Abstract
Tumour necrosis factor receptor 1 (TNFR1)-activated TNFα reverse signalling, in which membrane-integrated TNFα functions as a receptor for TNFR1, enhances axon growth from developing sympathetic neurons and plays a crucial role in establishing sympathetic innervation. Here, we have investigated the link between TNFα reverse signalling and axon growth in cultured sympathetic neurons. TNFR1-activated TNFα reverse signalling promotes Ca2+ influx, and highly selective T-type Ca2+ channel inhibitors, but not pharmacological inhibitors of L-type, N-type and P/Q-type Ca2+ channels, prevented enhanced axon growth. T-type Ca2+ channel-specific inhibitors eliminated Ca2+ spikes promoted by TNFα reverse signalling in axons and prevented enhanced axon growth when applied locally to axons, but not when applied to cell somata. Blocking action potential generation did not affect the effect of TNFα reverse signalling on axon growth, suggesting that propagated action potentials are not required for enhanced axon growth. TNFα reverse signalling enhanced protein kinase C (PKC) activation, and pharmacological inhibition of PKC prevented the axon growth response. These results suggest that TNFα reverse signalling promotes opening of T-type Ca2+ channels along sympathetic axons, which is required for enhanced axon growth.
Highlights
A variety of extracellular signals participate in regulating the establishment of sympathetic innervation in the developing peripheral nervous system [1,2]
Using a combination of pharmacological studies, electrophysiology, Ca2þ reporter studies and western blot analysis, we show that activation of TNFa reverse signalling in sympathetic axons increases T-type Ca2þ channel activation and the subsequent activation of protein kinase C (PKC) and ERK1/ERK2 are required for enhanced axon growth
Low density dissociated cultures of superior cervical ganglion (SCG) neurons were plated in medium containing nerve growth factor (NGF) to sustain their survival and were treated with a divalent tumour necrosis factor receptor 1 (TNFR1)-Fc chimera to activate TNFa reverse signalling [9] in the presence and absence of dotarizine
Summary
A variety of extracellular signals participate in regulating the establishment of sympathetic innervation in the developing peripheral nervous system [1,2]. NGF acts on sympathetic axon terminals within target tissues to promote growth and branching [4]. Whereas retrograde PI3-kinase/Akt signalling to the cell body plays an important role in mediating NGF-promoted survival, activation of ERK1/ ERK2 downstream of TrkA, the NGF receptor tyrosine kinase, plays a major role in mediating the local axon growth-promoting effects of NGF [5,6,7,8]. A recently discovered target-derived signal that promotes sympathetic axon growth and branching during the stage in development when sympathetic axons are ramifying in their targets is tumour necrosis factor receptor 1 (TNFR1) [9]. TNFR1 expressed by sympathetic target tissues acts as a ligand for membrane-integrated TNFa expressed along sympathetic axons, and TNFR1-activated TNFa reverse signalling enhances sympathetic axon growth
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call