Circulating factors induced by caloric restriction in the nonhuman primate Macaca mulatta activate angiogenic processes in endothelial cells

Moderate caloric restriction (CR) without malnutrition increases healthspan in virtually every species studied, including nonhuman primates. In mice, CR exerts significant microvascular protective effects resulting in increased microvascular density in the heart and the brain, which likely contribute to enhanced tolerance to ischemia and improved cardiac performance and cognitive function. Yet, the underlying mechanisms by which CR confer microvascular protection remain elusive. To test the hypothesis that circulating factors triggered by CR regulate endothelial angiogenic capacity, we treated cultured human endothelial cells with sera derived from Macaca mulatta on long-term (over 10 years) CR. Cells treated with sera derived from ad-libitum-fed control monkeys served as controls. We found that factors present in CR sera upregulate vascular endothelial growth factor (VEGF) signaling and stimulate angiogenic processes, including endothelial cell proliferation and formation of capillary-like structures. Treatment with CR sera also tended to increase cellular migration (measured by a wound-healing assay using electric cell-substrate impedance sensing [ECIS] technology) and adhesion to collagen. Collectively, we find that circulating factors induced by CR promote endothelial angiogenic processes, suggesting that increased angiogenesis may be a potential mechanism by which CR improves cardiac function and prevents vascular cognitive impairment.

Disruption of Nrf2 signaling impairs angiogenic capacity of endothelial cells: implications for microvascular aging

The redox-sensitive transcription factor NF-E2-related factor 2 (Nrf2) plays a key role in preserving a healthy endothelial phenotype and maintaining the functional integrity of the vasculature. Previous studies demonstrated that aging is associated with Nrf2 dysfunction in endothelial cells, which alters redox signaling and likely promotes the development of large vessel disease. Much less is known about the consequences of Nrf2 dysfunction at the level of the microcirculation. To test the hypothesis that Nrf2 regulates angiogenic capacity of endothelial cells, we determined whether disruption of Nrf2 signaling (by siRNA knockdown of Nrf2 and overexpression of Keap1, the cytosolic repressor of Nrf2) impairs angiogenic processes in cultured human coronary arterial endothelial cells stimulated with vascular endothelial growth factor and insulin-like growth factor-1. In the absence of functional Nrf2, coronary arterial endothelial cells exhibited impaired proliferation and adhesion to vitronectin and collagen. Disruption of Nrf2 signaling also reduced cellular migration (measured by a wound-healing assay using electric cell-substrate impedance sensing technology) and impaired the ability of coronary arterial endothelial cells to form capillary-like structures. Collectively, we find that Nrf2 is essential for normal endothelial angiogenic processes, suggesting that Nrf2 dysfunction may be a potential mechanism underlying impaired angiogenesis and microvascular rarefaction in aging.

Growth hormone and IGF-1 deficiency exacerbate high-fat diet-induced endothelial impairment in obese Lewis dwarf rats: implications for vascular aging

Previous studies suggest that the age-related decline in circulating growth hormone (GH) and insulin-like growth factor-1 (IGF-1) levels significantly contribute to vascular dysfunction in aging by impairing cellular oxidative stress resistance pathways. Obesity in elderly individuals is increasing at alarming rates, and there is evidence suggesting that elderly individuals are more vulnerable to the deleterious cardiovascular effects of obesity than younger individuals. However, the specific mechanisms through which aging, GH/IGF-1 deficiency, and obesity interact to promote the development of cardiovascular disease remain unclear. To test the hypothesis that low circulating GH/IGF-1 levels exacerbate the pro-oxidant and proinflammatory vascular effects of obesity, GH/IGF-1-deficient Lewis dwarf rats and heterozygous control rats were fed either a standard diet or a high-fat diet (HFD) for 7 months. Feeding an HFD resulted in similar relative weight gains and increases in body fat content in Lewis dwarf rats and control rats. HFD-fed Lewis dwarf rats exhibited a relative increase in blood glucose levels, lower insulin, and impaired glucose tolerance as compared with HFD-fed control rats. Analysis of serum cytokine expression signatures indicated that chronic GH/IGF-1 deficiency exacerbates HFD-induced inflammation. GH/IGF-1 deficiency also exacerbated HFD-induced endothelial dysfunction, oxidative stress, and expression of inflammatory markers (tumor necrosis factor-α, ICAM-1) in aortas of Lewis dwarf rats. Overall, our results are consistent with the available clinical and experimental evidence suggesting that GH/IGF-1 deficiency renders the cardiovascular system more vulnerable to the deleterious effects of obesity.

