Immunohistochemical localization of phosphorylated protein kinase R and phosphorylated eukaryotic initiation factor‐2α in the central nervous system of SJL mice with experimental allergic encephalomyelitis

Abstract

Inflammatory cells enter the CNS and target myelin in multiple sclerosis (MS) and experimental allergic encephalomyelitis (EAE), a model of MS, and inflammation is thought to induce stress responses in the CNS. Protein kinase R (PKR) and eukaryotic initiation factor-2 alpha (eIF2 alpha) undergo phosphorylation in response to stress, and the phosphorylated forms of these proteins play a key role in regulating protein synthesis. The objective of this study was to investigate the expression profile of phospho-PKR and phospho-eIF2 alpha during the course of EAE in order to advance the understanding of the stress response in this disease. In control animals (no encephalitogen with no emulsion; no encephalitogen with emulsion) and in preclinical EAE animals, phospho-PKR immunoreactivity was present in oligodendrocytes and some neurons, whereas, in EAE animals with active disease there was widespread labeling of inflammatory cells, and these cells were present during the recovery period of EAE, albeit to a lesser extent. Double-labeling studies revealed that T cells and a few macrophages were phospho-PKR(+). Phospho-eIF2 alpha immunoreactivity was detected in some oligodendrocytes in hindbrain sections of control animals. In EAE animals with active disease, the number of labeled oligodendrocytes increased, and inflammatory T cells also were labeled. Insofar as phospho-PKR activates nuclear factor-kappa B, it may facilitate cytokines expression by T cells. Alternatively, phospho-PKR and phospho-eIF2 alpha may promote apoptosis as a way to regulate T-cell number in the CNS. The expression of phospho-eIF2 alpha in oligodendrocytes during EAE likely is involved with inhibition of protein translation, which is a protective mechanism used to promote cell survival in response to inflammation.

The integrated stress response prevents demyelination by protecting oligodendrocytes against immune-mediated damage

“…Interestingly, the induction of ISR targeting genes such as that encoding activating transcription factor 4 (ATF4) has been demonstrated in MS lesions (47). We found modestly elevated p-eIF2α and p-PERK immunoreactivity in oligodendrocytes in the course of EAE, as previously described (35). Moreover, CNS delivery of IFN-γ before EAE onset markedly activated the PERK-eIF2α pathway in oligodendrocytes, and the protective effects of IFN-γ in EAE were dependent on the PERK pathway.…”

“…To determine whether the PERK pathway is involved in the protective effects of IFN-γ in EAE-induced demyelination, we monitored the level of p-PERK and p-eIF2α in oligodendrocytes during the course of EAE. Colocalization analysis with the CC1 antibody revealed that few oligodendrocytes were p-PERK-positive and p-eIF2α-positive in the spinal cords of control mice at EAE onset, consistent with a previous report (35). In contrast, CNS delivery of IFN-γ markedly enhanced the activation of the PERK-eIF2α pathway in oligodendrocytes of IFN-γ CNS+ ;Perk +/+ mice ( IFN-γ CNS-;Perk +/+ mice at PID14 (Supplemental Figure 3).…”

Distinct roles of protein kinase R and toll‐like receptor 3 in the activation of astrocytes by viral stimuli

“…Our findings support those in other cell types for an additional role of PKR in the induction of IFNs, cytokines, and chemokines (Melchjorsen et al, 2002;Yang et al, 1995). Phosphorylated PKR or phosphorylated eIF2a have been observed in models of MS and other neurodegenerative diseases, particularly Alzheimer's disease and Huntington's disease (Chakrabarty et al, 2004;Chang et al, 2002;Peel and Bredesen, 2003;Peel et al, 2001). Astrogliosis is a common feature of these diseases (Hedreen and Folstein, 1995;Minagar et al, 2002), and whether PKR contributes to the activation of astrocytes under these conditions remains to be determined.…”

Quantifying immunohistochemical staining of phospho-eIF2α, heme oxygenase-2 and NADPH cytochrome P450 reductase in oligodendrocytes during experimental autoimmune encephalomyelitis

“…More recently, Chakrabarty et al (2004) showed that phospho-PKR and phospho-eIF2␣ were present in oligodendrocytes of both control and EAE animals, and the use of a semi-quantitative scoring scale revealed that the number of phospho-eIF2␣ positive oligodendrocytes was enhanced during EAE. This semiquantitative approach relied on the notion that a percentage of oligodendrocytes was unstained in control animals, due to a very low or absent expression of phospho-eIF2␣, while the number of oligodendrocytes expressing phospho-eIF2␣ increased in the stressed cells.…”