Projekt finansowany przez Narodowe Centrum Nauki w ramach konkursu „Opus – 21”.

Czy astrocyty kontrolują połączenia synaptyczne w sieciach nerwowych istotnych dla chorób psychiatrycznych?

Nr projektu: UMO-2021/41/B/NZ3/04099
Wartość projektu: 2.598.600,00 PLN
Wartość dofinansowania: 2.598.600,00 PLN
Okres realizacji projektu: 29/4/2022 – 28/04/202

Kierownik projektu: dr Michał Ślęzak

Major depressive disorder (MDD) is ranked by the WHO among largest contributors to global disability. Current therapies of depression MDD are suboptimal, with only one third of patients responding to first line treatment, and a majority failing to achieve full remission. These deficiencies highlight the urgent need of designing improved therapeutic strategies, driven by understanding the biological basics of the disease. Previous studies identified lowered expression of genes encoding synaptic proteins and decreased number of synapses as one of the neurobiological hallmarks of the brain of MDD patients. These changes were prominent particularly in the prefrontal cortex (PFC), a brain center integrating stress response.

Similar changes were observed in rodent models of chronic stress and were shown to engage signaling of main stress hormone, corticosterone (CORT), through glucocorticoid receptors (GR). In rodent models, beneficial action of antidepressants, including ketamine, was reported to correlate with reversal of synaptic deficits in the PFC. These observations led to the notion that restoration of functional and structural synaptic plasticity represents crucial mechanisms for successful outcome of antidepressant treatment. However, mechanisms underlying neural circuit remodeling in stress and depression remain unclear. We recently found that the expression of astrocyte-specific genes known to control developmental synapse formation and elimination was downregulated in the PFC of MDD patients and in rodents exposed to chronic stress. In mice, these changes were largely prevented by astrocyte-specific elimination of GR.

Our data suggest therefore a hitherto unknown mechanism of synapse loss in MDD: stress-induced downregulation of astrocyte-specific genes controlling synaptic connectivity. In this project, we will directly test this hypothesis. To this end, we will perform a systematic analysis of the impact of knock down of astrocyte-specific genes mediating synapse formation or elimination on PFC-controlled behavior, namely social interactions. For this purpose, we will deliver viral vectors encoding respective shRNA and evaluate the impact of this intervention on approx. 60 voluntary behaviors in groups of mice, using Social Box. In parallel, we will genetically perturb astrocytes in mice using our recently established method for cell-type-specific, inducible gene knockdown employing in utero electroporation.

This method offers several advantages, including optical dissection of regions of Thy1-GFP dendrites which contact either sparsely labeled, genetically modified astrocytes or their wild-type neighbors, for direct comparison in the same mouse. Next, we will employ longitudinal 2-photon-imaging to examine the impact of astrocyte-specific knockdown of investigated genes on stress- or ketamine-induced dendritic spine turnover. For genes where combined behavioral and structural deficits are found, we will perform detailed ultrastructural analysis of previously imaged astrocyte-synapse interactions, using correlative light and electron microscopy. In summary, the completion of this project shall result in unprecedented insight to the contribution of astrocytes to remodeling of adult neural circuits. At the same time, our data will bring significant progress in understanding neurobiological dysfunctions in the course of psychiatric disorders and may help designing novel therapeutic strategies.