Tubulin tyrosination regulates synaptic function and is disrupted in Alzheimer's disease

: Microtubules play fundamental roles in the maintenance of neuronal processes and in synaptic function and plasticity. While dynamic microtubules are mainly composed of tyrosinated tubulin, long-lived microtubules contain detyrosinated tubulin, suggesting that the tubulin tyrosination/detyrosination cycle is a key player in the maintenance of microtubule dynamics and neuronal homeostasis, conditions which go awry in neurodegenerative diseases. In the tyrosination/detyrosination cycle, the C-terminal tyrosine of α-tubulin is removed by tubulin carboxypeptidases and re-added by tubulin tyrosine ligase. Here we show that tubulin tyrosine ligase hemizygous mice exhibit decreased tyrosinated microtubules, reduced dendritic spine density, and both synaptic plasticity and memory deficits. We further report decreased tubulin tyrosine ligase expression in sporadic and familial Alzheimer's disease, and reduced microtubule dynamics in human neurons harboring the familial APP-V717I mutation. Finally, we show that synapses visited by dynamic microtubules are more resistant to oligomeric amyloid β peptide toxicity and that expression of tubulin tyrosine ligase, by restoring microtubule entry into spines, suppresses the loss of synapses induced by amyloid β peptide. Together, our results demonstrate that a balanced tyrosination/detyrosination tubulin cycle is necessary for the maintenance of synaptic plasticity, is protective against amyloid β peptide-induced synaptic damage, and that this balance is lost in Alzheimer's disease, providing evidence that defective tubulin retyrosination may contribute to circuit dysfunction during neurodegeneration in Alzheimer's disease

Enhancement of Vaccinia Virus Based Oncolysis with Histone Deacetylase Inhibitors

Histone deacetylase inhibitors (HDI) dampen cellular innate immune response by decreasing interferon production and have been shown to increase the growth of vesicular stomatitis virus and HSV. As attenuated tumour-selective oncolytic vaccinia viruses (VV) are already undergoing clinical evaluation, the goal of this study is to determine whether HDI can also enhance the potency of these poxviruses in infection-resistant cancer cell lines. Multiple HDIs were tested and Trichostatin A (TSA) was found to potently enhance the spread and replication of a tumour selective vaccinia virus in several infection-resistant cancer cell lines. TSA significantly decreased the number of lung metastases in a syngeneic B16F10LacZ lung metastasis model yet did not increase the replication of vaccinia in normal tissues. The combination of TSA and VV increased survival of mice harbouring human HCT116 colon tumour xenografts as compared to mice treated with either agent alone. We conclude that TSA can selectively and effectively enhance the replication and spread of oncolytic vaccinia virus in cancer cells

Directed Evolution Generates a Novel Oncolytic Virus for the Treatment of Colon Cancer

Background Viral-mediated oncolysis is a novel cancer therapeutic approach with the potential to be more effective and less toxic than current therapies due to the agents selective growth and amplification in tumor cells. To date, these agents have been highly safe in patients but have generally fallen short of their expected therapeutic value as monotherapies. Consequently, new approaches to generating highly potent oncolytic viruses are needed. To address this need, we developed a new method that we term “Directed Evolution” for creating highly potent oncolytic viruses. Methodology/Principal Findings Taking the “Directed Evolution” approach, viral diversity was increased by pooling an array of serotypes, then passaging the pools under conditions that invite recombination between serotypes. These highly diverse viral pools were then placed under stringent directed selection to generate and identify highly potent agents. ColoAd1, a complex Ad3/Ad11p chimeric virus, was the initial oncolytic virus derived by this novel methodology. ColoAd1, the first described non-Ad5-based oncolytic Ad, is 2–3 logs more potent and selective than the parent serotypes or the most clinically advanced oncolytic Ad, ONYX-015, in vitro. ColoAd1's efficacy was further tested in vivo in a colon cancer liver metastasis xenograft model following intravenous injection and its ex vivo selectivity was demonstrated on surgically-derived human colorectal tumor tissues. Lastly, we demonstrated the ability to arm ColoAd1 with an exogenous gene establishing the potential to impact the treatment of cancer on multiple levels from a single agent. Conclusions/Significance Using the “Directed Evolution” methodology, we have generated ColoAd1, a novel chimeric oncolytic virus. In vitro, this virus demonstrated a >2 log increase in both potency and selectivity when compared to ONYX-015 on colon cancer cells. These results were further supported by in vivo and ex vivo studies. Furthermore, these results have validated this methodology as a new general approach for deriving clinically-relevant, highly potent anti-cancer virotherapies

