Laure Favot

Specific increase in caspase-1 activity and secretion of IL-1 family cytokines: a putative link between mevalonate kinase deficiency and inflammation

The mevalonate kinase deficiency (MKD), including hyperimmunoglobulinemia D periodic fever syndrome (HIDS) and the more severe mevalonic aciduria are rare, autosomal recessive, autoinflammatory diseases belonging to the hereditary periodic fever (HPF) family. Other members include: familial mediterranean fever (FMF), the cryopyrin-associated periodic syndromes (CAPS) and TNFR-associated periodic syndromes (TRAPS). MKD is caused by mutations in the gene encoding mevalonate kinase (MK), an enzyme of the cholesterol pathway, leading to its inactivation. The molecular mechanisms linking MKD and abnormalities of isoprenoid biosynthesis to cytokine production and inflammation have yet to be fully elucidated. Statins, which are extensively prescribed for lowering cholesterol, are potent inhibitors of 3-hydroxy-3-methylglutaryl-CoA reductase, the enzyme directly upstream of MK. In this review, we discuss recent reports demonstrating that in vitro inhibition of the mevalonate pathway by statins specifically increases the production, by activated monocytes, of cytokines of the IL-1 family, by enhancing caspase-1 activity, the enzyme responsible for IL-1beta and IL-18 maturation. The molecular mechanisms involve geranylgeranylation and the enhancement of the activity of G proteins such as Rac-1. Interestingly, activated fibroblasts from MKD patients secrete more IL-1beta than fibroblasts from healthy donors. Taken together, these data highlight the specific enhancement of the IL-1 family of cytokines, the maturation of which is caspase-1-dependent in MKD. Finally, the spectacular decrease in febrile attacks in patients with severe HIDS under IL-1 receptor antagonist (anakinra) treatment, reinforces this hypothesis. Deregulated caspase-1 activation could be responsible for the inflammatory component of MKD, thereby mechanistically linking MKD to FMF and CAPS through cytokines of the IL-1 family.

Design, synthesis and biological evaluation of new thalidomide analogues as TNF-α and IL-6 production inhibitors.

Several thalidomide analogues were synthesized and compared to thalidomide and its more active analogue, lenalidomide, for their ability to inhibit the production of the pro-inflammatory cytokine tumour necrosis factor (TNF)-α and interleukin (IL)-6 by LPS-activated peripheral blood mononuclear cells (PBMCs). Among these compounds, two analogues containing sulfonyl group displayed interesting downregulation of TNF-α and IL-6 production.

IMQ-induced skin inflammation in mice is dependent on IL-1R1 and MyD88 signaling but independent of the NLRP3 inflammasome.

The pathogenesis of inflammatory skin diseases such as psoriasis involves the release of numerous proinflammatory cytokines, including members of the IL‐1 family. Here we report overexpression of IL‐1α, IL‐1β, and IL‐1 receptor antagonist mRNA, associated to expression of IL‐23p19, IL‐17A, and IL‐22 in skin cells, upon topical application of the TLR7 agonist imiquimod (IMQ) in C57BL/6J mice. IMQ‐induced skin inflammation was partially reduced in mice deficient for both IL‐1α/IL‐1β or for IL‐1 receptor type 1 (IL‐1R1), but not in IL‐1α‐ or IL‐1β‐deficient mice, demonstrating the redundant activity of IL‐1α and IL‐1β for skin inflammation. NLRP3 or apoptosis‐associated Speck‐like protein containing a Caspase recruitment domain‐deficient mice had no significant reduction of skin inflammation in response to IMQ treatment, mainly due to the redundancy of IL‐1α. However, IMQ‐induced skin inflammation was abolished in the absence of MyD88, the adaptor protein shared by IL‐1R and TLR signaling pathways. These results are consistent with the TLR7 dependence of IMQ‐induced skin inflammation. Thus, IL‐1R1 contributes to the IMQ‐induced skin inflammation, and disruption of MyD88 signaling completely abrogates this response.

