Katušić, Zvonimir S.

The present study is aimed at investigating the contribution of endothelial nitric oxide synthase (eNOS) to erythropoietin (EPO)‐induced mobilization of stem (c‐kit + ,sca‐1 + ,lin‐1 − ; KSL) cells and hematopoietic progenitor (CD34 + ) cells. Wild type (WT) and eNOS −/− mice were injected biweekly with recombinant erythropoietin (1000 U/kg, s.c.) for 14 days. The percentage of KSL cells in spleen, bone marrow and peripheral blood were quantitated by flow cytometry (Becton Dickinson) and analyzed by Cell Quest software. The effect of EPO on number of CD34 + cells in peripheral blood was quantitated by ProCount Progenitor Cell Enumeration Kit (BD Biosciences). Treatment of eNOS −/− mice with EPO increased the percentage of KSL cells by two folds only in bone marrow and spleen, while the percentage of KSL cells in peripheral blood remained unchanged. Treatment with EPO significantly increased the number of CD34 + cells in blood of WT mice (2.75 ± 0.30 cells in WT, 38.39 ± 10.35 in WT+EPO, n=5, P<0.01). However, the number of CD34 + cells remained unchanged in blood of eNOS −/− mice (2.51 ± 1.31 in eNOS −/− , 4.65 ± 1.40 in eNOS −/− + EPO, n=5, P=ns). Results of the present study suggest that eNOS plays an important role in the mobilization of hematopoietic stem/progenitor cells by erythropoietin.

Reduced cerebral blood flow and reactivity may explain age‐related changes in cognitive function. We examined cerebrovascular reactivity, and the potential role of prostaglandins, in young and old healthy humans. Middle cerebral artery velocity (MCAv) responses to stepped hypercapnia were measured in young (26±2y; 6M/5F) and old (66±2y, 3M/4F) adults before (PRE) and 90 min after (POST) oral indomethacin (1.2mg/kg). To account for any changes in blood pressure, cerebrovascular conductance index (CVCi) was calculated as the MCAv divided by mean arterial pressure. Cerebrovascular reactivity slopes were calculated using linear regression between either MCA velocity or CVCi and end‐tidal CO 2 . There were no differences between young and old adults in height, weight, BMI, or brachial blood pressures. Young adults demonstrated greater MCAv (53.7±6.7 vs. 32.0±3.3), MCAv reactivity (1.62±0.21 vs. 0.94±0.10), and CVCi (0.66±0.08 vs. 0.39±0.04) compared with old adults at PRE (P<0.05 for all). In both young and old adults, MCAv, MCAv reactivity, CVCi, and CVCi reactivity decreased between PRE and POST measurements. Furthermore, any age‐related differences in these cerebrovascular variables were abolished by indomethacin. These results suggest that cerebral blood flow and cerebrovascular reactivity is attenuated in aging adults and that this reduction may be mediated by prostaglandins. NIH: AG16574‐11PP2

Aging and other cardiovascular risk factors are associated with increased incidence of Alzheimer's disease (AD). A common feature of cardiovascular risk factors is decreased endothelial nitric oxide (NO). We studied the effect of a loss of endothelial NO on amyloid precursor protein (APP) related phenotype in aged (14–15 month) endothelial nitric oxide synthase deficient (eNOS −/− ) mice. APP, β‐site APP cleaving enzyme 1, and amyloid beta (Aβ) levels were significantly higher in the brains of aged eNOS −/− mice as compared to aged wild type mice. APP and Aβ 1–40 were increased in hippocampal tissue of eNOS −/− mice as compared to wild type mice. Aged eNOS −/− mice displayed an increased inflammatory phenotype as compared to aged wild type mice. Importantly, aged eNOS −/− mice performed worse in a radial arm maze test of spatial learning and memory as compared to aged wild type mice. These data suggest that chronic loss of endothelial NO may be an important contributor to both Aβ related pathology and cognitive decline. Research was supported by NIH grants HL‐111062 and HL‐91867, the Mayo Alzheimer's Disease Research Center (Z.S.K.), AHA scientist development grant (0835436N, A.V.S.), AHA postdoctoral fellowship 12POST8550003 (S.A.A.), Clinical Pharmacology Training Grant (T32 GM08685) (Trainee S.A.A.), the Samuel Johnson Foundation for Genomics of Addiction Program at Mayo Clinic (D.‐S.C.) and the Mayo Foundation.

