In a monocrotaline (MCT) induced-pulmonary arterial hypertension (PAH) rat animal model, the dynamic stress-strain relation was investigated in the circumferential and axial directions using a linear elastic response model within the quasi-linear viscoelasticity theory framework. Right and left pulmonary arterial segments (RPA and LPA) were mechanically tested in a tubular biaxial device at the early stage (1 week post-MCT treatment) and at the advanced stage of the disease (4 weeks post-MCT treatment). The vessels were tested circumferentially at the in vivo axial length with matching in vivo measured pressure ranges. Subsequently, the vessels were tested axially at the mean pulmonary arterial pressure by stretching them from in vivo plus 5% of their length. Parameter estimation showed that the LPA and RPA remodel at different rates: axially, both vessels decreased in Young's modulus at the early stage of the disease, and increased at the advanced disease stage. Circumferentially, the Young's modulus increased in advanced PAH, but it was only significant in the RPA. The damping properties also changed in PAH; in the LPA relaxation times decreased continuously as the disease progressed, while in the RPA they initially increased and then decreased. Our modeling efforts were corroborated by the restructuring organization of the fibers imaged under multiphoton microscopy, where the collagen fibers become strongly aligned to the 45 deg angle in the RPA from an uncrimped and randomly organized state. Additionally, collagen content increased almost 10% in the RPA from the placebo to advanced PAH.

While pulmonary arterial hypertension (PAH) leads to right ventricle (RV) hypertrophy and structural remodeling, the relative contributions of changes in myocardial geometric and mechanical properties to systolic and diastolic chamber dysfunction and their time courses remain unknown. Using measurements of RV hemodynamic and morphological changes over 10 weeks in a male rat model of PAH and a mathematical model of RV mechanics, we discriminated the contributions of RV geometric remodeling and alterations of myocardial material properties to changes in systolic and diastolic chamber function. Significant and rapid RV hypertrophic wall thickening was sufficient to stabilize ejection fraction in response to increased pulmonary arterial pressure by week 4 without significant changes in systolic myofilament activation. After week 4, RV end-diastolic pressure increased significantly with no corresponding changes in end-diastolic volume. Significant RV diastolic chamber stiffening by week 5 was not explained by RV hypertrophy. Instead, model analysis showed that the increases in RV end-diastolic chamber stiffness were entirely attributable to increased resting myocardial material stiffness that was not associated with significant myocardial fibrosis or changes in myocardial collagen content or type. These findings suggest that whereas systolic volume in this model of RV pressure overload is stabilized by early RV hypertrophy, diastolic dilation is prevented by subsequent resting myocardial stiffening.

Pulmonary arterial hypertension (PAH) commonly leads to right ventricular (RV) hypertrophy and fibrosis that affect the mechanical properties of the RV myocardium (MYO). To investigate the effects of PAH on the mechanics of the RV MYO and extracellular matrix (ECM), we compared RV wall samples, isolated from rats in which PAH was induced using the SuHx protocol, with samples from control animals before and after the tissues were decellularized. Planar biaxial mechanical testing, a technique first adapted to living soft biological tissues by Fung, was performed on intact and decellularized samples. Fung's anisotropic exponential strain energy function fitted the full range of biaxial test results with high fidelity in control and PAH samples both before and after they were decellularized. Mean RV myocardial apex-to-outflow tract and circumferential stresses during equibiaxial strain were significantly greater in PAH than control samples. Mean RV ECM circumferential but not apex-to-outflow tract stresses during equibiaxial strain were significantly greater in the PAH than control group. The ratio of ECM to myocardial stresses at matched strains did not change significantly between groups. Circumferential stresses were significantly higher than apex-to-outflow tract stresses for all groups. These findings confirm the predictions of a mathematical model based on changes in RV hemodynamics and morphology in rat PAH, and may provide a foundation for a new constitutive analysis of the contributions of ECM remodeling to changes in RV filling properties during PAH.

Pulmonary arterial hypertension (PAH) is a disease characterized by elevated blood pressure (mean pulmonary arterial pressure above 25 mmHg. Remodeling of pulmonary arteries due to this elevated blood pressure compromises their normal physiological function. Our previous work showed that the right pulmonary artery significantly stiffens circumferentially in PAH and collagen fibers become engaged and significantly aligned in the medial layer (Pursell et al 2016). To better understand the changes in tissue mechanical response, here we explore the distributions of collagen orientation and tortuosity through the vessel wall. Methods To induce PAH, four male Sprague‐Dawley rats were injected with 60 mg/kg monocrotaline. Once PAH was established (4 weeks post‐injection), pulmonary arteries were harvested, and collagen imaged via multiphoton microscopy. A custom MATLAB code was then used to determine collagen fiber orientation and tortuosity. Results MPM images of collagen fibers from the intima, media, and adventitia of normotensive and hypertensive rat RPAs were traced with our custom MATLAB code. In the hypertensive animals, fiber direction and tortuosity varied more between vascular wall layers than those of normotensive animals. Conclusions While our previous study only examined the medial layer, this study determined that fiber distribution varies throughout the vessel wall. This will significantly affect the mechanics or behavior of pulmonary vessels. Therefore, future studies will need to incorporate collagen structures from multiple vessel layers to better understand the relationship between vascular remodeling and mechanics.

The protocol to purify and fluorescently label proteins typically includes lengthy purification steps and stochastically governed labelling methods. When multi-labelled proteins are required, poor yields, waste of valuable reagents, and lengthy sample preparation times are generally inevitable. In addition, many fluorophore combinations are incompatible, which makes the task of efficiently producing multi-labelled, high-purity proteins very difficult.Here, we describe a novel method that enables the preparation of purified and labelled proteins in only a few hours. Our protocol gives high yield of the desired protein product using minimal mutations, high specificity of labelling, and ease of chemically orthogonal attachment of other fluorescent probes in later steps. This technique takes advantage of native chemical ligation in a single-step, in one liquid-chromatography column, by the addition of one reagent, with the ability to purify and label any protein using any desired fluorescent probe. We demonstrate the efficacy of this method on the eukaryotic initiation factor 4E binding partner 2 (4E-BP2).This translational regulation protein is intrinsically disordered and is implicated in autism and neurodegenerative diseases. Proof-of-principle biophysical experiments such as Förster resonance energy transfer (FRET) and fluorescence correlation spectroscopy (FCS) were performed on the 4E-BP2 protein labelled using our new method. The results highlight the quality of the novel sample preparation technique, as well as help reveal new dynamic information about the disordered C-terminal region of this protein.

have been shown to be involved in neurological inflammation and pain sensation. Whether the two receptors assemble exclusively as homotrimers or also as heterotrimers is still a matter of debate. We investigated the expression of P2X receptors in BV-2 microglia cells applying the whole-cell voltage-clamp technique. We dissected P2X4 and P2X7 receptor-mediated current components by using specific P2X4 and P2X7 receptor blockers and by their characteristic current kinetics. We found that P2X4 and P2X7 receptors are activated independently from each other, indicating that P2X4/P2X7 heteromers are not of functional significance in these cells. The pro-inflammatory mediators lipopolysaccharide and interferon g, if applied in combination, upregulated P2X4, but not P2X7 receptor-dependent current components also arguing against phenotypically relevant heteromerization of P2X4 and P2X7 receptor subunits.