Proteasome and Autophagy-Mediated Impairment of Late Long-Term Potentiation (l-LTP) after Traumatic Brain Injury in the Somatosensory Cortex of Mice

Abstract

Traumatic brain injury (TBI) can lead to impaired cognition and memory consolidation.The acute phase (24–48 h) after TBI is often characterized by neural dysfunction in the vicinity ofthe lesion, but also in remote areas like the contralateral hemisphere. Protein homeostasis is crucialfor synaptic long-term plasticity including the protein degradation systems, proteasome andautophagy. Still, little is known about the acute effects of TBI on synaptic long-term plasticity andprotein degradation. Thus, we investigated TBI in a controlled cortical impact (CCI) model in themotor and somatosensory cortex of mice ex vivo-in vitro. Late long-term potentiation (l-LTP) wasinduced by theta-burst stimulation in acute brain slices after survival times of 1–2 days. Proteinlevels for the plasticity related protein calcium/calmodulin-dependent protein kinase II (CaMKII)was quantified by Western blots, and the protein degradation activity by enzymatical assays. Weobserved missing maintenance of l-LTP in the ipsilateral hemisphere, however not in thecontralateral hemisphere after TBI. Protein levels of CaMKII were not changed but, interestingly,the protein degradation revealed bidirectional changes with a reduced proteasome activity and anincreased autophagic flux in the ipsilateral hemisphere. Finally, LTP recordings in the presence ofpharmacologically modified protein degradation systems also led to an impaired synaptic plasticity:bath-applied MG132, a proteasome inhibitor, or rapamycin, an activator of autophagy, bothadministered during theta burst stimulation, blocked the induction of LTP. These data indicate thatalterations in protein degradation pathways likely contribute to cognitive deficits in the acute phaseafter TBI, which could be interesting for future approaches towards neuroprotective treatmentsearly after traumatic brain injury.