Genetic variation in the serotonin receptor gene affects immune responses in rheumatoid arthritis

Fibroblast expression of neurotransmitter receptor HTR2A associates with inflammation in rheumatoid arthritis joint

The study of neuroimmune crosstalk and the involvement of neurotransmitters in inflammation and bone health has illustrated their significance in joint-related conditions. One important mode of cell-to-cell communication in the synovial fluid (SF) is through extracellular vesicles (EVs) carrying microRNAs (miRNAs). The role of neurotransmitter receptors in the pathogenesis of inflammatory joint diseases, and whether there are specific miRNAs regulating differentially expressed HTR2A, contributing to the inflammatory processes and bone metabolism is unclear. Expression of neurotransmitter receptors and their correlated inflammatory molecules were identified in rheumatoid arthritis (RA) and osteoarthritis (OA) synovium from a scRNA-seq dataset. Immunohistochemistry staining of synovial tissue (ST) from RA and OA patients was performed for validation. Expression of miRNAs targeting HTR2A carried by SF EVs was screened in low- and high-grade inflammation RA from a public dataset and validated by qPCR. HTR2A reduction by target miRNAs was verified by miRNAs mimics transfection into RA fibroblasts. HTR2A was found to be highly expressed in fibroblasts derived from RA synovial tissue. Its expression showed a positive correlation with the degree of inflammation observed. 5 miRNAs targeting HTR2A were decreased in RA SF EVs compared to OA, three of which, miR-214-3p, miR-3120-5p and miR-615-3p, mainly derived from monocytes in the SF, were validated as regulators of HTR2A expression. The findings suggest that fibroblast HTR2A may play a contributory role in inflammation and the pathogenesis of RA. Additionally, targeting miRNAs that act upon HTR2A could present novel therapeutic strategies for alleviating inflammation in RA.

Serum serotonin levels are elevated in patients with increased risk of rheumatoid arthritis

Background

Even though serotonin (5-HT) has been ascribed immunomodulatory features, very little is known about its role in chronic inflammatory diseases. Serotonin is implicated in inflammation and increased levels have been associated with progression of bone erosions in RA.

Objective

To investigate serum serotonin levels in patients with increased risk of rheumatoid arthritis (RA) and patients with recent-onset disease. Moreover, we aimed to determine the prognostic value of serotonin for arthritis development and the disease course.

Methods

Two prospective observational patient cohorts were studied; anti-citrullinated protein antibody (ACPA) -positive patients with musculoskeletal pain without clinical arthritis (n = 82) and patients with early RA (n = 412). Serotonin levels were measured by enzyme-linked immunosorbent assay (ELISA) in baseline serum samples from both cohorts, and longitudinally in at-risk individuals.

Results

Compared to healthy controls (median 65 ng/ml), serotonin levels were significantly higher in both at-risk individuals (median 111 ng/ml, p < 0.0001) and patients with early RA (median 135 ng/ml, p < 0.0001). No significant differences were found between at-risk individuals and patients with early RA. At-risk individuals progressing to arthritis had similar levels as those not progressing, and no significant differences were seen over time. Baseline levels in early RA did not associate with mean 28-joint disease activity scores during 3 years follow-up.

Conclusion

Serum serotonin levels are elevated both at, and prior to, onset of RA. However, increased serotonin is not prognostic for arthritis development or disease course.

Circulating methylation level of HTR2A is associated with inflammation and disease activity in rheumatoid arthritis

Objectives

HTR2A is previously identified as a susceptibility gene for rheumatoid arthritis (RA). In this study, we performed the association analysis between DNA methylation of HTR2A with RA within peripheral blood samples.

Methods

We enrolled peripheral blood samples from 235 patients with RA, 30 osteoarthritis (OA) patients, and 30 healthy controls. The DNA methylation levels of about 218 bp from chr13: 46898190 to chr13: 46897973 (GRCh38/hg38) around HTR2A cg15692052 from patients were analyzed by targeted methylation sequencing.

