Lars E. French

Inflammasome activation and IL-1β target IL-1α for secretion as opposed to surface expression

Interleukin-1α (IL-1α) and -β both bind to the same IL-1 receptor (IL-1R) and are potent proinflammatory cytokines. Production of proinflammatory (pro)–IL-1α and pro–IL-1β is induced by Toll-like receptor (TLR)-mediated NF-κB activation. Additional stimulus involving activation of the inflammasome and caspase-1 is required for proteolytic cleavage and secretion of mature IL-1β. The regulation of IL-1α maturation and secretion, however, remains elusive. IL-1α exists as a cell surface-associated form and as a mature secreted form. Here we show that both forms of IL-1α, the surface and secreted form, are differentially regulated. Surface IL-1α requires NF-κB activation only, whereas secretion of mature IL-1α requires additional activation of the inflammasome and caspase-1. Surprisingly, secretion of IL-1α also required the presence of IL-1β, as demonstrated in IL-1β–deficient mice. We further demonstrate that IL-1β directly binds IL-1α, thus identifying IL-1β as a shuttle for another proinflammatory cytokine. These results have direct impact on selective treatment modalities of inflammatory diseases.

The mTOR inhibitor rapamycin significantly improves facial angiofibroma lesions in a patient with tuberous sclerosis

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder with an incidence of approximately one in 6000. It arises from a genetic abnormality involving either the TSC1 gene on chromosome 9 or the TSC2 gene on chromosome 16. The protein product of TSC1 is hamartin and that of TSC2 is tuberin. In cells, hamartin and tuberin form a complex which inhibits the mammalian target of rapamycin (mTOR), a central controller of cell growth and proliferation. Angiofibroma affects 70–80% of patients with TSC, typically on the face. We report a patient with TSC with recurrent life‐threatening haemorrhage from both kidneys due to extensive angiomyolipoma formation leading to bilateral nephrectomy and renal transplantation. Immunosuppressive treatment with rapamycin, a specific mTOR inhibitor, initiated because of renal transplantation, reduced facial angiofibroma dramatically.

Caspase-4 Is Required for Activation of Inflammasomes

IL-1β and IL-18 are crucial regulators of inflammation and immunity. Both cytokines are initially expressed as inactive precursors, which require processing by the protease caspase-1 for biological activity. Caspase-1 itself is activated in different innate immune complexes called inflammasomes. In addition, caspase-1 activity regulates unconventional protein secretion of many other proteins involved in inflammation and repair. Human caspase-4 is a poorly characterized member of the caspase family, which is supposed to be involved in endoplasmic reticulum stress-induced apoptosis. However, its gene is located on the same locus as the caspase-1 gene, which raises the possibility that caspase-4 plays a role in inflammation. In this study, we show that caspase-4 expression is required for UVB-induced activation of proIL-1β and for unconventional protein secretion by skin-derived keratinocytes. These processes require expression of the nucleotide-binding domain leucine-rich repeat containing, Pyrin domain containing-3 inflammasome, and caspase-4 physically interacts with its central molecule caspase-1. As the active site of caspase-4 is required for activation of caspase-1, the latter most likely represents a substrate of caspase-4. Caspase-4 expression is also essential for efficient nucleotide-binding domain leucine-rich repeat containing, Pyrin domain containing-3 and for absent in melanoma 2 inflammasome-dependent proIL-1β activation in macrophages. These results demonstrate an important role of caspase-4 in inflammation and innate immunity through activation of caspase-1. Therefore, caspase-4 represents a novel target for the treatment of (auto)inflammatory diseases.

Neurotrophins and Their Receptors Stimulate Melanoma Cell Proliferation and Migration

Melanoma is a highly aggressive skin tumor that originates in the epidermis from melanocytes. As melanocytes share with the nervous system a common neuroectodermal origin and express all neurotrophins (NTs), we evaluated the expression and function of NTs and their receptors in melanoma. We report that primary and metastatic melanoma cell lines synthesize and secrete all NTs. Moreover, melanoma cells express the low-affinity (p75NTR) and the high-affinity tyrosine kinase NT receptors (Trk). The inhibition of Trk receptors by either K252a or Trk/Fc chimeras prevents proliferation, indicating that autocrine NTs are responsible for this effect. NT-3, NT-4, and nerve growth factor (NGF) induce cell migration, with a stronger effect on metastatic cell lines. Transfection with p75NTR small interfering RNA (p75NTRsiRNA) or treatment with K252a inhibits NT-induced melanoma cell migration, indicating that both the low- and high-affinity NT receptors mediate this effect. All melanoma cell lines express the p75NTR coreceptor sortilin by which proNGF stimulates migration in melanoma cells, but not in cells transfected with p75NTRsiRNA. These results indicate that NTs, through their receptors, play a critical role in the progression of melanoma.

The Nlrp3 inflammasome regulates acute graft-versus-host disease.

