Analysis of a functional serotonin transporter promoter polymorphism in psoriasis vulgaris

A systematic review on shared biological mechanisms of depression and anxiety in comorbidity with psoriasis, atopic dermatitis, and hidradenitis suppurativa

BACKGROUND

Mental disorders in comorbidity with chronic skin diseases may worsen disease outcome and patients' quality of life. We hypothesized the comorbidity of depression, anxiety syndromes, or symptoms as attributable to biological mechanisms that the combined diseases share.

METHODS

We conducted a systematic review based on the Preferred Reporting Items for Systematic Review and Meta-Analysis statement searching into PubMed, PsycInfo, and Scopus databases. We examined the literature regarding the comorbidity of psoriasis (Ps), atopic dermatitis (AD), or hidradenitis suppurativa with depression and/or anxiety in adults ≥18 years and the hypothetical shared underlying biological mechanisms.

RESULTS

Sixteen studies were analyzed, mostly regarding Ps and AD. Brain-derived neurotrophic factor/tropomyosin receptor kinase B signaling and nuclear factor kappa-light-chain-enhancer of activated B cells/p38 mitogen-activated protein kinase pathways arose as shared mechanisms in Ps animal models with depression- and/or anxiety-like behaviors. Activated microglia and neuroinflammatory responses emerged in AD depressive models. As to genetic studies, atopic-dermatitis patients with comorbid anxiety traits carried the short variant of serotonin transporter and a polymorphism of the human translocator protein gene. A GA genotype of catechol-O-methyltransferase gene was instead associated with Ps. Reduced natural killer cell activity, IL-4, serotonin serum levels, and increased plasma cortisol and IgE levels were hypothesized in comorbid depressive AD patients. In Ps patients with comorbid depression, high serum concentrations of IL-6 and IL-18, as well as IL-17A, were presumed to act as shared inflammatory mechanisms.

CONCLUSIONS

Further studies should investigate mental disorders and chronic skin diseases concurrently across patients' life course and identify their temporal relation and biological correlates. Future research should also identify biological characteristics of individuals at high risk of the comorbid disorders and associated complications.

The role of immune genes in the association between depression and inflammation: a review of recent clinical studies

The role for dysregulation of the immune system in the pathogenesis of depressive disorder is well established, and emerging research suggests the role of an underlying genetic vulnerability. The purpose of this review is to summarize the existing literature on the genetic variants involved in neurobiological pathways associated with both immune activation and depression. Using PubMed, Scopus, The Cochrane Library, Embase, Ovid of Medline, PsycINFO and ISI web of Knowledge, we selected 52 papers which are relevant for this literature review. Findings across the literature suggest that functional allelic variants of genes for interleukin-1beta (IL)-1β, tumor necrosis factor-alpha (TNF-α) and C-reactive protein (CRP), as well as genetic variations affecting T-cell function, may increase the risk for depression. Moreover, single nucleotide polymorphisms (SNPs) in the IL-1β, IL-6 and IL-11 genes, and in those regulating T-cell function may be associated with reduced responsiveness to antidepressant therapy. There is also some evidence indicative of a role of genetic variants of the enzymes, Cyclo-oxygenase2 (COX-2) and Phospholipase2 (PLA2), in the aetiology of depression. Finally, SNPs in genes related to the serotonin pathway may play a fundamental role in the shared genetic liability to both immune activation and depressive symptoms. Our review confirms that genetic variants influence the biological mechanisms by which the innate immune system contributes to the development of depression. However, future studies are necessary to identify the molecular mechanisms underlying these associations.

