GRIK2 & Bipolar Disorder Ashley Bateman

Bipolar Disorder (BPD) Manic-depressive disorder Extreme and unusual shifts in mood, energy, and ability to function Damages relationships & performance Often ends in suicide Affects > 5 million Americans, 3 in 100 adults

Diagnosis

Major Depressive Episode Persistent feelings of: Sadness Anxiety Guilt Anger Isolation Hopelessness Disturbances in sleep and appetite Fatigue and loss of interest in sexual activity Irritability Lack of motivation Morbid suicidal ideation

Manic Episode Distinct period of: Elevated, expansive, irritable mood state Racing thoughts Low attention span Easily distracted Impaired judgment Spending sprees, unusual behavior Substance abuse (esp. alcohol, stimulants) Aggressive behavior Increased sexual drive

Famous People with BPD Hollywood: Britney Spears Jim Carey Robert Downey Jr. Linda Hamilton Vivien Leigh Ben Stiller Robin Williams Richard Dreyfuss Marilyn Monroe Tim Burton Francis Ford Coppola Musicians: Beethoven Mozart DMX Jimi Hendrix Axl Rose Sting Brian Wilson Kurt Cobain Ozzy Ozbourne Politicians: Winston Churchill Theodore Roosevelt Abraham Lincoln Napoleon Bonaparte Writers: Edgar Allen Poe Mark Twain Virginia Woolf Charles Dickens Ralph Waldo Emerson F. Scott Fitzgerald Ernest Hemingway Kurt Vonnegut Emily Dickinson T.S. Eliot Hans Christian Anderson Victor Hugo

Scientists: Sir Isaac Newton Florence Nightingale Sigmund Freud Plato Charles Darwin!

Genetic Cause of BPD? Many chromosomal regions and candidate genes appear to relate to the development of BPD Inconsistent results and scattered focus, results not replicated Epigenetics & environment? Heritability =

Part 1 Understand Gene & Protein

GRIK2 (humans) Neurological Correlates: The Neuroscience of Dysfunctional Behavior. Image retrieved on February 3rd, Localized on chromosome 6 Glutamate, Receptor, Ionotropic, Kainate 2 Glutamate ligand Excitatory and inhibitor neurotransmission GluR6 subunit mutation impairs binding site Arrows indicate gluR6 mutation sites

Isoforms 2nd variant: additional exon at the 3’ end Frameshift & early translation termination Shorter with distinct C-terminus GRIK2 gene: bp GRIK2 coding mRNA: 4550 bp

Gene function: Ontology GO Consortium Biological process Cellular component & molecular function Glutamate signaling pathway, kainate selective glutamate receptor activity Neuronal transmission events: synaptic transmission and plasticity Cell death & apoptosis

GRIK2 Homologs

GRIK2 homologues: Phylogeny Multiple alignment using Muscle & Tcoffee Phylogeny created using Phylogeny.fr

Protein Motifs PFAM/SMART Identical result for every species’ sequence query Highly conserved nature of putative functional domains

Localization in the Cell Based on what we know about receptor function, should be localized to the plasma membrane ESLpred: nucleus??? TargetP: secretory pathway signal peptide (SP) LOCATE: secreted protein? & type I membrane protein & multipass membrane protein pTARGET: 100% confidence = plasma membrane

Protein Networks

Key Protein Players PSD95 GRIP1 PICK1 SDCBP KLHL17 KIF17 GRIK4 PRKAA1 FOS SENP1 Interacts at postsynaptic sites, form scaffold Glutamate Receptor Interacting Protein: localized scaffold, mediation of trafficking of binding partners Protein Interacting w/ Protein Kinase C: adaptor that organizes subcellular location of membrane proteins Scaffold Protein Periplasmic Binding Protein: binds the C- terminal domains of transmembrane proteins May play a role in neuronal function Kinesin Family Member: transports NMDA vesicles Glutamate Receptor, Ionotropic, Kainate 4: excitatory neurotransmitter at synapses in CNS Protein Kinase, AMP-activated, Alpha1 subunit: cellular energy sensor conserved in all eukaryotic cells Switch Regulatory Protein, associated with apoptotic cell death Sentrin/SUMO-specific protease: covalent modification of proteins by the small ubiquitin-like protein SUMO

Part 2 Phenotypic Studies

Primary Literature Very few studies done on phenotype of GRIK2 mutant, other putative genes for BPD

Rationale Recent human genetic studies: GRIK2 as potential BPD susceptibility gene Genetic linkage of BPD to chromosome 6 Genome-wide significant linkage est. by meta-analysis Specific haplotype associated with BPD Post-mortem studies Expression of kainate receptors in areas for mood regulation

Study Questions 1.Used GluR6 KO mice in behavioral tests to elucidate role of GRIK2 receptor in regards to phenotypic patterns of BPD 2. Determine potential specificity of this receptor (receptor control = GluR5) 3.Effects of lithium on GluR6 KO mice 4.Biochemical tests

Behavioral Tests Passive-avoidance test Open-field test Monitoring home cage activity Social interaction test Elevated plus-maze test Forced swim test Resident intruder test Same tests done with amphetamine & lithium

Lithium Results Specific biochemical mechanism of action in mania unknown Reduced spontaneous locomotor activity Decreased aggressive behavior Decreased activity in anxiety-provoking regions Effect on elevated plus maze test Reduced immobility time in forced swim test summary/summary.cgi?cid=11125 &loc=ec_rcshttp://dailymed.nlm. nih.gov/dailymed/drugInfo.cfm?i d=401

Amphetamine Results GluR6 KO mice: exhibited more spontaneous activity more responsive to amphetamine more aggressive less anxious/more risk- taking behavior less immobility in forced swim test

Future Directions Mice mutant KO of other putative BPD genes RNAi difficult because of neuronal tissue TAP tags for protein complexes of GRIK2 More (repeated) genetic linkage and mapping studies of bipolar families Role of lithium MORE RESEARCH!