Results

We measured methylation status for 7 CpGs in the promoter region of HTR2A and obseved overall methylation status are signficantly increased in RA compared with normal inviduals (FDR= 9.05 x 10^-5). The average cg15692052 methylation levels (methylation score) showed a positive correlation with CRP (r=0.15, P=0.023). Compared with the OA group or HC group, the proportion of haplotypes CCCCCCC (FDR=0.02 and 2.81 x 10^-6) is signficantly increased while TTTTTCC (FDR =0.01) and TTTTTTT(FDR =6.92 x 10^-3) are significantly decreased in RA. We find methylation haplotypes combining with RF and CCP could signficantly enhance the performance of the diagnosing RA and its comorbidities (hypertension, interstitial lung disease, and osteoporosis), especially in interstitial lung disease.

Conclusions

In our study, we found signficant hypermethylation of promoter region of HTR2A which indicates the potential clinical diagnostic role in rheumatoid arthritis.

Major depression favors the expansion of Th17-like cells and decrease the proportion of CD39+Treg cell subsets in response to myelin antigen in multiple sclerosis patients

BACKGROUND

Mood disorders have been associated with risk of clinical relapses in multiple sclerosis (MS), a demyelinating disease mediated by myelin-specific T cells.

OBJECTIVES

We aimed to investigate the impact of major depressive disorder (MDD) and cytokine profile of T-cells in relapsing remitting MS patients.

METHODS

For our study, plasma and PBMC were obtained from 60 MS patients (30 with lifetime MDD) in remission phase. The PBMC cultures were stimulated with anti-CD3/anti-CD28 beads or myelin basic protein (MBP), and effector and regulatory T cell phenotypes were determined by flow cytometry. The cytokine levels, both in the plasma or in the supernatants collected from PBMC cultures, were quantified by Luminex. In some experiments, the effect of serotonin (5-HT) was investigated.

RESULTS

Here, higher Th17-related cytokine levels in response to anti-CD3/anti-CD28 and MBP were quantified in the plasma and PBMC cultures of the MS/MDD group in comparison with MS patients. Further, elevated frequency of CD4+ and CD8+ T cells capable of producing IL-17, IL-22 and GM-CSF was observed in depressed patients. Interestingly, the percentage of myelin-specific IFN-γ+IL-17+ and IFN-γ+GM-CSF+ CD4+ T cells directly correlated with neurological disabilities. In contrast, the occurrence of MDD reduced the proportion of MBP-specific CD39+Tregs subsets. Notably, the severity of both neurological disorder and depressive symptoms inversely correlated with these Tregs. Finally, the addition of 5-HT downregulated the release of Th17-related cytokines in response to anti-CD3/anti-CD28 and myelin antigen.

CONCLUSIONS

In summary, our findings suggested that recurrent major depression, by favoring imbalances of effector Th17 and Treg cell subsets, contributes to MS severity.

Selective serotonin reuptake inhibitor attenuates the hyperresponsiveness of TLR2+ and TLR4+ Th17/Tc17-like cells in multiple sclerosis patients with major depression

Elevated frequency of Th17-like cells expressing Toll-like receptors (TLRs) has been recently associated with relapsing-remitting multiple sclerosis (MS) pathogenesis, a chronic inflammatory demyelinating autoimmune disease of the central nervous system. We aimed to investigate the impact of current major depressive disorder (MDD) on the behaviour of these cells following in vitro stimulation with TLR2, TLR4, TLR5 and TLR9 agonists. Here, the level of both cell proliferation and cytokine production related to Th17/Tc17 phenotypes in response to TLR2 (Pam3C) and TLR4 (LPS) ligands was significantly higher in CD4+ and CD8+ T-cell cultures from MS/MDD patients when compared to non-depressed patients. These cytokine levels were positively associated with neurological disabilities in patients. No difference for responsiveness to TLR5 (flagellin) and TLR9 (ODN) agonists was observed. LPS, but not Pam3C, induced significant IL-10 release, mainly in patients without MDD. Interestingly, more intense expression of TLR2 and TLR4 on these cells was observed in MDD patients. Finally, in vitro addition of serotonin and treatment of MDD patients with selective serotonin reuptake inhibitors (SSRIs) reduced the production of Th17/Tc17-related cytokines by CD4+ and CD8+ T cells in response to Pam3C and LPS. However, only SSRI therapy diminished the frequency and intensity of TLR2 and TLR4 expression on circulating CD4+ and CD8+ T cells. In summary, although preliminary, our findings suggest that adverse events that elevate circulating levels of TLR2 and TLR4 ligands can affect MS pathogenesis, particularly among depressed patients.

