Barua M.,Beth Israel Deaconess Medical Center |
Barua M.,Harvard University |
Shieh E.,Harvard University |
Schlondorff J.,Beth Israel Deaconess Medical Center |
And 7 more authors.
Kidney International | Year: 2014
Our understanding of focal and segmental glomerulosclerosis (FSGS) has advanced significantly from the studies of rare, monogenic forms of the disease. These studies have demonstrated the critical roles of multiple aspects of podocyte function in maintaining glomerular function. A substantial body of research has suggested that the integral membrane protein podocalyxin (PODXL) is required for proper functioning of podocytes, possibly by preserving the patency of the slit diaphragm by negative charge-based repulsion. Exome sequencing of affected cousins from an autosomal dominant pedigree with FSGS identified a cosegregating private variant, PODXL p.L442R, affecting the transmembrane region of the protein. Of the remaining 11 shared gene variants, two segregated with disease, but their gene products were not detected in the glomerulus. In comparison with wild type, this disease-segregating PODXL variant facilitated dimerization. By contrast, this change does not alter protein stability, extracellular domain glycosylation, cell surface expression, global subcellular localization, or interaction with its intracellular binding partner ezrin. Thus, a variant form of PODXL remains the most likely candidate causing FSGS in one family with autosomal dominant inheritance, but its full effect on protein function remains unknown. Our work highlights the challenge faced in the clinical interpretation of whole-exome data for small pedigrees with autosomal dominant diseases © 2013 International Society of Nephrology. Source
Kokel D.,Massachusetts General Hospital |
Kokel D.,Cambridge Broad Institute |
Bryan J.,University of British Columbia |
Laggner C.,University of California at San Francisco |
And 17 more authors.
Nature Chemical Biology | Year: 2010
Neuroactive small molecules are indispensable tools for treating mental illnesses and dissecting nervous system function. However, it has been difficult to discover novel neuroactive drugs. Here, we describe a high-throughput, behavior-based approach to neuroactive small molecule discovery in the zebrafish. We used automated screening assays to evaluate thousands of chemical compounds and found that diverse classes of neuroactive molecules caused distinct patterns of behavior. These 'behavioral barcodes' can be used to rapidly identify new psychotropic chemicals and to predict their molecular targets. For example, we identified new acetylcholinesterase and monoamine oxidase inhibitors using phenotypic comparisons and computational techniques. By combining high-throughput screening technologies with behavioral phenotyping in vivo, behavior-based chemical screens can accelerate the pace of neuroactive drug discovery and provide small-molecule tools for understanding vertebrate behavior. © 2010 Nature America, Inc. All rights reserved. Source
Strengthening and weakening the connections between neurons, known as synapses, is vital to the brain’s development and everyday function. One way that neurons weaken their synapses is by swallowing up receptors on their surfaces that normally respond to glutamate, one of the brain’s excitatory chemicals. In a new study, MIT neuroscientists have detailed how this receptor reabsorption takes place, allowing neurons to get rid of unwanted connections and to dampen their sensitivity in cases of overexcitation. “Pulling in and putting out receptors is a dynamic process, and it’s highly regulated by a neuron’s environment,” said Elly Nedivi, a professor of brain and cognitive sciences and member of MIT’s Picower Institute for Learning and Memory. “Our understanding of how receptors are pulled in and how regulatory pathways impact that has been quite poor.” Nedivi and colleagues found that a protein known as CPG2 is key to this regulation, which is notable because mutations in the human version of CPG2 have been previously linked to bipolar disorder. “This sets the stage for testing various human mutations and their impact at the cellular level,” said Nedivi, who is the senior author of a Jan. 14 Current Biology paper describing the findings. The paper’s lead author is former Picower Institute postdoc Sven Loebrich. Other