scholarly journals During Adipocyte Remodeling, Lipid Droplet Configurations Regulate Insulin Sensitivity through F-Actin and G-Actin Reorganization

2019 ◽  
Vol 39 (20) ◽  
Author(s):  
Jong In Kim ◽  
Jeu Park ◽  
Yul Ji ◽  
Kyuri Jo ◽  
Sang Mun Han ◽  
...  
Keyword(s):  
Insulin Sensitivity ◽  
Glucose Uptake ◽  
Lipid Droplet ◽  
Actin Polymerization ◽  
Actin Dynamics ◽  
Filamentous Actin ◽  
Cytoskeleton Reorganization ◽  
Beige Adipocytes ◽  
Actin Structure ◽  
Insulin Dependent

ABSTRACT Adipocytes have unique morphological traits in insulin sensitivity control. However, how the appearance of adipocytes can determine insulin sensitivity has not been understood. Here, we demonstrate that actin cytoskeleton reorganization upon lipid droplet (LD) configurations in adipocytes plays important roles in insulin-dependent glucose uptake by regulating GLUT4 trafficking. Compared to white adipocytes, brown/beige adipocytes with multilocular LDs exhibited well-developed filamentous actin (F-actin) structure and potentiated GLUT4 translocation to the plasma membrane in the presence of insulin. In contrast, LD enlargement and unilocularization in adipocytes downregulated cortical F-actin formation, eventually leading to decreased F-actin-to-globular actin (G-actin) ratio and suppression of insulin-dependent GLUT4 trafficking. Pharmacological inhibition of actin polymerization accompanied with impaired F/G-actin dynamics reduced glucose uptake in adipose tissue and conferred systemic insulin resistance in mice. Thus, our study reveals that adipocyte remodeling with different LD configurations could be an important factor to determine insulin sensitivity by modulating F/G-actin dynamics.

scholarly journals Coxiella burnetii Induces Reorganization of the Actin Cytoskeleton in Human Monocytes

1998 ◽  
Vol 66 (11) ◽  
pp. 5527-5533 ◽  
Author(s):  
Sonia Meconi ◽  
Véronique Jacomo ◽  
Patrice Boquet ◽  
Didier Raoult ◽  
Jean-Louis Mege ◽  
...  
Keyword(s):  
Actin Cytoskeleton ◽  
Coxiella Burnetii ◽  
Actin Polymerization ◽  
Q Fever ◽  
Morphological Changes ◽  
Critical Role ◽  
Filamentous Actin ◽  
Cytoskeleton Reorganization ◽  
Membrane Protrusions ◽  
Actin Protrusions

ABSTRACT Coxiella burnetii, an obligate intracellular bacterium which survives in myeloid cells, causes Q fever in humans. We previously demonstrated that virulent C. burnetiiorganisms are poorly internalized by monocytes compared to avirulent variants. We hypothesized that a differential mobilization of the actin cytoskeleton may account for this distinct phagocytic behavior. Scanning electron microscopy demonstrated that virulent C. burnetii stimulated profound and polymorphic changes in the morphology of THP-1 monocytes, consisting of membrane protrusions and polarized projections. These changes were transient, requiring 5 min to reach their maximum extent and vanishing after 60 min of incubation. In contrast, avirulent variants of C. burnetii did not induce any significant changes in cell morphology. The distribution of filamentous actin (F-actin) was then studied with a specific probe, bodipy phallacidin. Virulent C. burnetii induced a profound and transient reorganization of F-actin, accompanied by an increase in the F-actin content of THP-1 cells. F-actin was colocalized with myosin in cell protrusions, suggesting that actin polymerization and the tension of actin-myosin filaments play a role in C. burnetii-induced morphological changes. In addition, contact between the cell and the bacterium seems to be necessary to induce cytoskeleton reorganization. Bacterial supernatants did not stimulate actin remodeling, and virulent C. burnetii organisms were found in close apposition with F-actin protrusions. The manipulation of the actin cytoskeleton by C. burnetiimay therefore play a critical role in the internalization strategy of this bacterium.