An Insight into the Roles of Dietary Tryptophan and Its Metabolites in Intestinal Inflammation and Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is complex, chronic, and relapsing gastrointestinal inflammatory disorders, which includes mainly two conditions, namely ulcerative colitis (UC) and Crohn's disease (CD). Development of IBD in any individual is closely related to his/her autoimmune regulation, gene-microbiota interactions, and dietary factors. Dietary tryptophan (Trp) is an essential amino acid for intestinal mucosal cells, and it is associated with the intestinal inflammation, epithelial barrier, and energy homeostasis of the host. According to recent studies, Trp and its three major metabolic pathways, namely kynurenine (KYN) pathway, indole pathway, and 5-hydroxytryptamine (5-HT) pathway, have vital roles in the regulation of intestinal inflammation by acting directly or indirectly on the pro/anti-inflammatory cytokines, functions of various immune cells, as well as the intestinal microbial composition and homeostasis. In this review, recent advances in Trp- and its metabolites-associated intestinal inflammation are summarized. It further discusses the complex mechanisms and interrelationships of the three major metabolic pathways of Trp in regulating inflammation, which could elucidate the value of dietary Trp to be used as a nutrient for IBD patients.

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.

Platelets: emerging facilitators of cellular crosstalk in rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease in which a variety of circulating pro-inflammatory cells and dysregulated molecules are involved in disease aetiology and progression. Platelets are an important cellular element in the circulation that can bind several dysregulated molecules (such as collagen, thrombin and fibrinogen) that are present both in the synovium and the circulation of patients with RA. Platelets not only respond to dysregulated molecules in their environment but also transport and express their own inflammatory mediators, and serve as regulators at the boundary between haemostasis and immunity. Activated platelets also produce microparticles, which further convey signalling molecules and receptors to the synovium and circulation, thereby positioning these platelet-derived particles as strategic regulators of inflammation. These diverse functions come together to make platelets facilitators of cellular crosstalk in RA. Thus, the receptor functions, ligand binding potential and dysregulated signalling pathways in platelets are becoming increasingly important for treatment in RA. This Review aims to highlight the role of platelets in RA and the need to closely examine platelets as health indicators when designing effective pharmaceutical targets in this disease.

Serotonin decreases the production of Th1/Th17 cytokines and elevates the frequency of regulatory CD4+ T-cell subsets in multiple sclerosis patients

Excessive levels of proinflammatory cytokines in the CNS are associated with reduced serotonin (5-HT) synthesis, a neurotransmitter with diverse immune effects. In this study, we evaluated the ability of exogenous 5-HT to modulate the T-cell behavior of patients with MS, a demyelinating autoimmune disease mediated by Th1 and Th17 cytokines. Here, 5-HT attenuated, in vitro, T-cell proliferation and Th1 and Th17 cytokines production in cell cultures from MS patients. Additionally, 5-HT reduced IFN-γ and IL-17 release by CD8⁺ T cells. By contrast, 5-HT increased IL-10 production by CD4⁺ T cells from MS patients. A more accurate analysis of these IL-10-secreting CD4⁺ T cells revealed that 5-HT favors the expansion of FoxP3⁺ CD39⁺ regulatory T cells (Tregs) and type 1 regulatory T cells. Notably, this neurotransmitter also elevated the frequency of Treg17 cells, a novel regulatory T-cell subset. The effect of 5-HT in upregulating CD39⁺ Treg and Treg17 cells was inversely correlated with the number of active brain lesions. Finally, in addition to directly reducing cytokine production by purified Th1 and Th17 cells, 5-HT enhanced in vitro Treg function. In summary, our data suggest that serotonin may play a protective role in the pathogenesis of MS.

