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Some 500 Genes Differ in Bipolar Patients’ Neurons

Wed, 07/02/2014 - 3:16pm
Cynthia Fox, Science Editor
Neurons of patients with bipolar disorder (BP) differ from the norm in a “striking” 500 or so genes.
 
This is according to preliminary data, generated using the Nobel-Prize-winning iPSC (induced pluripotent stem cell) approach, by Salk Institute neuroscientist Fred Gage. Speaking at the annual meeting of the International Society for Stem Cell Research (ISSCR), Gage said the iPSC approach helped his team, for the first time, pick out both BP-specific genes, and gene expression patterns distinguishing lithium-responsive from non-responsive BP patients. 
 
When these new data are published and repeated, they may lead to far better drug discovery, and drug prescribing, for bipolar disorder.
 
“Absolutely wonderful talk,” said the forum moderator, Neural Stem Cell Institute researcher Sally Temple.
 
Three to four percent of Americans are diagnosed BP at some point in their lives. BP takes 9.2 years off life. One in five patients commit suicide. “Even worse, 70 percent of bipolar patients are misdiagnosed in the first three years,” Gage said. “Until they are correctly diagnosed, there is not a lot you can do for them.”
 
Often, doctors must randomly “cycle” patients through many side-effect-ridden drugs, stopping when one seems to work. “They have found lithium evens-out mood swings, and is quite effective for some populations, but a large population diagnosed with BP is refractory, with no response to lithium.”
 
A massive roadblock has been the inability to test drugs pre-clinically. Animal models of psychiatric disorders are woefully inadequate. Human neurons are rare, as no one (understandably) wants to part with theirs, and they do not replicate. 
 
But in 2007, Kyoto University's Shinya Yamanaka published a paper in Cell showing he had turned back the clock on ordinary human cells, making limitless stem cells from them. (He won the Nobel for it in 2012.) Stem cells can turn into any cells in the body. Could the clock be cranked forward to create limitless neurons from limitless iPSCs? A few groups —including Gage’s— earlier found the answer was yes.
 
Armed with this, Gage’s group partnered with a psychogenetic clinical program that provided four control patients, and three BP patients who respond to lithium; three BP patients who don’t.
 
His team took adult cells from the patients. Using the iPSC approach, he reprogrammed those into granule neurons of the dentate gyrus, a brain region involved in learning and depression. Some 80 percent were excitatory neurons. Three to seven percent were gabaergic neurons. From 60 to 70 percent were Prox1 positive. (Prox1 is a protein associated with neural stem cell maturation.)
 
In the group’s first analysis of differential gene expression, “there were pretty striking differences,” Gage said. “Nearly 500 genes were statistically different between the controls and experimental groups.” The group confirmed differences via phenotype comparisons (e.g., comparing hyper-excitability of the different cells) and by qPCR (real time polymerase chain reaction).
 
The group examined the cells for other qualities, including evoked responses and induced currents. "The most striking thing came up right away, and that was every BP patients’ granule neurons showed hyper-excitability, evident both by frequency of firing, which was quite dramatic, as well as amplitude," Gage said. Sodium peak currents were also higher. "So there was a remarkably intrinsic difference between these patients."
 
The group also tested differences between lithium-responding and non-responding patients. An RNAseq test "found 456 genes significantly changed in lithium responders, while only 40 genes changed in non-responders…It was like there were two completely different groups of individuals." 
 
His team then tested for physiological responses. "Quite remarkably, the lithium-responding patients’ brain cells responded to lithium in a dish, whereas the non-responders weren’t touched" in terms of sodium peaks and currents, and evoked responses and frequencies.
 
Using calcium dyes, which allow monitoring of multiple cells at a time in culture, the group also saw differences in the amount of calcium activity in lithium responders versus non responders. And differences were detected between responders and non -responders to the anti-epileptic, lamotrigine.
 
Gage concluded that psychiatrists think the data may bring relief to patients suffering from the stigma associated with BP. “They are struck that this seems to be an intrinsic, genetic disease. It is likely not a result of poor upbringing if you can detect it in a dish in defined cell types.” 
 
BP can be “genetically and molecularly separated, we think, into two classes, so for the first time you have two functionally different types of patients”: lithium responsive and unresponsive. Hopefully, the field can “use that in a personalized-medicine way to identify, early on, patients who will be refractory to lithium, and to screen them for other drugs.”
 
Gage said the lithium non-responders are now trying anti-epileptics.
 
Date: July 2, 2014
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