Lysophosphatidic acid-mediated augmentation of cardiomyocyte lipoprotein lipase involves actin cytoskeleton reorganization

2005 ◽  
Vol 288 (6) ◽  
pp. H2802-H2810 ◽  
Author(s):  
Thomas Pulinilkunnil ◽  
Ding An ◽  
Sanjoy Ghosh ◽  
Dake Qi ◽  
Girish Kewalramani ◽  
...  
Keyword(s):  
Actin Cytoskeleton ◽  
Lipoprotein Lipase ◽  
Lysophosphatidic Acid ◽  
Actin Polymerization ◽  
Contractile Function ◽  
Rho Kinase ◽  
Filamentous Actin ◽  
Membrane Translocation ◽  
Downstream Effector ◽  
Cytoskeleton Reorganization

The lipoprotein lipase (LPL)-augmenting property of lysophosphatidylcholine requires the formation of lysophosphatidic acid (LPA) ( J Mol Cell Cardiol 37: 931–938, 2004). Given that the actin cytoskeleton has been implicated in regulating cardiomyocyte LPL, we examined whether LPL secretion after LPA involves actin cytoskeleton reassembly. Incubation of myocytes with LPA (1–100 nM) increased basal and heparin-releasable LPL (HR-LPL), an effect that was independent of shifts in LPL mRNA. The influence of LPA on myocyte LPL was reflected at the coronary lumen, with substantial increases of the enzyme at this location. Incubation of myocytes with cytochalasin D not only blocked LPA-induced augmentation of HR-LPL but also abrogated filamentous actin formation. These effects of LPA were likely receptor mediated. Exposure of myocytes to LPA facilitated significant membrane translocation of RhoA and its downstream effector Rho kinase I (ROCK I), and blocking this effect with Y-27632 appreciably reduced basal and HR-LPL activity. Incubation of adipose tissue with LPA also significantly enhanced basal and HR-LPL activity, suggesting that sarcomeric actin likely has a limited role in influencing the LPL secretory function of LPA in the myocyte. Comparable to LPA, hyperglycemia also caused significant membrane translocation of RhoA and ROCK I in hearts isolated from diazoxide-treated animals, effects that were abrogated using insulin. Overall, our data suggest that comparable to hyperglycemia, LPA-induced increases in cardiac LPL occurred via posttranscriptional mechanisms and processes that likely required RhoA activation and actin polymerization. Whether this increase in LPL augments triglyceride deposition in the heart leading to eventual impairment in contractile function is currently unknown.

scholarly journals Mammalian Adenylyl Cyclase-associated Protein 1 (CAP1) Regulates Cofilin Function, the Actin Cytoskeleton, and Cell Adhesion

2013 ◽  
Vol 288 (29) ◽  
pp. 20966-20977 ◽  
Author(s):  
Haitao Zhang ◽  
Pooja Ghai ◽  
Huhehasi Wu ◽  
Changhui Wang ◽  
Jeffrey Field ◽  
...  
Keyword(s):  
Cell Adhesion ◽  
Actin Cytoskeleton ◽  
Hela Cells ◽  
Actin Polymerization ◽  
Actin Dynamics ◽  
Ras Signaling ◽  
Filamentous Actin ◽  
Camp Pathway

CAP (adenylyl cyclase-associated protein) was first identified in yeast as a protein that regulates both the actin cytoskeleton and the Ras/cAMP pathway. Although the role in Ras signaling does not extend beyond yeast, evidence supports that CAP regulates the actin cytoskeleton in all eukaryotes including mammals. In vitro actin polymerization assays show that both mammalian and yeast CAP homologues facilitate cofilin-driven actin filament turnover. We generated HeLa cells with stable CAP1 knockdown using RNA interference. Depletion of CAP1 led to larger cell size and remarkably developed lamellipodia as well as accumulation of filamentous actin (F-actin). Moreover, we found that CAP1 depletion also led to changes in cofilin phosphorylation and localization as well as activation of focal adhesion kinase (FAK) and enhanced cell spreading. CAP1 forms complexes with the adhesion molecules FAK and Talin, which likely underlie the cell adhesion phenotypes through inside-out activation of integrin signaling. CAP1-depleted HeLa cells also had substantially elevated cell motility as well as invasion through Matrigel. In summary, in addition to generating in vitro and in vivo evidence further establishing the role of mammalian CAP1 in actin dynamics, we identified a novel cellular function for CAP1 in regulating cell adhesion.

scholarly journals Arp2/3- and Cofilin-coordinated Actin Dynamics Is Required for Insulin-mediated GLUT4 Translocation to the Surface of Muscle Cells

2010 ◽  
Vol 21 (20) ◽  
pp. 3529-3539 ◽  
Author(s):  
Tim Ting Chiu ◽  
Nish Patel ◽  
Alisa E. Shaw ◽  
James R. Bamburg ◽  
Amira Klip
Keyword(s):  
Actin Polymerization ◽  
Molecular Mechanisms ◽  
Muscle Cells ◽  
Actin Dynamics ◽  
Cell Cortex ◽  
Glut4 Translocation ◽  
Filamentous Actin ◽  
Cortical Actin ◽  
Rac Gtpase ◽  
Skeletal Myoblasts

