Frontiers in Neurology (Mar 2016)
Rapid eye movement sleep loss induces neuronal apoptosis in the rat brain by noradrenaline acting on alpha 1-adrenoceptor and by triggering mitochondrial intrinsic pathway
Abstract
Many neurodegenerative disorders are associated with rapid eye movement sleep (REMS)-loss, however the mechanism was unknown. As REMS-loss elevates noradrenaline (NA) level in the brain as well as induces neuronal apoptosis and degeneration, in this study we have delineated the intracellular molecular pathway involved in REMS deprivation (REMSD) associated NA-induced neuronal apoptosis. Rats were REMS deprived for 6 days by the classical flower-pot method, suitable controls were conducted and the effects on apoptosis markers evaluated. Further, the role of NA was studied by one, intraperitoneal (i.p.) injection of NA-ergic alpha1-adrenoceptor antagonist prazosin (PRZ) and two, by down-regulation of NA synthesis in locus coeruleus (LC) neurons by local microinjection of tyrosine hydroxylase siRNA (TH-siRNA). Immunoblot estimates showed that the expressions of pro-apoptotic proteins viz. Bcl2-associated death promoter (BAD) protein, apoptotic protease activating factor-1 (Apaf-1), cytochrome c, caspase9, caspase3 were elevated in the REMS-deprived rat brains, while caspase8 level remained unaffected; PRZ treatment did not allow elevation of these pro-apoptotic factors. Further, REMSD increased cytochrome c expression, which was prevented if the NA synthesis from the LC neurons was blocked by microinjection of TH-siRNA in vivo into the LC during REMSD in freely moving normal rats. Mitochondrial damage was re-confirmed by transmission electron microscopy (TEM), which showed distinctly swollen mitochondria with disintegrated cristae, chromosomal condensation and clumping along the nuclear membrane and all these changes were prevented in PRZ treated rats. Combining findings of this study along with earlier reports we propose that upon REMSD NA level increases in the brain as the LC NA-ergic REM-OFF neurons do not cease firing and TH is up-regulated in those neurons. This elevated NA acting on alpha1-adrenoceptors damages mitochondria causing release of cytochrome c to activate intrinsic pathway for inducing neuronal apoptosis in REMS deprived rat brain.
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