Posttraumatic Reduction of Edema with Aquaporin-4 RNA Interference Improves Acute and Chronic Functional Recovery

Abstract

Traumatic brain injury (TBI) is common in young children and adolescents and is associated with long-term disability and mortality. The neuropathologic sequelae that result from juvenile TBI are a complex cascade of events that include edema formation and brain swelling. Brain aquaporin-4 (AQP4) has a key role in edema formation. Thus, development of novel treatments targeting AQP4 to reduce edema could lessen the neuropathologic sequelae. We hypothesized that inhibiting AQP4 expression by injection of small-interfering RNA (siRNA) targeting AQP4 (siAQP4) after juvenile TBI would decrease edema formation, neuroinflammation, neuronal cell death, and improve neurologic outcomes. The siAQP4 or a RNA-induced silencing complex (RISC)-free control siRNA (siGLO) was injected lateral to the trauma site after controlled cortical impact in postnatal day 17 rats. Magnetic resonance imaging, neurologic testing, and immunohistochemistry were performed to assess outcomes. Pups treated with siAQP4 showed acute (3 days after injury) improvements in motor function and in spatial memory at long term (60 days after injury) compared with siGLO-treated animals. These improvements were associated with decreased edema formation, increased microglial activation, decreased blood-brain barrier disruption, reduced astrogliosis and neuronal cell death. The effectiveness of our treatment paradigm was associated with a 30% decrease in AQP4 expression at the injection site.

Real-Time Monitoring of Changes in Brain Extracellular Sodium and Potassium Concentrations and Intracranial Pressure after Selective Vasopressin-1a Receptor Inhibition following Focal Traumatic Brain Injury in Rats

“…Others support the idea that AQP4 expression increases following similar insults and may provide a key avenue for strategies aimed at reducing its effects. [57][58][59] On the other hand, a decrease in AQP4 expression was reported using a CCI model at more chronic time points 60 but these authors concluded 1264 FILIPPIDIS ET AL.…”

Improved long-term outcome after transient cerebral ischemia in aquaporin-4 knockout mice

“…21 All tests at each time-point were carried out on WT and AQP4 À/À mice within a 3-h morning time-block (8-11 am) and WT and AQP4 À/À were interleaved during the testing sequence. Foot-fault testing was carried out on an elevated platform (50 cm  155 cm, ClosetMaid, Ocala, FL, USA) with parallel wire bars 1.5 cm apart and raised 100 cm above the floor.…”

“…The tissue section with the largest lesion was selected and the NeuN positive cells were counted in an automated fashion via the Mercator software and the density was determined. 21 Statistics MRI and behavioral data were analyzed by two-way repeated measures analysis of variance with a post hoc Bonferroni test. One-way ANOVA was used for immunohistochemistry analysis.…”

“…T2 and DWI data were post-processed for quantitative T2 maps and apparent diffusion coefficients (ADC) using in-house software written in Matlab (Mathworks, Natick, MA, USA) as described previously. 21 Lesion, total brain, and hemispheric volumes were calculated using our recently developed automated Hierarchical Region Splitting (HRS) software. 22 Our previous studies established that automatically derived core and penumbral lesion volumes co-localized with those determined by immunohistochemistry or diffusion-perfusion mismatch.…”

Combination Therapies for Traumatic Brain Injury: Retrospective Considerations

“…Within 10 min after unilateral controlled cortical impact (CCI), immature (P17) male rats were injected intracortically with siAQP4 adjacent to the site of the impact. 37,38 A second siRNA injection was repeated 2 days later, to maintain the decrease of AQP4 expression. 23 Based on previous monotherapy studies with D-JNKI-1 in juvenile animals, 35 11 mg/kg was administered IP at 3 h postinjury.…”