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Autophagy and GLUT4: The missing pieces

Elhassan SAM, Candasamy M, Chan EWL, Bhattamisra SK

Diabetes Metab Syndr, 2018 Nov;12(6):1109-1116.
PMID: 29843994 DOI: 10.1016/j.dsx.2018.05.020

BACKGROUND: Autophagy is a process devoted to degrade and recycle cellular components inside mammalian cells through lysosomal system. It plays a main function in the pathophysiology of several diseases. In type 2 diabetes, works demonstrated the dual functions of autophagy in diabetes biology. Studies had approved the role of autophagy in promoting different routes for movement of integral membrane proteins to the plasma membrane. But its role in regulation of GLUT4 trafficking has not been widely observed. In normal conditions, insulin promotes GLUT4 translocation from intracellular membrane compartments to the plasma membrane, while in type 2 diabetes defects occur in this translocation.
METHOD: Intriguing evidences discussed the contribution of different intracellular compartments in autophagy membrane formation. Furthermore, autophagy serves to mobilise membranes within cells, thereby promoting cytoplasmic components reorganisation. The intent of this review is to focus on the possibility of autophagy to act as a carrier for GLUT4 through regulating GLUT4 endocytosis, intracellular trafficking in different compartments, and translocation to cell membrane.
RESULTS: The common themes of autophagy and GLUT4 have been highlighted. The review discussed the overlapping of endocytosis mechanism and intracellular compartments, and has shown that autophagy and GLUT4 utilise similar proteins (SNAREs) which are used for exocytosis. On top of that, PI3K and AMPK also control both autophagy and GLUT4.
CONCLUSION: The control of GLUT4 trafficking through autophagy could be a promising field for treating type 2 diabetes.

Matched MeSH terms: Endosomes/metabolism
Endosomal-lysosomal dysfunctions in Alzheimer's disease: Pathogenesis and therapeutic interventions

Lai SSM, Ng KY, Koh RY, Chok KC, Chye SM

Metab Brain Dis, 2021 08;36(6):1087-1100.
PMID: 33881723 DOI: 10.1007/s11011-021-00737-0

The endosomal-lysosomal system mediates the process of protein degradation through endocytic pathway. This system consists of early endosomes, late endosomes, recycling endosomes and lysosomes. Each component in the endosomal-lysosomal system plays individual crucial role and they work concordantly to ensure protein degradation can be carried out functionally. Dysregulation in the endosomal-lysosomal system can contribute to the pathogenesis of neurodegenerative diseases such as Alzheimer's disease (AD). In AD endosomal-lysosomal abnormalities are the earliest pathological features to note and hence it is important to understand the involvement of endosomal-lysosomal dysfunction in the pathogenesis of AD. In-depth understanding of this dysfunction can allow development of new therapeutic intervention to prevent and treat AD.

Matched MeSH terms: Endosomes/metabolism*
Evaluating ligand-receptor networks of TGF-beta with membrane computing

Muniyandi RC, Zin AM

Pak J Biol Sci, 2011 Dec 15;14(24):1100-8.
PMID: 22335049

Ligand-Receptor Networks of TGF-beta plays essential role in transmitting a wide range of extracellular signals that affect many cellular processes such as cell growth. However, the modeling of these networks with conventional approach such as ordinary differential equations has not taken into account, the spatial structure and stochastic behavior of processes involve in these networks. Membrane computing as the alternatives approach provides spatial structure for molecular computation in which processes are evaluated in a non-deterministic and maximally parallel way. This study is carried out to evaluate the membrane computing model of Ligand-Receptor Networks of TGF-beta with model checking approach. The results show that membrane computing model has sustained the behaviors and properties of Ligand-Receptor Networks of TGF-beta. This reinforce that membrane computing is capable in analyzing processes and behaviors in hierarchical structure of cell such as Ligand-Receptor Networks of TGF-beta better than the deterministic approach of conventional mathematical models.

Matched MeSH terms: Endosomes/metabolism
The influenza A virus matrix protein 2 undergoes retrograde transport from the endoplasmic reticulum into the cytoplasm and bypasses cytoplasmic proteasomal degradation

Bhowmick S, Chakravarty C, Sellathamby S, Lal SK

Arch Virol, 2017 Apr;162(4):919-929.
PMID: 27942972 DOI: 10.1007/s00705-016-3153-8

The matrix protein 2 (M2) is a spliced product of segment 7 genome of influenza A virus. Previous studies indicate its role in uncoating of the viral ribonucleoprotein complex during viral entry and in membrane scission while budding. Despite its crucial role in the viral life cycle, little is known about its subcellular distribution and dynamics. In this study, we have shown that the M2 protein is translocated from the membrane to the cytoplasm by a retrograde route via endosomes and the Golgi network. It utilizes retromer cargo while moving from the endosome to the trans-Golgi network and prevents endosome fusion with the lysosome. Further, M2 interacts with the endoplasmic-reticulum-resident AAA-ATPase p97 for its release into the cytoplasm. Our study also revealed that the M2 protein in the cellular milieu does not undergo ubiquitin-mediated proteasomal degradation. The migration of M2 through this pathway inside the infected cell suggests possible new roles that the M2 protein may have in the host cytoplasm, apart from its previously described functions.

Matched MeSH terms: Endosomes/metabolism
Cell-penetrating mechanism of intracellular targeting albumin: Contribution of macropinocytosis induction and endosomal escape

Ichimizu S, Watanabe H, Maeda H, Hamasaki K, Ikegami K, Chuang VTG, et al.

J Control Release, 2019 06 28;304:156-163.
PMID: 31082432 DOI: 10.1016/j.jconrel.2019.05.015

We recently developed a cell-penetrating drug carrier composed of albumin (HSA) combined with palmitoyl-cyclic-(D-Arg)12. While it is possible that the palmitoyl-cyclic-(D-Arg)12/HSA enters the cell mainly via macropinocytosis, the mechanism responsible for the induction of macropinocytosis and endosomal escape remain unknown. We report herein that palmitoyl-cyclic-(D-Arg)12/HSA might interact with heparan sulfate proteoglycan and the chemokine receptor CXCR4 followed by multiple activations of the PKC/PI3K/JNK/mTOR signaling pathways to induce macropinocytosis. This result was further confirmed by a co-treatment with 70 kDa dextran, a macropinocytosis marker. Using liposomes that mimic endosomes, the leakage of 5,6-carboxyfluorescein from liposome was observed in the presence of palmitoyl-cyclic-(D-Arg)12/HSA only in the case of the anionic late endosome-like liposomes but not the neutral early endosome-like liposomes. Heparin largely inhibited this leakage, suggesting the importance of electrostatic interactions between palmitoyl-cyclic-(D-Arg)12/HSA and the late-endosomal membrane. Immunofluorescence staining and Western blotting data indicated that the intact HSA could be transferred from endosomes to the cytosol. These collective data suggest that the palmitoyl-cyclic-(D-Arg)12/HSA is internalized via macropinocytosis and intact HSA is released from the late endosomes to the cytoplasm before the endosomes fuse with lysosomes. Palmitoyl-cyclic-(D-Arg)12/HSA not only functions as an intracellular drug delivery carrier but also as an inducer of macropinocytosis.

Matched MeSH terms: Endosomes/metabolism*