醫(yī)學(xué)神經(jīng)生物學(xué)：08 神經(jīng)營養(yǎng)因子

1、Chap 16 Neurotrophic Factors 神經(jīng)營養(yǎng)因子 History It was known that extracellular signals can promote the growth and differentiation of nerve cells in more than half a century ago. Nerve growth factor (NGF) was first discovered by Bueker in 1948. Rita Levi-Montalcini and Victor Hamburger demonstrated NGF

2、is necessary for sympathetic and sensory neurons to keep their survival. Neurotrophic factors (NTFs) influence the growth, differentiation and survival of neurons during development. NTFs are also re-activated in adulthood in tissue renewal or regeneration. The signaling failure of NTFs may underlie

3、 neurodegenerative disorders such as Alzheimer disease (AD), Parkinson disease (PD), huntington disease (HD) and amyotrophic lateral sclerosis (ALS). Neurite (神經(jīng)突起) Neuritic branch is described axon and dendrite. Especially, it is available for growing neuritic which did not assured axon or dendrite

4、. The effect of NGF on cultured spinal neurons (Levi-Montalcini R. 1987. Science 237:1157) The term of Neurotrophic factor The term Neurotrophic Factor refers to any molecule that affects the nerves system by influencing the growth, differentiation, or cell cycles of neurons or glia. The difference

5、between of NTFs and Neuropeptides: 1) NTFs are large molecular proteins, but neuropeptides are the small molecule proteins (14kDa NTF is produced in cell body. Small, 14kDa1kDa SynthesisProducted in cell body produced at the terminal Storagelarge densecored vesiclesSynaptic vesicles Release Determin

6、ed active-dependent synthesis. Determined depolarization. Determined Low-frequency stimulation Determined depolarization. breakdown Protease hydrolyzation, Enshroud by incativation- receptor reuptake, re-use, Signaling The binding to Trk receptor lead to many of the biologic effects The binding G-pr

7、otein couple receptor and the second messenger lead to the biologic effects. Action Retograde, anterograde, autocrine, paracrine transmission. anterograde, autocrine, paracrine transmission. acting as quick transmitter. 分分 類類 Neurotrophic FactorsReceptors Neurotrophins NGF, BDNF, NT-3, NT-4 Trk （R-P

8、TKs） TrkA, TrkB, TrkC1 GDNF family GDNF, neurturin, persephin, LIFR Coupled to Ret GFR1,GFR2,nuknown CNTF family CNTF、LIF、IL-6 Coupled to Janus kinase（JAK ） GP130、CNTFFR Ephrins Eph (R-PTKs) EGF family EGF, TGF, neuregulns2 ErbB (R-PTKs) Other growth factors Insulin, IGF, FGF, PDGF R-PTKS interleuki

9、ns and related cytokines IL-1, IL-2, IL-3, IL-5,TNF, TNF IL-IR coupled to PS/TK, R-PTK Coupled to JAK, Related to p753 TGF family: TGFR-PS/TRs Other cytokinesCoupled to JAK, R-PTKs Chemokines CC chemokines (IL-8) CXC chemokines (MIP, MCP) CX3C chemokines (neurotactin) G protein-coupled receotors CC1

10、-CC8R CXC1-CXC4R Cx3C1R Neurotrophins Neurotrophins are small proteins. They play their physiologic roles through Trk receptor. Family members：NGF、BDNF、Neurotrophin-3(NT-3)、NT-4/5. Effections neuronal survival To prevent neuronal death neurogenesis To promote the growth of axons and dendrites neurit

11、e To promote neurite in adult anabolismTo enhance the size of neurons differentiationTo synthesis proteins which are necessary for Neuronal phenotype regulating the transmittal To increase the synthesis of neurotransmittors, neuropeptides and their synthetases electrical excitability To alter the ac

12、tivation and level of ion channels NGFBDNFNT-3 composing of amino acides 116 3 disulfide bonds 119 3 disulfide bonds 119 3 disulfide bonds MW13kDa13kDa13kDa distribution Widely distribute in CNS, PNS and peripheral tissues In CNS: hypothalamus, cortex, hippocampus in developing; In peripheral tissue

13、s: BDNF mRNA was highly expressed in muscle tissues Widely distrubut in CNS, PNS receptorsTrkATrkBTrkC Signaling pathway Trk receptor signaling pathway Characteristic of neurotrphins NGF的結(jié)構(gòu) The -NGF dimer (1 subunit light blue and 2 darker blue) is at the center with the subunits in red and the subu

14、nits in green. Interactions between the 1 and 1 (and 2 and 2) subunits are mediated by a zinc ion (off-white spheres). 7S NGF Neurotrophins receptorTrk-R Transmembrance receptor Glycoproteins whose molecular weight range from 140 to145kDa. Different types of Trk-R Neurotrophins and receptors Distrib

15、ution of TrkR in nerval cells The most of TrkAs were found in sensory and sympathetic neurons, a few in brain neurons. TrkB and TrkC express in the most of neurons. Trk truncation was existed in astrocytes and oligodendrocytes. P75 receptor a 75-kDa protein as the low-affinity neurotrophin receptor.

