Abstract
Blood-brain barrier (BBB) breakdown and the associated microvascular hyperpermeability followed by brain edema are hallmark features of several brain pathologies, including traumatic brain injuries (TBI). Recent studies indicate that pro-inflammatory cytokine interleukin-1β (IL-1β) that is up-regulated following traumatic injuries also promotes BBB dysfunction and hyperpermeability, but the underlying mechanisms are not clearly known. The objective of this study was to determine the role of calpains in mediating BBB dysfunction and hyperpermeability and to test the effect of calpain inhibition on the BBB following traumatic insults to the brain. In these studies, rat brain microvascular endothelial cell monolayers exposed to calpain inhibitors (calpain inhibitor III and calpastatin) or transfected with calpain-1 siRNA demonstrated attenuation of IL-1β-induced monolayer hyperpermeability. Calpain inhibition led to protection against IL-1β-induced loss of zonula occludens-1 (ZO-1) at the tight junctions and alterations in F-actin cytoskeletal assembly. IL-1β treatment had no effect on ZO-1 gene (tjp1) or protein expression. Calpain inhibition via calpain inhibitor III and calpastatin decreased IL-1β-induced calpain activity significantly (p < 0.05). IL-1β had no detectable effect on intracellular calcium mobilization or endothelial cell viability. Furthermore, calpain inhibition preserved BBB integrity/permeability in a mouse controlled cortical impact model of TBI when studied using Evans blue assay and intravital microscopy. These studies demonstrate that calpain-1 acts as a mediator of IL-1β-induced loss of BBB integrity and permeability by altering tight junction integrity, promoting the displacement of ZO-1, and disorganization of cytoskeletal assembly. IL-1β-mediated alterations in permeability are neither due to the changes in ZO-1 expression nor cell viability. Calpain inhibition has beneficial effects against TBI-induced BBB hyperpermeability.
Highlights
Blood-brain barrier (BBB) breakdown and the associated microvascular hyperpermeability followed by brain edema are hallmark features of several brain pathologies, including traumatic brain injuries (TBI)
Calpain Inhibition Attenuates IL-1-induced Endothelial Cell Hyperpermeability—RBMEC monolayers were pretreated with calpain inhibitor III or calpastatin to confirm the contribution of calpains in mediating IL-1 (10 ng/ml for 2 h)-induced endothelial cell hyperpermeability
The major findings of this study are as follows: 1) calpain(s) promote BBB dysfunction and hyperpermeability via disruption of the tight junctions (TJs) in vitro; 2) IL-1 is an inducer of calpain-mediated BBB dysfunction and hyperpermeability in vitro; 3) inhibition of calpain activation provides protection against BBB hyperpermeability via preservation of TJ integrity in vitro; 4) calpain-mediated loss of barrier functions are independent of [Ca2ϩ]i mobilization or loss of cell viability; and 5) pharmacological inhibition of calpains provide protection against BBB hyperpermeability in a mouse model of TBI
Summary
Blood-brain barrier (BBB) breakdown and the associated microvascular hyperpermeability followed by brain edema are hallmark features of several brain pathologies, including traumatic brain injuries (TBI). The objective of this study was to determine the role of calpains in mediating BBB dysfunction and hyperpermeability and to test the effect of calpain inhibition on the BBB following traumatic insults to the brain. Calpain inhibition preserved BBB integrity/permeability in a mouse controlled cortical impact model of TBI when studied using Evans blue assay and intravital microscopy These studies demonstrate that calpain-1 acts as a mediator of IL-1-induced loss of BBB integrity and permeability by altering tight junction integrity, promoting the displacement of ZO-1, and disorganization of cytoskeletal assembly. Calpain-dependent cleavage of intracellular cytoplasmic protein ZO-1 has been studied in human lung endothelial cells [13] Their contribution in regulating BBB endothelial dysfunction and hyperpermeability is largely unknown
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