Heistad, Donald D.

Angiotensin II produces oxidative stress and endothelial dysfunction. ACE2 converts angiotensin II to angiotensin 1–7 and may protect against effects of angiotensin II. We tested the hypothesis that ACE2 deficiency increases oxidative stress and vasomotor dysfunction in cerebral arteries, and examined the role of ACE2 in vascular aging. ACE2 was present at relatively low levels in cerebral arteries. Systolic arterial pressure was similar in adult and old ACE2 knockout (KO) and wild‐type (WT) mice. Maximal dilatation to acetylcholine (ACh) was impaired in the basilar artery from adult ACE2 KO mice compared to adult WT. In old mice, maximal dilatation to ACh was impaired in WT mice but severely impaired in ACE2 KO mice (P<0.05). The antioxidant tempol (1 mM) improved responses to ACh in adult and old ACE2 KO and WT mice. Nitrotyrosine staining in the basilar artery was increased in adult ACE2 KO mice and in old ACE2 KO and WT mice. Expression of NAD(P)H oxidase subunits Nox2 and p47phox, and of pro‐inflammatory molecules Rcan1 and TNFα, was increased in cerebral arteries from old ACE2 KO and WT animals. In summary, ACE2 deficiency impaired vasomotor function in cerebral arteries from adult mice and augments endothelial dysfunction during aging. Oxidative stress plays a critical role in cerebrovascular dysfunction induced by ACE2 deficiency and aging. NIH grants NS‐24621, HL‐38091, HL‐62984; AHA 0815525G, 10PRE3780044.

Our goal was to develop a model of accelerated hypertension with renal microangiopathy. Transgenic mice that are hypertensive because of overexpression of human renin (R + mice) and human angiotensin (A + mice) genes were studied. To Increase arterial pressure to levels comparable to those that may be seen in malignant hypertension, high salt was added to the diet and/or the nitric oxide synthase inhibitor, N ω -nitro-L-arginine methylester (L-NAME), was added to the drinking water. Renal lesions, decline in renal function, and proteinuria developed within 10 weeks in R + /A + mice given both L-NAME and a high-salt diet, and within 24 weeks in mice given either L-NAME or a high-salt diet. Renal morphology showed features of severe thrombotic microangiopathy, with extensive vascular and glomerular lesions in all R + /A + mice on high salt, L-NAME, or high salt plus L-NAME. Vascular lesions included fibrin thrombi and onion skinning of the vessel walls, whereas glomerular lesions Included segmental sclerosis, mesangiolysis, fibrin thrombi within glomerular capillaries, and double-contour formation of glomerular capillary walls. Renal morphology was normal in control mice fed high salt and/or L-NAME. No R + /A + mice fed a normal diet developed vascular lesions, whereas a few mice developed mild focal glomerular lesions. In summary, these studies characterize vascular and glomerular lesions in R + /A + mice fed high salt, L-NAME, or both high salt and L-NAME, and provide a murine model of malignant hypertension with renal thrombotic microangiopathy.

Studies in vitro and in vivo continue to identify complex-regulated mechanisms leading to overt fibrocalcific aortic valve disease (FCAVD). Assessment of the functional impact of those processes requires careful studies of models of FCAVD in vivo. Although the genetic basis for FCAVD is unknown for most patients with FCAVD, several disease-associated genes have been identified in humans and mice. Some gene products which regulate valve development in utero also protect against fibrocalcific disease during postnatal aging. Valve calcification can occur via processes that resemble bone formation. But valve calcification can also occur by nonosteogenic mechanisms, such as formation of calcific apoptotic nodules. Anticalcific interventions might preferentially target either osteogenic or nonosteogenic calcification. Although FCAVD and atherosclerosis share several risk factors and mechanisms, there are fundamental differences between arteries and the aortic valve, with respect to disease mechanisms and responses to therapeutic interventions. Both innate and acquired immunity are likely to contribute to FCAVD. Angiogenesis is a feature of inflammation, but may also contribute independently to progression of FCAVD, possibly by actions of pericytes that are associated with new blood vessels. Several therapeutic interventions seem to be effective in attenuating the development of FCAVD in mice. Therapies which are effective early in the course of FCAVD, however, are not necessarily effective in established disease.