16、 also appears to modulate Trk signaling; the increases phosphorylation of Trk and then enhances the activity of Trk. may allow Trk-R to response to the low concentration of NGF and the other neurotrophins is believed to play a key role in cell death pathways. The signaling pathway of Neurotrophins T

17、rk was activated by autophosphorylation of Try (Y490、 Y785) in the intracellular domain and subsequently forms to dimer, and then enables phosphorylation the intracellular signaling protein by interacting with its SH2 domain, e.g. Shc and PLC . Three signaling pathways: Ras/MAPK cascades PI3K/AKT PL

18、C/IP3-dependent Ca2+ release IP3 DAG Ca2+釋放釋放 The signaling pathway of Neurotrophins Ras/MAPK Ras protein： . 21kD phosphorylating protein; a small G- protein; switch between inactivation of GDP-bound formation and activation of GTP-bound formation; GTP-bound formation keeps the activation of cell gr

19、owth and activates the cells to overproliferation a cascade of TrkA activates Ras Shc Sos Ras Grb 2 A cascade of Ras/Raf/MEK/ERK ERK Raf The effect of Ras/Raf/MEK cascade in neurite growth PC12 originates from pheochromocytoma TrkA and p75 are expressed in membrane of PC12 NGF treatment may stimulat

20、e the neurite growth on PC12 cells. The effect of Ras/Raf/MEK cascade in neurite growth Disease of Ras signaling pathway Defects of that NTFs activated the signaling pathways in the intracellular can lead to the overproliferation of cells, and in turn can give rise to various disorders. Neurofibroma

21、tosis is an genetic disease caused by mutation of the Ras-modulatory protein. Oncogenic Ras gene is a mutation form that cause Ras to remain in its active state by two Ras forms: 1) reduced the intrinsic GTPase activity of Ras; 2) inhibited the sensitivity of Ras to GTPase activating proteins (GAPs)

22、. Neurotrophins and Trk-R knockout mice Mice, in which the genes encoding NGF or TrkA have been inactivated, exhibited a loss of sympathetic neurons as well as sensory neurons in dorsal root ganglia of the trigeminal system. NGF or TrkA KO mice also exhibited a partial loss of the cholinergic neuron

23、s in the basal forebrain that project to the hippocampus and cerebral cortex. TrkB KO mice exhibited the death of cranial motor neurons and trigeminal ganglion neurons. BDNF KO mice exhibited no a loss of facial or spinal motor neurons. In contrast, TrkB KO mice showed significant motor neurons loss

24、. ALS was characterized the degeneration of cortical and spinal motor neurons. The effects of Neurotrophins NGF activated neurite growth. BDNF maintains survival of motor neurons. NT-4 is important for supporting survival of motor neurons in development. The effect of NT-3, maintaining survival of m

25、otor neurons, is less than BDNF and NT-4. The effects of NGF Fast effect Regulating or participating in the release of neurotransmitter：altering the activation of ion channels；enhancing the synthesis of transmitters, peptides and its synthetase. Slow effect: Preventing against death of neurons； main

26、taining development of sympathetic neurons; maintaining neuronal function and plasticity in adult. Regulating or participating in the release of neurotransmitter: To promote the differentiation of embryonic neurons into the functional neurons； The critical affect for maintenance of neuronal survival

27、 in maturate. NGF induces the chemotactic direction for nerve fibre growth. Neuritic directions are along the NGF concentrational grads NGF ensures survival of neuronal synaptic afferent in sensory and sympathetic neurons To promote survival of cholinergic neurons: To promote survival of neurons As

28、the same of NGF, BDNF also can promote survival of cholinergic neurons and differentiation of their phenotype in vitro. But both effect in different growth phases of cholingergic neurons, BDNF in forepart but NGF in anaphase. BDNF、NT-3 and NT-4 can promote survival of some motorial cortical neurons

29、and hippocampal neurons. Neurotrophins can promote survival of the neurons which were activated by NE, DA, 5-HT in brain stem. To regulate synaptic plasticity Studies in the formation of ocular dominance columns in the developing visual cortex have be confirmed that neurotrophins mediate forms of sy

30、naptic plasticity. Neurotrophins also are involved in regulating synaptic plasticity in the fully differentiated adult brain. Neurotrophins can modulate synaptic transmission and regulate the formation and strengthening of synapses. Neurotrophins also regulate synaptic transmission in the hippocampu

31、s. But this still controversial. GDNF Family GDNF was first isolated from culturing glial cell line that maintains survival of mesencephalic dopaminergic neurons. Glial cell line-Derived Neurotrophic Factor GDNF, a glycosylated protein of 18 kDa. GDNF family includes Neurturin、persphin GDNF receptor

32、s and its signaling pathway GDNF plays a role via activation of protein tyrosine kinase. But such activation is achieved indirectly through the receptor protein inserted. A GDNF dimer binds to a specific receptor, termed GFR1, a protein of 40 kDa, which is anchored to the plasma membrane by GPI. GDN

