Neuroprotective signal transduction in model motor neurons exposed to thrombin: G-protein modulation effects on neurite outgrowth, Ca(2+) mobilization, and apoptosis.
Thrombin, the ultimate protease in the blood coagulation cascade, mediates its known cellular effects by unique proteolytic activation of G-protein-coupled protease-activated receptors (PARs), such as PAR1, PAR3, and PAR4, and a "tethered ligand" mechanism. PAR1 is variably expressed in subpopulations of neurons and largely determines thrombin's effects on morphology, calcium mobilization, and caspase-mediated apoptosis. In spinal cord motoneurons, PAR1 expression correlates with transient thrombin-mediated [Ca(2+)](i) flux, receptor cleavage, and elevation of rest [Ca(2+)](i) activating intracellular proteases. At nanomolar concentrations, thrombin retracts neurites via PAR1 activation of the monomeric, 21 kDa Ras G-protein RhoA, which is also involved in neuroprotection at lower thrombin concentrations. Such results suggest potential downstream targets for thrombin's injurious effects. Consequently, we employed several G-protein-specific modulators prior to thrombin exposure in an attempt to uncouple both heterotrimeric and monomeric G-proteins from motoneuronal PAR1. Cholera toxin, stimulating Gs, and lovastatin, which blocks isoprenylation of Rho, reduced thrombin-induced calcium mobilization. In contrast, pertussis toxin and mastoparan, inhibiting or stimulating G(o)/G(i), were found to exacerbate thrombin action. Effects on neuronal rounding and apoptosis were also detected, suggesting therapeutic utility may result from interference with downstream components of thrombin signaling pathways in human motor neuron disorders, and possibly other neurodegenerative diseases. Published 2001 John Wiley & Sons, Inc.
Smirnova
I V
IV
Neurobiology Research Laboratory, Department of Veterans Affairs Heartland Network, Kansas City, Missouri 64128, USA.
Citron
B A
BA
Arnold
P M
PM
Festoff
B W
BW
D000924:Anticholesteremic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D020013:Calcium Signaling / Q000187:drug effects*; D061945:Caspase Inhibitors; D002460:Cell Line; D002772:Cholera Toxin / Q000494:pharmacology; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism; D006490:Hemostatics / Q000494:pharmacology*; D036341:Intercellular Signaling Peptides and Proteins; D008148:Lovastatin / Q000494:pharmacology; D009046:Motor Neurons / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D016501:Neurites / Q000187:drug effects / Q000502:physiology; D009842:Oligopeptides / Q000494:pharmacology; D010455:Peptides; D037342:Pertussis Toxin; D044463:Receptor, PAR-1; D018179:Receptors, Thrombin / Q000378:metabolism; D013917:Thrombin / Q000494:pharmacology*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D014862:Wasp Venoms / Q000494:pharmacology
D000924:Anticholesteremic Agents; D061945:Caspase Inhibitors; D015853:Cysteine Proteinase Inhibitors; D006490:Hemostatics; D036341:Intercellular Signaling Peptides and Proteins; D009842:Oligopeptides; D010455:Peptides; D044463:Receptor, PAR-1; D018179:Receptors, Thrombin; D010566:Virulence Factors, Bordetella; D014862:Wasp Venoms; C110772:benzoylcarbonyl-aspartyl-glutamyl-valyl-aspartyl-fluoromethyl ketone; C037500:mastoparan; D002772:Cholera Toxin; D008148:Lovastatin; D037342:Pertussis Toxin; D013917:Thrombin; D019204:GTP-Binding Proteins