Lung and Heart Biology of the Dp16 Mouse Model of down Syndrome: Implications for Studying Cardiopulmonary Disease.

(1) Background: We sought to investigate the baseline lung and heart biology of the Dp16 mouse model of Down syndrome (DS) as a prelude to the investigation of recurrent respiratory tract infection. (2) Methods: In controls vs. Dp16 mice, we compared peripheral blood cell and plasma analytes. We examined baseline gene expression in lungs and hearts for key parameters related to susceptibility of lung infection. We investigated lung and heart protein expression and performed lung morphometry. Finally, and for the first time each in a model of DS, we performed pulmonary function testing and a hemodynamic assessment of cardiac function. (3) Results: Dp16 mice circulate unique blood plasma cytokines and chemokines. Dp16 mouse lungs over-express the mRNA of triplicated genes, but not necessarily corresponding proteins. We found a sex-specific decrease in the protein expression of interferon α receptors, yet an increased signal transducer and activator of transcription (STAT)-3 and phospho-STAT3. Platelet-activating factor receptor protein was not elevated in Dp16 mice. The lungs of Dp16 mice showed increased stiffness and mean linear intercept and contained bronchus-associated lymphoid tissue. The heart ventricles of Dp16 mice displayed hypotonicity. Finally, Dp16 mice required more ketamine to achieve an anesthetized state. (4) Conclusions: The Dp16 mouse model of DS displays key aspects of lung heart biology akin to people with DS. As such, it has the potential to be an extremely valuable model of recurrent severe respiratory tract infection in DS.

Cigarette smoke-induced airspace disease in mice develops independently of HIF-1α signaling in leukocytes.

The pathogenesis of chronic obstructive pulmonary disease (COPD), a prevalent disease primarily caused by cigarette smoke exposure, is incompletely elucidated. Studies in humans and mice have suggested that hypoxia-inducible factor-1α (HIF-1α) may play a role. Reduced lung levels of HIF-1α are associated with decreased vascular density, whereas increased leukocyte HIF-1α may be responsible for increased inflammation. To elucidate the specific role of leukocyte HIF-1α in COPD, we exposed transgenic mice with conditional deletion or overexpression of HIF-1α in leukocytes to cigarette smoke for 7 mo. Outcomes included pulmonary physiology, aerated lung volumes via microcomputed tomography, lung morphometry and histology, and cardiopulmonary hemodynamics. On aggregate, cigarette smoke increased the aerated lung volume, quasi-static lung compliance, inspiratory capacity of all strains while reducing the total alveolar septal volume. Independent of smoke exposure, mice with leukocyte-specific HIF-1α overexpression had increased quasi-static compliance, inspiratory capacity, and alveolar septal volume compared with mice with leukocyte-specific HIF-1α deletion. However, the overall development of cigarette smoke-induced lung disease did not vary relative to control mice for either of the conditional strains. This suggests that the development of murine cigarette smoke-induced airspace disease occurs independently of leukocyte HIF-1α signaling.

Contribution of fatty acid oxidation to the pathogenesis of pulmonary hypertension.

Dysregulated metabolism characterizes both animal and human forms of pulmonary hypertension (PH). Enzymes involved in fatty acid metabolism have previously not been assessed in human pulmonary arteries affected by pulmonary arterial hypertension (PAH), and how inhibition of fatty acid oxidation (FAO) may attenuate PH remains unclear. Fatty acid metabolism gene transcription was quantified in laser-dissected pulmonary arteries from 10 explanted lungs with advanced PAH (5 idiopathic, 5 associated with systemic sclerosis), and 5 donors without lung diseases. Effects of oxfenicine, a FAO inhibitor, on female Sugen 5416-chronic hypoxia (SuHx) rats were studied in vivo using right heart catheterization, and ex vivo using perfused lungs and pulmonary artery ring segments. The impact of pharmacologic (oxfenicine) and genetic (carnitine palmitoyltransferase 1a heterozygosity) FAO suppression was additionally probed in mouse models of Schistosoma and hypoxia-induced PH. Potential mechanisms underlying FAO-induced PH pathogenesis were examined by quantifying ATP and mitochondrial mass in oxfenicine-treated SuHx pulmonary arterial cells, and by assessing pulmonary arterial macrophage infiltration with immunohistochemistry. We found upregulated pulmonary arterial transcription of 26 and 13 FAO genes in idiopathic and systemic sclerosis-associated PAH, respectively. In addition to promoting de-remodeling of pulmonary arteries in SuHx rats, oxfenicine attenuated endothelin-1-induced vasoconstriction. FAO inhibition also conferred modest benefit in the two mouse models of PH. Oxfenicine increased mitochondrial mass in cultured rat pulmonary arterial cells, and decreased the density of perivascular macrophage infiltration in pulmonary arteries of treated SuHx rats. In summary, FAO inhibition attenuated experimental PH, and may be beneficial in human PAH.

