Elevated miR-103b in exosomes derived from brain-metastatic triple-negative breast cancer cells remodels the brain pre-metastatic niche (PMN)

BACKGROUND: Triple-negative breast cancer (TNBC) is a highly aggressive breast cancer with high brain metastatic (BM) potential. Tumor-derived exosomes are implicated as key modulators during the formation of the pre-metastatic niche (PMN). However, the regulation of TNBC-BM-derived exosomes on brain PMN remains enigmatic. METHODS: The morphology and uptake of exosomes were identified using transmission electron microscopy and live-cell imaging, respectively. Differentially secreted miRNAs and mRNA were identified using high-throughput sequencing. The permeability of the blood‒brain barrier (BBB) and tight junction integrity were examined using immunofluorescence staining. Cell viability was examined using the CCK-8 assay. The apoptosis and intracellular ROS were investigated using fluorescence staining. The expression of mRNAs was examined using qPCR. RESULTS: miR-103b was significantly increased in exosomes derived from TNBC-BM cells. miR-103b compromised the tight junctions of HUVECs and increased BBB permeability in mice. Additionally, miR-103b promoted apoptosis and increased intracellular ROS in HUVECs and U251 cells, two cell lines commonly used as surrogates for brain microvascular endothelial cells and astrocytes, respectively. miR-103b-regulated differentially expressed genes modulated tight junction, apoptosis, oxidative stress, inflammation, and metabolism. Target analysis identified 216 targets of miR-103b, among which hub targets were associated with biological processes involved in maintaining the BBB and the glucose metabolism signaling pathway. CONCLUSION: Collectively, our findings for the first time reveal that exosomal miR-103b from TNBC-BM cells potentially regulates the two major cellular constituents of the brain PMN, highlighting its role in the formation of the brain PMN during TNBC-BM and its potential as a promising therapeutic target.