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

Global and Dimensions of Mental Health in Arthritis Patients

Arthritis is one of the main clusters of long-lasting musculoskeletal and joint disorders. Recently, there has been increasing interest in the impact of arthritis patients' mental health, which has mainly focused on depression and anxiety in clinical samples. However, much less is known about how domains of mental health based on the widely used 12-item version of the general health survey (GHQ-12) are affected by arthritis. The current research answered this question using confirmatory factor analysis, general linear models, and one-sample t-tests on a nationally representative sample from the United Kingdom with 5588 arthritis patients and 8794 participants indicating that they were not clinically diagnosed with arthritis. The current study found that (1) a total of three factors of GHQ-12 that are labeled GHQ-12A (social dysfunction and anhedonia; six items), GHQ-12B (depression and anxiety; four items), and GHQ-12C (loss of confidence; two items), and (2) both the global mental health and dimensions of mental health are negatively affected by arthritis. Clinicians could use the results from the present study to make better treatment decisions for patients with arthritis.

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.

Fecal microbiota transplantation from patients with rheumatoid arthritis causes depression-like behaviors in mice through abnormal T cells activation

Depression is common in patients with rheumatoid arthritis (RA); however, the precise mechanisms underlying a link between depression and RA remain unclear. Accumulating evidence suggests the role of gut-microbiota-brain axis in depression. In this study, we investigated whether collagen-induced arthritis (CIA) mice produce depression-like behaviors and abnormal composition of gut microbiota. Furthermore, we investigated whether fecal microbiota transplantation (FMT) from RA patients causes depression-like phenotypes in antibiotic cocktail (ABX)-treated mice. CIA mice displayed depression-like behaviors, increased blood levels of pro-inflammatory cytokine interleukin-6 (IL-6), decreased expression of synaptic proteins in the prefrontal cortex (PFC), and abnormal composition of gut microbiota. Furthermore, FMT from RA patients caused depression-like phenotypes, alterations of gut microbiota composition, increased levels of IL-6 and tumor necrosis factor-α (TNF-α), and downregulation of synaptic proteins in the PFC compared to FMT from healthy controls. There were correlations between relative abundance of microbiota and plasma cytokines, expression of synaptic proteins in the PFC or depression-like behaviors. Interestingly, FMT from RA patients induced T cells differentiation in Peyer's patches and spleen. Reduced percentage of Treg cells with an increase of Th1/Th2 index was observed in the mice after FMT from RA patients. These findings suggest that CIA mice exhibit depression-like behaviors, systemic inflammation, and abnormal composition of gut microbiota, and that FMT from RA patients produces depression-like behaviors in ABX-treated mice via T cells differentiation. Therefore, abnormalities in gut microbiota in RA patients may contribute to depression via gut-microbiota-brain axis.

Sustained microglial activation in the area postrema of collagen-induced arthritis mice

Background

Central nervous system (CNS)-mediated symptoms, such as fatigue, depression, and hyperalgesia, are common complications among patients with rheumatoid arthritis (RA). However, it remains unclear how the peripheral pathology of RA spreads to the brain. Accumulated evidence showing an association between serum cytokine levels and aberrant CNS function suggests that humoral factors participate in this mechanism. In contrast to the well-known early responses of microglia (CNS-resident immune cells) in the area postrema [AP; a brain region lacking a blood–brain barrier (BBB)] to experimental inflammation, microglial alterations in the AP during chronic inflammation like RA remain unclear. Therefore, to determine whether microglia in the AP can react to persistent autoimmune-arthritis conditions, we analyzed these cells in a mouse model of collagen-induced arthritis (CIA).

Methods

Microglial number and morphology were analyzed in the AP of CIA and control mice (administered Freund’s adjuvant or saline). Immunostaining for ionized calcium-binding adaptor molecule-1 was performed at various disease phases: “pre-onset” [post-immunization day (PID) 21], “establishment” (PID 35), and “chronic” (PID 56 and 84). Quantitative analyses of microglial number and morphology were performed, with principal component analysis used to classify microglia. Interleukin-1β (IL-1β) mRNA expression was analyzed by multiple fluorescent in situ hybridization and real-time polymerase chain reaction. Behavioral changes were assessed by sucrose preference test.

Results

Microglia in the AP significantly increased in density and exhibited changes in morphology during the establishment and chronic phases, but not the pre-onset phase. Non-subjective clustering classification of cell morphology (CIA, 1,256 cells; saline, 852 cells) showed that the proportion of highly activated microglia increased in the CIA group during establishment and chronic phases. Moreover, the density of IL-1β-positive microglia, a hallmark of functional activation, was increased in the AP. Sucrose preferences in CIA mice negatively correlated with IL-1β expression in brain regions containing the AP.

Conclusions

Our findings demonstrate that microglia in the AP can sustain their activated state during persistent autoimmune arthritis, which suggests that chronic inflammation, such as RA, may affect microglia in brain regions lacking a BBB and have various neural consequences.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-021-02657-x.

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.

A reconciling hypothesis centred on brain-derived neurotrophic factor to explain neuropsychiatric manifestations in rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune chronic inflammatory disease characterized by synovitis leading to joint destruction, pain and disability. Despite efficient antirheumatic drugs, neuropsychiatric troubles including depression and cognitive dysfunction are common in RA but the underlying mechanisms are unclear. However, converging evidence strongly suggests that deficit in brain-derived neurotrophic factor (BDNF) signalling contributes to impaired cognition and depression. Therefore, this review summarizes the current knowledge on BDNF in RA, proposes possible mechanisms linking RA and brain BDNF deficiency including neuroinflammation, cerebral endothelial dysfunction and sedentary behaviour, and discusses neuromuscular electrical stimulation as an attractive therapeutic option.

