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Cerebral nitric oxide represses choroid plexus NF?B-dependent gateway activity for leukocyte trafficking.

ABSTRACT: Chronic neuroinflammation is evident in brain aging and neurodegenerative disorders and is often associated with excessive nitric oxide (NO) production within the central nervous system (CNS). Under such conditions, increased NO levels are observed at the choroid plexus (CP), an epithelial layer that forms the blood-cerebrospinal fluid barrier (BCSFB) and serves as a selective gateway for leukocyte entry to the CNS in homeostasis and following injury. Here, we hypothesized that elevated cerebral NO levels interfere with CP gateway activity. We found that induction of leukocyte trafficking determinants by the CP and sequential leukocyte entry to the CSF are dependent on the CP epithelial NF?B/p65 signaling pathway, which was inhibited upon exposure to NO. Examining the CP in 5XFAD transgenic mouse model of Alzheimer's disease (AD-Tg) revealed impaired ability to mount an NF?B/p65-dependent response. Systemic administration of an NO scavenger in AD-Tg mice alleviated NF?B/p65 suppression at the CP and augmented its gateway activity. Together, our findings identify cerebral NO as a negative regulator of CP gateway activity for immune cell trafficking to the CNS.

SUBMITTER: Baruch K

PROVIDER: S-EPMC4516433 | biostudies-literature | 2015 Jul

REPOSITORIES: biostudies-literature

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Cerebral nitric oxide represses choroid plexus NFκB-dependent gateway activity for leukocyte trafficking.

Baruch Kuti K Kertser Alexander A Porat Ziv Z Schwartz Michal M

The EMBO journal 20150504 13

Chronic neuroinflammation is evident in brain aging and neurodegenerative disorders and is often associated with excessive nitric oxide (NO) production within the central nervous system (CNS). Under such conditions, increased NO levels are observed at the choroid plexus (CP), an epithelial layer that forms the blood-cerebrospinal fluid barrier (BCSFB) and serves as a selective gateway for leukocyte entry to the CNS in homeostasis and following injury. Here, we hypothesized that elevated cerebral ...[more]

PMID: 25940071

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Project description:Perinatal infection and inflammation are major risk factors for injury in the developing brain, however, underlying mechanisms are not fully understood. Leukocyte migration to the cerebrospinal fluid (CSF) and brain is a hallmark of many pathologies of the central nervous system including those in neonates. We previously reported that systemic activation of Toll-like receptor (TLR) 2, a major receptor for gram-positive bacteria, by agonist Pam3CSK4 (P3C) resulted in dramatic neutrophil and monocyte infiltration to the CSF and periventricular brain of neonatal mice, an effect that was absent by the TLR4 agonist, LPS. Here we first report that choroid plexus is a route of TLR2-mediated leukocyte infiltration to the CSF by performing flow cytometry and transmission electron microscopy (TEM) of the choroid plexus. Next, we exploited the striking discrepancy between P3C and LPS effects on cell migration to determine the pathways regulating leukocyte trafficking through the choroid plexus. We performed RNA sequencing on the choroid plexus after administration of P3C and LPS to postnatal day 8 mice. A cluster gene analysis revealed a TLR2-specific signature of chemotaxis represented by 80-fold increased expression of the gene Ccl3 and 1000-fold increased expression of the gene Cxcl2. Ingenuity pathway analysis (IPA) revealed TLR2-specific molecular signaling related to cytoskeleton organization (e.g. actin signaling) as well as inositol phospholipids biosynthesis and degradation. This included upregulation of genes such as Rac2 and Micall2. In support of IPA results, ultrastructural analysis by TEM revealed clefting and perforations in the basement membrane of the choroid plexus epithelial cells in P3C-treated mice. In summary, we show that the choroid plexus is a route of TLR2-mediated transmigration of neutrophils and monocytes to the developing brain, and reveal previously unrecognized mechanisms that includes a specific chemotaxis profile as well as pathways regulating cytoskeleton and basement membrane remodeling.

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Project description:The choroid plexus (CP) consists of specialized ependymal cells and underlying blood vessels and stroma producing the bulk of the cerebrospinal fluid (CSF). CP epithelial cells are considered the site of the internal blood-cerebrospinal fluid barrier, show epithelial characteristics (basal lamina, tight junctions), and express aquaporin-1 (AQP1) apically. In this study, we analyzed the expression of aquaporins in the human CP using immunofluorescence and qPCR. As previously reported, AQP1 was expressed apically in CP epithelial cells. Surprisingly, and previously unknown, many cells in the CP epithelium were also positive for aquaporin-4 (AQP4), normally restricted to ventricle-lining ependymal cells and astrocytes in the brain. Expression of AQP1 and AQP4 was found in the CP of all eight body donors investigated (3 males, 5 females; age 74-91). These results were confirmed by qPCR, and by electron microscopy detecting orthogonal arrays of particles. To find out whether AQP4 expression correlated with the expression pattern of relevant transport-related proteins we also investigated expression of NKCC1, and Na/K-ATPase. Immunostaining with NKCC1 was similar to AQP1 and revealed no particular pattern related to AQP4. Co-staining of AQP4 and Na/K-ATPase indicated a trend for an inverse correlation of their expression. We hypothesized that AQP4 expression in the CP was caused by age-related changes. To address this, we investigated mouse brains from young (2 months), adult (12 months) and old (30 months) mice. We found a significant increase of AQP4 on the mRNA level in old mice compared to young and adult animals. Taken together, we provide evidence for AQP4 expression in the CP of the aging brain which likely contributes to the water flow through the CP epithelium and CSF production. In two alternative hypotheses, we discuss this as a beneficial compensatory, or a detrimental mechanism influencing the previously observed CSF changes during aging.

Dataset Information

Cerebral nitric oxide represses choroid plexus NF?B-dependent gateway activity for leukocyte trafficking.

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Cerebral nitric oxide represses choroid plexus NFκB-dependent gateway activity for leukocyte trafficking.

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