Conditioning therapies before transplantation induce the release of uric acid, which triggers the NLRP3 inflammasome and IL-1β production contributing to graft-versus-host disease.

Interleukin-1, inflammasomes and the skin

Interleukin (IL)-1 is a highly active and pleiotropic pro-inflammatory cytokine. Recent data impressively demonstrate that activating mutations in a human gene involved in proIL-1beta maturation or loss-of-function mutations in the gene encoding IL-1 receptor antagonist (IL-1Ra) cause excessive activity of this cytokine. This can result in life-threatening systemic and local inflammation, particularly in the skin. Interestingly, experiments in mice revealed that epidermal keratinocytes can secrete large amounts of IL-1alpha, which induces an inflammatory response in the skin. Secretion of IL-1 requires caspase-1 activity, and activation of the protease takes place in innate immune complexes, called inflammasomes. As keratinocytes express and activate caspase-1 in an inflammasome-dependent manner, these epithelial cells might be critically involved in the innate immunity of the skin. In this review we summarize the current knowledge on IL-1 and inflammasomes in the skin, particularly their involvement in skin homeostasis and disease. In addition, we discuss the hypothesis that keratinocytes are not only static bricks of the epidermal wall, but immunologically active cells critically involved in different (auto)-inflammatory (skin) diseases.

IL-31 expression by inflammatory cells is preferentially elevated in atopic dermatitis.

Interleukin-31 (IL-31) is a recently discovered cytokine expressed in many human tissues, and predominantly by activated CD4(+) T cells. IL-31 signals through a heterodimeric receptor consisting of IL-31 receptor alpha (IL-31RA) and oncostatin M receptor beta (OSMR). Earlier studies have shown involvement of IL-31 and its receptor components IL-31RA and OSMR in atopic dermatitis, pruritus and Th2-weighted inflammation at the mRNA level. The aim of this study was to investigate IL-31 protein expression in skin of such conditions. Immunohistochemical staining for IL-31, IL-31RA and OSMR was performed in formalin-fixed paraffin-embedded biopsy specimens. IL-31 expression was increased in the inflammatory infiltrates from skin biopsies taken from subjects with atopic dermatitis, compared with controls (p ≤ 0.05). IL-31, IL-31RA and OSMR protein immunoreactivity was not increased in biopsies from subjects with other Th2-weighted and pruritic skin diseases. Our results confirm, at the protein level, the relationship between IL-31 expression and atopic dermatitis. Our results do not support a general relationship between expression of IL-31/IL-31R and pruritic or Th2-mediated diseases.

Guidelines on the use of extracorporeal photopheresis

After the first investigational study on the use of extracorporeal photopheresis for the treatment of cutaneous T‐cell lymphoma was published in 1983 with its subsequent recognition by the FDA for its refractory forms, the technology has shown significant promise in the treatment of other severe and refractory conditions in a multi‐disciplinary setting. Among the major studied conditions are graft versus host disease after allogeneic bone marrow transplantation, systemic sclerosis, solid organ transplant rejection and inflammatory bowel disease.

Extracorporeal photopheresis: Past, present, and future

Extracorporeal photopheresis (ECP) is a leukapheresis-based therapy that uses 8-methoxypsoralen and ultraviolet A irradiation. Used alone or in combination with biological agents, ECP is an established and effective therapy for advanced cutaneous T-cell lymphoma. ECP has also shown promising efficacy in a number of other severe and difficult-to-treat conditions, including systemic sclerosis, graft-versus-host disease, prevention and treatment of rejection in solid organ transplantation, and Crohn disease. Furthermore, the use of ECP in some of these conditions may allow a significant reduction in the use of systemic steroids and other immunosuppressants, reducing long-term morbidity and mortality. The accumulated experience shows ECP to be well tolerated, with no clinically significant side effects. Progress is also being made in the search for understanding of the mechanisms of action of ECP, which will ultimately facilitate improvements in the use of this therapy.

IL-1β drives inflammatory responses to propionibacterium acnes in vitro and in vivo.

Acne vulgaris is potentially a severe skin disease associated with colonization of the pilo-sebaceous unit by the commensal bacterium Propionibacterium acnes and inflammation. P. acnes is considered to contribute to inflammation in acne, but the pathways involved are unclear. Here we reveal a mechanism that regulates inflammatory responses to P. acnes. We show that IL-1β mRNA and the active processed form of IL-1β are abundant in inflammatory acne lesions. Moreover, we identify P. acnes as a trigger of monocyte-macrophage NLRP3-inflammasome activation, IL-1β processing and secretion that is dependent on phagocytosis, lysosomal destabilization, reactive oxygen species, and cellular K+ efflux. In mice, inflammation induced by P. acnes is critically dependent on IL-1β and the NLRP3 inflammasome of myeloid cells. These findings show that the commensal P. acnes-by activating the inflammasome-can trigger an innate immune response in the skin, thus establishing the NLRP3-inflammasome and IL-1β as possible therapeutic targets in acne.