This study reports on what we believe are novel mechanism(s) of the vascular protective action of adiponectin. We used intravital microscopy to measure leukocyte-endothelium interactions in adiponectin-deficient (Ad -/-) mice and found that adiponectin deficiency was associated with a 2-fold increase in leukocyte rolling and a 5-fold increase in leukocyte adhesion in the microcirculation. Measurement of endothelial NO (eNO) revealed that adiponectin deficiency drastically reduced levels of eNO in the vascular wall. Immunohistochemistry demonstrated increased expression of E-selectin and VCAM-1 in the vascular endothelium of Ad -/-mice. Systemic administration of the recombinant globular adiponectin domain (gAd) to Ad -/-mice significantly attenuated leukocyte-endothelium interactions and adhesion molecule expression in addition to restoring physiologic levels of eNO. Importantly, prior administration of gAd also protected WT mice against TNF-α-induced leukocyte-endothelium interactions, indicating a pharmacologic action of gAd. Mechanistically, blockade of eNOS with N ω -nitro-l-arginine methyl ester (l-NAME) abolished the inhibitory effect of gAd on leukocyte adhesion, demonstrating the obligatory role of eNOS signaling in the antiinflammatory action of gAd. We believe this is the first demonstration that gAd protects the vasculature in vivo via increased NO bioavailability with suppression of leukocyte-endothelium interactions. Overall, we provide evidence that loss of adiponectin induces a primary state of endothelial dysfunction with increased leukocyte-endothelium adhesiveness.

Abstract-S100A1, a Ca 2ϩ -binding protein of the EF-hand type, is known to modulate sarcoplasmic reticulum Ca 2ϩ handling in skeletal muscle and cardiomyocytes. Recently, S100A1 has been shown to be expressed in endothelial cells (ECs). Because intracellular Ca 2ϩ ([Ca 2ϩ ] i ) transients can be involved in important EC functions and endothelial NO synthase activity, we sought to investigate the impact of endothelial S100A1 on the regulation of endothelial and vascular function. Thoracic aortas from S100A1 knockout mice (SKO) showed significantly reduced relaxation in response to acetylcholine compared with wild-type vessels, whereas direct vessel relaxation using sodium nitroprusside was unaltered. Endothelial dysfunction attributable to the lack of S100A1 expression could also be demonstrated in vivo and translated into hypertension of SKO. Mechanistically, both basal and acetylcholine-induced endothelial NO release of SKO aortas was significantly reduced compared with wild type. Impaired endothelial NO production in SKO could be attributed, at least in part, to diminished agonist-induced [Ca 2ϩ ] i transients in ECs. Consistently, silencing endothelial S100A1 expression in wild type also reduced [Ca 2ϩ ] i and NO generation. Moreover, S100A1 overexpression in ECs further increased NO generation that was blocked by the inositol-1,4,5-triphosphate receptor blocker 2-aminoethoxydiphenylborate. Finally, cardiac endothelial S100A1 expression was shown to be downregulated in heart failure in vivo. Collectively, endothelial S100A1 critically modulates vascular function because lack of S100A1 expression leads to decreased [Ca 2ϩ ] i and endothelial NO release, which contributes, at least partially, to impaired endothelium-dependent vascular relaxation and hypertension in SKO mice. Targeting endothelial S100A1 expression may, therefore, be a novel therapeutic means to improve endothelial function in vascular disease or heart failure.

Increased permeability to albumin is a well-known feature of diabetic microvasculature and a negative prognostic factor of vascular complications. The mechanisms responsible for loss of the physiological albumin barrier in diabetic organs remain only partially understood. We have recently demonstrated that the protease -calpain is activated in hyperglycemia, which causes endothelial dysfunction and vascular inflammation. In the present study, we investigated whether -calpain is involved in the hyperpermeability of the diabetic vasculature. We also investigated the mechanistic roles of hyperglycemia and leukocyte adhesion in this process. Albumin permeability in the intact microcirculation of the Zucker diabetic fatty (ZDF) rat was quantified by intravital microscopy. Extravasation of albumin in the microcirculation of ZDF rats was significantly increased when compared with nondiabetic Zucker lean (ZL) rats. Microvascular albumin leakage was prevented by either antisense depletion of -calpain or pharmacological inhibition of calpain in vivo. Calpain inhibition also attenuated urinary albumin excretion in ZDF rats. Glucose concentrations in the range of those found in the blood of ZDF rats increased albumin permeability in nondiabetic ZL rats. Thus, this demonstrates a mechanistic role for hyperglycemia in the hypermeability of diabetes. Depletion of polymorphonuclear leukocytes in vivo failed to prevent glucose-induced hypermeability, which suggests that hyperglycemia can disrupt the physiological endothelial cell barrier of the microcirculation, even in the absence of increased overt leukocyte-endothelium interactions.

Rationale The cytosolic protease calpain has been recently implicated in the vascular remodeling of angiotensin II (AngII) type-1 receptor (AT1r) signaling. The role of AngII/AT1r/calpain signaling on endothelial function, an important and early determinant of vascular pathology, remains though totally unknown. Accordingly, we investigated the role of calpain in the endothelial dysfunction of AngII. Objective To demonstrate a mechanistic role for calpain in the endothelial dysfunction induced by AngII/AT1r signaling. To establish endothelial-expressed calpains as an important target of AT1r signaling. Methods and Results Subchronic administration of nonpressor doses of AngII to rats and mice significantly increased vascular calpain activity via AT1r signaling. Intravital microscopy studies revealed that activation of vascular expressed calpains causes endothelial dysfunction with increased leukocyte-endothelium interactions and albumin permeability in the microcirculation. Western blot and immunohistochemistry studies confirmed that AngII/AT1r signaling preferentially activates the constitutively expressed μ-calpain isoform and demonstrated a calpain-dependent degradation of IκBα, along with upregulation of NF-κB-regulated endothelial cell adhesion molecules (eCAMs). These physiological and biochemical parameters were nearly normalized following inhibition of AT1r or calpain in vivo. Antisense depletion studies in microvascular endothelial cells along with knockout and transgenic mouse studies further confirmed the role of μ-calpain in the endothelial adhesiveness induced by AngII. Conclusions This study uncovers a novel role for calpain in the endothelial dysfunction of AngII/AT1r signaling and establishes the calpain system as a novel molecular target of the vascular protective action of RAS inhibition. Our results may have significant clinical implications in vascular disease.

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