The menopausal transition does not influence skeletal muscle capillary growth in response to cycle training in women

The influence of the menopausal transition, with a consequent loss of oestrogen, on capillary growth in response to exercise training remains unknown. In the present study, we evaluated the effect of a period of intense endurance training on skeletal muscle angiogenesis in late pre-menopausal and recently post-menopausal women with an age difference of <4 years. Skeletal muscle biopsies were obtained from the thigh muscle prior to and after 12 weeks of intense aerobic cycle training, and analyzed for capillarization, fiber type distribution and content of vascular endothelial growth factor (VEGF). At baseline, there was no difference in capillary per fiber ratio (C:F; 1.41 ± 0.22 vs 1.40 ± 0.30), capillary density (CD; 305±61 vs 336±52 mm2), muscle fiber area (MFA) or percentage distribution of muscle fiber type I (47.3±10.1 vs 49.3±15.1 %) and type II (52.7±10.1 vs 50.7±15.1%) between the pre- and post-menopausal women. The training period resulted in a similar increase in C:F in pre- and post-menopausal women (by 9.2 vs 12.1 %, respectively) and CD (by 6.9 vs 8.9 %, respectively), whereas MFA and fiber type distribution remained unaltered. Skeletal muscle VEGF protein content was similar between groups at baseline and increased to a similar extent with training (by 21.1 vs 27.2 %, respectively) in the pre- and post-menopausal women. In conclusion, the loss of oestrogen per se at menopause does not influence the capillary growth response to intense aerobic exercise training.

Hormetic modulation of angiogenic factors by exercise-induced mechanical and metabolic stress in human skeletal muscle

Skeletal muscle capillary growth is orchestrated by angiogenic factors sensitive to mechanical and metabolic signals. In this study, we employed an integrative exercise model to synergistically target, yet to different extents and for different durations, the mechanical and metabolic components of muscle activity that promote angiogenesis. Our results suggest that the magnitude of the myocellular perturbations incurred during exercise determines the amplitude of the angiogenic molecular signals, implying hormetic modulation of skeletal muscle angiogenesis by exercise-induced mechanical and metabolic stress.

Beneficial effects of endurance exercise training on skeletal muscle microvasculature in sickle cell disease patients

In a Plenary Paper, Merlet et al report a provocative and elegant study demonstrating that exercise training leads to muscle capillary growth in patients with sickle cell disease, a finding with potential to improve their lives.

Coronary arterial development is regulated by a Dll4-Jag1-EphrinB2 signaling cascade

Coronaries are essential for myocardial growth and heart function. Notch is crucial for mouse embryonic angiogenesis, but its role in coronary development remains uncertain. We show Jag1, Dll4 and activated Notch1 receptor expression in sinus venosus (SV) endocardium. Endocardial Jag1 removal blocks SV capillary sprouting, while Dll4 inactivation stimulates excessive capillary growth, suggesting that ligand antagonism regulates coronary primary plexus formation. Later endothelial ligand removal, or forced expression of Dll4 or the glycosyltransferase Mfng, blocks coronary plexus remodeling, arterial differentiation, and perivascular cell maturation. Endocardial deletion of Efnb2 phenocopies the coronary arterial defects of Notch mutants. Angiogenic rescue experiments in ventricular explants, or in primary human endothelial cells, indicate that EphrinB2 is a critical effector of antagonistic Dll4 and Jag1 functions in arterial morphogenesis. Thus, coronary arterial precursors are specified in the SV prior to primary coronary plexus formation and subsequent arterial differentiation depends on a Dll4-Jag1-EphrinB2 signaling cascade.

Coronary arterial development is regulated by a Dll4-Jag1-EphrinB2 signaling cascade

Coronaries are essential for myocardial growth and heart function. Notch is crucial for mouse embryonic angiogenesis, but its role in coronary development remains uncertain. We show Jag1, Dll4 and activated Notch1 receptor expression in sinus venosus (SV) endocardium. Endocardial Jag1 removal blocks SV capillary sprouting, while Dll4 inactivation stimulates excessive capillary growth, suggesting that ligand antagonism regulates coronary primary plexus formation. Later endothelial ligand removal, or forced expression of Dll4 or the glycosyltransferase MFng, blocks coronary plexus remodeling, arterial differentiation, and perivascular cell maturation. Endocardial deletion of Efnb2 phenocopies the coronary arterial defects of Notch mutants. Angiogenic rescue experiments in ventricular explants, or in primary human endothelial cells, indicate that EphrinB2 is a critical effector of antagonistic Dll4 and Jag1 functions in arterial morphogenesis. Thus, coronary arterial precursors are specified in the SV prior to primary coronary plexus formation and subsequent arterial differentiation depends on a Dll4-Jag1-EphrinB2 signaling cascade.