Inflammatory vulnerability associated with the rh5-HTTLPR genotype in juvenile rhesus monkeys

Individual variation in serotonergic function is associated with reactivity, risk for affective disorders, as well as an altered response to disease. Our study used a nonhuman primate model to further investigate whether a functional polymorphism in the promoter region for the serotonin transporter gene helps to explain differences in proinflammatory responses. Homology between the human and rhesus monkey polymorphisms provided the opportunity to determine how this genetic variation influences the relationship between a psychosocial stressor and immune responsiveness. Leukocyte numbers in blood and interleukin-6 (IL-6) responses are sensitive to stressful challenges and are indicative of immune status. The neutrophil-to-lymphocyte ratio and cellular IL-6 responses to in vitro lipopolysaccharide stimulation were assessed in 27 juvenile male rhesus monkeys while housed in stable social groups (NLL  = 16, NS  = 11) and also in 18 animals after relocation to novel housing (NLL  = 13, NS  = 5). Short allele monkeys had significantly higher neutrophil-to-lymphocyte ratios than homozygous Long allele carriers at baseline [t(25) = 2.18, P = 0.02], indicative of an aroused state even in the absence of disturbance. In addition, following the housing manipulation, IL-6 responses were more inhibited in short allele carriers (F1,16  = 8.59, P = 0.01). The findings confirm that the serotonin transporter gene-linked polymorphism is a distinctive marker of reactivity and inflammatory bias, perhaps in a more consistent manner in monkeys than found in many human studies.

The expression of serotonin transporter protein correlates with the severity of psoriasis and chronic stress

Psoriasis may be worsened by stress and mood disorders. There is an increased expression of the serotonin transporter protein (SERT) in involved psoriatic skin as compared to non-involved psoriatic skin and normal skin. The aim of this study was to investigate if the increased expression of SERT in psoriasis correlates with the severity of disease, chronic stress, and depression. Biopsies from involved and non-involved skin from the back of 20 patients with chronic plaque psoriasis were immunohistochemically analysed, using a monoclonal antibody to SERT. The severity of psoriasis was assessed for each patient using the Psoriasis area and severity index (PASI). Levels of depression and chronic stress were measured using Beck's Depression Inventory (BDI) and the salivary cortisol test, respectively. A positive correlation (r = 0.53; p < 0.05) between PASI and the numbers of SERT-positive dendritic cells in the epidermis of involved psoriatic skin was determined. We also observed a negative correlation (r = -0.46; p < 0.05) between salivary cortisol ratio levels and the numbers of SERT-positive cells in the epidermis of involved psoriatic skin, indicating a correlation between SERT expression and chronic stress. The serotonergic system may be involved in the chronic inflammation evident in psoriatic skin. Through modulating the levels of SERT, there might be a therapeutic possibility for reducing chronic inflammation in psoriasis.

Polymorphisms in the serotonin transporter gene of patients with atopic dermatitis-association with personality traits related to high level of anxiety

CONTEXT

The symptoms of atopic dermatitis (AD) are often aggravated by anxiety, and the serotonin transporter (5-HTT) has been shown to be of importance in this context. Three polymorphisms affecting transcription of this gene are known: a repetitive element, in the promoter region (5HTTLPR), a variable number tandem repeats (VNTR) within intron 2 referred to as STin2, and a single-nucleotide (A/G) polymorphism (SNP) located within the 5-HTTLPR.

OBJECTIVE

To examine for possible relationships between these polymorphisms and aggravation of AD by stress.

MATERIALS AND METHODS

Thirty-three patients with a history of such aggravation, together with 33 age- and gendermatched healthy control subjects, were recruited. The Karolinska Scales of Personality questionnaire was employed to evaluate anxiety-related personality traits and genomic DNA was extracted from blood samples and analyzed using the polymerase chain reaction.

RESULTS

Although the prevalence of the short and long alleles of 5-HTTLPR did not differ between the patients and healthy controls, there was a tendency towards high prevalence of the short (10-copy) variant of STin2 among the patients. When the study population was further analysed by subdivision into subgroups all AD patients with high- anxiety traits carried the short variant of STin2. In the corresponding healthy control group, the prevalences of the 10-and 12-copy variants were 62% and 38%, respectively (P < 0.01).

CONCLUSION

These findings indicate a possible association between the 10-copy variant of STin2 and aggravation of AD by anxiety.