Imaging Bioluminescence by Detecting Localized Haemodynamic Contrast from Photosensitized Vasculature

Cardiovascular System Basic Medical Sciences Bioengineering Biophysics Medical Imaging Life Sciences Medicine
bioluminescence haemodynamics photosensitive enzyme fluorescent protein rodent experiments magnetic resonance imaging light signal

Academic News Report: New MRI Technology Achieves Biological Fluorescence Imaging by Detecting Local Hemodynamics of Photosensitive Blood Vessels

Academic Background Introduction

Imaging Principle Bioluminescent probes are widely used for monitoring biomedical processes and cellular targets in living animals. However, the absorption and scattering of visible light by tissues greatly limit the depth and resolution of bioluminescence detection. Specifically in the brain, the skull blocks photon propagation of short-wavelength light, resulting in bioluminescence imaging (BLI) data being often confined to shallow sources and mostly two-dimensional projections lacking depth information.

To overcome these limitations, researchers have developed photoacoustic tomography and other methods based on light scattering reconstruction. However, these methods require a priori knowledge and the registration of anatomical information from independent imaging modalities. Another approach is to locally convert bioluminescence output into different types of signals that can be detected using deep tissue imaging methods such as X-ray tomography, ultrasound, or magnetic resonance imaging (MRI). Although some probe architectures are already capable of converting light into signals detectable by MRI, these methods lack sufficient resolution and sensitivity to support in vivo BLI applications.

Source of the Paper

This research was published in Nature Biomedical Engineering. The research team comes from the Department of Biological Engineering, the Department of Brain and Cognitive Sciences, and the Department of Nuclear Science and Engineering at the Massachusetts Institute of Technology (MIT). Contributions also come from the Max Planck Institute for Biological Cybernetics and the University of Texas Southwestern Medical Center. Robert Ohlendorf and Nan Li are co-first authors of this paper, and the corresponding author is Alan Jasanoff.

Introduction of Research Process and Methods

a) Research Process

The core concept of this study is to use light-activatable proteins (bpac) expressed in blood vessels to sense bioluminescent sources and generate hemodynamic signals. The specific process is as follows:

  1. In vitro characterization of photoreceptor protein bpac: First, the light output of various blue bioluminescent luciferases, including NanoLuc, modified Gaussia luciferase (Gluc), and Glucm23, was measured. The study found that Glucm23 was the brightest and thus selected it as the bioluminescent source for subsequent experiments.

  2. Cell experiments: Chinese hamster ovary (CHO) cells and vascular smooth muscle cells (VSMCs) were chosen to trigger cAMP signaling via the photoreceptor protein bpac, simulating and testing the feasibility of photoreceptor-induced hemodynamic changes in vivo.

  3. In vivo experiments: Light activation and MRI: An adenovirus containing bpac was injected into specific parts of the rat brain, followed by light exposure experiments. Blue light was transmitted through optical fibers, achieving significant local blood flow changes upon light activation.

  4. In vivo experiments: Detection of bioluminescent xenografted cells: Cells expressing Glucm23 were implanted in brain areas transfected with bpac and a luminescent protein. Continuous MRI scans detected hemodynamic changes induced by the luminous cells deep within the brain.

b) Main Research Results

  1. In vitro characterization results: Measuring the brightness of bioluminescent luciferases, Glucm23 was found to be brighter than NanoLuc and Gluc. This determined the choice of Glucm23 for further studies. The experiments also showed that the photoreceptor protein bpac could effectively produce light-dependent cAMP in VSMCs.

  2. In vitro experiments with bpac photoreceptor in VSMCs: Experiments indicated that the mechanism of cAMP production by glucose could significantly generate intracellular signals under light conditions.

  3. In vivo light activation experiment results: By introducing the photoreceptor protein into the rat brain blood vessels, significant signal changes in the light-activated areas were successfully detected under high magnetic field strength, proving the feasibility of detecting light-induced hemodynamic signals.

  4. Bioluminescence detection of xenografted cells: After implanting bioluminescent cells in brain areas expressing bpac, continuous MRI scans successfully captured blood flow changes induced by the luminous cells, indicating the effective detection of bioluminescence signals in deep brain tissue.

Research Conclusion and Significance

The study showed that by activating photoreceptors in vascular smooth muscle cells, bioluminescent signals could be converted into hemodynamic signals and detected by MRI. This method significantly broadens the application range of bioluminescent probes in deep tissues, especially in brain science research.

Given the extensive application of bioluminescence in foundational and preclinical biology, this research holds high scientific and practical value. For example, it can be used for more in-depth studies of neural processes and more precise tumor detection and angiogenesis monitoring.

Research Highlights

  1. Technological Innovation: Converting bioluminescent signals into more easily detectable hemodynamic signals fundamentally addresses the limitation of light propagation in deep tissues.

  2. Broad Application Prospects: The method is not only suitable for brain science research but can also be extended to other fields requiring deep tissue imaging.

  3. Imaging Resolution and Depth: By using high magnetic field strength MRI, high-resolution and deep imaging were achieved, successfully detecting bioluminescent signals in deep brain tissues.

Additionally, this research demonstrates possibilities for further optimization and improvement, such as achieving more uniform distribution of photoreceptor proteins to enhance imaging accuracy and sensitivity. The research team’s next steps include exploring broader distributions of photoreceptor proteins across various tissue types and the feasibility of detecting these signals under other imaging modalities.

Summary

This research achieved an innovative method of converting bioluminescent signals into hemodynamic mechanisms detectable by MRI. This groundbreaking technology paves new pathways for the application of light probes in deep tissue and various biomedical research, providing new insights for more comprehensive and precise biological imaging techniques.