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Reduced spine densities and age-dependent accumulation of amyloid β and tau pathology are shared features of Down syndrome (DS) and Alzheimer's disease (AD). Both spine morphology and the synaptic plasticity that supports learning depend upon the actin cytoskeleton, suggesting that disturbances in actin regulatory signaling might underlie spine defects in both disorders. The present study evaluated the synaptic levels of two proteins that promote filamentous actin stabilization, the Rho GTPase effector p21-activated kinase 3 (PAK3) and Arp2, in DS vs. AD. Fluorescent deconvolution tomography was used to determine postsynaptic PAK3 and Arp2 levels for large numbers of excitatory synapses in the parietal cortex of individuals with DS plus AD pathology (DS + AD) or AD alone relative to age-matched controls. Though numbers of excitatory synapses were not different between groups, synaptic PAK3 levels were greatly reduced in DS + AD and AD individuals vs. controls. Synaptic Arp2 levels also were reduced in both disorders, but to a greater degree in AD. Western blotting detected reduced Arp2 levels in the AD group, but there was no correlation with phosphorylated tau levels suggesting that the Arp2 loss does not contribute to mechanisms that drive tau pathology progression. Overall, the results demonstrate marked synaptic disturbances in two actin regulatory proteins in adult DS and AD brains, with greater effects in individuals with AD alone. As both PAK and the Arp2/3 complex play roles in the actin stabilization that supports synaptic plasticity, reductions in these proteins at synapses may be early events in spine dysfunction that contribute to cognitive impairment in these disorders.

mRNA translation is regulated by diverse mechanisms that converge at the initiation and elongation steps to determine the rate, profile, and localization of proteins synthesized. A consistently relevant feature of these mechanisms is the spatial re-distribution of translation machinery, a process of particular importance in neural cells. This process has, however, been largely overlooked with respect to its potential role in regulating the local concentration of cytoplasmic tRNAs, even as a multitude of data suggest that spatial regulation of the tRNA pool may help explain the remarkably high rates of peptide elongation. Here, we report that Cy3/Cy5-labeled bulk tRNAs transfected into neural cells distribute into granule-like structures - "tRNA granules" - that exhibit dynamic mixing of tRNAs between granules and rapid, bi-directional vectorial movement within neurites. Imaging of endogenous tRNAgly and tRNAlys by fluorescent in situ hybridization revealed a similar granular distribution of tRNAs in somata and neurites; this distribution was highly overlapping with granules imaged by introduction of exogenous Cy5-tRNAthr and Cy3-tRNAval. A subset of tRNA granules located in the cell body, neurite branch points and growth cones displayed fluorescence resonance energy transfer (FRET) between Cy3 and Cy5-labeled tRNAs indicative of translation, and co-localization with elongation machinery. A population of smaller, rapidly trafficked granules in neurites lacked FRET and showed poor colocalization with translation initiation and elongation factors, suggesting that they are a translationally inactive tRNA transport particle. Our data suggest that tRNAs are packaged into granules that are rapidly transported to loci where translation is needed, where they may greatly increase the local concentration of tRNAs in support of efficient elongation. The potential implications of this newly described structure for channeling of elongation, local translation, and diseases associated with altered tRNA levels or function are discussed.

Background: Nasopharyngeal cancer (NPC) is associated with a poor survival rate. The ability of cancer cells to evade apoptosis and exhibit limitless replication potential allows for the progression of cancer. The aim of this study was to investigate in vitro the effect of the isoflavone phenoxodiol on human NPC cell line and T cells, which has previously been shown to inhibit cell proliferation and promote apoptosis in a range of cancer cell lines and in anti-CD3/anti-CD28-activated murine splenocytes. Methods: Four NPC cancer cell lines-C666, C17, and paired NPC43 EBV-positive and its respective EBV-negative cell lines were cultured in vitro, and then treated with phenoxodiol for 72h or 5 days. The migration and proliferation was investigated by transwell and XTT, respectively. Conditioned medium of treated NPC cell lines were collected and incubated with human PBMC for 5 days. CD4 and CD8 surface staining were analyzed by flow cytometry. Result: We demonstrated that phenoxodiol inhibited NPC migration and cell proliferation (IC50 4µM). Among all the NPC cell lines, the proliferation effect on EBV-negative cell line (NPC43-ve) is least responsive to phenoxodiol. A dose-dependent of apoptosis in NPC cell lines by phenoxodiol [early apoptotic cells (Annexin V+/PI- at 1µM); late apoptotic cells (Annexin V+/PI+ at 2µM), and necrotic cells (Annexin V-/PI+, at 4µM) were distinguished. Interestingly, phenoxodiol reduced frequency of CD4 T cells while promoting the number of CD8 T cells. Conclusions: Phenoxodiol demonstrates an ability in NPC cancer cells to induce its apoptosis while inhibit its migration and proliferation. Moreover, the ability of phenoxodiol to modulate T cells population indicates that phenoxodiol would be effective as a potential future treatment for NPC. Note: This abstract was not presented at the meeting. Citation Format: Ngar Woon Kam, See Wing Chan, George Sai-Wah Tsao, Xin-Yuan Guan, Dora Lai Wan Kwong. Nasopharyngeal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2957.