Cleavage-Mediated Regulation of Myd88 Signaling by Inflammasome-Activated Caspase-1

RNase L represses hair follicle regeneration through altered innate immune signaling

Mammalian injury responses are predominantly characterized by fibrosis and scarring rather than functional regeneration. This limited regenerative capacity in mammals could reflect a loss of proregeneration programs or active suppression by genes functioning akin to tumor suppressors. To uncover programs governing regeneration in mammals, we screened transcripts in human participants following laser rejuvenation treatment and compared them with mice with enhanced wound-induced hair neogenesis (WIHN), a rare example of mammalian organogenesis. We found that Rnasel-/- mice exhibit an increased regenerative capacity, with elevated WIHN through enhanced IL-36α. Consistent with RNase L's known role to stimulate caspase-1, we found that pharmacologic inhibition of caspases promoted regeneration in an IL-36-dependent manner in multiple epithelial tissues. We identified a negative feedback loop, where RNase L-activated caspase-1 restrains the proregenerative dsRNA-TLR3 signaling cascade through the cleavage of toll-like adaptor protein TRIF. Through integrated single-cell RNA-seq and spatial transcriptomic profiling, we confirmed OAS & IL-36 genes to be highly expressed at the site of wounding and elevated in Rnasel-/- mouse wounds. This work suggests that RNase L functions as a regeneration repressor gene, in a functional trade off that tempers immune hyperactivation during viral infection at the cost of inhibiting regeneration.

Rational design and therapeutic potential of MyD88 inhibitory peptide in psoriasis

Myeloid differentiation primary-response 88 (MyD88) is a crucial adaptor protein for initiating immune responses via Toll-like receptors (TLRs). This study employed a rational peptide design approach to develop MyD88 inhibitory peptides targeting the MyD88 interaction interface. The designed peptide, MyDIP2-4, was evaluated for its efficacy in inhibiting MyD88-dependent signaling in human and mouse cell lines. In vitro analyses demonstrated that MyDIP2-4 effectively inhibited MyD88-mediated signaling in both the TLR- and IL-1R-mediated pathways. Surface plasmon resonance experiments confirmed that MyDIP2-4 specifically interacted with MyD88 in a concentration-dependent manner. In an imiquimod-induced psoriasis model, MyDIP2-4 significantly inhibited disease progression, as evidenced by a reduction in psoriasis area and severity index scores. Histological staining revealed decreased epidermal thickness, while immunohistochemical analysis showed downregulation of IL-17 levels following treatment. These findings suggest that MyDIP2-4 is a promising candidate for the treatment of psoriasis. Targeting the Toll/interleukin-1 receptor domain of MyD88 through rational peptide design offers a novel strategy for developing therapeutics for autoimmune diseases.

Background and Clinical Features of a Unique and Mysterious Autoinflammatory Disease, Schnitzler Syndrome

Schnitzler syndrome is a unique autoinflammatory disease, of which 747 cases have been described worldwide to date. The main features of the syndrome are a triad of recurrent urticaria, monoclonal IgM gammopathy, systemic inflammation associated with recurrent fever, joint and bone pain, and atypical bone remodeling (osteosclerosis). The abnormal activation of the NLRP3 inflammasome produces IL-1, which drives the disease pathology, but it also involves IL-6 and IL-18. Unlike other autoinflammatory diseases, Schnitzler syndrome lacks evidence of the gene divergence causing the abnormal activation of NLRP3. However, mutations in the MEFV and MYD88 genes can be associated with the development of the disease. Due to its rarity, diagnosing the disease can be a challenging task. IL-1 inhibitors (i.e., anakinra, canakinumab, and rilonacept) are prominent in the treatment of the disease, but the IL-6 receptor inhibitor tocilizumab and the Bruton's tyrosine kinase inhibitor ibrutinib are also promising alternatives. In this summary article, we aim to provide a comprehensive overview of the clinical and molecular background of the disease and potential therapeutic targets, based on the cases reported so far. We diagnosed a patient who, to the best of our knowledge, represents the 748th documented case of this specific pathology. In the context of this patient, we would also like to draw attention to the potential pathogenic role of two novel gene mutations (variants of the MEFV gene "c.2084A>G" and the F2 gene "3'UTR c.*97G>A").

Integrin β2 regulates titanium particle‑induced inflammation in macrophages: In vitro aseptic loosening model

