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Aims Circadian rhythms orchestrate important functions in the cardiovascular system: the contribution of microvascular rhythms to cardiovascular disease progression/severity is unknown. This study hypothesized that (i) myogenic reactivity in skeletal muscle resistance arteries is rhythmic and (ii) disrupting this rhythmicity would alter cardiac injury post-myocardial infarction (MI). Methods and results Cremaster skeletal muscle resistance arteries were isolated and assessed using standard pressure myography. Circadian rhythmicity was globally disrupted with the ClockΔ19/Δ19 mutation or discretely through smooth muscle cell-specific Bmal1 deletion (Sm-Bmal1 KO). Cardiac structure and function were determined by echocardiographic, hemodynamic and histological assessments. Myogenic reactivity in cremaster muscle resistance arteries is rhythmic. This rhythm is putatively mediated by the circadian modulation of a mechanosensitive signalosome incorporating tumour necrosis factor and casein kinase 1. Following left anterior descending coronary artery ligation, myogenic responsiveness is locked at the circadian maximum, although circadian molecular clock gene expression cycles normally. Disrupting the molecular clock abolishes myogenic rhythmicity: myogenic tone is suspended at the circadian minimum and is no longer augmented by MI. The reduced myogenic tone in ClockΔ19/Δ19 mice and Sm-Bmal1 KO mice associates with reduced total peripheral resistance (TPR), improved cardiac function and reduced infarct expansion post-MI. Conclusions Augmented microvascular constriction aggravates cardiac injury post-MI. Following MI, skeletal muscle resistance artery myogenic reactivity increases specifically within the rest phase, when TPR would normally decline. Disrupting the circadian clock interrupts the MI-induced augmentation in myogenic reactivity: therapeutics targeting the molecular clock, therefore, may be useful for improving MI outcomes. [ABSTRACT FROM AUTHOR]

This study reports a new methodology for right heart imaging by ultrasound in mice under right ventricular (RV) pressure overload. Pulmonary artery constriction (PAC) or sham surgeries were performed on C57BL/6 male mice at 8 wk of age. Ultrasound imaging was conducted at 2, 4, and 8 wk postsurgery using both classical and advanced ultrasound imaging modalities including electrocardiogram (ECG)-based kilohertz visualization, anatomical M-mode, and strain imaging. Based on pulsed Doppler, the PAC group demonstrated dramatically enhanced pressure gradient in the main pulmonary artery (MPA) as compared with the sham group. By the application of advanced imaging modalities in novel short-axis views of the ventricles, the PAC group demonstrated increased thickness of RV free wall, enlarged RV chamber, and reduced RV fractional shortening compared with the sham group. The PAC group also showed prolonged RV contraction, asynchronous interplay between RV and left ventricle (LV), and passive leftward motion of the interventricular septum (IVS) at early diastole. Consequently, the PAC group exhibited prolongation of LV isovolumic relaxation time, without change in LV wall thickness or systolic function. Significant correlations were found between the maximal pressure gradient in MPA measured by Doppler and the RV systolic pressure by catheterization, as well as the morphological and functional parameters of RV by ultrasound. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO) inhibits vascular contraction by activating cGMP-dependent protein kinase I-[alpha] (PKGI-[alpha]), which causes dephosphorylation of myosin light chain (MLC) and vascular smooth muscle relaxation. Here we show that PKGI-[alpha] attenuates signaling by the thrombin receptor protease-activated receptor-1 (PAR-1) through direct activation of regulator of G-protein signaling-2 (RGS-2). NO donors and cGMP cause cGMP-mediated inhibition of PAR-1 and membrane localization of RGS-2. PKGI-[alpha] binds directly to and phosphorylates RGS-2, which significantly increases GTPase activity of G[sub.q], terminating PAR-1 signaling. Disruption of the RGS-2-PKGI-[alpha] interaction reverses inhibition of PAR-1 signaling by nitrovasodilators and cGMP. Rgs2[sup.-/-] mice develop marked hypertension, and their blood vessels show enhanced contraction and decreased cGMP-mediated relaxation. Thus, PKGI-[alpha] binds to, phosphorylates and activates RGS-2, attenuating receptor-mediated vascular contraction. Our study shows that RGS-2 is required for normal vascular function and blood pressure and is a new drug development target for hypertension., Author(s): Mary Tang [1]; Guang Wang [1]; Ping Lu [1, 4]; Richard H Karas [1]; Mark Aronovitz [1]; Scott P Heximer [2]; Kevin M Kaltenbronn [2]; Kendall J Blumer [2]; [...]