Age-associated vascular oxidative stress, Nrf2 dysfunction, and NF-{kappa}B activation in the nonhuman primate Macaca mulatta

Aging promotes oxidative stress in vascular endothelial and smooth muscle cells, which contribute to the development of cardiovascular diseases. NF-E2-related factor 2 (Nrf2) is a transcription factor, which is activated by reactive oxygen species in the vasculature of young animals, leading to adaptive upregulation of numerous reactive oxygen species detoxifying and antioxidant genes. The present study was designed to elucidate age-associated changes in the homeostatic role of Nrf2-driven free radical detoxification mechanisms in the vasculature of nonhuman primates. We found that carotid arteries of aged rhesus macaques (Macaca mulatta, age: ≥20 years) exhibit significant oxidative stress (as indicated by the increased 8-iso-PGF2α and 4-HNE content and decreased glutathione and ascorbate levels) as compared with vessels of young macaques (age:~10 years) that is associated with activation of the redox-sensitive proinflammatory transcription factor, nuclear factor-kappaB. However, age-related oxidative stress does not activate Nrf2 and does not induce Nrf2 target genes (NQO1, GCLC, and HMOX1). In cultured vascular smooth muscle cells (VSMCs) derived from young M mulatta, treatment with H(2)O(2) and high glucose significantly increases transcriptional activity of Nrf2 and upregulates the expression of Nrf2 target genes. In contrast, in cultured vascular smooth muscle cells cells derived from aged macaques, H(2)O(2)- and high glucose-induced Nrf2 activity and Nrf2-driven gene expression are blunted. High glucose-induced H(2)O(2) production was significantly increased in aged vascular smooth muscle cells compared with that in vascular smooth muscle cells from young M mulatta. Taken together, aging is associated with Nrf2 dysfunction in M mulatta arteries, which likely exacerbates age-related cellular oxidative stress, promoting nuclear factor-kappaB activation and vascular inflammation in aging.

Vascular oxidative stress in aging: a homeostatic failure due to dysregulation of NRF2-mediated antioxidant response

There is strong evidence showing that aging is associated with vascular oxidative stress, which has been causally linked to the development of cardiovascular diseases. NF-E2-related factor-2 (Nrf2) is a transcription factor, which is activated by reactive oxygen species in the vasculature of young animals leading to the upregulation of various antioxidant genes. The present study was designed to elucidate age-related changes in the homeostatic role of Nrf2-driven free radical detoxification mechanisms in the vasculature. We found that in the aorta of Fischer 344 × Brown Norway rats, aging results in a progressive increase in O(2)(·-) production, and downregulates protein and mRNA expression of Nrf2, which is associated with a decreased nuclear Nrf2 activity and a decrease in the Nrf2 target genes NAD(P)H:quinone oxidoreductase 1, γ-glutamylcysteine synthetase, and heme oxygenase-1. There was an inverse relationship between vascular expression of Nrf2 target genes and age-related increases in the expression of the NF-κB target genes ICAM-1 and IL-6, which was significant by regression analysis. In cultured aorta segments of young (3 mo old) rats treatment with H(2)O(2) and high glucose significantly increases nuclear translocation of Nrf2 and upregulates the expression of Nrf2 target genes. In contrast, in cultured aorta segments of aged (24 mo old) rats, the induction of Nrf2-dependent responses by H(2)O(2) and high glucose are blunted. High glucose-induced vascular oxidative stress was more severe in aortas of aged rats, as shown by the significantly increased H(2)O(2) production in these vessels, compared with responses obtained in aortas from young rats. Moreover, we found that aging progressively increases vascular sensitivity to the proapoptotic effects of H(2)O(2) and high glucose treatments. Taken together, aging is associated with Nrf2 dysfunction in the vasculature, which likely exacerbates age-related cellular oxidative stress and increases sensitivity of aged vessels to oxidative stress-induced cellular damage.

