The samples came from the frontal cortices of four cognitively healthy people and four with AD.Ĭell-Cell Contacts. These refreshed samples were then labeled with a panel of 32 oligonucleotide-barcoded antibodies to identify proteins chosen for their cell specificity, activation state, anatomical location, or toxicity. This suppresses notorious autofluorescence that typically drowns out fluorescent antibody signals in paraffin-embedded tissue. Co-first authors Paula Sanchez-Molina of OHSU and Aditya Pratapa of Akoya pretreated the brain slices with a trip to the spa, of sorts, bathing them in hydrogen peroxide under LED lights. For their part, Ajami’s group improved on CODEX, aka Co-detection by indexing, which can label up to 100 proteins in a sample ( Black et al., 2021). Yet transcripts do not always translate into proteins.Įnter spatial proteomics-a collection of new techniques that quantify many proteins at once, with single-cell resolution, and all within intact, fixed human brain tissue. Spatial transcriptomics can help, and has just started to integrate proteins-think Aβ plaques and tau tangles-into the equation ( Feb 2023 news). Proteomics can measure thousands at once in tissue extracts, but say nothing about where in the brain the proteins come from or which cells make them ( May 2020 news). “These two papers address that kind of technology gap.”Ījami posted a preprint on Research Square on May 2, while Bendall’s study was published last November in Acta Neuropathologica Communications.Ĭonventional immunohistochemistry measures just a few proteins at a time. “There is great need for a better mechanistic understanding of RNA expression, metabolites, and proteins at the single-cell level, without sacrificing tissue architecture or cell-cell interactions,” said Costantino Iadecola of Weill Cornell Medical College in New York. “It can tell us which cells are producing the proteins detected in biofluids, and how they are interacting with brain pathology.” Spatial proteomics adds critical information missing from conventional proteomics or neuropathological studies, said Tijms. “The level of detail achieved with these techniques is stunning,” said Betty Tijms of Amsterdam University Medical Center, who conducts proteomics studies in biofluids. Neurons expressing MFN2, a mitochondrial protein, may be resilient to tau pathology.Microglia subtypes surround Aβ plaques, tau tangles, and sickly neurons.Spatial proteomics detects dozens of proteins at single-cell resolution in fixed brain samples.Besides hinting at novel cellular mechanisms underlying neurodegenerative disease, these proof-of-concept studies grace the field with remarkable images of cells going about their business within the grand metropolis of the brain. They found microglia tangoing with tau tangles, and a potentially resilient population of neurons packed with mitofusin-2, which stabilizes mitochondria. The second study, led by Sean Bendall of Stanford University in Palo Alto, California, used antibodies tagged with metal isotopes that can be detected via mass spectrometry to survey proteins across entire coronal sections of the human hippocampus. The authors pinpointed distinct microglial subtypes encircling Aβ plaques. Scientists led by Bahareh Ajami at Oregon Health & Science University in Portland and Oliver Braubach of Akoya Biosciences in Marlborough, Massachusetts, adapted a method called CODEX, which makes use of antibodies affixed with DNA barcodes, to unveil the cytoarchitecture of the frontal cortex, and to zoom in on cell-cell interactions there. Two recent studies offer a glimpse of this heterogeneity by wielding multiplex spatial proteomics at single-cell resolution within fixed postmortem samples from human brain tissue. The mind-boggling variety of cell subtypes in the brain is strongly tied to local environments.
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