Functional, structural and molecular characterization of a new mitral valve prolapse animal model: the FLNA-P637Q KI rat

Introduction

Mitral Valve Prolapse (MVP) affects 3% of the population and is characterized by a heterogeneous mitral leaflet remodeling. The pathophysiological mechanisms involved in MVP development are not fully understood, the only therapeutic option remains the surgical valve replacement. We previously identified FLNA as the first gene causing MVP and recently generated a unique knock-in rat model for the FLNA-P637Q mutation that now paves the road to study the molecular mechanisms involved in MVP development.

Purpose

The aim of our study was to characterize the morphological, functional and molecular expression of the valvular disease in our unique KI rat model.

Methods

5 wild-type (WT) and 10 KI rats were evaluated at 3, 6 and 13 weeks. Comprehensive 2D echocardiography was performed to determine valve function and morphology. 3D quantitative analysis of the mitral valve (MV) remodelling was done using micro computed tomography (microCT). MV tissue composition was analysed based on histological and immunohistochemistry. Transcriptomic comparison was performed using RNA-sequencing approach.

Results

Based on the qualitative echocardiographic assessment of the valve, a high genotype-phenotype concordance was established for WT and KI animals (100%, 93% and 100% matching for each time points). The anterior leaflet was longer in KI comparatively to WT rats (+12 to +14% increase at all time points (p<0.01)). Increased lengths corroborated the increased leaflets volume assessed by microCT analysis (+20 to +58% in KI compared to WT all time points (p<0.05)). Histological and immunohistological analyses (leaflet's thickening, hypercellularity, proteoglycans accumulation without calcification) pointed out towards a myxomatous valve disease. The differential gene expression profile established by RNAseq analysis revealed that inflammation, epithelial cell migration or mechanical transduction pathways were specifically activated in KI valves. Genes such as Itgb2 (+1.30x), Ccl12 (+2.44x), Ccl2 (+1.79x), Ccl28 (+1.53x), Ccl7 (+2.95x), S100a8 (+8.40x) or S100a9 (+2.67x) were significantly upregulated in the GO:0060326 “cell chemotaxis”, p=2.31x10–5. In the GO:0043542 “endothelial cell migration”, p=1.59x10–6, Klf4 (+1.31x) and Tgfbr1 (+1.21x) were upregulated. Genes part of the GO:0048771 “tissue remodelling” (p=5.52x10–5) were also found upregulated.

Conclusion

These results establish that our unique KI FLNA-P637Q rat develops a myxomatous MV dystrophy comparable to the one described in MVP patients and thus constitutes a pertinent model to study the pathophysiological molecular mechanisms associated with MVP development. Our results point to molecular pathways including inflammation and epithelial activation, which constitute potential therapeutic targets.

Funding Acknowledgement

Type of funding sources: Public Institution(s). Main funding source(s): Connect Talent

P3697A reappraisal of bioprosthetic aortic valve failure related to structural valve degeneration

Background

Structural valve degeneration (SVD) remains a major complication of aortic bioprostheses.

Purpose

We aimed to assess the mode of SVD leading to bioprosthetic aortic valve failure (BVF) in a large series of patients.

Methods

Between 2010 and 2017, we prospectively enrolled 261 consecutive patients with BVF related to SVD. All patients underwent a clinical work-up. Explanted bioprostheses were analysed for assessing the mechanism of SVD.

Results

The delay from surgery to SVD diagnosis was 8.5±3.3 (1.7 to 21.4) years, 10 years after exclusion of a specific type of bioprosthesis. Of the 261 SVD patients, 150 (57%) had mainly a stenotic type, and 111 (43%) a regurgitant type. In regurgitant SVD bioprosthesis was more frequently porcine (19 vs 7%, P=0.002), prosthesis diameter was larger (23.2±2.5 vs 21.6±1.9 mm; P<0.0001), severe mismatch was less frequent (6 vs 17%, P=0.005), cardiovascular risk factors and especially diabetes, obesity and hypertension were less frequent, patients were more often in NYHA class 3–4 (64 vs 49%; p=0.015), Nt-pro BNP was significantly higher (P<0.0001), and diuretic treatment was more frequent (73 vs 61%, P=0.04). Bioprostheses were explanted during redo surgery in 112 (43%) patients. Of these 112 bioprostheses, moderate to severe calcifications were present in 94 (83.9%) and was the main cause of either stenotic (n=64, 57.1%) or regurgitant SVD. A cusp tear (n=46) accounted for 41.1% of the explanted SVD. A perforation, a recent thrombus or a delamination process were occasionally identified. Structural degeneration developed with minimal calcification in 18 (16.1%) bioprostheses.

Conclusion

Structural valve degeneration remains a matter of concern in current practice with a mean delay of 8 to 10 years after surgery. Beside classical SVD with extensive calcification process other types of SVD can be observed with minimal calcification.

Analysis of brain biocompatibility of drug-releasing biodegradable microspheres by scanning and transmission electron microscopy

OBJECT

Stereotactically guided implantation of biodegradable microspheres is a promising strategy for delivery of neurotrophic factors in a precise and spatially defined brain area. The goal in this study was to show the biocompatibility of poly(D,L,lactide-co-glycolide) microspheres with brain tissue at the ultrastructural level and to analyze the three-dimensional (3D) ultrastructure after intrastriatal implantation of these microparticles.

METHODS

Scanning and transmission electron microscopy were used to study the microspheres and their environment after implantation in an inert material (gelatin) and in the rat striatum. Observations were made at different time periods, ranging from 24 hours to 2 months postimplantation.

CONCLUSIONS

The progressive degradation of the microspheres, with vacuolization, deformation, and shrinkage, was well visualized. This degradation was identical in microspheres implanted in the inert material and in the rat brain tissue, independent of the presence of macrophages. The studies preformed in the striatum permitted the authors to demonstrate the structural integrity of axons in contact with microspheres, confirming the biocompatibility of the polymer. Furthermore, scanning electron microscopy showed the preservation of the 3D ultrastructure of the striatum around the microparticles. These microparticles, which can be stereotactically implanted in functional areas of the brain and can release neurotrophic factors, could represent, for some indications, an alternative to gene therapy.

Signaling of type II oncostatin M receptor

Oncostatin M (OSM) mediates its bioactivities through two different heterodimer receptors. They both involve the gp130-transducing receptor, which dimerizes with either leukemia inhibitory receptor beta or with OSM receptor beta (OSMRbeta) to generate, respectively, type I and type II OSM receptors. Co-precipitation of gp130-associated proteins, flow cytometry, polymerase chain reaction, and tyrosine phosphorylation analyses allowed the characterization of both types of OSM receptors expressed on the surface of different cell lines. It also allowed the detection of a large size protein, p250, that specifically associates to the type II OSM receptor components and that is tyrosine-phosphorylated after the activation peak of the gp130.OSMRbeta heterocomplex. The restricted expression of type I OSM receptor by the JAR choriocarcinoma cell line, and type II receptor by the A375 melanoma cell line, permitted the characterization of their signaling machineries. Both type I and type II OSM receptors activated Jak1, Jak2, and Tyk2 receptor-associated tyrosine kinases. The information is next relayed to the nucleus by the STAT3 transcriptional activator, which is recruited by both types of OSM receptors. In addition, STAT5b was specifically activated through the gp130.OSMRbeta type II heterocomplex. The signaling pathway differences observed between the common type I LIF/OSM receptor and the specific type II OSM receptor might explain some of the bioactivities specifically displayed by OSM.