RGS (regulators of G protein signaling) proteins are GTPase activating proteins that inhibit signaling by heterotrimeric G proteins. All RGS proteins studied to date act on members of the Gi[Alpha] family, but not Gs[Alpha] or G12[Alpha]. RGS4 regulates Gi[Alpha] family members and Gq[Alpha]. RGS2 (GOS8) is exceptional because the G proteins it regulates have not been identified. We report that RGS2 is a selective and potent inhibitor of Gq[Alpha] function. RGS2 selectively binds Gq[Alpha], but not other G[Alpha] proteins (Gi, Go, Gs, G12/13) in brain membranes; RGS4 binds Gq[Alpha] and Gi[Alpha] family members. RGS2 binds purified recombinant Gq[Alpha], but not Go[Alpha], whereas RGS4 binds either. RGS2 does not stimulate the GTPase activities of Gs[Alpha] or Gi[Alpha] family members, even at a protein concentration 3000-fold higher than is sufficient to observe effects of RGS4 on Gi[Alpha] family members. In contrast, RGS2 and RGS4 completely inhibit Gq-directed activation of phospholipase C in cell membranes. When reconstituted with phospholipid vesicles, RGS2 is 10-fold more potent than RGS4 in blocking Gq[Alpha]-directed activation of phospholipase C[Beta]1. These results identify a clear physiological role for RGS2, and describe the first example of an RGS protein that is a selective inhibitor of Gq[Alpha] function.

The proto-oncogene c-myb (and corresponding nuclear transcription factor, c-Myb) regulates the proliferation and differentiation of hematologic and vascular smooth muscle cells; however, the role of c-Myb in blood pressure regulation is unknown. Here, we show that mice homozygous for a hypomorphic c-myb allele ( c-myb h/h) conferring reduced c-Myb activity manifest reduced peripheral blood and kidney B220+ B-cells and have decreased systolic (104±2 versus 120±1 mm Hg; P<0.0001) and diastolic blood pressure (71±2 versus 83±1 mm Hg; P<0.0001) compared with WT (wild type) mice. Additionally, c-myb h/h mice had lower susceptibility to deoxycorticosterone acetate-salt experimental hypertension. Although cardiac (echocardiography) and resistance artery (perfusion myography) functions were normal, metabolic cage studies revealed that c-myb h/h mice had increased 24-hour urine output and sodium excretion versus WT. Reconstitution of WT mice with c-myb h/h bone marrow transplant and chimeric bone marrow transplant using mice lacking B-cells ( J H T; h/h>WT and h/h:J H T>WT, respectively) decreased blood pressure and increased 24-hour urine output compared with controls ( WT>WT; WT:J H T>WT). J H T mice also had decreased systolic (103±2 versus 115±1 mm Hg; P<0.0001) and diastolic blood pressure (71±2 versus 79±1; P<0.01) and increased 24-hour urine output versus WT. Real-time quantitative reverse transcription polymerase chain reaction of kidney medulla revealed reduced V2R (vasopressin receptor 2) expression in c-myb h/h and J H T mice. These data implicate B-cells in the regulation of V2R and its associated effects on salt and water handling and blood pressure homeostasis. [ABSTRACT FROM AUTHOR]