ABSTRACT
Mitochondrial probe SiRPFA was synthesized by attaching a long perfluoroalkyl chain on Si-rhodamine cationic dye. High lipophilicity endowed SiRPFA with mitochondrial membrane potential independent properties. Under stimulated emission depletion microscopy, SiRPFA clearly revealed changes in mitochondrial cristae morphology during autophagy induced by starvation or apoptosis.
Subject(s)
Mitochondria , Mitochondrial Membranes , Rhodamines/metabolism , Mitochondrial Membranes/metabolism , Mitochondria/metabolism , Microscopy, Fluorescence/methods , Membrane Potential, MitochondrialABSTRACT
Triggering receptor expressed on myeloid cells-2 (TREM2), a cell surface receptor mainly expressed on microglia, has been shown to play a critical role in Alzheimer's disease (AD) pathogenesis and progression. Our recent results showed that overexpression of TREM2 inhibited inflammatory response in APP/PS1 mice and BV2 cells. Several studies indicated that TREM2 ameliorated tau hyperphosphorylation might be ascribed to the inhibition of neuroinflammation. However, the precise signaling pathways underlying the effect of TREM2 on tau pathology and neuronal apoptosis have not been fully elucidated. In the present study, upregulation of TREM2 significantly inhibited tau hyperphosphorylation at Ser199, Ser396, and Thr205, respectively, as well as prevented neuronal loss and apoptosis. We also found that upregulation of TREM2 alleviated behavioral deficits and improved the spatial cognitive ability of APP/PS1 mice. Further study revealed that TREM2 could activate phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signaling pathway, resulting in an inhibitory effect on glycogen synthase kinase-3ß (GSK-3ß), which is a major kinase responsible for tau hyperphosphorylation in AD. In line with in vivo findings, TREM2-overexpressing BV2 microglia following ß-amyloid (Aß) stimulation led to a significant increase in the phosphorylation of PI3K, Akt, and GSK-3ß, accompanied by a decrease in tau hyperphosphorylation and apoptosis in co-cultured SH-SY5Y cells. Furthermore, LY294002, a specific PI3K inhibitor, was observed to abolish the beneficial effects of TREM2 on tau hyperphosphorylation, neuronal apoptosis, and spatial cognitive impairments in vivo and in vitro. Thus, our findings indicated that TREM2 inhibits tau hyperphosphorylation and neuronal apoptosis, at least in part, by the activation of the PI3K/Akt/GSK-3ß signaling pathway. Taken together, the above results allow us to better understand how TREM2 protects against tau pathology and suggest that upregulation of TREM2 may provide new ideas and therapeutic targets for AD.
Subject(s)
Alzheimer Disease , Neuroblastoma , Animals , Humans , Mice , Alzheimer Disease/pathology , Apoptosis , Glycogen Synthase Kinase 3 beta/metabolism , Membrane Glycoproteins/metabolism , Phosphatidylinositol 3-Kinases/metabolism , Phosphorylation , Proto-Oncogene Proteins c-akt/metabolism , Receptors, Immunologic/metabolism , Signal Transduction , tau Proteins/metabolism , Cyclic AMP-Dependent Protein Kinases/metabolismABSTRACT
Due to their strong hydrophobicity and the aggregation-caused quenching effect, the application of perylene diimide (PDI) dyes in biological and medicinal fields lags far behind that of other dyes. Based on a multifunctional encapsulation strategy, we prepared isopropylphenyl sulfone encapsulated PDI dyes (SFPDIs). The four hydrophilic sulfone groups on the bay position of the PDIs not only effectively inhibit the fluorescence quenching caused by π-aggregation but also endow the SFPDIs with good live-cell permeability. The six lipophilic isopropylphenyl groups encapsulate PDI emitters and confer SFPDIs with excellent lipid droplet-targeting ability. Furthermore, the strong electron-withdrawing sulfone groups give the PDIs excellent anti-oxidation ability.
Subject(s)
Perylene , Fluorescence , Fluorescent Dyes/toxicity , Hydrophobic and Hydrophilic Interactions , Lipid DropletsABSTRACT
Activation of glial cells and neuroinflammation play an important role in the onset and development of Alzheimer's disease (AD). Triggering receptor expressed on myeloid cells 2 (TREM2) is a microglia-specific receptor in the brain that is involved in regulating neuroinflammation. However, the precise effects of TREM2 on neuroinflammatory responses and its underlying molecular mechanisms in AD have not been studied in detail. Here, we employed a lentiviral-mediated strategy to downregulation of TREM2 expression on microglia in the brain of APPswe/PS1dE9 (APP/PS1) transgenic mice and BV2 cells. Our results showed that downregulation of TREM2 significantly aggravated AD-related neuropathology including Aß accumulation, peri-plaque microgliosis and astrocytosis, as well as neuronal and synapse-associated proteins loss, which was accompanied by a decline in cognitive ability. The further mechanistic study revealed that downregulation of TREM2 expression initiated neuroinflammatory responses through toll-like receptor 4 (TLR4)-mediated mitogen-activated protein kinase (MAPK) signaling pathway and subsequent stimulating the production of pro-inflammatory cytokines in vivo and in vitro. Moreover, blockade of p38, JNK, and ERK1/2 inhibited the release of tumor necrosis factor-α (TNF-α), interleukin-1ß (IL-1ß), and interleukin-6 (IL-6) induced by Aß1-42 in TREM2-knocked down BV2 cells. Taken together, these findings indicated that TREM2 might be a potential therapeutic target for AD and other neuroinflammation-related diseases.
