In the nervous system, Notch pathway has a prominent role in the control of neuronal morphology and in the determination of the astrocyte fate. However, the role of Notch in morphological astrocyte plasticity is unknown. Here, we have explored the role of Notch activity on the morphological reactivity of primary astrocytes in response to LPS, an inflammatory stimulus. We found that LPS induces reactive astrocyte morphology by the inhibition of Notch signaling via NFκB activation and Jagged upregulation. In contrast, IGF-1, an anti-inflammatory molecule, inhibits LPS-induced reactive astrocyte morphological phenotype by enhancing Notch signaling through the inhibition of NFκB and the activation of MAPK. Therefore, Notch signaling pathway emerges as a mediator of the regulation of astrocyte morphology by inflammatory and anti-inflammatory stimuli.

Obesity is associated with an increase in the brain levels of saturated free fatty acids, such as palmitic acid (PA). Previous studies have shown that PA exerts proinflammatory actions and reduces cell viability in astrocyte cultures. In this study, we have assessed whether an alteration in autophagy is involved in the effects of PA on astrocytes. Primary astrocytes were obtained from the cerebral cortex of male and female CD1 mouse pups and were incubated for 4.5 or 24 h with 250-500 μM PA. PA increased the levels of LC3-II, an autophagosome marker, and reduced LC3-II flux in astrocytes, suggesting a blockade of autophagy. This effect was observed both after 4.5 and 24 h of treatment with PA. PA had additional effects after treatment for 24 h, increasing the expression of proinflammatory cytokines, decreasing cell viability, and increasing the levels of an endoplasmic reticulum stress marker. In addition, PA decreased the expression of estrogen receptors, but only in female astrocytes. However, the treatment with estradiol, estrogen receptor agonists, or inhibitor of estradiol synthesis did not counteract the action of PA on cell viability. Rapamycin, an autophagy inducer, was unable to prevent the effect of PA on cell viability. In addition, hydroxychloroquine, an autophagy blocker, did not cause per se astrocyte death. These findings suggest that the effect of PA on autophagy is not sufficient to induce astrocyte loss, which is only observed when prolonged PA treatment causes other alterations in astrocytes, such as increased inflammation and endoplasmic reticulum stress.

Testosterone produced by the foetal testis is converted by male neurons to oestradiol, which masculinizes neuronal morphology. Female neurons are known to synthesize oestradiol in absence of exogenous testosterone. However, the role of neuronal oestradiol on the differentiation of foetal female neurons is unknown. Here we show that, due to endogenous neuronal oestradiol synthesis, female hippocampal neurons have higher expression of the neuritogenic protein Neurogenin 3 and enhanced neuritogenesis than males. Exogenous application of testosterone or its metabolite dihydrotestosterone increases Neurogenin 3 expression and promotes neuritogenesis in males, but reduces these parameters in females. Together our data indicate that gonadal-independent oestradiol synthesis by female neurons participates in the generation of sex differences in hippocampal neuronal development.