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.