Stephanie H. Witt

Neural Mechanisms of a Genome-Wide Supported Psychosis Variant

A genetic polymorphism associated with schizophrenia conveys a risk for abnormal connectivity between brain regions. Schizophrenia is a devastating, highly heritable brain disorder of unknown etiology. Recently, the first common genetic variant associated on a genome-wide level with schizophrenia and possibly bipolar disorder was discovered in ZNF804A (rs1344706). We show, by using an imaging genetics approach, that healthy carriers of rs1344706 risk genotypes exhibit no changes in regional activity but pronounced gene dosage–dependent alterations in functional coupling (correlated activity) of dorsolateral prefrontal cortex (DLPFC) across hemispheres and with hippocampus, mirroring findings in patients, and abnormal coupling of amygdala. Our findings establish disturbed connectivity as a neurogenetic risk mechanism for psychosis supported by genome-wide association, show that rs1344706 or variation in linkage disequilibrium is functional in human brain, and validate the intermediate phenotype strategy in psychiatry.

Multiple Independent Loci at Chromosome 15q25.1 Affect Smoking Quantity: a Meta-Analysis and Comparison with Lung Cancer and COPD

Recently, genetic association findings for nicotine dependence, smoking behavior, and smoking-related diseases converged to implicate the chromosome 15q25.1 region, which includes the CHRNA5-CHRNA3-CHRNB4 cholinergic nicotinic receptor subunit genes. In particular, association with the nonsynonymous CHRNA5 SNP rs16969968 and correlates has been replicated in several independent studies. Extensive genotyping of this region has suggested additional statistically distinct signals for nicotine dependence, tagged by rs578776 and rs588765. One goal of the Consortium for the Genetic Analysis of Smoking Phenotypes (CGASP) is to elucidate the associations among these markers and dichotomous smoking quantity (heavy versus light smoking), lung cancer, and chronic obstructive pulmonary disease (COPD). We performed a meta-analysis across 34 datasets of European-ancestry subjects, including 38,617 smokers who were assessed for cigarettes-per-day, 7,700 lung cancer cases and 5,914 lung-cancer-free controls (all smokers), and 2,614 COPD cases and 3,568 COPD-free controls (all smokers). We demonstrate statistically independent associations of rs16969968 and rs588765 with smoking (mutually adjusted p-values<10−35 and <10−8 respectively). Because the risk alleles at these loci are negatively correlated, their association with smoking is stronger in the joint model than when each SNP is analyzed alone. Rs578776 also demonstrates association with smoking after adjustment for rs16969968 (p<10−6). In models adjusting for cigarettes-per-day, we confirm the association between rs16969968 and lung cancer (p<10−20) and observe a nominally significant association with COPD (p = 0.01); the other loci are not significantly associated with either lung cancer or COPD after adjusting for rs16969968. This study provides strong evidence that multiple statistically distinct loci in this region affect smoking behavior. This study is also the first report of association between rs588765 (and correlates) and smoking that achieves genome-wide significance; these SNPs have previously been associated with mRNA levels of CHRNA5 in brain and lung tissue.

