Inhibition of HDAC increases BDNF expression and promotes neuronal rewiring and functional recovery after brain injury

Sada et al. Cell Death and Disease (2020)11:655 https://doi.org/10.1038/s41419-020-02897-w ARTICLE Cell Death & Disease Open Access Inhibition of HDAC increases BDNF expression and promotes neuronal rewiring and functional recovery after brain injury 1234567890():,; 1234567890():,; 1234567890():,; 1234567890():,; Naoki Sada1, Yuki Fujita1,2, Nanano Mizuta1, Masaki Ueno3, Takahisa Furukawa4 and Toshihide Yamashita 1,2,5,6 Abstract Brain injury causes serious motor, sensory, and cognitive disabilities. Accumulating evidence has demonstrated that histone deacetylase (HDAC) inhibitors exert neuroprotective effects against various insults to the central nervous system (CNS). In this study, we investigated the effects of the HDAC inhibition on the expression of brain-derived neurotrophic factor (BDNF) and functional recovery after traumatic brain injury (TBI) in mice. Administration of class I HDAC inhibitor increased the number of synaptic boutons in rewiring corticospinal fibers and improved the recovery of motor functions after TBI. Immunohistochemistry results showed that HDAC2 is mainly expressed in the neurons of the mouse spinal cord under normal conditions. After TBI, HDAC2 expression was increased in the spinal cord after 35 days, whereas BDNF expression was decreased after 42 days. Administration of CI-994 increased BDNF expression after TBI. Knockdown of HDAC2 elevated H4K5ac enrichment at the BDNF promoter, which was decreased following TBI. Together, our findings suggest that HDAC inhibition increases expression of neurotrophic factors, and promote neuronal rewiring and functional recovery following TBI. Introduction Traumatic brain injury (TBI) induces severe, longlasting neurological disabilities, including motor, sensory, and cognitive dysfunctions. Studies support the view that partial functional motor recovery can occur spontaneously after focal cerebral cortex injury1–6. Such recovery is correlated with functional organization of remnant neuronal networks7,8. It has been shown that reorganization of the corticospinal tract (CST), a major descending motor pathway in mammals which projects from the cortex to the spinal cord, can contribute to post-injury functional motor recovery9–16. The CST from the intact Correspondence: Yuki Fujita () or Toshihide Yamashita () 1 Department of Molecular Neuroscience, Graduate School of Medicine, Osaka University, 2-2, Yamadaoka, Suita, Osaka 565-0871, Japan 2 WPI Immunology Frontier Research Center, Osaka University, Suita, Osaka 5650871, Japan Full list of author information is available at the end of the article. These authors contributed equally: Naoki Sada, Yuki Fujita Edited by F. Strappazzon side extends axon collaterals into the denervated side of the spinal cord and forms synapses with target neurons, which plays a role in facilitating improved post-injury functional outcomes in mice11. During reorganization, remnant CST fibers sprout collaterals, and then, they form synapses with interneurons to construct compensatory neural pathways. The period of spontaneous motor function recovery during which CST fibers sprout can be observed until around 14 days after brain injury in mice. Once synapse formation begins, additional recovery is limited. We previously reported that brain-derived neurotrophic factor (BDNF) signaling is required for CST fiber rewiring and behavioral recovery post-injury in mice11. BDNF expression in the denervated cervical spinal cords was significantly increased 14 days after brain injury; thereafter, the number of fibers recrossing towards the denervated side gradually increased, peaking at day 2811. siRNA-mediated BDNF knockdown led to reduce CST axonal branching. However, the molecular mechanisms © The Author(s) 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. Official journal of the Cell Death Differentiation Association Sada et al. Cell Death and Disease (2020)11:655 underlying induction of BDNF expression and synapse formation during CST rewiring remain unclear. Here, we aimed to investigate what mechanism controls the synapse formation, and whether increased synapse formation could contribute to motor function recovery. Histone deacetylases (HDACs) are enzyme that remove acetyl groups from lysine residues in the amino-terminal tails of histone proteins, leading to chromatin compaction, which is associated with transcriptional and translational repression17,18. Structurally, HDACs can be classified into class I (HDAC1, 2, 3, and 8), II (HDAC4, 5, 6, 7, and 9), III (SIRT1–SIRT7), or IV (HDAC11)19. Evidence suggests that HDAC expression is altered after central nervous system (CNS) injury, and that HDAC inhibitors can exert neuroprotective effects20,21. In particular, HDAC2 has been shown to negatively regulate synaptic plasticity in animal models of neurodegeneration22. Increased HDAC2 expression decreased the expression of synaptic plasticity-related genes such as BDNF and synaptophysin. In this study, we assess whether a class 1 HDAC inhibitor (4-acetamido-N-(2-aminophenyl) benzamide [CI-994]) or virus-mediated HDAC2 knockdown enhances synapse formation and motor function of the affected paw after brain injury in mice. Materials and methods Animals C57BL/6J mice obtained from Japan SLC, Inc. (Shizuoka, Japan) were bred and maintained at the Institute of Experimental Animal Sciences, Osaka University Graduate School of Medicine. Chx10-CreERT2 transgenic mouse were generated by Dr. Takahisa Furukawa (Osaka University) using bacterial artificial chromosome (BAC) transgenesis. Cre-ERT2-poly A signal cassette was inserted into mouse Chx10 locus. Ai14 female mice (B6.Cg-Gt (ROSA)26Sortm14(CAG-tdTomato)Hze/J)23 and R26-CAGLSL-Sun1-sfGFP-Myc knock-in mice (B6;129-Gt(ROSA) 26Sortm5(CAG-Sun1/sfGFP)Nat/J)24 were obtained from The Jackson Laboratory for the INTACT method. This study was approved by the institutional committee of Osaka University. All experiments were performed in accordance with the Osaka University Medical School Guide for the Care and Use of Laboratory Animals. Animals were randomized to treatment groups. Experiments, assessments, and analyses were performed in a blinded fashion. (...truncated)