The effect of dietary nitrate supplementation on the speed-duration relationship in mice with sickle cell disease.

Sickle cell disease (SCD) causes exercise intolerance likely due to impaired skeletal muscle function and low nitric oxide (NO) bioavailability. Dietary nitrate improves hemodynamic and metabolic control during exercise in humans and animals. The purpose of this investigation was to assess the impact of nitrate supplementation on exercise capacity as measured by the running speed to exercise duration relationship [critical speed (CS)]in mice with SCD. We tested the hypothesis that nitrate supplementation via beetroot juice (BR) would attenuate the exercise intolerance observed in mice with SCD. Ten wild-type (WT) and 18 Berkley sickle-cell mice (BERK) received water (WT: n = 10, BERK: n = 10) or nitrate-rich BR (BERK+BR: n = 8, nitrate dose 1 mmol/kg/day) for 5 days. Following the supplementation period, all mice performed 3-5 constant-speed treadmill tests that resulted in exhaustion within 1.5 to 20 min. Time to exhaustion vs. treadmill speed was fit to a hyperbolic model to determine CS. CS was significantly lower in BERK vs. WT and BERK+BR with no significant difference between WT and BERK+BR (WT: 36.6 ± 1.6, BERK: 23.8 ± 1.5, BERK+BR: 31.1 ± 2.1 m/min, P < 0.05). Exercise tolerance, measured via CS, was significantly lower in BERK mice relative to WT. However, BERK mice receiving 5 days of nitrate supplementation exhibited no difference in exercise tolerance when compared with WT. These results support the potential utility of a dietary nitrate intervention to improve functionality in SCD patients.NEW & NOTEWORTHY Sickle cell disease compromises muscle O2 delivery resulting in exercise intolerance. Dietary nitrate supplementation increases skeletal muscle blood flow during exercise and may improve exercise capacity in a mouse model of sickle cell disease. We investigated the effects of dietary nitrate supplementation on exercise tolerance in a mouse model of sickle cell disease using the treadmill speed-duration relationship (critical speed). Mice with sickle cell disease provided with a dietary nitrate supplement had a critical speed not significantly different from healthy wild-type mice.

Optimization of combined measures of airway physiology and cardiovascular hemodynamics in mice.

Pulmonary hypertension may arise as a complication of chronic lung disease typically associated with tissue hypoxia, as well as infectious agents or injury eliciting a type 2 immune response. The onset of pulmonary hypertension in this setting (classified as Group 3) often complicates treatment and worsens prognosis of chronic lung disease. Chronic lung diseases such as chronic obstructive lung disease (COPD), emphysema, and interstitial lung fibrosis impair airflow and alter lung elastance in addition to affecting pulmonary vascular hemodynamics that may culminate in right ventricle dysfunction. To date, functional endpoints in murine models of chronic lung disease have typically been limited to separately measuring airway and lung parenchyma physiology. These approaches may be lengthy and require a large number of animals per experiment. Here, we provide a detailed protocol for combined assessment of airway physiology with cardiovascular hemodynamics in mice. Ultimately, a comprehensive overview of pulmonary function in murine models of injury and disease will facilitate the integration of studies of the airway and vascular biology necessary to understand underlying pathophysiology of Group 3 pulmonary hypertension.

An Hb-mediated circulating macrophage contributing to pulmonary vascular remodeling in sickle cell disease.

