NMDA receptors, mTOR signaling, synaptic plasticity, epigenetics, autism, Fragile X syndrome, schizophrenia and stroke.

Research in our laboratory addresses molecular and cellular mechanisms underlying neuronal death. A particular focus centers on epigenetic mechanisms that underlie neuronal death in animal models of stroke. We are studying the role of the gene silencing transcription factor REST and REST-dependent epigenetic remodeling of synaptic proteins. We found that REST is activated in response to neuronal insults such as global ischemia and orchestrates epigenetic remodeling of synaptic AMPA receptors. This, in turn, silences expression of the AMPA receptor subunit GluA2. This is significant in that GluA2 is the ion gate-keeper of synaptic AMPA receptors. Thus, loss of GluA2 promotes a switch from Ca2+-impermeable to Ca2+-permeable receptors and neuronal death. We found that REST is causally related to ischemia-induced neuronal death. Using an epigenome-wide search, we identified novel REST targets in the context of ischemia. New directions include 1) REST-dependent epigenetic remodeling and activation of the Kv7 (KCNQ) family of potassium channels implicated in dendritic excitability; and 2) epigenetic remodeling and silencing of microRNAs. Neuron-specific microRNAs silence networks of non-neuronal genes in neurons. We expect this research to have a major impact on amelioration of neuronal death and impaired cognition associated with stroke and AD. To perform this research, we use genetics, electrophysiology, behavior and delivery of engineered cDNA and shRNA constructs directly into the brains of living animals via the lentivirus expression system. We use clinically relevant models of stroke and global ischemia, and transgenic mice in which REST can be conditionally knocked out. A rotation project we are offering involves identification of the signal upstream of the decline in REST in AD.

In another direction, we are studying epigenetic mechanisms that regulate synaptic proteins during postnatal brain development. We discovered that REST is activated in hippocampal neurons in the critical period, a time of heightened plasticity during development.

We showed that REST drives the developmental switch in NMDARs receptors by orchestrating epigenetic modifications at the promoter of the gene encoding the NMDA receptor subunit GluN2B. We found that REST is causally related to the developmental switch. Importantly, adverse experience early in life in the form of maternal deprivation disrupts activation of REST and acquisition of the mature NMDA receptor phenotype. These findings document a role for REST in experience-dependent fine-tuning of genes involved in synaptic plasticity. We recently found that REST abundance in neurons is controlled at the level of protein stability and identified casein kinase 1 as an upstream signal that negatively regulates REST in neurons. New directions include how polycomb repressive proteins affect NMDARs, how miRNA-101 activates polycomb proteins and how DNA methylation ‘locks in’ silencing of REST targets. Findings from this research are expected to enhance our understanding of NMDAR function as it pertains to memory, synaptic stabilization, and cognitive information flow and how adverse experience acts via epigenetics to impair brain development. We are extending studies to mouse models of schizophrenia. A rotation project we are offering involves rescue of brain development in maternally-deprived pups by communal nesting of female mice and their litters.

In a third direction, we are studying mouse models of autism. Fragile X Syndrome is the most common inherited cause of intellectual disabilities and a leading cause of autism. New directions include a focus on mTORC2 and its role in aberrant spine structure and number. We discovered that not only mTORC1, but also mTORC2, is overactivated in the somatosensory cortex of Fragile X mice. We showed that the Rho GTPase Rac1, a downstream target of mTORC2 and its downstream target LIMK are also elevated and causally related to elevated phosphorylation (and blunted activity) of the actin depolymerizing factor cofilin, a major determinant of spine morphology. We rescued impaired cofilin signaling and spine abnormalities pharmacologically by administration of a small molecule inhibitor of PAK1 and genetically by viral delivery of a constitutively active cofilin mutant (cofilin-S3A) into the somatosensory cortex of neonatal Fragile X mice. These findings suggest a causal relationship between enhanced Rac1-cofilin signaling, synaptic defects, and impaired sensory processing in FXS and uncover a previously unappreciated role for impaired Rac1-cofilin signaling in the aberrant spine morphology and spine density associated with FXS. A rotation project could examine the impact of dysregulated cofilin signaling on contextual learning and cognition and a role for mTOR complex 2 in regulation of spine structure and cognition.

In another direction, we discovered that AMPAR receptor mRNA targeting to dendrites and transcription are under the control of the memory protein CPEB3. CPEB3 is elevated and causally related to elevated GluA2 mRNA in dendrites and at transcription sites in hippocampal neurons of Fragile X mice. We show that CPEB3 localizes to the gria2 promoter where it promotes active transcription of GluA2 through its interaction with STAT5b, an effect that is augmented in FXS neurons. The increase in GluA2 transcription is translated into an increase in GluA2 expression and switch in AMPAR phenotype from GluA2-lacking to GluA2-containing at excitatory synapses onto inhibitory interneurons. The switch in synaptic AMPAR phenotype could potentially alter the inhibitory to excitatory balance, an important theme in autism spectrum disorders. New directions for rotation students include the impact of CPEB3 on synaptic plasticity at inhibitory synapses and autism-relevant behaviors.

