Anti-Inflammatory Effects of the 70 kDa Heat Shock Protein in Experimental Stroke

Abstract

The 70-kDa heat shock protein (Hsp70) is involved in protecting the brain from a variety of insults including stroke. Although the mechanism has been largely considered to be because of its chaperone functions, recent work indicates that Hsp70 also modulates inflammatory responses. To explore how and whether Hsp70 regulate immune responses in brain ischemia, mice overexpressing Hsp70 (Hsp Tg) were subjected to 2 h middle cerebral artery occlusion, followed by 24 h reperfusion. Parallel experiments were performed using a brain inflammation model. Hsp Tg microglia cocultured with astrocytes were used to evaluate the direct effects of Hsp70 on cytotoxicity of microglia. Compared with wild-type (Wt) littermates, Hsp Tg mice showed decreased infarct size and improved neurological deficits. The number of activated microglia/macrophages were also reduced in ischemic brains of Hsp Tg mice. Similar observations were made in a model of brain inflammation that does not result in brain cell death. Overexpression of Hsp70 in microglia completely prevented microglia-induced cytotoxicity to astrocytes. Activation of the inflammatory transcription factor, nuclear factor-kappaB (NF-kappaB) was inhibited significantly in Hsp Tg mice and microglia. This was associated with decreased phosphorylation of NF-kappaB inhibitor protein, IkappaBalpha, and decreased expression of several NFkappaB-regulated genes. Co-immunoprecipitation studies revealed an interaction of Hsp70 with NF-kappaB and IkappaBalpha, but not with IkappaB kinase, IKKgamma, suggesting that Hsp70 binds to the NF-kappaB:IkappaB complex preventing IkappaB phosphorylation by IKK. The findings of the present work establish an anti-inflammatory role for Hsp70 in the context of brain ischemia as a novel mechanism of protection.

Transduction of Neural Precursor Cells with TAT-Heat Shock Protein 70 Chaperone: Therapeutic Potential Against Ischemic Stroke after Intrastriatal and Systemic Transplantation

“…In this context, we have previously shown that in vitro transduction of NPCs with TAT-Bcl-x L is efficient and results in sustained neuroprotection against stroke after intracerebral transplantation of TAT-Bcl-x L -transduced NPCs [19]. Although Hsp70-induced neuroprotection has been shown before [10,[52][53][54], this study shows for the first time that the fusion protein TAT-Hsp70 enhances resistance of NPCs against hypoxic-hypoglycemic injury. Since neuroprotection by the TAT domain itself has been described in vitro recently [55,56], we used TAT-HA as a negative control in order to exclude effects of the TAT domain itself on cell viability, neurosphere formation rates, NPC numbers, and differentiation patterns of NPCs.…”

Microglial Activation in Stroke: Therapeutic Targets

“…192 Using cocultures of astrocytes and microglia, HSP-70 transgenic microglia cultured with wild-type astrocytes experienced less injury to oxygen glucose deprivation (OGD) than did wild-type microglia cultured with wild-type astrocytes. 193 In a transgenic mouse model of HSP-70 overexpression, protection from experimental stroke was associated with decreased microglial activation. 193 Protein binding studies suggest that this is due to HSP-70 binding to the NF-B complex and blocking I B phosphorylation.…”

“…193 In a transgenic mouse model of HSP-70 overexpression, protection from experimental stroke was associated with decreased microglial activation. 193 Protein binding studies suggest that this is due to HSP-70 binding to the NF-B complex and blocking I B phosphorylation. 193 This anti-inflammatory may be due to the ability of HSP-70 to inhibit NF-B activation.…”

“…193 Protein binding studies suggest that this is due to HSP-70 binding to the NF-B complex and blocking I B phosphorylation. 193 This anti-inflammatory may be due to the ability of HSP-70 to inhibit NF-B activation. HSP-70 can interact with IKK, thereby preventing I B phosphorylation and activation.…”

“…HSP-70 can interact with IKK, thereby preventing I B phosphorylation and activation. 193,194 Glial cells exposed to heat shock or transfected with HSP-70 showed less nuclear NF B translocation and less iNOS expression (NF B-regulated protein) when treated with bacterial lipopolysaccharide. 195 Similarly, in brain inflammation elicited by bacterial lipopolysaccharide and cytokine injection, prior heat stress led to less microglial activation and less NF B activity.…”