Prior Exercise Improves Age-Dependent Vascular Endothelial Growth Factor Downregulation and Angiogenesis Responses to Hind-Limb Ischemia in Old Rats

The Role of Capillaries in the Lesser Ailments of Old Age and in Alzheimer's Disease and Vascular Dementia: The Potential of Pro-Therapeutic Angiogenesis

Apart from chronic diseases (arthritis, diabetes, etc.), old age is generally characterized by three lesser ailments: muscle weakness, minor memory lapses, and cold intolerance. This trio of complaints may have a common, underlying cause, namely, the age-associated reduced microcirculation in muscles, brain, skin, and elsewhere in the body. The Angiogenesis Hypothesis proposes that old age is in part a deficiency disease due to the decline in angiogenic (AG) factors, resulting in a reduced capillary density (CD) throughout the body. Over fifty published papers document waning levels of AG factors and/or decreased CD in various organ systems of aged animals and people, including those with Alzheimer's disease. The deficiency of AG factors is analogous to that of certain hormones (e.g., testosterone) whose blood levels also decline with age. In theory, therapeutic angiogenesis employing recombinant AG factors is a tenable treatment for the lesser ailments of old age and may improve the later years of human life. An optimal administration route may be intranasal.

Leonurine Improves Age-Dependent Impaired Angiogenesis: Possible Involvement of Mitochondrial Function and HIF-1α Dependent VEGF Activation

Objective: Advanced age is associated with impaired angiogenesis in part because of mitochondrial dysfunction. We have recently reported that leonurine exerts protective effects in neuron via regulation of mitochondrial function. The aim of this study was to explore whether leonurine is able to attenuate mitochondrial dysfunction and to enhance angiogenesis in old rats with hindlimb ischemia. Methods and Results: At day 14 after surgery, hypoxia-inducible factor (HIF)-1α and vascular endothelial growth factor (VEGF) expression was decreased in the ischemic muscle of aged animals, which was accompanied by enhanced oxidative stress, increased mitochondrial damage, decreased capillary density, and reduced limb perfusion compared with young mice. Importantly, these effects were inhibited by leonurine treatment in old animals. In vitro, we showed that the functional activities (migration and tube formation) of human umbilical vein endothelial cells (HUVECs) were significantly impaired in senescent compared to young. However, leonurine rescued HUVECs functional activities in senescent HUVECs. Mechanistically, we found that leonurine restored the age-dependent reduction in HIF activity and subsequent reduced VEGF expression in senescent HUVECs. Moreover, the mitochondrial oxidative stress was significantly augmented in senescent HUVECs, in association with reduced mitochondrial function. However, leonurine significantly reduced the mitochondrial oxidative stress and restored the mitochondrial membrane potential. Conclusion: Our results demonstrate that leonurine protects against age-dependent impairment of angiogenesis possibly through attenuation of mitochondrial dysfunction and subsequent VEGF up-regulation impairment.

Effects of remote ischemic post‑conditioning on fracture healing in rats

Remote ischemic post‑conditioning (RIPC) is an established method to activate the hypoxia‑inducible factor‑1α (HIF‑1α) pathway, which is involved in the impairment of fracture healing. However, the role of RIPC in fracture healing remains to be fully elucidated. In the present study, rats received fractures and were divided into two groups: Control and RIPC, in which hind limb occlusion was performed. Rats were sacrificed at 7, 14, 28 and 42 days subsequent to tibial fracture. Micro‑computed tomography was performed to measure healing of the bone tissue and biomechanical testing was used to test mechanical strength. In addition, the effects of hind limb occlusion on the expression of two primary angiogenic mediators, HIF‑1α and vascular endothelial growth factor (VEGF), as well as the osteoblast markers runt‑related transcription factor 2 (Runx2), alkaline phosphatase (ALP) and osteocalcin (OCN), were determined at the mRNA and protein levels by reverse transcription‑quantitative polymerase chain reaction, western blot analysis and immunohistochemistry. Systemic administration of hind limb occlusion (3 cycles/day, with each occlusion or release phase lasting 10 min) significantly promoted fracture healing and mechanical strength. The present study demonstrated that in rats treated with hind limb occlusion, the expression of HIF‑1α, VEGF, Runx2, ALP and OCN was significantly increased at the mRNA and protein levels, and that RIPC enhances fracture repair in vivo.

