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Peripherally derived macrophages can engraft the brain independent of irradiation and maintain an identity distinct from microglia

ABSTRACT: Peripherally derived macrophages infiltrate the brain after bone marrow transplantation and during central nervous system (CNS) inflammation. It was initially suggested that these engrafting cells were newly derived microglia and that irradiation was essential for engraftment to occur. However, it remains unclear whether brain-engrafting macrophages (beMφs) acquire a unique phenotype in the brain, whether long-term engraftment may occur without irradiation, and whether brain function is affected by the engrafted cells. In this study, we demonstrate that chronic, partial microglia depletion is sufficient for beMφs to populate the niche and that the presence of beMφs does not alter behavior. Furthermore, beMφs maintain a unique functional and transcriptional identity as compared with microglia. Overall, this study establishes beMφs as a unique CNS cell type and demonstrates that therapeutic engraftment of beMφs may be possible with irradiation-free conditioning regimens.

ORGANISM(S): Mus musculus

PROVIDER: GSE84819 | GEO | 2018/04/07

REPOSITORIES: GEO

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Project description:Expression profiling of distinct central nervous system (CNS) cell populations has been employed to facilitate disease classification and to provide insights into the molecular basis of brain pathology. One important cell type implicated in a wide variety of CNS disease states is the resident brain macrophage (microglia). In these studies, microglia are often isolated from dissociated brain tissue by flow sorting procedures [fluorescence-activated cell sorting (FACS)] or from postnatal glial cultures by mechanic isolation. Given the highly dynamic and state-dependent functions of these cells, the use of FACS or short-term culture methods may not accurately capture the biology of brain microglia. In the current study, we performed RNA-sequencing using Cx3cr1+/GFP labeled microglia isolated from the brainstem of 6-week-old mice to compare the transcriptomes of FACS-sorted versus laser capture microdissection (LCM). While both isolation techniques resulted in a large number of shared (common) transcripts, we identified transcripts unique to FACS-isolated and LCM-captured microglia. In particular, M-bM-^HM-<50% of these LCM-isolated microglial transcripts represented genes typically associated with neurons and glia. While these transcripts clearly localized to microglia using complementary methods, they were not translated into protein. Following the induction of murine experimental autoimmune encephalomyelitis, increased oligodendrocyte and neuronal transcripts were detected in microglia, while only the myelin basic protein oligodendrocyte transcript was increased in microglia after traumatic brain injury. Collectively, these findings have implications for the design and interpretation of microglia transcriptome-based investigations. Wildtype and GFP expressing microglia from mouse brainstems were flow sorted or captured by laser microdissection. Differences between the two isolation methods were verified and further examined in neurodegenerative disease models.

Project description:A major challenge in bone allogeneic marrow (BM) transplantation is overcoming engraftment resistance to avoid the clinical problem of graft rejection. Identifying genes and pathways that regulate BM engraftment may reveal molecular targets for overcoming these engraftment barriers. Previously, we developed a mouse model of BM transplantation that utilizes recipient conditioning with non-myeloablative total body irradiation followed by transplantation of allogeneic BM cells. We defined TBI doses that lead to graft rejection, that are permissive for engraftment, and mouse strain variation with regards to the permissive TBI dose. We now report gene expression analysis, using the Agilent Mouse 8x60K v3 expression arrays, in spleen of mice conditioned with TBI doses for evaluation in correlation to the expected engraftment phenotype. The spleens of mice given TBI demonstrated extensive differential gene expression, compared with un-irradiated controls, at both multiple testing-corrected P < .05 and fold change greater than or equal to 2 levels. Functional analysis revealed significant enrichment for up-regulation of canonical pathways involved in inflammation, even when treated with TBI doses not permissive for engraftment. Consistent with this the most significantly associated upstream regulators included lipopolysaccharide, tumor necrosis factor, and a toll-like receptor. Unique to engrafting mice, however, were enrichment for a down-regulated canonical pathway related to B-cell development. Results from this analysis have identified canonical pathways and upstream regulators of BM engraftment in mice and may lead to new approaches to overcome the problem of graft rejection complicating clinical BM transplantation. Each individual sample was pooled from 3 mice and performed in triplicate for each experimental group (TBI 300 cGy, 400 cGy, or 500 cGy) and for each strain mice (BALB.K or B10.BR) for statistical analysis. Additional arrays were perfromed for TBI 800 cGy (BALB.K) and TBI 900 cGy (B10.BR) for anlaysis of gene expressive after myeloablative condition.

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Peripherally derived macrophages can engraft the brain independent of irradiation and maintain an identity distinct from microglia

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