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Cell spreading and migration play central roles in many physiological and pathophysiological processes. We have previously shown that MFN2 regulates the migration of human neutrophil-like cells via suppressing Rac activation. Here, we show that in mouse embryonic fibroblasts, MFN2 suppresses RhoA activation and supports cell polarization. After initial spreading, the wild-type cells polarize and migrate, whereas theMfn2-/-cells maintain a circular shape. Increased cytosolic Ca2+resulting from the loss of Mfn2 is directly responsible for this phenotype, which can be rescued by expressing an artificial tether to bring mitochondria and endoplasmic reticulum to close vicinity. Elevated cytosolic Ca2+activates Ca2+/calmodulin-dependent protein kinase II, RhoA, and myosin light-chain kinase, causing an overactivation of nonmuscle myosin II, leading to a formation of a prominent F-actin ring at the cell periphery and increased cell contractility. The peripheral actin band alters cell physics and is dependent on substrate rigidity. Our results provide a novel molecular basis to understand how MFN2 regulates distinct signaling pathways in different cells and tissue environments, which is instrumental in understanding and treating MFN2-related diseases.
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This content will become publicly available on July 29, 2027
Mechanistic Modeling of MCUx Gatekeeping, Ca 2+ Transport, and Coupled Cytosolic-Mitochondrial Ca 2+ Dynamics
Mitochondrial Ca2+uptake is mediated by the mitochondrial calcium uniporter complex (MCUx), in which MICU1/2 serve as cytosolic Ca2+-sensing gatekeepers that set a Ca2+-dependent activation threshold. Coordinated control of MCUx activity is critical because mitochondrial Ca2+uptake couples cytosolic Ca2+signals to metabolic activation and must be regulated to prevent mitochondrial Ca2+overload and bioenergetic dysfunction. We developed a mechanistic model that incorporates explicit MICU1/2-dependent MCUx gatekeeping and a thermodynamically constrained Ca2+transport formulation that accounts for Mg2+inhibition and membrane potential dependence. Cytosolic and mitochondrial Ca2+dynamics were simulated by integrating the MCUx model into a mitochondrial cation-handling model under multiple Ca2+stimulation protocols. Because matrix-side Ca2+regulation of MCUx remains controversial, we also evaluated a putative matrix-side regulatory mechanism by comparing simulations with and without an added matrix-side regulatory module, rather than assuming such regulation as a required feature of the MCUx model. The model reproduces key experimental behaviors across genotypes. In wild-type mitochondria, MCUx-mediated Ca²⁺ uptake is negligible below a cytosolic Ca2+threshold (~0.2 µM), whereas MICU1-knockout mitochondria show constitutive uptake and MICU2-knockout mitochondria exhibit an intermediate, lowered threshold. Inclusion of matrix-side MCUx regulation transiently attenuated MCUx-mediated Ca²⁺ uptake over an intermediate mitochondrial Ca2+range, producing higher transient cytosolic Ca2+and lower transient mitochondrial Ca2+, while both cases approached similar steady states. In addition, cytosolic Mg2+acts as a graded inhibitor of MCUx-mediated Ca2+uptake, limiting mitochondrial Ca2+loading. These results provide a quantitative framework for coupled cytosolic-mitochondrial Ca²⁺ dynamics across diverse conditions.
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- PAR ID:
- 10711375
- Publisher / Repository:
- American Physiological Society
- Date Published:
- Journal Name:
- American Journal of Physiology-Cell Physiology
- ISSN:
- 0363-6143
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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