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Synthesis and Linear Viscoelasticity of Polystyrene Stars with a Polyketone Core
Polgar, L. M.,Lentzakis, H.,Collias, D.,Snijkers, F.,Lee, S.,Chang, T.,Sakellariou, G.,Wever, D. A. Z.,Toncelli, C.,Broekhuis, A. A.,Picchioni, F.,Gotsis, A. D.,Vlassopoulos, D. American Chemical Society 2015 Macromolecules Vol.48 No.18
<P>We report on a novel synthetic route to synthesize relatively large quantities of polystyrene (PS) star polymers with targeted arm functionality and molar mass and their rheological properties in the molten state. The synthetic route involves grafting styrene monomers onto a modified (aliphatic, alternating) polyketone backbone with a specific number of initiating grafting sites using controlled atom transfer radical polymerization (ATRP). Several polyketone precursors were used. This resulted in a large array of star polystyrenes with nonspherical cores and varying average arm length and number of arms. Their linear viscoelasticity was investigated and discussed in the context of the known response of anionically synthesized stars. Using a powerful characterization toolbox, including state-of-the-art interaction chromatography, rheometry, and tube modeling via the branch-on-branch (BoB) algorithm, we have assessed the viscoelasticity of these star polymers quantitatively. In particular, we have demonstrated a variability in molecular structure, which differs substantially from their anionically synthesized counterparts. Hence, whereas this new family of star polymers is not recommended for fundamental studies of polymer physics such as the molecular origin of relaxation mechanisms without prior extensive fractionation, they could be used in studies of mixtures as well as industrially relevant processing operations that require large amounts of polymeric stars.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/mamobx/2015/mamobx.2015.48.issue-18/acs.macromol.5b01434/production/images/medium/ma-2015-01434h_0012.gif'></P>
Fogelgren, Ben,Zuo, Xiaofeng,Buonato, Janine M.,Vasilyev, Aleksandr,Baek, Jeong-In,Choi, Soo Young,Chacon-Heszele, Maria F.,Palmyre, Auré,lien,Polgar, Noemi,Drummond, Iain,Park, Kwon Moo,Lazzara American Physiological Society 2014 American Journal of Physiology Vol.307 No.12
<P>Acute kidney injury is common and has a high mortality rate, and no effective treatment exists other than supportive care. Using cell culture models, we previously demonstrated that exocyst Sec10 overexpression reduced damage to renal tubule cells and speeded recovery and that the protective effect was mediated by higher basal levels of mitogen-activated protein kinase (MAPK) signaling. The exocyst, a highly-conserved eight-protein complex, is known for regulating protein trafficking. Here we show that the exocyst biochemically interacts with the epidermal growth factor receptor (EGFR), which is upstream of MAPK, and Sec10-overexpressing cells express greater levels of phosphorylated (active) ERK, the final step in the MAPK pathway, in response to EGF stimulation. EGFR endocytosis, which has been linked to activation of the MAPK pathway, increases in Sec10-overexpressing cells, and gefitinib, a specific EGFR inhibitor, and Dynasore, a dynamin inhibitor, both reduce EGFR endocytosis. In turn, inhibition of the MAPK pathway reduces ligand-mediated EGFR endocytosis, suggesting a potential feedback of elevated ERK activity on EGFR endocytosis. Gefitinib also decreases MAPK signaling in Sec10-overexpressing cells to levels seen in control cells and, demonstrating a causal role for EGFR, reverses the protective effect of Sec10 overexpression following cell injury in vitro. Finally, using an in vivo zebrafish model of acute kidney injury, morpholino-induced knockdown of <I>sec10</I> increases renal tubule cell susceptibility to injury. Taken together, these results suggest that the exocyst, acting through EGFR, endocytosis, and the MAPK pathway is a candidate therapeutic target for acute kidney injury.</P>