Optical Depolarization of DCX-Expressing Cells Promoted Cognitive Recovery and Maturation of Newborn Neurons via the Wnt/β-Catenin Pathway

Abstract

Electrical excitability by membrane depolarization is crucial for survival and maturation of newborn cells in the dentate gyrus of the hippocampus. However, traditional technology for membrane depolarization lacks temporal and spatial precision. Optogenetics can be used to activate channelrhodopsin-2 (ChR2), allowing cationic current to depolarize genetically targeted cells. In this study, we used ChR2-EGFP driven by doublecortin (DCX) to promote survival and maturation of newborn cells in the dentate gyrus after traumatic brain injury (TBI). C57BL/6 mice underwent lateral fluid percussion TBI. TBI mice were transfected with a lentivirus carrying the DCX-ChR2-EGFP gene. We observed that not only immature neurons but also type-2b intermediate progenitor (IPs) and neuroblasts expressed DCX-EGFP, indicating that DCX-expressing newborn cells could provide a long time window for electrical activity regulation. Quantitative results showed that the number of EGFP-expressing cells began to rise at 3 days after TBI and peaked at 9 days after TBI. By optical depolarization of DCX-EGFP-expressing cells between 3 and 12 days, we observed significantly improved cognitive deficits after TBI with enhanced survival and maturation of newborn cells in the dentate gyrus. We also investigated the role of optical depolarization in neural stem cells transfected with a lentivirus carrying the ChR2-DCX-EGFP gene in vitro. By administrating verapamil to block L-type calcium channels, we verified that the up-regulation of MAP2, NeuN, Neurog2, NeuroD1 and GluR2 in newborn cells was mediated by ChR2-elicted depolarization. By using β-catenin inhibitor Dkk1, we demonstrated that optical depolarization of DCX-EGFP-expressing cells facilitated survival and maturation probably through the Wnt/β-catenin signaling cascade.

Parkinson's disease, aging and adult neurogenesis: Wnt/β‐catenin signalling as the key to unlock the mystery of endogenous brain repair

“…Herein, after a description of the key Wnt‐signalling components and a synopsis of adult neurogenesis in PD, we will focus on the role of WβC‐signalling as a common final pathway in mediating NSC regulation, from development to aging and PD degeneration. We aim to survey recent literature in the field supporting the upregulation of WβC as a means to re‐activate neurogenesis and incite regeneration in the injured brain, particularly in the context of modalities through which the inherent self‐repair capacities of the aged PD brain, can be engaged (Chen et al, ; Kase et al, ; Kaur, Saunders, & Tolwinski, ; Mishra et al, ; Zeng et al, ; Zhao, et al, ; Zhang et al, a,b,c; and following sections).…”

Wnt Pathway: An Emerging Player in Vascular and Traumatic Mediated Brain Injuries

“…Interestingly, membrane depolarization plays a decisive role in mediating the survival and maturation of newborn neurons in the DG (Zhao et al, 2018). Optogenetic tools were applied to stimulate the membrane depolarization of Dcx + cells via the injection of LV-Dcx-channelrhodopsin-2 (ChR2)-EGFP gene into the brain of TBI mice (Zhao et al, 2018).…”

Optogenetic Modulation for the Treatment of Traumatic Brain Injury

“…Potential targets for optogenetic stimulation include neurons that would benefit from prolonged cell survival post-TBI to preserve cognitive ability, as well as, targets that can attenuate seizures postinjury. Stimulating areas of the SVZ and SGZ of the DG has been shown to enhance cognitive recovery long term in mouse models [95]. In addition, several areas of the brain have been shown to attenuate seizure activity when targeted with optogenetic therapeutics.…”

“…To date, there has been only one study examining the potential use of neural stem cells in combination with optogenetics for TBI mapping and treatment. In this study, Zhao et al used ChR2-EGFP (enhanced green fluorescence protein) coupled with doublecortin (DCX), a microtubuleassociated protein expressed by neuronal progenitor and postmitotic neuronal precursor cells, to monitor and encourage the survival and maturation of nascent neuronal cells following TBI [95]. To do this, a lentiviral vector carrying the DCX-ChR2-EGFP gene was constructed and injected into the hilus of the DG in C57BL/6 mice.…”

“…Furthermore, the TBI+ChR2 group showed increased maturation and migration of newborn neurons. At a molecular level, in vitro studies showed that optical stimulation specifically resulted in an upregulation of several neural marker transcripts, including microtubule-associated protein 2 (MAP2), neuronal nuclei (NeuN) antigen, Neurogenin 2 (Neurog2), neuronal differentiation 1 (NeuroD1), and glutamate receptor subunit 2 (GluR2) in newborn cells [95]. Altogether, these findings suggest that this technique promoted neurogenesis following depolarization of stem cells expressing the opsin, thus providing evidence for its future implications in not only TBI but also many other neurological disorders.…”