Verifying the Accuracy of Hemodynamic Analysis Using High Spatial Resolution 3D Phase-contrast MR Imaging on a 7T MR System: Comparison with a 3T System.

PURPOSE: Hemodynamics is important in the initiation, growth, and rupture of intracranial aneurysms. Since intracranial aneurysms are small, a high-field MR system with high spatial resolution and high SNR is desirable for this hemodynamic analysis. The purpose of this study was to investigate whether the accuracy of MR fluid dynamic (MRFD) results based on 3D phase-contrast MR (3D PC MR, non-electrocardiogram[ECG]-gated 4D Flow MRI) data from a human cerebrovascular phantom and human healthy subjects obtained by a 7T MR system was superior to those by a 3T MR system. METHODS: 3D PC MR and 3D time of flight MR angiography (3D TOF MRA) imaging were performed on a 3T MR system and a 7T MR system for a human cerebrovascular phantom and 10 healthy human subjects, and MRFD analysis was performed using these data. The MRFD results from each MR system were then compared with the following items based on the computational fluid dynamics (CFD) results: 3D velocity vector field; correlation coefficient (R), angular similarity index (ASI), and magnitude similarity index (MSI) of blood flow velocity vectors. RESULTS: In the MRFD results of 3D velocity vectors of the cerebrovascular phantom, noise-like vectors were observed near the vascular wall on the 3T MR system, but no noise was observed on the 7T MR system, showing results similar to those of CFD. In the MRFD results of the cerebrovascular phantom and healthy subjects, the correlation coefficients R, ASI, and MSI of the 7T MR system were higher than those of the 3T MR system, and ASI and MSI of healthy human subjects were significantly different between the two systems. CONCLUSIONS: The accuracy of high spatial resolution MRFD using the 7T MR system exceeded that of the 3T MR system.

A two-step screening to optimize the signal response of an auto-fluorescent protein-based biosensor.

Auto-fluorescent protein (AFP)-based biosensors transduce the structural change in their embedded recognition modules induced by recognition/reaction events to fluorescence signal changes of AFP. The lack of detailed structural information on the recognition module often makes it difficult to optimize AFP-based biosensors. To enhance the signal response derived from detecting the putative structural change in the nitric oxide (NO)-sensing segment of transient receptor potential canonical 5 (TRPC5) fused to enhanced green fluorescent protein (EGFP), EGFP-TRPC5, a facile two-step screening strategy, in silico first and in vitro second, was applied to variants of EGFP-TRPC5 deletion-mutated within the recognition module. In in silico screening, the structural changes of the recognition modules were evaluated as root-mean-square-deviation (RMSD) values, and 10 candidates were efficiently selected from 47 derivatives. Through in vitro screening, four mutants were identified that showed a larger change in signal response than the parent EGFP-TRPC5. One mutant in particular, 551-575, showed four times larger change upon reaction with NO and H2O2. Furthermore, mutant 551-575 also showed a signal response upon reaction with H2O2 in mammalian HEK293 cells, indicating that the mutant has the potential to be applied as a biosensor for cell measurement. Therefore, this two-step screening method effectively allows the selection of AFP-based biosensors with sufficiently enhanced signal responses for application in mammalian cells.

Fluorescence detection of the nitric oxide-induced structural change at the putative nitric oxide sensing segment of TRPC5.

The plausible nitric oxide (NO)-sensing module of TRPC5 was incorporated in a enhanced green fluorescent protein (EGFP) to evaluate its conformational change as an optical response upon the reaction with NO. Two cysteine residues located in the NO-sensing module have been proposed to form a disulfide bond through S-nitrosylation of the thiol group by NO. Modification of the cysteine residues by NO resulted a ratiometric change of EGFP emission through transducing the conformational change of NO-sensing module to the EGFP chromophore. The oxidized form of NO-sensing module fused EGFP changed the intensity of emission spectra upon reduction of the disulfide bond at the NO-reactive module. The NO-sensing module fused EGFP in its reduced form avidly reacted with NO and realized the ratiometric fluorescence intensity changes depending on the formation of disulfide bond. These results support the notion that NO induces a conformational change at the putative NO-sensing segment of TRPC5, and provide a prototype for the genetically encoded cellular NO sensors.

Detection of Inositol Phosphates by Split PH Domains.

The pleckstrin homology (PH) domain is a family of structurally conserved proteins which can bind inositol phosphate derivatives. Some proteins involved in cellular signaling and cytoskeletal organization possess split PH domains that assemble into a structure which can bind specific inositol phosphates. Here we describe the design of split PH domain from a structurally well-characterized PH domain of phospholipase C (PLC) δ1 and Bruton's tyrosine kinase (Btk), which selectively bind Ins(1,4,5)P3 and Ins(1,3,4,5)P4, respectively. The PH domains fold into a functional structure when the split halves are brought to close proximity, and can be utilized to detect specific inositol phosphate of interest.

Synchronization using environmental coupling in mercury beating heart oscillators.

We report synchronization of Mercury Beating Heart (MBH) oscillators using the environmental coupling mechanism. This mechanism involves interaction of the oscillators with a common medium/environment such that the oscillators do not interact among themselves. In the present work, we chose a modified MBH system as the common environment. In the absence of coupling, this modified system does not exhibit self sustained oscillations. It was observed that, as a result of the coupling of the MBH oscillators with this common environment, the electrical and the mechanical activities of both the oscillators synchronized simultaneously. Experimental results indicate the emergence of both lag and the complete synchronization in the MBH oscillators. Simulations of the phase oscillators were carried out in order to better understand the experimental observations.