Blocking H+ Extrusion Protein Reduces Gliosis and Functional Impairment in Experimental Concussion Model
John Bielanin1, Satya Paruchuri2, Shamseldin Metwally2, Helena Oft 1, Lin Lin2, Okan Capuk 2, Nicholas Pennock2, Shanshan Song2, Dandan Sun2
1University of Pittsburgh School of Medicine, 2Neurology, University of Pittsburgh
Objective:
To identify therapeutic targets for neuroinflammation, axonal damage, and neurological deficits in experimental concussion model.
Background:
Mild traumatic brain injury (mTBI) or concussion represents the most common type of brain injury, yet few therapies are currently available. Using an experimental repetitive-mild traumatic brain injury (r-mTBI) model, we investigated r-mTBI induced elevation of H+ extrusion protein Na+/H+ exchanger (NHE1) in the pathogenesis of r-mTBI and its efficacy as a therapeutic target.
Design/Methods:
R-mTBI model was induced in young adult C57BL/6J mice with five closed-skull concussions (with an interval of 48 hours). Behavioral tests were conducted one day prior to TBI induction as a baseline measure and at 15 or 40 days post-TBI (dpi). Histology with immunostaining was performed to detect chances in the NHE1 protein within GFAP+ reactive astrocytes, IBA1+ microglia, MAP2+ neuron filaments, and its association with amyloid precursor protein (APP) accumulation.
Results:
R-mTBI mice displayed impaired motor learning in the rotarod test at 15 dpi and exhibited spatial memory deficits in the Y-maze spatial recognition test at 40 dpi (p < 0.05). Immunohistochemistry studies revealed a significant elevation in NHE1 protein expression in neuronal filaments, reactive astrocytes, and microglia in the cerebral cortex (CTX), corpus callosum (CC), and hippocampus (CA1). This elevation was accompanied by an accumulation of APP (p < 0.05). In comparison to the vehicle control group, the post-injury administration of a potent NHE1 inhibitor, HOE642, from 9 to 15 dpi (0.3 mg/kg/day, b.i.d., i.p.), not only attenuated motor and cognitive function impairment (p < 0.01) but also abolished astrogliosis and significantly reduced microgliosis levels in all three brain regions (CTX, CC, and CA1) (p < 0.05).
Conclusions:
These findings imply that concussion-mediated NHE1 protein increase may play a role in the development of axonal damage, neuroinflammation, and neuronal function impairments. Pharmacological inhibition of NHE1 shows protective effects.