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

Abstract

The damage borne by the endothelial cells (ECs) forming the blood–brain barrier (BBB) during ischemic stroke and other neurological conditions disrupts the structure and function of the neurovascular unit and contributes to poor patient outcomes. We recently reported that structural aberrations in brain microvascular ECs—namely, uncontrolled actin polymerization and subsequent disassembly of junctional proteins, are a possible cause of the early onset BBB breach that arises within 30–60 min of reperfusion after transient focal ischemia. Here, we investigated the role of heat shock protein 27 (HSP27) as a direct inhibitor of actin polymerization and protectant against BBB disruption after ischemia/reperfusion (I/R). Using in vivo and in vitro models, we found that targeted overexpression of HSP27 specifically within ECs—but not within neurons—ameliorated BBB impairment 1–24 h after I/R. Mechanistically, HSP27 suppressed I/R-induced aberrant actin polymerization, stress fiber formation, and junctional protein translocation in brain microvascular ECs, independent of its protective actions against cell death. By preserving BBB integrity after I/R, EC-targeted HSP27 overexpression attenuated the infiltration of potentially destructive neutrophils and macrophages into brain parenchyma, thereby improving long-term stroke outcome. Notably, early poststroke administration of HSP27 attached to a cell-penetrating transduction domain (TAT-HSP27) rapidly elevated HSP27 levels in brain microvessels and ameliorated I/R-induced BBB disruption and subsequent neurological deficits. Thus, the present study demonstrates that HSP27 can function at the EC level to preserve BBB integrity after I/R brain injury. HSP27 may be a therapeutic agent for ischemic stroke and other neurological conditions involving BBB breakdown.

Mesenchymal stem cell therapy alleviates the neuroinflammation associated with acquired brain injury

“…9,13,14 Additionally, increased permeability of the blood-brain barrier (BBB) allows peripheral leukocytes to intrude the injured brain. 9,15,16 Further, sustained microglial activation exacerbates chronic inflammation throughout the CNS, fueling a toxic environment that continuously aggravates secondary axonal degeneration and neuronal death. 9,17 Consequently, therapeutically suppressing the neuroinflammatory cascade represents a major aim of recent investigative efforts to reduce neurological damage following stroke and TBI.…”

“…Following the onset of stroke, the acute inflammatory phase is characterized by elevated secretion of proinflammatory cytokines interleukin (IL)-6, IL-1β, and tumor necrosis factor (TNF)-⍺ into blood circulation and the cerebrospinal fluid (CSF). 15,16 While localized upregulation of TNF-⍺ and IL-1β has been primarily attributed to microglia 1 (M1) activated microglia, neurons also promote expression of IL-6. 16 Moreover, the ischemic microenvironment stimulates microglial elevation of cluster of differentiation 14 (CD14), a pattern recognition receptor on peripheral monocytes and a major component of innate immunity, indicating that resident microglia may mediate the acute inflammatory response following stroke.…”

“…9,23 A weakened endothelial cell barrier promotes infiltration of serum proteins and immune cells, contributing to secondary BBB disruption and heightening the original injury induced by stroke. 15 This worsens physiological damage by elevating cerebral pressure and increasing secondary cell loss. 15 Ischemic stroke prompts an autoimmune reaction to neuronal antigens that could perhaps escalate or mitigate lasting neuroinflammation.…”

Passive heat therapy for cerebral protection: new ideas of age‐old concepts

“…A recent study demonstrated that increased levels of microvascular endothelial HSP27 (achieved using transgenic mice with overexpression of HSP27) preserves the integrity of the blood–brain barrier during I/R and prevents the infiltration of macrophages and neutrophils into the brain parenchyma (Shi et al . ). Yacobi et al .…”

“…several weeks) to induce chronic HSP elevation. A recent study demonstrated that increased levels of microvascular endothelial HSP27 (achieved using transgenic mice with overexpression of HSP27) preserves the integrity of the blood-brain barrier during I/R and prevents the infiltration of macrophages and neutrophils into the brain parenchyma (Shi et al 2017). Yacobi et al (2014) also demonstrated the importance of glutamate receptors during hypoxic insults, which facilitate neuronal death via calcium penetration following a large glutamate surge.…”