Neuron-specific gene NSG1 binds to and positively regulates sortilin ectodomain shedding via a metalloproteinase-dependent mechanism.

Increasing evidence suggests that aberrant regulation of sortilin ectodomain shedding can contribute to amyloid-ß pathology and frontotemporal dementia, although the mechanism by which this occurs has not been elucidated. Here, we probed for novel binding partners of sortilin using multiple and complementary approaches and identified two proteins of the neuron-specific gene (NSG) family, NSG1 and NSG2, that physically interact and colocalize with sortilin. We show both NSG1 and NSG2 induce subcellular redistribution of sortilin to NSG1- and NSG2-enriched compartments. However, using cell surface biotinylation, we found only NSG1 reduced sortilin cell surface expression, which caused significant reductions in uptake of progranulin, a molecular determinant for frontotemporal dementia. In contrast, we demonstrate NSG2 has no effect on sortilin cell surface abundance or progranulin uptake, suggesting specificity for NSG1 in the regulation of sortilin cell surface expression. Using metalloproteinase inhibitors and A disintegrin and metalloproteinase 10 KO cells, we further show that NSG1-dependent reduction of cell surface sortilin occurred via proteolytic processing by A disintegrin and metalloproteinase 10 with a concomitant increase in shedding of sortilin ectodomain to the extracellular space. This represents a novel regulatory mechanism for sortilin ectodomain shedding that is regulated in a neuron-specific manner. Furthermore, this finding has implications for the development of strategies for brain-specific regulation of sortilin and possibly sortilin-driven pathologies.

A molecular perspective on mGluR5 regulation in the antidepressant effect of ketamine.

Ketamine, a non-competitive N-methyl-D-aspartate receptor (NMDAR) antagonist, has received much attention for its rapid antidepressant effects. A single administration of ketamine elicits rapid and sustained antidepressant effects in both humans and animals. Current efforts are focused on uncovering molecular mechanisms responsible for ketamine's antidepressant activity. Ketamine primarily acts via the glutamatergic pathway, and increasing evidence suggests that ketamine induces synaptic and structural plasticity through increased translation and release of neurotrophic factors, activation of mammalian target of rapamycin (mTOR), and α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR)-mediated synaptic potentiation. However, the initial events triggering activation of intracellular signaling cascades and the mechanisms responsible for the sustained antidepressant effects of ketamine remain poorly understood. Over the last few years, it has become apparent that in addition to the fast actions of the ligand-gated AMPARs and NMDARs, metabotropic glutamate receptors (mGluRs), and particularly mGluR5, may also play a role in the antidepressant action of ketamine. Although research on mGluR5 in relation to the beneficial actions of ketamine is still in its infancy, a careful evaluation of the existing literature can identify converging trends and provide new interpretations. Here, we review the current literature on mGluR5 regulation in response to ketamine from a molecular perspective and propose a possible mechanism linking NMDAR inhibition to mGluR5 modulation.

Cholesterol binding to a conserved site modulates the conformation, pharmacology, and transport kinetics of the human serotonin transporter.

The serotonin transporter (SERT) is important for reuptake of the neurotransmitter serotonin from the synaptic cleft and is also the target of most antidepressants. It has previously been shown that cholesterol in the membrane bilayer affects the conformation of SERT. Although recent crystal structures have identified several potential cholesterol-binding sites, it is unclear whether any of these potential cholesterol sites are occupied by cholesterol and functionally relevant. In the present study, we focus on the conserved cholesterol site 1 (CHOL1) located in a hydrophobic groove between TM1a, TM5, and TM7. By molecular dynamics simulations, we demonstrate a strong binding of cholesterol to CHOL1 in a membrane bilayer environment. In biochemical experiments, we find that cholesterol depletion induces a more inward-facing conformation favoring substrate analog binding. Consistent with this, we find that mutations in CHOL1 with a negative impact on cholesterol binding induce a more inward-facing conformation, and, vice versa, mutations with a positive impact on cholesterol binding induce a more outward-facing conformation. This shift in transporter conformation dictated by the ability to bind cholesterol in CHOL1 affects the apparent substrate affinity, maximum transport velocity, and turnover rates. Taken together, we show that occupation of CHOL1 by cholesterol is of major importance in the transporter conformational equilibrium, which in turn dictates ligand potency and serotonin transport activity. Based on our findings, we propose a mechanistic model that incorporates the role of cholesterol binding to CHOL1 in the function of SERT.

