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The Role of Bax and Bak in Necrotic Cell Death

Karch, Jason
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1353099747

Abstract Details

2012, PhD, University of Cincinnati, Medicine: Cell and Molecular Biology.
Historically, necrosis has been viewed as a non-regulated form of cell death. Recently studies have shown that necrosis, like apoptosis, can be a regulated form of cell death, suggesting the existence of a programmed necrotic pathway. For instance, necrotic cell death is inhibited in cells deficient for Cyclophilin D (CypD), a mitochondrial prolyl isomerase that resides in the matrix of the mitochondria. CypD is required for programmed necrosis because it regulates the mitochondrial permeability transition pore (MPTP). The MPTP is thought to span the intermembrane space of the mitochondria and to consist of both an inner and outer component on the mitochondrial membranes. The molecular identity of these two membrane components of the MPTP remains unresolved. Upon opening of the MPTP, mitochondrial swelling, loss of energy production, and initiation of necrotic cell death occurs. MPTP opening takes place in response to high Calcium and/or reactive oxygen species (ROS) stimulation. Here we determined that Bax and Bak, Bcl-2 family members that are master regulators of apoptosis, are also required for programmed necrosis induced by Calcium, ROS, and DNA alkylation. These results led us to hypothesize that Bax and Bak are required for MPTP opening. Indeed, isolated mitochondria deficient in Bax and Bak were resistant to MPTP-dependent mitochondrial swelling accompanied by greater Calcium uptake capacity, similar to CypD deficient mitochondria. Furthermore, outer mitochondrial membrane permeability was reduced Bax/Bak null mitochondria, and reconstitution with Bax mutants that are unable to form apoptotic pores permitted MPTP-dependent calcium release and restored necrosis. These results suggest that the function of Bax/Bak during necrosis is unique from their role in apoptosis. In addition, monomeric recombinant Bax can directly enhance permeability of Bax/Bak null mitochondria and reconstituted liposomes. Furthermore, non-specific pore forming reagents completely restored MPTP activity in mitochondria absent for Bax and Bak. Finally, the existence of the MPTP was observed by patch clamping the inner mitochondrial membrane in Bax and Bak deficient mitochondria. Collectively, our results suggest that Bax and Bak are essential for the deleterious effects of the MPTP, but act in a permissive manner by altering the permeability of the outer mitochondrial membrane. Therefore, in our model, the MPTP is composed of only an inner membrane pore regulated by CypD, although Bax and Bak on the outer membrane permit swelling and organelle rupture post MPTP opening. Overall, Bax and Bak are required for programmed necrosis, serving as an indispensable functional outer membrane component of the MPTP. In contrast, during apoptosis Bax and Bak are required for the formation of large pores in the outer mitochondrial membrane that are responsible for the release of apoptogentic factors. These separate functions of Bax/Bak place them at the bifurcation point of mitochondrial dependent apoptosis and necrosis.
Jeff Molkentin, Ph.D. (Committee Chair)
Robert Brackenbury, Ph.D. (Committee Member)
David Hildeman, Ph.D. (Committee Member)
Linda Parysek, Ph.D. (Committee Member)
David Plas, Ph.D. (Committee Member)
135 p.
Cellular Biology
Bax; Bak; MPTP; necrosis; programmed; permeability;

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Citations

  • Karch, J. (2012). The Role of Bax and Bak in Necrotic Cell Death [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1353099747

    APA Style (7th edition)

  • Karch, Jason. The Role of Bax and Bak in Necrotic Cell Death. 2012. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1353099747.

    MLA Style (8th edition)

  • Karch, Jason. "The Role of Bax and Bak in Necrotic Cell Death." Doctoral dissertation, University of Cincinnati, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1353099747

    Chicago Manual of Style (17th edition)

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© 2012, all rights reserved.
This open access ETD is published by University of Cincinnati and OhioLINK.