(From a total of 194 peer-reviewed papers and 41 book chapters)

Gompers A, Hwang J-Y, Monday HR, Buxbaum A, Yan J, Sawicka K, Castillo PE, Singer RH, Zukin RS The memory protein CPEB3 reduces synaptic incorporation of Ca2+-permeable AMPARs and loss of anti-Hebbian LTP at synapses onto inhibitory interneurons in Fragile X mice. Nat Neurosci, in review, 2017.

Yan J, Porch WM, Court-Vazquez B, Bennett MV, Zukin RS Activation of autophagy rescues synaptic and cognitive deficits in Fragile X mice Proc. Natl. Acad. Sci. USA, 2018. PMID:30242133.

Hwang JY, Zukin RS REST, a master transcriptional regulator in neurodegenerative disease. Curr Opin Neurobiol. 48:193-200, 2018. PMID:29351877.

Pyronneau A, Qionger H, Hwang J-Y, Contractor A, Zukin RS Enhanced Rac1/cofilin signaling is critical to dendritic spine defects, synaptic dysfunction and impaired sensory perception in Fragile X Syndrome. Sci Signal 10: pii: eaan0852, 2017. PMID:29114038.

Hwang J-Y, Aromolaran KA, Zukin RS The emerging field of epigenetics in neurodegeneration and neuroprotection. Nat Rev Neurosci 18:347-361, 2017. PMID: 28515491

Hwang J-Y, Gertner MJ, Pontarelli F, Bennett MVL, Ofengeim D, Zukin RS Global ischemia induces lysosomal-mediated degradation of mTOR and activation of autophagy in hippocampal neurons destined to die. Cell Death Differ 24:317-329, 2017. PMID: 27935582

Sawicka K, Pyronneau A, Chao M, Bennett MV, Zukin RS Elevated ERK/p90 ribosomal S6 kinase activity underlies audiogenic seizure susceptibility in fragile X mice. Proc Natl Acad Sci USA 113:E6290-E6297, 2016. PMID: 27663742

Choi CH et al., Multiple drug treatments that increase cAMP signaling restore long-term memory and aberrant signaling in Fragile X syndrome models. Front Behav Neurosci 10:136-142. 2016. PMID:27445731

Puckerin A, Aromolaran KA, Chang DD, Zukin RS, Colecraft HM, Boutjdir M, Aromolaran AS. hERG 1a LQT2 C-terminus truncation mutants display hERG 1b-dependent dominant negative mechanisms. Heart Rhythm. 13:1121-30, 2016. PMID: 26775140

Huber KM, Klann E, Costa-Mattioli M, Zukin RS. Dysregulation of Mammalian Target of Rapamycin Signaling in Mouse Models of Autism. J Neurosci. 35:13836-42, 2015. PMID: 26468183

Tamminga CA, Zukin RS. Schizophrenia: Evidence implicating hippocampal GluN2B protein and REST epigenetics in psychosis pathophysiology. Neuroscience. 309:233-42, 2015. PMID: 26211447

Choi CH et al., PDE-4 inhibiton rescues aberrant synaptic plasticity in Drosophila and mouse models of fragile X syndrome. J Neurosci 35:396-408, 2015. PMID: 25568131

Takeuchi K*, Yang Y*, Takayasu Y, Gertner M, Hwang J-Y, Aromolaran KA, Bennett MVL, Zukin RS. Estradiol pretreatment ameliorates impaired synaptic plasticity at synapses of insulted CA1 neurons after transient global ischemia. Brain Res 1621:222-30, 2015. PMID: 25463028

Hwang JY, Kaneko N, Noh KM, Pontarelli F, Zukin RS. The Gene Silencing Transcription Factor REST represses miR-132 expression in Hippocampal Neurons Destined to Die. J Mol Biol 426:3454-66, 2014. PMID: 25108103

Kaneko N, Hwang J-Y, Gertner M, Pontarelli F, Zukin RS. Casein kinase 1 suppresses activation of REST in insulted hippocampal neurons and halts ischemia-induced neuronal death. J Neurosci, 34:6030-9, 2014. PMID: 24760862

Murphy J*, Stein IS*, Lau GC, Peixoto R, Kaneko N, Aromolaran K, Saulnier J, Sabatini BL, Hell JW, Zukin RS. Phosphorylation of Ser1166 on GluN2B by PKA is critical to synaptic NMDA receptor function and Ca²⁺ signaling in spines. J Neurosci, 34:869-879, 2014. PMID: 24431445

Sehara Y, Sawicka K, Hwang JY, Latuszek-Barrantes A, Etgen AM, Zukin RS. Survivin is a transcriptional target of STAT3 critical to estradiol neuroprotection in global ischemia. J Neurosci 33:12364-74, 2013. PMID: 23884942

Takeuchi K, Gertner MJ, Zhou J, Parada LF, Bennett MVL, Zukin RS. Dysregulation of synaptic plasticity precedes morphological defects in a Pten conditional knockout mouse model of autism. Proc Natl Acad Sci USA 110:4738-43, 2013. PMID: 23487788