Brain Function in Carriers of a Genome-wide Supported Bipolar Disorder Variant

CONTEXT The neural abnormalities underlying genetic risk for bipolar disorder, a severe, common, and highly heritable psychiatric condition, are largely unknown. An opportunity to define these mechanisms is provided by the recent discovery, through genome-wide association, of a single-nucleotide polymorphism (rs1006737) strongly associated with bipolar disorder within the CACNA1C gene, encoding the alpha subunit of the L-type voltage-dependent calcium channel Ca(v)1.2. OBJECTIVE To determine whether the genetic risk associated with rs1006737 is mediated through hippocampal function. DESIGN Functional magnetic resonance imaging study. SETTING University hospital. PARTICIPANTS A total of 110 healthy volunteers of both sexes and of German descent in the Hardy-Weinberg equilibrium for rs1006737. MAIN OUTCOME MEASURES Blood oxygen level-dependent signal during an episodic memory task and behavioral and psychopathological measures. RESULTS Using an intermediate phenotype approach, we show that healthy carriers of the CACNA1C risk variant exhibit a pronounced reduction of bilateral hippocampal activation during episodic memory recall and diminished functional coupling between left and right hippocampal regions. Furthermore, risk allele carriers exhibit activation deficits of the subgenual anterior cingulate cortex, a region repeatedly associated with affective disorders and the mediation of adaptive stress-related responses. The relevance of these findings for affective disorders is supported by significantly higher psychopathology scores for depression, anxiety, obsessive-compulsive thoughts, interpersonal sensitivity, and neuroticism in risk allele carriers, correlating negatively with the observed regional brain activation. CONCLUSIONS Our data demonstrate that rs1006737 or genetic variants in linkage disequilibrium with it are functional in the human brain and provide a neurogenetic risk mechanism for bipolar disorder backed by genome-wide evidence.

Genome-wide association study reveals two new risk loci for bipolar disorder

Bipolar disorder (BD) is a common and highly heritable mental illness and genome-wide association studies (GWAS) have robustly identified the first common genetic variants involved in disease aetiology. The data also provide strong evidence for the presence of multiple additional risk loci, each contributing a relatively small effect to BD susceptibility. Large samples are necessary to detect these risk loci. Here we present results from the largest BD GWAS to date by investigating 2.3 million single-nucleotide polymorphisms (SNPs) in a sample of 24,025 patients and controls. We detect 56 genome-wide significant SNPs in five chromosomal regions including previously reported risk loci ANK3, ODZ4 and TRANK1, as well as the risk locus ADCY2 (5p15.31) and a region between MIR2113 and POU3F2 (6q16.1). ADCY2 is a key enzyme in cAMP signalling and our finding provides new insights into the biological mechanisms involved in the development of BD.

Cooperative control of striated muscle mass and metabolism by MuRF1 and MuRF2

The muscle‐specific RING finger proteins MuRF1 and MuRF2 have been proposed to regulate protein degradation and gene expression in muscle tissues. We have tested the in vivo roles of MuRF1 and MuRF2 for muscle metabolism by using knockout (KO) mouse models. Single MuRF1 and MuRF2 KO mice are healthy and have normal muscles. Double knockout (dKO) mice obtained by the inactivation of all four MuRF1 and MuRF2 alleles developed extreme cardiac and milder skeletal muscle hypertrophy. Muscle hypertrophy in dKO mice was maintained throughout the murine life span and was associated with chronically activated muscle protein synthesis. During ageing (months 4–18), skeletal muscle mass remained stable, whereas body fat content did not increase in dKO mice as compared with wild‐type controls. Other catabolic factors such as MAFbox/atrogin1 were expressed at normal levels and did not respond to or prevent muscle hypertrophy in dKO mice. Thus, combined inhibition of MuRF1/MuRF2 could provide a potent strategy to stimulate striated muscles anabolically and to protect muscles from sarcopenia during ageing.

Effects of a genome-wide supported psychosis risk variant on neural activation during a theory-of-mind task.

Schizophrenia is associated with marked deficits in theory of mind (ToM), a higher-order form of social cognition representing the thoughts, emotions and intentions of others. Altered brain activation in the medial prefrontal cortex and temporo-parietal cortex during ToM tasks has been found in patients with schizophrenia, but the relevance of these neuroimaging findings for the heritable risk for schizophrenia is unclear. We tested the hypothesis that activation of the ToM network is altered in healthy risk allele carriers of the single-nucleotide polymorphism rs1344706 in the gene ZNF804A, a recently discovered risk variant for psychosis with genome-wide support. In all, 109 healthy volunteers of both sexes in Hardy–Weinberg equilibrium for rs1344706 were investigated with functional magnetic resonance imaging during a ToM task. As hypothesised, risk carriers exhibited a significant (P<0.05 false discovery rate, corrected for multiple comparisons) risk allele dose effect on neural activity in the medial prefrontal cortex and left temporo-parietal cortex. Moreover, the same effect was found in the left inferior parietal cortex and left inferior frontal cortex, which are part of the human analogue of the mirror neuron system. In addition, in an exploratory analysis (P<0.001 uncorrected), we found evidence for aberrant functional connectivity between the frontal and temporo-parietal regions in risk allele carriers. To conclude, we show that a dysfunction of the ToM network is associated with a genome-wide supported genetic risk variant for schizophrenia and has promise as an intermediate phenotype that can be mined for the development of biological interventions targeted to social dysfunction in psychiatry.