Circulating macrophages recruited to the lung contribute to pulmonary vascular remodeling in various forms of pulmonary hypertension (PH). In this study we investigated a macrophage phenotype characterized by intracellular iron accumulation and expression of antioxidant (HO-1), vasoactive (ET-1), and proinflammatory (IL-6) mediators observed in the lung tissue of deceased sickle cell disease (SCD) patients with diagnosed PH. To this end, we evaluated an established rat model of group 5 PH that is simultaneously exposed to free hemoglobin (Hb) and hypobaric hypoxia (HX). Here, we tested the hypothesis that pulmonary vascular remodeling observed in human SCD with concomitant PH could be replicated and mechanistically driven in our rat model by a similar macrophage phenotype with iron accumulation and expression of a similar mixture of antioxidant (HO-1), vasoactive (ET-1), and inflammatory (IL-6) proteins. Our data suggest phenotypic similarities between pulmonary perivascular macrophages in our rat model and human SCD with PH, indicating a potentially novel maladaptive immune response to concomitant bouts of Hb and HX exposure. Moreover, by knocking out circulating macrophages with gadolinium trichloride (GdCl3), the response to combined Hb and hypobaric HX was significantly attenuated in rats, suggesting a critical role for macrophages in the exacerbation of SCD PH.

Inactivation of Tsc2 in Abcg2 lineage-derived cells drives the appearance of polycystic lesions and fibrosis in the adult kidney.

Tuberous sclerosis complex 2 (TSC2), or tuberin, is a pivotal regulator of the mechanistic target of rapamycin signaling pathway that controls cell survival, proliferation, growth, and migration. Loss of Tsc2 function manifests in organ-specific consequences, the mechanisms of which remain incompletely understood. Recent single cell analysis of the kidney has identified ATP-binding cassette G2 (Abcg2) expression in renal proximal tubules of adult mice as well as a in a novel cell population. The impact in adult kidney of Tsc2 knockdown in the Abcg2-expressing lineage has not been evaluated. We engineered an inducible system in which expression of truncated Tsc2, lacking exons 36-37 with an intact 3' region and polycystin 1, is driven by Abcg2. Here, we demonstrate that selective expression of Tsc2fl36-37 in the Abcg2pos lineage drives recombination in proximal tubule epithelial and rare perivascular mesenchymal cells, which results in progressive proximal tubule injury, impaired kidney function, formation of cystic lesions, and fibrosis in adult mice. These data illustrate the critical importance of Tsc2 function in the Abcg2-expressing proximal tubule epithelium and mesenchyme during the development of cystic lesions and remodeling of kidney parenchyma.

Pre-clinical assessment of a water-in-fluorocarbon emulsion for the treatment of pulmonary vascular diseases.

Hypoxic pulmonary vasoconstriction (HPV) is a well-characterized vascular response to low oxygen pressures and is involved in life-threatening conditions such as high-altitude pulmonary edema (HAPE) and pulmonary arterial hypertension (PAH). While the efficacy of oral therapies can be affected by drug metabolism, or dose-limiting systemic toxicity, inhaled treatment via pressured metered dose inhalers (pMDI) may be an effective, nontoxic, practical alternative. We hypothesized that a stable water-in-perfluorooctyl bromide (PFOB) emulsion that provides solubility in common pMDI propellants, engineered for intrapulmonary delivery of pulmonary vasodilators, reverses HPV during acute hypoxia (HX). Male Sprague Dawley rats received two 10-min bouts of HX (13% O2) with 20 min of room air and drug application between exposures. Treatment groups: intrapulmonary delivery (PUL) of (1) saline; (2) ambrisentan in saline (0.1 mg/kg); (3) empty emulsion; (4) emulsion encapsulating ambrisentan or sodium nitrite (NaNO2) (0.1 and 0.5 mg/kg each); and intravenous (5) ambrisentan (0.1 mg/kg) or (6) NaNO2 (0.5 mg/kg). Neither PUL of saline or empty emulsion, nor infusions of drugs prevented pulmonary artery pressure (PAP) elevation (32.6 ± 3.2, 31.5 ± 1.2, 29.3 ± 1.8, and 30.2 ± 2.5 mmHg, respectively). In contrast, PUL of aqueous ambrisentan and both drug emulsions reduced PAP by 20-30% during HX, compared to controls. IL6 expression in bronchoalveolar lavage fluid and whole lung 24 h post-PUL did not differ among cohorts. We demonstrate proof-of-concept for delivering pulmonary vasodilators via aerosolized water-in-PFOB emulsion. This concept opens a potentially feasible and effective route of treating pulmonary vascular pathologies via pMDI.

