ABSTRACT
The endocytic adaptor protein 2 (AP-2) complex binds dynactin as part of its noncanonical function, which is necessary for dynein-driven autophagosome transport along microtubules in neuronal axons. The absence of this AP-2-dependent transport causes neuronal morphology simplification and neurodegeneration. The mechanisms that lead to formation of the AP-2-dynactin complex have not been studied to date. However, the inhibition of mammalian/mechanistic target of rapamycin complex 1 (mTORC1) enhances the transport of newly formed autophagosomes by influencing the biogenesis and protein interactions of Rab-interacting lysosomal protein (RILP), another dynein cargo adaptor. We tested effects of mTORC1 inhibition on interactions between the AP-2 and dynactin complexes, with a focus on their two essential subunits, AP-2ß and p150Glued. We found that the mTORC1 inhibitor rapamycin enhanced p150Glued-AP-2ß complex formation in both neurons and non-neuronal cells. Additional analysis revealed that the p150Glued-AP-2ß interaction was indirect and required integrity of the dynactin complex. In non-neuronal cells rapamycin-driven enhancement of the p150Glued-AP-2ß interaction also required the presence of cytoplasmic linker protein 170 (CLIP-170), the activation of autophagy, and an undisturbed endolysosomal system. The rapamycin-dependent p150Glued-AP-2ß interaction occurred on lysosomal-associated membrane protein 1 (Lamp-1)-positive organelles but without the need for autolysosome formation. Rapamycin treatment also increased the acidification and number of acidic organelles and increased speed of the long-distance retrograde movement of Lamp-1-positive organelles. Altogether, our results indicate that autophagy regulates the p150Glued-AP-2ß interaction, possibly to coordinate sufficient motor-adaptor complex availability for effective lysosome transport.
Subject(s)
Autophagy , Dynactin Complex , Lysosomes , Mechanistic Target of Rapamycin Complex 1 , Neurons , Lysosomes/metabolism , Dynactin Complex/metabolism , Animals , Humans , Mechanistic Target of Rapamycin Complex 1/metabolism , Neurons/metabolism , Adaptor Protein Complex 2/metabolism , Sirolimus/pharmacology , Mice , Lysosomal-Associated Membrane Protein 1/metabolism , Autophagosomes/metabolism , Protein BindingABSTRACT
BACKGROUND: Alzheimer's disease (AD) is the progressive brain disorder which degenerates brain cells connection and causes memory loss. Although AD is irreversible, it is not impossible to arrest or slow down the progression of the disease. However, this would only be possible if the disease is diagnosed at an early stage, and early diagnosis requires clear understanding of the pathogenesis at molecular level. Overactivity of GSK-3ß and p53 accounts for tau hyperphosphorylation and the formation of amyloid-ß plaques. OBJECTIVE: Here, we explored GSK-3ß and p53 as blood-based biomarkers for early detection of AD. METHODS: The levels of GSK-3ß, p53, and their phosphorylated states were measured using surface plasmon resonance and verified using western blot in serum from AD, mild cognitive impairment (MCI), and geriatric-control (GC) subjects. The neurotoxic SH-SY5Y cell line was treated with antioxidant Emblica Officinalis (EO) for rescue effect. RESULTS: GSK-3ß, p53, and their phosphorylated states were significantly over expressed (pâ>â0.001) in AD and MCI compared to GC and can differentiate AD and MCI from GC. The expression level of GSK-3ß and p53 proteins were found to be downregulated in a dose-dependent manner after the treatment with EO in amyloid-b-induced neurotoxic cells. CONCLUSION: These proteins can serve as potential blood markers for the diagnosis of AD and EO can suppress their level. This work has translational value and clinical utility in the future.
