Browsing by Author "Chung, Chang Y"

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    Bimodal analysis reveals a general scaling law governing nondirected and chemotactic cell motility.
    (Biophysical journal, 2010-07) Gruver, J Scott; Potdar, Alka A; Jeon, Junhwan; Sai, Jiqing; Anderson, Bridget; Webb, Donna; Richmond, Ann; Quaranta, Vito; Cummings, Peter T; Chung, Chang Y
    Cell motility is a fundamental process with relevance to embryonic development, immune response, and metastasis. Cells move either spontaneously, in a nondirected fashion, or in response to chemotactic signals, in a directed fashion. Even though they are often studied separately, both forms of motility share many complex processes at the molecular and subcellular scale, e.g., orchestrated cytoskeletal rearrangements and polarization. In addition, at the cellular level both types of motility include persistent runs interspersed with reorientation pauses. Because there is a great range of variability in motility among different cell types, a key challenge in the field is to integrate these multiscale processes into a coherent framework. We analyzed the motility of Dictyostelium cells with bimodal analysis, a method that compares time spent in persistent versus reorientation mode. Unexpectedly, we found that reorientation time is coupled with persistent time in an inverse correlation and, surprisingly, the inverse correlation holds for both nondirected and chemotactic motility, so that the full range of Dictyostelium motility can be described by a single scaling relationship. Additionally, we found an identical scaling relationship for three human cell lines, indicating that the coupling of reorientation and persistence holds across species and making it possible to describe the complexity of cell motility in a surprisingly general and simple manner. With this new perspective, we analyzed the motility of Dictyostelium mutants, and found four in which the coupling between two modes was altered. Our results point to a fundamental underlying principle, described by a simple scaling law, unifying mechanisms of eukaryotic cell motility at several scales.
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    Differential regulation of adhesion and phagocytosis of resting and activated microglia by dopamine
    (Frontiers in Cellular Neuroscience, 2018-09-11) Fan, Yang; Chen, Zhilu; Pathak, Janak L; Carneiro, Ana MD; Chung, Chang Y
    © 2018 Fan, Chen, Pathak, Carneiro and Chung. Microglia, the immune competent cells of the central nervous system (CNS), normally exist in a resting state characterized by a ramified morphology with many processes, and become activated to amoeboid morphology in response to brain injury, infection, and a variety of neuroinflammatory stimuli. Many studies focused on how neurotransmitters affect microglia activation in pathophysiological circumstances. In this study, we tried to gain mechanistic insights on how dopamine (DA) released from neurons modulates cellular functions of resting and activated microglia. DA induced the reduction of the number of cellular processes, the increase of cell adhesion/spreading, and the increase of vimentin filaments in resting primary and BV2 microglia. In contrast to resting cells, DA downregulated the cell spreading and phagocytosis of microglia activated by LPS. DA also significantly downregulated ERK1/2 phosphorylation in activated microglia, but not in resting microglia. Downregulation of ERK1/2 by DA in activated microglia required receptor signaling. In contrast, we found a significant increase of p38MAPK activity by DA treatment in resting, but not in activated microglia. These latter effects required the uptake of DA through the high-affinity transporter but did not require receptor signaling. Activation of p38MAPK resulted in the increase of focal adhesion number via phosphorylation of paxillin at Ser83. These results indicate that DA might have a differential, depending upon the activation stage of microglia, impact on cellular functions such as adhesion and phagocytosis.
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    Mefenamic acid can attenuate depressive symptoms by suppressing microglia activation induced upon chronic stress.
    (Brain research, 2020-08) Feng, Xiaoye; Fan, Yang; Chung, Chang Y
    BACKGROUND:Depression is the most debilitating neuropsychiatric disorder, and psychosocial stressors are major risk factors for the onset of depression. Depression is closely associated with chronic inflammation and microglia are the principal mediators of inflammation in the central nervous system (CNS). Mefenamic acid (MA) and celecoxib are nonselective and selective inhibitors of cyclooxygenase (COX), respectively. COX is a key enzyme in mediating inflammatory response in microglia. In this study, we examine the effects of inhibiting COX by MA on depressive-like behaviors and microglia activation in the hippocampus. METHODS:We evaluate the effect of MA on chronic mild stress (CMS) induced depressive-like behavior by sucrose preference and forced swimming tests. Effect of MA on microglia activation in dentate gyrus (DG) of hippocampus was examined by immunohistochemistry. In vitro experiments including western blotting and phagocytosis assay were used to investigate the effect of MA on microglia activation. RESULTS:Behavioral assays reveal MA and celecoxib ameliorate CMS-induced depressive-like behavior. Compared to the stressed mice, the number of activated/phagocytic microglia (Iba1+/CD68+) in DG of hippocampus significantly decreases in stressed mice treated with MA or celecoxib. MA and celecoxib play a role in inhibiting microglia activation by inhibiting of ERK1/2 and P38 MAPK activation and iNOS expression. MA or celecoxib also reduce the high phagocytic activity of activated microglia. CONCLUSION:MA inhibits microglia activation/phagocytosis induced upon chronic stress in the hippocampus, which might result in the improvement of depressive symptoms.
