Patchy deletion of Bmpr1a potentiates proximal pulmonary artery remodeling in mice exposed to chronic hypoxia

Reduced vascular expression of bone morphogenetic protein type IA receptor (Bmpr1a) has been found in patients with pulmonary arterial hypertension. Our previous studies in mice with patchy deletion of Bmpr1a in vascular smooth muscle cells and cardiac myocytes showed decreased distal vascular remodeling despite a similar severity of hypoxic pulmonary hypertension (HPH). We speculate increased stiffness from ectopic deposition of collagen in proximal pulmonary arteries might account for HPH. Pulsatile pressure-flow relationships were measured in isolated, ventilated, perfused lungs of SM22α;TRE-Cre;R26R;Bmpr1a ^flox/flox (KO) mice and wild-type littermates, following 21 days (hypoxia) and 0 days (control) of chronic hypoxia. Pulmonary vascular impedance, which yields insight into proximal and distal arterial remodeling, was calculated. Reduced Bmpr1a expression had no effect on input impedance Z ₀ (P = 0.52) or characteristic impedance Z _C (P = 0.18) under control conditions; it also had no effect on the decrease in Z ₀ via acute rho kinase inhibition. However, following chronic hypoxia, reduced Bmpr1a expression increased Z _C (P < 0.001) without affecting Z ₀ (P = 0.72). These results demonstrate that Bmpr1a deficiency does not significantly alter the hemodynamic function of the distal vasculature or its response to chronic hypoxia but larger, more proximal arteries are affected. In particular, reduced Bmpr1a expression likely decreased dilatation and increased stiffening in response to hypoxia, probably by collagen accumulation. Increased PA stiffness can have a significant impact on right ventricular function. This study illustrates for the first time how proximal pulmonary artery changes in the absence of distal pulmonary artery changes contribute to pulmonary arterial hypertension.     

Intercellular communication in the rat anterior pituitary gland: an in vivo and in vitro study

The concept of "stimulus-secretion coupling" suggested by Douglas and co-workers to explain the events related to monamine discharge by the adrenal medulla (5, 7) may be applied to other endocrine tissues, such as adrenal cortex (36), pancreatic islets (4), and magnocellular hypothalamic neurons (6), which exhibit a similar ion-dependent process of hormone elaboration. In addition, they share another feature, that of joining neighbor cells via membrane junctions (12, 26, and Fletcher, unpublished observation). Given this, and the reports that hormone secretion by the pars distalis also involves a secretagogue-induced decrease in membrane bioelectric potential accompanied by a rise in cellular [Ca++] (27, 34, 41), it was appropriate to test the possibility that cells of the anterior pituitary gland are united by junctions.     

Airway cellularity, lipid laden macrophages and microbiology of gastric juice and airways in children with reflux oesophagitis

Background and methods

Human metapneumovirus (hMPV) is a recently discovered respiratory virus associated with bronchiolitis, pneumonia, croup and exacerbations of asthma. Since respiratory viruses are frequently detected in patients with acute exacerbations of COPD (AE-COPD) it was our aim to investigate the frequency of hMPV detection in a prospective cohort of hospitalized patients with AE-COPD compared to patients with stable COPD and to smokers without by means of quantitative real-time RT-PCR.

Results

We analysed nasal lavage and induced sputum of 130 patients with AE-COPD, 65 patients with stable COPD and 34 smokers without COPD. HMPV was detected in 3/130 (2.3%) AE-COPD patients with a mean of 6.5 × 10⁵ viral copies/ml in nasal lavage and 1.88 × 10⁵ viral copies/ml in induced sputum. It was not found in patients with stable COPD or smokers without COPD.

Conclusion

HMPV is only found in a very small number of patients with AE-COPD. However it should be considered as a further possible viral trigger of AE-COPD because asymptomatic carriage is unlikely.     