GLUT4 vesicles are actively recruited to the muscle cell surface upon insulin stimulation. Key to this process is Rac-dependent reorganization of filamentous actin beneath the plasma membrane, but the underlying molecular mechanisms have yet to be elucidated. Using L6 rat skeletal myoblasts stably expressing myc-tagged GLUT4, we found that Arp2/3, acting downstream of Rac GTPase, is responsible for the cortical actin polymerization evoked by insulin. siRNA-mediated silencing of either Arp3 or p34 subunits of the Arp2/3 complex abrogated actin remodeling and impaired GLUT4 translocation. Insulin also led to dephosphorylation of the actin-severing protein cofilin on Ser-3, mediated by the phosphatase slingshot. Cofilin dephosphorylation was prevented by strategies depolymerizing remodeled actin (latrunculin B or p34 silencing), suggesting that accumulation of polymerized actin drives severing to enact a dynamic actin cycling. Cofilin knockdown via siRNA caused overwhelming actin polymerization that subsequently inhibited GLUT4 translocation. This inhibition was relieved by reexpressing Xenopus wild-type cofilin-GFP but not the S3E-cofilin-GFP mutant that emulates permanent phosphorylation. Transferrin recycling was not affected by depleting Arp2/3 or cofilin. These results suggest that cofilin dephosphorylation is required for GLUT4 translocation. We propose that Arp2/3 and cofilin coordinate a dynamic cycle of actin branching and severing at the cell cortex, essential for insulin-mediated GLUT4 translocation in muscle cells.

scholarly journals Hippocampal Dendritic Spines Are Segregated Depending on Their Actin Polymerization

2016 ◽  
Vol 2016 ◽  
pp. 1-13 ◽  
Author(s):  
Nuria Domínguez-Iturza ◽  
María Calvo ◽  
Marion Benoist ◽  
José Antonio Esteban ◽  
Miguel Morales
Keyword(s):  
Dendritic Spines ◽  
Hippocampal Neurons ◽  
Actin Polymerization ◽  
Close Contact ◽  
Postsynaptic Membrane ◽  
Actin Dynamics ◽  
Filamentous Actin ◽  
Virtual Absence ◽  
Spine Shape ◽  
Mobile Fraction

Dendritic spines are mushroom-shaped protrusions of the postsynaptic membrane. Spines receive the majority of glutamatergic synaptic inputs. Their morphology, dynamics, and density have been related to synaptic plasticity and learning. The main determinant of spine shape is filamentous actin. Using FRAP, we have reexamined the actin dynamics of individual spines from pyramidal hippocampal neurons, both in cultures and in hippocampal organotypic slices. Our results indicate that, in cultures, the actin mobile fraction is independently regulated at the individual spine level, and mobile fraction values do not correlate with either age or distance from the soma. The most significant factor regulating actin mobile fraction was the presence of astrocytes in the culture substrate. Spines from neurons growing in the virtual absence of astrocytes have a more stable actin cytoskeleton, while spines from neurons growing in close contact with astrocytes show a more dynamic cytoskeleton. According to their recovery time, spines were distributed into two populations with slower and faster recovery times, while spines from slice cultures were grouped into one population. Finally, employing fast lineal acquisition protocols, we confirmed the existence of loci with high polymerization rates within the spine.

scholarly journals Loss of cortical actin filaments in insulin-resistant skeletal muscle cells impairs GLUT4 vesicle trafficking and glucose transport

2006 ◽  
Vol 291 (5) ◽  
pp. C860-C868 ◽  
Author(s):  
Alicia M. McCarthy ◽  
Kristen O. Spisak ◽  
Joseph T. Brozinick ◽  
Jeffrey S. Elmendorf
Keyword(s):  
Skeletal Muscle ◽  
Plasma Membrane ◽  
Glucose Uptake ◽  
Glucose Transport ◽  
Filamentous Actin ◽  
Cortical Actin ◽  
Insulin Resistant ◽  
Actin Structure ◽  
Insulin Responsiveness

