Serial Systemic Injections of Endotoxin (LPS) Elicit Neuroprotective Spinal Cord Microglia through IL-1-Dependent Cross Talk with Endothelial Cells.

Microglia are dynamic immunosurveillance cells in the CNS. Whether microglia are protective or pathologic is context dependent; the outcome varies as a function of time relative to the stimulus, activation state of neighboring cells in the microenvironment or within progression of a particular disease. Although brain microglia can be "primed" using bacterial lipopolysaccharide (LPS)/endotoxin, it is unknown whether LPS delivered systemically can also induce neuroprotective microglia in the spinal cord. Here, we show that serial systemic injections of LPS (1 mg/kg, i.p., daily) for 4 consecutive days (LPSx4) consistently elicit a reactive spinal cord microglia response marked by dramatic morphologic changes, increased production of IL-1, and enhanced proliferation without triggering leukocyte recruitment or overt neuropathology. Following LPSx4, reactive microglia frequently contact spinal cord endothelial cells. Targeted ablation or selective expression of IL-1 and IL-1 receptor (IL-1R) in either microglia or endothelia reveal that IL-1-dependent signaling between these cells mediates microglia activation. Using a mouse model of ischemic spinal cord injury in male and female mice, we show that preoperative LPSx4 provides complete protection from ischemia-induced neuron loss and hindlimb paralysis. Neuroprotection is partly reversed by either pharmacological elimination of microglia or selective removal of IL-1R in microglia or endothelia. These data indicate that spinal cord microglia are amenable to therapeutic reprogramming via systemic manipulation and that this potential can be harnessed to protect the spinal cord from injury.SIGNIFICANCE STATEMENT Data in this report indicate that a neuroprotective spinal cord microglia response can be triggered by daily systemic injections of LPS over a period of 4 d (LPSx4). The LPSx4 regimen induces morphologic transformation and enhances proliferation of spinal cord microglia without causing neuropathology. Using advanced transgenic mouse technology, we show that IL-1-dependent microglia-endothelia cross talk is necessary for eliciting this spinal cord microglia phenotype and also for conferring optimal protection to spinal motor neurons from ischemic spinal cord injury (ISCI). Collectively, these novel data show that it is possible to consistently elicit spinal cord microglia via systemic delivery of inflammogens to achieve a therapeutically effective neuroprotective response against ISCI.

Antibody-mediated inhibition of syndecan-4 dimerisation reduces interleukin (IL)-1 receptor trafficking and signalling.

OBJECTIVE: Syndecan-4 (sdc4) is a cell-anchored proteoglycan that consists of a transmembrane core protein and glucosaminoglycan (GAG) side chains. Binding of soluble factors to the GAG chains of sdc4 may result in the dimerisation of sdc4 and the initiation of downstream signalling cascades. However, the question of how sdc4 dimerisation and signalling affects the response of cells to inflammatory stimuli is unknown. METHODS: Sdc4 immunostaining was performed on rheumatoid arthritis (RA) tissue sections. Interleukin (IL)-1 induced extracellular signal-regulated kinases (ERK) phosphorylation and matrix metalloproteinase-3 production was investigated. Il-1 binding to sdc4 was investigated using immunoprecipitation. IL-1 receptor (IL1R1) staining on wild-type, sdc4 and IL1R1 knockout fibroblasts was performed in fluorescence-activated cell sorting analyses. A blocking sdc4 antibody was used to investigate sdc4 dimerisation, IL1R1 expression and the histological paw destruction in the human tumour necrosis factor-alpha transgenic mouse. RESULTS: We show that in fibroblasts, the loss of sdc4 or the antibody-mediated inhibition of sdc4 dimerisation reduces the cell surface expression of the IL-1R and regulates the sensitivity of fibroblasts to IL-1. We demonstrate that IL-1 directly binds to sdc4 and in an IL-1R-independent manner leads to its dimerisation. IL-1-induced dimerisation of sdc4 regulates caveolin vesicle-mediated trafficking of the IL1R1, which in turn determines the responsiveness to IL-1. Administration of antibodies (Ab) against the dimerisation domain of sdc4, thus, strongly reduces the expression IL1R1 on arthritic fibroblasts both in vitro and an animal model of human RA. CONCLUSION: Collectively, our data suggest that Ab that specifically inhibit sdc4 dimerisation may support anti-IL-1 strategies in diseases such as inflammatory arthritis.

Pitavastatin up-regulates the induction of iNOS through enhanced stabilization of its mRNA in pro-inflammatory cytokine-stimulated hepatocytes.

