LI, Xianhe (2023). SPOTs: A Novel Mitochondrial Response to Stress at the Outer Mitochondrial Membrane. PhD thesis, Universität zu Köln.

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Mitochondria are essential organelles with multiple functions, including energy production, metabolic homeostasis, programmed cell death, and immune signaling. Because of their diverse functions, mitochondria have complex quality control systems and intricate coordination cellular processes with other organelles. The outer mitochondrial membrane (OMM) is considered the gateway between mitochondria and the rest of the cell and ensures its homeostasis. Although the OMM responses to artificial drugs have been described, whether the OMM responds to natural stress remains unknown.    Infection is an ideal model to study the occurrence of natural OMM stress due to effector proteins secreted by pathogens that affect the OMM. Toxoplasma gondii (Toxoplasma) is of particular interest due to the physical contact between the parasite vacuole and the OMM of the host mitochondria. To address how Toxoplasma affected the OMM, we infected OMM-targeted GFP expressing mammalian cells with Toxoplasma and observed the OMM response by live-cell imaging.   We found that mitochondria in contact with the Toxoplasma vacuole released large structures which we termed “SPOTs” (structures positive for OMM). SPOTs were positive for OMM but lacked markers of the inner mitochondrial membrane (IMM) and matrix and have an average size of 2.6 μm. TgMAF1 (Toxoplasma mitochondrial association factor 1), which is required for the contact between host mitochondria and parasite vacuole, was required for SPOT formation and led to the decrease of the OMM dynamic-related proteins Mitofusin (MFN) 1 and 2 - which mediate a nutritional defense against Toxoplasma by promoting mitochondrial uptake of fatty acids.     SPOT formation induced by TgMAF1 also depends on its binding to the host OMM protein TOM70 (translocase of the outer membrane 70), whose role as a receptor of mitochondrial precursor proteins is impaired by the interaction. TOM70 was beneficial for parasite growth and enabled the interaction between TgMAF1 and the OMM translocase SAM50 (sorting assembly machinery 50 kDa subunit). SAM50 is the only known component of host mitochondrial import machinery with a defined role in bridging the OMM and IMM. In the absence of infection, the genetic ablation of SAM50 or the overexpression of an OMM-targeted protein induced the formation of SPOT structures.   Collectively, these results support a model in which OMM stress is triggered by TgMAF1 which sequesters the mitochondrial precursor receptor TOM70 and interacts with SAM50 during infection. This enables Toxoplasma to hijack a cellular response to OMM stress—the formation of SPOTs—and drive the constitutive shedding of the OMM. The finding of OMM remodeling during infection and infection-independent scenarios sheds light on potential cellular mechanisms that safeguard OMM function.

Item Type: Thesis (PhD thesis)
CreatorsEmailORCIDORCID Put Code
Scientific advisorPernas,
URN: urn:nbn:de:hbz:38-647927
Date: 20 January 2023
Language: English
Faculty: Faculty of Mathematics and Natural Sciences
Divisions: Außeruniversitäre Forschungseinrichtungen > MPI for Biology of Ageing
Subjects: Natural sciences and mathematics
Uncontrolled Keywords:
Date of oral exam: 20 January 2023
NameAcademic Title
LI, XianheProfessor
Refereed: Yes


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