Peter Vanderklish, Ph.D.
Principal Investigator
Scripps Research Institute, San Diego, CA

FRAXA Awards:
  $50,000 in 2007
  $80,000 in 2006
  $50,000 in 2005
  $95,000 in 2004


update by Michael Tranfaglia, FRAXA, 3/2007

This research group at Scripps is using the most sophisticated proteomic techniques currently available to understand exactly how the absence of FMRP affects levels of other proteins in neurons. "Our proteomic work is motivated by the fact that the most critical gap in our understanding of the molecular basis of FXS resides in the identification of proteins that are dysregulated in the absence of FMRP. Studies of the mRNAs associated with FMRP suggest that it regulates the synthesis of several proteins that can affect synaptic structure and function. However, the number of validated changes in proteins is relatively small compared to the estimated number of FMRP target mRNAs, and there is as yet no reliable way to estimate protein changes from mRNA data. In addition, mRNA methods are not sensitive to potential changes in proteins encoded by mRNAs that are not FMRP targets. Given these and other considerations, it is likely that many more protein changes are critically involved in producing the synaptic alterations seen in FXS."

This investigation has already led to identification of several proteins that may contribute to the abnormalities in synaptic shape seen in fragile X and also a few proteins which have been implicated in autism. One protein presents a potential opportunity for therapeutic intervention with drugs taht are currently in clinical trials for unrelated indications.

Before he became a Fragile X investigator, Dr. Peter Vanderklish had demonstrated that activation of group I metabotropic glutamate receptors (mGluR1 and mGluR5) could cause rapid changes in dendritic spine shape. In as little as 15 minutes, spines of cultured neurons could become long, thin, and immaturelooking. Since this shape is characteristic of the spine shape previously seen in Fragile X brains, this would appear to support the notion that excessive function of these mGluR pathways might be the primary pathology in Fragile X.

Since 2003 when Dr.Vanderklish attended a Fragile X Banbury meeting, he has been studying neurons from the Fragile X knockout mouse in great depth. Initial studies in his lab have shown therapeutic effects of MPEP (the prototype mGluR5 antagonist) in his model system. One of the most intriguing aspects of this line of inquiry is that it strongly suggests that some structural changes seen in Fragile X brains may not only be treatable, but may reverse surprisingly rapidly with specific treatment.

by Pete Vanderklish, 3/2004

Our Previous Work

Consistent with the mGluR theory (see Mark Bear's abstract ), we observed that stimulation of mGluRs leads to elongation of dendritic spines. These changes in dendritic spine shape are dependent on protein synthesis and resemble those that occur in the Fragile X brain. Interestingly, multiple lines of evidence indicate that LTD and spine elongation are mechanistically linked; that is, that longer, thinner spines express the depressed synaptic state. Thus, altered synaptic plasticity and morphology (shape) may result from the same translation-dependent process that, once induced, is not properly limited in the Fragile X brain. As the saying goes, form follows function.

Our 2004-5 Project

We are testing three predictions of the mGluR theory:

1. Mark Bear and Kim Huber have already shown that LTD is enhanced in mice lacking FMRP. We predict that mGluR-induced spine elongation should be exaggerated in these mice. We are using live-cell imaging techniques to test this possibility and the ability of candidate pharmacological therapies for Fragile X, such as Ampakines and MPEP, to correct any imbalances.

2.We have evidence that two modes of translation initiation operate in dendrites (CAP-dependent and IRESdependent), and that stimulation of mGluRs primarily activates just one of these (cap-dependent). The mGluR hypothesis predicts that lack of FMRP increases CAP-dependent translation; we are testing to see if this is true.

3. Finally, we are testing whether preponderance of long, thin, and presumably lower efficacy, synapses in the Fragile X brain leads to compensatory changes in neurons. Recent research has shown that neurons adapt to deficits in net input by lowering firing thresholds and altering a number of intrinsic properties. If long, thin spines reduce net synaptic input, we would expect to see such changes, and they could underlie a number of symptoms of Fragile X. We are characterizing the intrinsic properties of neurons in the cortex and hippocampus of mice lacking FMRP. If differences are found with respect to control animals, this system could provide a testbed to see if potential therapeutic drugs (such as Ampakines and MPEP) can restore basic neuronal properties to their normal state.