Extracellular calcium deprivation in astrocytes: regulation of mRNA expression and apoptosis.
Cell viability and gene expression were studied in primary astroglial cells cultured in a nominally calcium-free medium. Ca2+ deprivation reduced progressively the astrocytes' viability, starting from 12 h; the restoration of a normal Ca2+ concentration (1.8 mM) in the medium after 12-h deprivation reversed the degenerative effect within 24 h. Biochemical and morphological examinations indicated that cell death induced by Ca2+ deprivation was mediated by apoptosis. This was associated with the expression of c-fos, c-jun, and c-myc, which, with different time courses, were induced in astrocytes after Ca2+ deprivation. Furthermore, shifting to a Ca2+-free medium modified the expression of Ich-1S transcript and rapidly increased intracellular cyclic AMP, which has been implicated in the transcriptional activation of immediate-early genes. The absence of Ca2+ in the medium reduced the expression of constitutive proteins such as alpha-actin, clusterin, glial fibrillary acidic protein, amyloid precursor protein, and glucose-6-phosphate dehydrogenase. The expression of these mRNAs was reduced >50% after 8 h of Ca2+ deprivation, when the effect on cell viability was negligible. When Ca2+ deprivation was prolonged for 24 h the expression of mRNA dropped completely, and restoration of the Ca2+ ions in the medium for 48 h did not reverse this effect. In contrast with general assumption, the apoptotic machinery in astrocytes is activated similarly not only by increased Ca2+ influx but also with the extracellular Ca2+ deprivation.
Chiesa
R
R
Biology of Neurodegenerative Disorders Laboratory, Istituto di Ricerche Farmacologiche Mario Negri, Milano, Italy.
Angeretti
N
N
Del Bo
R
R
Lucca
E
E
Munna
E
E
Forloni
G
G
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D001253:Astrocytes / Q000378:metabolism*; D002118:Calcium / Q000172:deficiency*; D053143:Caspase 2; D020169:Caspases; D003470:Culture Media / Q000737:chemistry / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D009457:Neuroglia / Q000378:metabolism; D011506:Proteins / Q000235:genetics; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats
D003470:Culture Media; D011506:Proteins; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D000242:Cyclic AMP; D053143:Caspase 2; D020169:Caspases; D002118:Calcium