Psilocybin lacks antidepressant-like effect in the Flinders Sensitive Line rat.

OBJECTIVE: Psilocybin is a serotonin receptor agonist with a therapeutic potential for treatment-resistant depression and other psychiatric illnesses. We investigated whether the administration of psilocybin had an antidepressant-like effect in a rat model of depression. METHODS: Using the Flinders Sensitive Line (FSL) rat model of depression, we assessed the antidepressant-like effect of psilocin and psilocybin, measured as a reduction in immobility time in the forced swim test (FST). We measured locomotor activity in an open field test (OFT) to control for stimulant properties of the drugs. We performed a set of experiments to test different doses, treatment paradigms, and timing of the tests in relation to the drug administration. RESULTS: Psilocin and psilocybin showed no effect on immobility, struggling, or swimming behaviour in the FST and no effect on locomotor activity in the OFT. FSL rats did show significantly more immobility than their control strain, the Flinders Resistant Line, as expected. CONCLUSION: Psilocin and psilocybin showed no antidepressant-like effect in the FSL rats, despite a positive effect in humans. This suggests that other animal models of depression and other behavioural tests may be more appropriate for translational studies in the effects of psilocybin.

Gene expression related to serotonergic and glutamatergic neurotransmission is altered in the flinders sensitive line rat model of depression: Effect of ketamine.

Major depressive disorder (MDD) is associated with dysfunctional serotonergic and glutamatergic neurotransmission, and the genetic animal model of depression Flinders Sensitive Line (FSL) rats display alterations in these systems relatively to their control strain Flinders Resistant Line (FRL). However, changes on transcript level related to serotonergic and glutamatergic signaling have only been sparsely studied in this model. The non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist ketamine has fast-onset antidepressant properties, and recent data implicate serotonergic neurotransmission in ketamine's antidepressant-like activities in rodents. Here, we investigated the transcript levels of 40 genes involved in serotonergic and glutamatergic neurotransmission in FSL and FRL rats in response to a single dose of ketamine (15 mg/kg; 90 min prior to euthanization). Using real-time quantitative polymerase chain reaction, we studied the effect of ketamine in the hippocampus, whereas strain differences were investigated in both hippocampus and frontal cortex. The expression of genes involved in serotonergic and glutamatergic neurotransmission were unaffected by a single dose of ketamine in the hippocampus. Relative to FRL rats, FSL rats displayed enhanced hippocampal transcript levels of 5-ht2c , and P11, whereas the expression was reduced for 5-ht2a , Nr2a, and Mglur2. In the frontal cortex, we found higher transcript levels of 5-ht2c and Mglur2, whereas the expression of 5-ht2a was reduced in FSL rats. Thus, ketamine is not associated with hippocampal alterations in serotonergic or glutamatergic genes at 90 min after an antidepressant dose. Furthermore, FSL rats display serotonergic and glutamatergic abnormalities on gene expression level that partly may resemble findings in MDD patients.

Differential expression of postsynaptic NMDA and AMPA receptor subunits in the hippocampus and prefrontal cortex of the flinders sensitive line rat model of depression.

Glutamatergic abnormalities have recently been implicated in the pathophysiology of depression, and the ionotropic glutamate receptors in particular have been suggested as possible underlying molecular determinants. The Flinders Sensitive Line (FSL) rats constitute a validated model of depression with dysfunctional regulation of glutamate transmission relatively to their control strain Flinders Resistant Line (FRL). To gain insight into how signaling through glutamate receptors may be altered in the FSL rats, we investigated the expression and phosphorylation of AMPA and NMDA receptor subunits in an enriched postsynaptic fraction of the hippocampus and prefrontal cortex. Compared to the hippocampal postsynaptic fractions of FRL rats, FSL rats exhibited decreased and increased levels of the NMDA receptor subunits GluN2A and GluN2B, respectively, causing a lower ratio of GluN2A/GluN2B. The GluA2/GluA3 AMPA receptor subunit ratio was significantly decreased while the expression of the individual GluA1, GluA2, and GluA3 subunits were unaltered including phosphorylation levels of GluA1 at S831 and S845. There were no changes in the prefrontal cortex. These results support altered expression of postsynaptic glutamate receptors in the hippocampus of FSL rats, which may contribute to the depressive-like phenotype of these rats.

