Neuronal Guidance Proteins Research Articles

The guidance receptor neogenin promotes pulmonary inflammation during lung injury

Lung injury is marked by a persistent self-propagating inflammation within the pulmonary tissue that is initiated by the migration of leukocytes into the alveolar space. Recent work has demonstrated that neuronal guidance proteins are involved into the orchestration of leukocyte migration. Neogenin is a crucial guidance receptor for axonal migration, yet its role during leukocyte migration and acute inflammation is to date unknown. Here, we report that neogenin influences neutrophil migration across endothelial HMEC-1 and alveolar A549 monolayers in vitro. In vivo, Neo1(-/-) mice demonstrated 59% reduced cell count, 41% reduced TNF-α, and 76% reduced IL-6 levels within the alveolar space during lung injury. In studies employing chimeric animals, the presence of Neo1(-/-) bone marrow was associated with a 42% reduction of cell count and reduced inflammatory changes within pulmonary tissue during lung injury. The functional inhibition of neogenin through antibody injection confirmed these results and the role of neogenin for the inflammatory changes within the alveolar space. Previously unappreciated, the guidance receptor neogenin has a significant effect on the orchestration of leukocyte migration and the control of acute inflammation.

Netrin-1 Dampens Pulmonary Inflammation during Acute Lung Injury

Acute lung injury (ALI) is an inflammatory disorder characterized by hypoxemia and diffuse infiltration of neutrophils into the alveolar space. The migration and extravasation of neutrophils is guided through positive guidance cues, such as chemokines. Recent work has identified the neuronal guidance protein netrin-1 to be a negative guidance cue for leukocyte migration and to hold antiinflammatory potential. To test the role of pulmonary netrin-1 during ALI. Pulmonary netrin-1 expression was evaluated during acute inflammation in vitro and in vivo; the netrin-1 promoter was studied using pGL4 luciferase reporter. ALI was induced through LPS inhalation and mechanical ventilation in wild-type, Ntn1(+/-), and A2BAR(-/-) animals. Exogenous netrin-1 was used to evaluate its impact on pulmonary inflammation. Wild-type animals demonstrated repression of pulmonary netrin-1 after LPS inhalation. In vitro studies confirmed the repression of netrin-1. Studies in the putative netrin-1 promoter identified a nuclear factor-kappaB-dependent mechanism to be involved in this repression. Ntn1(+/-) animals demonstrated increased inflammatory changes after LPS inhalation compared with Ntn1(+/+) animals. Reconstitution with netrin-1 dampened the infiltration of neutrophils and cytokine production in the alveolar space. This effect was dependent on the adenosine 2b receptor. The importance of netrin-1 for the control of pulmonary inflammation could be corroborated in a model of ventilator-induced lung injury. Pulmonary netrin-1 levels are repressed during ALI. This results in pronounced pulmonary damage, an increased infiltration of neutrophils, and increased pulmonary inflammation. Exogenous netrin-1 significantly dampens the extent of ALI through the adenosine 2B receptor.

The neuronal guidance protein netrin-1 reduces alveolar inflammation in a porcine model of acute lung injury

IntroductionAcute lung injury (ALI) is an inflammatory disorder of pulmonary or extrapulmonary origin. We have previously demonstrated that netrin-1 dampens murine ALI, and in an attempt to advance this finding into future clinical practice we evaluated whether netrin-1 would reduce alveolar inflammation during porcine ALI.MethodsThis was a controlled in vivo experimental study in pigs. We induced ALI through lipoploysaccharide (LPS) infusion (50 μg/kg) for 2 hours. Following this, we exposed animals to either vehicle, intravenous netrin-1 (netrin-1 i.v.) or inhaled netrin-1 (netrin-1 inh.). Serum samples and bronchoalveolar lavage (BAL) were obtained to determine levels of tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, interleukin-6 and interleukin-8 at baseline and 6 hours following treatment. Myeloperoxidase activity (MPO) and protein levels were determined in the BAL, and tissue samples were obtained for histological evaluation. Finally, animals were scanned with spiral CT.ResultsFollowing LPS infusion, animals developed acute pulmonary injury. Serum levels of TNF-α and IL-6 were significantly reduced in the netrin-1 i.v. group. BAL demonstrated significantly reduced cytokine levels 6 hours post-netrin-1 treatment (TNF-α: vehicle 633 ± 172 pg/ml, netrin-1 i.v. 84 ± 5 pg/ml, netrin-1 inh. 168 ± 74 pg/ml; both P < 0.05). MPO activity and protein content were significantly reduced in BAL samples from netrin-1-treated animals. Histological sections confirmed reduced inflammatory changes in the netrin-1-treated animals. Computed tomography corroborated reduced pulmonary damage in both netrin-1-treated groups.ConclusionsWe conclude that treatment with the endogenous anti-inflammatory protein netrin-1 reduces pulmonary inflammation during the initial stages of ALI and should be pursued as a future therapeutic option.

Netrin requires focal adhesion kinase and Src family kinases for axon outgrowth and attraction

Although netrins are an important family of neuronal guidance proteins, intracellular mechanisms that mediate netrin function are not well understood. Here we show that netrin-1 induces tyrosine phosphorylation of proteins including focal adhesion kinase (FAK) and the Src family kinase Fyn. Blockers of Src family kinases inhibited FAK phosphorylation and axon outgrowth and attraction by netrin. Dominant-negative FAK and Fyn mutants inhibited the attractive turning response to netrin. Axon outgrowth and attraction induced by netrin-1 were significantly reduced in neurons lacking the FAK gene. Our results show the biochemical and functional links between netrin, a prototypical neuronal guidance cue, and FAK, a central player in intracellular signaling that is crucial for cell migration.

Changes in the Molecular Structure of the Brain in Bipolar Disorder: Findings using Human Postmortem Brain Tissue

Summary: Human postmortem brain studies are beginning to suggest mechanisms that underlie the pathology of bipolar disorder. Evidence that implicates abnormalities in G-protein, neurotransmitter turnover, nemo-transmitter receptors and neurotransmitter receptor signal amplification will be reviewed. In addition, individual studies that suggest roles for pre-synaptic proteins, neuronal guidance proteins, neuropeptides, intra-neuronal ion homeostasis and environmental factor reactive proteins in the pathology of the disorder are also presented. Together these studies confirm that the pathology of bipolar disorder is complex but is yielding to intense study of the molecular architecture of postmortem brain tissue from subjects with the illness.