Jamie L. Harden

The Immunogenetics of Psoriasis: A Comprehensive Review

Psoriasis vulgaris is a common, chronic inflammatory skin disease with a complex etiology involving genetic risk factors and environmental triggers. Here we describe the many known genetic predispositions of psoriasis with respect to immune genes and their encoded pathways in psoriasis susceptibility. These genes span an array of functions that involve antigen presentation (HLA-Cw6, ERAP1, ERAP2, MICA), the IL-23 axis (IL12Bp40, IL23Ap19, IL23R, JAK2, TYK2), T-cell development and T-cells polarization (RUNX1, RUNX3, STAT3, TAGAP, IL4, IL13), innate immunity (CARD14, c-REL, TRAF3IP2, DDX58, IFIH1), and negative regulators of immune responses (TNIP1, TNFAIP3, NFKBIA, ZC3H12C, IL36RN, SOCS1). The contribution of some of these gene products to psoriatic disease has also been revealed in recent years through targeting of key immune components, such as the Th17/IL-23 axis which has been highly successful in disease treatment. However, many of the genetic findings involve immune genes with less clear roles in psoriasis pathogenesis. This is particularly the case for those genes involved in innate immunity and negative regulation of immune specific pathways. It is possible that risk alleles of these genes decrease the threshold for the initial activation of the innate immune response. This could then lead to the onslaught of the pathogenic adaptive immune response known to be active in psoriatic skin. However, precisely how these various genes affect immunobiology need to be determined and some are speculated upon in this review. These novel genetic findings also open opportunities to explore novel therapeutic targets and potentially the development of personalized medicine, as well as discover new biology of human skin disease.

TREM-1 as a Potential Therapeutic Target in Psoriasis

Our group recently described a population of antigen presenting cells that appear to be critical in psoriasis pathogenesis, termed inflammatory myeloid dendritic cells (CD11c+ BDCA1−). Triggering receptor expressed on myeloid cells type-1 (TREM-1) Signaling was a major canonical pathway in the published transcriptome of these cells. TREM-1 is a member of the immunoglobulin superfamily, active through the DAP12 signaling pathway, with an unknown ligand. Activation through TREM-1 induces inflammatory cytokines including IL-8, MCP/CCL2 and TNF. We now show that TREM-1 was expressed in the skin of healthy and psoriatic patients, and there was increased soluble TREM-1 in the circulation of psoriasis patients. In psoriasis lesions, TREM-1 was co-localized with dendritic cells as well as CD31+ endothelial cells. TREM-1 expression was reduced with successful NB-UVB, etanercept and anti-IL-17 treatments. An in vitro model of PGN-activated monocytes as inflammatory myeloid DCs was developed to study TREM-1 blockade, and treatment with a TREM-1 blocking chimera decreased allogeneic Th17 activation as well as IL-17 production. Furthermore, TREM-1 blockade of ex vivo psoriatic dendritic cells in an alloMLR also showed a decrease in IL-17. Together, these data suggest that the TREM-1 signaling pathway may be a previously unidentified therapeutic target to prevent the effects of inflammatory myeloid DCs in psoriasis.

CARD14 Expression in Dermal Endothelial Cells in Psoriasis

Mutations in the caspase recruitment domain, family member 14 (CARD14) gene have recently been described in psoriasis patients, and explain the psoriasis susceptibility locus 2 (PSORS2). CARD14 is a scaffolding protein that regulates NF-κB activation, and psoriasis-associated CARD14 mutations lead to enhanced NF-κB signaling. CARD14 is expressed mainly in epidermal keratinocytes, but also in unidentified dermal cells. In this manuscript, the identity of the dermal cell types expressing CARD14, as well the potential functional consequence of overactive CARD14 in these dermal cell types, was determined. Using two-color immunofluorescence, dermal CARD14 did not co-localize with T-cells, dendritic cells, or macrophages. However, dermal CARD14 did highly co-localize with CD31+ endothelial cells (ECs). CARD14 was also expressed non-dermal endothelial cells, such as aortic endothelial cells, which may indicate a role of CARD14+ECs in the systemic inflammation and cardiovascular comorbidities associated with psoriasis. Additionally, phosphorylated NF-κB was found in psoriatic CARD14+ CD31+ ECs, demonstrating this pathway is active in dermal ECs in psoriasis. Transfection of dermal ECs with psoriasis-associated CARD14 mutations resulted in increased expression of several chemokines, including CXCL10, IL-8, and CCL2. These results provide preliminary evidence that CARD14 expression in ECs may contribute to psoriasis through increased expression of chemokines and facilitating recruitment of immune cells into skin.

The tryptophan metabolism enzyme L-kynureninase is a novel inflammatory factor in psoriasis and other inflammatory diseases

