Deletion of the BH3-only protein puma protects motoneurons from ER stress-induced apoptosis and delays motoneuron loss in ALS mice

doi:10.1073/pnas.0707906105

Deletion of the BH3-only protein puma protects motoneurons from ER stress-induced apoptosis and delays motoneuron loss in ALS mice

*Department of Physiology and Medical Physics and Royal College of Surgeons in Ireland Neuroscience Research Centre, Royal College of Surgeons in Ireland, 123 St. Stephen's Green, Dublin 2, Ireland;
^†Division of Developmental Immunology, Biocenter, Innsbruck Medical University, A-6020 Innsbruck, Austria; and
^‡The Walter and Eliza Hall Institute of Medical Research, Melbourne 3050, Australia

Edited by Joan Selverstone Valentine, University of California, Los Angeles, CA, and approved November 2, 2007 (received for review August 22, 2007)

Abstract

BH3-only proteins couple diverse stress signals to the evolutionarily conserved mitochondrial apoptosis pathway. Previously, we reported that the activation of the BH3-only protein p53-up-regulated mediator of apoptosis (Puma) was necessary and sufficient for endoplasmic reticulum (ER) stress- and proteasome inhibition-induced apoptosis in neuroblastoma and other cancer cells. Defects in protein quality control have also been suggested to be a key event in ALS, a fatal neurodegenerative condition characterized by motoneuron degeneration. Using the SOD1 ^G93A mouse model as well as human post mortem samples from ALS patients, we show evidence for increased ER stress and defects in protein degradation in motoneurons during disease progression. Before symptom onset, we detected a significant up-regulation of Puma in motoneurons of SOD1 ^G93A mice. Genetic deletion of puma significantly improved motoneuron survival and delayed disease onset and motor dysfunction in SOD1 ^G93A mice. However, it had no significant effect on lifespan, suggesting that other ER stress-related cell-death proteins or other factors, such as excitotoxicity, necrosis, or inflammatory injury, may contribute at later disease stages. Indeed, further experiments using cultured motoneurons revealed that genetic deletion of puma protected motoneurons against ER stress-induced apoptosis but showed no effect against excitotoxic injury. These findings demonstrate that a single BH3-only protein, the ER stress-associated protein Puma, plays an important role during the early stages of chronic neurodegeneration in vivo.

Footnotes

^§To whom correspondence should be addressed. E-mail: jprehn{at}rcsi.ie
Author contributions: D.K. and J.H.M.P. designed research; D.K. and I.W. performed research; A.V. and A.S. contributed new reagents/analytic tools; D.K. analyzed data; and D.K., A.V., A.S., and J.H.M.P. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0707906105/DC1.