Apoptosis Has a Prolonged Role in the Neurodegeneration after Hypoxic Ischemia in the Newborn Rat

Abstract

Birth asphyxia can cause moderate to severe brain injury. It is unclear to what degree apoptotic or necrotic mechanisms of cell death account for damage after neonatal hypoxia-ischemia (HI). In a 7-d-old rat HI model, we determined the contributions of apoptosis and necrosis to neuronal injury in adjacent Nisslstained, hematoxylin and eosin-stained, and terminal deoxynucleotidyl transferase-mediated UTP nick end-labeled sections. We found an apoptotic-necrotic continuum in the morphology of injured neurons in all regions examined. Eosinophilic necrotic neurons, typical in adult models, were rarely observed in neonatal HI. Electron microscopic analysis showed "classic" apoptotic and necrotic neurons and "hybrid" cells with intermediate characteristics. The time course of apoptotic injury varied regionally. In CA3, dentate gyrus, medial habenula, and laterodorsal thalamus, the density of apoptotic cells was highest at 24-72 hr after HI and then declined. In contrast, densities remained elevated from 12 hr to 7 d after HI in most cortical areas and in the basal ganglia. Temporal and regional patterns of neuronal death were compared with expression of caspase-3, a cysteine protease involved in the execution phase of apoptosis. Immunocytochemical and Western blot analyses showed increased caspase-3 expression in damaged hemispheres 24 hr to 7 d after HI. A p17 peptide fragment, which results from the proteolytic activation of the caspase-3 precursor, was detected in hippocampus, thalamus, and striatum but not in cerebral cortex. The continued expression of activated caspase-3 and the persistence of cells with an apoptotic morphology for days after HI suggests a prolonged role for apoptosis in neonatal hypoxic ischemic brain injury. Key words: apoptosis; necrosis; hypoxia-ischemia; cysteine proteases; caspase-3 cleavage; cell death continuum; cerebral palsy; newborn brain injury; developmental brainBirth asphyxia can cause cerebral hypoxic ischemic injury, resulting in severe neurological sequelae and death. Survivors of perinatal asphyxia frequently have moderate to severe brain injury for which there currently is no promising therapy (Johnston, 1997). The results of morphological, histochemical, and molecular studies indicate that apoptotic and necrotic mechanisms account for neuronal death after cerebral hypoxia-ischemia (HI) in different neonatal animal models (Mehmet et al., 1994; Charriaut-Marlangue et al., 1996a,b;Chopp and Li, 1996;Macaya, 1996;Yue et al., 1997;Banasiak and Haddad, 1998;Pulera et al., 1998;Renolleau et al., 1998). For example, a neonatal ischemia-reperfusion model showed terminal deoxynucleotidyl transferase-mediated UTP nick end labeling (TUNEL)-positive nuclei from 4 hr to 30 d after reperfusion (Renolleau et al., 1998). A human study demonstrated apoptotic and necrotic forms of cell death after hypoxic injury, whereas in some brains from stillbirths, only apoptotic figures were observed (Scott and Hegyi, 1997). The form of cell death also may depend on the severity of ischemic injury (Kerr...

Plasticity in the developing brain: Implications for rehabilitation

“…For example, infant rodents demonstrate extensive neuronal apoptosis in response to sciatic nerve lesions, leading to more restricted cortical reorganization than adults from similar lesions [Cusick, 1996]. Neonatal rodents are also more prone to apoptosis from trauma and hypoxia-ischemia than adults, probably related to the importance of apoptosis in normal developmental programs [Nakajima et al, 2000]. The developing brain is also more vulnerable to drugs that impair neuronal activity, such as glutamate antagonists and GABA agonist sedatives [Ikonomidou et al, 2001].…”

Hypothermic neuroprotection

“…48 Generally apoptosis-like or programmed cell death seems to be more important in the developing brain than in adults. 56,57,[61][62][63][64][65][66] Regardless of the precise pattern of delayed death, the concept remains an important one, since if neuronal and glia cell death is an active response (preprogrammed or functionally mediated by secondary mechanisms such as cytotoxin exposure), then it should logically be possible to interrupt these events.…”

Failure to complete apoptosis following neonatal hypoxia–ischemia manifests as “continuum” phenotype of cell death and occurs with multiple manifestations of mitochondrial dysfunction in rodent forebrain

“…Another name for this is "pathological apoptosis" . Cells with this hybrid appearance have been observed in the forebrain of neonatal rats following HI (Northington et al, 2001b) (Nakajima et al, 2000) (Sheldon et al, 2001), but the mechanisms for this type of cell death are not known. In this study, we describe the "apoptotic-necrotic continuum" as a major form of neurodegeneration in the neonatal rat forebrain emerging in the first 24 hours following HI as the result of an interruption of apoptosis signaling by mitochondrial structural and functional failure.…”