ATAD3A: A Key Regulator of Mitochondria-Associated Diseases

Advancements in unravelling the fundamental function of the ATAD3 protein in multicellular organisms

ATPase family AAA domain containing protein 3, commonly known as ATAD3 is a versatile mitochondrial protein that is involved in a large number of pathways. ATAD3 is a transmembrane protein that spans both the inner mitochondrial membrane and outer mitochondrial membrane. It, therefore, functions as a connecting link between the mitochondrial lumen and endoplasmic reticulum facilitating their cross-talk. ATAD3 contains an N-terminal domain which is amphipathic in nature and is inserted into the membranous space of the mitochondria, while the C-terminal domain is present towards the lumen of the mitochondria and contains the ATPase domain. ATAD3 is known to be involved in mitochondrial biogenesis, cholesterol transport, hormone synthesis, apoptosis and several other pathways. It has also been implicated to be involved in cancer and many neurological disorders making it an interesting target for extensive studies. This review aims to provide an updated comprehensive account of the role of ATAD3 in the mitochondria especially in lipid transport, mitochondrial-endoplasmic reticulum interactions, cancer and inhibition of mitophagy.

Mitochondrial DNA release and sensing in innate immune responses

Mitochondria are pleiotropic organelles central to an array of cellular pathways including metabolism, signal transduction, and programmed cell death. Mitochondria are also key drivers of mammalian immune responses, functioning as scaffolds for innate immune signaling, governing metabolic switches required for immune cell activation, and releasing agonists that promote inflammation. Mitochondrial DNA (mtDNA) is a potent immunostimulatory agonist, triggering pro-inflammatory and type I interferon responses in a host of mammalian cell types. Here we review recent advances in how mtDNA is detected by nucleic acid sensors of the innate immune system upon release into the cytoplasm and extracellular space. We also discuss how the interplay between mtDNA release and sensing impacts cellular innate immune endpoints relevant to health and disease.

Cristae shaping and dynamics in mitochondrial function

Mitochondria are multifunctional organelles of key importance for cell homeostasis. The outer mitochondrial membrane (OMM) envelops the organelle, and the inner mitochondrial membrane (IMM) is folded into invaginations called cristae. As cristae composition and functions depend on the cell type and stress conditions, they recently started to be considered as a dynamic compartment. A number of proteins are known to play a role in cristae architecture, such as OPA1, MIC60, LETM1, the prohibitin (PHB) complex and the F1FO ATP synthase. Furthermore, phospholipids are involved in the maintenance of cristae ultrastructure and dynamics. The use of new technologies, including super-resolution microscopy to visualize cristae dynamics with superior spatiotemporal resolution, as well as high-content techniques and datasets have not only allowed the identification of new cristae proteins but also helped to explore cristae plasticity. However, a number of open questions remain in the field, such as whether cristae-resident proteins are capable of changing localization within mitochondria, or whether mitochondrial proteins can exit mitochondria through export. In this Review, we present the current view on cristae morphology, stability and composition, and address important outstanding issues that might pave the way to future discoveries.