiogenic cells (CACs), have been implicated in endothelial repair, angiogenesis and vascular homeostasis. Conversely, microparticles released from endothelial cells, platelets and leucocytes in response to injury or apoptosis are elevated in chronic diseases. We investigated the effect of acute exercise on CAC subpopulations, specifically CD34+/VEGFR2+, CD3+/CD31+, CD14+/CD31+ and CD62E+ PBMCs and CD62E+, CD31+/CD42b- and CD34+ MPs in men and women. Additionally, we examined angiogenesis-related gene expression in CD34+, CD31+ and CD62E+ PBMCs at baseline and after exercise. Finally, we examined whether acute exercisemodulates CD62E+ PBMC paracrine actions on cultured endothelial cells. Blood samples for CAC and MP analyses were obtained before and after cycling exercise at 70% peak oxygen uptake that elicited an energy expenditure of 600 kcal. Exercise produced a decrease in CD14+/CD31+ PBMCs, whereas CD62E expression on PBMCs increased with exercise. CD34+/VEGFR2+ and CD3+/CD31+ PBMC levels were not altered with exercise. Gene expression analysis revealed amore proangiogenic phenotype in CD62E+ cells at baseline compared with CD31+ and CD34+ cells. Conditioned media from CD62E+ PBMCs obtained after exercise exerted a proangiogenic influence on human umbilical vein endothelial cells, with increases in genes encoding receptors for growth factors (KDR, FGFR1 and EGFR) and inflammatory mediators (TLR4 and TNFR1). Finally, exercise increased CD62E+ endothelial MPs in men and increased CD34+ MPs in women. Our work highlights the potential role of CD62E+ cells as a novel, exercise-responsive proangiogenic cell population and demonstrates sex-specific exercise-induced changes in circulatingMPs. [ABSTRACT FROM AUTHOR]

We aimed to determine if chronic endurance-exercise habits affected redox status and paracrine function of CD34+ and CD34-/CD31+ circulating angiogenic cells (CACs). Subjects were healthy, nonsmoking men and women aged 18-35 yr and categorized by chronic physical activity habits. Blood was drawn from each subject for isolation and culture of CD34+ and CD34-/CD31+ CACs. No differences in redox status were found in any group across either cell type. Conditioned media (CM) was generated from the cultured CACs and used in an in vitro human umbilical vein endothelial cell-based tube assay. CM from CD34+ cells from inactive individuals resulted in tube structures that were 29% shorter in length (P < 0.05) and 45% less complex (P < 0.05) than the endurance-trained group. CD34-/CD31+ CM from inactive subjects resulted in tube structures that were 26% shorter in length (P < 0.05) and 42% less complex (P < 0.05) than endurance-trained individuals. Proteomics analyses identified S100A8 and S100A9 in the CM. S100A9 levels were 103% higher (P < 0.05) and S100A8 was 97% higher in the CD34-/CD31+ CM of inactive subjects compared with their endurance-trained counterparts with no significant differences in either protein in the CM of CD34+ CACs as a function of training status. Recombinant S100A8/A9 treatment at concentrations detected in inactive subjects' CD34-/CD31+ CAC CM also reduced tube formation (P < 0.05). These findings are the first, to our knowledge, to demonstrate a differential paracrine role in CD34+ and CD34-/CD31+ CACs on tube formation as a function of chronic physical activity habits and identifies a differential secretion of S100A9 by CD34-/CD31+ CACs due to habitual exercise. [ABSTRACT FROM AUTHOR]

Background: An acute bout of exercise can improve endothelial function and insulin sensitivity when measured on the day following exercise. Our aim was to compare acute high-intensity continuous exercise (HICE) to high-intensity interval exercise (HIIE) on circulating endothelial microparticles (EMPs) and insulin sensitivity in overweight/obese men and women. Methods: Inactive males (BMI = 30 ± 3, 25 ± 6 yr, n = 6) and females (BMI = 28 ± 2, 21 ± 3 yr, n = 7) participated in three experimental trials in a randomized counterbalanced crossover design: 1) No exercise control (Control); 2) HICE (20 min cycling @ just above ventilatory threshold); 3) HIIE (10 X 1-min @ ∼90% peak aerobic power). Exercise conditions were matched for external work and diet was controlled post-exercise. Fasting blood samples were obtained ∼18 hr after each condition. CD62E+ and CD31+/CD42b- EMPs were assessed by flow cytometry and insulin resistance (IR) was estimated by homeostasis model assessment (HOMA-IR). Results: There was a significant sex X exercise interaction for CD62E+ EMPs, CD31+/CD42b- EMPs, and HOMA-IR (all P<0.05). In males, both HICE and HIIE reduced EMPs compared to Control (P≤0.05). In females, HICE increased CD62E+ EMPs (P<0.05 vs. Control) whereas CD31+/CD42b- EMPs were unaltered by either exercise type. There was a significant increase in HOMA-IR in males but a decrease in females following HIIE compared to Control (P<0.05). Conclusions: Overweight/obese males and females appear to respond differently to acute bouts of high-intensity exercise. A single session of HICE and HIIE reduced circulating EMPs measured on the morning following exercise in males but in females CD62E+ EMPs were increased following HICE. Next day HOMA-IR paradoxically increased in males but was reduced in females following HIIE. Future research is needed to investigate mechanisms responsible for potential differential responses between males and females. [ABSTRACT FROM AUTHOR]

We employed next-generation RNA sequencing (RNA-Seq) technology to determine the extent to which exercise training alters global gene expression in skeletal muscle feed arteries and aortic endothelial cells o obese Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Transcriptional profiles of the soleus and gastrocnemius muscle feed arterie (SFA and GFA, respectively) and aortic endothelial cell-enriched samples from rats that underwent an endurance exercise training program (EndEx; n = 12) or a interval sprint training program (IST; n = 12) or remained sedentary (Sed; n = 12) were examined. In response to EndEx, there were 39 upregulated (e.g., MANF) and 20 downregulated (e.g., ALOX15) genes in SFA and 1 upregulated (i.e., Wisp2) and 1 downregulated (i.e., Crem) gene in GFA [false discovery rate (FDR) < 10%]. In response to IST, there were 305 upregulated (e.g., MANF, HSPA12B) and 324 downregulated genes in SFA and 101 upregulated and 66 downregulated genes in GFA, with an overlap of 32 genes between arteries. Furthermore, in aortic endothelial cells, there were 183 upregulated (e.g., eNOS, SOD-3) and 14 downregulated (e.g., ATF3, Clec1b, npy, leptin) genes with EndEx and 71 upregulated and 69 downregulated genes with IST, with an overlap of 35 between exercise programs. Expression of only two genes (Tubb2b and Slc9a3r2) was altered (i.e., increased) by exercise in all three arteries. The finding that both EndEx and IST produced greater transcriptional changes in the SFA compared with the GFA is intriguing when considering the fact that treadmill bouts of exercise are associated with greater relative increases in blood flow to the gastrocnemius muscle compared with the soleus muscle. [ABSTRACT FROM AUTHOR]