Oncostatin M overexpression induces skin inflammation but is not required in the mouse model of imiquimod-induced psoriasis-like inflammation

Oncostatin M (OSM) has been reported to be overexpressed in psoriasis skin lesions and to exert proinflammatory effects in vitro on human keratinocytes. Here, we report the proinflammatory role of OSM in vivo in a mouse model of skin inflammation induced by intradermal injection of murine OSM‐encoding adenovirus (AdOSM) and compare with that induced by IL‐6 injection. Here, we show that OSM potently regulates the expression of genes involved in skin inflammation and epidermal differentiation in murine primary keratinocytes. In vivo, intradermal injection of AdOSM in mouse ears provoked robust skin inflammation with epidermal thickening and keratinocyte proliferation, while minimal effect was observed after AdIL‐6 injection. OSM overexpression in the skin increased the expression of the S100A8/9 antimicrobial peptides, CXCL3, CCL2, CCL5, CCL20, and Th1/Th2 cytokines, in correlation with neutrophil and macrophage infiltration. In contrast, OSM downregulated the expression of epidermal differentiation genes, such as cytokeratin‐10 or filaggrin. Collectively, these results support the proinflammatory role of OSM when it is overexpressed in the skin. However, OSM expression was not required in the murine model of psoriasis induced by topical application of imiquimod, as demonstrated by the inflammatory phenotype of OSM‐deficient mice or wild‐type mice treated with anti‐OSM antibodies.

High-Fat Diet–Induced IL-17A Exacerbates Psoriasiform Dermatitis in a Mouse Model of Steatohepatitis

Recent studies suggest that psoriasis may be more severe in patients with nonalcoholic fatty liver disease, particularly in those with the inflammatory stage of steatohepatitis [nonalcoholic steatohepatitis (NASH)]. Herein, we investigated the impact of diet-induced steatohepatitis on the severity of imiquimod-induced psoriasiform dermatitis. Mice fed with a high-fat diet developed steatohepatitis reminiscent of human NASH with ballooning hepatocytes and significant liver fibrosis. Mice with steatohepatitis also displayed moderate cutaneous inflammation characterized by erythema, dermal infiltrates of CD45(+) leukocytes, and a local production of IL-17A. Moreover, steatohepatitis was associated with an epidermal activation of caspase-1 and cutaneous overexpression of IL-1β. Imiquimod-induced psoriasiform dermatitis was exacerbated in mice with steatohepatitis as compared to animals fed with a standard diet. Scale formation and acanthosis were aggravated, in correlation with increased IL-17A and IL-22 expression in inflamed skins. Finally, intradermal injection of IL-17A in standard diet-fed mice recapitulated the cutaneous pathology of mice with steatohepatitis. The results show that high-fat diet-induced steatohepatitis aggravates the inflammation in psoriasiform dermatitis, via the cutaneous production of IL-17A. In agreement with clinical data, this description of a novel extrahepatic manifestation of NASH should sensitize dermatologists to the screening and the management of fatty liver in psoriatic patients.

Involvement of IL-1 and Oncostatin M in Acanthosis Associated With Hypertensive Leg Ulcer

Hypertensive leg ulcer (HLU) is an inflammatory disease characterized by intense pain, alteration of vascularization, and skin necrosis. The optimal treatment relies on surgical removal of necrotic tissues covered by a split-skin graft. We studied the histomorphology of the lesions and investigated the involvement of inflammatory cells and cytokines to further define the physiopathology of HLU. We report epidermis acanthosis and a preferential occlusion of the precapillary arterioles with infiltration of neutrophils, macrophages, and T lymphocytes in the dermis. OSM, IL-1β, and IL-6 were overexpressed in the ulcer, whereas the Th17-derived cytokines were not. In vitro, the addition of IL-1β and OSM promoted acanthosis and destructuring of reconstructed epidermis. Exogenous IL-1β and OSM synergistically induced epidermal acanthosis in mice. These data show that OSM and IL-1β are not only a biological characteristic signature of HLU, but these cytokines reflect a specific inflammatory state, directly involved in the pathogenesis. We suggest that anti-cytokine biotherapies could be an alternative strategy to surgery to treat HLU.

Liver fibrosis is associated with cutaneous inflammation in the imiquimod‐induced murine model of psoriasiform dermatitis

Psoriasis exhibits several extracutaneous manifestations. Little is known about hepatic parameters specifically associated with psoriasis.

