Review of IL‐36 biochemistry and its role in immune cells in the skin and lung in normal homeostasis and under pathological conditions.
IL‐36α, IL‐36β, and IL‐36γ are members of the IL‐1 family of ...cytokines that signal through a common receptor composed of IL‐36R and IL‐1R/AcP to activate NF‐κB and MAPKs, such as p38 and JNK, and promote inflammatory responses. IL‐36Ra is a natural antagonist of the 3 IL‐36 agonists that binds to IL‐36R and inhibits binding of the agonistic ligands. These cytokines are expressed predominantly by epithelial cells and act on a number of cells, including immune cells, epithelial cells, and fibroblasts. Processing of the N terminus is required for full agonist or antagonist activity for all IL‐36 members. The role of IL‐36 has been demonstrated extensively in the skin, where it can act on keratinocytes and immune cells to induce a robust inflammatory response and is implicated strongly through functional and genetic evidence in the pathology of psoriatic disorders. Emerging data also suggest a role for this cytokine family in pulmonary physiology and pathology. Although much has been learned about the biochemistry of IL‐36 and its role in various tissues, it is clear that we are at an early stage in our understanding of the full biology of these cytokines.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Summary
The interleukin (IL)‐36 cytokines include 3 agonists, IL‐36α, IL‐36β, and IL‐36γ that bind to a common receptor composed of IL‐36R and IL‐1RAcP to stimulate inflammatory responses. IL‐36Ra is ...a natural antagonist that binds to IL‐36R, but does not recruit the co‐receptor IL‐1RAcP and does not stimulate any intracellular responses. The IL‐36 cytokines are expressed predominantly by epithelial cells and act on a number of cells including immune cells, epithelial cells, and fibroblasts. Processing of the N‐terminus is required for full agonist or antagonist activity for all IL‐36 members. The role of IL‐36 has been extensively demonstrated in the skin where it can act on keratinocytes and immune cells to induce a robust inflammatory response that has been implicated in psoriatic disorders. Emerging data also suggest a role for this cytokine family in pulmonary and intestinal physiology and pathology.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK
Inflammatory bowel disease (IBD) is associated with a loss of intestinal barrier function and dysregulated immune responses. It has been shown that short chain fatty acids (SCFAs) are protective in ...IBD and that GPR43 mediates the protective effects of SCFAs. In this study, we investigated the effects of SCFAs in comparison to highly specific GPR43 agonists on human intestinal epithelial and immune cells. Our results confirm that SCFAs are enhancers of barrier function in intestinal epithelial cells. Additionally, SCFAs also displayed potent immunoregulatory properties based upon the ability to inhibit LPS-induced cytokine production in PBMC, and human T cell proliferation and cytokine production. Unexpectedly, and in contrast to the current belief, specific GPR43 agonists failed to exhibit similar barrier enhancing and anti-inflammatory properties. These findings demonstrate that SCFA possess broad protective functions in IBD and agonizing GPR43 alone is unlikely to be beneficial in patients.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Although the histological changes seen in psoriasis have long been well characterized, the underlying cellular and molecular mechanisms have only begun to be elucidated over the past 20 years. ...Proinflammatory factors such as tumor necrosis factor (TNF)-α have a central role in psoriasis pathogenesis, and many T-helper 1 (Th1) cytokines and messenger RNAs are elevated in psoriatic lesions. IL-17A, IL-17F, and other Th17 cell–derived cytokines have been shown in murine models to induce features that mimic human psoriasis. This review focuses on the emerging biology of the IL-17 cytokine family in psoriasis, and on the molecular and genetic information gained from animal models and human clinical studies that confirm IL-17 as a crucial proinflammatory cytokine in psoriasis. Expression of IL-17A, IL-17C, and IL-17F is strikingly increased in psoriatic lesions, and successful therapy is associated with restoration of the expression of a wide range of genes (including effector molecules downstream of IL-17 such as cytokines, chemokines, and antimicrobial peptides) to near-normal levels. Therapeutic agents in development that target IL-17 are discussed, and an emerging model of the key role of IL-17 in the pathogenesis of psoriasis is presented.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Interleukin-23 (IL-23) and IL-17 are cytokines currently being targeted in clinical trials. Although inhibition of both of these cytokines is effective for treating psoriasis, IL-12 and IL-23 p40 ...inhibition attenuates Crohn’s disease, whereas IL-17A or IL-17 receptor A (IL-17RA) inhibition exacerbates Crohn’s disease. This dichotomy between IL-23 and IL-17 was effectively modeled in the multidrug resistance-1a-ablated (Abcb1a−/−) mouse model of colitis. IL-23 inhibition attenuated disease by decreasing colonic inflammation while enhancing regulatory T (Treg) cell accumulation. Exacerbation of colitis by IL-17A or IL-17RA inhibition was associated with severe weakening of the intestinal epithelial barrier, culminating in increased colonic inflammation and accelerated mortality. These data show that IL-17A acts on intestinal epithelium to promote barrier function and provide insight into mechanisms underlying exacerbation of Crohn’s disease when IL-17A or IL-17RA is inhibited.
