Comparison of contractile responses in isolated mouse aorta and pulmonary artery: Influence of strain and sex

Assessment of the Role of Endothelial and Vascular Smooth Muscle EGFR for Acute Blood Pressure Effects of Angiotensin II and Adrenergic Stimulation in Obese Mice

(1) Background: Obesity is associated with hypertension because of endocrine dysregulation of the adrenergic and the renin-angiotensin-aldosterone systems. The epidermal growth factor receptor (EGFR) is an important signaling hub in the cardiovascular system. In this study, we investigate the role of smooth muscle cell (VSMC) and endothelial cell (EC) EGFRs for blood pressure homeostasis and acute vascular reactivity in vivo. (2) Methods: Mice with deletion of the EGFR in the respective cell type received either a high-fat (HFD) or standard-fat diet (SFD) for 18 weeks. Intravascular blood pressure was measured via a Millar catheter in anesthetized animals upon vehicle load, angiotensin II (AII) and phenylephrine (PE) stimulation. (3) Results: We confirmed that deletion of the EGFR in VSMCs leads to reduced blood pressure and a most probably compensatory heart rate increase. EC-EGFR and VSMC-EGFR had only a minor impact on volume-load-induced blood pressure changes in lean as well as in obese wild-type animals. Regarding vasoactive substances, EC-EGFR seems to have no importance for angiotensin II action and counteracting HFD-induced prolonged blood pressure increase upon PE stimulation. VSMC-EGFR supports the blood pressure response to adrenergic and angiotensin II stimulation in lean animals. The responsiveness to AII and alpha-adrenergic stimulation was similar in lean and obese animals despite the known enhanced activity of the RAAS and the sympathetic nervous system under a high-fat diet. (4) Conclusions: We demonstrate that EGFRs in VSMCs and to a lesser extent in ECs modulate short-term vascular reactivity to AII, catecholamines and volume load in lean and obese animals.

Reduced Biaxial Contractility in the Descending Thoracic Aorta of Fibulin-5 Deficient Mice

The precise role of smooth muscle cell contractility in elastic arteries remains unclear, but accumulating evidence suggests that smooth muscle dysfunction plays an important role in the development of thoracic aortic aneurysms and dissections (TAADs). Given the increasing availability of mouse models of these conditions, there is a special opportunity to study roles of contractility ex vivo in intact vessels subjected to different mechanical loads. In parallel, of course, there is a similar need to study smooth muscle contractility in models that do not predispose to TAADs, particularly in cases where disease might be expected. Multiple mouse models having compromised glycoproteins that normally associate with elastin to form medial elastic fibers present with TAADs, yet those with fibulin-5 deficiency do not. In this paper, we show that deletion of the fibulin-5 gene results in a significantly diminished contractility of the thoracic aorta in response to potassium loading despite otherwise preserved characteristic active behaviors, including axial force generation and rates of contraction and relaxation. Interestingly, this diminished response manifests around an altered passive state that is defined primarily by a reduced in vivo axial stretch. Given this significant coupling between passive and active properties, a lack of significant changes in passive material stiffness may help to offset the diminished contractility and thereby protect the wall from detrimental mechanosensing and its sequelae.

Transcription factor cAMP response element modulator (Crem) restrains Pdgf-dependent proliferation of vascular smooth muscle cells in mice

Transcription factors of the cAMP response element-binding protein (Creb)/cAMP response element modulator (Crem) family were linked to the switch from a contractile to a proliferating phenotype in vascular smooth muscle cells (VSMCs). Here, we analyzed the vascular function of Crem in mice with a global inactivation of Crem (Crem(-/-)). CRE-mediated transcriptional activity was enhanced in primary Crem(-/-) VSMCs under nonstimulated conditions and under stimulation with Forskolin and platelet-derived growth factor (Pdgf) whereas stimulation with nitric oxide or cGMP showed no effect. This elevated CRE-mediated transcriptional activity as a result of Crem inactivation did not alter aortic contractility or fractions of proliferating or apoptotic aortic VSMCs in situ, and no impact of Crem inactivation on the development of atherosclerotic plaques was observed. Crem(-/-) mice exhibited an increased neointima formation after carotid ligation associated with an increased proliferation of VSMCs in the carotid media. Pdgf-stimulated proliferation of primary aortic Crem(-/-) VSMCs was increased along with an upregulation of messenger RNA (mRNA) levels of Pdgf receptor, alpha polypeptide (Pdgfra), cyclophilin A (Ppia), the regulator of G-protein signaling 5 (Rgs5), and Rho GTPase-activating protein 12 (Arhgap12). Taken together, our data reveal the inhibition of Pdgf-stimulated proliferation of VSMCs by repressing the Pdgf-stimulated CRE-mediated transcriptional activation as the predominant function of Crem in mouse vasculature suggesting an important role of Crem in vasculoproliferative diseases.

Constitutive phosphorylation of inhibitor-1 at Ser67 and Thr75 depresses calcium cycling in cardiomyocytes and leads to remodeling upon aging

The activity of protein phosphatase-1 (PP1) inhibitor-1 (I-1) is antithetically modulated by the cAMP-protein kinase A (PKA) and Ca(2+)-protein kinase C (PKC) signaling axes. β-adrenergic (β-AR) stimulation results in PKA-phosphorylation of I-1 at threonine 35 (Thr35) and depressed PP1 activity, while PKC phosphorylation at serine 67 (Ser67) and/or Thr75 increases PP1 activity. In heart failure, pThr35 is decreased while pSer67 and pThr75 are elevated. However, the role of Ser67/Thr75 phosphorylation in vivo and its effects on Ca(2+)-cycling are not known. Thus, our aim was to investigate the functional significance of Ser67 and Thr75 phosphorylation in intact hearts. We generated transgenic mice (TG) with cardiac-specific overexpression of constitutively phosphorylated I-1 at Ser67 and Thr75 (S67D/T75D) and evaluated cardiac function. The S67D/T75D cardiomyocytes exhibited significantly depressed Ca(2+)-kinetics and contractile parameters, compared with wild-type (WT) cells. The decreased Ca(2+)-cycling was associated with a 27 % increase in PP1 activity, no alterations in PP2 activity and impaired phosphorylation of myosin-binding protein-C (MyBPC). Upon aging, there was cardiac remodeling associated with increases in systolic and diastolic left ventricular internal diameter dimensions (at 16 months), compared with WTs. The results indicate that phosphorylation of I-1 at Ser67 and Thr75 is associated with increased PP1 activity and depressed cardiomyocyte Ca(2+)-cycling, which manifests in geometrical alterations over the long term. Thus, hyperphosphorylation of these sites in failing hearts may contribute to deteriorative remodeling.