Genetic polymorphisms in the serotonin receptor 7 (HTR7) gene are associated with cortisol levels in African American young adults

Introduction: Serotonin is a neurohormone involved in biological processes, such as behavior and immune function. Chronic psychosocial stressors may cause serotonin release resulting in immune system dysregulation, as evidenced by increased or far decreased levels of cortisol, a blood biomarker of stress and immune function. We hypothesize that genetic polymorphisms in the HTR7 gene are associated with both hypo- and hyper-cortisolism. Methods: The study population included 602 African American subjects between 18-34 years of age, living in Washington, D.C. Five single nucleotide polymorphisms (SNPs) in HTR7, rs2420367, rs12412496, rs2185706, rs7089533, and rs7093602 were genotyped by restriction fragment length polymorphism or the TaqMan assay. Statistical analysis, using the program SNPstat, was performed to determine their associations with cortisol measured in the study population. Results: While an increased risk of hypocortisolism was found to be associated with rs2420367, rs2185706, and rs7093602 in a gender specific manner, no genotypes could be associated with hypercortisolism. Inversely, a decreased risk of hypocortisolism was found with the haplotype CGGCC (p=0.033), which remained significant in males. When adjusting for gender, females associated with the haplotype AGACC. Hypercortisolism was also associated with a decreased risk for the haplotypes AAACC (p=0.042) and AAGTT (p=0.001). Discussion: Based on these results, genetic variation in the HTR7 gene may contribute to both stress and inflammation, and will provide a new glimpse into stress-related inflammation psychophysiology.

Increased risk of rheumatoid arthritis in patients with migraine: a population-based, propensity score-matched cohort study

Previous cross-sectional studies have suggested an association between migraine and rheumatoid arthritis (RA), but no longitudinal study has been performed to evaluate the temporal relationship between the two conditions. The purpose of the present population-based, propensity score-matched cohort study was to investigate whether migraineurs are at a higher risk of developing RA. A total of 58,749 subjects aged between 20 and 90 years with at least two ambulatory visits with a diagnosis of migraine were recruited in the migraine group. We fit a logistic regression model that included age, sex, comorbid conditions, and socioeconomic status as covariates to compute the propensity score. The non-migraine group consisted of 58,749 propensity score-matched, randomly sampled subjects without migraine. The RA-free survival curves were generated using the Kaplan-Meier method. Stratified Cox proportional hazard regression was used to estimate the effect of migraine on the risk of RA. During follow-up, 461 subjects in the migraine group and 220 in the non-migraine group developed RA. The incidence rate of RA was 3.18 (95% confidence interval [CI] 2.90-3.49) per 1000 person-years in the migraine group and 1.54 (95% CI 1.34-1.76) per 1000 person-years in the non-migraine group. Compared to the non-migraine group, the crude hazard ratio of RA for the migraine group was 2.15 (95% CI 1.82-2.56, P < 0.0001), and the multivariable-adjusted hazard ratio was 1.91 (95% CI 1.58-2.31, P < 0.0001). This study showed that patients with migraine had an increased risk of developing RA.

PTSD, a Disorder with an Immunological Component

Post-traumatic stress disorder (PTSD) has been associated with an inflammatory state. However, few studies have addressed the mechanisms underlying this immune imbalance that favors inflammation or how this imbalance contributes to PTSD. Whether the immune imbalance influences responsiveness or unresponsiveness of patients to PTSD treatments is currently not known. This review brings forward an immune emphasis to a mental health disorder that is unprecedented in its prevalence among combat Veterans of the ongoing conflicts in Iraq and Afghanistan and which also afflicts civilians who have undergone extreme traumatic experiences, such as following natural disasters, serious accidents, or assaults. Included is an overview of the correlative associations in human subjects between PTSD and inflammation and studies in animal models of PTSD, demonstrating causal contributions of inflammation and immune dysregulation to PTSD-like behavior following stress exposure.

Association of three SNPs in the PARP-1 gene with Hashimoto's thyroiditis

Poly(ADP-ribose) polymerase-1 (PARP-1) has a vital role in the progression of the inflammatory response, and its inhibition confers protection in various models of inflammatory disorders. Therefore, we investigated the effect of promoter and exon variations of the PARP-1 gene on the risk for the inflammatory disease Hashimoto's thyroiditis (HT). This case-control association study was comprised of 141 HT patients and 150 controls from a group of women in a Turkish population. Two polymorphisms in the promoter region of the PARP-1 gene, rs2793378 and rs7527192, were analyzed using the PCR-RFLP method. In addition, single nucleotide polymorphism (SNP) rs1136410, which is located at codon 762, was analyzed using bidirectional sequencing. The combined genotype and haplotype analyses of these polymorphisms were performed using SPSS 18 and Haploview 4.2. The results were statistically analyzed by calculating the odds ratios and 95% confidence interval using Pearson's χ (2)-test and Fisher's exact test (two-sided). Although we had a number of significant results, the associations became nonsignificant following a Bonferroni correction for multiple comparisons. Nonetheless, a protective factor against HT was still observed for the heterozygous genotype (TC) of SNP rs1136410 (P=0.001), even following Bonferroni correction, and according to the rs2793378-rs7527192 combined analysis, the occurrence of the TT/GA combined genotype was significantly higher in the controls (P=0.007). These results prove that the heterozygosity of SNP rs1136410 provides a protective effect against HT disease in a group of women in a Turkish population.

