17β‐Oestradiol Anti‐Inflammatory Effects in Primary Astrocytes Require Oestrogen Receptor β‐Mediated Neuroglobin Up‐Regulation

Neuroglobin (Ngb), so named after its initial discovery in brain neurones, has received great attention as a result of its neuroprotective effects both in vitro and in vivo . Recently, we demonstrated that, in neurones, Ngb is a 17β‐oestradiol (E 2 ) inducible protein that is pivotal for hormone‐induced anti‐apoptotic effects against H 2 O 2 toxicity. The involvement of Ngb in other brain cell populations, as well as in other neuroprotective effects of E 2 , is completely unknown at present. We demonstrate Ngb immunoreactivity in reactive astrocytes located in the proximity of a penetrating cortical injury in vivo and the involvement of Ngb in the E 2 ‐mediated anti‐inflammatory effect in primary cortical astrocytes. Upon binding to oestrogen receptor ( ER )β, E 2 enhances Ngb levels in a dose‐dependent manner. Although with a lesser degree than E 2 , the pro‐inflammatory stimulation with lipopolysaccharide ( LPS ) also induces the increase of Ngb protein levels via nuclear factor‐( NF )κB signal(s). Moreover, a negative cross‐talk between ER subtypes and NF κB signal(s) has been demonstrated. In particular, ER α‐activated signals prevent the NF κB‐mediated Ngb increase, whereas LPS impairs the ER β‐induced up‐regulation of Ngb. Therefore, the co‐expression of both ER α and ER β is pivotal for mediating E 2 ‐induced Ngb expression in the presence of NF κB‐activated signals. Interestingly, Ngb silencing prevents the effect of E 2 on the expression of inflammatory markers (i.e. interleukin 6 and interferon γ‐inducible protein 10). Ngb can be regarded as a key mediator of the different protective effects of E 2 in the brain, including protection against oxidative stress and the control of inflammation, both of which are at the root of several neurodegenerative diseases.