CREB is necessary for synaptic maintenance and learning-induced changes of the AMPA receptor GluA1 subunit

The transcription factor cAMP response element binding protein (CREB) is a key protein implicated in memory, synaptic plasticity and structural plasticity in mammals. Whether CREB regulates the synaptic incorporation of hippocampal glutamatergic receptors under basal and learning-induced conditions remains, however, mostly unknown. Using double-transgenic mice conditionally expressing a dominant negative form of CREB (CREBS133A, mCREB), we analyzed how chronic loss of CREB function in adult hippocampal glutamatergic neurons impacts the levels of the AMPA and NMDA receptors subunits within the post-synaptic densities (PSD). In basal (naïve) conditions, we report that inhibition of CREB function was associated with a specific reduction of the AMPAR subunit GluA1 and a proportional increase in its Ser845 phosphorylated form within the PSD. These molecular alterations correlated with a reduction in AMPA receptors mEPSC frequency, with a decrease in long-term potentiation (LTP), and with an increase in long-term depression (LTD). The basal levels other major synaptic proteins (GluA2/3, GluN1, GluN2A, and PSD95) within the PSD were not affected by CREB inhibition. Blocking CREB function also impaired contextual fear conditioning (CFC) and selectively blocked the CFC-driven enhancement of GluA1 and its Ser845 phosphorylated form within the PSD, molecular changes normally observed in wild-type mice. CFC-driven enhancement of other synaptic proteins (GluA2/3, GluN1, GluN2A, and PSD95) within the PSD was not significantly perturbed by the loss of CREB function. These findings provide the first evidence that, in vivo, CREB is necessary for the specific maintenance of the GluA1 subunit within the PSD of hippocampal neurons in basal conditions and for its trafficking within the PSD during the occurrence of learning.