Tetrahydrobiopterin (BH 4 ) is an essential cofactor for endothelial nitric oxide synthase (eNOS). Suboptimal level of BH 4 reduces formation of nitric oxide leading to uncoupling of eNOS. However, the exact molecular mechanisms underlying the effects of eNOS uncoupling on vascular endothelium in‐vivo are not completely understood. In the present study, we used the hph‐1 mouse, which displays GTP‐cyclohydrolase I deficiency. HPLC analysis revealed that BH 4 levels were significantly reduced in the aortas of hph‐1 mice (3.9±0.5 pmol/mg; P<0.05 vs. wild‐type mice: 5.9±0.6 pmol/mg), while oxidative products of BH 4 , 7,8‐dihydrobiopterin (7,8‐BH 2 ), were unchanged. Consequently, the BH 4 to 7,8‐BH 2 ratio was significantly reduced in the aorta of hph‐1 mice (P<0.05). Expression of eNOS protein was not different between wild‐type and hph‐1 mice. Unexpectedly, protein expressions of phosphorylated Ser 1177 ‐eNOS and Ser 473 ‐Akt1 were significantly increased in hph‐1 mice aortas (P<0.05). Consistent with uncoupling of eNOS, L‐NAME sensitive superoxide anion production and 3‐nitrotyrosine formation were significantly increased in aortas of hph‐1 mice (P<0.05). Protein expressions of CuZnSOD, MnSOD, and EC‐SOD were unaltered in the aortas of hph‐1 mice as compared with wild‐type mice. Our results suggest that uncoupling eNOS increases phosphorylation of Akt1 and eNOS. This effect is most likely mediated by increased formation of eNOS‐derived reactive oxygen species including superoxide anion and hydrogen peroxide.

Cilostazol is an inhibitor of phosphodiesterase type III that possesses both antiplatelet and vasodilator effects. The present study aimed to determine the vasodilator effect of cilostazol in eNOS deficient (eNOS −/− ) mice. Mouse aorta was contracted with sub‐maximal concentration of phenylephrine and concentration‐dependent relaxations to cilostazol (10 −8 –10 −5 mol/L) were obtained in aortic rings, isolated from wild type and eNOS −/− mice. As previously reported, in aortas of wild type mice with intact endothelium, relaxations to cilostazol were significantly augmented as compared to aortas without endothelium. Surprisingly, genetic inactivation of eNOS significantly enhanced relaxations to cilostazol suggesting that chronic loss of nitric oxide may unmask compensatory vasodilator mechanisms significantly enhanced by the treatment with cilostazol. The augmentation of relaxations to cilostazol in aortas of eNOS −/− mice was endothelium independent and not inhibited by indomethacin, a cyclooxygenase inhibitor. Our findings support the view that patients suffering from vascular endothelial dysfunction induced by reduced availability of nitric oxide, may exhibit enhanced vasodilator reactivity to cilostazol.

