Astrocyte activation in response to brain metastasis

Emma O'Brien, Sébastien Serres, James Larkin, Claire Bristow, Daniel Anthony, Nicola Sibson

Poster at NCRI Cancer Conference, Liverpool, UK (2011)


Background: Recent studies in vitro and in vivo suggest astrocyte activation occurs during the development of secondary cancer (metastasis) in the brain. Brain metastasis is predicted to affect 20-40% of cancer patients, yet the factors governing tumour development remain largely unknown. Therefore, we aim, to quantify astrocyte activation during metastasis induction and pathogenesis in a mouse model of metastatic breast cancer.

Method: Two models were used to quantify astrocyte activation in response to brain metastasis over a 28 day period. In the first, brain metastases were induced in female BALB/c at 6-7 weeks of age, via intra-cardiac injection of a Green Fluorescent Protein (GFP) transfected murine breast cancer cell line, 4T1. In the second model, GFP-4T1 cells were injected directly into the striatum, using a finely drawn micro-capillary. Brains were perfused-fixed at days 5, 10, 14, 21 and 28 post-injection (n=3 at each time point). In both cases, tumours were observed using immunohistochemical detection of GFP, whilst astrocyte activation was detected via immunohistochemical staining of Glial Fibrillary Acidic Protein (GFAP). Tumour area and area of astrocyte activation were quantified by demarcating areas with either a camera Lucida, or Image J.

Results: Brain metastases were found to be surrounded by a ring of activated astrocytes throughout the time course, and a positive correlation was found between the extent of astrogliosis and tumour size in both models. The area of astrocyte activation increased significantly with time, and interestingly to a greater extent than tumour area.

Conclusion: This study demonstrates robust activation of astrocytes in response to brain metastases, suggesting that astrocytes may play an important role in tumour pathogenesis. These findings provide the basis for further investigations aimed at ascertaining the nature of this interaction, and to determine the molecular pathways that drive the relationship.