The schizophrenia associated BRD1 gene regulates behavior, neurotransmission, and expression of schizophrenia risk enriched gene sets in mice

BackgroundThe schizophrenia-associated BRD1 gene encodes a transcriptional regulator whose comprehensive chromatin interactome is enriched with schizophrenia risk genes. However, the biology underlying the disease association of BRD1 remains speculative.MethodsThis study assessed the transcriptional drive of a schizophrenia-associated BRD1 risk variant in vitro. Accordingly, to examine the effects of reduced Brd1 expression, we generated a genetically modified Brd1+/- mouse and subjected it to behavioral, electrophysiological, molecular, and integrative genomic analyses with focus on schizophrenia-relevant parameters.ResultsBrd1+/- mice displayed cerebral histone H3K14 hypo-acetylation and a broad range of behavioral changes with translational relevance to schizophrenia. These behaviors were accompanied by striatal dopamine/serotonin abnormalities and cortical excitation-inhibition imbalances involving loss of parvalbumin immunoreactive interneurons. RNAseq analyses of cortical and striatal micropunches from Brd1+/- and wild-type mice revealed differential expression of genes enriched for schizophrenia risk including several schizophrenia GWAS risk genes (e.g. calcium channel subunits (Cacna1c and Cacnb2), cholinergic muscarinic receptor 4 (Chrm4), dopamine receptor D2 (Drd2), and transcription factor 4 (Tcf4)). Integrative analyses further found differentially expressed genes to cluster in functional networks and canonical pathways associated with mental illness and molecular signaling processes (e.g. glutamatergic, monaminergic, calcium, cAMP, DARPP-32, and CREB signaling).ConclusionsOur study bridges the gap between genetic association and pathogenic effects and yields novel insights into the unfolding molecular changes in the brain of a new schizophrenia model that incorporates genetic risk at three levels: allelic, chromatin interactomic, and brain transcriptomic

Plasticity of postsynaptic, but not presynaptic, GABA \u3c inf\u3e B receptors inSSADH deficient mice

Succinic semialdehyde dehydrogenase (SSADH) deficiency is an autosomal-recessively inherited disorder of γ-aminobutyrate (GABA) catabolism characterized by ataxia and epilepsy. Since SSADH is responsible for GABA break-down downstream of GABA transaminase, patients manifest high extracellular levels of GABA, as well as the GABAB receptor (GABABR) agonist γ-hydroxybutyrate (GHB). SSADH knockout (KO) mice display absence seizures, which progress into lethal tonic-clonic seizures at around 3weeks of age. It is hypothesized that desensitization of GABABRs plays an important role in the disease, although detailed studies of pre- and postsynaptic GABABRs are not available. We performed patch-clamp recordings from layer 2/3 pyramidal neurons in neocortical brain slices of wild-type (WT) and SSADH KO mice. Electrical stimulation of GABAergic fibers during wash in of the GABABR agonist baclofen revealed no difference in presynaptic GABABR mediated inhibition of GABA release between WT and SSADH KO mice. In contrast, a significant decrease in postsynaptic baclofen-induced potassium currents was seen in SSADH KO mice. This reduction was unlikely to be caused by accumulation of potassium, GABA or GHB in the brain slices, or an altered expression of regulators of G-protein signaling (RGS) proteins. Finally, adenosine-induced potassium currents were also reduced in SSADH KO mice, which could suggest heterologous desensitization of the G-protein dependent effectors, leading to a reduction in G-protein coupled inwardly rectifying potassium (GIRK) channel responses. Our findings indicate that high GABA and GHB levels desensitize postsynaptic, but not certain presynaptic, GABABRs, promoting a decrease in GIRK channel function. These changes could contribute to the development of seizures in SSADH KO mice and potentially also in affected patients. © 2010 Elsevier Inc

Presynaptic plasticity as a hallmark of rat stress susceptibility and antidepressant response.

Two main questions are important for understanding and treating affective disorders: why are certain individuals susceptible or resilient to stress, and what are the features of treatment response and resistance? To address these questions, we used a chronic mild stress (CMS) rat model of depression. When exposed to stress, a fraction of rats develops anhedonic-like behavior, a core symptom of major depression, while another subgroup of rats is resilient to CMS. Furthermore, the anhedonic-like state is reversed in about half the animals in response to chronic escitalopram treatment (responders), while the remaining animals are resistant (non-responder animals). Electrophysiology in hippocampal brain slices was used to identify a synaptic hallmark characterizing these groups of animals. Presynaptic properties were investigated at GABAergic synapses onto single dentate gyrus granule cells. Stress-susceptible rats displayed a reduced probability of GABA release judged by an altered paired-pulse ratio of evoked inhibitory postsynaptic currents (IPSCs) (1.48 ± 0.25) compared with control (0.81 ± 0.05) and stress-resilient rats (0.78 ± 0.03). Spontaneous IPSCs (sIPSCs) occurred less frequently in stress-susceptible rats compared with control and resilient rats. Finally, a subset of stress-susceptible rats responding to selective serotonin reuptake inhibitor (SSRI) treatment showed a normalization of the paired-pulse ratio (0.73 ± 0.06) whereas non-responder rats showed no normalization (1.2 ± 0.2). No changes in the number of parvalbumin-positive interneurons were observed. Thus, we provide evidence for a distinct GABAergic synaptopathy which associates closely with stress-susceptibility and treatment-resistance in an animal model of depression

