Raloxifene, a promising estrogen replacement, limits TDP-25 cell death by enhancing autophagy and suppressing apoptosis

Amyotrophic lateral sclerosis (ALS) is a fatal adult-onset neurodegenerative disease, and at present, therapies for ALS are limited. Estrogen is a potential therapeutic agent for ALS but has undesirable effects that might increase the risk of breast and uterine cancers or stroke. Raloxifene (Ral) has estrogenic properties but does not exhibit these adverse effects. However, the mechanism of Ral in ALS has not been studied. We thus investigated the effects of Ral in an NSC34 model of ALS that stably expresses the 25-kDa C-terminal fragment of TDP-43 (i.e., TDP-25 cells) and found that GPR30 (G protein-coupled receptor 30) and ER (estrogen receptor) α/ERβ were expressed in TDP-25 cells, which show significantly different morphology compared with controls. Both E2 (17β-estradiol) and Ral increased the expression of ERα and GPR30 and enhanced TDP-25 cell viability, and these effects were completely abolished by treatment with an ERα/β antagonist (ICI 182,780) or GPR30 antagonist (G15). The P62, caspase-9 and Bax levels were significantly decreased in TDP-25 cells treated with Ral or E2, and the LC3-II levels were elevated in E2-treated cells but reduced in Ral-treated cells. All these changes were abolished by treatment with ICI 182,780 or G15. These data suggest that Ral, similar to E2, enhances autophagy and suppresses apoptosis to limit motor neuron death by binding to ERα/β or GPR30 in TDP-25 cells. These results demonstrate the protective effects of Ral in an ALS cell model and suggest that Ral is a promising replacement for estrogen and a promising therapeutic strategy for ALS.