Novel synthetic biscoumarins target tumor necrosis factor-α in hepatocellular carcinoma in vitro and in vivo

TNF is a pleotropic cytokine known to be involved in the progression of several pro-inflammatory disorders. Many therapeutic agents have been designed to counteract the effect of TNF in rheumatoid arthritis as well as a number of cancers. In the present study we have synthesized and evaluated the anti-cancer activity of novel biscoumarins in vitro and in vivo. Among new compounds, BIHC was found to be the most cytotoxic agent against the HepG2 cell line while exhibiting less toxicity toward normal hepatocytes. Furthermore, BIHC inhibited the proliferation of various hepatocellular carcinoma (HCC) cells in a dose- and time-dependent manner. Subsequently, using in silico target prediction, BIHC was predicted as a TNF blocker. Experimental validation was able to confirm this hypothesis, where BIHC could significantly inhibit the recombinant mouse TNF-α binding to its antibody with an IC50 of 16.5 μM. Furthermore, in silico docking suggested a binding mode of BIHC similar to a ligand known to disrupt the native, trimeric structure of TNF, and also validated with molecular dynamics simulations. Moreover, we have demonstrated the down-regulation of p65 phosphorylation and other NF-κB-regulated gene products upon BIHC treatment, and on the phenotypic level the compound shows inhibition of CXCL12-induced invasion of HepG2 cells. Also, we demonstrate that BIHC inhibits infiltration of macrophages to the peritoneal cavity and suppresses the activity of TNF-α in vivo in mice primed with thioglycollate broth and lipopolysaccharide. We comprehensively validated the TNF-α inhibitory efficacy of BIHC in an inflammatory bowel disease mice model.

Neuroendocrine signaling via the serotonin transporter regulates clearance of apoptotic cells

Serotonin (5-hydroxytryptamine; 5-HT) is a CNS neurotransmitter increasingly recognized to exert immunomodulatory effects outside the CNS that contribute to the pathogenesis of autoimmune and chronic inflammatory diseases. 5-HT signals to activate the RhoA/Rho kinase (ROCK) pathway, a pathway known for its ability to regulate phagocytosis. The clearance of apoptotic cells (i.e. efferocytosis) is a key modulator of the immune response that is inhibited by the RhoA/ROCK pathway. Because efferocytosis is defective in many of the same illnesses where 5-HT has been implicated in disease pathogenesis, we hypothesized that 5-HT would suppress efferocytosis via activation of RhoA/ROCK. The effect of 5-HT on efferocytosis was examined in murine peritoneal and human alveolar macrophages, and its mechanisms were investigated using pharmacologic blockade and genetic deletion. 5-HT impaired efferocytosis by murine peritoneal macrophages and human alveolar macrophages. 5-HT increased phosphorylation of myosin phosphatase subunit 1 (Mypt-1), a known ROCK target, and inhibitors of RhoA and ROCK reversed the suppressive effect of 5-HT on efferocytosis. Peritoneal macrophages expressed the 5-HT transporter and 5-HT receptors (R) 2a, 2b, but not 2c. Inhibition of 5-HTR2a and 5-HTR2b had no effect on efferocytosis, but blockade of the 5-HT transporter prevented 5-HT-impaired efferocytosis. Genetic deletion of the 5-HT transporter inhibited 5-HT uptake into peritoneal macrophages, prevented 5-HT-induced phosphorylation of Mypt-1, reversed the inhibitory effect of 5-HT on efferocytosis, and decreased cellular peritoneal inflammation. These results suggest a novel mechanism by which 5-HT might disrupt efferocytosis and contribute to the pathogenesis of autoimmune and chronic inflammatory diseases.