ATG9A is an autophagy-related protein that serves as a multi-spanning membrane protein, playing a crucial role in the process of autophagy. It aids in the expansion of phagophore membranes during the early stages of autophagy by flipping phospholipids between the two membrane leaflets, which assists in the formation of autophagosomes. Research has indicated that the absence of ATG9A not only inhibits autophagy but also increases the size and number of lipid droplets in human cell lines. Furthermore, the depletion of ATG9A prevents the transfer of fatty acids from lipid droplets to mitochondria, thereby hindering the utilization of fatty acids in mitochondrial respiration. ATG9A also plays a role in intracellular lipid homeostasis, particularly in relation to lipid droplets. The knockout or knockdown of ATG9A leads to an increase in the number and size of lipid droplets, and impedes the transport of fatty acids from lipid droplets to mitochondria, resulting in decreased mitochondrial fatty acid beta-oxidation. Additionally, ATG9A is closely associated with a subdomain of the endoplasmic reticulum that is rich in TMEM41B, and both structures are found near phagophores, lipid droplets, and mitochondria, highlighting the key role of ATG9A in lipid mobilization. Under heat stress conditions, ATG9A is involved in the regulation of Golgi apparatus dynamics and its functional molecular mechanisms.
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