PKCγ Promotes Axonal Remodeling in the Cortico-Spinal Tract via GSK3β/β-Catenin Signaling after Traumatic Brain Injury

Background: Traumatic brain injury (TBI) is a common cause of death and disability. Enhancing the midline-crossing of the contralateral corticospinal tract (CST) to the denervated side of spinal cord facilitates functional recovery after TBI. Activation of the gamma isoform of PKC (PKCγ) in contralateral CST implicates its roles in promoting CST remodeling after TBI. Methods: Using in vitro approaches, we deploy loss and gain of function strategies to resolve the role of PKCγ during the differentiation and neurite/axonal growth of N2a cells and primary cortical neurons. rAAV2/9-mediated delivery of PKCγin vivo was additionally used to investigate the therapeutic potential of constitutive PKCγ in the corticospinal tract after unilateral TBI. Findings: PKCγ is not only important but necessary for neural differentiation, neurite outgrowth and axonal branching but not for axonal extension. Mechanically, through the phosphorylation of GSK3β, PKCγ stabilizes the expression of cytosolic β-catenin and increase GAP43 expression, thus promoting axonal outgrowth. In vivo, specifically delivery of active PKCγ mutant to cortical neuron promotes midline crossing of corticospinal fibers from the uninjured side to the denervated cervical spinal cord. This PKCγ- mediated injury response promoted sensorimotor functional recovery. Interpretation: PKCγ mediates stability of β-catenin through the phosphorylation of GSK3β to facilitate1 neuronal differentiation, neurite outgrowth and axonal branching. It demonstrates that PKCγ is a novel therapeutic target for physiological and functional recovery after TBI. Funding Statement: This work was supported by Natural Science Foundation of China (NFSC) grants (81572468, 81372710, 81671219), Natural Science Foundation of Jiangsu Province (BK20151105, BK20151109), “333” Engineering Project Jiangsu Province ((2016)III-0605), Six Talent Peaks Project of Jiangsu (2015-WSN 087), Medical Young Talents Program of Jiangsu Province (QNRC2016188, QNRC2016192), Wuxi Key Medical Talents (ZDRC001). Declaration of Interests: The authors declare that they have no conflicts of interest to this work. Ethics Approval Statement: All study procedures were approved by the Institutional Review Board of Nanjing Medical University (Permit number: KYLLH2018006). No mice were excluded from scoring. All animal experiments were conducted in a double-blinded manner