Treatment of hind limb ischemia using angiogenic peptide nanofibers

For a proangiogenic therapy to be successful, it must promote the development of mature vasculature for rapid reperfusion of ischemic tissue. Whole growth factor, stem cell, and gene therapies have yet to achieve the clinical success needed to become FDA-approved revascularization therapies. Herein, we characterize a biodegradable peptide-based scaffold engineered to mimic VEGF and self-assemble into a nanofibrous, thixotropic hydrogel, SLanc. We found that this injectable hydrogel was rapidly infiltrated by host cells and could be degraded while promoting the generation of neovessels. In mice with induced hind limb ischemia, this synthetic peptide scaffold promoted angiogenesis and ischemic tissue recovery, as shown by Doppler-quantified limb perfusion and a treadmill endurance test. Thirteen-month-old mice showed significant recovery within 7 days of treatment. Biodistribution studies in healthy mice showed that the hydrogel is safe when administered intramuscularly, subcutaneously, or intravenously. These preclinical studies help establish the efficacy of this treatment for peripheral artery disease due to diminished microvascular perfusion, a necessary step before clinical translation. This peptide-based approach eliminates the need for cell transplantation or viral gene transfection (therapies currently being assessed in clinical trials) and could be a more effective regenerative medicine approach to microvascular tissue engineering.

Long-Term Exercise Improves Memory Deficits via Restoration of Myelin and Microvessel Damage, and Enhancement of Neurogenesis in the Aged Gerbil Hippocampus After Ischemic Stroke

BACKGROUND

The positive correlation between therapeutic exercise and memory recovery in cases of ischemia has been extensively studied; however, long-term exercise begun after ischemic neuronal death as a chronic neurorestorative strategy has not yet been thoroughly examined.

OBJECTIVE

The purpose of this study is to investigate possible mechanisms by which exercise ameliorates ischemia-induced memory impairment in the aged gerbil hippocampus after transient cerebral ischemia.

METHODS

Treadmill exercise was begun 5 days after ischemia-reperfusion (I-R) and lasted for 1 or 4 weeks. The animals were sacrificed 31 days after the induction of ischemia. Changes in short-term memory, as well as the hippocampal expression of markers of cell proliferation, neuroblast differentiation, neurogenesis, myelin and microvessel repair, and growth factors were examined by immunohistochemistry and/or western blots.

RESULTS

Four weeks of exercise facilitated memory recovery despite neuronal damage in the stratum pyramidale (SP) of the hippocampal CA1 region and in the polymorphic layer (PoL) of the dentate gyrus (DG) after I-R. Long-term exercise enhanced cell proliferation and neuroblast differentiation in a time-dependent manner, and newly generated mature cells were found in the granule cell layer of the DG, but not in the SP of the CA1 region or in the PoL of the DG. In addition, long-term exercise ameliorated ischemia-induced damage of myelin and microvessels, which was correlated with increased BDNF expression in the CA1 region and the DG.

CONCLUSIONS

These results suggest that long-term treadmill exercise after I-R can restore memory function through replacement of multiple damaged structures in the ischemic aged hippocampus.

