title: Bax regulates primary necrosis through mitochondrial dynamics.
abstract: The defining event in apoptosis is mitochondrial outer membrane permeabilization (MOMP), allowing apoptogen release. In contrast, the triggering event in primary necrosis is early opening of the inner membrane mitochondrial permeability transition pore (mPTP), precipitating mitochondrial dysfunction and cessation of ATP synthesis. Bcl-2 proteins Bax and Bak are the principal activators of MOMP and apoptosis. Unexpectedly, we find that deletion of Bax and Bak dramatically reduces necrotic injury during myocardial infarction in vivo. Triple knockout mice lacking Bax/Bak and cyclophilin D, a key regulator of necrosis, fail to show further reduction in infarct size over those deficient in Bax/Bak. Absence of Bax/Bak renders cells resistant to mPTP opening and necrosis, effects confirmed in isolated mitochondria. Reconstitution of these cells or mitochondria with wild-type Bax, or an oligomerization-deficient mutant that cannot support MOMP and apoptosis, restores mPTP opening and necrosis, implicating distinct mechanisms for Bax-regulated necrosis and apoptosis. Both forms of Bax restore mitochondrial fusion in Bax/Bak-null cells, which otherwise exhibit fragmented mitochondria. Cells lacking mitofusin 2 (Mfn2), which exhibit similar fusion defects, are protected to the same extent as Bax/Bak-null cells. Conversely, restoration of fused mitochondria through inhibition of fission potentiates mPTP opening in the absence of Bax/Bak or Mfn2, indicating that the fused state itself is critical. These data demonstrate that Bax-driven fusion lowers the threshold for mPTP opening and necrosis. Thus, Bax and Bak play wider roles in cell death than previously appreciated and may be optimal therapeutic targets for diseases that involve both forms of cell death.
authors.affiliation: Department of Medicine, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
authors.forename: Russell S
authors.initials: RS
authors.lastname: Whelan
authors.forename: Klitos
authors.initials: K
authors.lastname: Konstantinidis
authors.forename: An-Chi
authors.initials: AC
authors.lastname: Wei
authors.forename: Yun
authors.initials: Y
authors.lastname: Chen
authors.forename: Denis E
authors.initials: DE
authors.lastname: Reyna
authors.forename: Saurabh
authors.initials: S
authors.lastname: Jha
authors.forename: Ying
authors.initials: Y
authors.lastname: Yang
authors.forename: John W
authors.initials: JW
authors.lastname: Calvert
authors.forename: Tullia
authors.initials: T
authors.lastname: Lindsten
authors.forename: Craig B
authors.initials: CB
authors.lastname: Thompson
authors.forename: Michael T
authors.initials: MT
authors.lastname: Crow
authors.forename: Evripidis
authors.initials: E
authors.lastname: Gavathiotis
authors.forename: Gerald W
authors.initials: GW
authors.lastname: Dorn
authors.forename: Brian
authors.initials: B
authors.lastname: O'Rourke
authors.forename: Richard N
authors.initials: RN
authors.lastname: Kitsis
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis; D000818:Animals; D051379:Mice; D018345:Mice, Knockout; D008928:Mitochondria / Q000502:physiology*; D009203:Myocardial Infarction / Q000235:genetics / Q000503:physiopathology; D009336:Necrosis; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000502:physiology*
chemical_list: D051028:bcl-2-Associated X Protein; D000255:Adenosine Triphosphate