33、F bind triggers GFR1 to combine with Ret. Ret is a transmembrane protein tyrosinekinase of about 150 kDa. This binding results in activation of Ret, which is believed that lead to many biologic effects of GDNF via triggering the phosphorylation of specific substrates. The autophosphorylated Ret in t

34、urn activates several intracellular signaling proteins that regulate cell survival, differentiation, proliferation, migration, neurite growth and synaptic modulation. These signaling proteins, belonging to protein and lipid kinases and phospholipases, act on several signal transduction pathways. PLC

35、- Regulate Ca2+i MAP kinase neurite growth neuronal survival PI3K neuronal survival neurite growth Several signal transduction pathways: Ret signaling by GDNF mediated can interact with and activate the Src-family kinases eliciting optimal neurite outgrowth and neuronal survival. In Ret deficient ce

36、ll lines and primary neurons, GDNF triggers Src-family kinase activation and phosphorylation of ERK/MAP kinase, PLC- and the transcription factor CREB, and production of Fos GDNF family receptors complex The effects of GDNF family 1. Dopamine Neurons GDNF selectively enhanced the survival and develo

37、pment of dopaminergic neurons. In vitro, GDNF protected mesencephalic dopaminergic cells against the effects of the neurotoxin MPP+. GDNF improved the survival of cells, prevented further cell death, and stimulated the re-growth of dopaminergic fibers with damaged by MPP+. In vivo, in PD model induc

38、ed by the administration of the 6-OHDA into the medial forebrain bundle, GDNF has been shown to reverse apomorphine-induced rotation and rescue dopaminergic neurons lesion. GDNF may be a valuable therapeutic agent in treating Parkinsons disease. Neurturin is also a factor for treatment of PD. The ef

39、fects of GDNF family 2. Motor neurons GDNF was shown to protect facial motoneurons from injury-induced cell death. GDNF can affect motoneuron development and motoneuron survival after axotomy, novel approaches for motor neuron disease are suggested. GDNF can rescue some spinal motoneuron from progra

40、mmed cell death in development and promote its survival. GDNF can prevent the neuronal degeneration which was caused by axon broken. The effects of GDNF family 3.PNS neurons GDNF promotes the survival and neurite outgrowth of cultured sympathetic neurons, parasympathetic ciliary ganglion neurons and

41、 sensory dorsal root ganglion neurons. GDNF is important for the developing of enteric neurons and renal neurons. Ret ( loss-of-function) mutation has the same symptoms as human Hirschsprung disease. Ret (gain-of-function) mutation has the same symptoms as neural crest malignancies, e. g. mult- aden

42、omatosis, medullar thyroid cancer. CNTF family(Ciliary neurotriphic factor) CNTF family Receptors (JAK-coupled receptors) CNTF Gp130 LIFR CNTFR LIF (leukemia inhibitory factor) IL-6，prolactin, growth hormone, leptin IL-11、OSM(oncostatin M ) CNTF family CNTF, a protein approximately 24 kDa in size, w

43、as studied as a survival factor for chick ciliary genglion neurons. CNTF is one of cytokine that plays a role among several processes within the human body from endogenous neuroprotection to regulatethe energy expenditure. CNTF is a pluripotent neurochtokine expressed by glial cells in the perophera

44、l nerves and in the CNS. The family members include LIF, IL-6, OSM, IL- 1, prolactin, growth hormone, leptin and interferons. CNTF receptor complex Consists of three components: CNTF family, CNTFR, , and signal transducing receptor component（LIFR, gp130） The effects of CNTF CNTF has been proven to r

45、egulate the survival or differentiation of many other neuronal cells, including sympathetic neurons, sensory neurons, motor neurons, cultured hippocampal neurons and mesencephalic dopaminergic neurons. CNTF on motor neurons plays the more significant role： CNTF not only supports the neuronal surviva

46、l in vitro, but also prevents nerve degeneration after axotomy. CNTF improves some motor against motor neuron defects in murine. LIF and IL-6 may regulate the survival or differentiation of neurons. IL-6 promotes the survival of septal cholinergic, mesencephalic catecholaminergic, and hypothalamic n

47、eurons in vitro. CNTF and CNTFR CNTF KO nice develop normally, exhibiting only mild motor neuron defects during adulthood. Approximately 2.5% of the Japanese population are homozygous for inactivation mutations of CNTF and thus they are human CNTF “knockouts” , like CNTF KO mice. In contrast, mice l

48、acking the CNTFR lost almost all of their motor neurons and died within 24h after birth. It suggested the existence of another endogenous ligand for CNTFR, but that has not been discovered yet. Therapeutic agents directed at NTF Treatment with BDNF, CNTF, or combination of these factors has been sho

49、wn to slow or attest the progression of motor neuron degengration in the wobbler mouse Wobbler. Due to BDNF, GDNG, and other factors have enhanced the survival of dopaminergic neurons in animal models, the use of NTFs in the treatment of PD is a top research priority. Investigators are exploring the use of NGF as a tr