Stimulated Raman Scattering Microscopy Facilitates the Discovery of Diacylglycerol O-Acyltransferase 2 as a Target to Enhance Iodine Uptake in Papillary Thyroid Carcinoma

Radioactive ¹³¹I therapy is a primary treatment for papillary thyroid carcinoma (PTC), with approximately 30% of patients developing iodine-refractory disease. There is an urgent clinical need to improve iodine uptake in PTC. Previous research suggested a connection between triglyceride (TG) accumulation and decreased iodine uptake in benign thyroid cells. Notably, TG accumulation has been found to be a marker of aggressive human PTC. Therefore, it is crucial to elucidate whether TG accumulation affects iodine uptake in PTC, which may lead to a new way for enhancement of iodine uptake. Here, by combining stimulated Raman scattering (SRS) microscopy and deuterated Raman tags, we first quantitatively analyzed the level of TG and its source in the K1 cell with low iodine uptake and the TPC-1 cell with high iodine uptake. It was found that K1 cells had significantly greater TG accumulation than TPC-1 cells, primarily due to an increased exogenous uptake of fatty acids. Further RNA-seq transcriptome experiments revealed that the underlying mechanism could be upregulation of lipid biosynthesis, uptake, and transport-related genes, along with down-regulation of fatty acid β-oxidation and lipolysis-related genes in K1 cells. Among the upregulated lipid biosynthesis genes, diacylglycerol O-acyltransferase 2 (DGAT2) is of great importance as the rate-limiting enzyme in TG biosynthesis. Notably, the inhibition of DGAT2 led to a significant increase in the expression of iodine uptake-related proteins, namely, sodium iodide symporter (NIS) and thyroglobulin (Tg), in K1 cells. Further Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses unraveled that DGAT2 inhibition could enhance thyroid hormone synthesis, for which iodine is an essential raw material, by alleviating endoplasmic reticulum stress and upregulating the pathways related to protein glycosylation and transmembrane transport. In summary, our study has shown that SRS microscopy facilitates the discovery of DGAT2 as a potential target to enhance iodine uptake in PTC, which holds promise for improving treatment outcome of iodine-refractory PTC.