β Adrenergic Receptor Kinase C-Terminal Peptide Gene-Therapy Improves β2-Adrenergic Receptor-Dependent Neoangiogenesis after Hindlimb Ischemia

After hindlimb ischemia (HI), increased catecholamine levels within the ischemic muscle can cause dysregulation of β2-adrenergic receptor (β2AR) signaling, leading to reduced revascularization. Indeed, in vivo β2AR overexpression via gene therapy enhances angiogenesis in a rat model of HI. G protein-coupled receptor kinase 2 (GRK2) is a key regulator of βAR signaling, and β adrenergic receptor kinase C-terminal peptide (βARKct), a peptide inhibitor of GRK2, has been shown to prevent βAR down-regulation and to protect cardiac myocytes and stem cells from ischemic injury through restoration of β2AR protective signaling (i.e., protein kinase B/endothelial nitric oxide synthase). Herein, we tested the potential therapeutic effects of adenoviral-mediated βARKct gene transfer in an experimental model of HI and its effects on βAR signaling and on endothelial cell (EC) function in vitro. Accordingly, in this study, we surgically induced HI in rats by femoral artery resection (FAR). Fifteen days of ischemia resulted in significant βAR down-regulation that was paralleled by an approximately 2-fold increase in GRK2 levels in the ischemic muscle. Importantly, in vivo gene transfer of the βARKct in the hindlimb of rats at the time of FAR resulted in a marked improvement of hindlimb perfusion, with increased capillary and βAR density in the ischemic muscle, compared with control groups. The effect of βARKct expression was also assessed in vitro in cultured ECs. Interestingly, ECs expressing the βARKct fenoterol, a β2AR-agonist, induced enhanced β2AR proangiogenic signaling and increased EC function. Our results suggest that βARKct gene therapy and subsequent GRK2 inhibition promotes angiogenesis in a model of HI by preventing ischemia-induced β2AR down-regulation.

Muscle weakness during aging: a deficiency state involving declining angiogenesis

This essay begins by proposing that muscle weakness of old age from sarcopenia is due in large part to reduced capillary density in the muscles, as documented in 9 reports of aged persons and animals. Capillary density (CD) is determined by local levels of various angiogenic factors, which also decline in muscles with aging, as reported in 7 studies of old persons and animals. There are also numerous reports of reduced CD in the aged brain and other studies showing reduced CD in the kidney and heart of aged animals. Thus a waning angiogenesis throughout the body may be a natural occurrence in later years and may account significantly for the lesser ailments (physical and cognitive) of elderly people. Old age is regarded here as a deficiency state which may be corrected by therapeutic angiogenesis, much as a hormonal deficiency can be relieved by the appropriate hormone therapy. Such therapy could employ recombinant angiogenic factors which are now commercially available.

Effects of physical activity on endothelial progenitor cells (EPCs)

Physical activity has a therapeutic role in cardiovascular disease (CVD), through its beneficial effects on endothelial function and cardiovascular system. Circulating endothelial progenitor cells (EPCs) are bone marrow (BM) derived cells that represent a novel therapeutic target in CVD patients, because of their ability to home to sites of ischemic injury and repair the damaged vessels. Several studies show that physical activity results in a significant increase in circulating EPCs, and, in particular, there are some evidence of the beneficial exercise-induced effects on EPCs activity in CVD settings, including coronary artery disease (CAD), heart failure (HF), and peripheral artery disease (PAD). The aim of this paper is to review the current evidence about the beneficial effects of physical exercise on endothelial function and EPCs levels and activity in both healthy subjects and patients with CVD.

Molecular aspects of the cardioprotective effect of exercise in the elderly

Aging is a well-recognized risk factor for several different forms of cardiovascular disease. However, mechanisms by which aging exerts its negative effect on outcome have been only partially clarified. Numerous evidence indicate that aging is associated with alterations of several mechanisms whose integrity confers protective action on the heart and vasculature. The present review aims to focus on the beneficial effects of exercise, which plays a pivotal role in primary and secondary prevention of cardiovascular diseases, in counteracting age-related deterioration of protective mechanisms that are crucially involved in the homeostasis of cardiovascular system. In this regard, animal and human studies indicate that exercise training is able: (1) to improve the inotropic reserve of the aging heart through restoration of cardiac β-adrenergic receptor signaling; (2) to rescue the mechanism of cardiac preconditioning and angiogenesis whose integrity has been shown to confer cardioprotection against ischemia and to improve post-myocardial infarction left ventricular remodeling; (3) to counteract age-related reduction of antioxidant systems that is associated to decreased cellular resistance to reactive oxygen species accumulation. Moreover, this review also describes the molecular effects induced by different exercise training protocols (endurance vs. resistance) in the attempt to better explain what kind of exercise strategy could be more efficacious to improve cardiovascular performance in the elderly population.