Chronic restraint stress increases the protein expression of VEGF and its receptor VEGFR-2 in the prefrontal cortex.

In the present study the central and peripheral regulation of VEGF, its cognate receptors, and regulators were examined after acute and chronic restraint stress in rats. After chronic restraint stress (6 h per day for 21 days) the protein levels of VEGF (175 ± 24%) and its receptor VEGFR-2 (169 ± 17%) increased significantly in the prefrontal cortex (A and B). mRNA levels of VEGFR-2 (132 ± 11%) were also significantly increased (D). In the hippocampus no significant changes were observed at the mRNA or protein levels. In serum there was a tendency towards increased VEGF protein expression after both acute and chronic restraint stress (C).

Chronic lipopolysaccharide infusion fails to induce depressive-like behaviour in adult male rats.

BACKGROUND: Chronic inflammation is implicated in numerous diseases, including major depression and type 2 diabetes mellitus (T2DM). Since depression and T2DM often co-exist, inflammatory pathways are suggested as a possible link. Hence, the establishment of an immune-mediated animal model would shed light on mechanisms possibly linking depression and metabolic alterations. OBJECTIVE: In this study we investigated a behavioural and metabolic paradigm following chronic infusion with low doses of lipopolysaccharide (LPS) using osmotic minipumps in male rats. METHODS: Behavioural testing consisted of evaluating activity level in the open field and depressive-like behaviour in the forced swim test. Metabolic assessment included measurement of body weight, food and water intake, and glucose and insulin levels during an oral glucose tolerance test. RESULTS: LPS-infused rats showed acute signs of sickness behaviour, but chronic LPS infusion did not induce behavioural or metabolic changes. CONCLUSION: These results suggest that although inflammation is immediately induced as indicated by acute sickness, 4 weeks of chronic LPS administration via osmotic minipumps did not result in behavioural changes. Therefore, this paradigm may not be a suitable model for studying the underlying mechanisms that link depression and T2DM.

Repeated cannabidiol treatment affects neuroplasticity and endocannabinoid signaling in the prefrontal cortex of the Flinders Sensitive Line (FSL) rat model of depression.

Delayed therapeutic responses and limited efficacy are the main challenges of existing antidepressant drugs, thereby incentivizing the search for new potential treatments. Cannabidiol (CBD), non-psychotomimetic component of cannabis, has shown promising antidepressant effects in different rodent models, but its mechanism of action remains unclear. Herein, we investigated the antidepressant-like effects of repeated CBD treatment on behavior, neuroplasticity markers and lipidomic profile in the prefrontal cortex (PFC) of Flinders Sensitive Line (FSL), a genetic animal model of depression, and their control counterparts Flinders Resistant Line (FRL) rats. Male FSL animals were treated with CBD (10 mg/kg; i.p.) or vehicle (7 days) followed by Open Field Test (OFT) and the Forced Swimming Test (FST). The PFC was analyzed by a) western blotting to assess markers of synaptic plasticity and cannabinoid signaling in synaptosome and cytosolic fractions; b) mass spectrometry-based lipidomics to investigate endocannabinoid levels (eCB). CBD attenuated the increased immobility observed in FSL, compared to FRL in FST, without changing the locomotor behavior in the OFT. In synaptosomes, CBD increased ERK1, mGluR5, and Synaptophysin, but failed to reverse the reduced CB1 and CB2 levels in FSL rats. In the cytosolic fraction, CBD increased ERK2 and decreased mGluR5 expression in FSL rats. Surprisingly, there were no significant changes in eCB levels in response to CBD treatment. These findings suggest that CBD effects in FSL animals are associated with changes in synaptic plasticity markers involving mGluR5, ERK1, ERK2, and synaptophysin signaling in the PFC, without increasing the levels of endocannabinoids in this brain region.

Kappa opioid activation changes protein profiles in different regions of the brain relevant to depression.

