PLA₂ and secondary metabolites of arachidonic acid control filopodial behavior in neuronal growth cones

Abstract

The neuronal growth cone provides the sensory and motor structure that guides neuronal processes to their target. The ability of a growth cone to navigate correctly depends on its filopodia, which sample the environment by continually extending and retracting as the growth cone advances. Several second messengers systems that are activated upon contact with extracellular cues have been reported to affect growth cone morphology by changing the length and number of filopodia. Because recent studies have suggested that guidance cues can signal via G-protein coupled receptors to regulate phospholipases, we here investigated whether phospholipase A2 (PLA2) may control filopodial dynamics and could thereby affect neuronal pathfinding. Employing identified Helisoma neurons in vitro, we demonstrate that inhibition of PLA2 with 2 microM BPB caused a 40.3% increase in average filopodial length, as well as a 37.3% reduction in the number of filopodia on a growth cone. The effect of PLA2 inhibition on filopodial length was mimicked by the inhibition of G-proteins with 500 ng/ml pertussis toxin and was partially blocked by the simultaneous activation of PLA2 with 50 nM melittin. We provide evidence that PLA2 acts via production of arachidonic acid (AA), because (1) the effect of inhibition of PLA2 could be counteracted by supplying AA exogenously, and (2) the inhibition of cyclooxygenase, which metabolizes AA into prostaglandins, also increased filopodial length. We conclude that filopodial contact with extracellular signals that alter the activity of PLA2 can control growth cone morphology and may affect neuronal pathfinding by regulating the sensory radius of navigating growth cones.

Group IVA phospholipase A2 is necessary for growth cone repulsion and collapse

“…Certain PLA 2 blockers inhibit the outgrowth of DRG neurons from adult mouse (Hornfelt et al, 1999) and frog (Edstrom et al, 1996). PLA 2 activity and its products (including AA) have also been shown to regulate filopodial length and number (Geddis et al, 2004). These effects may well be related to the role of PLA 2 in growth cone navigation described here.…”

Melittin stimulates fatty acid release through non-phospholipase-mediated mechanisms and interacts with the dopamine transporter and other membrane-spanning proteins

“…Melittin activates arachidonic acid signaling pathways in neurons (Geddis et al, 2004; Muzzio al., 2001) and in multiple cell lines including rat PC12 and mouse L1210 cells (Lee et al, 2001; Palomba et al, 2004), possibly through phospholipase A 2 stimulation. Additionally melittin acts through non-phospholipase A 2 -mediated mechanisms to release fatty acids and alter cell function (Lee et al, 2001).…”

Development of prostaglandin endoperoxide synthase expression in the ovine fetal central nervous system and pituitary

“…Extensive neuronal proliferation and synapse formation mark this period of gestation (Nelson et al, 1995; Makarenko et al, 2005; Cudd, 2005). Metabolites of arachidonic acid have been found to control filopodial behavior in neurons (Geddis et al, 2004). It is therefore possible that the dramatic upregulation of PGHS expression in cortical regions during the latter half of gestation may be involved in neuronal guidance and synaptogenesis during this period of gestation.…”