Thrombospondin-1, CD47, and SIRPα Display Cell-Specific Molecular Signatures in Human Islets and Pancreata.
Am J Physiol Endocrinol Metab 2023;
324:E347-E357. [PMID:
36791324 DOI:
10.1152/ajpendo.00221.2022]
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Abstract
BACKGROUND
Thrombospondin-1 (TSP1) is a secreted protein minimally expressed in health but increased in disease and age. TSP1 binds to the cell membrane receptor CD47, which itself engages signal regulatory protein α (SIRPα) and the latter creates a checkpoint for immune activation. Individuals with cancer administered checkpoint blocking molecules developed insulin-dependent diabetes. Relevant to this, CD47 blocking antibodies and SIRPα fusion proteins are in clinical trials. We characterized the molecular signature of TSP1, CD47, and SIRPα in human islets and pancreata.
METHODS
Fresh islets and pancreatic tissue from non-diabetic individuals were obtained. The expression of THBS1, CD47, and SIRPA was determined using single-cell mRNA sequencing, immunofluorescence microscopy, Western blot, and flow cytometry. Islets were exposed to diabetes-affiliated inflammatory cytokines and changes in protein expression determined.
RESULTS
CD47 mRNA was expressed in all islet cell types. THBS1 mRNA was restricted primarily to endothelial and mesenchymal cells, while SIRPA mRNA was found mostly in macrophages. Immunofluorescence staining showed CD47 protein expressed by beta cells and present in the exocrine pancreas. TSP1 and SIRPα proteins were not seen in islets or the exocrine pancreas. Western blot and flow cytometry confirmed immunofluorescent expression patterns. Importantly, human islets produced substantial quantities of secreted TSP1.
CONCLUSIONS
Human pancreatic exocrine and endocrine tissue expressed CD47 whereas fresh islets displayed cell surface CD47 and secreted TSP1 at baseline and in inflammation. These findings suggest unexpected effects on islets from agents that intersect TSP1-CD47-SIRPα.
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