Muscle RING-finger protein-1 (MuRF1) as a connector of muscle energy metabolism and protein synthesis

During pathophysiological muscle wasting, a family of ubiquitin ligases, including muscle RING-finger protein-1 (MuRF1), has been proposed to trigger muscle protein degradation via ubiquitination. Here, we characterized skeletal muscles from wild-type (WT) and MuRF1 knockout (KO) mice under amino acid (AA) deprivation as a model for physiological protein degradation, where skeletal muscles altruistically waste themselves to provide AAs to other organs. When WT and MuRF1 KO mice were fed a diet lacking AA, MuRF1 KO mice were less susceptible to muscle wasting, for both myocardium and skeletal muscles. Under AA depletion, WT mice had reduced muscle protein synthesis, while MuRF1 KO mice maintained nonphysiologically elevated levels of skeletal muscle protein de novo synthesis. Consistent with a role of MuRF1 for muscle protein turnover during starvation, the concentrations of essential AAs, especially branched-chain AAs, in the blood plasma significantly decreased in MuRF1 KO mice under AA deprivation. To clarify the molecular roles of MuRF1 for muscle metabolism during wasting, we searched for MuRF1-associated proteins using pull-down assays and mass spectrometry. Muscle-type creatine kinase (M-CK), an essential enzyme for energy metabolism, was identified among the interacting proteins. Coexpression studies revealed that M-CK interacts with the central regions of MuRF1 including its B-box domain and that MuRF1 ubiquitinates M-CK, which triggers the degradation of M-CK via proteasomes. Consistent with MuRF1s role of adjusting CK activities in skeletal muscles by regulating its turnover in vivo, we found that CK levels were significantly higher in the MuRF1 KO mice than in WT mice. Glucocorticoid modulatory element binding protein-1 and 3-hydroxyisobutyrate dehydrogenase, previously identified as potential MuRF1-interacting proteins, were also ubiquitinated MuRF1-dependently. Taken together, these data suggest that, in a multifaceted manner, MuRF1 participates in the regulation of AA metabolism, including the control of free AAs and their supply to other organs under catabolic conditions, and in the regulation of ATP synthesis under metabolic-stress conditions where MuRF1 expression is induced.

Cognitive state and connectivity effects of the genome-wide significant psychosis variant in ZNF804A

Alterations of connectivity are central to the systems-level pathophysiology of schizophrenia. One of the best-established genome-wide significant risk variants for this highly heritable disorder, the rs1344706 single nucleotide polymorphism in ZNF804A, was recently shown to modulate connectivity in healthy carriers during working memory (WM) in a pattern mirroring that which was found in overt disease. However, it was unclear whether this finding is specific to WM or if it is present regardless of cognitive state. Therefore, we examined genotype effects on connectivity in healthy carriers during rest and an emotion processing task without WM component. 111 healthy German subjects performed a battery of functional imaging tasks. Functional connectivity with the right dorsolateral prefrontal cortex during rest and an implicit emotion recognition task was determined using the seed voxel method and compared to results during WM. During rest and during the emotional task, a pattern of reduced interhemispheric prefrontal connectivity with increasing number of rs1344706 risk alleles could be seen that was close to identical to that during WM, suggesting a state-independent influence of the genetic variant on interhemispheric processing, possibly through structural effects. By contrast, the abnormal prefronto-hippocampal connectivity was only seen during the WM task, indicating a degree of task specificity in agreement with prior results in patients with schizophrenia. Our findings confirm a key role for disturbed functional connectivity in the genetic risk architecture of schizophrenia and identify cognitive state-dependent and independent components with regard to WM function.