Adaptive induction of NF-E2-related factor-2-driven antioxidant genes in endothelial cells in response to hyperglycemia

Hyperglycemia in diabetes mellitus promotes oxidative stress in endothelial cells, which contributes to development of cardiovascular diseases. Nuclear factor erythroid 2-related factor-2 (Nrf2) is a transcription factor activated by oxidative stress that regulates expression of numerous reactive oxygen species (ROS) detoxifying and antioxidant genes. This study was designed to elucidate the homeostatic role of adaptive induction of Nrf2-driven free radical detoxification mechanisms in endothelial protection under diabetic conditions. Using a Nrf2/antioxidant response element (ARE)-driven luciferase reporter gene assay we found that in a cultured coronary arterial endothelial cell model hyperglycemia (10-30 mmol/l glucose) significantly increases transcriptional activity of Nrf2 and upregulates the expression of the Nrf2 target genes NQO1, GCLC, and HMOX1. These effects of high glucose were significantly attenuated by small interfering RNA (siRNA) downregulation of Nrf2 or overexpression of Keap-1, which inactivates Nrf2. High-glucose-induced upregulation of NQO1, GCLC, and HMOX1 was also prevented by pretreatment with polyethylene glycol (PEG)-catalase or N-acetylcysteine, whereas administration of H(2)O(2) mimicked the effect of high glucose. To test the effects of metabolic stress in vivo, Nrf2(+/+) and Nrf2(-/-) mice were fed a high-fat diet (HFD). HFD elicited significant increases in mRNA expression of Gclc and Hmox1 in aortas of Nrf2(+/+) mice, but not Nrf2(-/-) mice, compared with respective standard diet-fed control mice. Additionally, HFD-induced increases in vascular ROS levels were significantly greater in Nrf2(-/-) than Nrf2(+/+) mice. HFD-induced endothelial dysfunction was more severe in Nrf2(-/-) mice, as shown by the significantly diminished acetylcholine-induced relaxation of aorta of these animals compared with HFD-fed Nrf2(+/+) mice. Our results suggest that adaptive activation of the Nrf2/ARE pathway confers endothelial protection under diabetic conditions.

Vasoprotective effects of life span-extending peripubertal GH replacement in Lewis dwarf rats

In humans, growth hormone deficiency (GHD) and low circulating levels of insulin-like growth factor 1 (IGF-1) significantly increase the risk for cerebrovascular disease. Genetic growth hormone (GH)/IGF-1 deficiency in Lewis dwarf rats significantly increases the incidence of late-life strokes, similar to the effects of GHD in elderly humans. Peripubertal treatment of Lewis dwarf rats with GH delays the occurrence of late-life stroke, which results in a significant extension of life span. The present study was designed to characterize the vascular effects of life span-extending peripubertal GH replacement in Lewis dwarf rats. Here, we report, based on measurements of dihydroethidium fluorescence, tissue isoprostane, GSH, and ascorbate content, that peripubertal GH/IGF-1 deficiency in Lewis dwarf rats increases vascular oxidative stress, which is prevented by GH replacement. Peripubertal GHD did not alter superoxide dismutase or catalase activities in the aorta nor the expression of Cu-Zn-SOD, Mn-SOD, and catalase in the cerebral arteries of dwarf rats. In contrast, cerebrovascular expression of glutathione peroxidase 1 was significantly decreased in dwarf vessels, and this effect was reversed by GH treatment. Peripubertal GHD significantly decreases expression of the Nrf2 target genes NQO1 and GCLC in the cerebral arteries, whereas it does not affect expression and activity of endothelial nitric oxide synthase and vascular expression of IGF-1, IGF-binding proteins, and inflammatory markers (tumor necrosis factor alpha, interluekin-6, interluekin-1β, inducible nitric oxide synthase, intercellular adhesion molecule 1, and monocyte chemotactic protein-1). In conclusion, peripubertal GH/IGF-1 deficiency confers pro-oxidative cellular effects, which likely promote an adverse functional and structural phenotype in the vasculature, and results in accelerated vascular impairments later in life.

Human tumor antigens Tn and sialyl Tn arise from mutations in Cosmc

Neoplastic lesions typically express specific carbohydrate antigens on glycolipids, mucins, and other glycoproteins. Such antigens are often under epigenetic control and are subject to reversion and loss upon therapeutic selective pressure. We report here that two of the most common tumor-associated carbohydrate antigens, Tn and sialyl Tn (STn), result from somatic mutations in the gene Cosmc that encodes a molecular chaperone required for formation of the active T-synthase. Diverse neoplastic lesions, including colon cancer and melanoma-derived cells lines, expressed both Tn and STn antigen due to loss-of-function mutations in Cosmc. In addition, two human cervical cancer specimens that showed expression of the Tn/STn antigens were also found to have mutations in Cosmc and loss of heterozygosity for the cross-linked Cosmc locus. This is the first example of somatic mutations in multiple types of cancers that cause global alterations in cell surface carbohydrate antigen expression.