Enhancement of Autophagic Flux after Neonatal Cerebral Hypoxia-Ischemia and Its Region-Specific Relationship to Apoptotic Mechanisms

Abstract

The multiplicity of cell death mechanisms induced by neonatal hypoxia-ischemia makes neuroprotective treatment against neonatal asphyxia more difficult to achieve. Whereas the roles of apoptosis and necrosis in such conditions have been studied intensively, the implication of autophagic cell death has only recently been considered. Here, we used the most clinically relevant rodent model of perinatal asphyxia to investigate the involvement of autophagy in hypoxic-ischemic brain injury. Seven-day-old rats underwent permanent ligation of the right common carotid artery, followed by 2 hours of hypoxia. This condition not only increased autophagosomal abundance (increase in microtubule-associated protein 1 light chain 3-11 level and punctuate labeling) but also lysosomal activities (cathepsin D, acid phosphatase, and ␤-Nacetylhexosaminidase) in cortical and hippocampal CA3-damaged neurons at 6 and 24 hours, demonstrating an increase in the autophagic flux. In the cortex, this enhanced autophagy may be related to apoptosis since some neurons presenting a high level of autophagy also expressed apoptotic features, including cleaved caspase-3. On the other hand, enhanced autophagy in CA3 was associated with a more purely autophagic cell death phenotype. In striking contrast to CA3 neurons, those in CA1 presented only a minimal increase in autophagy but strong apoptotic characteristics. These results suggest a role of enhanced autophagy in delayed neuronal death after severe hypoxia-ischemia that is differentially linked to apoptosis according to the cerebral region. (Am J Pathol 2009,

Death and survival of neuronal and astrocytic cells in ischemic brain injury: a role of autophagy

“…At 24 h after ischemia, cell shrinkage, large chromatin clumps, nuclear condensation/fragmentation, swollen cytoplasm, damaged organelles and deteriorated membranes co-exist in the same neuron [17] . In addition, intense vacuolization and numerous autophagosomes appear at 6 h post-HI and are npg more abundant at 24 h in the dying neurons [13] .…”

“…In 2008, Carloni et al showed that the autophagy marker, Beclin1, is significantly increased a short time after HI, both in the hippocampus and in the cerebral cortex in the neonatal cerebral HI model [12] . More recently, Ginet et al provide strong evidence that severe HI increases not only autophagosomal abundance (increase in LC3-II) but also lysosomal activities (cathepsin D, acid phosphatase, and β-N-acetylhexosaminidase) in the cortex and hippocampus, demonstrating an increase in autophagic flux [13] . Increasing evidence demonstrates that autophagy is also activated in damaged brain tissue after focal cerebral ischemia ( Table 1).…”

“…With electron microscopy, the intense vacuolization and numerous autophagosomes are observed in neurons in the ischemic region [8,11,13,17] . More importantly, in an adult mouse HI model, the activation of autophagy in different degrees of neuronal injury has been examined in detail.…”

“…In addition, autophagy is induced under starvation, differentiation, and normal growth control to maintain homeostasis and survival [1][2][3] ; however, it is also involved in neurodegenerative disorders and can trigger a form of programmed cell death (Type II death) distinct from apoptosis in neurons [4][5][6][7] . Accumulating evidence indicates that autophagy is activated and may be involved in the regulation of neuronal death in different animal models of ischemic brain injury, including hypoxiaischemia (HI) and global and focal ischemia [7][8][9][10][11][12][13][14][15][16][17] . Recently, using a permanent focal cerebral ischemia model of stroke and an oxygen and glucose deprivation (OGD) model in primary cultured astrocytes, the authors show that autophagy is activated in ischemic astrocytes and contributes to astrocytic cell death [18] .…”

β-Asarone protects PC12 cells against OGD/R-induced injury via attenuating Beclin-1-dependent autophagy

“…Autophagy, a process of self-eating, is usually induced by starvation, ischemia and hypoxia, growth factor deficiency, etc. It helps to maintain cell homeostasis [1][2][3] , but excessive autophagy may also leads to autophagic neuron death and apoptosis [4][5][6] . β-asarone, one of chief constituents from Acorus Tatarinowii Schott, can easily pass through the blood brain barrier [7] , and shows various neuroprotective effects such as protecting neuron against apoptosis [8][9][10][11] .…”