A March 2008 paper by Soong Ho Kim, Julie Markham, Ivan Jeanne Weiler, and Greenough in the Proceedings of the National Academy of Sciences titled Aberrant early-phase ERK inactivation impedes neuronal function in fragile X syndrome reported on their discovery of the role the enzyme ERK plays in the synaptic development processes that are disabled in those afflicted with Fragile X.
Greenough believes that because of that role, ERK can be used as a marker, or reporter, for testing the efficacy of drug therapies for treating FXS, the most common cause of inherited mental impairment and the most common known cause of autism. He said there currently are no effective drug treatments for Fragile X syndrome, so the lab's findings regarding ERK could be beneficial for creating new drugs for FXS or for testing drugs now used to treat other mental disorders, like the antidepressant lithium chloride, that might also prove effective for FXS.
"It would be nice to give a treatment and have some kind of immediate feedback that says yes the treatment is doing what you expected it to do," Greenough said. "A marker or a reporter that provides feedback as to the efficacy of drug treatment of Fragile X syndrome, I think will be very, very valuable."
In the paper the authors propose that "overactivation of phosphatases in synapses may be a key deficit in FXS, which affects synaptic translation, transcription, and synaptic receptor regulation."
Fragile X syndrome occurs when there is a lack of production of FMRP, deactivating the process which forms mature synapses. Greenough lab researcher Ivan Jeanne Weiler said their discovery that hyperactive enzymes disable the intricate process of balancing activation and deactivation that is required for RNA translation and production of synapses is a novel finding.
"What we have found is that one of the reasons that an enzyme is not activated properly in the Fragile X patients is that they have a hyperactive enzyme which is just continuously deactivating it all the time," she said. "The Fragile X protein has the function of binding a set of over 100 messenger RNAs, transporting them in the cell, and regulating protein production, synthesis, and translation. Of these 100 quite a few are cellular enzymes and if those are not transported to the right place or not translated at the right time and place, then this balance is going to be out of kilter. Then it's going to have multiple effects on the cell. One is going to be that receptors are at a lower level, enzyme cascade is less effective, and (there is) less maturation of synapses."
You can read the paper here.
Greenough's lab also produced a May 2008 paper for the American Journal of Medical Genetics titled Early phase ERK activation as a bio-marker for metabolic status in Fragile X syndrome with Ning Weng as the lead author. It reported on a method for comparing normal cells with Fragile X cells using lymphocytes from the blood of the human immune system. Since using a human brain for experimental purposes is not possible, blood from the immune system provides another method for testing metabolic processes related to Fragile X.
"It turns out that the immune system shares a lot of signaling proteins with the brain and access to the immune system, among other ways, is through the blood," Greenough said. "You can study lymphocytes in affected people or animal models and actually look at what is going on in enzymatic pathways in the brain."
The process requires selectively purifying lymphocytes, then staining them with an antibody to activated enzyme that has a color that can be seen in a cell sorter, which gives a count as to how many cells have changed enzyme activity. The results show that in untreated Fragile X patients, cells have slower enzyme activation versus cells from normal patients, confirming that ERK appears to be a promising reporter.
The paper states that this is the "first technique using kinetic analysis of the early phases of ERK activation to establish metabolic differences between lymphocytes from FXS patients and unaffected subjects. Measurement of the early-phase ERK activation response is particularly well qualified to quantify an imbalance of enzymes in a coordinated pathway in suspected cases of FXS and possibly other related syndromes, and might serve as well as an indicator for changes in responsiveness, for example as a result of treatment by pharmacological agents."