BENZODIAZEPINE DIAZEPAM INDUCES COGNITIVE IMPAIRMENT VIA TRANSLOCATOR PROTEIN (18 KDA): IMPLICATIONS ON DEMENTIA

Abstract Background Benzodiazepines are widely prescribed drugs for treating insomnia and anxiety and have been long suspected to cause cognitive impairment upon chronic use. However, the mechanism by which benzodiazepines might compromise cognitive functions remains unknown. In the central nervous system, benzodiazepines exert sedative, anxiolytic, and anticonvulsant properties by allosterically increasing the potency of the major inhibitory neurotransmitter γ-aminobutyric acid (GABA) by binding to synaptic γ- aminobutyric acid type A receptors (GABAARs). However, a number of conventional benzodiazepines, most notably diazepam, have also a significant binding affinity for the outer mitochondrial membrane protein – 18 kDa translocator protein (TSPO), whose functions have been equivocal. Here, to clarify the effects of benzodiazepines on cognition, we focus on dendritic spines, the highly dynamic small membranous protrusions from neuronal dendrites that are broadly regarded as the structural underpinning of cognitive processes. Aims & Objectives We aim to characterize how benzodiazepines affect dendritic spines and increase the risk of developing cognitive decline and dementia. Methods Using in vivo 2-photon microscopy, we monitored fluorescently labelled apical dendritic spines of cortical neurons in mice treated with diazepam and vehicle. We also fed diazepam and vehicle to similar-aged homozygous Gabra RRRR mice, which is inert to benzodiazepines, but not GABA. On the other hand, we validated our findings in diazepam- and vehicle-treated mice by supressing TSPO both pharmacologically and genetically. Parallel to in vivo studies, we utilised multichannel immunostaining and high-precision 3D reconstruction at super-resolutional level, to investigate how the microenvironment, such as microglia, surrounding dendritic spines, contributed to their alterations upon diazepam treatment. Results We observed that diazepam activates TSPO in microglia, leading to elevated microglial engulfment of synaptic materials and impaired dynamics of dendritic spine plasticity. Eventually, diazepam administration induces cognitive decline in WT mice. Interestingly, microglial alterations, as well as cognitive impairments were also observed in Gabra RRRR mice upon diazepam administration, indicating these are pathological processes independent of GABAARs. Discussion & Conclusion Based on these findings, it appears that abnormally activated TSPO accelerates the engulfment of dendritic spines by microglia, thereby causing cognitive decline and increasing the risk of dementia in response to benzodiazepine use. Given that TSPO activation is widely observed in a broad range of diseases with cognitive impairment, such as psychiatric disorders, like depression, and neurodegenerative diseases, such as Alzheimer’ s disease. The TSPO-mediated cognitive decline observed in our study may also be a crucial part of the pathophysiology of these diseases. However, extra evidence is necessary to position TSPO as a key player along the pathophysiology. Collectively, our study unveiled a previously unknown effect of benzodiazepines, suggesting that therapeutic strategies must take into account how sleep disorders and anxiety are treated in people at risk of dementia. In addition, our findings provide new insights into disease-related cognitive decline, pointing to TSPO as a potential therapeutic target for dementia. References 1.Shi Y, Cui M, Ochs K, Brendel M, Strü bing FL, Briel N, Eckenweber F, Zou C, Banati RB, Liu G-J, et al. Long-term diazepam treatment enhances microglial spine engulfment and impairs cognitive performance via the mitochondrial 18 kDa translocator protein (TSPO). Nature Neuroscience 2022, 25(3):317-329. Available from: SharedIt [https://rdcu.be/cHVS7].