Heat shock protein 27 upregulation and phosphorylation in rat experimental autoimmune encephalomyelitis

Following stress or inflammation, the 27-kDa heat shock protein (HSP27) is induced in various cell types, where it promotes cell survival and inhibits inflammatory reactions. We examined the expression of HSP27 and phosphorylated HSP27 (p-HSP27) in the spinal cords of Lewis rats with experimental autoimmune encephalomyelitis (EAE). Western blotting analysis revealed low levels of HSP27 and p-HSP27 in the normal spinal cords and significantly higher levels in EAE-affected spinal cords. Immunohistochemistry revealed that HSP27 was expressed constitutively in the neurons and some fibrous astrocytes of the spinal cords of normal rats. However, in EAE-affected spinal cords, HSP27 immunoreactivity was higher and located primarily in the fibrous astrocytes of the white matter, whereas few of the inflammatory cells were immunopositive for HSP27. Immunoreactivity for p-HSP27 was detected predominantly in the fibrous astrocytes of the normal controls and was markedly increased in EAE-affected spinal cords. Therefore, the levels of HSP27 expression and phosphorylation of HSP27 were increased primarily during reactive astrogliosis of spinal white matter affected by EAE. These observations suggest that in rat EAE, the increased expression and elevated activation of HSP27 modulate host cell activity, survival, and inflammation to counter the autoimmune inflammatory injury. Our results also suggest that HSP27 plays a role in spontaneous recovery from EAE-induced paralysis.