Vascular endothelial growth factor blockade prevents the beneficial effects of β-blocker therapy on cardiac function, angiogenesis, and remodeling in heart failure

BACKGROUND

Impaired angiogenesis in the post-myocardial infarction heart contributes to the progression to heart failure. The inhibition of vascular endothelial growth factor (VEGF) signaling has been shown to be crucial for the transition from compensatory hypertrophy to cardiac failure. Importantly, β-adrenergic receptor blocker therapy has been also shown to improve myocardial perfusion by enhancing neoangiogenesis in the failing heart.

METHODS AND RESULTS

Eight weeks from surgically induced myocardial infarction, heart failure rats were randomized to receive bisoprolol (B) or vehicle. At the end of a 10-week treatment period, echocardiography revealed reduced cardiac diameters and improved cardiac function in B-treated compared with vehicle-treated rats. Moreover, B treatment was associated with increased cardiac angiogenesis and in vivo coronary perfusion and reduced cardiac fibrosis. Importantly, 2 weeks after B treatment was started, increased cardiac VEGF expression and Akt and endothelial NO synthase activation were observed by comparing B-treated with drug-untreated failing hearts. To test whether the proangiogenic effects of B act via activation of VEGF pathway, rats were intravenously injected with adenoviral vector encoding a decoy VEGF receptor (Ad-Flk) or a control adenovirus (Ad-C), at the start of the treatment with B. After 10 weeks, histological analysis revealed reduced capillary and coronary perfusion in B-treated plus Ad-Flk rats compared with B-treated plus Ad-C rats. Moreover, VEGF inhibition counteracted the positive effects of B on cardiac function and remodeling.

CONCLUSIONS

β-Blockade promotes cardiac angiogenesis in heart failure via activation of VEGF signaling pathway. β-Blocker-induced enhancement of cardiac angiogenesis is essential for the favorable effects of this therapy on cardiac function and remodeling.

Effects of aging on angiogenesis

Aging is a dominant risk factor for most forms of cardiovascular disease. Impaired angiogenesis and endothelial dysfunction likely contribute to the increased prevalence of both cardiovascular diseases and their adverse sequelae in the elderly. Angiogenesis is both an essential adaptive response to physiological stress and an endogenous repair mechanism after ischemic injury. In addition, induction of angiogenesis is a promising therapeutic approach for ischemic diseases. For these reasons, understanding the basis of age-related impairment of angiogenesis and endothelial function has important implications for understanding and managing cardiovascular disease. In this review, we discuss the molecular mechanisms that contribute to impaired angiogenesis in the elderly and potential therapeutic approaches to improving vascular function and angiogenesis in aging patients.

Brain regional angiogenic potential at the neurovascular unit during normal aging

Given strong regional specialization of the brain, cerebral angiogenesis may be regionally modified during normal aging. To test this hypothesis, expression of a broad cadre of angiogenesis-associated genes was assayed at the neurovascular unit (NVU) in discrete brain regions of young versus aged mice by laser capture microdissection coupled to quantitative real-time polymerase chain reaction (PCR). Complementary quantitative capillary density/branching studies were performed as well. Effects of physical exercise were also assayed to determine if age-related trends could be reversed. Additionally, gene response to hypoxia was probed to highlight age-associated weaknesses in adapting to this angiogenic stress. Aging impacted resting expression of angiogenesis-associated genes at the NVU in a region-dependent manner. Physical exercise reversed some of these age-associated gene trends, as well as positively influenced cerebral capillary density/branching in a region-dependent way. Lastly, hypoxia revealed a weaker angiogenic response in aged brain. These results suggest heterogeneous changes in angiogenic capacity of the brain during normal aging, and imply a therapeutic benefit of physical exercise that acts at the level of the NVU.

