Increased glutathione biosynthesis by Nrf2 activation in astrocytes prevents p75^NTR‐dependent motor neuron apoptosis

Abstract

Astrocytes may modulate the survival of motor neurons in amyotrophic lateral sclerosis (ALS). We have previously shown that fibroblast growth factor-1 (FGF-1) activates astrocytes to increase secretion of nerve growth factor (NGF). NGF in turn induces apoptosis in co-cultured motor neurons expressing the p75 neurotrophin receptor (p75 NTR ) by a mechanism involving nitric oxide (NO) and peroxynitrite formation. We show here that FGF-1 increased the expression of inducible nitric oxide synthase and NO production in astrocytes, making adjacent motor neurons vulnerable to NGF-induced apoptosis. Spinal cord astrocytes isolated from transgenic SOD1 G93A rats displayed increased NO production and spontaneously induced apoptosis of co-cultured motor neurons. FGF-1 also activates the redox-sensitive transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) in astrocytes. Because Nrf2 increases glutathione (GSH) biosynthesis, we investigated the role of GSH production by astrocytes on p75 NTR -dependent motor neuron apoptosis. The combined treatment of astrocytes with FGF-1 and t-butylhydroquinone (tBHQ) increased GSH production and secretion, preventing motor neuron apoptosis. Moreover, Nrf2 activation in SOD1 G93A astrocytes abolished their apoptotic activity. The protection exerted by increased Nrf2 activity was overcome by adding the NO donor DETANONOate to the co-cultures or by inhibiting GSH synthesis and release from astrocytes. These results suggest that activation of Nrf2 in astrocytes can reduce NO-dependent toxicity to motor neurons by increasing GSH biosynthesis. Keywords: amyotrophic lateral sclerosis, astrocytes, glutathione, motor neurons, nuclear factor erythroid 2-related factor 2, p75 neurotrophin receptor. Degenerating neurons can trigger the activation of surrounding astrocytes through the secretion of several proinflammatory mediators. In turn, reactive astrocytes may either promote neuronal survival by providing trophic, metabolic and antioxidant support or stimulate apoptosis by diffusible factors that activate death receptors . Recent evidence showed that mobilization of fibroblast growth factor-1 (FGF-1) can follow motor neuron damage and cause astrocyte activation in an amyotrophic lateral sclerosis (ALS) animal model . Treatment of astrocytes with FGF-1 up-regulates the expression of nerve growth factor (NGF) (Yoshida and Gage 1991), which induces apoptosis of co-cultured motor neurons through activation of the p75 neurotrophin receptor (p75 NTR ) . Although p75NTR is not present in mature motor neurons, the receptor can be re-expressed in pathological conditions, including axotomy (Ernfors et al. 1989;Koliatsos et al. 1991;Rende et al. 1995;Wu 1996;Ferri et al. 1998) Abbreviations used: ALS, amyotrophic lateral sclerosis; ARE, antioxidant response element; BSO, buthionine sulfoximine; DTNB, 5,5¢-dithiobis(2-nitrobenzoic acid); FGF-1, fibroblast growth factor-1; GFAP, glial fibrillary acidic protein; GSH, reduced glutathione; GSSG, oxidized glutathione; HO-1, heme oxygena...

IFNγ triggers a LIGHT-dependent selective death of motoneurons contributing to the non-cell-autonomous effects of mutant SOD1

“…It has been demonstrated that IFNg induces NO production and increases levels of GFAP in primary astrocytes. 31 Expression of SOD1 G93A or SOD1 G37R in astrocytes is accompanied by increased levels of ROS, including NO, 4,7 and expression of SOD1 G93A in glioblastoma leads to the production of IFNg. 32 How IFNg and ROS cooperate in the acquisition or the consolidation of the reactive status of astrocytes expressing SOD1 mutations remains to be elucidated.…”

“…4,5,7,8 Among the potential actors of the neurotoxicity of mutant astrocytes, proinflammatory molecules have been proposed. In particular, it has been suggested that prostaglandin D 2 (PGD 2 ) contributes to astrocyte-derived toxicity.…”

“…We used a coculture system of highly purified wild-type rat motoneurons and rat astrocyte monolayers of different genotypes. 4 Firstly, we demonstrated that rat motoneurons are as responsive as mouse motoneurons to sLIGHT, agonistic anti-LT-bR antibodies and IFNg (Figure 5e). We next found that, in contrast to the wild type, SOD1 G93A astrocytes express substantial levels of IFNg, whereas we did not observe any difference in LIGHT levels ( Figure 5f).…”

“…3 Astrocytes have a pivotal role in the pathogenic process by determining the extent of the inflammatory response from microglia, 3 but also by releasing soluble factors selectively toxic for motoneurons. [4][5][6][7][8] The specificity of this toxicity toward motoneurons might be explained by the activation of a motoneuron-specific death pathway; a hypothesis that has been tested in several studies.…”

Sclérose latérale amyotrophique, jonction neuromusculaire et déficit énergétique

“…Parmi les candidats, se trouvent les cellules gliales (astrocytes, microglie, cellules de Schwann) ou les cellules musculaires [16]. Ainsi, le laboratoire de Luis Barbeito a montré que les astrocytes porteurs d'une SOD1m sont capables de provoquer l'apoptose de motoneurones sauvages via un méca-nisme impliquant le stress oxydant et le NGF (nerve growth factor) [17,18]. Ces travaux ont récemment été confirmés par d'autres [19,20] et suggèrent que l'astrocyte pourrait participer à la toxicité envers le motoneurone.…”