authors are technical assistant Marc Benoit, recent MIT graduate Jaclyn Konopka, former postdoc Joanne Gibson, and Jeffrey Cottrell, the director of translational research at the Stanley Center for Psychiatric Research at the Broad Institute. Neurons communicate at synapses via neurotransmitters such as glutamate, which flow from the presynaptic to the postsynaptic neuron. This communication allows the brain to coordinate activity and store information such as new memories. Previous studies have shown that postsynaptic cells can actively pull in some of their receptors in a phenomenon known as long-term depression (LTD). This important process allows cells to weaken and eventually eliminate poor connections, as well as to recalibrate their set point for further excitation. It can also protect them from overexcitation by making them less sensitive to an ongoing stimulus. Pulling in receptors requires the cytoskeleton, which provides the physical power, and a specialized complex of proteins known as the endocytic machinery. This machinery performs endocytosis — the process of pulling in a section of the cell membrane in the form of a vesicle, along with anything attached to its surface. At the synapse, this process is used to internalize receptors. Until now, it was unknown how the cytoskeleton and the endocytic machinery were linked. In the new study, Nedivi’s team found that the CPG2 protein forms a bridge between the cytoskeleton and the endocytic machinery. “CPG2 acts like a tether for the endocytic machinery, which the cytoskeleton can use to pull in the vesicles,” Nedivi said. “The glutamate receptors that are in the membrane will get pinched off and internalized.” They also found that CPG2 binds to the endocytic machinery through a protein called EndoB2. This CPG2-EndoB2 interaction occurs only during receptor internalization provoked by synaptic stimulation and is distinct from the constant recycling of glutamate receptors that also occurs in cells. Nedivi’s lab has previously shown that this process, which does not change the cells’ overall sensitivity to glutamate, is also governed by CPG2. “This study is intriguing because it shows that by engaging different complexes, CPG2 can regulate different types of endocytosis,” said Linda Van Aelst, a professor at Cold Spring Harbor Laboratory who was not involved in the research. When synapses are too active, it appears that an enzyme called protein kinase A (PKA) binds to CPG2 and causes it to launch activity-dependent receptor absorption. CPG2 may also be controlled by other factors that regulate PKA, including hormone levels, Nedivi said. In 2011, a large consortium including researchers from the Broad Institute discovered that a gene called SYNE1 is number two on the hit list of genes linked to susceptibility for bipolar disorder. They were excited to find that this gene encoded CPG2, a regulator of glutamate receptors, given prior evidence implicating these receptors in bipolar disorder. In a study published in December, Nedivi and colleagues, including Loebrich and co-lead author Mette Rathje, identified and isolated the human messenger RNA that encodes CPG2. They showed that when rat CPG2 was knocked out, its function could be restored by the human version of the protein, suggesting both versions have the same cellular function. Rathje, a Picower Institute postdoc in Nedivi’s lab, is now studying mutations in human CPG2 that have been linked to bipolar disorder. She is testing their effect on synaptic function in rats, in hopes of revealing how those mutations might disrupt synapses and influence the development of the disorder. Nedivi suspects that CPG2 is one player in a constellation of genes that influence susceptibility to bipolar disorder. “My prediction would be that in the general population there’s a range of CPG2 function, in terms of efficacy,” Nedivi said. “Within that range, it will depend what the rest of the genetic and environmental constellation is, to determine whether it gets to the point of causing a disease state.” The research was funded by the Picower Institute Innovation Fund and the Gail Steel Fund for Bipolar Research.
Genovese G.,Stanley Center for Psychiatric Research |
Genovese G.,Harvard University |
Handsaker R.E.,Stanley Center for Psychiatric Research |
Handsaker R.E.,Harvard University |
And 16 more authors.
