Terminal dUDP Nick-end Labeling Research Articles

Inhibition of rapamycin-induced autophagy causes necrotic cell death associated with Bax/Bad mitochondrial translocation

Rapamycin, a lipophilic macrolide antibiotic, has been found to reduce injury in different models of neurodegenerative disorders. We have previously shown that in neonatal rats subjected to hypoxia-ischemia (HI) the neuroprotective effect of rapamycin was associated with increased autophagy and decreased caspase-3 activation. We show here that the strong reduction of caspase-3 activation after rapamycin was due, at least in part, to its effect on the intrinsic apoptotic mitochondrial pathway because after rapamycin treatment there was a marked reduction of Bax and Bad translocation to mitochondria, cytochrome c release, and caspase-3 activation. Poly (ADP-ribose) polymerase 1 (PARP-1) cleavage and the number of terminal dUDP nick-end labeling (TUNEL)-positive cells were also reduced. To assess how the antiapoptotic effect of rapamycin was linked to the strong autophagy signal induced by the drug, we blocked the formation of autophagosomes with 3-methyladenine (3MA). 3MA administered 10 min after rapamycin, elicited again Bax and Bad translocation to the mitochondria but did not cause cytochrome c release and caspase-3 activation. After 3MA treatment, cells underwent necrotic cell death. These data indicate that rapamycin administered before HI prevents the apoptotic signaling taking place through the mitochondrial pathway. We hypothesize that rapamycin confers a preconditioning-like protection and suggest that caution is necessary before using pharmacological agents targeting autophagy in neuroprotection because they could interfere with endogenous protective mechanisms.

Role of calpain- and interleukin-1 beta converting enzyme-like proteases in the beta-amyloid-induced death of rat hippocampal neurons in culture.

We investigated the potential role of different proteases in the death of cultured rat hippocampal pyramidal neurons induced by beta-amyloid (A beta) (25-35). Both A beta(25-35)- and staurosporine-induced death of these neurons appeared to involve apoptosis, as indicated using Hoechst 33342 and terminal dUDP nick end labeling staining, whereas NMDA-induced death appeared more complex. Two irreversible inhibitors of the interleukin-1 beta converting enzyme (ICE) and related proteases, Z-Val-Ala-Asp-CH2F and acetyl-Tyr-Val-Ala-Asp-chloromethyl ketone, blocked neuronal death produced by A beta(25-35), staurosporine, and NMDA to differing extents. Furthermore, MDL 28,170, a selective inhibitor of the calcium-regulated protease calpain, also inhibited death induced by all agents. A beta(25-35) and staurosporine stimulated the breakdown of the protein spectrin, a calpain substrate. Spectrin breakdown was inhibited by MDL 28,170 but not by ICE inhibitors. Leupeptin was only effective in preventing NMDA-induced death. These results support the role of apoptosis in neuronal death due to A beta(25-35) treatment and also suggest a role for calcium-regulated proteases in this process.

Apoptosis as the mechanism of neurodegeneration in Batten's disease.

Batten's disease is a genetic neurodegenerative disease of childhood. Its hallmarks are retinitis pigmentosa and neuronal degeneration. As some types of photoreceptor death in mice are mediated by apoptosis, we investigated whether apoptosis is responsible for retinal and neuronal degeneration in the late infantile and juvenile forms of Batten's disease. Using the terminal dUDP nick end-labeling (TUNEL) staining method, we detected apoptotic neuronal cells in brain from patients and a canine model and in brain and retina from an ovine model for Batten's disease. We confirmed apoptosis by flow cytometry, electron microscopy, and DNA laddering. This is the first inherited neurodegenerative disease involving brain and retina in which apoptosis has been established as the mechanism of neuronal and photoreceptor cell death in both humans and animal models.