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Title: The role of MAP4K4 in cardiac muscle cell death
Author: Jenkins, Micaela Maria
ISNI:       0000 0004 7427 7870
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2018
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Mitogen-activated protein kinase kinase-kinase-kinase-4 (MAP4K4) is activated in failing human hearts and by apoptotic triggers in cultured cardiomyocytes and mouse hearts. Potent, highly selective inhibitors of human MAP4K4 were previously identified that protect against hydrogen peroxide (H2O2)-induced cell death in rat cardiomyocytes and human iPSC-derived cardiomyocytes (hiPSC-CMs), a newly emerging platform for improved target validation and cardiac drug development. Here, we investigate whether MAP4K4 activity influences mitochondrial function, contractility and calcium cycling in hiPSC-CMs using H2O2, menadione or doxorubicin as three inducers of reactive oxygen species (ROS). Human iPSC-CM metabolism was assessed using a Seahorse XF24 analyser to monitor oxygen consumption rate (OCR). Both exogenous (H2O2) and endogenous ROS (menadione) reduced mitochondrial respiration levels as measured by OCR. Pharmacological inhibition of MAP4K4 using three complementary inhibitors did not by itself affect mitochondrial function, demonstrating the lack of any potential adverse effect, and was at least partially protective against decreased mitochondrial function induced by H2O2 or menadione. Likewise, MAP4K4 inhibition protected against calcium cycling impairment by menadione, as measured by the % of wells with detectable calcium transients. To circumvent the limitations of using 2D cultures alone, human engineered heart tissue (hEHT) was also used, providing greater biochemical and functional maturity. None of the 3 MAP4K4 inhibitors altered spontaneous contraction frequency (beats per min, BPM) or force in hEHT. MAP4K4 inhibition was protective against menadione-induced cell death 24 after treatment, as measured by adenylate kinase (AK) release. Force, beating rate, time to peak contraction and time from peak to 80% relaxation were preserved for 24 hrs. These results identify MAP4K4 as a mediator of oxidative stress-induced cell death whose pharmacological inhibition preserves cell death, mitochondrial function and contractility in a human setting.
Supervisor: Schneider, Michael D. ; Harding, Sian E. ; Noseda, Michela Sponsor: British Heart Foundation
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral