New method improves proteoform imaging in human tissue

Investigators led by Neil Kelleher, Ph.D., professor of Medicine within the Division of Hematology and Oncology and of Biochemistry and Molecular Genetics, have developed a brand new imaging method that will increase the detection of intact proteoforms by fourfold when in comparison with present protein imaging strategies.

The imaging technique, detailed in a current paper revealed in Science Advances, offers high-resolution, high-throughput imaging of proteoforms, or all modified variations of proteins. Importantly, the method is “label-free,” doesn’t require antibodies and may establish entire proteoforms straight from any unfixed tissue. The method can at the moment detect roughly 1,000 proteoforms and localizes proteoforms with a spatial resolution of 40 to 70 microns.

Several strategies are generally used to picture proteins in human tissue, however only a few are able to imaging proteoforms. Those that may picture total proteoforms achieve this by separating the proteoform from tissue and ionizing them for mass spectrometry. However, these strategies supply low molecular specificity.

To tackle this subject, Kelleher’s staff developed proteoform imaging mass spectrometry (PiMS). The method works by extracting proteoforms from the tissue with nanodroplets, “weighing” the extracted proteoforms to establish them after which utilizing this information to assemble proteoform photographs of the scanned tissue.

“The real innovation with PiMS is that it couples a robust existing technique for extracting and ionizing proteoforms, nanoDESI, with a breakthrough technology for individual ion mass spectrometry that was co-invented by Thermo Fisher Scientific and Northwestern Proteomics. Compared to regular detection techniques, individual ion mass spectrometry offers up to 500 times more sensitivity and 20 times more resolving power. That significantly increases the power of the technique, and PiMS detects larger, rarer proteoforms and greatly extends the limits of proteome coverage,” mentioned Kelleher, who can also be director of Northwestern’s Proteomics Center of Excellence, the Robert H. Lurie Comprehensive Cancer Center’s Proteomics Core Facility and of Northwestern’s Chemistry of Life Processes Institute.

To reveal PiMS’ capabilities, Kelleher’s staff used the method to picture proteoforms from practical items of the human kidney. These photographs revealed distinct spatial localizations of proteoforms from totally different anatomical areas and practical tissue items just like the renal cortex versus the medulla.

PiMS’ elevated proteome protection additionally opens the door for wider purposes in molecular tissue mapping, figuring out novel biomarkers and bettering illness analysis, in accordance with Kelleher.

“Recently, there has been a big push in genomics and proteomics for single-cell biology: to better capture the heterogeneity of diseases by using spatial or single-cell approaches that preserve the many diverse signals instead of bulk approaches that mix all cell types and regions together. The spatial approach in particular adds a far greater precision for protein imaging and we are currently pushing it to identify thousands of proteoforms with single-cell resolution,” Kelleher mentioned.