Rett syndrome is a devastating neurological disorder characterized by autism, language skill loss, stereotyped behaviors, motor delays, cognitive deficits, seizures, and breathing abnormalities. Most cases result from mutations in or loss of the protein MeCP2, a transcription factor that binds to methylated CpG regions of DNA. Knockout of MeCP2 in mice recapitulates many Rett phenotypes and re-expression of MeCP2 in adult mouse neurons corrects phenotypic deficits, suggesting that treatments given after disease development may be therapeutically viable. However, children with MeCP2 Duplication syndrome also exhibit significant Rett-like symptoms, indicating that a precise level of MeCP2 is critical for maintaining normal neuronal function. We have found that the gene encoding metabotropic glutamate receptor 7 (GRM7/mGlu7), a receptor which modulates glutamate and GABA release, is positively regulated by MeCP2 both in vitro and in an in vivo Mecp2 knockout mouse model. Importantly, we have found that mGlu7 mRNA and protein levels are significantly decreased in multiple brain areas in Mecp2 KO mice. These results suggest that the GRM7 gene appears to be true and novel target of MeCP2. If correct, we predict that mGlu7 levels will be elevated in mice overexpressing MeCP2, which represent a model for MeCP2 Duplication syndrome. As one function of mGlu7 activation is to decrease glutamate release from presynaptic terminals, we hypothesized that aberrantly decreased levels of mGlu7 in Mecp2 KO mice enhances glutamatergic tone. It has been demonstrated in Mecp2 KO, knock-in, and overexpressing mice that synaptic transmission, as well as long term potentiation, at Schaffer Collateral-CA1 (SC-CA1) synapses is altered. Interestingly, the impairment in each case appears to be mediated, in part, by a presynaptic mechanism, with mice lacking Mecp2 exhibiting reduced paired pulse facilitation, an observation consistent with increased glutamate release from presynaptic terminals. In contrast, mice overexpressing Mecp2 show increases in paired pulse ratios, suggestive of decreased glutamate release. As mGlu7 is the predominant mGlu present at the SC-CA1 synapse in adult animals, these defects in neurotransmission, coupled with our findings that mGlu7 levels are reduced in Mecp2 KO mice, are consistent with a role for presynaptic mGlu7 as a major controller of glutamate release at SC-CA1 synapses, potentially resulting in cognitive deficits seen in these animals. We have confirmed previous results showing that synaptic plasticity and long term potentiation are altered in Mecp2-/y mice and show, importantly, that potentiation of mGlu7 activity can rescue these defects. We propose to test the hypotheses that mGlu7 levels are conversely increased in an MeCP2 Duplication mouse model, further substantiating a role for MeCP2 in mGlu7 gene regulation. Additionally, we will test the hypotheses that modulation of mGlu7 activity using pharmacological tools will normalize synaptic plasticity and behavioral deficits in mice under- and overexpressing the MeCP2 protein.

Public Health Relevance

We have found that the gene encoding metabotropic glutamate receptor 7 (mGlu7) is positively regulated by the transcription factor MeCP2, the causative gene for Rett syndrome, and mGlu7 levels are dramatically decreased in Mecp2 KO mice, potentially contributing to neuronal dysfunction in this disease. We propose to test the hypothesis that mGlu7 levels are conversely increased in an MeCP2 Duplication mouse model, further substantiating a role for MeCP2 in mGlu7 gene regulation. Additionally, we will test the hypotheses that modulation of mGlu7 activity using pharmacological tools will normalize synaptic plasticity and behavioral deficits in mice under- and overexpressing MeCP2.

Agency
National Institute of Health (NIH)
Institute
National Institute of Mental Health (NIMH)
Type
Exploratory/Developmental Grants (R21)
Project #
5R21MH102548-02
Application #
8898219
Study Section
Special Emphasis Panel (ZRG1-MDCN-P (57))
Program Officer
Nadler, Laurie S
Project Start
2014-08-01
Project End
2016-07-31
Budget Start
2015-08-01
Budget End
2016-07-31
Support Year
2
Fiscal Year
2015
Total Cost
$235,363
Indirect Cost
$85,363
Name
Vanderbilt University Medical Center
Department
Pharmacology
Type
Schools of Medicine
DUNS #
004413456
City
Nashville
State
TN
Country
United States
Zip Code
37212
Fisher, Nicole M; Gogliotti, Rocco G; Vermudez, Sheryl Anne D et al. (2018) Genetic Reduction or Negative Modulation of mGlu7 Does Not Impact Anxiety and Fear Learning Phenotypes in a Mouse Model of MECP2 Duplication Syndrome. ACS Chem Neurosci 9:2210-2217
Fisher, Nicole M; Seto, Mabel; Lindsley, Craig W et al. (2018) Metabotropic Glutamate Receptor 7: A New Therapeutic Target in Neurodevelopmental Disorders. Front Mol Neurosci 11:387
Abe, Masahito; Seto, Mabel; Gogliotti, Rocco G et al. (2017) Discovery of VU6005649, a CNS Penetrant mGlu7/8 Receptor PAM Derived from a Series of Pyrazolo[1,5-a]pyrimidines. ACS Med Chem Lett 8:1110-1115
Gogliotti, Rocco G; Senter, Rebecca K; Fisher, Nicole M et al. (2017) mGlu7 potentiation rescues cognitive, social, and respiratory phenotypes in a mouse model of Rett syndrome. Sci Transl Med 9:
Gogliotti, Rocco G; Senter, Rebecca K; Rook, Jerri M et al. (2016) mGlu5 positive allosteric modulation normalizes synaptic plasticity defects and motor phenotypes in a mouse model of Rett syndrome. Hum Mol Genet 25:1990-2004
Lindsley, Craig W; Emmitte, Kyle A; Hopkins, Corey R et al. (2016) Practical Strategies and Concepts in GPCR Allosteric Modulator Discovery: Recent Advances with Metabotropic Glutamate Receptors. Chem Rev 116:6707-41