BACKGROUND Many human diseases arise from or have pathogenic contributions from a dysregulated immune response. One pathway with immunomodulatory ability is the tryptophan metabolism pathway, which promotes immune suppression through the enzyme indoleamine 2,3-dioxygenase (IDO) and subsequent production of kynurenine. However, in patients with chronic inflammatory skin disease, such as psoriasis and atopic dermatitis (AD), another tryptophan metabolism enzyme downstream of IDO, L-kynureninase (KYNU), is heavily upregulated. The role of KYNU has not been explored in patients with these skin diseases or in general human immunology. OBJECTIVE We sought to explore the expression and potential immunologic function of the tryptophan metabolism enzyme KYNU in inflammatory skin disease and its potential contribution to general human immunology. METHODS Psoriatic skin biopsy specimens, as well as normal human skin, blood, and primary cells, were used to investigate the immunologic role of KYNU and tryptophan metabolites. RESULTS Here we show that KYNU(+) cells, predominantly of myeloid origin, infiltrate psoriatic lesional skin. KYNU expression positively correlates with disease severity and inflammation and is reduced on successful treatment of psoriasis or AD. Tryptophan metabolites downstream of KYNU upregulate several cytokines, chemokines, and cell adhesions. By mining data on several human diseases, we found that in patients with cancer, IDO is preferentially upregulated compared with KYNU, whereas in patients with inflammatory diseases, such as AD, KYNU is preferentially upregulated compared with IDO. CONCLUSION Our results suggest that tryptophan metabolism might dichotomously modulate immune responses, with KYNU as a switch between immunosuppressive versus inflammatory outcomes. Although tryptophan metabolism is increased in many human diseases, how tryptophan metabolism is proceeding might qualitatively affect the immune response in patients with that disease.

Homeostatic Tissue Responses in Skin Biopsies from NOMID Patients with Constitutive Overproduction of IL-1β

The autoinflammatory disorder, Neonatal-onset Multisystem Inflammatory Disease (NOMID) is the most severe phenotype of disorders caused by mutations in CIAS1 that result in increased production and secretion of active IL-1β. NOMID patients present with systemic and organ-specific inflammation of the skin, central nervous system and bone, and respond dramatically to treatment with IL-1 blocking agents. We compared the cellular infiltrates and transcriptome of skin biopsies from patients with NOMID (n = 14) before treatment (lesional (LS) and non-lesional (pre-NL) skin) and after treatment (post-NL) with the IL-1 blocker anakinra (recombinant IL-1 receptor antagonist, Kineret®, Swedish Orphan Biovitrum AB, SOBI), to normal skin (n = 5) to assess tissue responses in the context of untreated and treated disease. Abundant neutrophils distinguish LS skin from pre-NL and post-NL skin. CD11c+ dermal dendritic cells and CD163+ macrophages expressed activated caspase-1 and are a likely source of cutaneous IL-1 production. Treatment with anakinra led to the disappearance of neutrophils, but CD3+ T cells and HLA-DR+ cells remained elevated. Among the upregulated genes IL-6, IL-8, TNF, IL-17A, CCL20, and the neutrophil defensins DEFA1 and DEFA3 were differentially regulated in LS tissues (compared to normal skin). Important significantly downregulated pathways in LS skin included IL-1R/TLR signaling, type I and II cytokine receptor signaling, mitochondrial dysfunction, and antigen presentation. The differential expression and regulation of microRNAs and pathways involved in post-transcriptional modification were suggestive of epigenetic modification in the chronically inflamed tissue. Overall, the dysregulated genes and pathways suggest extensive “adaptive” mechanisms to control inflammation and maintain tissue homeostasis, likely triggered by chronic IL-1 release in the skin of patients with NOMID.

Deep Sequencing of the T-cell Receptor Repertoire Demonstrates Polyclonal T-cell Infiltrates in Psoriasis

It is well known that infiltration of pathogenic T-cells plays an important role in psoriasis pathogenesis. However, the antigen specificity of these activated T-cells is relatively unknown. Previous studies using T-cell receptor polymerase chain reaction technology (TCR-PCR) have suggested there are expanded T-cell receptor (TCR) clones in psoriatic skin, suggesting a response to an unknown psoriatic antigen. Here we describe the results of high-throughput deep sequencing of the entire αβ- and γδ- TCR repertoire in normal healthy skin and psoriatic lesional and non-lesional skin. From this study, we were able to determine that there is a significant increase in the abundance of unique β- and γ- TCR sequences in psoriatic lesional skin compared to non-lesional and normal skin, and that the entire T-cell repertoire in psoriasis is polyclonal, with similar diversity to normal and non-lesional skin. Comparison of the αβ- and γδ- TCR repertoire in paired non-lesional and lesional samples showed many common clones within a patient, and these close were often equally abundant in non-lesional and lesional skin, again suggesting a diverse T-cell repertoire. Although there were similar (and low) amounts of shared β-chain sequences between different patient samples, there was significantly increased sequence sharing of the γ-chain in psoriatic skin from different individuals compared to those without psoriasis. This suggests that although the T-cell response in psoriasis is highly polyclonal, particular γδ- T-cell subsets may be associated with this disease. Overall, our findings present the feasibility of this technology to determine the entire αβ- and γδ- T-cell repertoire in skin, and that psoriasis contains polyclonal and diverse αβ- and γδ- T-cell populations.

Raman microbeam spectrometer noninvasively measures biomoelcules to monitor the tryptophan metabolic pathway

Toward improving early detection of melanoma by accurate diagnosis and avoidance of unnecessary surgical excisions of common moles, we are developing noninvasive quantitative spectral fingerprinting of protein expression using Raman spectroscopy within confocally gated volumes of tissue. Our first target is the L-tryptophan catabolism pathway, which is unregulated in the tumor micro-environment and inhibits the immune response that usually is tumor suppressive. The tryptophan pathway is therefore worthy of diagnostic measurement and finding the ratio of L-tryptophan to its metabolites may aid a melanoma diagnosis. We report the intensity of the Raman signal from L-tryptophan and quinolinic acid, which are found during different stages of the tryptophan metabolic pathway.