New England Journal of Medicine | Year: 2014
Background Cancers arise from multiple acquired mutations, which presumably occur over many years. Early stages in cancer development might be present years before cancers become clinically apparent.METHODS We analyzed data from whole-exome sequencing of DNA in peripheral-blood cells from 12, 380 persons, unselected for cancer or hematologic phenotypes. We identified somatic mutations on the basis of unusual allelic fractions. We used data from Swedish national patient registers to follow health outcomes for 2 to 7 years after DNA sampling.RESULTS Clonal hematopoiesis with somatic mutations was observed in 10% of persons older than 65 years of age but in only 1% of those younger than 50 years of age. Detectable clonal expansions most frequently involved somatic mutations in three genes (DNMT3A, ASXL1, and TET2) that have previously been implicated in hematologic cancers. Clonal hematopoiesis was a strong risk factor for subsequent hematologic cancer (hazard ratio, 12.9; 95% confidence interval, 5.8 to 28.7). Approximately 42% of hematologic cancers in this cohort arose in persons who had clonality at the time of DNA sampling, more than 6 months before a first diagnosis of cancer. Analysis of bone marrow-biopsy specimens obtained from two patients at the time of diagnosis of acute myeloid leukemia revealed that their cancers arose from the earlier clones.CONCLUSIONS Clonal hematopoiesis with somatic mutations is readily detected by means of DNA sequencing, is increasingly common as people age, and is associated with increased risks of hematologic cancer and death. A subset of the genes that are mutated in patients with myeloid cancers is frequently mutated in apparently healthy persons; these mutations may represent characteristic early events in the development of hematologic cancers. Copyright © 2014 Massachusetts Medical Society. All rights reserved. Source
Researchers have identified a gene that increases the risk of schizophrenia, and they say they have a plausible theory as to how this gene may cause the devastating mental illness. After conducting studies in both humans and mice, the researchers said this new schizophrenia risk gene, called C4, appears to be involved in eliminating the connections between neurons — a process called "synaptic pruning," which, in humans, happens naturally in the teen years. It's possible that excessive or inappropriate "pruning" of neural connections could lead to the development of schizophrenia, the researchers speculated. This would explain why schizophrenia symptoms often first appear during the teen years, the researchers said. Further research is needed to validate the findings, but if the theory holds true, the study would mark one of the first times that researchers have found a biological explanation for the link between certain genes and schizophrenia. It's possible that one day, a new treatment for schizophrenia could be developed based on these findings that would target an underlying cause of the disease, instead of just the symptoms, as current treatments do, the researchers said. "We're far from having a treatment based on this, but it's exciting to think that one day, we might be able to turn down the pruning process in some individuals and decrease their risk" of developing the condition, Beth Stevens, a neuroscientist who worked on the new study, and an assistant professor of neurology at Boston Children's Hospital, said in a statement. The study, which also involved researchers at the Broad Institute's Stanley Center for Psychiatric Research at Harvard Medical School, is published today (Jan. 27) in the journal Nature. [Top 10 Mysteries of the Mind] From previous studies, the researchers knew that one of the strongest genetic predictors of people's risk of schizophrenia was found within a region of DNA located on chromosome 6. In the new study, the researchers focused on one of the genes in this region, called complement component 4, or C4, which is known to be involved in the immune system. Using postmortem human brain samples, the researchers found that variations in the number of copies of the C4 gene that people had, and the length of their gene, could predict how active the gene was in the brain. The researchers then turned to a genome database, and pulled information about the C4 gene in 28,800 people with schizophrenia, and 36,000 people without the disease, from 22 countries. From the genome data, they estimated people's C4 gene activity. They found that the higher the levels of C4 activity were, the greater a person's risk of developing schizophrenia was. The researchers also did experiments in mice, and found that the more C4 activity there was, the more synapses were pruned during brain development. Previous studies found that people with schizophrenia have fewer synapses in certain brain areas than people without the condition. But the new findings "are the first clear evidence for a molecular and cellular mechanism of synaptic loss in schizophrenia," said Jonathan Sebat, chief of the Beyster Center for Molecular Genomics of Neuropsychiatric Diseases at the University of California, San Diego, who was not involved in the study. Still, Sebat said that the studies in mice are preliminary. These experiments looked for signs of synaptic pruning in the mice but weren't able to directly observe the process occurring. More detailed studies of brain maturation are now needed to validate the findings, Sebat said. In addition, it remains to be seen whether synaptic pruning could be a target for antipsychotic drugs, but "it's promising," Sebat said. There are drugs in development to activate the part of the immune system in which C4 is involved, Sebat noted. Copyright 2016 LiveScience, a Purch company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.