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Cell 159, 33-45; September 25, 2014) During the preparation of Figure 1 in the article above, we inadvertently included lines separating the lanes in the western blot shown in Figure 1E. In that panel, the Vinculin control for ARC should not display separating lines, as all samples were loaded on consecutive lanes. We would like to clarify that the legends of Figures 1 and 2 should have indicated that the separating lines demarcate bands that come from nonconsecutive lanes of the same gel. Finally, in the legend of Figure 1, we did not mention that the Vinculin loading control for ARC and CamKIIa shown in Figure 1E is the same, as these proteins were detected in the same membrane. The errors do not in any way affect the results or interpretation of the figure. We apologize for any confusion that these errors may have caused.

No abstract

Elevated cerebrospinal fluid (CSF) levels of the glia-derived N-methyl-d-aspartic acid receptor antagonist kynurenic acid (KYNA) have consistently been implicated in schizophrenia and bipolar disorder. Here, we conducted a genome-wide association study based on CSF KYNA in bipolar disorder and found support for an association with a common variant within 1p21.3. After replication in an independent cohort, we linked this genetic variant—associated with reduced SNX7 expression—to positive psychotic symptoms and executive function deficits in bipolar disorder. A series of post-mortem brain tissue and in vitro experiments suggested SNX7 downregulation to result in a caspase-8-driven activation of interleukin-1β and a subsequent induction of the brain kynurenine pathway. The current study demonstrates the potential of using biomarkers in genetic studies of psychiatric disorders, and may help to identify novel drug targets in bipolar disorder.

Objective Over the past decade, clinical data has accumulated showing that inflammation might contribute to the pathophysiology of suicide. To evaluate associations and identify support for pathways linking inflammatory processes with suicidal behavior, a comprehensive review of the literature was undertaken. Method The search terms “cytokine”, “risk factors”, “kynurenine”, “asthma”, “allergy”, “autoimmunity”, “traumatic brain injury”, “infection” along with the terms “inflammation” and “suicide” were entered into PubMed and a thorough analysis of the publications and their reference lists was performed. Results The effects of inflammation on mood and behavior could partially be mediated by kynurenine pathway metabolites, modulating neuroinflammation and glutamate neurotransmission. At the same time, the triggers of the inflammatory changes documented in suicidal patients may be attributed to diverse mechanisms such as autoimmunity, neurotropic pathogens, stress or traumatic brain injury. Conclusion Targeting the inflammatory system might provide novel therapeutic approaches as well as potential biomarkers to identify patients at increased risk. For the goal of improved detection and treatment of suicidal individuals to be achieved, we need to develop a detailed understanding of the origin, mechanisms and outcomes of inflammation in suicidal behavior.

Physical exercise has emerged as an alternative treatment for patients with depressive disorder. Recent animal studies show that exercise protects from depression by increased skeletal muscle kynurenine aminotransferase (KAT) expression which shifts the kynurenine metabolism away from the neurotoxic kynurenine (KYN) to the production of kynurenic acid (KYNA). In the present study, we investigated the effect of exercise on kynurenine metabolism in humans. KAT gene and protein expression was increased in the muscles of endurance-trained subjects compared with untrained subjects. Endurance exercise caused an increase in plasma KYNA within the first hour after exercise. In contrast, a bout of high-intensity eccentric exercise did not lead to increased plasma KYNA concentration. Our results show that regular endurance exercise causes adaptations in kynurenine metabolism which can have implications for exercise recommendations for patients with depressive disorder.

Emerging evidence suggests that inflammation has a key role in depression and suicidal behavior. The kynurenine pathway is involved in neuroinflammation and regulates glutamate neurotransmission. In the cerebrospinal fluid (CSF) of suicidal patients, levels of inflammatory cytokines and the kynurenine metabolite quinolinic acid (QUIN), an N-methyl-d-aspartate receptor agonist, are increased. The enzyme amino-β-carboxymuconate-semialdehyde-decarboxylase (ACMSD) limits QUIN formation by competitive production of the neuroprotective metabolite picolinic acid (PIC). Therefore, decreased ACMSD activity can lead to excess QUIN. We tested the hypothesis that deficient ACMSD activity underlies suicidal behavior. We measured PIC and QUIN in CSF and plasma samples from 137 patients exhibiting suicidal behavior and 71 healthy controls. We used DSM-IV and the Montgomery-Åsberg Depression Rating Scale and Suicide Assessment Scale to assess behavioral changes. Finally, we genotyped ACMSD tag single-nucleotide polymorphisms (SNPs) in 77 of the patients and 150 population-based controls. Suicide attempters had reduced PIC and a decreased PIC/QUIN ratio in both CSF (P<0.001) and blood (P=0.001 and P<0.01, respectively). The reductions of PIC in CSF were sustained over 2 years after the suicide attempt based on repeated measures. The minor C allele of the ACMSD SNP rs2121337 was more prevalent in suicide attempters and associated with increased CSF QUIN. Taken together, our data suggest that increased QUIN levels may result from reduced activity of ACMSD in suicidal subjects. We conclude that measures of kynurenine metabolites can be explored as biomarkers of suicide risk, and that ACMSD is a potential therapeutic target in suicidal behavior.

Several lines of evidence are indicative of a role for immune activation in the pathophysiology of schizophrenia. Nevertheless, studies using positron emission tomography (PET) and radioligands for the translocator protein (TSPO), a marker for glial activation, have yielded inconsistent results. Whereas early studies using a radioligand with low signal-to-noise in small samples showed increases in patients, more recent studies with improved methodology have shown no differences or trend-level decreases. Importantly, all patients investigated thus far have been on antipsychotic medication, and as these compounds may dampen immune cell activity, this factor limits the conclusions that can be drawn. Here, we examined 16 drug-naive, first-episode psychosis patients and 16 healthy controls using PET and the TSPO radioligand [C]PBR28. Gray matter (GM) volume of distribution (V) derived from a two-tissue compartmental analysis with arterial input function was the main outcome measure. Statistical analyses were performed controlling for both TSPO genotype, which is known to affect [C]PBR28 binding, and gender. There was a significant reduction of [C]PBR28 V in patients compared with healthy controls in GM as well as in secondary regions of interest. No correlation was observed between GM V and clinical or cognitive measures after correction for multiple comparisons. The observed decrease in TSPO binding suggests reduced numbers or altered function of immune cells in brain in early-stage schizophrenia.