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Archive - Sep 21, 2017

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Exosomes May Be Missing Link to Insulin Resistance in Diabetes

Chronic tissue inflammation resulting from obesity is an underlying cause of insulin resistance and type 2 diabetes. But the mechanism by which this occurs has remained cloaked, until now. In a paper, published in the journal Cell on September 21, 2017, University of California San Diego School of Medicine researchers identified exosomes — extremely small vesicles or sacs secreted from most cell types — as the missing link. The article is titled “Adipose Tissue Macrophage-Derived Exosomal miRNAs Can Modulate In Vivo and In Vitro Insulin Sensitivity.” “The actions induced by exosomes as they move between tissues are likely to be an underlying cause of intercellular communication causing metabolic derangements of diabetes,” said Jerrold Olefsky, MD, Professor of Medicine in the Division of Endocrinology and Metabolism at UC San Diego School of Medicine and senior author of the paper. “By fluorescently labeling cells, we could see exosomes and the microRNA they carry moving from adipose (fat) tissue through the blood and infiltrating muscle and liver tissues.” During chronic inflammation, the primary tissue to become inflamed is adipose tissue. Forty percent of adipose tissue in obesity is comprised of macrophages — specialized immune cells that promote tissue inflammation. Macrophages in turn create and secrete exosomes. When exosomes get into other tissues, they use the microRNA (miRNA) they carry to induce actions in the recipient cells. The macrophage-secreted miRNAs are on the hunt for messenger RNAs. When the miRNA finds a target in RNA, it binds to it, rendering the messenger RNA inactive. The protein that would have been encoded by the messenger RNA is no longer made. Thus, the miRNAs are a way to inhibit the production of key proteins. A team led by Dr.

Tumor-Associated Macrophages (TAMs) Promote Neuroblastoma by STAT3 Phosphorylation and Up-Regulation of c-MYC

Investigators at the Children's Center for Cancer and Blood Diseases at Children's Hospital Los Angeles have reported new findings about an immune cell - called a tumor-associated macrophage - that promotes cancer instead of fighting it. They have identified the molecular pathway, known as STAT3, as the mechanism the immune cell uses to foster neuroblastoma, a pediatric cancer, and have demonstrated use of a clinically available agent, ruxolitinib, to block the pathway. Results of the study were published online in Oncotarget on September 20, 2017. The article is titled Tumor-Associated Macrophages Promote Neuroblastoma Via STAT3 Phosphorylation and Up-Regulation of c-MYC.” Neuroblastoma is the second most common solid tumor effecting children. Individuals with high-risk disease have a mortality rate of approximately 50 percent. Certain conditions are associated with high-risk disease. High levels of some chemicals involved with inflammation and the presence of an immune cell called a tumor-associated macrophage (TAM) are associated with high-risk disease and lower survival rates. Macrophages are a type of immune cell that typically function to battle disease, not encourage it. "The macrophages are essentially co-opted by the tumor cells to help them grow," said Shahab Asgharzadeh, MD, Director of the Basic and Translational Neuroblastoma program at CHLA and lead investigator of the study. "We're trying to find out more about the mechanisms that enable TAMs to help cancer grow so that we can target the pathways they use and block their pro-tumor effect."

Discovery by Doudna Lab & Collaborators Should Help Improve Accuracy of CRISPR-Cas9 Gene Editing

Scientists at the University of California, Berkeley, and Massachusetts General Hospital have identified a key region within the Cas9 protein that governs how accurately CRISPR-Cas9 homes in on a target DNA sequence, and have tweaked it to produce a hyper-accurate gene editor with the lowest level of off-target cutting to date. The protein domain the researchers identified as a master controller of DNA cutting is an obvious target for re-engineering to improve accuracy even further, the researchers say. This approach should help scientists customize variants of Cas9 - the protein that binds and cuts DNA - to minimize the chance that CRISPR-Cas9 will edit DNA at the wrong place, a key consideration when doing gene therapy in humans. One strategy to achieve improved accuracy is to create mutations in the governing protein domain, called REC3, and see which ones improve accuracy without impacting the efficiency of on-target cutting. "We have found that even minor alterations in the REC3 domain of Cas9 affect the differential between on- and off-target editing, which suggests that this domain is an obvious candidate for in-depth mutagenesis to improve targeting specificity. As an extension of this work, one could perform a more unbiased mutagenesis within REC3 than the targeted mutations we have made," said co-first author Janice Chen, a graduate student in the lab of Dr. Jennifer Doudna, who co-invented the CRISPR-Cas9 gene-editing tool. Co-first authors Chen, Yavuz Dagdas, and Benjamin Kleinstiver, and their colleagues at UC Berkeley, Massachusetts General Hospital, and Harvard University reported their results online on September 20, 2017 in Nature. The article is titled “Enhanced Proofreading Governs CRISPR–Cas9 Targeting Accuracy.” Since 2012, when Dr.