viral-mediated-labeling-transplantation-medial-ganglionic-eminence

Viral-mediated Labeling and Transplantation of Medial Ganglionic Eminence (MGE) Cells for <em>In Vivo</em> Studies

GABAergic cortical interneurons, derived from the embryonic medial and caudal ganglionic eminences (MGE and CGE), are functionally and morphologically ...

University of California San Francisco

In recent years, the classic view that glucocorticoids, the adrenal steroids secreted during stress, are universally anti-inflammatory has been challenged at a variety of levels. It was first observed that under some circumstances, acute GC exposure could have pro-inflammatory effects on the peripheral immune response. More recently, chronic exposure to GCs has been found to have pro-inflammatory effects on the specialized immune response to injury in the central nervous system. Here we review the evidence that in some cases, glucocorticoids can increase pro-inflammatory cell migration, cytokine production, and even transcription factor activity in the brain. We consider how these unexpected effects of glucocorticoids can co-exist with their well-established anti-inflammatory properties, as well as the considerable clinical implications of these findings.

An inflammatory review of glucocorticoid actions in the CNS.

Glucocorticoids can arm macrophages for innate immune battle.

Glucocorticoids (GCs) are hormones released during the stress response that are well known for their immunosuppressive and anti-inflammatory properties; however, recent advances have uncovered situations wherein they have effects in the opposite direction. The CNS is a particularly interesting example, both because of its unique immune environment, and because GCs affect immune responses differently in different brain regions. In this minireview we discuss the contexts wherein GCs increase CNS inflammation and point out directions for future investigation.

The stressed CNS: when glucocorticoids aggravate inflammation.

Although the anti-inflammatory actions of glucocorticoids (GCs) are well established, evidence has accumulated showing that proinflammatory GC effects can occur in the brain, in a poorly understood manner. Using electrophoretic mobility shift assay, real-time PCR, and immunoblotting, we investigated the ability of varying concentrations of corticosterone (CORT, the GC of rats) to modulate lipopolysaccharide (LPS)-induced activation of NF-κB (nuclear factor κB), expression of anti- and proinflammatory factors and of the MAP (mitogen-activated protein) kinase family [ERK (extracellular signal-regulated kinase), p38, and JNK/SAPK (c-Jun N-terminal protein kinase/stress-activated protein kinase)], and AKT. In the frontal cortex, elevated CORT levels were proinflammatory, exacerbating LPS effects on NF-κB, MAP kinases, and proinflammatory gene expression. Milder proinflammatory GCs effects occurred in the hippocampus. In the absence of LPS, elevated CORT levels increased basal activation of ERK1/2, p38, SAPK/JNK, and AKT in both regions. These findings suggest that GCs do not uniformly suppress neuroinflammation and can even enhance it at multiple levels in the pathway linking LPS exposure to inflammation.

Glucocorticoids exacerbate lipopolysaccharide-induced signaling in the frontal cortex and hippocampus in a dose-dependent manner.

Research with experimental stroke models has identified a wide range of therapeutic proteins that can prevent the brain damage caused by this form of acute neurological injury. Despite this, we do not yet have safe and effective ways to deliver therapeutic proteins to the injured brain, and this remains a major obstacle for clinical translation. Current targeted strategies typically involve invasive neurosurgery, whereas systemic approaches produce the undesirable outcome of non-specific protein delivery to the entire brain, rather than solely to the injury site. As a potential way to address this, we developed a protein delivery system modeled after the endogenous immune cell response to brain injury. Using ex-vivo-engineered dendritic cells (DCs), we find that these cells can transiently home to brain injury in a rat model of stroke with both temporal and spatial selectivity. We present a standardized method to derive injury-responsive DCs from bone marrow and show that injury targeting is dependent on culture conditions that maintain an immature DC phenotype. Further, we find evidence that when loaded with therapeutic cargo, cultured DCs can suppress initial neuron death caused by an ischemic injury. These results demonstrate a non-invasive method to target ischemic brain injury and may ultimately provide a way to selectively deliver therapeutic compounds to the injured brain.

Derivation of injury-responsive dendritic cells for acute brain targeting and therapeutic protein delivery in the stroke-injured rat.

Glucocorticoid stress hormones (GCs) are well known for being anti-inflammatory, but some reports suggest that GCs can also augment aspects of inflammation during acute brain injury. Because the GC receptor (GR) is ubiquitously expressed throughout the brain, it is difficult to know which cell types might mediate these unusual "proinflammatory" GC actions. We examined this with cell type-specific deletion or overexpression of GR in mice experiencing seizure or ischemia. Counter to their classical anti-inflammatory actions, GR signaling in myeloid cells increased Iba-1 and CD68 staining as well as nuclear p65 levels in the injured tissue. GCs also reduced levels of occludin, claudin 5, and caveolin 1, proteins central to blood-brain-barrier integrity; these effects required GR in endothelial cells. Finally, GCs compromised neuron survival, an effect mediated by GR in myeloid and endothelial cells to a greater extent than by neuronal GR.

Glucocorticoid signaling in myeloid cells worsens acute CNS injury and inflammation.

Relapse management is a crucial component of multiple sclerosis (MS) care. High-dose corticosteroids (CSs) are used to dampen inflammation, which is thought to hasten the recovery of MS relapse. A diversity of mechanisms drive the heterogeneous clinical response to exogenous CSs in patients with MS. Preclinical research is beginning to provide important insights into how CSs work, both in terms of intended and unintended effects. In this article we discuss cellular, systemic, and clinical characteristics that might contribute to intended and unintended CS effects when utilizing supraphysiological doses in clinical practice. The goal of this article is to consider recent insights about CS mechanisms of action in the context of MS.

Mechanistic insights into corticosteroids in multiple sclerosis: war horse or chameleon?.

Stress exacerbates neuron loss in many CNS injuries via the actions of adrenal glucocorticoid (GC) hormones. For some injuries, this GC endangerment of neurons is accompanied by greater immune cell activation in the CNS, a surprising outcome given the potent immunosuppressive properties of GCs.

Article	Year
An inflammatory review of glucocorticoid actions in the CNS. Brain, behavior, and immunity\| PubMed ID: 17194565	2007
Glucocorticoids can arm macrophages for innate immune battle. Brain, behavior, and immunity\| PubMed ID: 19822202	2010
The stressed CNS: when glucocorticoids aggravate inflammation. Neuron\| PubMed ID: 19840546	2009
Glucocorticoids exacerbate lipopolysaccharide-induced signaling in the frontal cortex and hippocampus in a dose-dependent manner. The Journal of neuroscience : the official journal of the Society for Neuroscience\| PubMed ID: 20943909	2010
Derivation of injury-responsive dendritic cells for acute brain targeting and therapeutic protein delivery in the stroke-injured rat. PloS one\| PubMed ID: 23613937	2013
Glucocorticoid signaling in myeloid cells worsens acute CNS injury and inflammation. The Journal of neuroscience : the official journal of the Society for Neuroscience\| PubMed ID: 23637179	2013
Mechanistic insights into corticosteroids in multiple sclerosis: war horse or chameleon?. Clinical neurology and neurosurgery\| PubMed ID: 24635918	2014
Glucocorticoids increase excitotoxic injury and inflammation in the hippocampus of adult male rats. Neuroendocrinology\| PubMed ID: 25228100	2014

Shawn F. Sorrells

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