Aberrant inflammasome activation as a driving force of human autoimmune skin disease

Associations between type 1 diabetes and autoimmune skin diseases: Mendelian randomization analysis

Background

Type 1 diabetes mellitus (T1DM) may be associated with various autoimmune diseases, but the causal relationship between T1DM and autoimmune skin diseases is not yet clear.

Methods

The summary statistical data on T1DM and nine autoimmune skin diseases in European populations were extracted for mendelian randomization (MR) analysis. Subsequently, the analysis was replicated in East Asian populations. In the MR estimation, inverse variance-weighted (IVW), MR-Egger, weighted median, simple mode, and weighted mode methods were utilized. Outliers were excluded using MR-PRESSO, and horizontal pleiotropy was assessed with MR-Egger. Additionally, a multivariable MR analysis was conducted to investigate whether T1DM has an independent effect on autoimmune skin diseases after adjusting for potential confounders.

Results

In Europe, the MR estimated based on IVW method indicated a causal association between genetically determined T1DM and systemic lupus erythematosus (SLE) (OR = 1.38, 95%CI: 1.26-1.50, p＜0.01), rheumatoid arthritis (RA) (OR = 1.15, 95%CI: 1.05-1.25, p＜0.01), as well as multiple sclerosis (MS) (OR = 1.17, 95%CI: 1.01-1.36, p = 0.04), but there is no association between T1DM and atopic dermatitis (AD), vitiligo, lichen planus (LP), hidradenitis suppurativa (HS), alopecia areata (AA) and systemic sclerosis (SS). After adjusting for time spent watching television, body mass index, type 2 diabetes mellitus, and body fat percentage, we found a causal relationship between T1DM and SLE (OR = 1.29, 95%CI: 1.16-1.44, p < 0.01), RA (OR = 1.28, 95%CI: 1.20-1.38 p < 0.01) and MS (OR = 1.11, 95%CI: 1.04-1.18, p < 0.01). Then, no genetic causal association was found between TIDM and SLE, and AD in East Asia. These results didn't exhibit horizontal pleiotropy, and "leave-one-out" analysis demonstrated result stability.

Conclusion

Our MR research indicates a causal relationship between T1DM and SLE, RA, and MS in Europe. However, no causal relationship between T1DM and SLE has been observed in East Asia. Therefore, it is important to regularly monitor relevant immunological markers of SLE, RA, and MS in T1DM patients and take preventive measures.

A guide to cell death pathways

Regulated cell death mediated by dedicated molecular machines, known as programmed cell death, plays important roles in health and disease. Apoptosis, necroptosis and pyroptosis are three such programmed cell death modalities. The caspase family of cysteine proteases serve as key regulators of programmed cell death. During apoptosis, a cascade of caspase activation mediates signal transduction and cellular destruction, whereas pyroptosis occurs when activated caspases cleave gasdermins, which can then form pores in the plasma membrane. Necroptosis, a form of caspase-independent programmed necrosis mediated by RIPK3 and MLKL, is inhibited by caspase-8-mediated cleavage of RIPK1. Disruption of cellular homeostatic mechanisms that are essential for cell survival, such as normal ionic and redox balance and lysosomal flux, can also induce cell death without invoking programmed cell death mechanisms. Excitotoxicity, ferroptosis and lysosomal cell death are examples of such cell death modes. In this Review, we provide an overview of the major cell death mechanisms, highlighting the latest insights into their complex regulation and execution, and their relevance to human diseases.

Role of the NLRP1 inflammasome in skin cancer and inflammatory skin diseases

Inflammasomes are cytoplasmic protein complexes that play a crucial role in protecting the host against pathogenic and sterile stressors by initiating inflammation. Upon activation, these complexes directly regulate the proteolytic processing and activation of proinflammatory cytokines interleukin (IL)-1β and IL-18 to induce a potent inflammatory response, and induce a programmed form of cell death called pyroptosis to expose intracellular pathogens to the surveillance of the immune system, thus perpetuating inflammation. There are various types of inflammasome complexes, with the NLRP1 (nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-1) inflammasome being the first one identified and currently recognized as the predominant inflammasome sensor protein in human keratinocytes. Human NLRP1 exhibits a unique domain structure, containing both an N-terminal pyrin (PYD) domain and an effector C-terminal caspase recruitment domain (CARD). It can be activated by diverse stimuli, such as viruses, ultraviolet B radiation and ribotoxic stress responses. Specific mutations in NLRP1 or related genes have been associated with rare monogenic skin disorders, such as multiple self-healing palmoplantar carcinoma; familial keratosis lichenoides chronica; autoinflammation with arthritis and dyskeratosis; and dipeptidyl peptidase 9 deficiency. Recent research breakthroughs have also highlighted the involvement of dysfunctions in the NLRP1 pathway in a handful of seemingly unrelated dermatological conditions. These range from monogenic autoinflammatory diseases to polygenic autoimmune diseases such as vitiligo, psoriasis, atopic dermatitis and skin cancer, including squamous cell carcinoma, melanoma and Kaposi sarcoma. Additionally, emerging evidence implicates NLRP1 in systemic lupus erythematosus, pemphigus vulgaris, Addison disease, Papillon-Lefèvre syndrome and leprosy. The aim of this review is to shed light on the implications of pathological dysregulation of the NLRP1 inflammasome in skin diseases and investigate the potential rationale for targeting this pathway as a future therapeutic approach.

Triggers for the onset and recurrence of psoriasis: a review and update

Psoriasis is an immune-mediated inflammatory skin disease, involving a complex interplay between genetic and environmental factors. Previous studies have demonstrated that genetic factors play a major role in the pathogenesis of psoriasis. However, non-genetic factors are also necessary to trigger the onset and recurrence of psoriasis in genetically predisposed individuals, which include infections, microbiota dysbiosis of the skin and gut, dysregulated lipid metabolism, dysregulated sex hormones, and mental illness. Psoriasis can also be induced by other environmental triggers, such as skin trauma, unhealthy lifestyles, and medications. Understanding how these triggers play a role in the onset and recurrence of psoriasis provides insights into psoriasis pathogenesis, as well as better clinical administration. In this review, we summarize the triggers for the onset and recurrence of psoriasis and update the current evidence on the underlying mechanism of how these factors elicit the disease. Video Abstract.