Rodenas-Ruano A, Chávez AE, Cossio MJ, Castillo PE, Zukin RS. REST-dependent epigenetic remodeling drives the developmental switch in synaptic NMDA receptors in vivo. Nat Neurosci 15:1382-90, 2012. PMID: 22960932

Udagawa T, Swanger SA, Takeuchi K, Kim JH, Nalavadi V, Shin J, Lorenz LJ, Zukin RS, Bassell GJ, Richter JD. Bidirectional control of mRNA translation and synaptic plasticity by the cytoplasmic polyadenylation complex. Mol Cell 47:253-66, 2012. PMID: 22727665

Noh KM*, Hwang JY*, Follenzi A, Athanasiadou R, Miyawaki T, Greally JM, Bennett MVL, Zukin RS. Repressor element-1 silencing transcription factor (REST)-dependent epigenetic remodeling is critical to ischemia-induced neuronal death. Proc Natl Acad Sci USA 109:E962-71, 2012. PMID: 22371606

Hoeffer CA, Sanchez E, Hagerman RJ, Mu Y, Nguyen DV, Wong H, Whelan AM, Zukin RS, Klann E, Tassone F. Altered mTOR signaling and enhanced CYFIP2 expression levels in subjects with fragile X syndrome. Genes Brain Behav 11:332-341, 2012. PMID: 22268788

Ofengeim D, Chen YB, Miyawaki T, Li H, Sacchetti S, Flannery RJ, Alavian KN, Pontarelli F, Roelofs BA, Hickman JA, Hardwick JM, Zukin RS, Jonas EA. N-terminally cleaved Bcl-x(L) mediates ischemia-induced neuronal death. Nat Neurosci 15:574-80, 2012. PMID: 22366758

Paek H, Hwang J-Y, Zukin RS, Hébert JM. β-catenin-dependent FGF signaling maintains cell survival in the anterior embryonic head by countering Smad4. Dev Cell 20:689-99, 2011. PMID: 21571225

Philpot BD, Zukin RS. Synapse-specific metaplasticity: to be silenced is not to silence 2B. Neuron 66:814-6, 2010. PMID: 20620866

Liu Y, Formisano L, Savtchouk I, Takayasu Y, Szabò G, Zukin RS, Liu SQJ. A single fear-inducing stimulus induces a transcription-dependent switch in synaptic AMPA receptor phenotype. Nat Neurosci 13:223-31, 2010. PMID: 20037575

Sharma A, Hoeffer C, Takayasu Y, Miyawaki T, McBride SM, Klann E, Zukin RS. Dysregulation of mTOR signaling in the Fragile X mouse. J Neurosci 30:694-702, 2010. PMID: 20071534

Lau CG, Takayasu Y, Rodenas-Ruano A, Paternain AV, Lerma J, Bennett MVL, Zukin RS. SNAP-25 is a target of PKC phosphorylation critical to NMDA receptor trafficking. J Neurosci 30:242-54, 2010. PMID: 20053906

Takayasu Y, Kumari R*, Takeuchi K*, Bennett, MVL, Zukin RS, Francesconi A. Caveolin-1 knockout mice exhibit impaired induction of mGluR-dependent long-term depression at CA3-CA1 synapses. Proc Natl Acad Sci USA 107:21778-83, 2010. PMID: 21098662

Huang YH, Lin Y, Mu P, Lee BR, Brown TE, Wayman G, Marie H, Liu W, Yan Z, Sorg BA, Schluter OM, Zukin RS, Dong Y. In vivo cocaine experience generates nascent synapses. Neuron 63:40-7, 2009. PMID: 19607791

Miyawaki T*, Ofengeim D*, Noh K-M, Latuszek-Barrantes A, Hemmings BA, Follenzi A, Zukin RS. The endogenous inhibitor of Akt, CTMP, is critical to ischemia-induced neuronal death. Nat Neurosci 12:618-26, 2009. PMID: 19349976

Lau CG, Zukin RS. NMDA receptor trafficking in synaptic plasticity and neuropsychiatric disorders. Nat Rev Neurosci 8:413-26, 2007. PMID: 17514195

Liu, S-QJ, Zukin RS. Ca²⁺-permeable AMPA receptors in synaptic plasticity and neuronal death. Trends Neurosci 30:126-34, 2007. PMID: 17275103

Grooms SY*, Noh K-M*, Regis R, Bassell GJ, Bryan MK, Carroll RC, Zukin RS. Activity bidirectionally regulates AMPAR mRNA abundance in dendrites of hippocampal neurons. J Neurosci 26:8339-51, 2006. PMID: 16899729

Skeberdis VA, Chevaleyre V, Lau CG, Goldberg JH, Pettit DL, Suadicani SO, Lin Y, Bennett MV, Yuste R, Castillo PE, Zukin RS. PKA regulates calcium permeability of NMDA receptors. Nat Neurosci 9:501-10, 2006. PMID: 16531999

Lan J-Y, Skeberdis VA, Jover T, Grooms SY, Lin Y, Araneda RC, Zheng X, Bennett MVL, Zukin RS. Protein kinase C modulates NMDA receptor trafficking and gating. Nat Neurosci 4: 382-390, 2001. PMID: 11276228