Biology subjects

Nystrom, N. N.

Publications and source records attributed to Nystrom, N. N..

4 recordsLinked to original sources

bioRxiv2024

Multiplexed ultrasound imaging of gene expression

Acoustic reporter genes (ARGs) have enabled the imaging of gene expression with ultrasound, which provides high-resolution access to deep, optically opaque living tissues. However, unlike their fluorescent counterparts, ARGs have so far been limited to a single "color," preventing multiplexed imaging of cellular states or populations. Here, we use rational protein design and directed evolution to develop two novel ARGs that can be distinguished from each other based on their acoustic pressure response profiles, enabling "two-color" ultrasound imaging of gene expression. We demonstrate the utility of multiplexed ARGs for delineating bacterial cell species and cell states in vitro, and then apply them towards imaging distinct subpopulations of probiotics in the mouse gastrointestinal tract and in tumor-colonizing bacterial agents in vivo. Just as the first wavelength-shifted derivatives of fluorescent proteins opened a vivid world for optical microscopy, our next-generation acoustic proteins set the stage for a richer symphony of ultrasound signals from living subjects.

bioengineering↗

bioRxiv2022

Geometric effects in gas vesicle buckling under ultrasound

Acoustic reporter genes based on gas vesicles (GVs) have enabled the use of ultrasound to noninvasively visualize cellular function in vivo. The specific detection of GV signals relative to background acoustic scattering in tissues is facilitated by nonlinear ultrasound imaging techniques taking advantage of the sonomechanical buckling of GVs. However, the effect of geometry on the buckling behavior of GVs under exposure to ultrasound has not been studied. To understand such geometric effects, we developed computational models of GVs of various lengths and diameters and used finite element simulations to predict their threshold buckling pressures and post-buckling deformations. We demonstrated that the GV diameter has an inverse cubic relation to the threshold buckling pressure, whereas length has no substantial effect. To complement these simulations, we experimentally probed the effect of geometry on the mechanical properties of GVs and the corresponding nonlinear ultrasound signals. The results of these experiments corroborate our computational predictions. This study provides fundamental insights into how geometry affects the sonomechanical properties of GVs, which, in turn, can inform further engineering of these nanostructures for high-contrast, nonlinear ultrasound imaging. STATEMENT OF SIGNIFICANCEGas vesicles (GVs) are an emerging class of genetically encodable and engineerable imaging agents for ultrasound whose sonomechanical buckling generates nonlinear contrast to enable sensitive and specific imaging in highly scattering biological systems. Though the effect of protein composition on GV buckling has been studied, the effect of geometry has not previously been addressed. This study reveals that geometry, especially GV diameter, significantly alters the threshold acoustic pressures required to induce GV buckling. Our computational predictions and experimental results provide fundamental understanding of the relationship between GV geometry and buckling properties and underscore the utility of GVs for nonlinear ultrasound imaging. Additionally, our results provide suggestions to further engineer GVs to enable in vivo ultrasound imaging with greater sensitivity and higher contrast.

biophysics↗

bioRxiv2021

Gadolinium-free Magnetic Resonance Imaging of the Liver using an Oatp1-targeted Manganese(III) Porphyrin

Controversy surrounding gadolinium-based contrast agents (GBCAs) have rendered their continued utility highly contentious, but the liver-specific GBCA Gd(III) ethoxybenzyl-diethylene triamine pentaacetic acid (Gd(III)-EOB-DTPA) remains in use because it provides unique diagnostic information that could not be obtained by any other means. To address the need for an alternative liver-specific MRI contrast agent, we synthesized Mn(III) 20-(4-ethoxyphenyl) porphyrin-5,10,15-tricarboxylate (Mn(III)TriCP-PhOEt), which exhibited significantly higher r1 relaxivity than Gd(III)-EOB-DTPA, and targeted organic anion-transporting polypeptide 1 (Oatp1) channels as a biomarker of hepatocyte viability. Mn(III)TriCP-PhoEt increased the r1 relaxation rate of cells expressing rodent Oatp1a1 and human Oatp1b3, relative to control cells not expressing these liver channels. In mice, Mn(III)TriCP-PhoEt resulted in significant and specific increases in liver signal intensity on T1-weighted images, and significant decreases in liver T1 time relative to precontrast measurements. Our findings suggest that Mn(III)TriCP-PhOEt operates as a specific and sensitive MR contrast agent for in vivo liver imaging.

biophysics↗

bioRxiv2019

A human photoacoustic imaging reporter gene using the clinical dye indocyanine green.

Photoacoustic imaging (PAI) combines optical contrast with the resolution and depth-detection of ultrasound and is increasingly being utilized for medical imaging in patients. PAI reporter genes would allow for monitoring of cell and gene therapies, but current reporters have immunogenicity and/or toxicity concerns that may limit clinical translation. Here we report a PAI reporter system employing the ability of human organic anion transporting polypeptide 1b3 (Oatp1b3) to take up the clinical dye indocyanine green (ICG) into cells. Following ICG administration, cells synthetically expressing Oatp1b3 exhibited significantly increased PAI signals compared to control cells both in vitro and in mice. Several benefits of this technology are the human derivation of Oatp1b3, and the high extinction coefficient, low quantum yield and pre-existing clinical approval of ICG. We posit that the Oatp1b3-ICG reporter system could be useful for in vivo gene and cell tracking in preclinical and clinical applications.

bioengineering↗