Effects of living at moderate altitude on pulmonary vascular function and exercise capacity in mice with sickle cell anaemia.

KEY POINTS: Sickle cell disease (SCD) results in cardiopulmonary dysfunction, which may be exacerbated by prolonged exposure to environmental hypoxia. It is currently unknown whether exposure to mild and moderate altitude exacerbates SCD associated cardiopulmonary and systemic complications. Three months of exposure to mild (1609 m) and moderate (2438 m) altitude increased rates of haemolysis and right ventricular systolic pressures in mice with SCD compared to healthy wild-type cohorts and SCD mice at sea level. The haemodynamic changes in SCD mice that had lived at mild and moderate altitude were accompanied by changes in the balance between pulmonary vascular endothelial nitric oxide synthase and endothelin receptor expression and impaired exercise tolerance. These data demonstrate that chronic altitude exposure exacerbates the complications associated with SCD and provides pertinent information for the clinical counselling of SCD patients. ABSTRACT: Exposure to high altitude worsens symptoms and crises in patients with sickle cell disease (SCD). However, it remains unclear whether prolonged exposure to low barometric pressures exacerbates SCD aetiologies or impairs quality of life. We tested the hypothesis that, relative to wild-type (WT) mice, Berkley sickle cell mice (BERK-SS) residing at sea level, mild (1609 m) and moderate (2438 m) altitude would have a higher rate of haemolysis, impaired cardiac function and reduced exercise tolerance, and that the level of altitude would worsen these decrements. Following 3 months of altitude exposure, right ventricular systolic pressure was measured (solid-state transducer). In addition, the adaptive balance between pulmonary vascular endothelial nitric oxide synthase and endothelin was assessed in lung tissue to determine differences in pulmonary vascular adaptation and the speed/duration relationship (critical speed) was used to evaluate treadmill exercise tolerance. At all altitudes, BERK-SS mice had a significantly lower percentage haemocrit and higher total bilirubin and free haemoglobin concentration (P < 0.05 for all). right ventricular systolic pressures in BERK-SS were higher than WT at moderate altitude and also compared to BERK-SS at sea level (P < 0.05, for both). Critical speed was significantly lower in BERK-SS at mild and moderate altitude (P < 0.05). BERK-SS demonstrated exacerbated SCD complications and reduced exercise capacity associated with an increase in altitude. These results suggest that exposure to mild and moderate altitude enhances the progression of SCD in BERK-SS mice compared to healthy WT cohorts and BERK-SS mice at sea level and provides crucial information for the clinical counselling of SCD patients.

An Optimized Evans Blue Protocol to Assess Vascular Leak in the Mouse.

Vascular leak, or plasma extravasation, has a number of causes, and may be a serious consequence or symptom of an inflammatory response. This study may ultimately lead to new knowledge concerning the causes of or new ways to inhibit or treat plasma extravasation. It is important that researchers have the proper tools, including the best methods available, for studying plasma extravasation. In this article, we describe a protocol, using the Evans blue dye method, for assessing plasma extravasation in the organs of FVBN mice. This protocol is intentionally simple, to as great a degree as possible, but provides high quality data. Evans blue dye has been chosen primarily because it is easy for the average laboratory to use. We have used this protocol to provide evidence and support for the hypothesis that the enzyme neprilysin may protect the vasculature against plasma extravasation. However, this protocol may be experimentally used and easily adapted for use in other strains of mice or in other species, in many different organs or tissues, for studies which may involve other factors that are important in understanding, preventing, or treating plasma extravasation. This protocol has been extensively optimized and modified from existing protocols, and combines reliability, ease of use, economy, and general availability of materials and equipment, making this protocol superior for the average laboratory to use in quantifying plasma extravasation from organs.

Impact of cell-free hemoglobin on contracting skeletal muscle microvascular oxygen pressure dynamics.

