The integrated stress response and oligodendrocyte survival after spinal cord injury

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Abstract. We identified the ER stress response (ERSR) as a potential target for therapeutic interventions against white matter loss and locomotor impairment after spinal cord injury (SCI). Specifically, the signaling pathway that involves the ERSR kinase PERK, the PERK target elongation initiation factor 2α (eIF2α), and PERK-activated transcription factor CHOP may be manipulated in a time-dependent manner to promote SCI recovery. PERK signaling has a partial overlap with the integrated stress response (ISR) that, via several stress-activated kinases, leads to increased levels of phospho-eIF2α (peIF2α), transient inhibition of protein synthesis, and activation of the transcription factor ATF4. ATF4 regulates CHOP as well as genes involved in ROS metabolism, translational regulation and amino acid synthesis. In this way, the ISR attempts to restore homeostasis. Excessive and prolonged activation of the ISR results in anabolism-associated oxidative stress, mitochondrial damage, cell death and inflammation. Pro-ISR stimuli such as hypoxia, lack of nutrients, oxidative stress, and ER stress are present after SCI. However, the role of the principal ISR components – eIF2α kinases other than PERK and their common downstream target ATF4 – has not been addressed in the context of white matter loss after contusive SCI. Our overarching hypothesis is that the ISR plays a critical role in pathogenesis of contusive SCI by promoting OL/OPC death and white matter loss. Aim 1 will examine the role of the 4 upstream ISR kinases (PERK, PKR, GCN2, HRI, which are activated by different stressors) that phosphorylate eIF2α, which in turn inhibits global translation and enhances stress-induced gene expression. We will use a combination of previously optimized gain and loss of function in vitro OPC/OL and in vivo SCI assays that utilize pharmacological inhibitors as well as Hri-/-, Pkr-/-, and Gcn2-/-mice. Preliminary data from ER stressed OPCs or SCI tissue show activation of these kinases as well as compensatory activation of the ISR pathway when PERK is inhibited. Aim 2 will examine the role of the central ISR effector ATF4 in SCI- associated white matter loss. Our preliminary data show activation of ATF4 after SCI or in ER-stressed OPCs. We will determine whether ATF4 is a mediator of OL/OPC death, white matter damage, and functional decline after contusive SCI. In summary, current experimental design is based on data from our previous characterization of the ERSR after SCI. Here, we propose to delineate novel mechanisms of ISR-mediated cell death after SCI as well as define which of ISR mediators may best be suited for therapeutic translation to acutely treat SCI patients. Such treatments are likely to be applicable to other types of CNS trauma such as TBI and stroke.