A lipoxygenase product, hepoxilin A 3, enhances nerve growth factor-dependent neurite regeneration post-axotomy in rat superior cervical ganglion neurons in vitro

Abstract

Hepoxilins are 12-lipoxygenase metabolites of arachidonic acid found in the CNS. They can modulate neuronal signaling but their functions are not known. We examined the effects of hepoxilin A 3 on neurite outgrowth post-axotomy in an in vitro model of spinal cord transection using superior cervical ganglion neurons. In the absence of nerve growth factor, hepoxilin A 3 did not support neuronal survival, or regeneration post-axotomy but did significantly enhance neurite regeneration in the presence of nerve growth factor. As early as 1 h post-injury hepoxilin A 3-treated cultures (+nerve growth factor) had significantly more neurites than controls (nerve growth factor alone). Average hourly rates of outgrowth in hepoxilin A 3-treated cultures were significantly higher than in controls for at least 12 h post-injury, suggesting that the effect of hepoxilin A 3 is maintained in vitro for several hours post-injury. In uninjured neurons hepoxilin A 3 caused a rapid but transient increase in intracellular calcium in the somata; by 2 min post-addition, calcium levels decreased to a new stable plateau significantly higher than pre treatment levels. In injured neurons, hepoxilin A 3 addition immediately post-transection caused a rapid transient increase in intracellular calcium in cell bodies; however, peak calcium levels were significantly lower than in uninjured neurons and the new baseline lower than in uninjured cells. In uninjured cells hepoxilin A 3 addition in zero calcium produced the same pattern, a transient elevation and subsequent decline to a new stable baseline significantly above rest but in injured cells levels fell rapidly to pretreatment values. Taken overall, these findings demonstrate a novel role for hepoxilins as a potentiator of neurite regeneration. They also provide the first evidence that this lipoxygenase metabolite can alter intracellular calcium in neurons by causing release of calcium from intracellular stores and modulating calcium influx mechanisms.