Free hemoglobin (Hb) associated with hemolysis extravasates into vascular tissue and depletes nitric oxide (NO), which leads to impaired vascular function and could impair skeletal muscle metabolic control during exercise. We tested the hypothesis that: 1) free Hb would extravasate into skeletal muscle tissue, reducing the contracting skeletal muscle O2 delivery/O2 utilization ratio (microvascular PO2, PO2mv) to a similar extent as that observed following NO synthase (NOS) blockade, and 2) that the Hb scavenging protein haptoglobin (Hp) would prevent Hb extravasation and inhibit these skeletal muscle tissue effects. PO2mv was measured in eight rats (phosphorescence quenching) at rest and during 180 s of electrically induced (1-Hz) twitch spinotrapezius muscle contractions (experiment 1). A second group of seven rats was also used to investigate the effects of Hb + Hp (experiment 2). For both experiments, measurements were made: 1) during control conditions, 2) following a bolus infusion of either Hb (50 mg/kg) or Hb + Hp (50 mg/kg), and 3) following local superfusion of NG-nitro-l-arginine methyl ester (L-NAME; 10 mg/kg). Additional experiments were completed to visualize Hb extravasation into the muscular tissue using Click chemistry techniques. There were no significant differences in the PO2mv observed at rest for any condition in either experiment (p > 0.05 for all). In experiment 1, both Hb and L-NAME reduced the PO2mv significantly during the steady-state of muscle contractions when compared to control conditions with no differences between Hb and L-NAME (control: 24 ±â€¯1, Hb: 21 ±â€¯1, L-NAME: 20 ±â€¯1 mmHg, p < 0.05). In experiment 2, only L-NAME resulted in a significantly lower PO2mv during the steady-state of muscle contractions (control: 25 ± 1, Hb + Hp: 22 ± 2, L-NAME: 18 ± 1 mmHg, p < 0.05). Free Hb lowered the blood-myocyte O2 driving force to a level not significantly different from L-NAME. However, infusing Hb bound to Hp resulted in no significant differences in steady-state PO2mv during muscle contractions when compared to control. Surprisingly, we did not observe Hb accumulation in skeletal muscle tissue. Taken together these data suggests that free Hb impairs O2 delivery/utilization via a NO scavenging effect. Furthermore, the unchanged PO2mv steady-state observed following Hb + Hp further indicates that vascular compartmentalization of Hb by the scavenger protein haptoglobin may improve skeletal muscle metabolic control and potentially exercise tolerance in those afflicted with hemolytic diseases.

Protection against vascular leak in neprilysin transgenic mice with complex overexpression pattern.

Neprilysin (NEP) is a cell surface metallopeptidase found in many tissues. Based mostly on pharmacological manipulations, NEP has been thought to protect blood vessels from plasma extravasation. We have suggested that NEP may protect against pulmonary vascular injury. However, these prior studies did not utilize mice which overexpress NEP. The aims of the present investigation were to develop and characterize doubly transgenic (DT) mice that overexpress NEP universally and conditionally, and to investigate the protective effect that overexpressed NEP may have against plasma extravasation in the vasculature. The duodenum, which is often used to assess vascular permeability, and in which the NEP protein was overexpressed in our DT mice two-fold, was selected as our experimental preparation. We found that substance P-induced plasma extravasation was decreased substantially (3.5-fold) in the duodenums of our doxycycline-treated DT mice, giving independent evidence of NEP's protective effects against plasma extravasation. Transgenic lung NEP protein was not stably expressed in the DT mice, so we were not able to test the effect of NEP overexpression in the lung. Although initially overexpressed nearly nine-fold at that site, pulmonary NEP protein overexpression eventually dissipated. Surprisingly, at a time when there was no lung transgenic NEP protein overexpression, lung NEP mRNA expression was still increased 23-fold, indicating that the expression defect probably is not transcriptional. These studies help to characterize our complex transgenic model of NEP overexpression and further demonstrate NEP's protective effects against plasma extravasation.

Intrauterine endotoxin-induced impairs pulmonary vascular function and right ventricular performance in infant rats and improvement with early vitamin D therapy.

