Yi Sun

Background: Apolipoprotein E4 (ApoE4) dysregulates cholesterol metabolism in the brain promoting the accumulation of lipid droplets, synaptic dysfunction and associates with a greater Alzheimer’s disease risk. We previously demonstrated that ApoE4 reduces the function of ATP‐binding cassette transporters A1 (ABCA1) which has important roles in cholesterol transport. The mechanisms of how ApoE4 induces less ABCA1 activity are poorly understood.Method: ABCA1 binding proteins were analyzed with mass spectrum after immunoprecipitation. Immortalized astrocytes, primary astrocytes, mouse brain and human postmortem brain samples were used to test the association of ABCA1 and caveolin‐1 levels. Small interfere RNA was used to knockdown caveolin‐1 expression and 3H labelled cholesterol was used to test the cholesterol efflux of ABCA1.Result: Here, we enriched ABCA1 binding protein complexes from ABCA1‐overexpressing cells treated with recombinant ApoE3 or ApoE4 proteins for a proteomic screen implicating endocytosis as a major pathway differentiating ApoE3 from ApoE4. Among the protein targets discovered, caveolin‐1 expression increased after ApoE4 treatment. Caveolin‐1 and ABCA1 interactions were confirmed using immunoprecipitation experiments. Cholesterol accumulation in astrocytes induced caveolin‐1 expression and promoted ABCA1 degradation. Greater caveolin‐1 and lower ABCA1 expression was observed in brains of 8, 18 and 22 months‐old ApoE4‐TR mice compared with the corresponding ApoE3‐TR mice. Isolation of single cell types from adult mouse ApoE‐TR brains confirmed lower ABCA1 and greater caveolin‐1 expression was largely driven by astrocytes and not microglia or neurons enriched fractions.Conclusion: In conclusion, cholesterol accumulation induced by ApoE4 promotes ABCA1 degradation in astrocytes partly through a caveolin‐1 dependent endocytosis pathway.

Ruben Barroso, Roy Bicknell, George E. Rainger, Steve P Watson, Yi Sun; AVEXIS technology identifies novel platelet-leukocyte binding partners including CD148-C

Background: Vascular injury induces the exposure of subendothelial extracellular matrix (ECM) important to serve as substrate for platelets to adhere to the injured vessel wall to avoid massive blood loss. Different ECM proteins are known to initiate platelet adhesion and activation. In atherosclerotic mice, the small, leucine-rich proteoglycan biglycan is important for the regulation of thrombin activity via heparin cofactor II. However, nothing is known about the role of biglycan for hemostasis and thrombosis under nonatherosclerotic conditions. Methods: The role of biglycan for platelet adhesion and thrombus formation was investigated using a recombinant protein and biglycan knockout mice. Results: The present study identified biglycan as important ECM protein for the adhesion and activation of platelets, and the formation of three-dimensional thrombi under flow conditions. Platelet adhesion to immobilized biglycan induces the reorganization of the platelet cytoskeleton. Mechanistically, biglycan binds and activates the major collagen receptor glycoprotein (GP)VI, because reduced platelet adhesion to recombinant biglycan was observed when GPVI was blocked and enhanced tyrosine phosphorylation in a GPVI-dependent manner was observed when platelets were stimulated with biglycan. In vivo, the deficiency of biglycan resulted in reduced platelet adhesion to the injured carotid artery and prolonged bleeding times. Conclusions: Loss of biglycan in the vessel wall of mice but not in platelets led to reduced platelet adhesion at the injured carotid artery and prolonged bleeding times, suggesting a crucial role for biglycan as ECM protein that binds and activates platelets via GPVI upon vessel injury.

Dysfunction of embryo transport causes ectopic pregnancy which affects approximately 2% of conceptions in the US and Europe, and is the most common cause of pregnancy-related death in the first trimester. Embryo transit involves a valve-like tubal-locking phenomenon that temporarily arrests oocytes at the ampullary-isthmic junction (AIJ) where fertilisation occurs, but the mechanisms involved are unknown. Here we show that female mice lacking the orphan adhesion G-protein coupled receptor Adgrd1 are sterile because they do not relieve the AIJ restraining mechanism, inappropriately retaining embryos within the oviduct. Adgrd1 is expressed on the oviductal epithelium and the post-ovulatory attenuation of tubal fluid flow is dysregulated in Adgrd1-deficient mice. Using a large-scale extracellular protein interaction screen, we identified Plxdc2 as an activating ligand for Adgrd1 displayed on cumulus cells. Our findings demonstrate that regulating oviductal fluid flow by Adgrd1 controls embryo transit and we present a model where embryo arrest at the AIJ is due to the balance of abovarial ciliary action and the force of adovarial tubal fluid flow, and in wild-type oviducts, fluid flow is gradually attenuated through Adgrd1 activation to enable embryo release. Our findings provide important insights into the molecular mechanisms involved in embryo transport in mice.

Multiple receptors on platelets drive Alzheimer’s disease–associated amyloid deposits in brain vessels.

Dysfunction of oviductal embryo transport can lead to ectopic pregnancy which affects 1 to 2% of all conceptions in the United States and Europe, and is the most common cause of pregnancy-related death in the first trimester ^{1, 2} . Ectopic pregnancies almost always occur in the Fallopian tube, emphasizing the critical role of oviductal transport in human reproduction ³ . Oviductal transit is regulated and involves a valve-like “tubal-locking” phenomenon that temporarily arrests oocytes at the ampullary-isthmic junction (AIJ) where fertilization occurs ⁴ . Here, we show that female mice lacking the orphan adhesion G-protein coupled receptor Adgrd1 are sterile because they are unable to unlock the restraining mechanism at the AIJ, inappropriately retaining embryos within the oviduct. Adgrd1 is expressed on the oviductal epithelium and the post-ovulatory attenuation of tubal fluid production is dysregulated in Adgrd1 -deficient mice. We identified Plxdc2 as an activating ligand for Adgrd1 displayed on the surface of cumulus cells. Our findings suggest that regulating oviductal luminal fluid production by Adgrd1 controls embryo transit, and provides important insights into the genetic regulation and molecular mechanisms involved embryo tubal transport.

An efficient tandem cyclization—acetoxylation of o‐acyl‐anilines (I) mediated by the combination of iodobenzene diacetate and Bu₄NI provides a new route to 2‐acetoxy indolin‐3‐ones (III).