Differential effects of neurotrophins and schwann cell-derived signals on neuronal survival/growth and synaptogenesis.
Recent studies have shown that the survival of mammalian motoneurons in vitro is promoted by neurotrophins (NTs) and cAMP. There is also evidence that neurotrophins enhance transmitter release. We thus investigated whether these agents also promote synaptogenesis. Cultured Xenopus spinal cord neurons were treated with a mixture of BDNF, glia-derived neurotrophic factor, NT-3, and NT-4, in addition to forskolin and IBMX or the cell-permeant form of cAMP, to elevate the cAMP level. The outgrowth and survival of neurons were dramatically increased by this trophic stimulation. However, when these neurons were cocultured with muscle cells, the trophic agents resulted in a failure of synaptogenesis. Specifically, the induction of ACh receptor (AChR) clustering in cultured muscle cells was inhibited at nerve-muscle contacts, in sharp contrast to control, untreated cocultures. Because AChR clustering induced by agrin or growth factor-coated beads in muscle cells was unaffected by trophic stimulation, its effect on synaptogenesis is presynaptic in origin. In the control, agrin was deposited along the neurite and at nerve-muscle contacts. This was significantly downregulated in cultures treated with trophic stimuli. Reverse transcriptase-PCR analyses showed that this decrease in agrin deposition was caused by an inhibition of agrin synthesis by trophic stimuli. Both agrin synthesis and induction of AChR clustering were restored under trophic stimulation when Schwann cell-conditioned medium was introduced. These results suggest that trophic stimulation maintains spinal neurons in the growth state, and Schwann cell-derived factors allow them to switch to the synaptogenic state.
Peng
H Benjamin
HB
Department of Biology, Hong Kong University of Science and Technology, Kowloon, Hong Kong. penghb@ust.hk
Yang
Jie-Fei
JF
Dai
Zhengshan
Z
Lee
Chi Wai
CW
Hung
Hiu Wai
HW
Feng
Zhi Hua
ZH
Ko
Chien-Ping
CP
D018171:Agrin / Q000378:metabolism; D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D017077:Culture Media, Conditioned / Q000378:metabolism / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology; D032342:Muscle Cells / Q000166:cytology; D009414:Nerve Growth Factors / Q000494:pharmacology*; D016501:Neurites / Q000187:drug effects / Q000502:physiology; D009469:Neuromuscular Junction / Q000187:drug effects / Q000254:growth & development / Q000502:physiology; D009474:Neurons / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D011940:Receptor Aggregation; D011950:Receptors, Cholinergic / Q000378:metabolism; D012583:Schwann Cells / Q000166:cytology / Q000378:metabolism*; D012584:Sciatic Nerve / Q000166:cytology; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D013569:Synapses / Q000187:drug effects* / Q000502:physiology; D014981:Xenopus
D018171:Agrin; D017077:Culture Media, Conditioned; D009414:Nerve Growth Factors; D011950:Receptors, Cholinergic; D000242:Cyclic AMP