LDL receptor-related protein-1 regulates NFκB and microRNA-155 in macrophages to control the inflammatory response

LDL receptor-related protein-1 (LRP1) is an endocytic and cell-signaling 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, α2-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

Tissue-type plasminogen activator-primed human iPSC-derived neural progenitor cells promote motor recovery after severe spinal cord injury.

The goal of stem cell therapy for spinal cord injury (SCI) is to restore motor function without exacerbating pain. Induced pluripotent stem cells (iPSC) may be administered by autologous transplantation, avoiding immunologic challenges. Identifying strategies to optimize iPSC-derived neural progenitor cells (hiNPC) for cell transplantation is an important objective. Herein, we report a method that takes advantage of the growth factor-like and anti-inflammatory activities of the fibrinolysis protease, tissue plasminogen activator tPA, without effects on hemostasis. We demonstrate that conditioning hiNPC with enzymatically-inactive tissue-type plasminogen activator (EI-tPA), prior to grafting into a T3 lesion site in a clinically relevant severe SCI model, significantly improves motor outcomes. EI-tPA-primed hiNPC grafted into lesion sites survived, differentiated, acquired markers of motor neuron maturation, and extended βIII-tubulin-positive axons several spinal segments below the lesion. Importantly, only SCI rats that received EI-tPA primed hiNPC demonstrated significantly improved motor function, without exacerbating pain. When hiNPC were treated with EI-tPA in culture, NMDA-R-dependent cell signaling was initiated, expression of genes associated with stemness (Nestin, Sox2) was regulated, and thrombin-induced cell death was prevented. EI-tPA emerges as a novel agent capable of improving the efficacy of stem cell therapy in SCI

The Neuropeptide PACAP, a Potent Disease Modifier Candidate for Brain Stroke Treatment

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LRP1 deficiency in microglia blocks neuro-inflammation in the spinal dorsal horn and neuropathic pain processing.

Following injury to the peripheral nervous system (PNS), microglia in the spinal dorsal horn (SDH) become activated and contribute to the development of local neuro-inflammation, which may regulate neuropathic pain processing. The molecular mechanisms that control microglial activation and its effects on neuropathic pain remain incompletely understood. We deleted the gene encoding the plasma membrane receptor, LDL Receptor-related Protein-1 (LRP1), conditionally in microglia using two distinct promoter-Cre recombinase systems in mice. LRP1 deletion in microglia blocked development of tactile allodynia, a neuropathic pain-related behavior, after partial sciatic nerve ligation (PNL). LRP1 deletion also substantially attenuated microglial activation and pro-inflammatory cytokine expression in the SDH following PNL. Because LRP1 shedding from microglial plasma membranes generates a highly pro-inflammatory soluble product, we demonstrated that factors which activate spinal cord microglia, including lipopolysaccharide (LPS) and colony-stimulating factor-1, promote LRP1 shedding. Proteinases known to mediate LRP1 shedding, including ADAM10 and ADAM17, were expressed at increased levels in the SDH after PNL. Furthermore, LRP1-deficient microglia in cell culture expressed significantly decreased levels of interleukin-1β and interleukin-6 when treated with LPS. We conclude that in the SDH, microglial LRP1 plays an important role in establishing and/or amplifying local neuro-inflammation and neuropathic pain following PNS injury. The responsible mechanism most likely involves proteolytic release of LRP1 from the plasma membrane to generate a soluble product that functions similarly to pro-inflammatory cytokines in mediating crosstalk between cells in the SDH and in regulating neuropathic pain

LRP1 deficiency in microglia blocks neuro-inflammation in the spinal dorsal horn and neuropathic pain processing.

Following injury to the peripheral nervous system (PNS), microglia in the spinal dorsal horn (SDH) become activated and contribute to the development of local neuro-inflammation, which may regulate neuropathic pain processing. The molecular mechanisms that control microglial activation and its effects on neuropathic pain remain incompletely understood. We deleted the gene encoding the plasma membrane receptor, LDL Receptor-related Protein-1 (LRP1), conditionally in microglia using two distinct promoter-Cre recombinase systems in mice. LRP1 deletion in microglia blocked development of tactile allodynia, a neuropathic pain-related behavior, after partial sciatic nerve ligation (PNL). LRP1 deletion also substantially attenuated microglial activation and pro-inflammatory cytokine expression in the SDH following PNL. Because LRP1 shedding from microglial plasma membranes generates a highly pro-inflammatory soluble product, we demonstrated that factors which activate spinal cord microglia, including lipopolysaccharide (LPS) and colony-stimulating factor-1, promote LRP1 shedding. Proteinases known to mediate LRP1 shedding, including ADAM10 and ADAM17, were expressed at increased levels in the SDH after PNL. Furthermore, LRP1-deficient microglia in cell culture expressed significantly decreased levels of interleukin-1β and interleukin-6 when treated with LPS. We conclude that in the SDH, microglial LRP1 plays an important role in establishing and/or amplifying local neuro-inflammation and neuropathic pain following PNS injury. The responsible mechanism most likely involves proteolytic release of LRP1 from the plasma membrane to generate a soluble product that functions similarly to pro-inflammatory cytokines in mediating crosstalk between cells in the SDH and in regulating neuropathic pain

Delayed transplantation of PACAP expressing-stem cells improves functional recovery after brain stroke

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