IntroductionGlobal diabetes prevalence has been increasing. It was estimated that there were 529 million people with diabetes worldwide in 2021; this number was projected to exceed one billion by 20501. Inflammation is involved in the pathogenesis of the most common types of diabetes, namely type 1, type 2 and gestational diabetes2,3,4,5. Monocytes, a critical component of the innate immune system, play a key role in propagating inflammation under hyperglycemic conditions6,7,8,9.MicroRNAs (miRNAs) are a class of short, noncoding, single-stranded RNA molecules approximately 22 nucleotides in length; they regulate gene expression post-transcriptionally by binding to the 3’-untranslated region of mRNAs10,11. Since their discovery over three decades ago12,13, miRNAs have been extensively explored for their involvement in the pathophysiology of various diseases, including cancer14,15,16, cardiovascular disease17,18,19,20, and diabetes21,22,23. Many clinical studies of diabetic patients have shown alterations in circulating miRNAs and the altered miRNAs were investigated as potential disease biomarkers24,25,26,27,28. It has also been shown that miRNAs participate in various aspects of the actions of insulin that include insulin production, resistance, and cellular signaling29,30,31. In addition, miRNAs are implicated in the endothelial dysfunction observed in diabetes32,33,34. In contrast, although a few studies have described miRNA dysregulation in monocytes from patients with type 2 diabetes, they did not examine, or show, miRNA regulation of monocyte inflammatory activity35,36,37. This study aimed to investigate miRNA dysregulation in THP-1 monocytes in the presence of high glucose and its effects on cellular inflammatory function. The following miRNAs, i.e., miR-19a, miR-24, let-7b, miR-22, miR-139-5p and miR-152 were chosen for this study as they have been shown to regulate monocyte/macrophage inflammatory reactions38,39,40,41,42,43,44,45,46,47.ResultsmiR-139-5p and its target CXCR4 were dysregulated by high glucoseAmong the miRNAs assayed, miR-139-5p was significantly downregulated in THP-1 cells by 25 mM glucose (Fig. 1a), while expression of other miRNAs did not alter substantially (Supplementary Fig. 1). There was no marked difference in miR-139-5p levels between cells treated with 5 mM glucose and cells treated with 25 mM mannitol (Fig. 1b). CXCR4 and c-Jun, two key regulators of monocyte inflammatory activity, are predicted targets of miR-139-5p (https://mirdb.org/cgi-bin/search.cgi?searchType=miRNA&full=mirbase&searchBox=MIMAT0000250). Therefore, they were chosen for further analysis. Western blot analysis showed that high glucose did not affect c-Jun expression but markedly increased CXCR4 production (Fig. 2).Fig. 1MiRNA measurement. RT-qPCR analysis revealed a significantly lower level of miR-139-5p in THP-1 cells treated with 25 mM glucose than in those treated with 5 mM glucose (panel a). In contrast, there was no significant difference in miR-139-3p levels between 5 mM glucose- and 25 mM mannitol-treated cells (panel b).Full size imageFig. 2c-Jun and CXCR4 protein measurement. c-Jun and CXCR4 levels were determined by Western blotting. While no significant difference was found in c-Jun levels between THP-1 cells treated with 5 mM and 25 mM glucose (panels a and b), CXCR4 levels were significantly higher in the 25 mM glucose cell group than in the 5 mM glucose cell group (panels c and d).Full size imageHigh glucose did not affect THP-1 growth but enhanced cell migration towards SDF-1 (CXCL12)As shown in Fig. 3a, there were no significant differences in cell growth between 5 and 25 mM glucose treated cells. We further looked into the ability of cell migration towards SDF-1, a cognate ligand for CXCR4. Of interest, treatment with 25 mM glucose led to a remarkable increase in THP-1 cell migration towards SDF-1 (Fig. 3b).Fig. 3THP-1 cell growth and migration assessment. Cell growth and migration were assayed by Calcein-AM staining as described in the Materials and Methods section. As shown in panel a, in cell growth analysis, the fluorescent intensity between the two groups of cells were not significantly different. As shown in panel b, in the presence of SDF-1, the fluorescent intensity of migrated cells was significantly greater in the 25 mM glucose cell group than in the 5 mM glucose cell group. * indicates p