In glioma, microglia and infiltrating macrophages are exposed to factors that force them to produce cytokines and chemokines, contributing to tumor growth and maintaining a pro-tumor, immunosuppressed microenvironment. We have recently demonstrated that housing glioma-bearing mice in enriched environment (EE) reduced tumor growth, with effects mediated by BDNF and IL-15 (Garofalo et al., 2015). We now want to investigate whether housing glioma-bearing mice in EE reverts the immunosuppressive phenotype of invading myeloid cells. At this aim we will monitor myeloid cells for changes in their expression of inflammatory genes, in cell branching and in patrolling and phagocytic activity. We will also investigate whether the effects of EE are mediated by the interferon-(IFN)-gamma produced by NK cells, and by IL-15, a well known NK cell activator. These studies will be performed using a syngeneic mouse model of glioma, and will require the use of specific antibodies to deplete the NK cell population or the endogenous IFN-gamma, as well as the implantation of osmotic pumps for the controlled release of IL-15 or BDNF in the brain of glioma bearing mice, housed in the different conditions. BDNF+/- and IL-15ra-/- mice will be also used. At the end of the project, we will be able to describe the chain of molecular and cellular events involved in the modulation of myeloid cell phenotype eventually induced in glioma-bearing mice by the environmental changes.
Myeloid cells have key roles in glioma progression. In different mouse models of glioma, infiltrating microglia/macrophages acquire a predominant anti-inflammatory phenotype, and efforts to re-educate these cells toward a pro-inflammatory, anti-tumor phenotype, successfully reduce tumor size and increase the mean survival times (Mieczkowski et al, 2015). GAM, however, cannot be simply considered as M2-like cells, since they assume a plethora of different phenotypes, partially overlapping with the classical M1- or M2-macrophages, and in large part unique to GAMs (Szulzewsky et al., 2015). At difference, in human GAM, genes associated with immune pathways are not up-regulated (Szulzewsky et al., 2016), thus suggesting that additional models of GBM must be considered before translating the results obtained in mouse models to patients. Nevertheless, the importance of myeloid cells in brain tumors is also recognized in humans, thus supporting the need for further investigations, and also for exploring different approaches. It is known that living in environments that are enriched with sensorial, physical, and social stimuli can modulate brain microenvironment, affecting the levels of hormones involved in feeding behavior or linked to hypophyseal pituitary axis such as adiponectin, norepinephrine, BDNF and glucocorticoids (Cao et al., 2010). The external environment affects microglial cell proliferation in a brain region-specific manner (Ehninger et al., 2003, 2013); modifies brain-infiltrating myeloid cells in mouse model of depression, where the expression of pro-inflammatory genes is high, altering the response to antidepressant treatment (Alboni et al., 2016), and changes microglial number and morphology in a mouse model of Alzheimer's disease (Rodríguez et al., 2015). The mechanistic links between the macro-environment modifications and myeloid cell regulation is however lacking: possible candidates of this communication are the BDNF produced in the brain upon environmental stimuli, but also other molecules secreted by peripheral and infiltrating immune cells.
To exploit these hypotheses, we will investigated the effects of an EE on myeloid cell phenotype, and the possible intermediate role played by NK cells. Contrasting evidence describe positive or no effects on tumor progression for EE, considered as a sum of eu-stressing stimuli (Cao et al., 2010; Garofalo et al., 2015; Westwood et al., 2013). Clinical studies demonstrated that specific distressing stimuli, like depression, feelings of loneliness and lack of social relationships represent solid risk factors for cancer development and progression (Armaiz-Pena et al., 2009).
The proposed project will contribute to the description of the cellular and molecular mechanisms linking macro- to micro-environment modifications, and their impact on innate immune system activity in brain tumors.
REFERENCES
Alboni et al. (2016) Brain BehavImmun.;58:261-271.
Armaiz-Pena et al. (2009) Brain Behav Immun.;23(1):10-5.
Branchi et al. (2004) Behav Pharmacol 15: 353-362.
Cao, et al. (2010) Cell; 142(1):52-64.
Chabry et al. (2015)Brain Behav Immun. 50:275-87.
Coniglio et al. (2012) Matrix Biol;32(7-8):372-80.
Duluc, et al. (2009) Int J Cancer.; 125(2):367-73.
Dunn et al (2006) Nat Rev Immunol;6 (11):836-48.
Ehninger et al. (2003) Cereb Cortex; 13(8):845-51.
Ehninger et al. (2011) Cell Tissue Res; 345(1): 69¿86.
Gabrusiewicz K, et al. (2011) PLoS One;6(8):e23902.
Garofalo et al., (2015) Nat Commun; 6:6623.
Graeber, et al. (2002). Glia 40, 252¿259.
Jung et al. (2000) Mol Cell Biol. (11):4106-14.
Kaplan et al. (1998) Proc Natl Acad Sci U S A.;95(13):7556-61.
Koka et al. (2003) J Exp Med: 197:977-984.
Markovic et al. (2009) Proc Natl Acad Sci USA; 106 (30):12530-5.
Markovic et al (2005) Neuropathol. Exp. Neurol., 64: 754-762.
Mieczkowski et al. (2015) Oncotarget; 6(32):33077-90.
Murray et al (2014) Immunity. 17;41(1):14-20.
Nachat-Kappes et al., (2012) PLoS One;7(12):e51525.
Parker et al (2016) Nat Rev Cancer.;16(3):131-44.
Quail DF, & Joyce JA (2017) Cancer Cell. 31: 326-341
Rattazzi et al (2016) Profile Front Immunol.; 7: 381.
Rodríguez et al (2015) Brain Struct Funct; 220(2):941-53.
Sale et al (2014) Physiol Rev 94: 189-234.
Sica et al (2008) Semin Cancer Biol. (5):349-55.
Song Y, et al., (2017) Cancer Res;77(7):1611-1622.
Stabile et al (2017) Front Immunol; 8: 293.
Szulzewsky et al. (2015) PLoS One; 10(2):e0116644.
Szulzewsky, et al (2016) Glia; 64(8):1416-36.
Westwood et al (2013) F1000 Res 2, 140.
Ye et al (1999) Cancer Res.;59(17):4383-91.
Yu et al. (2006) Immunity; 24(5):575-90.
Vivier E, et al. (2011) Science; 331(6013):44-9.