Depression is a widespread disorder with a significant burden on individuals and society. There are various available treatments for patients with depression. However, not all patients respond adequately to their treatment. Recently, the opioid system has regained interest in depression studies. Research in animals and humans suggest that blocking the kappa opioid receptor (KOR) may potentially alleviate the symptoms of depression. The mechanism behind this effect is not fully understood. Stress and alterations in hypothalamic-pituitary-adrenal axis (HPA-axis) activity are thought to play a crucial role in depression. This study aimed to characterize stress hormones and stress-related protein expression following activation of KOR using a selective agonist. The longitudinal effect was investigated 24 h after KOR activation using the selective agonist U50,488 in Sprague Dawley rats. Stress-related hormones and protein expression patterns were explored using multiplex bead-based assays and western blotting. We found that KOR activation caused an increase in both adrenocorticotropic hormone (ACTH) and corticosterone (CORT) in serum. Regarding protein assays in different brain regions, phosphorylated glucocorticoid receptors also increased significantly in thalamus (THL), hypothalamus (HTH), and striatum (STR). C-Fos increased time-dependently in THL following KOR activation, extracellular signal-regulated kinases 1/2 (ERK1/2) increased significantly in STR and amygdala (AMG), while phosphorylated ERK1/2 decreased during the first 2 h and then increased again in AMG and prefrontal cortex (PFC). This study shows that KOR activation alters the HPA axis and ERK signaling which may cause to develop mood disorders.

Linking Hypothermia and Altered Metabolism with TrkB Activation.

Many mechanisms have been proposed to explain acute antidepressant drug-induced activation of TrkB neurotrophin receptors, but several questions remain. In a series of pharmacological experiments, we observed that TrkB activation induced by antidepressants and several other drugs correlated with sedation, and most importantly, coinciding hypothermia. Untargeted metabolomics of pharmacologically dissimilar TrkB activating treatments revealed effects on shared bioenergetic targets involved in adenosine triphosphate (ATP) breakdown and synthesis, demonstrating a common perturbation in metabolic activity. Both activation of TrkB signaling and hypothermia were recapitulated by administration of inhibitors of glucose and lipid metabolism, supporting a close relationship between metabolic inhibition and neurotrophic signaling. Drug-induced TrkB phosphorylation was independent of electroencephalography slow-wave activity and remained unaltered in knock-in mice with the brain-derived neurotrophic factor (BDNF) Val66Met allele, which have impaired activity-dependent BDNF release, alluding to an activation mechanism independent from BDNF and neuronal activity. Instead, we demonstrated that the active maintenance of body temperature prevents activation of TrkB and other targets associated with antidepressants, including p70S6 kinase downstream of the mammalian target of rapamycin (mTOR) and glycogen synthase kinase 3ß (GSK3ß). Increased TrkB, GSK3ß, and p70S6K phosphorylation was also observed during recovery sleep following sleep deprivation, when a physiological temperature drop is known to occur. Our results suggest that the changes in bioenergetics and thermoregulation are causally connected to TrkB activation and may act as physiological regulators of signaling processes involved in neuronal plasticity.

Single dose S-ketamine rescues transcriptional dysregulation of Mtor and Nrp2 in the prefrontal cortex of FSL rats 1 hour but not 14 days post dosing.

There is a pressing need to identify biological indicators of major depression to help guide proper diagnosis and optimize treatment. Animal models mimicking aspects of depression constitute essential tools for early-stage exploration of relevant pathways. In this study, we used the Flinders Sensitive and Resistant Line (FSL/FRL) to explore central and peripheral transcriptional changes in vascular endothelial growth factor (VEGF) pathway genes and their temporal regulation after a single dose of S-ketamine (15 mg/kg). We found that S-ketamine induced both rapid (1 hour) and sustained (2 and 14 days) antidepressant-like effects in the FSL rats. Analysis of mRNA expression revealed significant strain effects of Vegf, Vegf164, Vegfr-1, Nrp1, Nrp2, Rictor, and Raptor in the prefrontal cortex (PFC) and of Vegf164, GbetaL, and Tsc1 in the hippocampus (HIP), which indicates suppression of VEGF signaling in the FSL rats compared to FRL rats. This notion was further substantiated by reduced expression of Vegf and Mtor in plasma from FSL rats. In the brain, S-ketamine induced transcriptional changes in the acute phase, not the sustained phase. There were significant treatment effects of S-ketamine on Vegfr-2 in both PFC and HIP and on Vegf and Vegfr-1 in HIP. Moreover, we found that S-ketamine specifically restored reduced levels of Nrp2 and Mtor in the PFC of the FSL rats. In conclusion, this study substantiates the use of the FRL/FSL rats to explore the depressive-like behavior at the transcriptional level of the VEGF pathway genes and study their regulation in response to various treatment paradigms.

