Robert Bauchwitz, M.D., Ph.D., Principal Investigator
Qijiang Yan, Ph.D., Postdoctoral Fellow
Columbia University

FRAXA Awards:
  $170,000 in 2006
  $126,000 in 2005
  $107,000 in 2004
  $93,000 in 2003

Dr. Bauchwitz’s work on seizures in Fragile X mice suggests that mGluR5 antagonists may effectively treat a range of symptoms of Fragile X. Much of his current effort is devoted to pre-clinical testing of potential therapeutic agents in the knockout mouse model. These experiments are the essential "proof-of-principle" which will enable pharmaceutical development and human trials of several important new classes of therapeutic compounds for fragile X. This work is enormously labor-intensive, and requires maintenance of the largest colony of fmr1 knockout mice in the world.

by Rob Bauchwitz, 3/2004

mGluR receptors have been implicated in the abnormal neuronal responses observed in Fragile X syndrome. To address whether reversing mGluR signaling alterations might ameliorate the effects of Fragile X, we have tested a drug,MPEP, which specifically blocks one type of group 1 mGluR receptor (mGluR5). Using MPEP, we have been able to reverse the susceptibility that Fragile X mice have to audiogenic seizures, which are triggered by very loud sound.

We have also shown that the degree of rescue is equivalent to that found by placing a copy of the human FMR1 gene into the genome of Fragile X mice, suggesting that MPEP can compensate for lack of FMRP in protecting against audiogenic seizures.We are also testing the effects of mGluR5 antagonists in other learning and behavioral assays. Finally, we are producing new mouse models of Fragile X which might give more robust learning deficits comparable to those observed in humans. If that is the case, we will use such animals to further assess the effectiveness of mGluR antagonists and other compounds on Fragile X cognition.

Our laboratory specializes in the production and study of mouse models of Fragile X, to identify treatments for the disorder in the short term and a cure in the longer term. We have created 15 FMR1 transgenic mouse lines. These mice lack the normal mouse FMR1 gene, but have various portions of the human X chromosome spanning the FMR1 gene inserted into their genome. Our goal is to produce a viable FMR1 sequence for use in human gene therapy for Fragile X syndrome. One of the challenges of gene therapy is to introduce a new gene (transgene) into cells in such a way that it functions precisely like the normal gene, producing the right amount of its protein product, FMRP, at the right time and in the right cells.We aim to find the smallest piece of DNA (the FMR1 gene and regulatory sequences) necessary for the gene to function properly. Our transgenic mice have already given us important information on the acceptable and necessary dose of FMRP which can be present in mice in order to restore function without causing toxicity. These studies are now being extended through cognitive testing of the animals.

We have also continued our extensive molecular and cognitive analysis of the original mouse model for Fragile X, the FMR1 tm1Cgr mutant.We are assessing the effects of novel pharmacologic agents on intelligence in these mice. One agent we are testing is MPEP, which blocks mGluR5, a receptor involved in protein synthesis dependent LTD (long term depression). LTD, a response that neurons can make when stimulated, may be important in Fragile X, since Huber and Bear have recently shown that it is elevated in the Fragile X knockout mouse brain.We are investigating whether blocking the mGluR5 receptor with MPEP in the Fragile X knockout mice makes their behavior more similar to that of their otherwise identical wild type brothers. This is exciting work because MPEP has the potential to be one of the first drugs to provide an enhancement of intellectual function in Fragile X.

REFERENCES
Suppression of two major Fragile X Syndrome mouse model phenotypes by the mGluR5 antagonist MPEP.
Yan QJ, Rammal M, Tranfaglia M, Bauchwitz RP.
Department of Neurology, St. Luke's-Roosevelt Institute for Health Sciences, Columbia University, New York, NY, USA.

Fragile X Syndrome is the most common form of inherited mental retardation worldwide. A Fragile X mouse model, fmr1(tm1Cgr), with a disruption in the X-linked Fmr1 gene, has three substantial deficits observed in several strains: (1) sensitivity to audiogenic seizures (AGS), (2) tendency to spend significantly more time in the center of an open field, and (3) enlarged testes. Alterations in metabotropic glutamate receptor group I signaling were previously identified in the fmr1(tm1Cgr) mouse. In this study, we examined the effect of MPEP, an antagonist of the group I metabotropic glutamate receptor mGluR5, on audiogenic seizures and open field activity of fmr1(tm1Cgr) mice. Genetic analysis revealed synergistic reactions between fmr1(tm1Cgr) and inbred AGS alleles. In addition, AGS sensitivity due to the fmr1(tm1Cgr) allele was restricted during development. Examination of phenotypes combining mGluR5 inhibition and Fmr1 mutation indicated that absence of FMRP may affect mGluR5 signaling through indirect as well as direct pathways. All strains of fmr1(tm1Cgr) mice tested (FVB/NJ, C57BL/6J, and an F1 hybrid of the two) had a more excitable AGS pathway than wild-type, and consequently required more MPEP to achieve seizure suppression. At high doses of mGluR5 antagonists, a Fragile X specific tolerance (loss of drug activity) was observed. The tolerance effect could be overcome by a further increase in drug dose. In open field tests, MPEP reduced fmr1(tm1Cgr) center field behavior to one indistinguishable from wild-type. Therefore, mGluR5 antagonists were able to rescue two of the major phenotypes of the FX mouse. Modulation of mGluR5 signaling may allow amelioration of symptoms of Fragile X Syndrome.

Prolonged epileptiform discharges induced by altered group I metabotropic glutamate receptor-mediated synaptic responses in hippocampal slices of a fragile X mouse model.
Chuang SC, Zhao W, Bauchwitz R, Yan Q, Bianchi R, Wong RK.
Journal of Neuroscience, 2005 Aug 31
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Odor Based Behavioral Tasks Confounded by Distance Dependent Detection: Modification of a Murine Digging Paradigm
KATZ, EMILY and ROTHSCHILD, OLIVER and HERRERA, ANDRIANA and HUANG, SOFIA and WONG, ANNA and WOJCIECHOWSKI, YVETTE and GIL, AIDA and YAN, QI JIANG and BAUCHWITZ, ROBERT (2003)
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