The Intrinsic Mitochondrial Apoptosis Pathway

MitochondrialA variety of stress stimuli including growth factor withdrawal, heat shock, and DNA damage activate the apoptosis intrinsic or mitochondrial pathway. Mitochondria are involved in both caspase-dependent and caspase-independent apoptosis pathways. Oxidative damage through the generation of endogenous reactive oxygen species (ROS) by mitochondria can lead to plasma membrane alterations as part of the apoptotic degradation phase.

View our range of apoptosis antibodies and kits available in different formats and suitable for many applications.

Bcl-2 family

The Bcl-2 family regulates mitochondrial outer membrane permeabilization (MOMP).

Pro-apoptotic Bcl-2 proteins form mitochondrial apoptosis-induced channels (MAC) in the outer mitochondrial membrane.

These mitochondrial membrane pores cause MOMP, releasing cytochrome c and other cytotoxic proteins into the cytosol.

Cytochrome c

Cytochrome c interacts with the cytosolic adapter protein Apaf-1 which recruits initiator procaspase-9. These proteins form a multimeric caspase-activating complex called the apoptosome. Apaf-1 and procaspase-9 bind through a shared homotypic interaction motif called the caspase recruitment domain (CARD). The apoptosome cleaves and activates procaspase-9 into caspase 9 which triggers the caspase cascade by activating the effector caspases 3, caspase 6 and caspase 7. Many proteins are degraded by caspase 3, caspase 6 and caspase 7 causing morphological and biochemical damage with eventual cell death.

Other proteins released from mitochondria into the cytosol after MOMP include:

Smac/Diablo and HtrA2/OMI, which are negative regulators of inhibitor of apoptosis (IAP) proteins.

Apoptosis inducing factor (AIF) and Endonuclease G, which translocate to the nucleus and cleave chromatin causing DNA fragmentation.

Easy Detection of the Mitochondrial Permeability Transition Event

During apoptosis, the electrochemical gradient across the mitochondrial membrane collapses. This is called the mitochondrial permeability transition (PT) event. It is mediated by the opening of PT pore complexes comprised of adenine nucleoside translocator (ANT) in the inner mitochondrial membrane interacting with voltage dependent anion channel (VDAC) in the outer mitochondrial membrane. Cytosolic components along with osmotic water diffuse through the open channel into the mitochondrial matrix. This eventually swells and ruptures the mitochondrion releasing pro-apoptotic proteins, e.g. cytochrome c, into the cytosol.

Our quick and easy-to-use JC-1, TMRE and TMRM MitoPT™ Kits allow clear differentiation between non-apoptotic and apoptotic cells through the simple and reproducible fluorescence detection of the mitochondrial permeability transition event.

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References

Mitochondrial Released Proteins

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  • Li, P. et al. (1997) Cytochrome c and dATP-dependent formation of Apaf-1/caspase-9 complex initiates an apoptosis protease cascade.
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Mitochondrial Permeability Transition Event

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  • Lim, M. L. R. et al. (2001) The protonophore CCCP induces mitochondrial permeability transition without cytochrome c release in human osteosarcoma cells.
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