LDL receptor-related protein-1 (LRP1) is an endocytic and cellsignaling receptor. In mice in which LRP1 is deleted in myeloid cells, the response to lipopolysaccharide (LPS) was greatly exacerbated. LRP1 deletion in macrophages in vitro, under the control of tamoxifen-activated Cre-ER T fusion protein, robustly increased expression of proinflammatory cytokines and chemokines. In LRP1-expressing macrophages, proinflammatory mediator expression was regulated by LRP1 ligands in a ligand-specific manner. The LRP1 agonists, α 2 -macroglobulin and tissue-type plasminogen activator, attenuated expression of inflammatory mediators, even in the presence of LPS. The antagonists, receptor-associated protein (RAP) and lactoferrin (LF), and LRP1-specific antibody had the entirely opposite effect, promoting inflammatory mediator expression and mimicking LRP1 deletion. NFκB was rapidly activated in response to RAP and LF and responsible for the initial increase in expression of proinflammatory mediators. RAP and LF also significantly increased expression of microRNA-155 (miR-155) after a lag phase of about 4 h. miR-155 expression reflected, at least in part, activation of secondary cell-signaling pathways downstream of TNFα. Although miR-155 was not involved in the initial induction of cytokine expression in response to LRP1 antagonists, miR-155 was essential for sustaining the proinflammatory response. We conclude that LRP1, NFκB, and miR-155 function as members of a previously unidentified system that has the potential to inhibit or sustain inflammation, depending on the continuum of LRP1 ligands present in the macrophage microenvironment.LDL receptor-related protein-1 | tissue-type plasminogen activator | lipopolysaccharide | NFκB | microRNA-155

Tissue-type plasminogen activator (tPA) is the major intravascular activator of fibrinolysis and a ligand for receptors involved in cell signaling. In cultured macrophages, tPA inhibits the response to lipopolysaccharide (LPS) by a pathway that apparently requires low-density lipoprotein receptor-related protein-1 (LRP1). Herein, we show that the mechanism by which tPA neutralizes LPS involves rapid reversal of IκBα phosphorylation. tPA independently induced transient IκBα phosphorylation and extracellular signal-regulated kinase 1/2 (ERK1/2) activation in macrophages; however, these events did not trigger inflammatory mediator expression. The tPA signaling response was distinguished from the signature of signaling events elicited by proinflammatory LRP1 ligands, such as receptor-associated protein (RAP), which included sustained IκBα phosphorylation and activation of all 3 MAP kinases (ERK1/2, c-Jun kinase, and p38 MAP kinase). Enzymatically active and inactive tPA demonstrated similar immune modulatory activity. Intravascular administration of enzymatically inactive tPA in mice blocked the toxicity of LPS. In mice not treated with exogenous tPA, the plasma concentration of endogenous tPA increased 3-fold in response to LPS, to 116 ± 15 pM, but remained below the approximate threshold for eliciting anti-inflammatory cell signaling in macrophages (∼2.0 nM). This threshold is readily achieved in patients when tPA is administered therapeutically for stroke. In addition to LRP1, we demonstrate that the -methyl-D-aspartic acid receptor (NMDA-R) is expressed by macrophages and essential for anti-inflammatory cell signaling and regulation of cytokine expression by tPA. The NMDA-R and Toll-like receptor-4 were not required for proinflammatory RAP signaling. By mediating the tPA response in macrophages, the NMDA-R provides a pathway by which the fibrinolysis system may regulate innate immunity.

520S troke is a leading cause of death and long-term disabilities worldwide. Despite years of intense research and preclinical identification of numerous potential neuroprotective compounds, the only available treatment for brain ischemia relies on thrombolysis through injection of a recombinant tissuetype plasminogen activator. However, the treatment benefits to <10% of stroke victims because of a narrow therapeutical time window (<4.5 hours after stroke onset) and side effects. Consequently, there is a crucial need for the development of other strategies that could target later phases of the pathophysiological cascade of events after stroke.Since its initial discovery, several studies have highlighted the neuroprotective effect of pituitary adenylate cyclase-activating polypeptide (PACAP) 2 in in vitro and in vivo models of neurodegenerative diseases.3,4 Administered either before or few hours after middle cerebral artery occlusion, PACAP reduces the infarct volume area and improves functional outcomes. [5][6][7] Beside its well-known antiapoptotic activity, the neuropeptide PACAP exerts potent anti-inflammatory properties on innate immune compartment as illustrated by the decrease of the production of proinflammatory mediators interleukin (IL)-12, tumor necrosis factor (TNF)-α, and nitric oxide and the induction of the anti-inflammatory cytokine IL-10 in PACAP-treated macrophages stimulated by lipopolysaccharides.8-10 Whether PACAP acts directly by reducing apoptotic neuronal death 11 or indirectly via modulation of Background and Purpose-Until now, except thrombolysis, the therapeutical strategies targeting the acute phase of cerebral ischemia have been proven ineffective, and no approach is available to attenuate the delayed cell death mechanisms and the resulting functional deficits in the late phase. Then, we investigated whether a targeted and delayed delivery of pituitary adenylate cyclase-activating polypeptide (PACAP), a peptide known to exert neuroprotective activities, may dampen delayed pathophysiological processes improving functional recovery. Methods-Three days after permanent focal ischemia, PACAP-producing stem cells were transplanted intracerebroventricularly in nonimmunosuppressed mice. At 7 and 14 days post ischemia, the effects of this stem cell-based targeted delivery of PACAP on functional recovery, volume lesions, and inflammatory processes were analyzed. Results-The