Effects of detraining on the temporal expression of positive and negative angioregulatory proteins in skeletal muscle of mice

Abstract

Key pointsr Skeletal muscle capillary regression is associated with elevated thrombospondin-1 and vascular endothelial growth factor protein expression with detraining.r Vascular endothelial growth factor and nucleolin responses to acute exercise are blunted in the triceps surae muscles following exercise training. In the plantaris and soleus muscles, this blunted response persists up to 28 days after cessation of training.r Effects of detraining on skeletal muscle microvascular density appears to be similar among skeletal muscle of varying oxidative potential and is poorly associated with expression of matrix metalloproteinases-2 and -9 and endostatin.Abstract Temporal expression of positive and negative angiogenic factors in response to detraining is poorly understood. We report the protein expression of anti-angiogenic peptides (thrombospondin-1, TSP-1; and endostatin) as well as pro-angiogenic factors (vascular endothelial growth factor, VEGF; matrix metalloproteinases-2 and -9), and nucleolin (a nuclear protein involved with synthesis and maturation of ribosomes) in response to detraining in triceps surae muscles of C57BL/6 mice. Male mice were allowed to exercise voluntarily for 21 days, and then basal and acute response to exercise were evaluated at 1, 7, 14 and 28 days detraining (D1, D7, D14, D28, respectively, n = 12/group). As seen in the D1 mice, training resulted in the increased muscle capillary-to-fibre ratio (C/F), increased maximal running time and elevated basal expression of VEGF and matrix metalloproteinase-9 (P < 0.05). After 7 days of detraining (D7), C/F levels were similar to control levels, but both basal VEGF and TSP-1 were elevated (P < 0.05). At D14 and D28, TSP-1 protein was not different compared to baseline levels; however, VEGF was elevated in gastrocnemius (GA), but not the soleus (SOL) or plantaris (PLT) muscles, of D14 mice. Endostatin tended to decrease in D14 and D28 compared to controls. Timing of nucleolin protein expression differed between muscle groups, with increases at D1, D7 and D14 in the PLT, SOL and GA muscles, respectively. The response of VEGF and nucleolin to acute exercise was blunted with training, and remained blunted in the PLT and SOL even after 28 days of detraining, at a time point long after muscle capillarization was observed to be similar to pre-training levels. These data suggest that TSP-1 may be a mediator of capillary regression with detraining, even in the face of elevated VEGF, suggesting that pro-angiogenic regulators may not be able to prevent the regression of skeletal muscle capillaries under physiological conditions. The responses of matrix metalloproteinases, endostatin and nucleolin poorly correlated with detraining-induced capillary regression.

Physiological Capillary Regression is not Dependent on Reducing VEGF Expression

“…detraining), and that at this timeframe, muscle capillarity had already reverted back to pretraining levels (despite the presistent elevation in muscle VEGF) [74]. This was a robust response seen in several muscles of the distal hindlimb (i.e., soleus, gastrocnemius, plantaris) ( Table 1), each representing varying degrees of oxidative and glycolytic potential [74]. Consistent with this observation, two prior studies involving exercise training in rats, have also found detraining-induced capillary regression whilst basal muscle VEGF expression is elevated [46,65] (Table 1).…”

“…These studies provide the seemingly provocative observation that physiologically mediated capillary regression is not dependent on the withdrawal of VEGF. Two of aforementioned studies, Huttemann, Lee and Malek [46] and Olenich et al [74], report the additional finding of elevated skeletal muscle expression of TSP-1, a potent negative angiogenic regulator. The temporal correlation of TSP-1 with detraining-induced capillary regression suggests that TSP-1, or perhaps more generally negative angiogenic regulators, may be the key determinant in initiating and regulating capillary regression.…”

Shear stress‐induced angiogenesis in mouse muscle is independent of the vasodilator mechanism and quickly reversible

“…In addition to the complexities of VEGF involvement (Wagner 2011), the pro-and antiangiogenic responses to short-term exercise and withdrawal have only recently been reported (Hellsten & Hoier 2014, Olenich et al 2014), but parallel studies on blood flow have not been conducted.…”

“…1979), and more recently in exercise‐trained mice where a complex pattern of pro‐ and antiangiogenic factor changes was observed (Olenich et al . 2014). The speed of vascular regression is important as it may influence the progression of impaired function associated with, for example, bed rest and the use of angiotherapies.…”

“…During development and adaptive remodelling in adult organs, newly grown blood vessels are often pruned to optimize functional capacity of the microcirculation, a process known as angioadaptation . Vascular remodelling after the withdrawal of a specific angiogenic stimulus has not been widely studied, although a decrease in capillary supply may follow the reduced muscle activity, for example a 6.3% reduction in capillary density in longdistance runners only 2 weeks after stopping training (Houston et al 1979), and more recently in exercisetrained mice where a complex pattern of pro-and antiangiogenic factor changes was observed (Olenich et al 2014). The speed of vascular regression is important as it may influence the progression of impaired function associated with, for example, bed rest and the use of angiotherapies.…”