Impaired endothelial function in cardiovascular disorders is mediated, in part, by uncoupling of eNOS caused by reduced availability of tetrahydrobiopterin (BH 4 ). Endothelial progenitor cells (EPCs), originating from bone marrow, contribute to repair of vascular system by either neovascularization following tissue ischemia or re‐endothelialization after endothelial injury. The contribution of BH 4 to the angiogenic function has not been studied. In the present study, we investigated the role of BH 4 in angiogenesis and mobilization of cells enriched in EPCs in hph‐1 mutant mice, a genetic model of GTP‐cyclohydrolase I deficiency. HPLC analysis revealed that enzymatic activity of GTP‐cyclohydrolase I is reduced by 65% in bone marrow of hph‐1 mice (22±4 pmol neopterin/mg/h; P<0.05 vs. wild‐type mice: 63±4 pmol/mg/h). Basal counts of cells co‐expressing CD34 and VEGFR2 (Flk‐1) were reduced in bone marrow and peripheral blood of hph‐1 mice. Fourteen days after hind limb ischemia, recovery of blood flow was significantly reduced in hph‐1 mice as compared to blood flow in ischemic limb of wild type mice. Our findings suggest that reduced bioavailability of BH 4 impairs mobilization of cells enriched in EPCs. This effect may help to explain impaired angiogenesis in hph‐1 mice.

Mobilization of hematopoietic progenitor cells is predictive of functional recovery in stroke. In the present study, alterations in progenitor cell counts were studied in an experimental model of subarachnoid hemorrhage (SAH)‐induced cerebral vasospasm in rabbits. Injection of autologous arterial blood into cisterna magna resulted in significant vasospasm of the basilar arteries forty eight hours following injection. Concomitantly, the number of hematopoietic progenitor cells (CD34 + cells) and CD34 + /Flk‐1 + cells, believed to be enriched in endothelial progenitor cells (EPCs), were significantly increased in the peripheral blood. The levels of the chemokine stromal cell‐derived factor‐1α (SDF‐1α), known to play a key role in the recruitment and retention of CXCR4 + ‐progenitor cells, significantly increased in the plasma of rabbits subjected to SAH. However, levels of SDF‐1α in the cerebrospinal fluid as well as the content of SDF‐1α in the spastic basilar arteries remained unaffected forty eight hours after SAH. In summary, cerebral vasospasm was accompanied by mobilization of hematopoietic progenitor cells and EPCs. We speculate that the pathogenesis of cerebral vasospasm following SAH may be mediated, in part, by impaired recruitment and homing of CXCR4 + ‐ progenitor cells.

High salt diet (HS) impairment of endothelial nitric oxide (NO) signaling has been described in human and rodents. The mechanisms which mediate this dysfunction remain unknown. We and others have previously shown histone deacetylase 1 (HDAC1) decreases endothelial NO production. We therefore sought to investigate the mechanisms by which HS initiates endothelial dysfunction and if it is HDAC1‐dependent. We first investigated if HS induced endothelial dysfunction is acutely regulated by a circulating factor. Male Sprague Dawley rats were fed normal salt diet (NS; 0.49% NaCl) or 2 weeks of HS (4.0% NaCl). Afferent arteriole vasoconstrictor responses to the NOS inhibitor, L‐NAME, were monitored using the in vitro, blood perfused juxtamedullary nephron preparation. Arterioles from HS fed rats perfused with blood from HS fed rats demonstrated blunted constriction to L‐NAME (96 ± 2% of Con) compared to arterioles from NS fed rats perfused with blood from NS fed rats (76.2 ± 2% of Con; P=0.0017). Perfusing arterioles from NS fed rats with blood HS fed rats blunted constriction to L‐NAME (88 ± 1% of Con) compared to perfusing with blood from NS fed rats (P=0.0003), but not to the same extent as arterioles from HS fed rats perfused with blood from HS fed rats (P=0.0095). HS arterioles perfused with blood from NS fed rats had similar L‐NAME‐induced constriction (75 ± 2% of Con) compared to arterioles from NS fed rats perfused with blood from NS fed rats (P=0.9107). In short, the impaired constriction to L‐NAME is dependent up on the diet of the blood donor and not the diet of the arteriole donor suggesting HS impairs endothelial function through an acute‐acting circulating factor. This was not due to increased plasma arginase activity (NS: 7.96 ± 3.73 U/L vs HS: 5.42 ± 1.83 U/L P=0.5813), changes in plasma tetrahydrobiopterin (NS: 65.09 ± 11.57 pmol/ml vs HS: 53.54 ± 5.59 pmol/ml, P=0.311) or changes in plasma dihydrobiopterin (NS: 98.18 ± 7.84 pmol/ml vs HS: 87.45 ± 13.28 pmol/ml, P=0.530). We then investigated if HS increased endothelial HDAC1 activity. Renal endothelial cells were isolated from NS and HS fed rats and incubated in plasma from the same rat. HDAC1 activity was defined as the MS‐275 (HDAC1 specific inhibitor) inhibitable portion of total HDAC activity. We found HS significantly increased renal endothelial HDAC1 activity (NS: 0.38 ± 0.03 pmol/min vs HS:0.94 ± 0.19 pmol/min, P=0.01). Furthermore, in vitro HDAC1 inhibition with 300 nM MS‐275 restored the arteriolar vasoconstrictor responses in HS rats (79 ± 3% of Con) to values similar to NS fed rats (P=0.969) and to NS rats + MS‐275 (79 ± 1% of Con; P>0.998). When plasma from HS fed rats was combined with erythrocytes from NS fed rats and perfused through arterioles from NS fed rats, constriction to L‐NAME was blunted (85 ± 3% of Con; P=0.0129). Under these same conditions, HDAC1 inhibition restored constriction (75.7 ± 0.95 % of Con) similar to controls (P=0.979). We conclude that HS disruption of renal microvascular NO signaling is initiated by a circulating factor(s) that increases endothelial HDAC1 activity.