Interleukin-17A-induced production of acute serum amyloid A by keratinocytes contributes to psoriasis pathogenesis

Background Acute-serum Amyloid A (A-SAA), one of the major acute-phase proteins, is mainly produced in the liver but extra-hepatic synthesis involving the skin has been reported. Its expression is regulated by the transcription factors NF-κB, C/EBPβ, STAT3 activated by proinflammatory cytokines. Objectives We investigated A-SAA synthesis by resting and cytokine-activated Normal Human Epidermal Keratinocytes (NHEK), and their inflammatory response to A-SAA stimulation. A-SAA expression was also studied in mouse skin and liver in a model mimicking psoriasis and in the skin and sera of psoriatic and atopic dermatitis (AD) patients. Methods NHEK were stimulated by A-SAA or the cytokines IL-1α, IL-17A, IL-22, OSM, TNF-α alone or in combination, previously reported to reproduce features of psoriasis. Murine skins were treated by imiquimod cream. Human skins and sera were obtained from patients with psoriasis and AD. A-SAA mRNA was quantified by RT qPCR. A-SAA proteins were dosed by ELISA or immunonephelemetry assay. Results IL-1α, TNF-α and mainly IL-17A induced A-SAA expression by NHEK. A-SAA induced its own production and the synthesis of hBD2 and CCL20, both ligands for CCR6, a chemokine receptor involved in the trafficking of Th17 lymphocytes. A-SAA expression was increased in skins and livers from imiquimod-treated mice and in patient skins with psoriasis, but not significantly in those with AD. Correlations between A-SAA and psoriasis severity and duration were observed. Conclusion Keratinocytes could contribute to psoriasis pathogenesis via A-SAA production, maintaining a cutaneous inflammatory environment, activating innate immunity and Th17 lymphocyte recruitment.

Development of a new model of reconstituted mouse epidermis and characterization of its response to proinflammatory cytokines

The development of three‐dimensional models of reconstituted mouse epidermis (RME) has been hampered by the difficulty to maintain murine primary keratinocyte cultures and to achieve a complete epidermal stratification. In this study, a new protocol is proposed for the rapid and convenient generation of RME, which reproduces accurately the architecture of a normal mouse epidermis. During RME morphogenesis, the expression of differentiation markers such as keratins, loricrin, filaggrin, E‐cadherin and connexins was followed, showing that RME structure at day 5 was similar to those of a normal mouse epidermis, with the acquisition of the natural barrier function. It was also demonstrated that RME responded to skin‐relevant proinflammatory cytokines by increasing the expression of antimicrobial peptides and chemokines, and inhibiting epidermal differentiation markers, as in the human system. This new model of RME is therefore suitable to investigate mouse epidermis physiology further and opens new perspectives to generate reconstituted epidermis from transgenic mice.

Characterization of skin Th17 transcriptional profiles in psoriatic patients under adalimumab biotherapy

BackgroundIn psoriasis, a specific cytokine network has been described to play a central role in the pathophysiology of the disease. Anti-cytokine therapeutic approaches have been largely developed and TNFα constitutes the main target. Adalimumab is a human anti-TNFα monoclonal antibody that has been reported to demonstrate clinical efficacy and safety, resulting in reversal of epidermal hyperplasia and cutaneous inflammation.ObjectivesWe aimed to analyse changes in the skin inflammatory transcriptomic profile in psoriatic patients during adalimumabtherapy. In addition, the circulating cytokine profilewas analysed to define systemic inflammation.Materials&methodsEighteen patients with chronic plaque psoriasis were treated with adalimumab. After four and 16 weeks, clinical efficacy was assessed using PASI and DLQI, and skin mRNA profiles were determined and circulating cytokines quantified.ResultsWe identified a rapid effect of adalimumab therapy on a large array of Th17 cytokines of the skin, which may account for the modification of keratinocyte expression profile and clinical response. In contrast, analysis of serum cytokine concentrations was uninformative, confirming the need for characterization of local cytokines in skin lesions. Finally, in non-responders, local cytokine expression was shown to be unchanged.ConclusionWe showthat TNFα inhibition in psoriasis patients treated with adalimumab has a broad effect on the expression profile of cytokines and keratinocyte markers of skin inflammation, which may account for its clinical efficacy.