The footage captures a neuron firing, letting researchers watch the signal flowing through an entire cell for the first time. Seeing these cells at work may let researchers track and measure brain activity, including firing patterns of cells affected by disorders like epilepsy or multiple sclerosis.
The video, published online in the journal Nature Methods in June, shows a new method for converting electrical activity into fluorescent light. This nascent technology was discovered by 35-year-old Harvard University neuroscientist Adam Cohen, a native New Yorker with two doctorates under his belt. Pharmaceutical companies from Biogen Idec Inc. to GlaxoSmithKline Plc have already lined up to collaborate with Cohen’s biotechnology firm, Q-State Biosciences, hoping to advance drug development.
“Getting a good voltage sensor has been a holy grail in the field for 40 years," said Michael Hausser, a neuroscientist at University College London who wasn’t involved in Cohen’s project. “The signals are the language of the brain — if you have a good sensor, it opens up a whole world of different experiments and potentially new therapies."
Cohen’s work is based on a single-celled organism from the Dead Sea, Halorubrum sodomense, which has a protein that converts light into energy. While similar proteins had been used by other researchers to stimulate mice brains with light, Cohen had a different idea: Could he run the protein in reverse, so it would sense electricity and turn it into light?
If his idea worked, researchers might be able to visualize electrical activity in neurons, the cells that are key components of the brain, spinal cord and central nervous system.
For decades, scientists have struggled to find a way to monitor neural conversations, stymied by the complexity and the delicate nature of the brain, which makes it difficult to access.
Daniel Hochbaum, a postdoctoral fellow in Cohen’s lab, likens a neuron to a meatball with spaghetti strands. With current technology, scientists can track electrical activity only in the heart of the neuron — the meatball — by carefully inserting probes or injecting dyes with tiny glass pipettes, a process that is slow and delicate and only lets researchers track one cell at a time.
One other way currently used to monitor brain cell activity is via calcium imaging, since calcium concentration is affected when neurons fire. However, this is an indirect way of reading activity.
“There really are no other alternatives to studying the individual cells," Hochbaum said by phone. “You’re not going to scoop them out of a live human’s brain."
With Cohen’s proteins, however, voltage changes are tracked through the entire neuron, even down to the tiny arms — the spaghetti strands — that probes can’t penetrate. It’s also more efficient: under a microscope, Cohen’s lab can watch dozens of neurons in a petri dish fire in concert.
In short, “you can throw away the electrodes," said Hausser.
Cohen first had the idea to reverse-engineer the light- sensitive proteins in 2009, but tried and failed with more than 40 candidates. Hochbaum spent about a year toiling over a single protein that worked in bacteria but refused to comply in a mammalian cell.
After coming across Halorubrum sodomense in an academic paper on another topic, the researchers gave it a try — and it worked right away. Hochbaum vividly remembers his first time watching the recording. When he started to see the fluorescence fluctuate in sync with the voltage, he jumped out of his seat. “I was dancing everywhere," he said.
When he showed Cohen the data, however, they were mystified to see that halfway through the recording, the signals started degrading. They couldn’t figure out what was causing the recording quality to drop, so they ran the trial again.
“Then we noticed that the degradation started as soon we started getting excited, because we’d start jumping around and we were messing with the equipment and screwing up the signal," Hochbaum said. “As soon as we calmed down, it worked perfectly."
Cohen’s neuron work is part of a life that’s been passionately devoted to science. He graduated at the top of his class at Hunter College High School in New York and spent his undergraduate years at Harvard, then earned two doctorates in six years, first from Cambridge University, then from Stanford University. (Returning to his high school in 2011 to deliver a graduation speech, Cohen noted that as a senior, he missed prom because he was at physics camp.)
Too many ideas
While his curriculum vitae lists 20 awards and honors, the lanky professor was quick to heap praise on his graduate students. “It’s a little bit silly for the professors to take all the credit when the actual work is done by our students," he said, interrupting himself mid-narrative to rattle off student names. Instead of discussing his own accolades, he eagerly showed off a crocheted hyperbolic plane his aunt knit for him.
“He’s always coming up with ideas — too many ideas," said Hochbaum, who said Cohen’s hands-on attitude was a major reason he joined the lab. “He does not respect the boundaries that people put in place in science, saying someone’s a physicist, someone’s a chemist, someone’s a biologist. If he’s interested in tackling a problem, we end up learning on the fly what we need to know."
As word spread about his work, Cohen was besieged with requests from researchers wanting to collaborate with him. He started Q-State in April 2013 to create a platform for these partnerships, and since then had been in discussions with nearly “all the big pharma companies in the world," he said. He said he couldn’t name most of them because the partnerships are private.
The name Q-State comes from “the conformational substate of Archaerhodopsin 3 which gives rise to its voltage-sensitive fluorescence," wrote Cohen in an e-mail. “But of course I don’t expect anybody to know this — I just liked the way it sounded."
Q-State is funded by early-stage investors including Fidelity Biosciences Research Initiative, as well as grants from the US National Institutes of Health and revenue from clients that want to use Q-State’s technology for research.
Biotechnology firm Biogen is one of these clients. Biogen, which like Harvard is based in Cambridge, Massachusetts, specializes in neurological diseases including multiple sclerosis, which affects about 3.2 million worldwide and has no cure. The company declined to elaborate on what it’s working on with Cohen.
London-based drugmaker GlaxoSmithKline has also asked Cohen to help the company study cardiac safety by looking at electrical activity in the heart.
“One of the challenges that every drug company faces is the risk of cardiac side effects for the drug," said Cohen. “If a drug fixes your sinus condition but stops your heart, that’s undesirable."
The challenge is to predict cardiac risk before giving the drugs to patients, and Q-State conducted a proof-of-concept study with Glaxo, applying known drugs to heart cells and watching to see if they behaved as expected.
“It worked beautifully," said John McNeish, Glaxo’s head of research in regenerative medicine, who ran the study with Cohen, testing about a dozen compounds. “If the experiment was done in laboratories with single-cell patch clamping, it could have taken months to do. This took a week or two. So there’s money and impact written all over it."
Cohen’s current focus is on epilepsy and amyotrophic lateral sclerosis, also known as Lou Gehrig’s disease. Working with Q-State co-founder Kevin Eggan, also a Harvard researcher specializing in stem-cell research, Cohen’s group takes skin cells from patients and regrows them as genetically identical brain cells. Already, the researchers can see differences in the diseased cells’ firing patterns compared to normal cells, Cohen said.
The next step for Cohen is to continue improving the protein, which sensitive to voltage but needs intense levels of light to function. That’s not a problem for cells in a petri dish, but as Cohen works up to live mice, the intensity of the light could overheat their brains, Hausser said.
If Cohen can adjust the light levels needed, someday scientists may even be able to visualize electrical activity in humans, just by shining lights through the skull, Hausser said. “Everyone’s hoping he’s going to hit the jackpot." Bloomberg