•IL-17 inhibition exacerbates Crohn’s disease and Abcb1a−/− mouse colitis•IL-17 inhibition weakens intestinal epithelial barrier function•IL-23 inhibition attenuates Crohn’s disease and Abcb1a−/− mouse colitis•IL-23 inhibition promotes a regulatory, anti-inflammatory environment in the gut
IL-17 and IL-23 are potent inflammatory cytokines, yet their inhibition induced opposing effects in Crohn’s disease clinical trials. Using a mouse model of IBD, Maxwell et al. show that IL-17 inhibition weakens intestinal epithelial barrier function and increases inflammation whereas IL-23 inhibition enhances regulatory T cell accumulation, thereby dampening inflammation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Tissue homeostasis is perturbed in a diversity of inflammatory pathologies. These changes can elicit endoplasmic reticulum (ER) stress, protein misfolding, and cell death. ER stress triggers the ...unfolded protein response (UPR), which can promote recovery of ER proteostasis and cell survival or trigger programmed cell death. Here, we leveraged single-cell RNA sequencing to define dynamic transcriptional states associated with the adaptive versus terminal UPR in the mouse intestinal epithelium. We integrated these transcriptional programs with genome-scale CRISPR screening to dissect the UPR pathway functionally. We identified QRICH1 as a key effector of the PERK-eIF2α axis of the UPR. QRICH1 controlled a transcriptional program associated with translation and secretory networks that were specifically up-regulated in inflammatory pathologies. Thus, QRICH1 dictates cell fate in response to pathological ER stress.
IL-36α, IL-36β, and IL-36γ (formerly IL-1F6, IL-1F8, and IL-1F9) are IL-1 family members that signal through the IL-1 receptor family members IL-1Rrp2 (IL-1RL2) and IL-1RAcP. IL-36Ra (formerly ...IL-1F5) has been reported to antagonize IL-36γ. However, our previous attempts to demonstrate IL-36Ra antagonism were unsuccessful. Here, we demonstrate that IL-36Ra antagonist activity is dependent upon removal of its N-terminal methionine. IL-36Ra starting at Val-2 is fully active and capable of inhibiting not only IL-36γ but also IL-36α and IL-36β. Val-2 of IL-36Ra lies 9 amino acids N-terminal to an A-X-Asp motif conserved in all IL-1 family members. In further experiments, we show that truncation of IL-36α, IL-36β, and IL-36γ to this same point increased their specific activity by ∼103–104-fold (from EC50 1 μg/ml to EC50 1 ng/ml). Inhibition of truncated IL-36β activity required ∼102–103-fold excess IL-36Ra, similar to the ratio required for IL-1Ra to inhibit IL-1β. Chimeric receptor experiments demonstrated that the extracellular (but not cytoplasmic) domain of IL-1Rrp2 or IL-1R1 is required for inhibition by their respective natural antagonists. IL-36Ra bound to IL-1Rrp2, and pretreatment of IL-1Rrp2-expressing cells with IL-36Ra prevented IL-36β-mediated co-immunoprecipitation of IL-1Rrp2 with IL-1RAcP. Taken together, these results suggest that the mechanism of IL-36Ra antagonism is analogous to that of IL-1Ra, such that IL-36Ra binds to IL-1Rrp2 and prevents IL-1RAcP recruitment and the formation of a functional signaling complex. In addition, truncation of IL-36α, IL-36β, and IL-36γ dramatically enhances their activity, suggesting that post-translational processing is required for full activity.