Background and Purpose— Angiotensin II produces oxidative stress and endothelial dysfunction in cerebral arteries, and angiotensin II type I receptors may play a role in longevity and vascular aging. Angiotensin-converting enzyme type 2 (ACE2) converts angiotensin II to angiotensin (1–7) and thus, may protect against effects of angiotensin II. We hypothesized that ACE2 deficiency increases oxidative stress and endothelial dysfunction in cerebral arteries and examined the role of ACE2 in age-related cerebrovascular dysfunction. Methods— Endothelial function, expression of angiotensin system components, NADPH oxidase subunits, and proinflammatory cytokines were examined in cerebral arteries from adult (12 months old) and old (24 months old) ACE2 knockout (KO) and wild-type (WT) mice. The superoxide scavenger tempol was used to examine the role of oxidative stress on endothelial function. Results— Vasodilatation to acetylcholine was impaired in adult ACE2 KO (24±6% [mean±SE]) compared with WT mice (52±7%; P <0.05). In old mice, vasodilatation to acetylcholine was impaired in WT mice (29±6%) and severely impaired in ACE2 KO mice (7±5%). Tempol improved endothelial function in adult and old ACE2 KO and WT mice. Aging increased mRNA for tumor necrosis factor-α in WT mice, and significantly increased mRNA levels of NAPDH oxidase 2, p47 phox , and Regulator of calcineurin 1 in both ACE2 KO and WT mice. mRNA levels of angiotensin system components did not change during aging. Conclusions— ACE2 deficiency impaired endothelial function in cerebral arteries from adult mice and augmented endothelial dysfunction during aging. Oxidative stress plays a critical role in cerebrovascular dysfunction induced by ACE2 deficiency and aging.

Calcific aortic valve stenosis (CAVS) is a major health problem facing aging societies. The identification of osteoblast-like and osteoclast-like cells in human tissue has led to a major paradigm shift in the field. CAVS was thought to be a passive, degenerative process, whereas now the progression of calcification in CAVS is considered to be actively regulated. Mechanistic studies examining the contributions of true ectopic osteogenesis, nonosseous calcification, and ectopic osteoblast-like cells (that appear to function differently from skeletal osteoblasts) to valvular dysfunction have been facilitated by the development of mouse models of CAVS. Recent studies also suggest that valvular fibrosis, as well as calcification, may play an important role in restricting cusp movement, and CAVS may be more appropriately viewed as a fibrocalcific disease. High-resolution echocardiography and magnetic resonance imaging have emerged as useful tools for testing the efficacy of pharmacological and genetic interventions in vivo. Key studies in humans and animals are reviewed that have shaped current paradigms in the field of CAVS, and suggest promising future areas for research.

The National Heart, Lung, and Blood Institute (NHLBI) convened a conference call working group, consisting of experts in stroke and cerebrovascular biology on January 28, 2005. The purpose of this working group was to develop a prioritized set of recommendations for NHLBI to establish a focused and comprehensive set of research activities in cerebrovascular biology and disease. Three thematic areas of research emerged: (1) molecular and cellular neurobiology of cerebral blood vessels, focusing on genomics and proteomics, neurovascular signaling and cerebrovascular embryogenesis, development and plasticity; (2) resource development, involving the development of new methodological approaches for normal and altered function of the neurovascular unit, collaborative research, and training in cerebrovascular pathobiology; and (3) cerebrovascular diseases and translational approaches, addressing vascular mechanisms of disease, the role of risk factors, importance of biomarkers with the ultimate goal of developing new treatments.