Global loss of Neuron-specific gene 1 causes alterations in motor coordination, increased anxiety, and diurnal hyperactivity in male mice.

The Neuron-specific gene family (NSG1-3) consists of small endolysosomal proteins that are critical for trafficking multiple receptors and signaling molecules in neurons. NSG1 has been shown to play a critical role in AMPAR recycling from endosomes to plasma membrane during synaptic plasticity. However, to date nothing is known about whether NSG1 is required for normal behavior at an organismal level. Here we performed a battery of behavioral tests to determine whether loss of NSG1 would affect motor, cognitive, and/or affective behaviors, as well as circadian-related activity. Consistent with unique cerebellar expression of NSG1 among family members, we found that NSG1 was obligatory for motor coordination but not for gross motor function or learning. NSG1 knockout (KO) also altered performance across other behavioral modalities including anxiety-related and diurnal activity paradigms. Surprisingly, NSG1 KO did not cause significant impairments across all tasks within a given modality, but had specific effects within each modality. For instance, we found increases in anxiety-related behaviors in tasks with multiple stressors (e.g., elevation and exposure), but not those with a single main stressor (e.g., exposure). Interestingly, NSG1 KO animals displayed a significant increase in locomotor activity during subjective daytime, suggesting a possible impact on diurnal activity rhythms or vigilance. Surprisingly, loss of NSG1 had no effect on hippocampal-dependent learning despite previous studies showing deficits in CA1 long-term potentiation. Together, these findings do not support a role of NSG1 in hippocampal-dependent learning, but support a role in mediating proper neuronal function across amygdalar and cerebellar circuits.

Transcriptional regulation in the rat prefrontal cortex and hippocampus after a single administration of psilocybin.

BACKGROUND: Psilocybin is a serotonergic psychedelic found in "magic mushrooms" with a putative therapeutic potential for treatment-resistant depression, anxiety, obsessive-compulsive disorder, and addiction. In rodents, psilocybin acutely induces plasticity-related immediate early genes in cortical tissue; however, studies into the effects on subcortical regions, of different doses, and the subsequent translation of corresponding proteins are lacking. METHODS: We examined the acute effects of a single administration of psilocybin (0.5-20 mg/kg) on the expression of selected genes in the prefrontal cortex and hippocampus. In total, 46 target genes and eight reference genes were assessed using real-time quantitative polymerase chain reaction. Corresponding protein levels of the three most commonly regulated genes were assessed using Western blotting. RESULTS: In the prefrontal cortex, psilocybin increased the expression of Cebpb, c-Fos, Dups1, Fosb, Junb, Iκß-α, Nr4a1, P11, Psd95, and Sgk1, and decreased the expression of Clk1. In the hippocampus, psilocybin strongly increased the expression of Arrdc2, Dusp1, Iκß-α, and Sgk1 in a dose-dependent manner, and decreased the expression of Arc, Clk1, Egr2, and Ptgs2. Protein levels of Sgk1, Dusp1, and Iκß-α showed only partial agreement with transcriptional patterns, stressing the importance of assessing downstream translation when investigating rapid gene responses. CONCLUSION: The present study demonstrates that psilocybin rapidly induces gene expression related to neuroplasticity, biased towards the prefrontal cortex, compared to the hippocampus. Our findings provide further evidence for the rapid plasticity-promoting effects of psilocybin.

A Long-Term Energy-Rich Diet Increases Prefrontal BDNF in Sprague-Dawley Rats.

