Astrocytes aged in vitro show a decreased neuroprotective capacity

Abstract

Alterations in astrocyte function that may affect neuronal viability occur with brain aging. In this study, we evaluate the neuroprotective capacity of astrocytes in an experimental model of in vitro aging. Changes in oxidative stress, glutamate uptake and protein expression were evaluated in rat cortical astrocytes cultured for 10 and 90 days in vitro (DIV). Levels of glial fibrillary acidic protein and S100b increased at 90 days when cells were positive for the senescence b-galactosidase marker. In long-term astrocyte cultures, the generation of reactive oxygen species was enhanced and mitochondrial activity decreased. Simultaneously, there was an increase in proteins that stained positively for nitrotyrosine. The expression of Cu/Zn-superoxide dismutase (SOD-1) and haeme oxygenase-1 (HO-1) proteins and inducible nitric oxide synthase (iNOS) increased in aged astrocytes. Glutamate uptake in 90-DIV astrocytes was higher than in 10 DIV ones, and was more vulnerable to inhibition by H 2 O 2 exposure. Enhanced glutamate uptake was probably because of up-regulation of the glutamate/aspartate transporter protein. Aged astrocytes had a reduced ability to maintain neuronal survival. These findings indicate that astrocytes may partially loose their neuroprotective ability during aging. The results also suggest that aged astrocytes may contribute to exacerbating neuronal injury in age-related neurodegenerative processes.

Dysfunction of astrocytes in senescence‐accelerated mice SAMP8 reduces their neuroprotective capacity

“…Trotti et al (1997) reported that glutamate transporters are vulnerable to oxidants due to the fact that they possess a redox regulatory mechanism. We were unable to reverse the inhibition of glutamate uptake in SAMP8 astrocytes using trolox and curcumin antioxidant treatments, even though we did reverse H 2 O 2 -induced glutamate uptake inhibition in astrocyte aged in culture (Pertusa et al, 2007). It is possible that a different antioxidant pattern treatment is required to reverse long-time oxidative effects.…”

“…Recent studies have shown that PC12 cells co-cultured with old astrocytes were more sensitive to the oxidant tert -buthyl H 2 O 2 than those co-cultured with young astrocytes (Lin et al, 2006). In addition, we have shown that astrocytes aged in vitro have a reduced ability to maintain neuronal survival (Pertusa et al, 2007).…”

“…Furthermore, these results support previous hypotheses contending that glial oxidative stress is involved in the aging process. In this context, several authors have demonstrated increased superoxide production, lipoperoxidation, protein oxidation and iron staining in astrocytes aged in culture (Papadopoulos et al, 1998;Gottfried et al, 2002;Klamt et al, 2002;Pertusa et al, 2007). It has been proposed that ROS generated by mitochondria accumulate during aging and are not only responsible for the damage present in mitochondrial components, but also cause degradative processes (Cadenas & Davis, 2000;Lenaz et al, 2006).…”

“…Furthermore, changes in glial glutamate uptake have been observed during brain aging (for a review, see Segovia et al ., 2001). In aged astrocytes in culture, glutamate uptake was more vulnerable to inhibition by H 2 O 2 exposition Pertusa et al ., 2007). Recent studies have shown that PC12 cells co-cultured with old astrocytes were more sensitive to the oxidant tert -buthyl H 2 O 2 than those co-cultured with young astrocytes (Lin et al, 2006).…”

“…Heightened expression of glial fibrillary acidic protein (GFAP) and S100 β protein have been detected during aging in regions of the mouse and rat brain (O'Callaghan & Miller, 1991;Kohama et al ., 1995;Amenta et al ., 1998), as well as in mouse and rat cortical astrocytes aged in culture (Papadopoulos et al ., 1998;Gottfried et al ., 2002;Tramontina et al ., 2002;Pertusa et al ., 2007). Superoxide production, lipoperoxidation, protein oxidation, and iron staining remained elevated in aged astrocyte cultures, even though antioxidant defences had been maintained or increased (Papadopoulos et al ., 1998;Gottfried et al ., 2002;Klamt et al ., 2002;Pertusa et al ., 2007). Mitochondrial membrane potential in old astrocytes proved more depolarized than in young astrocytes (Lin et al ., 2006).…”