Gerard H. Daly

Mechanically Unloading the Left Ventricle Before Coronary Reperfusion Reduces Left Ventricular Wall Stress and Myocardial Infarct Size

Background— Ischemia/reperfusion injury worsens infarct size, a major determinant of morbidity and mortality after acute myocardial infarction (MI). We tested the hypothesis that reducing left ventricular wall stress with a percutaneous left atrial-to-femoral artery centrifugal bypass system while delaying coronary reperfusion limits myocardial injury in a model of acute MI. Methods and Results— MI was induced by balloon occlusion of the left anterior descending artery in adult male swine. In the MI group (n=4), 120 minutes of left anterior descending artery occlusion was followed by 120 minutes of reperfusion without mechanical support. In the mechanically supported group (MI+unload; n=4), percutaneous left atrial–to–femoral artery bypass was initiated after 120 minutes of ischemia, and left anterior descending artery occlusion was prolonged for an additional 30 minutes, followed by 120 minutes of reperfusion with device support. All animals were euthanized after reperfusion, and infarct size was quantified by triphenyltetrazolium chloride staining. Compared with baseline, mean left ventricular wall stress and stroke work were not changed at any point in the MI group but were decreased after reperfusion in the MI+unload group (mean left ventricular wall stress, 44 658 versus 22 963 dynes/cm2; stroke work, 2823 versus 655 mm Hg·mL, MI versus MI+unload). Phosphorylation of reperfusion injury salvage kinase pathway proteins from noninfarcted left ventricular tissue was unchanged in the MI group but was increased in the MI+unload group. Compared with the MI group, total infarct size was reduced in the MI+unload group (49% versus 28%, MI versus MI+unload). Conclusions— These data support that first unloading the left ventricle despite delaying coronary reperfusion during an acute MI reduces myocardial injury.

Defective Formation of the Inner Limiting Membrane in Laminin β2- and γ3-Null Mice Produces Retinal Dysplasia

PURPOSE Retinal basement membranes (BMs) serve as attachment sites for retinal pigment epithelial cells on Bruchs membrane and Müller cells (MCs) on the inner limiting membrane (ILM), providing polarity cues to adherent cells. The beta2 and gamma3 chains of laminin are key components of retinal BMs throughout development, suggesting that they play key roles in retinal histogenesis. This study was conducted to analyze how the absence of both beta2- and gamma3-containing laminins affects retinal development. Methods. The function of the beta2- and gamma3-containing laminins was tested by producing a compound deletion of both the beta2 and the gamma3 laminin genes in the mouse and assaying the effect on postnatal retinal development by using anatomic and electrophysiological techniques. Results. Despite the widespread expression of beta2 and gamma3 laminin chains in wild-type (WT) retinal BMs, the development of only one, the ILM, was disrupted. The postnatal consequence of the ILM disruption was an alteration of MC attachment and a resultant disruption in MC apical-basal polarity, which culminated in retinal dysplasia. Of importance, although their density was altered, retinal cell fates were unaffected. The laminin mutants have a markedly decreased visual function, resulting in part from photoreceptor dysgenesis. Conclusions. These data suggest that beta2 and gamma3 laminin isoforms are critical for the formation and stability of the ILM. These data also suggest that attachment of the MC to the ILM provides important polarity cues to the MC and for postnatal retinal histogenesis.

The γ3 Chain of Laminin is Widely But Differentially Expressed in Murine Basement Membranes: Expression and Functional Studies

Laminins are heterotrimeric extracellular glycoproteins found in, but not confined to, basement membranes (BMs). They are important components in formation of the molecular networks of BMs as well as in cell polarity, cell differentiation and tissue morphogenesis. Each laminin is composed by an α, a β and a γ chain. Previous studies have shown that the γ3 chain is partnered with either the β1 chain (in placenta) or β2 chain (in the CNS) (Libby et al., 2000). Several studies, including our own, suggested that the γ3 chain is expressed in both apical and basal compartments (Koch et al., 1999; Gersdorff et al., 2005; Yan and Cheng, 2006). This study investigates the expression pattern of the γ3 chain in mouse. We developed three new γ3-reactive antibodies, and we show that the γ3 chain is present in BMs. The distribution pattern is considerably more restricted than that of the γ1 chain and within any tissue there is differential deposition into BM compartments. This is particularly true in the retina and brain, where γ3 is uniquely expressed in a subset of the vascular basement membranes and the pial surface. We used conventional genetic ablation techniques to remove the γ3 chain in mice; unlike other laminin null mice (α5, β2, γ1 nulls), these mice live a normal lifespan and have only minor abnormalities, the most striking of which are ectopic granule cells in the cerebellum and an apparent increase in capillary branching in the outer retina. These data support the suggestion that the γ3 chain is deposited in BMs and contributes some unique properties to their function, particularly in the nervous system.

