Role Of MICU1 Research Articles

Role of MICU1 in the control of the cardiac mitochondrial Ca2+ uniporter

Role of MICU1 in the control of the cardiac mitochondrial Ca2+ uniporter

Role of MICU1 in the control of the cardiac mitochondrial calcium uniporter

Mitochondrial Ca2+ uptake is mediated by a multiprotein complex, the mitochondrial Ca2+ uniporter (mtCU) that includes the pore forming MCU and the Ca2+ sensing gatekeeper MICU1. In heart, MICU1 abundance and ratio to MCU is low. It is elusive if the cardiac mtCU lacks Ca2+ dependent gating. To address this problem, we used both genetic targeting of MICU1 and pharmacological inhibition by MCU-i11 that binds specifically to MICU1, in isolated murine cardiomyocytes. Lifelong striated muscle-specific knockout of Micu1 (lifelongKO) and tamoxifen induced Mer-Cre-Mer cardiac specific knockout of MICU1 (transientKO) and their relevant controls (CTL) were studied.

The Function of Mitochondrial Calcium Uniporter at the Whole-Cell and Single Mitochondrion Levels in WT, MICU1 KO, and MICU2 KO Cells

Mitochondrial Ca2+ ([Ca2+]M) uptake through its Ca2+ uniporter (MCU) is central to many cell functions such as bioenergetics, spatiotemporal organization of Ca2+ signals, and apoptosis. MCU activity is regulated by several intrinsic proteins including MICU1, MICU2, and EMRE. While significant details about the role of MICU1, MICU2, and EMRE in MCU function have emerged recently, a key challenge for the future experiments is to investigate how these regulatory proteins modulate mitochondrial Ca2+ influx through MCU in intact cells under pathophysiological conditions. This is further complicated by the fact that several variables affecting MCU function change dynamically as cell functions. To overcome this void, we develop a data-driven model that closely replicates the behavior of MCU under a wide range of cytosolic Ca2+ ([Ca2+]C), [Ca2+]M, and mitochondrial membrane potential values in WT, MICU1 knockout (KO), and MICU2 KO cells at the single mitochondrion and whole-cell levels. The model is extended to investigate how MICU1 or MICU2 KO affect mitochondrial function. Moreover, we show how Ca2+ buffering proteins, the separation between mitochondrion and Ca2+-releasing stores, and the duration of opening of Ca2+-releasing channels affect mitochondrial function under different conditions. Finally, we demonstrate an easy extension of the model to single channel function of MCU.

MICU1, the Ca2+ Sensing Regulator of the Mitochondrial Ca2+ Uniporter is Required for Adaptation to Postnatal Life

Over the past four years, the molecular composition of the mitochondrial Ca2+ uniporter has been sorted out, in particular the pore forming protein MCU and its Ca2+ sensing regulator MICU1 have been characterized. However, the physiological role of the mitochondrial Ca2+ uniporter is still not understood. Indeed, MCU-KO mice display embryonic lethality and normal development, depending on the background used. Moreover, loss of function mutations of MICU1 have been linked to neurological and skeletal muscle disease. This emerging link between MICU1 and human disease emphasizes the need to study MICU1 in vivo. Here, we sought to determine the physiological role of MICU1 by characterizing the first MICU1-deleted mouse. Utilizing the Cre-loxP system of gene targeting, we generated healthy and fertile MICU1+/- mice. While their progeny followed a Mendelian distribution until e18.5, with normal cardiac function assessed by fetal echocardiography, the MICU1-/- mice died within the first hours of birth with no gross morphological defects. To avoid fatalities resulting from labor stress, e18.5 mice were delivered by C-section but all animals that sustained normal breathing and vocalized intermittently had at least one copy of MICU1. Blinded histopathological analysis of the placenta and major organs (heart, liver and lung) of e18.5 animals did not reveal structural changes that could have accounted for perinatal lethality. However, examination of brainstem nuclei in toluidine blue-stained sections revealed a trend towards decreased numbers of neurons in the nucleus ambiguus (a focus of expiratory control) and the nucleus facialis. Altogether, these observations point to a functional cause of death in MICU1-/- mice, presumably through defective regulation of basic functions postnatally and suggests a vital role for MICU1 regulation of the mitochondrial calcium uniporter in adaptation to postnatal life.

Molecular Mechanisms of Mitochondrial Ca2+ Uptake: Role of MICU1 and its Paralogs

Mitochondrial Ca2+ uptake is central to cell metabolism, signaling and survival. Recent studies identified MCU as the pore of the mitochondrial Ca2+ uniporter and MICU1 as its critical regulator. MICU1 and its paralogs, MICU2 and MICU3 are EF-hand proteins and are the primary candidates to confer Ca2+ sensitivity to the Ca2+ uniporter. We will present studies of the molecular mechanisms of the MICU-dependent closure of the uniporter at low [Ca2+] levels and its cooperative activation when [Ca2+] increases. Furthermore, we will present clues to the MICU-dependence of the tissue specific mitochondrial Ca2+ uptake profiles.