Background: IL-36 proteins are IL-1 family members with a key role in the skin.
Results: Truncation of IL-36 ligands and IL-36Ra is required for full activity. IL-36Ra binds IL-1Rrp2 and prevents signaling.
Conclusion: The mechanism of action of IL-36Ra is directly analogous to that of IL-1Ra.
Significance: Protease(s) that activate IL-36 cytokines could be excellent drug targets for psoriasis.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
IL-1 family members are central mediators of host defense. In this article, we show that the novel IL-1 family member IL-36γ was expressed during experimental colitis and human inflammatory bowel ...disease. Germ-free mice failed to induce IL-36γ in response to dextran sodium sulfate (DSS)-induced damage, suggesting that gut microbiota are involved in its induction. Surprisingly, IL-36R-deficient (Il1rl2(-/-)) mice exhibited defective recovery following DSS-induced damage and impaired closure of colonic mucosal biopsy wounds, which coincided with impaired neutrophil accumulation in the wound bed. Failure of Il1rl2(-/-) mice to recover from DSS-induced damage was associated with a profound reduction in IL-22 expression, particularly by colonic neutrophils. Defective recovery of Il1rl2(-/-) mice could be rescued by an aryl hydrocarbon receptor agonist, which was sufficient to restore IL-22 expression and promote full recovery from DSS-induced damage. These findings implicate the IL-36/IL-36R axis in the resolution of intestinal mucosal wounds.
•The IL-36 family of cytokines includes three pro-inflammatory agonists (IL-36α, IL-36β, and IL-36γ) and a receptor antagonist (IL-36Ra).•Signaling through the IL-36 receptor induces expression of ...antimicrobial peptides and pro-inflammatory cytokines and chemokines by keratinocytes and immune cells.•IL-36 is a driver of inflammation in several mouse models of inflammatory skin disease.•Dysregulated IL-36 pathway activation has been linked to inflammatory skin diseases including various forms of psoriasis, hidradenitis suppurativa, atopic dermatitis, and allergic contact dermatitis.
The IL-36 family of cytokines includes three pro-inflammatory agonists (IL-36α, IL-36β, and IL-36γ) and a receptor antagonist (IL-36Ra), which bind and signal through a heterodimeric receptor composed of IL-36R and the IL-1R accessory protein (IL-1RAcP). Individuals with inactivating mutations in the gene encoding IL-36Ra develop generalized pustular psoriasis, a severe form of psoriasis, a finding which clearly links dysregulated IL-36 pathway activation to inflammatory skin conditions. The purpose of this review is to highlight the cellular source of IL-36 cytokines, the effects of IL-36 signaling across cell types, and the association of IL-36 to a spectrum of inflammatory skin diseases including various forms of psoriasis as well as hidradenitis suppurativa, atopic dermatitis, and allergic contact dermatitis.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A study of families from southern Tunisia affected by general pustular psoriasis uncovered the genetic cause of their disease: a mutation affecting the function of the interleukin-36–receptor ...antagonist.
Psoriasis is a chronic inflammatory skin disease affecting 2 to 3% of persons of European descent.
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Psoriasis vulgaris, the most common form of the disease, accounts for 80% of cases and has a strong, albeit complex, genetic component.
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Numerous chromosomal loci have been implicated in genomewide association studies, but analyses of these loci have yielded only a few candidate genes, which mediate inflammatory cytokine signaling and adaptive immune responses.
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The disease follows mendelian transmission in a small minority of families.
Generalized pustular psoriasis is a life-threatening, multisystemic inflammatory disease involving repeated flare-ups of sudden onset, which are characterized by . . .
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