Does the MK2-dependent Production of TNFα Regulate mGluR-dependent Synaptic Plasticity?

MS275 reduces seizure-induced brain damage in developing rats by regulating p38 MAPK signaling pathways and epigenetic modification

Seizure is a common acute and severe disease in infants and children. Recurrent seizures or persistent seizures may cause irreversible brain damage. Mitogen activated protein kinase (MAPK) signaling pathway is associated with an inflammatory response, however it's involvement in the pathological process of seizures is not clear. Histone deacetylase inhibitors (HDACi) have promising neuroprotective effects through epigenetic regulation. Therefore, this study aimed to investigate the mechanism of HDACi MS275 on p38 MAPK signaling pathway and p38 histone modifications in developing rats post-seizure. Intraperitoneal administration of Pentylenetetrazole (PTZ) was used to induce developing rat seizures, and MS275 (5 or 10 mg/kg) was injected intraperitoneally 2 h before PTZ injection. Hippocampal tissues were sampled at 24 h post-seizures for protein and mRNA levels of p38、MK2、CREB and IL-6. Neuronal apoptosis and microglia activation significantly increased after PTZ treatment. However, pretreatment with MS275 attenuated these effects as well as increased seizure latency and decreased seizure scores. Furthermore, MS275 was found to inhibit the expression of p38 by increasing histone H3 and H4 acetylation and decreasing histone H3 and H4 methylation. This study thereby demonstrates that HDACi MS275 can reduce the inflammatory response associated with seizure-induced brain injury through inhibiting the p38 MAPK signaling pathway and p38 gene expression.

The MK2 cascade regulates mGluR-dependent synaptic plasticity and reversal learning

The ability to either erase or update the memories of a previously learned spatial task is an essential process that is required to modify behaviour in a changing environment. Current evidence suggests that the neural representation of such cognitive flexibility involves the balancing of synaptic potentiation (acquisition of memories) with synaptic depression (modulation and updating previously acquired memories). Here we demonstrate that the p38 MAPK/MAPK-activated protein kinase 2 (MK2) cascade is required to maintain the precise tuning of long-term potentiation and long-term depression at CA1 synapses of the hippocampus which is correlated with efficient reversal learning. Using the MK2 knockout (KO) mouse, we show that mGluR-LTD, but not NMDAR-LTD, is markedly impaired in mice aged between 4 and 5 weeks (juvenile) to 7 months (mature adult). Although the amplitude of LTP was the same as in wildtype mice, priming of LTP by the activation of group I metabotropic receptors was impaired in MK2 KO mice. Consistent with unaltered LTP amplitude and compromised mGluR-LTD, MK2 KO mice had intact spatial learning when performing the Barnes maze task, but showed specific deficits in selecting the most efficient combination of search strategies to perform the task reversal. Findings from this study suggest that the mGluR-p38-MK2 cascade is important for cognitive flexibility by regulating LTD amplitude and the priming of LTP.