Measurements of mouse pulmonary artery biomechanics

BACKGROUND: Robust techniques for characterizing the biomechanical properties of mouse pulmonary arteries will permit exciting gene-level hypotheses regarding pulmonary vascular disease to be tested in genetically engineered animals. In this paper, we present the first measurements of the biomechanical properties of mouse pulmonary arteries. METHOD OF APPROACH: In an isolated vessel perfusion system, transmural pressure, internal diameter and wall thickness were measured during inflation and deflation of mouse pulmonary arteries over low (5-40 mmHg) and high (10-120 mmHg) pressure ranges representing physiological pressures in the pulmonary and systemic circulations, respectively. RESULTS: During inflation, circumferential stress versus strain showed the nonlinear "J"-shape typical of arteries. Hudetz's incremental elastic modulus ranged from 27 +/- 13 kPa (n = 7) during low-pressure inflation to 2,700 +/- 1,700 kPa (n = 9) during high-pressure inflation. The low and high-pressure testing protocols yielded quantitatively indistinguishable stress-strain and modulus-strain results. Histology performed to assess the state of the tissue after mechanical testing showed intact medial and adventitial architecture with some loss of endothelium, suggesting that smooth muscle cell contractile strength could also be measured with these techniques. CONCLUSIONS: The measurement techniques described demonstrate the feasibility of quantifying mouse pulmonary artery biomechanical properties. Stress-strain behavior and incremental modulus values are presented for normal, healthy arteries over a wide pressure range. These techniques will be useful for investigations into biomechanical abnormalities in pulmonary vascular disease.     

Axon-glia interactions and the domain organization of myelinated axons requires neurexin IV/Caspr/Paranodin

Myelinated fibers are organized into distinct domains that are necessary for saltatory conduction. These domains include the nodes of Ranvier and the flanking paranodal regions where glial cells closely appose and form specialized septate-like junctions with axons. These junctions contain a Drosophila Neurexin IV-related protein, Caspr/Paranodin (NCP1). Mice that lack NCP1 exhibit tremor, ataxia, and significant motor paresis. In the absence of NCP1, normal paranodal junctions fail to form, and the organization of the paranodal loops is disrupted. Contactin is undetectable in the paranodes, and K(+) channels are displaced from the juxtaparanodal into the paranodal domains. Loss of NCP1 also results in a severe decrease in peripheral nerve conduction velocity. These results show a critical role for NCP1 in the delineation of specific axonal domains and the axon-glia interactions required for normal saltatory conduction.     

The role of IFN-gamma in immune responses to viral infections of the central nervous system

Interferon (IFN)-γ, is not only a marker of T_H1 CD4, CD8 and natural killer (NK) cells, it is also a critical antiviral mediator which is central to the elimination of viruses from the CNS. In this review, we describe IFN-γ, its receptor, signal transduction from receptor engagement, and antiviral downstream mediators. We demonstrate that although neurons are post-mitotic and non-renewing, they respond to IFN-γ in a fashion similar to peripheral fibroblasts or lymphocytes. We have illustrated this review with details about studies on the role(s) of IFN-γ in the pathogenesis of measles virus (MV), herpes simplex virus (HSV) type 1, and vesicular stomatitis virus (VSV) infections of the CNS. For VSV infection, IFN-γ signals through Jaks 1 and 2 and STAT1 to activate (interferon regulatory factor) IRF-1; although viral protein synthesis is inhibited, PKR is not a critical mediator in the antiviral response to VSV in murine neurons. In contrast, induction of nitric oxide synthase (NOS) type 1 and its production of nitric oxide is essential in the elimination of viruses from neurons.     

Particle deposition in arteries ex vivo: effects of pressure,flow, and waveform

The goal of this study was to quantify the effect of hemodynamic pressure, flow and waveform perturbations on the deposition of protein-sized particles in porcine carotid arteries ex vivo. An ex vivo perfusion system was used to control the pressure and flow environment for excised arterial tissue. Confocal laser microscopy images revealed that 200 nm particles were deposited intimally and that more spheres were evident along vessels perfused under oscillatory waveform conditions than all others. Under all pressure, flow and waveform conditions, particles were excluded from the media and adventitia of the vessel wall. The steady flow data support the use of Darcy's Law with pressure-dependent hydraulic permeability to model arterial tissue.     