1. Targeting Slit2-Robo Signaling as a Novel Therapy for Diabetic Nephropathy

Diabetes is a chronic disease that can lead to life-threatening complications such as diabetic nephropathy (DN). An early manifestation of DN is hyperfiltration, a predictor of poor renal outcomes. Hyperfiltration is partly driven by capillary growth (angiogenesis) within the glomeruli, the filtration units of the kidney. A major stimulus for diabetic glomerular angiogenesis is vascular endothelial growth factor (VEGF). VEGF neutralization blocks hyperfiltration in diabetes, but VEGF blockade itself can lead to renal injury. Endothelial cells express Robo1 and Robo4, which serve as receptors for the secreted ligand Slit2. Robo4 activation by Slit2 inhibits endothelial angiogenesis, whereas Slit2 activation of Robo1 promotes angiogenesis.In search of novel therapies for diabetes-induced glomerular hyperfiltration, we hypothesized that diabetes affects the expression of Slit2 and/or its Robo receptors. We further tested whether Slit2 administration attenuates VEGF-driven diabetic capillary growth.Diabetes was induced by injection of streptozocin (STZ) in male rats. Age- and gender-matched non-diabetic rats were followed as controls. 3 weeks later, kidneys were harvested from both groups, and the expression of Slit2, Robo1 and Robo4 analyzed. In parallel, male diabetic rats were randomized to receive Slit2 or saline injections every 3 days. After 3 weeks, kidney filtration and capillary growth were measured in both groups.Diabetes was associated with a reduction in kidney Robo4 expression, whereas Slit2 and Robo1 mRNA levels were unchanged. Slit2 administration attenuated the diabetes-induced rise in kidney filtration and glomerular capillary growth. Our results suggest that targeting Slit2-Robo signalling may have therapeutic importance for early diabetic nephropathy.

Heat therapy promotes the expression of angiogenic regulators in human skeletal muscle

Heat therapy has been shown to promote capillary growth in skeletal muscle and in the heart in several animal models, but the effects of this therapy on angiogenic signaling in humans are unknown. We evaluated the acute effect of lower body heating (LBH) and unilateral thigh heating (TH) on the expression of angiogenic regulators and heat shock proteins (HSPs) in healthy young individuals. Exposure to LBH ( n = 18) increased core temperature (Tc) from 36.9 ± 0.1 to 37.4 ± 0.1°C ( P < 0.01) and average leg skin temperature (Tleg) from 33.1 ± 0.1 to 39.6 ± 0.1°C ( P < 0.01), but did not alter the levels of circulating angiogenic cytokines and bone marrow-derived proangiogenic cells (CD34+CD133+). In skeletal muscle, the change in mRNA expression from baseline of vascular endothelial growth factor (VEGF), angiopoietin 2 (ANGPT2), chemokines CCL2 and CX3CL1, platelet factor-4 (PF4), and several members of the HSP family was higher 30 min after the intervention in the individuals exposed to LBH ( n = 11) compared with the control group ( n = 12). LBH also reduced the expression of transcription factor FOXO1 ( P = 0.03). Exposure to TH ( n = 14) increased Tlegfrom 32.8 ± 0.2 to 40.3 ± 0.1°C ( P < 0.05) but Tcremained unaltered (36.8 ± 0.1°C at baseline and 36.9 ± 0.1°C at 90 min). This intervention upregulated the expression of VEGF, ANGPT1, ANGPT2, CCL2, and HSPs in skeletal muscle but did not affect the levels of CX3CL1, FOXO-1, and PF4. These findings suggest that both LBH and TH increase the expression of factors associated with capillary growth in human skeletal muscle.

Regulation of skeletal muscle capillary growth in exercise and disease

Capillaries, which are the smallest and most abundant type of blood vessel, form the primary site of gas, nutrient, and waste transfer between the vascular and tissue compartments. Skeletal muscle exhibits the capacity to generate new capillaries (angiogenesis) as an adaptation to exercise training, thus ensuring that the heightened metabolic demand of the active muscle is matched by an improved capacity for distribution of gases, nutrients, and waste products. This review summarizes the current understanding of the regulation of skeletal muscle capillary growth. The multi-step process of angiogenesis is coordinated through the integration of a diverse array of signals associated with hypoxic, metabolic, hemodynamic, and mechanical stresses within the active muscle. The contributions of metabolic and mechanical factors to the modulation of key pro- and anti-angiogenic molecules are discussed within the context of responses to a single aerobic exercise bout and short-term and long-term training. Finally, the paradoxical lack of angiogenesis in peripheral artery disease and diabetes and the implications for disease progression and muscle health are discussed. Future studies that emphasize an integrated analysis of the mechanisms that control skeletal muscle capillary growth will enable development of targeted exercise programs that effectively promote angiogenesis in healthy individuals and in patient populations.