[PUBLICATION] Brain immune cells characterization in UCMS exposed P2X7 Knock-Out mouse

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 Brain immune cells characterization in UCMS exposed P2X7 Knock-Out mouse
Brain immune cells characterization in UCMS exposed P2X7 Knock-Out mouse

le 12 mars 2021

Published in Brain Behav Immun

Collaborative research project by Prof. Vincent Camus


Background: Several lines of evidence suggest that neuroinflammation might be a key neurobiological mechanism of depression. In particular, the P2X7 receptor (P2X7R), an ATP-gated ion channel involved in activation of the pro-inflammatory interleukin IL-1β, has been shown to be a potential new pharmacological target in depression. The aim of this study was to explore the impact of unpredictable chronic mild stress (UCMS) on behavioural changes, hippocampal neurogenesis, and cellular characterisation of brain immune cells, in P2X7R KO mice.

Methods: P2X7R knock-out (KO) and wild-type (WT) mice were subjected to a 6-week UCMS protocol and received a conventional oral antidepressant (15 mg/kg fluoxetine) or water per os. The mice then underwent behavioural tests consisting of the tail suspension test (TST), the elevated plus maze (EPM) test, the open field test, the splash test and the nest building test (week 7). Doublecortin immunostaining (DCX) of brain slices was used to assess neurogenesis in the dentate gyrus. Iba1 and TMEM119 immunostaining was used to characterise brain immune cells, Iba1 as a macrophage marker (including microglial cells) and TMEM119 as a potential specific resident microglial cells marker.

Results: After a 6-week UCMS exposure, P2X7R KO mice exhibited less deterioration of their coat state, spent a significantly smaller amount of time immobile in the TST and spent a larger amount of time in the open arms of the EPM. As expected, adult ventral hippocampal neurogenesis was significantly decreased by UCMS in WT mice, while P2X7R KO mice maintained ventral hippocampal neurogenesis at similar levels in both control and UCMS conditions. In stress-related brain regions, P2X7R KO mice also exhibited less recruitment of Iba1+/TMEM119+ and Iba1+/TMEM119- cells in the brain. The ratio between these two staining patterns revealed that brain immune cells were mostly composed of Iba1+/TMEM119+ cells (87 to 99%), and this ratio was affected neither by P2X7R genetic depletion nor by antidepressant treatment.

Discussion: Behavioural patterns, neurogenesis levels and density of brain immune cells in P2X7R KO mice after exposure to UCMS significantly differed from control conditions. Brain immune cells were mostly increased in brain regions known to be sensitive to UCMS exposure in WT but not in P2X7R KO mice. Considering Iba1+/TMEM119 - staining might characterize peripheral immune cells, the ratio of Iba1+/TMEM119+ /IBA1+/TMEM119- cells, suggests that the rate of peripheral immune cells recruitment may not be modified neither by P2X7R gene expression nor by antidepressant treatment.


P2X7 receptor; TMEM119; depression; neurogenesis; neuroinflammation; unpredictable chronic mild stress (UCMS).

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