Increased protein kinase Mζ expression by Minocycline and N-acetylcysteine restoreslate-phase long-term potentiation and spatial learning after closed head injury in mice
Cognitive deficits frequently arise after traumatic brain injury. The murine closed head injury (CHI) models these deficits since injured mice cannot acquire Barnes maze. Dosing of minocycline plus N-acetylcysteine beginning 12 hours post-CHI (MN12) restores Barnes maze acquisition by an unknown mechanism. Increased hippocampal synaptic efficacy is needed to acquire Barnes maze, synaptic long-term potentiation (LTP) models this increased synaptic efficacy in vitro. LTP has an early phase (E-LTP) lasting up to one hour that is mediated by second messengers that is followed by a late phase (L-LTP) that needs new synthesis of protein kinase M zeta (PKM{zeta}). PKM{zeta} has constitutive kinase activity because it lacks the autoinhibitory regulatory domain found in other PKCs. Due to its constitutive activity, the amount of PKM{zeta} kinase activity is determined by PKM{zeta} protein levels. We report that CHI bilaterally decreases PKM{zeta} levels in the CA3 and CA1 hippocampus. MN12 increases CA1 PKM{zeta} expression. CHI inhibits E-LTP in slices from the ipsilesional hippocampus and inhibits L-LTP in slices from both hippocamppi. MN12 treatment reestablishes both E-LTP and L-LTP in slices from the injured MN12-treated hippocampus. The restoration of L-LTP from injured MN12-treated hippocampus is mediated by PKM{zeta} because L-LTP is blocked by the specific PKM{zeta} inhibitor, {zeta}-stat. Hippocampal {zeta}-stat infusions also prevents Barnes maze acquisition in injured, MN12-treated mice. These data suggest that post-injury minocycline plus N-acetylcysteine targets PKM{zeta} to improve synaptic plasticity and cognition in mice with closed-head injury.