Frequency of spontaneous IPSCs in dentate gyrus granule cells is reduced in stress-susceptible, but not in stress-resilient, rats.

<p>A. sIPSC traces recorded in the presence of kynurenic acid (3 mM) to block ionotropic glutamate receptors (V_hold-70 mV). B. Histogram displaying the significant (<i>P</i> < 0.05) reduction in frequency of sIPSCs in stress-susceptible rats (n = 35 cells/10 rats), but not stress-resilient rats (n = 41 cells/9 rats).</p

Paired-pulse depression of evoked IPSCs turns into facilitation in stress-susceptible, but not stress-resilient, rat dentate gyrus granule cells.

<p>A. Evoked GABA_A receptor mediated IPSCs showing paired-pulse behavior in granule cells from unchallenged control, stress-susceptible and stress-resilient rats. Traces are averages of 10–15 sweeps. B. Line plot depicting the paired-pulse ratio at different inter-pulse intervals (50, 500 and 1000 ms) in the three groups. C. Bar graph showing the significant differences (<i>P</i> < 0.05) between control (n = 23 cells/6 rats), stress-susceptible (n = 21 cells/6 rats) and stress-resilient (n = 18 cells/6 rats) at a paired-pulse interval of 50 ms. Susceptible rats show paired-pulse facilitation, indicating a reduction in GABA release probability, while resilient rats are similar to control. D. Sucrose consumption for controls (circles), stress-resilients (triangles) and stress-susceptible (squares).</p

No difference in number of parvalbumin-positive interneurons in dentate gyrus between control, stress-susceptible and stress-resilient rats.

<p>A. Immunostainings of parvalbumin-positive interneurons in rat dentate gyrus of control, stress-susceptible and stress-resilient animals (R, rostral; L, lateral). B. Histogram displaying the number of cells per section in the granule cell layer or hilus, and the total number. No significant differences (<i>P</i> > 0.05) were found between the groups (PARV+: parvalbumin-positive).</p

Miniature inhibitory postsynaptic currents (mIPSCs) are similar in control, stress-susceptible and-resilient rats.

<p>Miniature IPSCs (mIPSCs) reflect functional properties of single GABAergic synapses under conditions of unitary GABA vesicle release, achieved by blocking action potentials with 1 μM tetrodotoxin (TTX). A. Traces displaying the average mIPSC waveform in unchallenged control, stress-susceptible and stress-resilient animals. B. Average mIPSC parameters including frequency, amplitude, decay time constants and 10–90% rise-time showed no differences (<i>P</i> > 0.05) between groups (control n = 13 cells/4 rats; stress-susceptible n = 19 cells/4 rats; resilient n = 11 cells/4 rats), indicating that synaptic GABA_A receptor properties in granule cells are unaltered following CMS.</p

Treatment for 8 weeks with escitalopram restores paired-pulse ratio and sIPSC frequency in a responder subset of stress-susceptible animals.

<p>A. Average traces of evoked IPSCs showing paired-pulse depression in responder (n = 9 cells/3 rats) and paired-pulse facilitation in non-responder (n = 18 cells/5 rats) animals. B. Line plot displaying different inter-pulse intervals (50, 500 and 1000 ms) in responder and non-responder animals. Dashed line indicates a paired-pulse ratio of 1. C. Histogram depicting the significant difference (<i>P</i> < 0.05) between responder and non-responder in the paired-pulse ratio with a 50 ms inter-stimulus interval. It is noteworthy that non-responder rats showed values not significantly different to stress-susceptible rats. Dashed line indicates the control value. D. sIPSCs recorded from responder (n = 43 cells/11 rats) and non-responder rats (n = 20 cells/6 rats). E. Histogram showing the significant (<i>P</i> < 0.05) recovery in responder animals compared with non-responders, which maintained a low sIPSC frequency similar to stress-susceptible rats. F. Relative sucrose consumption in the three groups.</p