Sex differences in circulating inflammatory mediators as a function of substance use disorder

BACKGROUND

Substance use disorders (SUD) with comorbid depression and anxiety are linked to poor treatment outcome and relapse. Although some depressed individuals exhibit elevated blood-based inflammation (interleukin-6 [IL-6] and C reactive protein [CRP]), few studies have examined whether the presence of SUD exacerbates inflammation.

METHODS

Treatment-seeking individuals with major depressive disorder (MDD), anxiety disorders, and/or SUD (N = 160; 80 % with MDD) recruited into the Tulsa 1000 study provided blood samples, participated in clinical interviews, and completed a questionnaire battery querying symptoms of current psychopathology and emotional processing. Analyses followed a multistep process. First, groups were created on the presence versus absence of 1+ lifetime SUD diagnoses: SUD+ (37 F, 43 M) and SUD- (60 F, 20 M). Second, a principal component analysis (PCA) of questionnaire data resulted in two factors, one indexing negative emotionality/withdrawal motivation and one measuring positive emotionality/approach motivation. Third, SUD groups, extracted PCA factors, and nuisance covariates (age, body mass index [BMI], nicotine use, psychotropic medication [and hormone/contraception use in females]) were entered as simultaneous predictors of blood-based inflammation (IL-6, IL-8, IL-10, tumor necrosis factor-α, and CRP).

RESULTS

Within females, SUD + exhibited higher IL-8 and IL-10 but lower CRP levels than SUD-. In contrast, SUD was not associated with biomarker levels in males. Across sexes, higher BMI was linked to higher IL-6 and CRP levels, and within the five biomarkers, IL-6 and CRP shared the most variance.

CONCLUSION

These findings point to sex-specific inflammatory profiles as a function of SUD that may provide new targets for intervention.

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.

Amino Acid Metabolism in Rheumatoid Arthritis: Friend or Foe?

In mammals, amino acid metabolism has evolved to act as a critical regulator of innate and adaptive immune responses. Rheumatoid arthritis (RA) is the most common form of inflammatory arthropathy sustained by autoimmune responses. We examine here the current knowledge of tryptophan and arginine metabolisms and the main immunoregulatory pathways in amino acid catabolism, in both RA patients and experimental models of arthritis. We found that l-tryptophan (Trp) metabolism and, in particular, the kynurenine pathway would exert protective effects in all experimental models and in some, but not all, RA patients, possibly due to single nucleotide polymorphisms in the gene coding for indoleamine 2,3-dioxygenase 1 (IDO1; the enzyme catalyzing the rate-limiting step of the kynurenine pathway). The function, i.e., either protective or pathogenetic, of the l-arginine (Arg) metabolism in RA was less clear. In fact, although immunoregulatory arginase 1 (ARG1) was highly induced at the synovial level in RA patients, its true functional role is still unknown, possibly because of few available preclinical data. Therefore, our analysis would indicate that amino acid metabolism represents a fruitful area of research for new drug targets for a more effective and safe therapy of RA and that further studies are demanding to pursue such an important objective.

Serotonin: A Potent Immune Cell Modulator in Autoimmune Diseases

Serotonin, also known as 5-hydroxytryptamine (5-HT) is a signaling mediator that regulates emotion, behavior, and cognition. Previous studies have focused more on the roles of 5-HT in the central nervous system (CNS). However, 5-HT also shares a strong relationship with the pathological cases of tumor, inflammation, and pathogen infection. 5-HT participates in tumor cell migration, metastatic dissemination, and angiogenesis. In addition, 5-HT affects immune regulation via different 5-HT receptors (5-HTRs) expressed immune cells, including both innate and adaptive immune system. Recently, drugs targeting at 5-HT signaling were tested to be beneficial in mouse models and clinical trials of multiple sclerosis (MS) and inflammatory bowel disease (IBD). Thus, it is reasonable to assume that 5-HT participates in the pathogenesis of autoimmune diseases. However, the underlying mechanism by 5-HT modulates the development of autoimmune diseases has not been fully understood. Based on our previous studies and pertinent literature, we provide circumstantial evidence for an essential role of 5-HT, especially the regulation of 5-HT on immune cells in the pathogenesis of autoimmune diseases, which may provide a new point cut for the treatment of autoimmune diseases.

Neuroimmune Activation Drives Multiple Brain States

Neuroimmune signaling is increasingly identified as a critical component of neuronal processes underlying memory, emotion and cognition. The interactions of microglia and astrocytes with neurons and synapses, and the individual cytokines and immune signaling molecules that mediate these interactions are a current focus of much research. Here, we discuss neuroimmune activation as a mechanism triggering different states that modulate cognitive and affective processes to allow for appropriate behavior during and after illness or injury. We propose that these states lie on a continuum from a naïve homeostatic baseline state in the absence of stimulation, to acute neuroimmune activity and chronic activation. Importantly, consequences of illness or injury including cognitive deficits and mood impairments can persist long after resolution of immune signaling. This suggests that neuroimmune activation also results in an enduring shift in the homeostatic baseline state with long lasting consequences for neural function and behavior. Such different states can be identified in a multidimensional way, using patterns of cytokine and glial activation, behavioral and cognitive changes, and epigenetic signatures. Identifying distinct neuroimmune states and their consequences for neural function will provide a framework for predicting vulnerability to disorders of memory, cognition and emotion both during and long after recovery from illness.