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

S Carloni1, G Buonocore, M Longini

  • 1Department of Biomolecular Sciences, University of Urbino Carlo Bo, Via S. Chiara 27, 61029 Urbino, Italy.

Neuroscience
|January 3, 2012
PubMed

Insights

Rapamycin reduces brain injury from hypoxia-ischemia (HI) by inhibiting the mitochondrial apoptotic pathway. Blocking autophagy with 3-methyladenine (3MA) after rapamycin treatment led to necrosis, not apoptosis.

Area of Science:

  • Neuroscience
  • Cell Biology
  • Pharmacology

Background:

  • Rapamycin (a macrolide antibiotic) has shown neuroprotective effects in models of neurodegenerative disorders.
  • Previous studies indicated rapamycin reduces injury in neonatal rats after hypoxia-ischemia (HI), linked to increased autophagy and decreased caspase-3 activation.

Purpose of the Study:

  • To investigate the mechanism by which rapamycin reduces apoptosis after HI.
  • To explore the interplay between rapamycin's anti-apoptotic effects and its induction of autophagy.

Main Methods:

  • Neonatal rats were subjected to HI and treated with rapamycin.
  • Mitochondrial apoptotic pathway markers (Bax, Bad translocation, cytochrome c release, caspase-3 activation, PARP-1 cleavage) were assessed.
  • Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay was used to quantify cell death.
  • Autophagosome formation was blocked using 3-methyladenine (3MA) post-rapamycin treatment.

Main Results:

  • Rapamycin significantly reduced caspase-3 activation, Bax and Bad translocation to mitochondria, cytochrome c release, PARP-1 cleavage, and TUNEL-positive cells after HI.
  • Blocking autophagy with 3MA after rapamycin treatment prevented apoptosis but resulted in necrotic cell death.
  • These findings suggest rapamycin's neuroprotection involves inhibiting the intrinsic apoptotic pathway.

Conclusions:

  • Rapamycin administered before HI confers preconditioning-like protection by preventing apoptotic signaling via the mitochondrial pathway.
  • Targeting autophagy pharmacologically for neuroprotection requires caution due to potential interference with endogenous protective mechanisms.

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