Study has demonstrated an essential role of cortical filamentous actin (F-actin) in insulin-regulated glucose uptake by skeletal muscle. Here, we tested whether perturbations in F-actin contributed to impaired insulin responsiveness provoked by hyperinsulinemia. In L6 myotubes stably expressing GLUT4 that carries an exofacial myc-epitope tag, acute insulin stimulation (20 min, 100 nM) increased GLUT4myc translocation and glucose uptake by ∼2-fold. In contrast, a hyperinsulinemic state, induced by inclusion of 5 nM insulin in the medium for 12 h decreased the ability of insulin to stimulate these processes. Defects in insulin signaling did not readily account for the observed disruption. In contrast, hyperinsulinemia reduced cortical F-actin. This occurred concomitant with a loss of plasma membrane phosphatidylinositol 4,5-bisphosphate (PIP2), a lipid involved in cytoskeletal regulation. Restoration of plasma membrane PIP2 in hyperinsulinemic cells restored F-actin and insulin responsiveness. Consistent with these in vitro observations suggesting that the hyperinsulinemic state negatively affects cortical F-actin structure, epitrochlearis skeletal muscle from insulin-resistant hyperinsulinemic Zucker fatty rats displayed a similar loss of F-actin structure compared with that in muscle from lean insulin-sensitive littermates. We propose that a component of insulin-induced insulin resistance in skeletal muscle involves defects in PIP2/F-actin structure essential for insulin-regulated glucose transport.

scholarly journals TetraThymosinβ Is Required for Actin Dynamics in Caenorhabditis elegans and Acts via Functionally Different Actin-binding Repeats

2004 ◽  
Vol 15 (10) ◽  
pp. 4735-4748 ◽  
Author(s):  
Marleen Van Troys ◽  
Kanako Ono ◽  
Daisy Dewitte ◽  
Veronique Jonckheere ◽  
Natalie De Ruyck ◽  
...  
Keyword(s):  
Caenorhabditis Elegans ◽  
Actin Filament ◽  
Actin Polymerization ◽  
Actin Dynamics ◽  
Actin Binding ◽  
In Vitro Assays ◽  
Filamentous Actin ◽  
Lethal Mutant ◽  
Interaction Sites

Generating specific actin structures via controlled actin polymerization is a prerequisite for eukaryote development and reproduction. We here report on an essential Caenorhabditis elegans protein tetraThymosinβ expressed in developing neurons and crucial during oocyte maturation in adults. TetraThymosinβ has four repeats, each related to the actin monomer-sequestering protein thymosinβ 4 and assists in actin filament elongation. For homologues with similar multirepeat structures, a profilin-like mechanism of ushering actin onto filament barbed ends, based on the formation of a 1:1 complex, is proposed to underlie this activity. We, however, demonstrate that tetraThymosinβ binds multiple actin monomers via different repeats and in addition also interacts with filamentous actin. All repeats need to be functional for attaining full activity in various in vitro assays. The activities on actin are thus a direct consequence of the repeated structure. In containing both G- and F-actin interaction sites, tetraThymosinβ may be reminiscent of nonhomologous multimodular actin regulatory proteins implicated in actin filament dynamics. A mutation that suppresses expression of tetraThymosinβ is homozygous lethal. Mutant organisms develop into adults but display a dumpy phenotype and fail to reproduce as their oocytes lack essential actin structures. This strongly suggests that the activity of tetraThymosinβ is of crucial importance at specific developmental stages requiring actin polymerization.

scholarly journals An animal model of gestational obesity and prediabetes: HISS-dependent insulin resistance induced by a high sucrose diet in Sprague Dawley rats.

2020 ◽  
Author(s):  
Nicole Eleanore Jacqueline Lovat ◽  
Dallas J. Legare ◽  
W. Wayne Lautt
Keyword(s):  
Insulin Resistance ◽  
Animal Model ◽  
Insulin Sensitivity ◽  
Glucose Uptake ◽  
Complete Recovery ◽  
Partial Recovery ◽  
Sprague Dawley ◽  
Sprague Dawley Rats ◽  
Nutrient Partitioning ◽  
Insulin Dependent

This study developed an animal model of gestational obesity and prediabetes in Sprague Dawley rats using 35% sucrose supplementation (SS). Postprandially, insulin stimulates glucose uptake and nutrient partitioning via insulin-dependent as well as Hepatic Insulin Sensitizing Substance (HISS)-dependent action. HISS is glycogenic in heart, kidney, and skeletal muscle (contrasting insulin’s lipogenic actions in liver and adipose tissue) and is responsible for the vasodilatory action of insulin. Post-prandial insulin sensitivity was quantified using the Rapid Insulin Sensitivity Test (RIST). 15-day gestation and virgin animals received SS for 8-weeks (with a 2-week recovery), 10-weeks or 22-weeks. SS in pregnant and virgin rats eliminated HISS-dependent glucose uptake, resulting in compensatory hyperinsulinemia and resultant hypertriglyceridemia and obesity. In groups with SS for 8-weeks followed by a 2-week recovery, there was spontaneous partial recovery of HISS-dependent glucose uptake in virgins and complete recovery in pregnancy. 10-week SS resulted in complete absence of HISS-dependent glucose uptake and produced a model of gestational obesity and prediabetes. 22-week SS did not produce hyperglycemia or worsen hyperinsulinemia but did increase hypertriglyceridemia above 10-week SS. This substantiates the use of 10-week SS as a model of gestational obesity/prediabetes, allowing further studies into treatments of gestational obesity and insulin resistance.

