Response of the neurovascular unit to brain metastatic breast cancer cells

Abstract

Therapeutic resistance of cerebral secondary tumours largely depends on unique aspects linked to the neurovascular unit, especially cerebral endothelial cells and astrocytes. By using advanced microscopy techniques, here we explored novel mechanisms related to the neurovascular unit during extravasation and proliferation of triple negative breast cancer cells in the brain. Metastatic mammary carcinoma cells arrested and elongated within one hour in cerebral microvessels, but their number decreased by almost 80% in the first two days. Interestingly, malignant cells induced vasoconstriction and development of intraluminal endothelial plugs, which isolated invading cells from the circulation. During diapedesis – which usually took place on day four and five after inoculation of the tumour cells – continuity of cerebral endothelial tight junctions remained intact, indicating migration of cancer cells through the transcellular pathway. In addition, metastatic cells induced formation of multiluminal vessels and claudin-5-positive endothelial blebs. However, even severe endothelial blebbing could be reversed and the vessel morphology was restored shortly after the tumour cells completed transendothelial migration. Similar to neuro-inflammatory leukocytes, tumour cells migrated not only through the endothelial layer, but through the glia limitans perivascularis as well. Nevertheless, along with the growth of metastatic lesions by co-option of pre-existing capillaries, astrocytes and astrocyte end-feet were gradually expelled from the vessels to the border of the tumour. Taken together, we identified previously unknown mechanisms involved in the reaction of brain resident cells to invading breast cancer cells. Our results contribute to a better understanding of the complex cross-talk between tumour cells and host cells in the brain, which is essential for the identification of new therapeutic targets in this devastating disease. Electronic supplementary material The online version of this article (10.1186/s40478-019-0788-1) contains supplementary material, which is available to authorized users.

Downregulation of circulating miR 802‐5p and miR 194‐5p and upregulation of brain MEF2C along breast cancer brain metastasization

“…Cells belonging to the neurovascular unit, including microglia and astrocytes, are known to interact with malignant cells after the transmigration through the BBB (Hasko et al , ). An interesting observation from this study was the MEF2C expression in star‐shaped cells close to the metastatic lesions, as early as at 3 days, but not in controls (Fig.…”

“…So, we used the murine mammary carcinoma 4T1 cell line, which is an aggressive triple‐negative tumor model that is highly tumorigenic and invasive, and metastasizes with a pattern very similar to that of human mammary cancer (Pulaski and Ostrand‐Rosenberg, ). The cells were injected in the common carotid artery, as an experimental model of brain metastasis (Zhang et al , ), already applied successfully by us (Hasko et al , ; Herman et al , ). To ascertain brain specificity, metastatic progression was followed in different brain regions and peripheral organs.…”

Pericyte‐secreted IGF2 promotes breast cancer brain metastasis formation

“…Venus-YFP-expressing primary mouse brain endothelial cells were isolated from 6-to 8-week-old FVB/Ant: TgCAG-yfp_sb #27 mice, as described previously [16]. Murine pericytes were collected in parallel with endothelial cells after the first enzymatic digestion.…”

“…All mice were housed and treated in accordance with widely accepted standards, and the protocols were approved by the institutional care and the Regional Animal Health and Food Control Station of Csongr ad County (permit number: XVI./764/2018). Surgeries were carried out on 6-to 10-week-old female FVB/ Ant:TgCAG-yfp_sb #27 mice (obtained from Institute of Experimental Medicine, Budapest, Hungary), as described previously [16]. For ex vivo experiments, 6to 10-week-old female mice received 10 6 4T1-tdTomato cells in 100 µL into the right common carotid artery.…”

“…We have previously shown that TNBC cells proliferate along capillaries in the mouse brain, co-opting the endothelium, but expelling astrocytes and astrocyte end-feet to the surface of the tumor [16]. Since tumor co-opted endothelial cells maintained tight junctions in the absence of astrocyte end-foot coverage, we investigated whether pericytes-another cell type involved in the induction of barrier properties of CECs [9,10]-remained in contact with the vessels, as previously described in a different metastatic model [20].…”