Adult alcohol drinking and emotional tone are mediated by neutral sphingomyelinase during development in males.

Alcohol use, abuse, and addiction, and resulting health hazards are highly sex-dependent with unknown mechanisms. Previously, strong links between the SMPD3 gene and its coded protein neutral sphingomyelinase 2 (NSM) and alcohol abuse, emotional behavior, and bone defects were discovered and multiple mechanisms were identified for females. Here we report strong sex-dimorphisms for central, but not for peripheral mechanisms of NSM action in mouse models. Reduced NSM activity resulted in enhanced alcohol consumption in males, but delayed conditioned rewarding effects. It enhanced the acute dopamine response to alcohol, but decreased monoaminergic systems adaptations to chronic alcohol. Reduced NSM activity increased depression- and anxiety-like behavior, but was not involved in alcohol use for the self-management of the emotional state. Constitutively reduced NSM activity impaired structural development in the brain and enhanced lipidomic sensitivity to chronic alcohol. While the central effects were mostly opposite to NSM function in females, similar roles in bone-mediated osteocalcin release and its effects on alcohol drinking and emotional behavior were observed. These findings support the view that the NSM and multiple downstream mechanism may be a source of the sex-differences in alcohol use and emotional behavior.

Neutral sphingomyelinase mediates the co-morbidity trias of alcohol abuse, major depression and bone defects.

Mental disorders are highly comorbid and occur together with physical diseases, which are often considered to arise from separate pathogenic pathways. We observed in alcohol-dependent patients increased serum activity of neutral sphingomyelinase. A genetic association analysis in 456,693 volunteers found associations of haplotypes of SMPD3 coding for NSM-2 (NSM) with alcohol consumption, but also with affective state, and bone mineralisation. Functional analysis in mice showed that NSM controls alcohol consumption, affective behaviour, and their interaction by regulating hippocampal volume, cortical connectivity, and monoaminergic responses. Furthermore, NSM controlled bone-brain communication by enhancing osteocalcin signalling, which can independently supress alcohol consumption and reduce depressive behaviour. Altogether, we identified a single gene source for multiple pathways originating in the brain and bone, which interlink disorders of a mental-physical co-morbidity trias of alcohol abuse-depression/anxiety-bone disorder. Targeting NSM and osteocalcin signalling may, thus, provide a new systems approach in the treatment of a mental-physical co-morbidity trias.

Sex and brain region-specific regulation of serotonin transporter activity in synaptosomes in guanine nucleotide-binding protein G(q) alpha knockout mice.

The regulation of the serotonin transporter (SERT) by guanine nucleotide-binding protein alpha (Gα) q was investigated using Gαq knockout mice. In the absence of Gαq, SERT-mediated uptake of 5-hydroxytryptamine (5HT) was enhanced in midbrain and frontal cortex synaptosomes, but only in female mice. The mechanisms underlying this sexual dimorphism were investigated using quantitative western blot analysis revealing brain region-specific differences. In the frontal cortex, SERT protein expression was decreased in male knockout mice, seemingly explaining the sex-dependent variation in SERT activity. The differential expression of Gαi1 in female mice contributes to the sex differences in the midbrain. In fact, Gαi1 levels inversely correlate with 5HT uptake rates across both sexes and genotypes. Likely due to differential SERT regulation as well as sex differences in the expression of tryptophan hydroxylase 2, Gαq knockout mice also displayed sex- and genotype-dependent alterations in total 5HT tissue levels as determined by high-performance liquid chromatography. Gαq inhibitors, YM-254890 and BIM-46187, differentially affected SERT activity in both, synaptosomes and cultured cells. YM-254890 treatment mimicked the effect of Gαq knockout in the frontal cortex. BIM-46187, which promotes the nucleotide-free form of Gα proteins, substantially inhibited 5HT uptake, prompting us to hypothesise that Gαq interacts with SERT similarly as with G-protein-coupled receptors and inhibits SERT activity by modulating transport-associated conformational changes. Taken together, our findings reveal a novel mechanism of SERT regulation and impact our understanding of sex differences in diseases associated with dysregulation of serotonin transmission, such as depression and anxiety.

TNFα-dependent anhedonia and upregulation of hippocampal serotonin transporter activity in a mouse model of collagen-induced arthritis.

The serotonin transporter (SERT) facilitates high affinity reuptake of 5-HT from the extracellular fluid and dysregulation of transporter function has been implicated in a range of mood disorders including depression. Recent studies have linked immune system activation to depression as well as to altered serotonin transporter activity. Advancing previous studies, which have mainly focussed on acute effects of immune system activation, in this study we used collagen-induced arthritis (CIA) in mice as a model of chronic inflammatory disease, to investigate the effect of prolonged inflammation on brain SERT function and behaviour. We found that 5-6 weeks after immunisation, CIA mice display anhedonia, a core depression-like behaviour. Behavioural symptoms are temporally correlated with a region-specific upregulation of SERT activity in the hippocampus, which occurs at a post-translational level and is independent of SERT trafficking. Kinetic analysis of 5-HT uptake revealed that the elevation of transporter activity is due to an increase in 5-HT transport capacity (Vmax) with no change in apparent Km values, suggesting that different regulatory mechanisms govern SERT modulation under chronic versus acute inflammatory conditions. Protein expression of tumour necrosis factor receptor 1 (TNFR1) was specifically upregulated in the hippocampus of CIA mice, indicating altered TNFα signalling. Anti-TNFα treatment using etanercept not only diminished joint inflammation, but also prevented the development of anhedonia and the upregulation of SERT activity in the hippocampus, suggesting a key role for TNFα signalling in brain function regulation in this disease model. Our study provides novel insight into molecular mechanisms underlying mood symptoms in chronic inflammatory diseases, with particular relevance to rheumatoid arthritis.