Prevention of thrombin-induced motoneuron degeneration with different neurotrophic factors in highly enriched cultures

Previous reports have shown that neuronal and glial cells express functiona lly active thrombin receptors, The thrombin receptor (PAR-1), a member of a growing family of protease activated receptors (PARs), requires cleavage o f the extracellular amino-terminus domain by thrombin to induce signal tran sduction, Studies from our laboratory have shown that PAR-1 activation foll owing the addition of thrombin or a synthetic thrombin receptor activating peptide (TRAP) induces motoneuron cell death both in vitro and in vivo. In addition to increasing motoneuron cell death, PAR-1 activation leads to dec reases in the mean neurite length and side branching in highly enriched mot oneuron cultures, It has been suggested that motoneuron survival depends on access to sufficient target-derived neurotrophic factors through axonal br anching and synaptic contacts. However, whether the thrombin-induced effect s on motoneurons can be prevented by neurotrophic factors is still unknown. Using highly enriched avian motoneuron cultures, we show here that alone, soluble chick skeletal muscle extracts (CMX), brain-derived neurotrophic fa ctor (BDNF), ciliary neurotrophic factor (CNTF), and glial cell line-derive d neurotrophic factor (GDNF) significantly increased motoneuron survival co mpared to controls, whereas nerve growth factor (NGF) did not have a signif icant effect on motoneuron survival. Furthermore, cotreatment with muscle-d erived agents (i.e., CMX, BDNF, GDNF) significantly prevented the death of motoneurons induced by alpha-thrombin, Yet, non-muscle-derived agents (CNTF and NGF) had little or no significant effect in reversing thrombin-induced motoneuron death. CMX and CNTF significantly increased the mean length of neurites, whereas NGF, BDNF, and GDNF failed to enhance neurite outgrowth c ompared to controls. Furthermore, CMX and CNTF significantly prevented thro mbin-induced inhibition of neurite outgrowth, whereas BDNF and GDNF only pa rtially reversed thrombin-induced inhibition of neurite outgrowth, These fi ndings show differential effects of neurotrophic factors on thrombin-induce d motoneuron degeneration and suggest specific overlaps between the trophic and stress pathways activated by some neurotrophic agents and thrombin, re spectively, (C) 1999 John Wiley & Sons, Inc.