MarioHeart: Novel In-Vitro Flow Model for Testing Heart Valve Prostheses and Anticoagulant Therapies.

Mechanical heart valve (MHV) prostheses present a risk of thromboembolic complications despite antithrombotic therapy. Further steps in the development of more hemocompatible MHVs and new anticoagulants are impeded due to the lack of adequate in-vitro models. With the development of a novel in-vitro model (MarioHeart), a pulsatile flow similar to the arterial circulation is emulated. The MarioHeart design owns unique features as 1) a single MHV within a torus with low surface/volume ratio, 2) a closed loop system, and 3) a dedicated external control system driving the oscillating rotational motion of the torus. For verification purposes, a blood analog fluid seeded with particles was used to assess fluid velocity and flow rate using a speckle tracking method on high-speed video recordings of the rotating model. The flow rate resembled the physiological flow rate in the aortic root, in both shape and amplitude. Additional in-vitro runs with porcine blood showed thrombi on the MHV associated with the suture ring, which is similar to the in-vivo situation. MarioHeart is a simple design which induces well-defined fluid dynamics resulting in physiologically nonturbulent flow without stasis of the blood. MarioHeart seems suitable for testing the thrombogenicity of MHVs and the potential of new anticoagulants.

Aortic flow below and visceral circulation during aortic counterpulsation: Evaluation of an in vitro model.

INTRODUCTION: This study aimed to test a computer-driven cardiovascular model for the evaluation of the visceral flow during intra-aortic balloon pump (IABP) assistance. METHODS: The model includes a systemic and pulmonary circulation as well as a heart contraction model. The straight polyurethane tube aorta had a single visceral while four windkessel components mimicked resistance compliance of the brachiocephalic, renal and sub-mesenteric, pulmonary, and systemic circulation. Twelve flow probes were placed in the circuit to measure pressures and flows with the IABP on and off. RESULTS: With the balloon off, the meantime to reach the steady state was 48 ± 16 s; with the balloon on, this figure was 178 ± 20 s. The stability of pressure and flow signals was obtained after 72 ± 11 min. The number of cycles of stability of the system was 93 [86-103]. Measurements were reliable either with samples of 10 or 20 beats. Bland Altman method demonstrated the reliability of measurements. Finally, all measurements were comparable to published in vivo data. CONCLUSION: The presented mock circulation was reliable and gave values with high accuracy both at baseline and during mechanical assistance. This system allows evaluation of the mesenteric flow during IABP, under different clinical/hemodynamic conditions. Nonetheless, its translational potential needs to be further evaluated.

Fission yeast Cdk7 controls gene expression through both its CAK and C-terminal domain kinase activities.

Cyclin-dependent kinase (Cdk) activation and RNA polymerase II transcription are linked by the Cdk7 kinase, which phosphorylates Cdks as a trimeric Cdk-activating kinase (CAK) complex, and serine 5 within the polymerase II (Pol II) C-terminal domain (CTD) as transcription factor TFIIH-bound CAK. However, the physiological importance of integrating these processes is not understood. Besides the Cdk7 ortholog Mcs6, fission yeast possesses a second CAK, Csk1. The two enzymes have been proposed to act redundantly to activate Cdc2. Using an improved analogue-sensitive Mcs6-as kinase, we show that Csk1 is not a relevant CAK for Cdc2. Further analyses revealed that Csk1 lacks a 20-amino-acid sequence required for its budding yeast counterpart, Cak1, to bind Cdc2. Transcriptome profiling of the Mcs6-as mutant in the presence or absence of the budding yeast Cak1 kinase, in order to uncouple the CTD kinase and CAK activities of Mcs6, revealed an unanticipated role of the CAK branch in the transcriptional control of the cluster of genes implicated in ribosome biogenesis and cell growth. The analysis of a Cdc2 CAK site mutant confirmed these data. Our data show that the Cdk7 kinase modulates transcription through its well-described RNA Pol II CTD kinase activity and also through the Cdc2-activating kinase activity.

A protein domain-based interactome network for C. elegans early embryogenesis.

Many protein-protein interactions are mediated through independently folding modular domains. Proteome-wide efforts to model protein-protein interaction or "interactome" networks have largely ignored this modular organization of proteins. We developed an experimental strategy to efficiently identify interaction domains and generated a domain-based interactome network for proteins involved in C. elegans early-embryonic cell divisions. Minimal interacting regions were identified for over 200 proteins, providing important information on their domain organization. Furthermore, our approach increased the sensitivity of the two-hybrid system, resulting in a more complete interactome network. This interactome modeling strategy revealed insights into C. elegans centrosome function and is applicable to other biological processes in this and other organisms.