Penninger, Josef

Receptor activator of nuclear factor kappa B ligand (RANKL) is an essential cytokine that induces osteoclastic differentiation by monocyte-macrophage lineage precursors. Here, we showed that in addition to its conventional action, RANKL controls vascular permeability in the bone marrow, where it facilitates the mobilization of hematopoietic monocytic cells, including osteoclast precursors, and resultantly regulates bone metabolism. RANK, a cognate receptor for RANKL, is abundantly expressed in sinusoidal endothelial cells and controls vascular permeability by regulating the expression patterns of intercellular adhesion molecule 1 and vascular cell adhesion molecule 1. High RANKL expression was detected in perivascular C–X–C motif chemokine ligand 12-abundant reticular (CAR) stromal cells. Specific deletion of RANKL expression in CAR cells abrogated the vascular leakage, suggesting that perivascular RANKL is responsible for controlling permeability. In summary, our study revealed a role for RANK/RANKL signaling as a gatekeeper of bone marrow sinusoids in vivo.

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.

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.