Synaptic pruning in the female hippocampus is triggered at puberty by extrasynaptic GABA A receptors on dendritic spines

Abstract Adolescent synaptic pruning is thought to enable optimal cognition because it is disrupted in certain neuropathologies, yet the initiator of this process is unknown. One factor not yet considered is the a4bd GABA A receptor (GABAR), an extrasynaptic inhibitory receptor which first emerges on dendritic spines at puberty in female mice. Here we show that a4bd GABARs trigger adolescent pruning. Spine density of CA1 hippocampal pyramidal cells decreased by half post-pubertally in female wild-type but not a4 KO mice. This effect was associated with decreased expression of kalirin-7 (Kal7), a spine protein which controls actin cytoskeleton remodeling. Kal7 decreased at puberty as a result of reduced NMDAR activation due to a4bd-mediated inhibition. In the absence of this inhibition, Kal7 expression was unchanged at puberty. In the unpruned condition, spatial re-learning was impaired. These data suggest that pubertal pruning requires a4bd GABARs. In their absence, pruning is prevented and cognition is not optimal

Crosstalk between acetylation and the tyrosination/detyrosination cycle of α-tubulin in Alzheimer’s disease

International audienceMicrotubules (MTs) support a variety of neuronal functions, such as maintenance of cell structure, transport, and synaptic plasticity. Neuronal MTs are highly heterogeneous due to several tubulin isotypes and the presence of multiple post-translational modifications, such as detyrosination and acetylation. The tubulin tyrosination/detyrosination cycle is a key player in the maintenance of MT dynamics, as tyrosinated tubulin is associated with more dynamic MTs, while detyrosinated tubulin is linked to longer lived, more stable MTs. Dysfunction of tubulin re-tyrosination was recently correlated to Alzheimer’s disease progression. The implication of tubulin acetylation in Alzheimer’s disease has, however, remained controversial. Here, we demonstrate that tubulin acetylation accumulates in post-mortem brain tissues from Alzheimer’s disease patients and human neurons harboring the Alzheimer’s familial APP-V717I mutation. We further show that tubulin re-tyrosination, which is defective in Alzheimer’s disease, can control acetylated tubulin in primary neurons irrespective of the levels of the enzymes regulating tubulin acetylation, suggesting that reduced MT dynamics associated with impaired tubulin re-tyrosination might contribute to the accumulation of tubulin acetylation that we detected in Alzheimer’s disease

Impaired α-tubulin re-tyrosination leads to synaptic dysfunction and is a feature of Alzheimer’s disease

SUMMARY In neurons, dynamic microtubules play regulatory roles in neurotransmission and synaptic plasticity. While stable microtubules contain detyrosinated tubulin, dynamic microtubules are composed of tyrosinated tubulin, suggesting that the tubulin tyrosination/detyrosination (Tyr/deTyr) cycle modulates microtubule dynamics and synaptic function. In the Tyr/deTyr cycle, the C-terminal tyrosine of α-tubulin is re-added by tubulin-tyrosine-ligase (TTL). Here we show that TTL +/− mice exhibit decreased tyrosinated microtubules, synaptic plasticity and memory deficits, and that reduced TTL expression is a feature of sporadic and familial Alzheimer’s disease (AD), with human APPV717I neurons having less dynamic microtubules. We find that spines visited by dynamic microtubules are more resistant to Amyloidβ 1-42 and that TTL, by promoting microtubule entry into spines, prevents Aβ 1-42 -induced spine pruning. Our results demonstrate that the Tyr/deTyr cycle regulates synaptic plasticity, is protective against spine injury, and that tubulin re-tyrosination is lost in AD, providing evidence that a defective Tyr/deTyr cycle may contribute to neurodegeneration