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Sex differences in microglial colonization of the developing rat brain.

ABSTRACT: Microglia are the resident immune cells within the brain and their production of immune molecules such as cytokines and chemokines is critical for the processes of normal brain development including neurogenesis, axonal migration, synapse formation, and programmed cell death. Notably, sex differences exist in many of these processes throughout brain development; however, it is unknown whether a sex difference concurrently exists in the colonization, number, or morphology of microglia within the developing brain. We demonstrate for the first time that the number and morphology of microglia throughout development is dependent upon the sex and age of the individual, as well as the brain region of interest. Males have overall more microglia early in postnatal development [postnatal day (P) 4], whereas females have more microglia with an activated/amoeboid morphology later in development, as juveniles and adults (P30-60). Finally, gene expression of a large number of cytokines, chemokines and their receptors shifts dramatically over development, and is highly dependent upon sex. Taken together, these data warrant further research into the role that sex-dependent mechanisms may play in microglial colonization, number, and function, and their potential contribution to neural development, function, or potential dysfunction.

SUBMITTER: Schwarz JM

PROVIDER: S-EPMC3296888 | biostudies-literature | 2012 Mar

REPOSITORIES: biostudies-literature

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Sex differences in microglial colonization of the developing rat brain.

Schwarz Jaclyn M JM Sholar Paige W PW Bilbo Staci D SD

Journal of neurochemistry 20120209 6

Microglia are the resident immune cells within the brain and their production of immune molecules such as cytokines and chemokines is critical for the processes of normal brain development including neurogenesis, axonal migration, synapse formation, and programmed cell death. Notably, sex differences exist in many of these processes throughout brain development; however, it is unknown whether a sex difference concurrently exists in the colonization, number, or morphology of microglia within the ...[more]

PMID: 22182318

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Project description:Congenital cytomegalovirus infections are a leading cause of neurodevelopmental disorders in human and represent a major health care and socio-economical burden. In contrast with this medical importance, the pathophysiological events remain poorly known. Murine models of brain cytomegalovirus infection, mostly neonatal, have brought recent insights into the possible pathogenesis, with convergent evidence for the alteration and possible involvement of brain immune cells.In order to confirm and expand those findings, particularly concerning the early developmental stages following infection of the fetal brain, we have created a model of in utero cytomegalovirus infection in the developing rat brain. Rat cytomegalovirus was injected intraventricularly at embryonic day 15 (E15) and the brains analyzed at various stages until the first postnatal day, using a combination of gene expression analysis, immunohistochemistry and multicolor flow cytometry experiments.Rat cytomegalovirus infection was increasingly seen in various brain areas including the choroid plexi and the ventricular and subventricular areas and was prominently detected in CD45low/int, CD11b+ microglial cells, in CD45high, CD11b+ cells of the myeloid lineage including macrophages, and in CD45+, CD11b- lymphocytes and non-B non-T cells. In parallel, rat cytomegalovirus infection of the developing rat brain rapidly triggered a cascade of pathophysiological events comprising: chemokines upregulation, including CCL2-4, 7 and 12; infiltration by peripheral cells including B-cells and monocytes at E17 and P1, and T-cells at P1; and microglia activation at E17 and P1.In line with previous findings in neonatal murine models and in human specimen, our study further suggests that neuroimmune alterations might play critical roles in the early stages following cytomegalovirus infection of the brain in utero. Further studies are now needed to determine which role, whether favorable or detrimental, those putative double-edge swords events actually play.

Project description:During normal neurodevelopment, microglia perform a range of different functions that are crucial for the proper development, circuit integration, and function of neurons. These functions include certain types of synaptic pruning during critical stages of neurodevelopment (Schafer et al., 2012), and the production of cytokines and chemokines during normal physiological tasks, proteins which are important for homeostasis in addition to immune defense (Avital et al., 2003; Goshen et al., 2007). Microglia and the inflammatory cytokines they produce (e.g., in response to injury or infection) are also increasingly implicated in neural dysfunction during development and the risk of neuropsychiatric disorders. Increasing evidence suggests many neurological disorders emerge because of disrupted neuronal developmental trajectory (Marin, 2016). Considering the critical role of microglia for integration of neurons into their proper circuitry as well in proper synapse formation, there is a pressing need to understand the mechanisms underlying normal and abnormal microglia development, their interactions with specific neuronal subsets, and to understand the utility of these same analyses for human tissue. Moreover, as there are pronounced sex differences in the presentation of many neurological disorders, it is critical to understand these mechanisms in both males and females. Here we study developmental gene expression changes in male and female mice from E18 to P60. We isolated microglia from male and female hippocampi of mice from different developmental ages ranging from embryonic day 18 (E18) to postnatal day 60 (P60). Hippocampus was selected based on its importance to mental health, its marked vulnerability relative to other brain regions in response to diverse threats to homeostasis (epilepsy, stroke, and cardiac arrest (Fujioka et al., 2000; Petito, Feldmann, Pulsinelli, & Plum, 1987; Salmenpera, Kalviainen, Partanen, & Pitkanen, 1998; Sapolsky, Uno, Rebert, & Finch, 1990)), and due to evidence of morphological sex differences in microglial development in this region (Schwarz, Sholar, & Bilbo, 2012). It was found that developmental gene expression changes were more advanced in females at P60 and that treatment with LPS, a potent immune activator, could normalize developmental gene expression differences in males.

Dataset Information

Sex differences in microglial colonization of the developing rat brain.

Publications

Sex differences in microglial colonization of the developing rat brain.

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