Case-control association study of GRIA1, GRIA2 and GRIA4 polymorphisms in bipolar disorder

A comparison of anatomic and cellular transcriptome structures across 40 human brain diseases

Genes associated with risk for brain disease exhibit characteristic expression patterns that reflect both anatomical and cell type relationships. Brain-wide transcriptomic patterns of disease risk genes provide a molecular-based signature, based on differential co-expression, that is often unique to that disease. Brain diseases can be compared and aggregated based on the similarity of their signatures which often associates diseases from diverse phenotypic classes. Analysis of 40 common human brain diseases identifies 5 major transcriptional patterns, representing tumor-related, neurodegenerative, psychiatric and substance abuse, and 2 mixed groups of diseases affecting basal ganglia and hypothalamus. Further, for diseases with enriched expression in cortex, single-nucleus data in the middle temporal gyrus (MTG) exhibits a cell type expression gradient separating neurodegenerative, psychiatric, and substance abuse diseases, with unique excitatory cell type expression differentiating psychiatric diseases. Through mapping of homologous cell types between mouse and human, most disease risk genes are found to act in common cell types, while having species-specific expression in those types and preserving similar phenotypic classification within species. These results describe structural and cellular transcriptomic relationships of disease risk genes in the adult brain and provide a molecular-based strategy for classifying and comparing diseases, potentially identifying novel disease relationships.

The black sheep of the family- whole-exome sequencing in family of lithium response discordant bipolar monozygotic twins

Twin studies are among the most promising strategies for studying heritable disorders, including bipolar disorder (BD). The aim of the present study was to identify distinguishing genes between monozygotic (MZ) twins with different BD phenotype and compare them to their non-affected siblings. Whole-exome sequencing (WES) can identify rare and structural variants that could detect the polygenetic burden of complex disorders. WES was performed on a family composed of two MZ twins with BD, their unaffected brother and unaffected parents. The twins have a discordant response to lithium and distinct course of illness. Following WES, six genes of particular interest emerged: Neurofibromin type 1 (NF1), Biorientation of chromosomes in cell division 1 (BOD1), Golgi-associated gamma adaptin ear-containing ARF binding protein 3 (GGA3), Disrupted in schizophrenia 1 (DISC1), Neuromedin U receptor 2 (NMUR2), and Huntingtin interacting protein 1-related (HIP1R). Interestingly, many of these influence glutamatergic pathways and thus the findings may have therapeutical implications. These results may provide important insights to unveil genetic underpinnings of BD and the response to lithium.

Persistent accumulation of unrepaired DNA damage in rat cortical neurons: nuclear organization and ChIP-seq analysis of damaged DNA

Neurons are highly vulnerable to DNA damage induced by genotoxic agents such as topoisomerase activity, oxidative stress, ionizing radiation (IR) and chemotherapeutic drugs. To avert the detrimental effects of DNA lesions in genome stability, transcription and apoptosis, neurons activate robust DNA repair mechanisms. However, defective DNA repair with accumulation of unrepaired DNA are at the basis of brain ageing and several neurodegenerative diseases. Understanding the mechanisms by which neurons tolerate DNA damage accumulation as well as defining the genomic regions that are more vulnerable to DNA damage or refractory to DNA repair and therefore constitute potential targets in neurodegenerative diseases are essential issues in the field. In this work we investigated the nuclear topography and organization together with the genome-wide distribution of unrepaired DNA in rat cortical neurons 15 days upon IR. About 5% of non-irradiated and 55% of irradiated cells accumulate unrepaired DNA within persistent DNA damage foci (PDDF) of chromatin. These PDDF are featured by persistent activation of DNA damage/repair signaling, lack of transcription and localization in repressive nuclear microenvironments. Interestingly, the chromatin insulator CTCF is concentrated at the PDDF boundaries, likely contributing to isolate unrepaired DNA from intact transcriptionally active chromatin. By confining damaged DNA, PDDF would help preserving genomic integrity and preventing the production of aberrant proteins encoded by damaged genes.

ChIP-seq analysis of genome-wide γH2AX distribution revealed a number of genomic regions enriched in γH2AX signal in IR-treated cortical neurons. Some of these regions are in close proximity to genes encoding essential proteins for neuronal functions and human neurodegenerative disorders such as epm2a (Lafora disease), serpini1 (familial encephalopathy with neuroserpin inclusion bodies) and il1rpl1 (mental retardation, X-linked 21). Persistent γH2AX signal close to those regions suggests that nearby genes could be either more vulnerable to DNA damage or more refractory to DNA repair.

