Adaptive modifications in the calpain/calpastatin system in brain cells after persistent alteration in Ca2+ homeostasis.
Persistent dysregulation in Ca(2+) homeostasis is a pervasive pathogenic mechanism in most neurodegenerative diseases, and accordingly, calpain activation has been implicated in neuronal cells dysfunction and death. In this study we examined the intracellular functional state of the calpain-calpastatin system in -G93A(+) SOD1 transgenic mice to establish if and how uncontrolled activation of calpain can be prevented in vivo during the course of prolonged [Ca(2+)](i) elevation. The presented data indicate that 1) calpain activation is more extensive in motor cortex, in lumbar, and sacral spinal cord segments compared with the lower or almost undetectable activation of the protease in other brain areas, 2) direct measurements of the variations of Ca(2+) levels established that the degree of the protease activation is correlated to the extent of elevation of [Ca(2+)](i), 3) intracellular activation of calpain is always associated with diffusion of calpastatin from perinuclear aggregated forms into the cytosol and the formation of a calpain-calpastatin complex, and 4) a conservative fragmentation of calpastatin is accompanied by its increased expression and inhibitory capacity in conditions of prolonged increase in [Ca(2+)](i). Thus, calpastatin diffusion and formation of the calpain-calpastatin complex together with an increased synthesis of the inhibitor protein represent a cellular defense response to conditions of prolonged dysregulation in intracellular Ca(2+) homeostasis. Altogether these findings provide a new understanding of the in vivo molecular mechanisms governing calpain activation that can be extended to many neurodegenerative diseases, potentially useful for the development of new therapeutic approaches.
Stifanese
Roberto
R
Department of Experimental Medicine, Biochemistry Section, and Centre of Excellence for Biomedical Research, University of Genoa, Viale Benedetto XV, 1-16132 Genoa, Italy.
Averna
Monica
M
De Tullio
Roberta
R
Pedrazzi
Marco
M
Beccaria
Francesco
F
Salamino
Franca
F
Milanese
Marco
M
Bonanno
Giambattista
G
Pontremoli
Sandro
S
Melloni
Edon
E
D000818:Animals; D001921:Brain / Q000166:cytology* / Q000201:enzymology*; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D002154:Calpain / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation; D015971:Gene Expression Regulation, Enzymologic; D006706:Homeostasis; D006801:Humans; D042541:Intracellular Space / Q000201:enzymology; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D009132:Muscles / Q000166:cytology / Q000201:enzymology; D009474:Neurons / Q000166:cytology / Q000201:enzymology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D013116:Spinal Cord / Q000166:cytology / Q000201:enzymology; D013379:Substrate Specificity; D014020:Tissue Extracts
D002135:Calcium-Binding Proteins; D007527:Isoenzymes; D012333:RNA, Messenger; D014020:Tissue Extracts; C033668:calpastatin; D002154:Calpain; D002118:Calcium