Astrocytes are a crucial type of glial cells in the central nervous system, not only maintaining brain homeostasis, but also actively participating in the transmission of information within the brain. Astrocytes have a complex structure that includes the soma, various levels of processes, and end-feet. With the advancement of genetically encoded calcium indicators and imaging technologies, researchers have discovered numerous localized and small calcium activities in the fine processes and end-feet. These calcium activities were termed as microdomain calcium activities, which significantly differ from the calcium activities in the soma and can influence the activity of local neurons, synapses, and blood vessels. This article elaborates the detection and analysis, characteristics, sources, and functions of microdomain calcium activities, and discusses the impact of aging and neurodegenerative diseases on these activities, aiming to enhance the understanding of the role of astrocytes in the brain and to provide new insights for the treatment of brain disorders.
Astrocytes/cytology* ; Humans ; Animals ; Calcium/metabolism* ; Calcium Signaling/physiology* ; Brain/physiology* ; Aging/physiology* ; Membrane Microdomains/physiology* ; Neurodegenerative Diseases/physiopathology*

Human T cell leukemia virus type 1 (HTLV-1), an etiological factor that causes adult T cell leukemia and lymphoma (ATL), infects over 20 million people worldwide. About 1 million of HTLV-1-infected patients develop ATL, a highly aggressive non-Hodgkin's lymphoma without an effective therapy. The pX region of the HTLV-1 viral genome encodes an oncogenic protein, Tax, which plays a central role in transforming CD4+ T lymphocytes by deregulating oncogenic signaling pathways and promoting cell cycle progression. Expression of Tax following viral entry is critical for promoting survival and proliferation of human T cells and is required for initiation of oncogenesis. Tax exhibits diverse functions in host cells, and this oncoprotein primarily targets IκB kinase complex in the cytoplasm, resulting in persistent activation of NF-κB and upregulation of its responsive gene expressions that are crucial for T cell survival and cell cycle progression. We here review recent advances for the pathological roles of Tax in modulating IκB kinase activity. We also discuss our recent observation that Tax connects the IκB kinase complex to autophagy pathways. Understanding Tax-mediated pathogenesis will provide insights into development of new therapeutics in controlling HTLV-1-associated diseases.
Autophagy ; CD4-Positive T-Lymphocytes ; metabolism ; virology ; Cell Cycle ; Cell Transformation, Neoplastic ; genetics ; Gene Expression Regulation, Neoplastic ; Gene Products, tax ; genetics ; metabolism ; Human T-lymphotropic virus 1 ; physiology ; Humans ; I-kappa B Kinase ; genetics ; metabolism ; Leukemia-Lymphoma, Adult T-Cell ; genetics ; metabolism ; virology ; Membrane Microdomains ; metabolism ; virology ; NF-kappa B ; genetics ; metabolism ; Protein Binding ; Signal Transduction ; genetics

Neuronal apoptosis induced by amyloid beta-peptide (A beta) plays an important role in the pathophysiology of Alzheimer's disease (AD). However, the molecular mechanism underlying A beta-induced apoptosis remains undetermined. The disialoganglioside GD3 involves ceramide-, Fas- and TNF-alpha-mediated apoptosis in lymphoid cells and hepatocytes. Although the implication of GD3 has been suggested, the precise role of GD3 in A beta-induced apoptosis is still unclear. Here, we investsigated the changes of GD3 metabolism and characterized the distribution and trafficking of GD3 during A beta-induced apoptosis using human brain-derived TE671 cells. Extracellular A beta induced apoptosis in a mitochondrial-dependent manner. GD3 level was negligible in the basal condition. However, in response to extracellular A beta, both the expression of GD3 synthase mRNA and the intracellular GD3 level were dramatically increased. Neosynthesized GD3 rapidly accumulated in cell surface lipid microdomains, and was then translocated to mitochondria to execute the apoptosis. Disruption of membrane lipid microdomains with methyl-beta-cyclodextrin significantly prevented both GD3 accumulation in cell surface and A beta-induced apoptosis. Our data suggest that rapidly accumulated GD3 in plasma membrane lipid microdomains prior to mitochondrial translocation is one of the key events in A beta-induced apoptosis.
Amyloid beta-Peptides/*pharmacology ; *Apoptosis ; Cell Line ; Gangliosides/*metabolism/physiology ; Humans ; Membrane Microdomains/*metabolism ; Mitochondria/*metabolism ; Sialyltransferases/genetics/metabolism ; beta-Cyclodextrins/pharmacology

