The Mechanisms Of EGFR In The Regulating Intrinsic Growth Activity Of Central Neurons

The intrinsic growth activity of central neurons being in developmentaldependence loss. Studies confirm that mature nerve tissue have a low growth abilityafter injury. It related to the regulatory mechanism of neuron growth and development.A new hypothesis about the axon regeneration failure after CNS injury--Genes whichcontrol the growth and development of central neurons were suppressed in matureneurons. So, neurons unable to effective regeneration after injury.Developmental period of the nerve growth belongs to growth factors dependence,these growth factors including NGF, BDNF, NT-3, etc., they through their respectivesignal receptor pathways to make neurons grow. In many signaling pathways,PI3K/Akt this signaling pathway is thought to be the most closely relationship withthe neurons growth. By coincidence, mTOR regulator is a substrate of the signalingpathways. Recent studies have shown that mammalian target of rapamycin (mTOR) isa key regulator to intrinsic growth activity on injured neurons. This demonstrates thatneuron′s mTOR expression level of high and low directly determines the strength ofthe regeneration. Studies have found that the Epidermal Growth Factor Receptor(EGFR) is widely expressed in the central nerve development process, andphosphorylated EGFR could activate mTOR. The above facts are hints of EGFR andcentral neurons is closely related to develop and mature.So we assume that EGFR related to neural development could affect the activityof mTOR through PI3K/Akt signaling pathway, which influence central neuronintrinsic growth activity.The objections of this study was to understand the relationship between EGFRand axon regeneration and to investigate the mechanisms of how EGFR regulating theneuronal intrinsic growth activity. Central expressions of EGFR, total mTOR,p-mTORSer2448, total Akt and p-AktSer473were evaluated in rats of differentdevelopmental stage using Western blot analysis and Real-time PCR. Using serumfree medium and retinoic acid induced differentiation in vitro of neural stem cells. Itmakes the identification of neurons maturity by form and nerve electrophysiology.Neuron cells were cultured with different EGFR expression levels. Rapamycin wasused as an inhibitor of mTOR. Axon protein Tau, neuron proteins β-tubulin andneurofilament were assessed to evaluate the extent of the axon growth. Expressions of EGFR, total mTOR, p-mTORSer2448, total Akt and p-AktSer473were detected usingWestern blot analysis in cultured neuron. The expressions of EGFR and mTORdropped off with the aging of the rats. p-AktSer473and p-mTORSer2448were highlyexpressed in fetal and newborn rats but decreased obviously in adult rats. Under theaction of BDNF and cAMP in vitro differentiation of neural stem cells to neurons,trans retinoic acid can obviously promote the differentiation, improve the percentageof neurons in the cells. Patch clamp results show that the continuous differentiation invitro cultivation of14d neurons are mature and functional. Tau, β-tubulin and NFprotein were up-regulated when EGFR was overexpressed and down-regulated afterEGFR was blocked. The phosphorylation of mTOR and Akt were apparently elevatedwhen EGFR was overexpressed and decreased. When EGFR was raised, theupregulation effects of the mTOR by EGFR were blocked by rapamycin(100μmol/Ltreated for24h).So, i) EGFR has the potential to regulate the neuronal intrinsic growth, mTORand PI3K/Akt pathway activation may have an important role in it. ii) EGFR can relyon the activation of PI3K/Akt signal pathway, raised the expression of mTOR, finallypromoted the growth of central neurons.