Findings of the effect of high-fat feeding including "Cafeteria Diets" (CAF) on brain-derived neurotrophic factor (BDNF) in the hippocampus (HIP) and prefrontal cortex (PFC) in rodents are conflicting. CAF is a non-standardized, highly palatable energy-rich diet composed by everyday food items for human consumption and is known to induce metabolic syndrome and obesity in rats. However, the highly palatable nature of CAF may counteract a negative effect of chronic stress on anticipatory behavior and synaptic plasticity in the hippocampus, hence represent a confounding factor (e.g., when evaluating functional effects on the brain). This study investigated the effects of a chronic, restricted access to CAF on BDNF, monoamine neurotransmitters, and redox imbalance in HIP and PFC in male rats. Our results show that CAF induced BDNF and its receptor TrkB in PFC compared to the controls (p < 0.0005). No differences in monoamine neurotransmitters were detected in either PFC or HIP. CAF increased dehydroascorbic acid and decreased malondialdehyde in PFC (p < 0.05), suggesting an early redox imbalance insufficient to induce lipid peroxidation. This study supports that a chronic CAF on a restricted schedule increases BDNF levels in the PFC of rats, highlighting that this may be a suboptimal feeding regime when investigating the effects of diet-induced obesity in the brain and emphasizing this as a point of attention when comparing the findings.

Dysregulation of miR-185, miR-193a, and miR-450a in the skin are linked to the depressive phenotype.

BACKGROUND: Dysregulated microRNAs (miRNAs) in dermal fibroblasts of depressive subjects, indicate biomarker potential and can possibly aid clinical diagnostics. To overcome methodological challenges related to human experiments and fibroblast cultures, we here validate 38 miRNAs previously observed to be dysregulated in human fibroblasts from depressed subjects, in the skin of four distinct rat models of depression. METHODS: In the presented study male rats from the adrenocorticotropic hormone (ACTH) model (n = 10/group), the chronic mild stress model (n = 10/group), Wistar Kyoto/Wistar Hannover rats (n = 10/group), and Flinders Resistant/Flinders Sensitive Line rats (n = 8/group) were included. Real-time qPCR was utilized to investigate miRNA alterations in flash-frozen skin-biopsies from the ear and fibroblast cultures. RESULTS: In the ACTH rat model of depression, we identified nine dysregulated miRNAs in the skin and three in the fibroblasts. As the skin presented three times the amount of dysregulated miRNAs compared to the fibroblasts, skin instead of fibroblasts were continuously used for studies with the other rat models. In the skin from the four rat models of depression, 15 out of 38 miRNAs re-exhibited significant dysregulation in at least one of the rat models of depression and 67% were regulated in the same direction as in the human study. miR-450a and miR-193a presented dysregulation across rat models and miR-193a and miR-185 exhibited very strong dysregulation (30-fold and 50-fold, respectively). Lastly, an Ingenuity Pathway Analysis indicated functional overlap between dysregulated miRNAs, and common regulated pathways. CONCLUSION: Flash-frozen skin is a valid alternative to fibroblast cultures as the skin appear to retain more of the miRNA dysregulation present in vivo. A sub-population of 15 miRNAs appear to be specific for the depressive phenotype, as they are dysregulated in both human depressed patients and distinct rat models of depression. We propose miR-450a, miR-185, and miR-193a as biomarker candidates of particular interest.

DNA methylation of the KLK8 gene in depression symptomatology.

BACKGROUND: Depression is a common, complex, and debilitating mental disorder estimated to be under-diagnosed and insufficiently treated in society. Liability to depression is influenced by both genetic and environmental risk factors, which are both capable of impacting DNA methylation (DNAm). Accordingly, numerous studies have researched for DNAm signatures of this disorder. Recently, an epigenome-wide association study of monozygotic twins identified an association between DNAm status in the KLK8 (neuropsin) promoter region and severity of depression symptomatology. METHODS: In this study, we aimed to investigate: (i) if blood DNAm levels, quantified by pyrosequencing, at two CpG sites in the KLK8 promoter are associated with depression symptomatology and depression diagnosis in an independent clinical cohort and (ii) if KLK8 DNAm levels are associated with depression, postpartum depression, and depression symptomatology in four independent methylomic cohorts, with blood and brain DNAm quantified by either MBD-seq or 450 k methylation array. RESULTS: DNAm levels in KLK8 were not significantly different between depression cases and controls, and were not significantly associated with any of the depression symptomatology scores after correction for multiple testing (minimum p value for KLK8 CpG1 = 0.12 for 'Depressed mood,' and for CpG2 = 0.03 for 'Loss of self-confidence with other people'). However, investigation of the link between KLK8 promoter DNAm levels and depression-related phenotypes collected from four methylomic cohorts identified significant association (p value < 0.05) between severity of depression symptomatology and blood DNAm levels at seven CpG sites. CONCLUSIONS: Our findings suggest that variance in blood DNAm levels in KLK8 promoter region is associated with severity of depression symptoms, but not depression diagnosis.