The effects of vasoactivity and hypoxic pulmonary hypertension on extralobar pulmonary artery biomechanics

Loss of large artery compliance is an emerging novel predictor of cardiovascular mortality. Hypoxia-induced pulmonary hypertension (HPH) has been shown to decrease extralobar pulmonary artery (PA) compliance in the absence of smooth muscle cell (SMC) tone and to increase SMC tone in peripheral PAs. We sought to determine the impact of HPH on extralobar PA tone and the impact of SMC activation on extralobar PA biomechanics. To do so, C57BL6 mice were exposed to 0 (CTL) or 10 days (HPH) of hypoxia and isolated vessel tests were performed on extralobar PAs using either a physiological saline solution (PSS), a vasoconstrictor (U46619), two vasodilators (SNP and Y27632) or calcium free medium (relaxant solution; VBRS). The vasodilators and relaxant solution had no effect on extralobar artery diameter suggesting that basal SMC tone is essentially zero in CTL conditions and does not increase with HPH. HPH caused narrowing, decreased circumferential stretch (λ; p<0.0001), decreased local area compliance (C_A; p<0.0005) and increased incremental elastic modulus (E_inc; p<0.05) in the normal tone state (with PSS). In both CTL and HPH conditions, SMC activation decreased E_inc (p<0.0005) but also increased wall thickness (p<0.05) such that changes in C_A with SMC constriction were minimal; only in HPH PAs was a significant decrease with SMC constriction observed (p<0.05). Our results demonstrate that 10 days of hypoxia does not increase extralobar PA SMC tone and that HPH-induced decreases in compliance are caused by narrowing, wall thickening and increases in modulus, not persistent vasoconstriction.     

Measuring right ventricular function in the normal and hypertensive mouse hearts using admittance-derived pressure-volume loops

Mice are a widely used animal model for investigating cardiovascular disease. Novel technologies have been used to quantify left ventricular function in this species, but techniques appropriate for determining right ventricular (RV) function are less well demonstrated. Detecting RV dysfunction is critical to assessing the progression of pulmonary vascular diseases such as pulmonary hypertension. We used an admittance catheter to measure pressure-volume loops in anesthetized, open-chested mice before and during vena cava occlusion. Mice exposed to chronic hypoxia for 10 days, which causes hypoxia-induced pulmonary hypertension (HPH), were compared with control (CTL) mice. HPH resulted in a 27.9% increase in RV mass (P < 0.005), a 67.5% increase in RV systolic pressure (P < 0.005), and a 61.2% decrease in cardiac output (P < 0.05). Preload recruitable stroke work (PRSW) and slope of the maximum derivative of pressure (dP/dt(max))-end-diastolic volume (EDV) relationship increased with HPH (P < 0.05). Although HPH increased effective arterial elastance (E(a)) over fivefold (from 2.7 ± 1.2 to 16.4 ± 2.5 mmHg/μl), only a mild increase in the ventricular end-systolic elastance (E(es)) was observed. As a result, a dramatic decrease in the efficiency of ventricular-vascular coupling occurred (E(es)/E(a) decreased from 0.71 ± 0.27 to 0.35 ± 0.17; P < 0.005). Changes in cardiac reserve were evaluated by dobutamine infusion. In CTL mice, dobutamine significantly enhanced E(es) and dP/dt(max)-EDV but also increased E(a), causing a decrease in E(es)/E(a). In HPH mice, slight but nonsignificant decreases in E(es), PRSW, dP/dt(max)-EDV, and E(a) were observed. Thus 10 days of HPH resulted in RV hypertrophy, ventricular-vascular decoupling, and a mild decrease in RV contractile reserve. This study demonstrates the feasibility of obtaining RV pressure-volume measurements in mice. These measurements provide insight into ventricular-vascular interactions healthy and diseased states.