Biventricular Remodeling in Murine Models of Right Ventricular Pressure Overload

Right ventricular (RV) failure is a major cause of mortality in acute or chronic lung disease and left heart failure. The objective of this study was to demonstrate a percutaneous approach to study biventricular hemodynamics in murine models of primary and secondary RV pressure overload (RVPO) and further explore biventricular expression of two key proteins that regulate cardiac remodeling: calcineurin and transforming growth factor beta 1 (TGFβ1). Methods Adult, male mice underwent constriction of the pulmonary artery or thoracic aorta as models of primary and secondary RVPO, respectively. Conductance catheterization was performed followed by tissue analysis for changes in myocyte hypertrophy and fibrosis. Results Both primary and secondary RVPO decreased biventricular stroke work however RV instantaneous peak pressure (dP/dtmax) and end-systolic elastance (Ees) were preserved in both groups compared to controls. In contrast, left ventricular (LV) dP/dtmax and LV-Ees were unchanged by primary, but reduced in the secondary RVPO group. The ratio of RV:LV ventriculo-arterial coupling was increased in primary and reduced in secondary RVPO. Primary and secondary RVPO increased RV mass, while LV mass decreased in primary and increased in the secondary RVPO groups. RV fibrosis and hypertrophy were increased in both groups, while LV fibrosis and hypertrophy were increased in secondary RVPO only. RV calcineurin expression was increased in both groups, while LV expression increased in secondary RVPO only. Biventricular TGFβ1 expression was increased in both groups. Conclusion These data identify distinct effects of primary and secondary RVPO on biventricular structure, function, and expression of key remodeling pathways.

Reducing Endoglin Activity Limits Calcineurin and TRPC-6 Expression and Improves Survival in a Mouse Model of Right Ventricular Pressure Overload

Background Right ventricular (RV) failure is a major cause of mortality worldwide and is often a consequence of RV pressure overload (RVPO). Endoglin is a coreceptor for the profibrogenic cytokine, transforming growth factor beta 1 (TGF‐β1). TGF‐β1 signaling by the canonical transient receptor protein channel 6 (TRPC‐6) was recently reported to stimulate calcineurin‐mediated myofibroblast transformation, a critical component of cardiac fibrosis. We hypothesized that reduced activity of the TGF‐β1 coreceptor, endoglin, limits RV calcineurin expression and improves survival in RVPO. Methods and Results We first demonstrate that endoglin is required for TGF‐β1‐mediated calcineurin/TRPC‐6 expression and up‐regulation of alpha‐smooth muscle antigen (α‐SMA), a marker of myofibroblast transformation, in human RV fibroblasts. Using endoglin haploinsufficient mice (Eng+/−) we show that reduced endoglin activity preserves RV function, limits RV fibrosis, and attenuates activation of the calcineurin/TRPC‐6/α‐SMA pathway in a model of angio‐obliterative pulmonary hypertension. Next, using Eng+/− mice or a neutralizing antibody (Ab) against endoglin (N‐Eng) in wild‐type mice, we show that reduced endoglin activity improves survival and attenuates RV fibrosis in models of RVPO induced by pulmonary artery constriction. To explore the utility of targeting endoglin, we observed a reversal of RV fibrosis and calcineurin levels in wild‐type mice treated with a N‐Eng Ab, compared to an immunoglobulin G control. Conclusion These data establish endoglin as a regulator of TGF‐β1 signaling by calcineurin and TRPC‐6 in the RV and identify it as a potential therapeutic target to limit RV fibrosis and improve survival in RVPO, a common cause of death in cardiac and pulmonary disease.