EPIGENETICS
Radiotracer images epigenetics in the brain PET images could spot epigenetic changes in neurological diseases Cells deploy an arsenal of enzymes to chemically modify DNA and its protein packaging. These so-called epigenetic modifications regulate the expression of genes, tuning the function of individual cells. Neuroscientists have found that, in neurons, this enzymatic arsenal plays a significant role in learning and memory. And data suggest that dysfunction of epigenetic machinery is linked to neurological and psychiatric disorders, such as Alzheimer’s disease, schizophrenia, and depression. Now a team of researchers at Massachusetts General Hospital led by Jacob M. Hooker reports a way to study one kind of epigenetic enzyme in living people’s brains using positron emission tomography, or PET (Sci. Transl. Med. 2016, DOI: 10.1126/ scitranslmed.aaf7551). “It’s a powerful new tool,” says Javier González-Maeso of Virginia Commonwealth University, who was not involved in the work. The PET method maps the pattern of
expression of epigenetic enzymes called histone deacetylases (HDACs), which pull acetyl groups off of proteins that package DNA in cells. “All of the studies on these enzymes so far have been in tissue culture or in animal models—in mice and rats,” González-Maeso says. “So this is the first study showing the expression of these epigenetic targets in humans.” To measure the density of HDACs in the brain using PET, Hooker and his colleagues developed a radiolabeled molecule that can bind these enzymes. They tested hundreds of analogs of known HDAC inhibitors to pinpoint a molecule that could bind a specific class of HDACs, pass through the blood-brain barrier, and accurately quantify enzyme levels in the brains of rodents and nonhuman primates. The result was the molecule [11C]Martinostat. In the new study, the researchers used the molecule to image the brains of eight healthy volunteers. They found that the pattern of HDAC expression was similar among the subjects.
3-D PRINTING
CREDIT: SCI. TRANSL. MED. (BRAIN); APPL. PHYS. LETT. (AFM TIP)
AFM tips on demand Thanks to 3-D printing, scientists can directly ‘write’ custom AFM tips Tips for atomic force microscopy can now be added to the list of custom lab ware that commercial three-dimensional printers can create. Using a technique known as two-photon polymerization, researchers led by Hendrik Hölscher of Karlsruhe Institute of Technology have printed AFM tips of their own design with a resolution of about 25 nm (Appl. Phys. Lett. 2016, DOI: 10.1063/1.4960386). Scientists first created AFM tips with two-photon polymer-
ization more than 10 years ago, but the Karlsruhe team is the first to couple the technique’s resolution with the design flexibility and on-demand capabilities of 3-D printing. In one demonstration, the team printed long, narrow tips that could better trace the steep peaks and valleys of a rose petal’s surface than some standard tips. Although commercial tip
Researchers can 3-D print AFM tips like this one with commercial tools.
Using [11C]Martinostat and positron emission tomography, researchers mapped the density, from low (blue) to high (red), of histone deacetylases in healthy people’s brains. The team also performed a preliminary study in cell culture to better understand the genes regulated by the HDACs that [11C] Martinostat inhibits. By identifying the genes controlled by these HDACs, Hooker says researchers studying patients with certain neurological diseases could use density maps produced by [11C] Martinostat to determine the genes whose regulation is disrupted in that particular disorder. Hooker’s lab has already started imaging patients with schizophrenia, Huntington’s, and Alzheimer’s disease. Besides determining how HDAC expression differs in disease states in the brain, González-Maeso also thinks the technique could monitor how the enzyme levels change over the course of a patient’s treatment to assess the efficacy of the therapy and to better understand its mechanism.—MICHAEL TORRICE
providers offer a range of tip geometries, getting the best tip for a unique specimen can be costly, Hölscher explains. The two-photon printing technique is similar to standard stereolithography, which exposes photosensitive polymers called photoresists to ultraviolet light to controllably create 3-D shapes. The two-photon technique ups the resolution by constraining where curing happens using photoresists that must simultaneously absorb two photons, rather than a single photon, to polymerize. Although the printed polymer tips aren’t as sturdy as standard silicon or silicon nitride tips, they are surprisingly hardy, says Santiago D. Solares, who leads the scanning probe microscopy lab at George Washington University. Solares, who was not involved in the study, adds that printing customized tips “opens up many opportunities for both routine and specialized AFM users.”—
MATT DAVENPORT AUGUST 22, 2016 | CEN.ACS.ORG | C&EN
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