Mass Spectrometry Visualizes Proteins Produced During Inflammation

MRI Combined with Imaging Mass Spectrometry Visualizes Proteins Produced During Inflammation

A new 3-D view of the body’s response to infection — and the ability to identify proteins involved in the response — could point to novel biomarkers and therapeutic agents for infectious diseases.

Vanderbilt University scientists in multiple disciplines combined magnetic resonance imaging (MRI) and imaging mass spectrometry to visualize the inflammatory response to a bacterial infection in mice. The techniques, described in Cell Host & Microbe and featured on the journal cover, offer opportunities for discovering proteins not previously implicated in the inflammatory response.

Access to unique resources at Vanderbilt made the unprecedented 3-D infection imaging possible, said Eric Skaar, Ph.D., Ernest Goodpasture Chair in Pathology and one of the senior co-authors of the paper.

“The studies in this paper couldn’t have happened at any other university, because the resources simply don’t exist at most schools,” Skaar said.

The team using MRI and imaging mass spectrometry to visualize the inflammatory response includes (bottom row, from left) Lisa Manier, Erin Seeley, Ph.D., Eric Skaar, Ph.D., and Richard Caprioli, Ph.D., (top row, from left) Kristie Rose, Neal Hammer, Josh Nicklay, Kevin Wilson, MESc, and Daniel Colvin, Ph.D. (photo by Joe Howell)

The resources include animal imaging technologies available through the Vanderbilt University Institute of Imaging Science (VUIIS), directed by John Gore, Ph.D., and imaging mass spectrometry technologies available through the Mass Spectrometry Research Center (MSRC), directed by Richard Caprioli, Ph.D. Gore and Caprioli are also senior co-authors of the paper.

“The fact that my research group, which studies infectious diseases, has access to these powerful imaging and mass spectrometry technologies is a real strength at Vanderbilt and has allowed us to develop these new tools that will enable high impact discovery,” Skaar said.

Skaar and his team were interested in imaging infection in three dimensions — in the whole animal — while also being able to identify the proteins that are produced at sites of infection. MRI provides detailed anatomical images of tissue damage.

Attia et al., Cell Host & Microbe 11(6)

Imaging mass spectrometry is a unique technology that directly measures proteins, lipids and other metabolites and maps their distribution in a biopsy or other tissue sample.

Ahmed Attia, Ph.D., a former member of Skaar’s group now on the faculty at Cairo University, Egypt, infected mice with Staphylococcus aureus, a major cause of human disease.

He then delivered the infected animals to Daniel Colvin, Ph.D., in the VUIIS, who imaged them with MRI. Kaitlin Schroeder and Erin Seeley, Ph.D., in the MSRC then conducted imaging mass spectrometry studies.

Putting together the two technologies and multiple data sets accurately required the expertise of Kevin Wilson, MESc, in the VUIIS, who developed algorithms to show consolidated 3-D views of the inflammatory response.

“This is another example of the multi-modality approach we have been pursuing in general within the Imaging Institute,” Gore said.

The technologies allow the investigators to see a single image of an infected animal, look at how proteins of the immune system are responding, and identify where the infected tissue is located, Skaar said.

“Part of the strength of this work is not where the research is now, but where it allows us to go from here.”

His team plans to identify “proteins that are important at the interface between the host and the pathogen — the battleground between the immune system and the bacteria,” Skaar said.

The researchers will study the proteins they identify to discover new biomarkers for infection, which could improve diagnostic tools, or new targets for therapeutic intervention.

The technologies available through the MSRC and the VUIIS will be useful for any investigator interested in imaging the inflammatory response, which has roles in infectious diseases, cancer and autoimmune diseases, Skaar said.

And although the technology is not non-invasive (imaging mass spectrometry requires tissue sections), it could be applied to tissues removed from patients, such as tumors.

“Imaging mass spectrometry is extremely valuable for the discovery process because it does not require a target-specific reagent such as an antibody — that is, you do not have to know in advance what you’re looking for in order to correlate molecular changes with disease outcome,” Caprioli said. “An area of intense interest is the application of this technology to molecular pathology.”

The research was supported by grants from the National Institutes of Health (AI069233, AI091771, AI073843, GM058008), the establishment of an NIH-funded National Resource for Imaging Mass Spectrometry, and a Pfizer 2009 ASPIRE research award.

Skaar is a Burroughs Wellcome Fellow in the Pathogenesis of Infectious Diseases and is associate professor of Pathology, Microbiology and Immunology. Gore is University Professor of Radiology and Radiological Sciences and Hertha Ramsey Cress Chair in Medicine. Caprioli is Stanford Moore Chair in Biochemistry.

Highlights

IMS provides a whole-animal view of the inflammatory response to infection

IMS identifies protein masses that are abundant at sites of inflammation

Anatomic information at the site of infection can be generated by MRI

Integrated IMS and MRI enable a 3D view of the host-pathogen interaction

Summary

Systemic bacterial infection is characterized by a robust whole-organism inflammatory response. Analysis of the immune response to infection involves technologies that typically focus on single organ systems and lack spatial information. Additionally, the analysis of individual inflammatory proteins requires antibodies specific to the protein of interest, limiting the panel of proteins that can be analyzed. Herein we describe the application of matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI IMS) to mice systemically infected with Staphylococcus aureus to identify inflammatory protein masses that respond to infection throughout an entire infected animal. Integrating the resolution afforded by magnetic resonance imaging (MRI) with the sensitivity of MALDI IMS provides three-dimensional spatially resolved information regarding the distribution of innate immune proteins during systemic infection, allowing comparisons to in vivo structural information and soft-tissue contrast via MRI. Thus, integrating MALDI IMS with MRI provides a systems-biology approach to study inflammation during infection.

Inflammation is an important way the body fights disease and it is also a marker for the disease itself. There are limitations currently in understanding inflammation and the proteins involved, with researchers having to focus on individual organs and specific antibodies in their studies.

Cell Host Microbe cover MRI Combined with Imaging Mass Spectrometry Visualizes Proteins Produced During InflammationTo better understand inflammatory processes, researchers at Vanderbilt University successfully combined data sets from two imaging modalitites, magnetic resonance imaging (MRI) and imaging mass spectrometry, to visualize in 3D the proteins involved in inflammation throughout the entire body of a rat.

From the study abstract:

Systemic bacterial infection is characterized by a robust whole-organism inflammatory response. Analysis of the immune response to infection involves technologies that typically focus on single organ systems and lack spatial information. Additionally, the analysis of individual inflammatory proteins requires antibodies specific to the protein of interest, limiting the panel of proteins that can be analyzed. Herein we describe the application of matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI IMS) to mice systemically infected with Staphylococcus aureus to identify inflammatory protein masses that respond to infection throughout an entire infected animal. Integrating the resolution afforded by magnetic resonance imaging (MRI) with the sensitivity of MALDI IMS provides three-dimensional spatially resolved information regarding the distribution of innate immune proteins during systemic infection, allowing comparisons to in vivo structural information and soft-tissue contrast via MRI. Thus, integrating MALDI IMS with MRI provides a systems-biology approach to study inflammation during infection.

Source : http://news.vanderbilt.edu/2012/08/new-view-of-infection-response/

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