Regulation of the permeability transition pore is altered in mice lacking the mitochondrial calcium uniporter

Authors

• RJ Parks
• S Menazza
• AM Aponte
• T Finkel
• E Murphy

Abstract

Global knockout (KO) of the mitochondrial Ca2+ uniporter (MCU) abrogates rapid mitochondrial Ca2+ uptake and permeability transition pore (PTP) opening, but does not protect from ischemic injury. This study investigates the hypothesis that the lack of protection in MCU-KO may be explained by alterations in PTP opening. To examine whether PTP opens in MCU-KO, Ca2+ uptake and swelling were measured in isolated mitochondria in the presence of the Ca2+ ionophore ETH129 to permit Ca2+ entry. ETH129 enabled MCU-KO mitochondria to take up Ca2+ and undergo pore opening. When matrix Ca2+ was set to the same level in the two groups, KO underwent PTP opening at lower Ca2+ than WT, suggesting that PTP Ca2+ sensitivity is altered. To test whether PTP contributes to ischemic injury, hearts were Langendorff-perfused in the presence of a cyclophilin D-independent pore inhibitor. Preliminary data suggest that PTP inhibition decreases infarct size by ~30% in both WT and MCU-KO hearts, suggesting that pore opening does occur in MCU-KO. To better understand ischemic cell death mechanisms in MCU-KO hearts, the proteome of whole heart homogenates was compared to WT using tandem mass tags. Interestingly, two proteins of F1F0-ATP synthase, proposed to be a component of PTP, were altered. Subunit s and F1-complex assembly factor were 2.2- and 1.6-fold lower in MCU-KO. Interestingly, native PAGE revealed that the ratio of ATP synthase dimers to monomers was reduced in MCU-KO by ~20%. These results suggest that absence of MCU may alter PTP regulation, which might involve changes in ATP synthase.

Scientific Focus Area: Molecular Biology and Biochemistry

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