Abstract
The PKR-like ER kinase (PERK) a transmembrane protein resides in the endoplasmic reticulum (ER) and activation of PERK serve as a key sensor of ER-stress which has been implicated in Traumatic Brain Injury (TBI). The loss of memory is one of the most common symptoms following TBI; however, the precise role of PERK activation in memory impairment after TBI has not been well elucidated. Here we have shown that blocking the activation of PERK using GSK2656157 prevents the loss of dendritic spines and rescues memory deficits following TBI. To elucidate the molecular mechanism, we found that activated PERK directly phosphorylates CREB and PSD95 at S129 and T19 residues respectively. Phosphorylation of CREB protein prevents its interaction with a coactivator CBP and subsequently reduces BDNF level following TBI. On the other hand, phosphorylation of PSD95 leads to its downregulation in pericontusional cortex after TBI in male mice. Treatment with either GSK2656157 or overexpression of a kinase-dead mutant of PERK (PERK-K618A) rescues BDNF and PSD95 levels in the pericontusional cortex by reducing phosphorylation of CREB and PSD95 proteins following TBI. Similarly, administration of either GSK2656157 or overexpression of PERK-K618A in primary neurons rescues the loss of dendritic outgrowth and number of synapses after treatment with a PERK activator, tunicamycin. Thus, our study suggests that inhibition of PERK phosphorylation could be a potential therapeutic target to restore memory deficits following TBI.
Significance statement: TBI is the leading cause of death and disability around the world and it affects 1.7 million Americans each year. Here we have shown that TBI-activated PERK is responsible for memory deficiency which is the most common problem in TBI patients. A majority of PERK's biological activities have been attributed to its function as an eIF2α kinase. However, our study suggests that activated PERK mediates its function via increasing phosphorylation of CREB and PSD95 following TBI. Blocking PERK phosphorylation rescues spine loss and memory deficits independent of phosphorylation of eIF2α. Thus our study suggests that CREB and PSD95 are novel substrates of PERK and inhibition of PERK phosphorylation using GSK2656157 would be beneficial against memory impairment following TBI.
Footnotes
We would like to acknowledge NIH funding support (RO1NS094516 and RO1EY025622) for providing support to N.S, and R.G. We would also like to thank Dr. Alexis Stranahan from the Augusta University for providing generous help to carryout DiI staining to study the synaptic morphology.
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