PGC-1alpha mediates exercise-induced skeletal muscle VEGF expression in mice

The aim of the present study was to test the hypothesis that PGC-1alpha is required for exercise-induced VEGF expression in both young and old mice and that AMPK activation leads to increased VEGF expression through a PGC-1alpha-dependent mechanism. Whole body PGC-1alpha knockout (KO) and littermate wild-type (WT) mice were submitted to either 1) 5 wk of exercise training, 2) lifelong (from 2 to 13 mo of age) exercise training in activity wheel, 3) a single exercise bout, or 4) 4 wk of daily subcutaneous AICAR or saline injections. In skeletal muscle of PGC-1alpha KO mice, VEGF protein expression was approximately 60-80% lower and the capillary-to-fiber ratio approximately 20% lower than in WT. Basal VEGF mRNA expression was similar in WT and PGC-1alpha KO mice, but acute exercise and AICAR treatment increased the VEGF mRNA content in WT mice only. Exercise training of young mice increased skeletal muscle VEGF protein expression approximately 50% in WT mice but with no effect in PGC-1alpha KO mice. Furthermore, a training-induced prevention of an age-associated decline in VEGF protein content was observed in WT but not in PGC-1alpha KO muscles. In addition, repeated AICAR treatments increased skeletal muscle VEGF protein expression approximately 15% in WT but not in PGC-1alpha KO mice. This study shows that PGC-1alpha is essential for exercise-induced upregulation of skeletal muscle VEGF expression and for a training-induced prevention of an age-associated decline in VEGF protein content. Furthermore, the findings suggest an AMPK-mediated regulation of VEGF expression through PGC-1alpha.

Limb ischemia after iliac ligation in aged mice stimulates angiogenesis without arteriogenesis

OBJECTIVE

Older patients are thought to tolerate acute ischemia more poorly than younger patients. Since aging may depress both angiogenesis and arteriogenesis, we determined the effects of age on both angiogenesis and arteriogenesis in a model of severe acute limb ischemia.

METHODS

Young adult (3-months-old) and aged (18-months-old) C57BL/6 mice underwent right common iliac artery and vein ligation and transection. Data were collected on days 0, 7, and 14. Perfusion was measured with a laser Doppler scan and compared to the contralateral limb. Functional deficits were evaluated with the Tarlov scale. Capillary density and endothelial progenitor cell (EPC) number were determined by direct counting lectin-positive/alpha-actin-negative cells and VEGFR2/CXCR4 dually-positive cells, respectively; angiography was performed to directly assess arteriogenesis.

RESULTS

Young adult and aged mice had a similar degree of decreased perfusion after iliac ligation (young, n = 15: 20.4 +/- 1.9%, vs aged, n = 20: 19.6 +/- 1.3%; P = .72, analysis of variance [ANOVA]); however, young mice recovered faster and to a greater degree than aged mice (day 7, 35 +/- 6% vs 17 +/- 4%, P = .046; day 14, 60 +/- 5% vs 27 +/- 7%, P = .0014). Aged mice had worse functional recovery by day 14 compared to young mice (2.3 +/- 0.3 vs 4.3 +/- 0.4; P = .0021). Aged mice had increased capillary density (day 7, 12.9 +/- 4.4 vs 2.8 +/- 0.3 capillaries/hpf; P = .02) and increased number of EPC incorporated into the ischemic muscle (day 7, 8.1 +/- 0.9 vs 2.5 +/- 1.9 cells; P = .007) compared to young mice, but diminished numbers of collateral vessels to the ischemic limb (1 vs 9; P = .01), as seen on angiography.

CONCLUSION

After severe hind limb ischemia, aged animals become ischemic to a similar degree as young animals, but aged animals have significantly impaired arteriogenesis and functional recovery compared to younger animals. These results suggest that strategies to stimulate arteriogenesis may complement those that increase angiogenesis, and may result in improved relief of ischemia.