Phospholipase Cβ regulates negative associative memory through calcium dependent and independent mechanisms

The Gαq/PLCβ signaling plays a key role in learning and memory. In mice, the loss of PLCβ1 results in inappropriate responses to adverse events that is directly tied to the ability of PLCβ to mediate calcium signals. Besides this calcium-mobilizing function, PLCβ1 has been shown to have a cytosolic, activity-independent function that keeps stress granules disassembled until stimulation and mediates the nuclear localization of the transcription factor Early Growth Response -1 (EGR-1). Here, we assessed the impact of PLCβ on memory formation in the nematode, Caenorhabditis elegans, whose Gαq/PLCβ signaling system is analogous to mammalian systems. Wild-type N2 worms and egl-8^-/-mutant worms that lack PLCβ were studied using a negative associative memory paradigm involving subjecting them to an attractive odor while simultaneously starving them. We find that wild-type worms have a significantly lower attraction to the odor than controls, while egl-8^-/-worms showed a more pronounced response, supporting a role of PLCβ in long term adverse reaction behavior. Using immunostaining, we find that the egl-8^-/-mutants displaying strong memory formation had higher CREB levels and lower nuclear EGR-1. To better delineate the roles of PLCβ1 on memory, we overexpressed active and inactive PLCβ1 in PC12 cells. Increasing cellular PLCβ1 reduces CREB levels in accord with the worm studies. However, increasing active PLCβ1 increases activated CREB (p-CREB) levels. Both active and inactive PLCβ1 result in significantly higher levels of PSD95 higher nuclear, regardless of Gαq stimulation. Our results suggest that higher levels of PLCβ can suppress aversive associative memory by suppressing CREB levels.