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

Abstract

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.

Relationship Between Mitochondrial Structure and Bioenergetics in Pseudoxanthoma elasticum Dermal Fibroblasts

“…Interestingly, it is involved in the mild stress-induced mitochondria hyperfusion as a pro-survival response, acting in synergy with OPA1, a protein that is required for mitochondrial fusion and which was highly expressed in PXE mitochondria. Cell energy metabolism, ROS production, and calcium homeostasis, besides STML2, are further modulated by the overexpression of MCU, a calcium uniporter protein acting as a primary mediator of Ca 2+ influx into the mitochondria (Takeuchi et al, 2015) through a process dependent on the membrane potential of the inner mitochondrial membrane (Shah and Ullah, 2020). It is to be noted that MCU allows rapid and massive Ca 2+ entry at high cytosolic Ca 2+ concentrations (>10 µM).…”

Ca2+ Sensors Assemble: Function of the MCU Complex in the Pancreatic Beta Cell

“…This impaired Ca 2+ uptake resulted in structural changes including forming short tubular mitochondria. MICU1 knockout was not rescued by increased expression of MCU [35,37,62,63].…”

Implications of MCU complex in metabolic diseases

“…MICU1 knockout in islet β cells resulted in structural changes, including the formation of short tubular mitochondria. Increased expression of MCU did not rescue the results brought by MICU1 knockout 85 . Another study showed that siRNA‐mediated knockdown of MICU2 in islet β cell reduced insulin secretion by 41%–51% 54 .…”

“…Increased expression of MCU did not rescue the results brought by MICU1 knockout. 85 Another study showed that siRNA-mediated knockdown of MICU2 in islet β cell reduced insulin secretion by 41%-51%. 54 Similarly, mitochondrial Ca 2+ uptake is attenuated, and the electron transport chain (ETC) is not stimulated, and ATP is not transported to the cell membrane to close K + channels.…”