Chronic stress induces colonic tertiary lymphoid organ formation and protection against secondary injury through IL-23/IL-22 signaling.

Psychological stress has been previously reported to worsen symptoms of inflammatory bowel disease (IBD). Similarly, intestinal tertiary lymphoid organs (TLOs) are associated with more severe inflammation. While there is active debate about the role of TLOs and stress in IBD pathogenesis, there are no studies investigating TLO formation in the context of psychological stress. Our mouse model of Crohn's disease-like ileitis, the SAMP1/YitFc (SAMP) mouse, was subjected to 56 consecutive days of restraint stress (RS). Stressed mice had significantly increased colonic TLO formation. However, stress did not significantly increase small or large intestinal inflammation in the SAMP mice. Additionally, 16S analysis of the stressed SAMP microbiome revealed no genus-level changes. Fecal microbiome transplantation into germ-free SAMP mice using stool from unstressed and stressed mice replicated the behavioral phenotype seen in donor mice. However, there was no difference in TLO formation between recipient mice. Stress increased the TLO formation cytokines interleukin-23 (IL-23) and IL-22 followed by up-regulation of antimicrobial peptides. SAMP × IL-23r-/- (knockout [KO]) mice subjected to chronic RS did not have increased TLO formation. Furthermore, IL-23, but not IL-22, production was increased in KO mice, and administration of recombinant IL-22 rescued TLO formation. Following secondary colonic insult with dextran sodium sulfate, stressed mice had reduced colitis on both histology and colonoscopy. Our findings demonstrate that psychological stress induces colonic TLOs through intrinsic alterations in IL-23 signaling, not through extrinsic influence from the microbiome. Furthermore, chronic stress is protective against secondary insult from colitis, suggesting that TLOs may function to improve the mucosal barrier.

A Novel Role for TL1A/DR3 in Protection against Intestinal Injury and Infection.

TNF-like cytokine 1A (TL1A) is expressed on APCs and provides costimulatory signals to activated lymphocytes that bear its functional receptor, death receptor 3 (DR3). TL1A/DR3 signaling is involved in the pathogenesis of human and experimental inflammatory bowel disease. In the current study, we investigated the role of this cytokine/receptor pair in acute intestinal injury/repair pathways. We demonstrate that intact DR3 signaling protected mice from acute dextran sodium sulfate colitis because DR3(-/-) mice showed more severe mucosal inflammation and increased mortality. DR3(-/-) mice were compromised in their ability to maintain adequate numbers of CD4(+)CD25(+)Foxp3(+) regulatory T cells in response to acute mucosal damage. This defect in immune regulation led to a nonspecific upregulation of effector proinflammatory pathways, which was most prominent for the Th17 immunophenotype. TL1A(-/-) mice were similarly more susceptible to dextran sodium sulfate colitis, although without mortality and with delayed kinetics compared with DR3(-/-) mice, and also displayed significantly reduced numbers of regulatory T cells. Infection of DR3(-/-) mice with Salmonella typhimurium was associated with defective microbial clearance and elevated bacterial load. Taken together, our findings indicate a novel protective role for the TL1A/DR3 axis in the regulation of mucosal homeostasis during acute intestinal injury/repair, which contrasts with its known pathogenic function during chronic intestinal inflammation.

Suppression of TCF4 promotes a ZC3H12A-mediated self-sustaining inflammatory feedback cycle involving IL-17RA/IL-17RE epidermal signaling.

IL-17C is an epithelial cell-derived proinflammatory cytokine whose transcriptional regulation remains unclear. Analysis of the IL17C promoter region identified TCF4 as putative regulator, and siRNA knockdown of TCF4 in human keratinocytes (KCs) increased IL17C. IL-17C stimulation of KCs (along with IL-17A and TNF-α stimulation) decreased TCF4 and increased NFKBIZ and ZC3H12A expression in an IL-17RA/RE-dependent manner, thus creating a feedback loop. ZC3H12A (MCPIP1/Regnase-1), a transcriptional immune-response regulator, also increased following TCF4 siRNA knockdown, and siRNA knockdown of ZC3H12A decreased NFKBIZ, IL1B, IL36G, CCL20, and CXCL1, revealing a proinflammatory role for ZC3H12A. Examination of lesional skin from the KC-Tie2 inflammatory dermatitis mouse model identified decreases in TCF4 protein concomitant with increases in IL-17C and Zc3h12a that reversed following the genetic elimination of Il17c, Il17ra, and Il17re and improvement in the skin phenotype. Conversely, interference with Tcf4 in KC-Tie2 mouse skin increased Il17c and exacerbated the inflammatory skin phenotype. Together, these findings identify a role for TCF4 in the negative regulation of IL-17C, which, alone and with TNF-α and IL-17A, feed back to decrease TCF4 in an IL-17RA/RE-dependent manner. This loop is further amplified by IL-17C-TCF4 autocrine regulation of ZC3H12A and IL-17C regulation of NFKBIZ to promote self-sustaining skin inflammation.

IFN-κ Is a Rheostat for Development of Psoriasiform Inflammation.

Psoriasis is a common, inflammatory autoimmune skin disease. Early detection of an IFN-1 signature occurs in many psoriasis lesions, but the source of IFN production remains debated. IFN-κ is an important source of IFN-1 production in the epidermis. We identified a correlation between IFN-regulated and psoriasis-associated genes in human lesional skin. We thus wanted to explore the effects of IFN-κ in psoriasis using the well-characterized imiquimod psoriasis model. Three mouse strains aged 10 weeks were used: wild-type C57Bl/6, C57Bl/6 that overexpress Ifnk in the epidermis (i.e., transgenic), and total body Ifnk-/- (i.e., knockout) strain. Psoriasis was induced by topical application of imiquimod on both ears for 8 consecutive days. Notably, the severity of skin lesions and inflammatory cell infiltration was more significantly increased in transgenic than in wild-type than in knockout mice. Gene expression analysis identified greater upregulation of Mxa, Il1b, Tnfa, Il6, Il12, Il23, Il17, and Ifng in transgenic compared to wild-type compared to knockout mice after imiquimod treatment. Furthermore, imiquimod increased CD8+ and CD4+ T-cell infiltration more in transgenic than in wild-type than in knockout mice. In summary, we identified IFN-κ as a rheostat for initiation of psoriasiform inflammation. This suggests that targeting IFN-1s early in the disease may be an effective way of controlling psoriatic inflammation.

The female-biased factor VGLL3 drives cutaneous and systemic autoimmunity.

Autoimmune disease is 4 times more common in women than men. This bias is largely unexplained. Female skin is "autoimmunity prone," showing upregulation of many proinflammatory genes, even in healthy women. We previously identified VGLL3 as a putative transcription cofactor enriched in female skin. Here, we demonstrate that skin-directed overexpression of murine VGLL3 causes a severe lupus-like rash and systemic autoimmune disease that involves B cell expansion, autoantibody production, immune complex deposition, and end-organ damage. Excess epidermal VGLL3 drives a proinflammatory gene expression program that overlaps with both female skin and cutaneous lupus. This includes increased B cell-activating factor (BAFF), the only current biologic target in systemic lupus erythematosus (SLE); IFN-κ, a key inflammatory mediator in cutaneous lupus; and CXCL13, a biomarker of early-onset SLE and renal involvement. Our results demonstrate that skin-targeted overexpression of the female-biased factor VGLL3 is sufficient to drive cutaneous and systemic autoimmune disease that is strikingly similar to SLE. This work strongly implicates VGLL3 as a pivotal orchestrator of sex-biased autoimmunity.