To explore the role of lipid raft in assembly of human herpesvirus 6, the HHV-6 GS strain was applied to infect the HSB2 cells and then the lipid raft composition was extracted from the cells with non-ionic detergent Triton-X 100. The relationship between the HHV-6 envelope glycoprotein and lipid raft was analyzed by Western Blot. Immunofluorescence double-staining was used to study the colocalization of the HHV-6 glycoprotein B(gB) with GPI anchored protein CD59 and ganglioside GM respectively. HHV-6 envelope glycoprotein B, H, L, Q1 and Q2 (gB, gH, gL, gQ1 and gQ2) were all existed in the lipid raft. Moreover, CD59 and HHV-6 envelope glycoprotein B showed the same localization through the confocal microscope. We concluded the lipid raft provided the platform for HHV-6 assembly. This is the first report concerning to the role of lipid raft in assembly of human Herpesvirus 6.
CD59 Antigens ; analysis ; Fluorescent Antibody Technique ; G(M1) Ganglioside ; analysis ; Herpesvirus 6, Human ; physiology ; Membrane Microdomains ; physiology ; Viral Envelope Proteins ; analysis ; Virus Assembly

OBJECTIVETo investigate the relationship among a 50 Hz magnetic field (MF)-induced epidermal growth factor receptor (EGFR) clustering,lipid rafts and acid sphingomyelinase (ASM), and to explore its possible mechanism.

METHODSHuman amnion FL cells were exposed to 50 Hz, 0.4 mT MF for 15 min. EGF treatment was used as positive control. Nystatin was employed to study lipid rafts since it could disrupt lipid rafts structure.The EGF receptors, ASM and lipid rafts were labeled with polyclonal anti-EGFR antibody, anti-ASM antibody and FITC-Cholera toxin B, respectively. The images were observed by laser confocal scanning microscope.

RESULTBoth EGF treatment and 50 Hz MF exposure could induce EGFR clustering; however, nystatin pretreatment disrupted this effect. MF exposure turned ASM (labeled with Cy3) from a diffused state in the sham exposure group to a concentrated state on the cell membrane, which co-localized with lipid rafts (labeled with FITC).

CONCLUSIONThe results suggest that the EGFR clustering induced by 50 Hz MF depends on intact lipid rafts on cellular membrane, and the ASM might participate in the process of EGFR clustering.

Cell Membrane ; radiation effects ; Cells, Cultured ; Electromagnetic Fields ; Epidermal Growth Factor ; metabolism ; Humans ; Membrane Microdomains ; radiation effects ; Receptor, Epidermal Growth Factor ; metabolism ; radiation effects ; Signal Transduction ; physiology ; radiation effects ; Sphingomyelin Phosphodiesterase ; metabolism

Mitochondrial biogenesis is known to accompany adipogenesis to complement ATP and acetyl-CoA required for lipogenesis. Here, we demonstrated that mitochondrial proteins such as ATP synthase alpha and beta, and cytochrome c were highly expressed during the 3T3-L1 differentiation into adipocytes. Fully-differentiated adipocytes showed a significant increase of mitochondria under electron microscopy. Analysis by immunofluorescence, cellular fractionation, and surface biotinylation demonstrated the elevated levels of ATP synthase complex found not only in the mitochondria but also on the cell surface (particularly lipid rafts) of adipocytes. High rate of ATP (more than 30 micrometer) synthesis from the added ADP and Pi in the adipocyte media suggests the involvement of the surface ATP synthase complex for the exracellular ATP synthesis. In addition, this ATP synthesis was significantly inhibited in the presence of oligomycin, an ATP synthase inhibitor, and carbonyl cyanide m-chlorophenylhydrazone (CCCP), an ATP synthase uncoupler. Decrease of extracellular ATP synthesis in acidic but not in basic media further indicates that the surface ATP synthase may also be regulated by proton gradient through the plasma membrane.
Adenosine Triphosphate/analysis/*biosynthesis ; Adipocytes/*enzymology/ultrastructure ; Animals ; Cell Differentiation/physiology ; Cell Membrane/chemistry ; Cells, Cultured ; Humans ; Membrane Microdomains/chemistry/*enzymology ; Mice ; Mitochondria/metabolism/ultrastructure ; Mitochondrial Proton-Translocating ATPases/analysis/*physiology ; Research Support, Non-U.S. Gov't

Rafts, cholesterol- and sphingolipid-rich membrane microdomains, have been shown to play an important role in immune cell activation. More recently rafts were implicated in the signal transduction by members of the TNF receptor (TNFR) family. In this study, we provide evidences that the raft microdomain has a crucial role in RANK (receptor activator of NF-kappaB) signaling. We found that the majority of the ectopically expressed RANK and substantial portion of endogenous TRAF2 and TRAF6 were detected in the low-density raft fractions. In addition, TRAF6 association with rafts was increased by RANKL stimulation. The disruption of rafts blocked the TRAF6 translocation by RANK ligand and impeded the interaction between RANK and TRAF6. Our observations demonstrate that proper RANK signaling requires the function of raft membrane microdomains.
Carrier Proteins/metabolism ; Glycoproteins/*metabolism ; Human ; Membrane Glycoproteins/metabolism ; Membrane Microdomains/*metabolism ; Protein Transport/physiology ; Proteins/*metabolism ; Receptors, Cytoplasmic and Nuclear/*metabolism