title: Apolipoprotein E receptors mediate neurite outgrowth through activation of p44/42 mitogen-activated protein kinase in primary neurons.
abstract: Several ligands of the endocytic low density lipoprotein receptor-related protein (LRP), such as apoE-containing lipoproteins and activated alpha2-macroglobulin (alpha2M*), promote neurite outgrowth, suggesting that LRP may have signaling functions. In this study, we found that the treatment of neurons with alpha2M* significantly increased the individual length (by 71%) and numbers (by 139%) of neurites of primary mouse cortical neurons. These effects were blocked by the LRP antagonist, the receptor-associated protein. We found similar neurite outgrowth with purified apoE3 and a tandem apoE peptide containing only the receptor-binding domain. To investigate the intracellular pathway of the LRP signaling involved in neurite outgrowth, we tested the effects of alpha2M* on the phosphorylation of the mitogen-activated protein (MAP) extracellular signal-regulated kinases 1 and 2 (ERK1/2). We found that 1) phospho-MAP kinase levels were altered within 30 min after treatment with alpha2M*, 2) the MAP kinase inhibitor, PD98059, specifically blocked the alpha2M*-induced neurite outgrowth, 3) manipulating intracellular calcium by BayK or BAPTA altered the neurite outgrowth and associated changes in the phospho-MAP kinase levels, which were blunted by alpha2M*, 4) alpha2M* promoted the phosphorylation of the transcription factor CREB through MAP kinase, and 5) LRP-specific antibodies increased levels of phosphorylated MAP kinase and phosphorylated CREB. The effects of alpha2M*, apoE3, and apoE peptides increased LRP levels in the cortical neurons, whereas LRP receptor-associated protein reduced dendritic LRP expression. These results demonstrate that p44/42 MAP kinase plays an important role in LRP-mediated neurite outgrowth with activation involving the effects on calcium homeostasis and downstream effects involving the activation of gene transcription through CREB.
authors.affiliation: Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129, USA.
authors.forename: Zhihua
authors.initials: Z
authors.lastname: Qiu
authors.forename: Bradley T
authors.initials: BT
authors.lastname: Hyman
authors.forename: G William
authors.initials: GW
authors.lastname: Rebeck
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D008024:Ligands; D026503:Low Density Lipoprotein Receptor-Related Protein-1 / Q000502:physiology*; D020935:MAP Kinase Signaling System; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008954:Models, Biological; D009474:Neurons / Q000201:enzymology* / Q000378:metabolism / Q000502:physiology*; D010766:Phosphorylation; D015398:Signal Transduction; D013997:Time Factors
chemical_list: D004791:Enzyme Inhibitors; D005419:Flavonoids; D008024:Ligands; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D002118:Calcium