Studies have indicated that protective effects of statins (HMG-CoA reductase inhibitor) are associated with the regulation of endothelial nitric oxide synthase (eNOS) or inducible NOS (iNOS) in heart and liver diseases. Statins have been reported to enhance hepatic NO production and decrease the vascular tone in patients with cirrhosis. However, it is unclear which NOS contributes to the increased NO production. We hypothesized that statins are involved in the up-regulation of iNOS in inflammatory liver, resulting in decreased hepatic resistance. Primary cultured rat hepatocytes were treated with pro-inflammatory cytokine interleukin (IL)-1beta in the presence or absence of pitavastatin. Pretreatment of cells with pitavastatin resulted in up-regulation of iNOS induction by IL-1beta, followed by increased NO production. Pitavastatin had no effects on the degradation of IkappaB or activation of NF-kappaB. However, pitavastatin super-induced the up-regulation of type I IL-1 receptor (IL-1RI), which is essential for iNOS induction in addition to the IkappaB/NF-kappaB pathway. Mevalonate and geranylgeranylpyrophosphate blocked the stimulatory effects of pitavastatin on iNOS and IL-1RI induction. Transfection experiments revealed that pitavastatin increased the stability of iNOS mRNA rather than its promoter transactivation. In support of this observation, pitavastatin increased the antisense-transcript corresponding to the 3'-UTR of iNOS mRNA, which stabilizes iNOS mRNA by interacting with the 3'-UTR- and RNA-binding proteins. These findings demonstrate that pitavastatin up-regulates iNOS by the stabilization of its mRNA, presumably through the super-induction of IL-1RI and antisense-transcript. This implies that statins may contribute to a novel potentiated treatment in liver injuries including cirrhosis.

Rebamipide, anti-gastric ulcer drug, up-regulates the induction of iNOS in proinflammatory cytokine-stimulated hepatocytes.

Nitric oxide (NO) generated from inducible NO synthase (iNOS) during hepatic injury has been reported to contribute to cytoprotection or cellular damage. Rebamipide, anti-gastric ulcer drug, has protective effects in a variety of tissue and organ injury. However, it remains unknown whether rebamipide is involved in the regulation of iNOS gene expression under pathological conditions. We examined whether rebamipide influences the induction of iNOS in hepatocytes exposed to pro-inflammatory cytokine. Primary cultured rat hepatocytes were treated with interleukin (IL)-1beta in the presence or absence of rebamipide. Pretreatment of cells with rebamipide resulted in up-regulation of iNOS induction by IL-1beta, followed by increased NO production. Rebamipide enhanced the degradation of IkappaBalpha and the activation of NF-kappaB. Further, rebamipide super-induced the up-regulation of type I IL-1 receptor (IL-1RI), which is essential for iNOS induction in addition to the IkappaB/NF-kappaB pathway. Transfection experiments revealed that rebamipide increased the transactivation of iNOS promoter and the stability of iNOS mRNA. In the latter, rebamipide increased the antisense-transcript corresponding to the 3'-UTR of iNOS mRNA, which stabilizes iNOS mRNA by interacting with the 3'-UTR and RNA-binding proteins. These findings demonstrate that rebamipide up-regulates iNOS by iNOS promoter activation through NF-kappaB, and by its mRNA stabilization presumably through the super-induction of IL-1RI and antisense-transcript. Rebamipide may contribute to a novel potentiated treatment in liver injuries.

Endothelial-specific knockdown of interleukin-1 (IL-1) type 1 receptor differentially alters CNS responses to IL-1 depending on its route of administration.

Interleukin-1 (IL-1) has been implicated as a critical mediator of neuroimmune communication. In the brain, the functional receptor for IL-1, type 1 IL-1 receptor (IL-1R1), is localized primarily to the endothelial cells. In this study, we created an endothelial-specific IL-1R1 knockdown model to test the role of endothelial IL-1R1 in mediating the effects of IL-1. Neuronal activation in the hypothalamus was measured by c-fos expression in the paraventricular nucleus and the ventromedial preoptic area. In addition, two specific sickness symptoms, febrile response and reduction of locomotor activity, were studied. Intracerebroventricular injection of IL-1 induced leukocyte infiltration into the CNS, activation of hypothalamic neurons, fever, and reduced locomotor activity in normal mice. Endothelial-specific knockdown of IL-1R1 abrogated all these responses. Intraperitoneal injection of IL-1 also induced neuronal activation in the hypothalamus, fever, and reduced locomotor activity, without inducing leukocyte infiltration into the brain. Endothelial-specific knockdown of IL-1R1 suppressed intraperitoneal IL-1-induced fever, but not the induction of c-fos in hypothalamus. When IL-1 was given intravenously, endothelial knockdown of IL-1R1 abolished intravenous IL-1-induced CNS activation and the two monitored sickness symptoms. In addition, endothelial-specific knockdown of IL-1R1 blocked the induction of cyclooxygenase-2 expression induced by all three routes of IL-1 administration. These results show that the effects of intravenous and intracerebroventricular IL-1 are mediated by endothelial IL-1R1, whereas the effects of intraperitoneal IL-1 are partially dependent on endothelial IL-1R1.