ANKRD1, the gene encoding cardiac ankyrin repeat protein, is a novel dilated cardiomyopathy gene.

OBJECTIVES We evaluated ankyrin repeat domain 1 (ANKRD1), the gene encoding cardiac ankyrin repeat protein (CARP), as a novel candidate gene for dilated cardiomyopathy (DCM) through mutation analysis of a cohort of familial or idiopathic DCM patients, based on the hypothesis that inherited dysfunction of mechanical stretch-based signaling is present in a subset of DCM patients. BACKGROUND CARP, a transcription coinhibitor, is a member of the titin-N2A mechanosensory complex and translocates to the nucleus in response to stretch. It is up-regulated in cardiac failure and hypertrophy and represses expression of sarcomeric proteins. Its overexpression results in contractile dysfunction. METHODS In all, 208 DCM patients were screened for mutations/variants in the coding region of ANKRD1 using polymerase chain reaction, denaturing high-performance liquid chromatography, and direct deoxyribonucleic acid sequencing. In vitro functional analyses of the mutation were performed using yeast 2-hybrid assays and investigating the effect on stretch-mediated gene expression in myoblastoid cell lines using quantitative real-time reverse transcription-polymerase chain reaction. RESULTS Three missense heterozygous ANKRD1 mutations (P105S, V107L, and M184I) were identified in 4 DCM patients. The M184I mutation results in loss of CARP binding with Talin 1 and FHL2, and the P105S mutation in loss of Talin 1 binding. Intracellular localization of mutant CARP proteins is not altered. The mutations result in differential stretch-induced gene expression compared with wild-type CARP. CONCLUSIONS ANKRD1 is a novel DCM gene, with mutations present in 1.9% of DCM patients. The ANKRD1 mutations may cause DCM as a result of disruption of the normal cardiac stretch-based signaling.

Effects of the Circadian Rhythm Gene Period 1 (Per1) on Psychosocial Stress-Induced Alcohol Drinking

OBJECTIVE Circadian and stress-response systems mediate environmental changes that affect alcohol drinking. Psychosocial stress is an environmental risk factor for alcohol abuse. Circadian rhythm gene period 1 (Per1) is targeted by stress hormones and is transcriptionally activated in corticotropin releasing factor-expressing cells. The authors hypothesized that Per1 is involved in integrating stress response and circadian rhythmicity and explored its relevance to alcohol drinking. METHOD In mice, the effects of stress on ethanol intake in mPer1-mutant and wild-type mice were assessed. In humans, single nucleotide polymorphisms (SNPs) in hPer1 were tested for association with alcohol drinking behavior in 273 adolescents and an adult case-control sample of 1,006 alcohol-dependent patients and 1,178 comparison subjects. In vitro experiments were conducted to measure genotype-specific expression and transcription factor binding to hPer1. RESULTS The mPer1-mutant mice showed enhanced alcohol consumption in response to social defeat stress relative to their wild-type littermates. An association with the frequency of heavy drinking in adolescents with the hPer1 promoter SNP rs3027172 and with psychosocial adversity was found. There was significant interaction between the rs3027172 genotype and psychosocial adversity on this drinking measure. In a confirmatory analysis, association of hPer1 rs3027172 with alcohol dependence was shown. Cortisol-induced transcriptional activation of hPer1 was reduced in human B-lymphoblastoid cells carrying the risk genotype of rs3027172. Binding affinity of the transcription factor Snail1 to the risk allele of the hPer1 SNP rs3027172 was also reduced. CONCLUSIONS The findings indicate that the hPer1 gene regulates alcohol drinking behavior during stressful conditions and provide evidence for underlying neurobiological mechanisms.