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    Regulation of Integrin α6 Recycling by Calcium-independent Phospholipase A2 (iPLA2) to Promote Microglia Chemotaxis on Laminin.
    (The Journal of biological chemistry, 2016-11) Lee, Sang-Hyun; Sud, Neetu; Lee, Narae; Subramaniyam, Selvaraj; Chung, Chang Y
    Microglia are the immune effector cells that are activated in response to pathological changes in the central nervous system. Microglial activation is accompanied by the alteration of integrin expression on the microglia surface. However, changes of integrin expression upon chemoattractant (ADP) stimulation still remain unknown. In this study, we investigated whether ADP induces the alteration of integrin species on the cell surface, leading to changes in chemotactic ability on different extracellular matrix proteins. Flow cytometry scans and on-cell Western assays showed that ADP stimulation induced a significant increase of α6 integrin-GFP, but not α5, on the surface of microglia cells. Microglia also showed a greater motility increase on laminin than fibronectin after ADP stimulation. Time lapse microscopy and integrin endocytosis assay revealed the essential role of calcium-independent phospholipase A2 activity for the recycling of α6 integrin-GFP from the endosomal recycling complex to the plasma membrane. Lack of calcium-independent phospholipase A2 activity caused a reduced rate of focal adhesion formation on laminin at the leading edge. Our results suggest that the alteration of integrin-mediated adhesion may regulate the extent of microglial infiltration into the site of damage by controlling their chemotactic ability.
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    Role of iPLA(2) in the regulation of Src trafficking and microglia chemotaxis.
    (Traffic (Copenhagen, Denmark), 2011-07) Lee, Sang-Hyun; Schneider, Claus; Higdon, Ashlee N; Darley-Usmar, Victor M; Chung, Chang Y
    Microglia are immune effector cells in the central nervous system (CNS) and their activation, migration and proliferation play crucial roles in brain injuries and diseases. We examined the role of intracellular Ca(2+) -independent phospholipase A(2) (iPLA(2)) in the regulation of microglia chemotaxis toward ADP. Inhibition of iPLA(2) by 4-bromoenol lactone (BEL) or iPLA(2) knockdown exerted a significant inhibition on phosphatidylinositol-3-kinase (PI3K) activation and chemotaxis. Further examination revealed that iPLA(2) knockdown abrogated Src activation, which is required for PI3K activation and chemotaxis. Colocalization studies showed that cSrc-GFP was retained in the endosomal recycling compartment (ERC) in iPLA(2) knockdown cells, but the addition of arachidonic acid (AA) could restore cSrc trafficking to the plasma membrane by allowing the formation/release of recycling endosomes associated with cSrc-GFP. Using BODIPY-AA, we showed that AA is selectively enriched in recycling endosomes. These results suggest that AA is required for the cSrc trafficking to the plasma membrane by controlling the formation/release of recycling endosomes from the ERC.
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    Signaling Pathways Controlling Microglia Chemotaxis.
    (Molecules and cells, 2017-03-17) Fan, Yang; Xie, Lirui; Chung, Chang Y
    Microglia are the primary resident immune cells of the central nervous system (CNS). They are the first line of defense of the brain's innate immune response against infection, injury, and diseases. Microglia respond to extracellular signals and engulf unwanted neuronal debris by phagocytosis, thereby maintaining normal cellular homeostasis in the CNS. Pathological stimuli such as neuronal injury induce transformation and activation of resting microglia with ramified morphology into a motile amoeboid form and activated microglia chemotax toward lesion site. This review outlines the current research on microglial activation and chemotaxis.
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    β-arrestin 2-dependent activation of ERK1/2 is required for ADP-induced paxillin phosphorylation at Ser(83) and microglia chemotaxis.
    (Glia, 2012-09) Lee, Sang-Hyun; Hollingsworth, Ryan; Kwon, Hyeok-Yil; Lee, Narae; Chung, Chang Y
    Microglia play crucial roles in increased inflammation in the central nervous system upon brain injuries and diseases. Extracellular ADP has been reported to induce microglia chemotaxis and membrane ruffle formation through P2Y(12) receptor. In this study, we examined the role of ERK1/2 activation in ADP-induced microglia chemotaxis. ADP stimulation increases the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) and paxillin phosphorylation at Tyr(31) and Ser(83) . Inhibition of ERK1/2 significantly inhibited paxillin phosphorylation at Ser(83) and the retraction of membrane ruffles, causing inefficient chemotaxis. Close examination of dynamics of focal adhesion (FA) formation with green fluorescent protein-paxillin revealed that the disassembly of FAs in U0126-treated cells was significantly impaired. Depletion of β-Arrestin 2 (β-Arr2) with short hairpin RNA markedly reduced the phosphorylation of ERK1/2 and Pax/Ser(83) , indicating that β-Arr2 is required for ERK1/2 activation upon ADP stimulation. A large fraction of phosphorylated ERK1/2 and β-Arr2 were translocated and co-localized at focal contacts in the newly forming lamellipodia. Examination of kinetics and rate constant of paxillin formation and disassembly revealed that the phosphorylation of paxillin at Tyr(31) by c-Src appears to be involved in adhesion formation upon ADP stimulation while Ser(83) required for adhesion disassembly.