Journal of Alzheimer’s Disease 51 (2016) 591–604 DOI 10.3233/JAD-150717 IOS Press 591 A Mercaptoacetamide-Based Class II Histone Deacetylase Inhibitor Increases Dendritic Spine Density via RasGRF1/ERK Pathway Jung Min Song a,1 , You Me Sung a,1 , Jin Han Nam d,1 , Hyejin Yoon e , Andrew Chung a , Emily Moffat a , Mira Jung b , Daniel T.S. Pak c , Jungsu Kim e,∗ and Hyang-Sook Hoe a,d,∗ a Department of Neuroscience, Georgetown University Medical Center, Washington, DC, USA b Department of Radiation Medicine, Lombardi Comprehensive Cancer Center, Georgetown University Medical Center, Washington, DC, USA c Department of Pharmacology, Georgetown University Medical Center, Washington, DC, USA d Department of Neural Development and Disease, Korea Brain Research Institute (KBRI), Dong-gu, Daegu, Korea e Department of Neuroscience, Neurobiology of Disease Graduate Program, Mayo Graduate School, Mayo Clinic College of Medicine, Jacksonville, FL, USA Accepted 15 December 2015 Abstract. Background: The accumulation of amyloid- (A) leads to the loss of dendritic spines and synapses, which is hypothesized to cause cognitive impairments in Alzheimer’s disease (AD) patients. In our previous study, we demonstrated that a novel mercaptoacetamide-based class II histone deacetylase inhibitor (HDACI), known as W2, decreased A levels and improved learning and memory in mice. However, the underlying mechanism of this effect is unknown. Objective: Because dendritic spine formation is associated with cognitive performance, here we investigated whether HDACI W2 regulates dendritic spine density and its molecular mechanism of action. Methods: To examine the effect of HDACI W2 on dendritic spine density, we conducted morphological analysis of dendritic spines using GFP transfection and Golgi staining. In addition, to determine the molecular mechanism of W2 effects on spines, we measured the levels of mRNAs and proteins involved in the Ras signaling pathway using quantitative real-time PCR, immunocytochemistry, and western analysis. Results: We found that HDACI W2 altered dendritic spine density and morphology in vitro and in vivo. Additionally, W2 increased the mRNA or protein levels of Ras GRF1 and phospho-ERK. Moreover, knockdown of RasGRF1 and inhibition of ERK activity prevented the W2-mediated spinogenesis in primary hippocampal neurons. Conclusion: Our Class II-selective HDACI W2 promotes the formation and growth of dendritic spines in a RasGRF1 and ERK dependent manner in primary hippocampal neurons. Keywords: Alzheimer’s disease, dendritic spine, HDAC inhibitor, ras signaling 1 These authors contributed equally to this work. ∗ Correspondence to: Hyang-Sook Hoe, PhD, Department of Neural Development and Disease, Korea Brain Research Insti- tute (KBRI), Cheomdan-ro 61, Dong-gu, Daegu, Korea 700-300. E-mail: sookhoe72@kbri.re.kr; Jungsu Kim, PhD, Department of Neuroscience, Mayo Clinic College of Medicine, Jacksonville, FL 32224, USA. E-mail: kim.jungsu@mayo.edu. ISSN 1387-2877/16/$35.00 © 2016 – IOS Press and the authors. All rights reserved