Role of BDNF-TrkB signaling in the improvement of motor function and neuroplasticity after ischemic stroke in rats by transcranial direct current stimulation
Yu Chen, Lin Mao, Qinxiang Zhou, Dingqun Bai, Yuhan Kong
Abstract
Transcranial direct current stimulation (tDCS) has an impact on improving cognitive and motor dysfunction induced by ischemia-reperfusion injury. However, to use this technology more rationally in clinical practice, a deepened understanding of the molecular mechanisms behind its therapeutic effects is needed. This study explored the role of the brain-derived neurotrophic factor(BDNF) and its associated receptor tropomyosin-receptor kinase B(TrkB) while deciphering the underlying mechanisms in transcranial direct current therapy to treat ischemic stroke. A middle cerebral artery occlusion-reperfusion(MCAO/R) model was established in rats to observe tDCS effects on brain damage. Behavioral tests, the modified neurologic severity score(mNSS), and the Hoffman reflex / the M wave(H max /M max ) ratio helped assess motor function and neurologic deficits. HE and Nissl staining helped observe the morphological changes and count of nerve cells. We tested the expression of growth-associated protein-43(Gap-43) and microtubule-associated protein-2(Map-2), K + -Cl - co-transporter 2(KCC2), γ-aminobutyric acid(GABA), and key BDNF-TrkB downstream signaling, the phospholipase C gamma(PLCγ) / CaMK IV / cAMP response element binding protein(CREB), and extracellular signal-regulated protein kinase(ERK1/2) / ribosomal S6 kinase(RSK) using western blotting. Moreover, BDNF was analyzed in plasma using the enzyme-linked immunosorbent assay (ELISA) to investigate the tDCS effect on human BDNF expression levels. Finally, a BDNF receptor antagonist, ANA-12, was administered to explore the tDCS mechanism mediating BDNF-TrkB signaling. After tDCS treatment, the mNSS was improved, and the motor function was restored. Moreover, tDCS decreased cell swelling after MCAO/R and enhanced the number of neurons. tDCS treatment increased: (1) BDNF, Gap-43, Map-2 expression, (2) KCC2, GABA, and (3) PLCγ, CaMK IV, CREB and ERK1/2, RSK. Furthermore, ELISA results indicate that tDCS elevated human plasma BDNF protein expression. However, the therapeutic effect of tDCS was suppressed to a certain extent by adding ANA-12. Our findings indicate that tDCS may exert a neuroprotective effect by activating the downstream key molecules of BDNF-TrkB expression, for instance, PLCγ/ CaMK IV/ CREB and ERK/ RSK pathway. Moreover, tDCS can control neuronal excitability, promote axonal regeneration, and accelerate motor function recovery in ischemia reperfusion-injured rats.