Studying the Effects of Radiation and Systemic Inflammation on Microglia Contribution to Brain Metastasis Outgrowth - PROJECT SUMMARY Brain metastasis is a complex process which involves the tumor cells, resident cells, and infiltrating immune cells. Glial cells are long lived and have been shown to react to both radiation therapy and peripheral stimuli such as systemic inflammation. Microglia can become continually reactive, inciting brain damage or creating a prolonged inflammatory environment. As radiation therapy is oftentimes the first treatment option for patients with brain metastasis, how glial cells and the broader niche responds, is critical to study. Various functions of microglia including their ability to engage in complement signaling is fundamental to their proper functioning. How radiation influences this pathway is not well understood. Furthermore, many people today have systemic inflammation, which will also influence glial responsiveness to treatment and further cancer growth. An emerging body of literature has demonstrated that non-adaptive immune cells have a form of ‘memory’ through epigenetic regulation, which results in either an increased or decreased ability to react to subsequent stimuli. How the systemic effect of inflammation, modeled by beta glucan, influences radiotherapy outcomes is not fully understood. In the brain metastasis context, many peripheral immune cells will migrate to the brain. Ccr2 positive myeloid cells increase proportionally in mice treated with radiation when compared to control mice. To gain a better understanding of what is occurring within the treated brain metastatic niche this proposal seeks to examine 1) the mechanisms through which radiation therapy-stimulated complement signaling in microglia and infiltration of peripheral myeloid cells regulate brain metastasis progression and 2) discover how systemic inflammation influences radiotherapy outcomes and how systemic inflammation could be treated to ensure proper microglial functioning. Utilizing cellular imaging, qPCR, and ATAC- and RNA-seq we will explore how microglial cells are trained by radiation, systemic inflammation, and how this could be treated. To discover how proper functioning of microglia is critical to positive outcomes we will use genetic knockouts. The overarching hypothesis is that radiation alone and radiation within the context of systemic inflammation leads to alterations within microglia which contribute to a pro-inflammatory and overactive phenotype. To test this hypothesis two specific aims will be explored. Experiments under Aim 1 will 1) if complement signaling is a factor in brain metastasis outgrowth and 2) uncover the role of Ccr2+ infiltrating myeloid cells within the brain metastatic niche. Aim 2 will focus on 1) how systemic inflammation trains microglia, 2) if the mechanism behind training is PI3K-AKT, and 3) if we can treat systemic inflammation trained microglia with drugs that work synergistically with radiotherapy. Collectively these data will reveal mechanisms important to metastatic growth within mice exposed to radiation alone or radiation in concert with systemic inflammation, focusing primarily on microglia. This research will have broad implications for understanding what is occurring within the brain metastatic niche as well as for potential avenues for therapeutic potential.