Abstract Vascular contributions to cognitive impairment and dementia (VCID) are characterized by the aging neurovascular unit being confronted with and failing to cope with biological insults due to systemic and cerebral vascular disease, proteinopathy including Alzheimer's biology, metabolic disease, or immune response, resulting in cognitive decline. This report summarizes the discussion and recommendations from a working group convened by the National Heart, Lung, and Blood Institute and the National Institute of Neurological Disorders and Stroke to evaluate the state of the field in VCID research, identify research priorities, and foster collaborations. As discussed in this report, advances in understanding the biological mechanisms of VCID across the wide spectrum of pathologies, chronic systemic comorbidities, and other risk factors may lead to potential prevention and new treatment strategies to decrease the burden of dementia. Better understanding of the social determinants of health that affect risks for both vascular disease and VCID could provide insight into strategies to reduce racial and ethnic disparities in VCID.

Abstract Idiopathic pulmonary fibrosis (IPF) is a progressive disease thought to result from impaired lung repair following injury and is strongly associated with aging. While vascular alterations have been associated with IPF previously, the contribution of lung vasculature during injury resolution and fibrosis is not well understood. To compare the role of endothelial cells (ECs) in resolving and non‐resolving models of lung fibrosis, we applied bleomycin intratracheally to young and aged mice. We found that injury in aged mice elicited capillary rarefaction, while injury in young mice resulted in increased capillary density. ECs from the lungs of injured aged mice relative to young mice demonstrated elevated pro‐fibrotic and reduced vascular homeostasis gene expression. Among the latter, Nos3 (encoding the enzyme endothelial nitric oxide synthase, eNOS) was transiently upregulated in lung ECs from young but not aged mice following injury. Young mice deficient in eNOS recapitulated the non‐resolving lung fibrosis observed in aged animals following injury, suggesting that eNOS directly participates in lung fibrosis resolution. Activation of the NO receptor soluble guanylate cyclase in human lung fibroblasts reduced TGFβ‐induced pro‐fibrotic gene and protein expression. Additionally, loss of eNOS in human lung ECs reduced the suppression of TGFβ‐induced lung fibroblast activation in 2D and 3D co‐cultures. Altogether, our results demonstrate that persistent lung fibrosis in aged mice is accompanied by capillary rarefaction, loss of EC identity, and impaired eNOS expression. Targeting vascular function may thus be critical to promote lung repair and fibrosis resolution in aging and IPF.