Lipotoxic Effects of Palmitic Acid on Astrocytes Are Associated with Autophagy Impairment

Abstract

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.

Autophagy in Astrocytes: Importance for Metabolism

“…To confirm the blockade of autophagy, autophagic flux was measured using hydroxychloroquine, a lysosomal inhibitor which avoids autophagosome fusion with lysosomes. LC3-II accumulation caused by hydroxychloroquine was reduced after PA treatment, which confirms the blockade of autophagy in astrocytes [113]. A reduction in autophagic activity has been also described in hypothalamic neurons exposed to PA [114].…”

“…These results suggest that autophagy is induced by PA in astrocytes, an opposite result compared to the blockade of autophagy found by Ortiz-Rodriguez et al [113]. The differences between these two studies could be caused by the use of astrocytes from different brain regions, as the response of cortical [113] and hippocampal [102] astrocytes was analysed. For instance, differences in the response to PA between hypothalamic and cortical astrocytes have been reported [115], which could explain the differences found in astrocyte autophagy.…”

“…Although autophagy flux and levels of autophagic substrates were not quantified, the inhibition of autophagosome formation by 3-MA avoided the changes induced by PA [102]. These results suggest that autophagy is induced by PA in astrocytes, an opposite result compared to the blockade of autophagy found by Ortiz-Rodriguez et al [113]. The differences between these two studies could be caused by the use of astrocytes from different brain regions, as the response of cortical [113] and hippocampal [102] astrocytes was analysed.…”

“…Using this in vitro model, the impact of saturated fatty acids on astrocyte autophagy has been analysed. PA exposure can modulate autophagy in astrocytes, but autophagy blockade and induction has been described [102,113]. PA simultaneously increases LC3-II and p62 levels in cultured astrocytes [113].…”

“…PA exposure can modulate autophagy in astrocytes, but autophagy blockade and induction has been described [102,113]. PA simultaneously increases LC3-II and p62 levels in cultured astrocytes [113]. The existence of high levels of LC3-II and accumulation of p62 suggested a reduction in autophagic activity.…”