Inverse correlation of brain and blood BDNF levels in a genetic rat model of depression.

There is accumulating evidence that brain-derived neurotrophic factor (BDNF) plays a critical role in the pathophysiology of depression. Decreased serum levels have been reported in major depression, and a correlation between BDNF reduction and the severity of the disease was found. Moreover, in post-mortem hippocampal tissue, increased levels of BDNF immunoreactivity have been reported in subjects treated with antidepressants compared to untreated subjects. These findings indicate parallel changes in brain and serum BDNF levels during depression. BDNF has been measured in selected brain areas in several animal models. In investigations between Flinders Sensitive Line (FSL) and Flinders Resistant Line (FRL) rats, a genetic rat model of depression, no differences were found in BDNF levels in the frontal cortex and hippocampus, areas believed to be core brain regions in depression. However, to our knowledge brain and serum BDNF levels have never been reported in parallel for any psychiatric disease model. Therefore, we examined the levels of BDNF in whole blood, serum, cerebrospinal fluid (CSF), hippocampus, and frontal cortex in male FSL and FRL rats. BDNF levels in serum and whole blood of FSL rats were significantly increased compared to FRL rats. In contrast, in the hippocampus the BDNF level was significantly decreased in FSL compared to FRL rats while no differences were found in the frontal cortex and CSF. The differential regulation of the BDNF levels in hippocampus, serum, and whole blood in FSL/FRL rats adds to the hypothesis that neurotrophic factors are related to the pathophysiology of depression.

Preclinical PET Studies of [11C]UCB-J Binding in Minipig Brain.

PURPOSE: Loss of neuronal synapse function is associated with a number of brain disorders. The [11C]UCB-J positron emission tomography (PET) tracer allows for in vivo examination of synaptic density, as it binds to synaptic vesicle glycoprotein 2A (SV2A) expressed in presynaptic terminals. Here, we characterise [11C]UCB-J imaging in Göttingen minipigs. PROCEDURES: Using PET imaging, we examined tracer specificity and compared kinetic models. We explored the use of a standard blood curve and centrum semiovale white matter as a reference region. We compared in vivo [11C]UCB-J PET imaging to in vitro autoradiography, Western blotting and real-time quantitative polymerase chain reaction. RESULTS: The uptake kinetics of [11C]UCB-J could be described using a 1-tissue compartment model and blocking of SV2A availability with levetiracetam showed dose-dependent specific binding. Population-based blood curves resulted in reliable [11C]UCB-J binding estimates, while it was not possible to use centrum semiovale white matter as a non-specific reference region. Brain [11C]UCB-J PET signals correlated well with [3H]UCB-J autoradiography and SV2A protein levels. CONCLUSIONS: [11C]UCB-J PET is a valid in vivo marker of synaptic density in the minipig brain, with binding values close to those reported for humans. Minipig models of disease could be valuable for investigating the efficacy of putative neuroprotective agents for preserving synaptic function in future non-invasive, longitudinal studies.

Membrane glycoprotein M6B interacts with the human serotonin transporter.

The serotonin transporter (SERT) belongs to a family of sodium- and chloride-dependent neurotransmitter transporters that are responsible for the active re-uptake of the neurotransmitter serotonin from the synapse. In the present study, using the yeast two-hybrid system, we identified the membrane glycoprotein M6B as a binding partner of SERT. This interaction was further verified by co-immunoprecipitation and glutathione-S-transferase pull-down assays. M6B belongs to a proteolipid protein family, which is expressed in neurons and in oligodendrocytes in the brain. The knowledge of the biological function of this protein family is sparse, but their expression in most brain regions have led to the hypothesis that they are involved in cellular housekeeping functions such as membrane trafficking and cell-to-cell communication. The co-expression of SERT with M6B results in a significant decrease in SERT-mediated serotonin uptake caused by a down-regulation of SERT surface expression. Furthermore, we find, using confocal microscopy, that M6B co-localizes with SERT when transiently expressed in HEK-MSR-293 cells and when endogenously expressed in RN46A cells. Taken together, our data suggest that M6B regulates the serotonin uptake by affecting cellular trafficking of the serotonin transporter.