High pulmonary vascular resistance (PVR), proximal pulmonary artery (PA) impedance, and right ventricular (RV) afterload due to remodeling contribute to the pathogenesis and severity of pulmonary hypertension (PH). Intra-amniotic exposure to endotoxin (ETX) causes sustained PH and high mortality in rat pups at birth, which are associated with impaired vascular growth and RV hypertrophy in survivors. Treatment of ETX-exposed pups with antenatal vitamin D (vit D) improves survival and lung growth, but the effects of ETX exposure on RV-PA coupling in the neonatal lung are unknown. We hypothesized that intrauterine ETX impairs RV-PA coupling through sustained abnormalities of PA stiffening and RV performance that are attenuated with vit D therapy. Fetal rats were exposed to intra-amniotic injections of ETX, ETX+vit D, or saline at 20 days gestation (term = 22 days). At postnatal day 14, pups had pressure-volume measurements of the RV and isolated proximal PA, respectively. Lung homogenates were assayed for extracellular matrix (ECM) composition by Western blot. We found that ETX lungs contain decreased α-elastin, lysyl oxidase, collagen I, and collagen III proteins (P < 0.05) compared control and ETX+vit D lungs. ETX-exposed animals have increased RV mechanical stroke work (P < 0.05 vs. control and ETX+vit D) and elastic potential energy (P < 0.05 vs. control and ETX+vit D). Mechanical stiffness and ECM remodeling are increased in the PA (P < 0.05 vs. control and ETX+vit D). We conclude that intrauterine exposure of fetal rats to ETX during late gestation causes persistent impairment of RV-PA coupling throughout infancy that can be prevented with early vit D treatment.

Obesity-related pulmonary arterial hypertension in rats correlates with increased circulating inflammatory cytokines and lipids and with oxidant damage in the arterial wall but not with hypoxia.

Obesity is causally linked to a number of comorbidities, including cardiovascular disease, diabetes, renal dysfunction, and cancer. Obesity has also been linked to pulmonary disorders, including pulmonary arterial hypertension (PAH). It was long believed that obesity-related PAH was the result of hypoventilation and hypoxia due to the increased mechanical load of excess body fat. However, in recent years it has been proposed that the metabolic and inflammatory disturbances of obesity may also play a role in the development of PAH. To determine whether PAH develops in obese rats in the absence of hypoxia, we assessed pulmonary hemodynamics and pulmonary artery (PA) structure in the diet-resistant/diet-induced obesity (DR/DIO) and Zucker lean/fatty rat models. We found that high-fat feeding (DR/DIO) or overfeeding (Zucker) elicited PA remodeling, neomuscularization of distal arterioles, and elevated PA pressure, accompanied by right ventricular (RV) hypertrophy. PA thickening and distal neomuscularization were also observed in DIO rats on a low-fat diet. No evidence of hypoventilation or chronic hypoxia was detected in either model, nor was there a correlation between blood glucose or insulin levels and PAH. However, circulating inflammatory cytokine levels were increased with high-fat feeding or calorie overload, and hyperlipidemia and oxidant damage in the PA wall correlated with PAH in the DR/DIO model. We conclude that hyperlipidemia and peripheral inflammation correlate with the development of PAH in obese subjects. Obesity-related inflammation may predispose to PAH even in the absence of hypoxia.

Cytoskeletal defects in Bmpr2-associated pulmonary arterial hypertension.

The heritable form of pulmonary arterial hypertension (PAH) is typically caused by a mutation in bone morphogenic protein receptor type 2 (BMPR2), and mice expressing Bmpr2 mutations develop PAH with features similar to human disease. BMPR2 is known to interact with the cytoskeleton, and human array studies in PAH patients confirm alterations in cytoskeletal pathways. The goal of this study was to evaluate cytoskeletal defects in BMPR2-associated PAH. Expression arrays on our Bmpr2 mutant mouse lungs revealed cytoskeletal defects as a prominent molecular consequence of universal expression of a Bmpr2 mutation (Rosa26-Bmpr2(R899X)). Pulmonary microvascular endothelial cells cultured from these mice have histological and functional cytoskeletal defects. Stable transfection of different BMPR2 mutations into pulmonary microvascular endothelial cells revealed that cytoskeletal defects are common to multiple BMPR2 mutations and are associated with activation of the Rho GTPase, Rac1. Rac1 defects are corrected in cell culture and in vivo through administration of exogenous recombinant human angiotensin-converting enzyme 2 (rhACE2). rhACE2 reverses 77% of gene expression changes in Rosa26-Bmpr2(R899X) transgenic mice, in particular, correcting defects in cytoskeletal function. Administration of rhACE2 to Rosa26-Bmpr2(R899X) mice with established PAH normalizes pulmonary pressures. Together, these findings suggest that cytoskeletal function is central to the development of BMPR2-associated PAH and that intervention against cytoskeletal defects may reverse established disease.