Mass spec imaging - a comprehensive view of molecular insights

Abstract

A single modality is very often not good enough to understand all functional, structural, temporal and chemical relations underlying certain biological conditions. Imaging a specimen with two or more complementary modalities creates an informative, composite view of a sample that spans all relevant resolution ranges. Here we shortly introduce the concept of MALDI Mass Spectrometry based imaging (MALDI MSI) and its potential to localize molecules in a tissue without a priori knowledge. Advantages, limitations, and potentials for applications are briefly highlighted. In this talk our investigations on aging skin are presented to show the potential of MALDI MSI. Our skin is continually subjected to sunlight, high oxygen levels, and environmental pollutants, which are significant stressors that expedite premature aging, inflammation, and skin cancer. The most noticeable clinical effect of skin aging is the alteration in skin appearance. To counteract oxidative stress, cells deploy several defense mechanisms. Oxidized lipids, such as oxidized phosphatidylcholines (OxPCs), function as danger-associated molecular patterns. In our research, we study the impact of UV light on human skin and compare a 3D skin model with human skin biopsies. The high mass accuracy of Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS), along with the spatial localization and relative abundance of analytes, enabled us to confidently identify various OxPCs and associate them with specific skin compartments. By integrating these findings with high-resolution light microscopy and immunohistology. Our observations in skin models were mirrored in samples from both young and elderly donors. We recently added more general metabolite data after developing an improved sample preparation strategy. Especially glucose distributions are of relvenance in aging as previously shown. We introduce a multimodal imaging workflow to explore spatially resolved, senescence-related alterations in the skin N-glycome, which affects the extracellular matrix and is a key determinant of skin aging. Age-related changes were studied by correlating N-glycan composition with MALDI-IHC, immunofluorescence, autofluorescence, and tissue staining, all conducted on a single tissue section. Additional tissue staining and spatial transcriptomics were performed on an adjacent section to reinforce the N-glycan data by co-registering all datasets at full resolution, and then integrating the data to create a common coordinate system and match readouts that accounted for the differences in spatial resolutions. This allowed for simultaneous viewing and enabled integrated spatial correlation analysis across assays, multi-omics tissue segmentation and differential expression analysis.