Multiplex target protein imaging in tissue sections by mass spectrometry--TAMSIM

Area of Science:

• Biochemistry
• Analytical Chemistry
• Histology

Background:

• Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-MS) is used for imaging molecules in histological sections.
• Current MALDI-MS imaging primarily detects naturally occurring molecules.
• There is a need for multiplex imaging of specific proteins, especially those present at low concentrations.

Purpose of the Study:

• To develop a novel method for multiplex imaging of candidate proteins using MALDI-MS.
• To enable the detection of proteins below the threshold of direct MALDI-MS imaging.
• To demonstrate the simultaneous visualization of multiple proteins in histological samples.

Main Methods:

• Antibodies were conjugated with photocleavable mass tags to target specific proteins.
• Histological sections were stained using these tagged antibodies, similar to immunohistochemical procedures.
• A 355 nm laser pulse released mass tags from antibodies without matrix, enabling detection by MALDI-MS.
• Mass spectrometry images were generated for each tag's mass, allowing for multiplexed protein localization.

Main Results:

• The TArgeted multiplex Mass Spectrometry IMaging (TAMSIM) method successfully performed multiplex protein imaging.
• Proteins below the detection threshold of direct MALDI-MS imaging were visualized.
• Simultaneous imaging of synaptophysin in pancreatic neuroendocrine cells and cancer markers (PS100, HMB45) in metastatic melanoma was achieved.
• Mass tags did not exhibit mutual quenching, unlike fluorescent tags.

Conclusions:

• TAMSIM is a novel and effective technique for multiplex protein imaging in histology.
• This method expands the capability of MALDI-MS imaging to detect low-abundance proteins.
• TAMSIM offers a non-quenching alternative to fluorescent tags for multiplexed molecular imaging.