Developmental and activity-dependent regulation of ARMS/Kidins220 in cultured rat hippocampal neurons

Neurotrophin activation of Trk receptors elicits diverse effects on neuronal survival, differentiation, and synaptic plasticity. One of the central questions is how specificity is encoded in neurotrophin receptor signaling and actions. A unique downstream protein is the Ankyrin-Repeat Rich Membrane Spanning (ARMS)/Kinase D-interacting substrate-220 kDa (Kidins220), a very abundant scaffold protein in the hippocampus. To determine the roles of ARMS/Kidins220 in hippocampal neurons, we have analyzed the effects of synaptic activity upon the regulation and distribution of ARMS/Kidins220. At early times in vitro (<7 DIV), synaptic activity was low and ARMS/Kidins220 levels were high. As synaptic activity and markers for synapse maturation, such as PSD-95, increased, ARMS/Kidins220 significantly decreased to a plateau by later times in vitro (>12 DIV). Immunocytochemistry showed ARMS/Kidins220 to be concentrated at the tips of growing processes in immature cultures, and more diffusely distributed in older cultures. To examine the apparent inverse relationship between activity and ARMS/Kidins220 levels, neuronal firing was manipulated pharmacologically. Chronic exposure to TTX increased ARMS/Kidins220 levels, whereas bicuculline caused the opposite effect. Moreover, using shRNA to decrease ARMS/Kidins220 levels produced a corresponding increase in synaptic activity. We find that ARMS/Kidins220 may function in neuronal development as an indicator and potentially as a homeostatic regulator of overall synaptic strength in hippocampal neurons.