Changes In The Activity Of Autophagy And Apoptosis In Aged Type 1 Astrocytes

Astrocytes are glial cells,which are the largest in numbers and widely distributied in central nervous system(CNS).According to the theory of astrocytes lineages,astrocytes can be divided into two types:type 1 astrocytes(T1A)and type 2 astrocytes(T2A).T1A play most functions of astrocytes in vivo.In the past few years,an unprecedented attention focused on astrocytes as a result of their unusual physiological function that have been found.It is known that,rather than being a mere supporter of neurons,astrocytes are actively involved in their modulation.Understanding the alteration in biological characteristics of aged T1A would be helpful for the research of neurodegenerative disease, in which astrocytes may play a critical role,and these findings Will lead to a new avenue to the clinical treatment of neurodegenerative disorders.Objective To investigate the alteration in biological characteristics of aged T1A in an experimental model of in vitro aging,and evaluate the possible roles in the process of Alzheimer's disease(AD),a age-related neurodegenerative disease.Methods Primary cultures of mixed glial cells were established from cerebral cortical tissue of new born Sprague-Dawley(SD)rats.Based on the differential properties of cellular adhesions,T1A were achieved by mechanical shaking and differential adhesion method;Considered T1A cultured for 21 days in vitro(21 DIV)as the control group,and 90 DIV T1A as the experimental group.With the immunocytochemical labeling,the expression ofβ-amyloid protein1-40(amyloid-β-protein 1-40,Aβ1-40)were observed in both the control and the experimental group;Microtubule-associated protein 1A/1B-light chain 3(LC3),which is a protein associated with autophagy/lysosomal pathway,and apoptosis associated protein caspase-3 and the anti-apoptotic protein Bcl-2 were evaluated by Western blotting in both groups.Results Purified T1A were obtained by mechanical shaking and differential adhesion method,and the experimental model of aged T1A was built successfully.In 90 DIV T1A cultures,there was an increase in proteins that stained positively for Aβ1-40, however,Aβ1-40 was stained negatively in 21DIV T1A cultures.Western blotting indicated that the generation of LC3Ⅱwas enhanced in the experimental group cells. Simultaneously,there was not any expression in the control group cells,which suggested that autophagy/lysosomal pathway was activated in aged T1A.In contrast to the situation in short-term T1A cultures,activated caspase-3 was increased and Bcl-2 were decreased in long-term T1A cultures,suggesting that apoptosis was activated in aged T1A.Conclusions Aged T1A express Aβ1-40,which may be the important source of Aβin senile plaque in Alzheimer's disease(AD).Autophagy/lysosomal pathway was obviously activated in aged T1A,suggests that it is probably associated with the expression and degradation of Aβ.However,further researches are needed to make its certain roles clear during the process of AD.In addition,as alteration of neurons in AD,apoptosis occurs in aged T1A.According to these phenomenons,it could be supposed that there are not only reactive gliosis but also apoptosis in astrocytes in AD,and Aβfrom aged T1A may be one of the initiating factors of apoptosis.Altogether,it is likely that these findings will open a new avenue to explore the roles of astrocytes in age-related neurodegenerative disease,and provide some valuable experimental evidences for the clinical therapy.