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Revealing How Cells Die

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BUFFALO, N.Y., Aug. 27, 2010 — Apoptosis, or programmed cell death, is essential to normal development, healthy immune system function and cancer prevention. The process dramatically transforms cellular structures, but the limitations of conventional microscopy methods have kept much about this structural reorganization a mystery. Now, scientists at the University at Buffalo have developed a biophotonic imaging approach capable of real-time monitoring of the transformations that cellular macromolecules undergo during apoptosis.

The work, which is featured in a recent issue of PNAS, could help realize the potential of customized molecular medicine, in which chemotherapy, for example, can be precisely targeted to cellular changes exhibited by individual patients. It can also be a valuable drug development tool for screening new compounds.

“This new ability provides us with a dynamic mapping of the transformations occurring in the cell at the molecular level,” said study co-author Paras N. Prasad, who is executive director of the university’s Institute for Lasers, Photonics and Biophotonics (ILPB). “It provides us with a very clear visual picture of the dynamics of proteins, DNA, RNA and lipids during the cell’s disintegration.”

Paras Prasad and a team of researchers have developed a biophotonic imaging approach to monitor apoptosis. (Image: Douglas Levere, University at Buffalo)

Prasad noted that molecular medicine, in which treatments or preventive measures can be tailored to cellular properties exhibited by individual patients, depends on much better methods of visualizing what’s happening during critical cellular processes.

“This research helps improve our understanding of cellular events at the molecular level,” he said. “If we know that specific molecular changes constitute an early signature of a disease, or what changes may predispose a patient to that disease, then we can take steps to target treatment or even prevent the disease from developing in the first place.”

To capture the cellular images, the interdisciplinary team of biologists, chemists and physicists, led by Prasad, utilized an advanced biophotonic approach that combines three techniques: coherent anti-Stokes Raman scattering, fluorescence recovery after photobleaching (to measure protein dynamics), and two-photon excited fluorescence, which images living tissue and cells at deep penetration.

“For the first time, this approach allows us to monitor in a single scan, four different types of images, characterizing the distribution of proteins, DNA, RNA and lipids in the cell,” said Aliaksandr V. Kachynski, research associate professor at the ILPB and co-author of the PNAS paper.

The resulting composite image integrates the information on all four types of biomolecules, with each type of molecule represented by a different color: proteins in red, RNA in green, DNA in blue and lipids in grey. Multiplex imaging provided new information on the rate at which proteins diffuse through the cell nucleus, the scientists reported.

Before apoptosis was induced, the distribution of proteins was relatively uniform, but once apoptosis developed, nuclear structures disintegrated, the proteins became irregularly distributed and their diffusion rate slowed down, said Artem Pliss, research assistant professor at the ILPB and another co-author on the paper.

“This research gives us the unique ability to study and improve our understanding of individual subcellular structures and the transformations they go through,” Pliss said.

Such precise information will be especially useful for monitoring how specific cancer drugs affect individual cells.

“For example, say drug therapy is being administered to a cancer patient; this system will allow for the monitoring of cellular changes throughout the treatment process,” Kachynski said. “Clinicians will be able to determine the optimal conditions to kill a cancer cell for the particular type of disease. An improved understanding of the drug-biomolecule interactions will help discover the optimal treatment doses so as to minimize side effects.”

Andrey Kuzmin, research assistant professor at the ILPB and co-author, added that a new paper from the team, forthcoming in Biophysical Journal, further extends this work.

“The benefits of the [University at Buffalo] multiplex imaging system and its molecular selectivity have been further extended into a new fundamental cellular study, structural reorganization throughout the mitotic cell cycle,” he said.

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Aug 2010
two-photon excited fluorescence
Two-photon excited fluorescence (TPEF) is a nonlinear optical method that allows imaging of biological cells and living tissue. The advantage of TPEF in comparison to conventional fluorescence microscopy is that it provides natural confocality and allows sectioning of the sample. Because it typically uses near-infrared excitation light, the penetration depth is significantly increased. TPEF is implemented as fast imaging microscopy for noninvasive optical pathology. TPEF has been used in...
Aliaksandr V. KachynskiAmericasAndrey KuzminApoptosisArtem PlissBiophotonicsBiophysical Journalcancercell cyclecellular structurecoherent anti-Stokes Raman scatteringDNAenergyfluorescence recovery after photobleachingILPBimagingimmune systemInstitute for Laserslight sourceslipidsmacromoleculesMicroscopymolecular medicinemultiplex imagingParas N. PrasadPhotonics and BiophotonicsPNASproteinsResearch & TechnologyRNAtwo-photon excited fluorescenceLEDs

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