Inhibition of Bcl-2 sensitizes mitochondrial permeability transition pore (MPTP) opening in ischemia-damaged mitochondria.

Abstract

BACKGROUND:

Mitochondria are critical to cardiac injury during reperfusion as a result of damage sustained during ischemia, including the loss of bcl-2. We asked if bcl-2 depletion not only leads to selective permeation of the outer mitochondrial membrane (MOMP) favoring cytochrome c release and programmed cell death, but also favors opening of the mitochondrial permeability transition pore (MPTP). An increase in MPTP susceptibility would support a role for bcl-2 depletion mediated cell death in the calcium overload setting of early reperfusion via MPTP as well as later in reperfusion via MOMP as myocardial calcium content normalizes.

METHODS:

Calcium retention capacity (CRC) was used to reflect the sensitivity of the MPTP opening in isolated cardiac mitochondria. To study the relationship between bcl-2 inhibition and MPTP opening, mitochondria were incubated with a bcl-2 inhibitor (HA14-1) and CRC measured. The contribution of preserved bcl-2 content to MPTP opening following ischemia-reperfusion was explored using transgenic bcl-2 overexpressed mice.

RESULTS:

CRC was decreased in mitochondria following reperfusion compared to ischemia alone, indicating that reperfusion further sensitizes to MPTP opening. Incubation of ischemia-damaged mitochondria with increasing HA14-1concentrations increased calcium-stimulated MPTP opening, supporting that functional inhibition of bcl-2 during simulated reperfusion favors MPTP opening. Moreover, HA14-1 sensitivity was increased by ischemia compared to non-ischemic controls. Overexpression of bcl-2 attenuated MPTP opening in following ischemia-reperfusion. HA14-1 inhibition also increased the permeability of the outer membrane in the absence of exogenous calcium, indicating that bcl-2 inhibition favors MOMP when calcium is low.

CONCLUSIONS:

The depletion and functional inhibition of bcl-2 contributes to cardiac injury by increasing susceptibility to MPTP opening in high calcium environments and MOMP in the absence of calcium overload. Thus, ischemia-damaged mitochondria with decreased bcl-2 content are susceptible to MPTP opening in early reperfusion and MOMP later in reperfusion when cytosolic calcium has normalized.

• Authors: Qun Chen, Haishan Xu, Aijun Xu, Thomas Ross, Elizabeth Bowler, Ying Hu, Edward J Lesnefsky
• Journal: PloS one (PLoS One) Vol. 10 Issue 3 Pg. e0118834 ( 2015) ISSN: 1932-6203 [Electronic] United States
• PMID: 25756500 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, Non-P.H.S.)

Chemical References

• Benzopyrans
• Mitochondrial Membrane Transport Proteins
• Mitochondrial Permeability Transition Pore
• Nitriles
• Proto-Oncogene Proteins c-bcl-2
• ethyl 2-amino-6-bromo-4-(1-cyano-2-ethoxy-2-oxoethyl)-4H-chromene-3-carboxylate
• Calcium

Topics

• Animals
• Benzopyrans (pharmacology)
• Calcium (metabolism)
• Cell Death
• Cells, Cultured
• Ischemia (metabolism, pathology)
• Mice
• Mitochondria, Heart (drug effects, metabolism, pathology)
• Mitochondrial Membrane Transport Proteins (metabolism)
• Mitochondrial Permeability Transition Pore
• Myocardial Reperfusion Injury (metabolism, pathology)
• Myocytes, Cardiac (drug effects, metabolism)
• Nitriles (pharmacology)
• Proto-Oncogene Proteins c-bcl-2 (antagonists & inhibitors, genetics)
• Rabbits