Elevated expression of the chemokine-scavenging receptor D6 is associated with impaired lesion development in psoriasis

Abstract

D6 is a scavenging-receptor for inflammatory CC chemokines that are essential for resolution of inflammatory responses in mice. Here, we demonstrate that D6 plays a central role in controlling cutaneous inflammation, and that D6 deficiency is associated with development of a psoriasis-like pathology in response to varied inflammatory stimuli in mice. Examination of D6 expression in human psoriatic skin revealed markedly elevated expression in both the epidermis and lymphatic endothelium in "uninvolved" psoriatic skin (ie, skin that was more than 8 cm distant from psoriatic plaques). Notably, this increased D6 expression is associated with elevated inflammatory chemokine expression, but an absence of plaque development, in uninvolved skin. Along with our previous observations of the ability of epidermally expressed transgenic D6 to impair cutaneous inflammatory responses, our data support a role for elevated D6 levels in suppressing inflammatory chemokine action and lesion development in uninvolved psoriatic skin. D6 expression consistently dropped in perilesional and lesional skin, coincident with development of psoriatic plaques. D6 expression in uninvolved skin also was reduced after trauma, indicative of a role for trauma-mediated reduction in D6 expression in triggering lesion development. Importantly, D6 is also elevated in peripheral blood leukocytes in psoriatic patients, indicating that upregulation may be a general protective response to inflammation. Together our data demonstrate a novel role for D6 as a regulator of the transition from uninvolved to lesional skin in psoriasis.

Figure 1

Dynamic D6 expression is associated with psoriasis. A: D6-deficient mice displayed psoriasis-like lesions after repeated liposome injection into tail skin as compared with WT mice. The Mice were subjected to injections every second day, and tissue was collected for histology at day 21. Note the markedly increased epidermal thickening (arrow) and dermal inflammatory infiltrate (asterisk) in D6-deficient skin. Scale bar = 100 μm. B: A psoriasis-like phenotype (arrow) is seen in D6-deficient mice after subcutaneous injection of complete Freund's adjuvant (CFA). CFA was injected subcutaneously into WT and D6-deficient mice, and skin was harvested for histology 3 days later. Scale bar = 200 μm. C: The psoriasis-like pathology developing in D6-deficient mice in response to TPA application is sensitive to topical hydrocortisone treatment and systemic treatment with antibodies to IL-1β and IL-17 and a receptor-based blocker of IL-15. Scale bar = 100 μm.

Figure 2

D6 is highly expressed and is coincident with inflammatory CC-chemokines in the epidermis of ‘uninvolved’ psoriatic skin. A: Relative expression of D6 in uninvolved, perilesional and lesional psoriatic skin compared with healthy control (control) skin which is set as the comparator of 1. P < 0.02 between control and uninvolved, P < 0.003 between uninvolved and both perilesional and lesional, and P < 0.03 between control and both perilesional and lesional expression. B: Expression of D6 in biopsy samples from healthy control skin and lesional atopic dermatitis skin. C: Expression levels of D6 in matched uninvolved (open bars) and lesional (filled bars) biopsy samples from 10 patients. D: Immunofluorescent detection of D6 expression (arrowed) in control, uninvolved, perilesional, and lesional skin (scale bar = 100 μm). E: Immunofluorescent detection of CCL2 (arrowed) in control, uninvolved, perilesional, and lesional skin (scale bar = 100 μm).

Figure 3

D6 is expressed by a range of cell types in psoriatic patients. A: Enumeration of D6+/podoplanin+lymphatic vessels in the dermis of control and psoriatic skin biopsy samples. Levels in uninvolved skin are significantly higher (*P < 0.0001) than in control, perilesional, or lesional skin. B: qPCR analysis of D6 expression in control and psoriatic peripheral blood leukocytes. *P < 0.0001.

Figure 4

D6 expression is regulated by psoriasis-relevant cytokines and trauma. IL-1α (A) and IFN-β (B) induce up-regulation of D6 expression in cultured keratinocytes in vitro at 6 hours (IL-1α) and 48 hours (IFN-β), respectively. Cytokines were used at 100 ng/mL. C: D6 protein levels were assessed as the number of D6+ cells per ×20 microscopic field and 10 fields were counted for control and for IFN-β–treated cell monolayers (left panel). Immunofluorescent staining demonstrates elevated D6 protein expression in IFN-β–treated compared with PBS-treated keratinocytes (right panels). D: Keratinocytes were treated with each of the indicated cytokines at 100 ng/mL for 6, 24, or 48 hours, and D6 expression levels were assessed by q-PCR. *P < 0.03; **P < 0.01; ***P < 0.002. E: Trauma induced by tape stripping causes a significant reduction in D6 transcript expression in full-thickness skin biopsy samples from “uninvolved” psoriatic skin by 24 hours, compared with expression in similar biopsy samples from nontraumatized uninvolved skin from the same donors (left panel), and (right panels) intensity of D6 immunostaining in biopsy samples from traumatized compared with matched, nontraumatized uninvolved skin at 48 hours Scale bar = 100 μm.