Hsp27 Protects against Ischemic Brain Injury via Attenuation of a Novel Stress-Response Cascade Upstream of Mitochondrial Cell Death Signaling

Abstract

Heat shock protein 27 (Hsp27), a recently discovered member of the heat shock protein family, is markedly induced in the brain after cerebral ischemia and other injury states. In non-neuronal systems, Hsp27 has potent cell death-suppressing functions. However, the mechanism of Hsp27-mediated neuroprotection has not yet been elucidated. Using transgenic and viral overexpression of Hsp27, we investigated the molecular mechanism by which Hsp27 exerts its neuroprotective effect. Overexpression of Hsp27 conferred long-lasting tissue preservation and neurobehavioral recovery, as measured by infarct volume, sensorimotor function, and cognitive tasks up to 3 weeks following focal cerebral ischemia. Examination of signaling pathways critical to neuronal death demonstrated that Hsp27 overexpression led to the suppression of the MKK4/JNK kinase cascade. While Hsp27 overexpression did not suppress activation of an upstream regulatory kinase of the MKK/JNK cascade, ASK1, Hsp27 effectively inhibited ASK1 activity via a physical association through its N-terminal domain and the kinase domain of ASK1. The N-terminal region of Hsp27 was required for neuroprotective function against in vitro ischemia. Moreover, knockdown of ASK1 or inhibition of the ASK1/MKK4 cascade effectively inhibited cell death following neuronal ischemia. This underscores the importance of this kinase cascade in the progression of ischemic neuronal death. Inhibition of PI3K had no effect on Hsp27-mediated neuroprotection, suggesting that Hsp27 does not promote cell survival via activation of PI3K/Akt. Based on these findings, we conclude that overexpression of Hsp27 confers long-lasting neuroprotection against ischemic brain injury via a previously unexplored association and inhibition of ASK1 kinase signaling.

Endothelium-targeted overexpression of heat shock protein 27 ameliorates blood–brain barrier disruption after ischemic brain injury

“…Under physiological conditions, the level of HSP27 is extremely low in the brain; however, HSP27 expression is transiently induced in brain glial cells and/or ECs at 24 h or later following cerebral I/R (14). Previous studies by our and other groups demonstrated robust neuroprotective effects of HSP27 overexpression against I/R brain injury (15)(16)(17)(18), which were largely credited to its antiapoptotic actions. However, HSP27 exerts additional actions on ECs (14).…”

“…We previously reported that transgenic mice with ubiquitous overexpression of HSP27 developed significantly less brain damage after cerebral I/R, including less BBB disruption (17,18,22). These beneficial effects of HSP27 were attributed mainly to its well-characterized antiapoptotic functions Fig.…”

Protein kinase D: a new player among the signaling proteins that regulate functions in the nervous system

“…Heat-shock protein 27 (HSP27) protects neurons during cerebral ischemia [65] through phosphorylation at Ser15 and Ser82, critical sites for neuroprotection. PKD also directly phosphorylates HSP27 [66] .…”

“…As PKCδ directly phosphorylates PKD1 in vivo, PKCδ loss-of-function may effectively inhibit PKD1 activation. It is worth noting that PKD1 loss-of-function by RNAi or overexpression of S916APKD1 enhances oxidative stress-induced apoptosis, while PKD1 gain-of-function inhibits this apoptosis [64] .Heat-shock protein 27 (HSP27) protects neurons during cerebral ischemia [65] through phosphorylation at Ser15 and Ser82, critical sites for neuroprotection. PKD also directly phosphorylates HSP27 [66] .…”

Overexpression of Heat Shock Protein 27 Reduces Cortical Damage after Cerebral Ischemia

“…Similarly, using a model of transient cerebral ischemia, HSP27 transgenic mice have been shown to develop a reduced infarct size (Stetler et al 2008).…”