scholarly journals The TRPC6-AMPK pathway is involved in cytoskeleton reorganization and glucose uptake in podocytes

2018 ◽  
Author(s):  
Patrycja Rachubik ◽  
Maria Szrejder ◽  
Dorota Rogacka ◽  
Irena Audzeyenka ◽  
Michał Rychłowski ◽  
...  
Keyword(s):  
Glucose Uptake ◽  
Glomerular Filtration ◽  
Glomerular Filtration Barrier ◽  
Filtration Barrier ◽  
Cytoskeleton Reorganization ◽  
Insulin Dependent ◽  
Trpc6 Channel ◽  
Amp Activated Protein Kinase ◽  
Glomerular Capillaries

AbstractPodocytes are dynamic polarized cells on the surface of glomerular capillaries that are an essential part of the glomerular filtration barrier. AMP-activated protein kinase (AMPK), a key regulator of glucose and fatty acid metabolism, plays a major role in obesity and type 2 diabetes. Accumulating evidence suggests that TRPC6 channels are crucial mediators of calcium transport in podocytes and are involved in regulating glomerular filtration barrier. Here we investigated whether the AMPK-TRPC6 pathway is involved in insulin-dependent cytoskeleton reorganization and glucose uptake in cultured rat podocytes. Insulin regulates the interaction of TRPC6 with AMPKα2 in cultured rat podocytes The results suggested a key role for the TRPC6 channel in the mediation of insulin-dependent activation of AMPKα2, actin cytoskeleton reorganization and glucose uptake in podocyte. Moreover, AMPK and TRPC6 activation were required to stimulate the Rac1 signaling pathway. These results suggest a potentially important new mechanism that regulates glucose transport in podocytes and that could be injurious during diabetes.

scholarly journals The TRPC6-AMPK Pathway is Involved in Insulin-Dependent Cytoskeleton Reorganization and Glucose Uptake in Cultured Rat Podocytes

2018 ◽  
Vol 51 (1) ◽  
pp. 393-410 ◽  
Author(s):  
Patrycja Rachubik ◽  
Maria Szrejder ◽  
Dorota Rogacka ◽  
Irena Audzeyenka ◽  
Michał Rychłowski ◽  
...  
Keyword(s):  
Glucose Uptake ◽  
Glomerular Filtration ◽  
Glucose Transport ◽  
Signaling Proteins ◽  
Filtration Barrier ◽  
Cytoskeleton Reorganization ◽  
Insulin Dependent ◽  
Trpc6 Channel ◽  
Amp Activated Protein Kinase

Background/Aims: Podocytes are dynamic polarized cells on the surface of glomerular capillaries that are an essential part of the glomerular filtration barrier. AMP-activated protein kinase (AMPK), a key regulator of glucose and fatty acid metabolism, plays a major role in obesity and type 2 diabetes. Accumulating evidence suggests that TRPC6 channels are crucial mediators of calcium transport in podocytes and are involved in regulating glomerular filtration. Here we investigated whether the AMPK-TRPC6 pathway is involved in insulin-dependent cytoskeleton reorganization and glucose uptake in cultured rat podocytes. Methods: Western blot and immunofluorescence analysis confirmed AMPKα and TRPC6 expression, the phosphorylation of proteins associated with actin cytoskeleton reorganization (PAK, rac1, and cofilin), and the expression of insulin signaling proteins (Akt, Insulin receptor). Coimmunoprecipitation and immunofluorescence results demonstrated AMPKα/TRPC6 interaction. To ask whether TRPC6 is involved in the insulin regulation of glucose transport, we measured insulin-dependent (1, 2-3H)-deoxy-D-glucose uptake into podocytes after reducing TRPC6 activity pharmacologically and biochemically (TRPC6 siRNA). Results: The results suggested a key role for the TRPC6 channel in the mediation of insulin-dependent activation of AMPKα2 and glucose uptake. Moreover, AMPK and TRPC6 activation were required to stimulate the Rac1 signaling pathway. Conclusion: These results suggest a potentially important new mechanism that regulates glucose transport in podocytes and that could be injurious during diabetes.

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