Genetic Studies on the Tripartite Glutamate Synapse in the Pathophysiology and Therapeutics of Mood Disorders

Both bipolar disorder (BD) and major depressive disorder (MDD) have high morbidity and share a genetic background. Treatment options for these mood disorders are currently suboptimal for many patients; however, specific genetic variables may be involved in both pathophysiology and response to treatment. Agents such as the glutamatergic modulator ketamine are effective in treatment-resistant mood disorders, underscoring the potential importance of the glutamatergic system as a target for improved therapeutics. Here we review genetic studies linking the glutamatergic system to the pathophysiology and therapeutics of mood disorders. We screened 763 original genetic studies of BD or MDD that investigated genes encoding targets of the pathway/mediators related to the so-called tripartite glutamate synapse, including pre- and post-synaptic neurons and glial cells; 60 papers were included in this review. The findings suggest the involvement of glutamate-related genes in risk for mood disorders, treatment response, and phenotypic characteristics, although there was no consistent evidence for a specific gene. Target genes of high interest included GRIA3 and GRIK2 (which likely play a role in emergent suicidal ideation after antidepressant treatment), GRIK4 (which may influence treatment response), and GRM7 (which potentially affects risk for mood disorders). There was stronger evidence that glutamate-related genes influence risk for BD compared with MDD. Taken together, the studies show a preliminary relationship between glutamate-related genes and risk for mood disorders, suicide, and treatment response, particularly with regard to targets on metabotropic and ionotropic receptors.

Emerging Synaptic Molecules as Candidates in the Etiology of Neurological Disorders

Synapses are complex structures that allow communication between neurons in the central nervous system. Studies conducted in vertebrate and invertebrate models have contributed to the knowledge of the function of synaptic proteins. The functional synapse requires numerous protein complexes with specialized functions that are regulated in space and time to allow synaptic plasticity. However, their interplay during neuronal development, learning, and memory is poorly understood. Accumulating evidence links synapse proteins to neurodevelopmental, neuropsychiatric, and neurodegenerative diseases. In this review, we describe the way in which several proteins that participate in cell adhesion, scaffolding, exocytosis, and neurotransmitter reception from presynaptic and postsynaptic compartments, mainly from excitatory synapses, have been associated with several synaptopathies, and we relate their functions to the disease phenotype.

Molecular actions and clinical pharmacogenetics of lithium therapy

Mood disorders, including bipolar disorder and depression, are relatively common human diseases for which pharmacological treatment options are often not optimal. Among existing pharmacological agents and mood stabilizers used for the treatment of mood disorders, lithium has a unique clinical profile. Lithium has efficacy in the treatment of bipolar disorder generally, and in particular mania, while also being useful in the adjunct treatment of refractory depression. In addition to antimanic and adjunct antidepressant efficacy, lithium is also proven effective in the reduction of suicide and suicidal behaviors. However, only a subset of patients manifests beneficial responses to lithium therapy and the underlying genetic factors of response are not exactly known. Here we discuss preclinical research suggesting mechanisms likely to underlie lithium's therapeutic actions including direct targets inositol monophosphatase and glycogen synthase kinase-3 (GSK-3) among others, as well as indirect actions including modulation of neurotrophic and neurotransmitter systems and circadian function. We follow with a discussion of current knowledge related to the pharmacogenetic underpinnings of effective lithium therapy in patients within this context. Progress in elucidation of genetic factors that may be involved in human response to lithium pharmacology has been slow, and there is still limited conclusive evidence for the role of a particular genetic factor. However, the development of new approaches such as genome-wide association studies (GWAS), and increased use of genetic testing and improved identification of mood disorder patients sub-groups will lead to improved elucidation of relevant genetic factors in the future.

Increased density of AKAP5-expressing neurons in the anterior cingulate cortex of subjects with bipolar disorder

Brain anatomical abnormalities as well as cognitive and emotional processing deficits have been reported for the prefrontal cortex in bipolar disorder, which are in part attributable to cellular and laminar abnormalities in postsynaptic protein expression. A kinase anchoring protein (AKAP) 5/79 plays a key role in postsynaptic signalling of excitatory synapses. We aimed to reveal if the cellular expression of AKAP5/79 protein is altered in the anterior cingulate cortex and the dorsolateral prefrontal cortex in bipolar disorder. Ten subjects with bipolar disorder and ten control cases were investigated by use of immunohistochemical and morphometric techniques. Compared with controls in subjects with bipolar disorder, the numerical density of AKAP5-expressing neurons was significantly increased in the left (p = 0.002) and right (p = 0.008) anterior cingulate cortex. Layer-specific counting revealed that left side layers II (p = 0.000), III (p = 0.001) and V (p = 0.005) as well as right side layers III (p = 0.007), IV (p = 0.007) and V (p = 0.004) had significantly increased AKAP5-positive cell densities in bipolar disorder. In contrast, no statistically significant differences were found for the dorsolateral prefrontal cortex. However, we observed a more intense intraneuronal immunostaining in both prefrontal areas in bipolar disorder patients. Elevated cell numbers and increased intracellular expression of AKAP, together with the altered expression patterns of most intracellular interaction partners of this protein in bipolar disorder as known from the literature, might point to disease-related abnormalities of the AKAP-associated signalosome in prefrontal cortex neurons.