Aseptic loosening is a major complication of joint replacement surgery, characterized by periprosthetic osteolysis and chronic inflammation at the bone‑implant interface. Cells release chemokines, cytokines and other pro‑inflammatory substances that perpetuate inflammation reactions, while other particle‑stimulated macrophages promote osteoclastic bone resorption and impair bone formation. The present study investigated integrin and inflammatory cytokine expression patterns in RAW 264.7 cells treated with titanium (Ti) particles to elucidate the role of integrins in Ti particle‑mediated inflammatory osteolysis. Assessment was performed by reverse transcription‑quantitative PCR, western blotting, confocal immunofluorescence, flow cytometry and enzyme‑linked immunosorbent assays. Cell migration was evaluated by wound healing assay. It was found that Ti particles significantly induced integrin expression in RAW 264.7 cells, including upregulation of integrins β2 (CD18), aL (CD11a), aM (CD11b) and aX (CD11c). Ti particles also enhanced the expression of Toll‑like receptors (TLRs; TLR1, TLR2, TLR3 and TLR4) and triggered the release of inflammatory cytokines such as tumor necrosis factor α, interleukin (IL)‑1β, IL‑8 and IL‑12. Proteomics showed higher expression and activity levels of TLR2 and TLR4, along with their downstream signaling adaptors myeloid differentiation primary response protein 88 (MyD88) and Mal/TIR‑domain‑containing adapter protein (TIRAP), following Ti treatment. Additionally, Ti treatment significantly enhanced the migration rate of RAW 264.7 cells. The present findings indicated that Ti particles regulate the inflammatory response of RAW 264.7 cells in an in vitro aseptic loosening model by activating the TLR/TIRAP/MyD88 signaling pathway.

Cytokine-armed pyroptosis induces antitumor immunity against diverse types of tumors

Inflammasomes are defense complexes that utilize cytokines and immunogenic cell death (ICD) to stimulate the immune system against pathogens. Inspired by their dual action, we present cytokine-armed pyroptosis as a strategy for boosting immune response against diverse types of tumors. To induce pyroptosis, we utilize designed tightly regulated gasdermin D variants comprising different pore-forming capabilities and diverse modes of activation, representing a toolbox of ICD inducers. We demonstrate that the electrogenic transfer of ICD effector-encoding plasmids into mouse melanoma tumors when combined with intratumoral expression of cytokines IL-1β, IL-12, or IL-18, enhanced anti-tumor immune responses. Careful selection of immunostimulatory molecules is, however, imperative as a combination of IL-1β and IL-18 antagonized the protective effect of pyroptosis by IFNγ-mediated upregulation of several immunosuppressive pathways. Additionally, we show that the intratumoral introduction of armed pyroptosis provides protection against distant tumors and proves effective across various tumor types without inducing systemic inflammation. Deconstructed inflammasomes thus serve as a powerful, tunable, and tumor-agnostic strategy to enhance antitumor response, even against the most resilient types of tumors.

MyD88 protein destabilization mitigates NF-κB-dependent protection against macrophage apoptosis

Various signaling pathways are essential for both the innate immune response and the maintenance of cell homeostasis, requiring coordinated interactions among them. In this study, a mutation in the caspase-1 recognition site within MyD88 abolished inflammasome-dependent negative regulation, causing phenotypic changes in mice with some similarities to human NEMO-deficiencies. The MyD88D162E mutation reduced MyD88 protein levels and colon inflammation in DSS-induced colitis mice but did not affect cytokine expression in bone marrow-derived macrophages (BMDMs). However, compared to MyD88wt counterparts, MyD88D162E BMDMs had increased oxidative stress and dysfunctional mitochondria, along with reduced prosurvival Bcl-xL and BTK expression, rendering cells more prone to apoptosis, exacerbated by ibrutinib treatment. NF-κB activation by lipopolysaccharide mitigated this sensitive phenotype. These findings underscore the importance of MyD88wt signaling for NF-κB activation, protecting against macrophage premature apoptosis at resting state. Targeting MyD88 quantity rather than just its signaling could be a promising strategy for MyD88-driven lymphoma treatment.

Effects of metal oxide nanoparticles on healthy and psoriasis-like human epidermal keratinocytes in vitro

The use of metal oxide nanoparticles (NPs) in skincare products has significantly increased human skin exposure, raising safety concerns. Whilst NP's ability to penetrate healthy skin is minimal, studies have demonstrated that metal oxide NPs can induce toxicity in keratinocytes through direct contact. Moreover, NP's effect on common skin disorders like psoriasis, where barrier impairments and underlying inflammation could potentially increase NP penetration and worsen nanotoxicity is largely unstudied. In this paper, we investigated whether psoriasis-like human keratinocytes (Pso HKs) would exhibit heightened toxic responses to titanium dioxide (TiO2), zinc oxide (ZnO), and/or silica (SiO2) NPs compared to healthy HKs. Cells were exposed to each NP at concentrations ranging between 0.5 and 500 µg/ml for 6, 24, and 48 h. Amongst the metal oxide NPs, ZnO NPs produced the most pronounced toxic effects in both cell types, affecting cell viability, inducing oxidative stress, and activating the inflammasome pathway. Notably, only in ZnO NPs-treated Pso HKs, trappin-2/pre-elafin was cleaved intracellularly through a non-canonical process. In addition, tissue remodelling-related cytokines were upregulated in ZnO NP-treated Pso HKs. The full impact of the observed outcomes on psoriatic symptoms will need further evaluation. Nonetheless, our findings indicate the importance of understanding the sub-lethal impacts of NP exposures on keratinocytes, even though direct exposure may be low, particularly in the context of skin disorders where repeated and long-term exposures are anticipated.

Schnitzler Syndrome: Insights into Its Pathogenesis, Clinical Manifestations, and Current Management

Schnitzler syndrome is a rare disorder characterized by a chronic urticarial rash associated with immunoglobulin M (IgM) monoclonal gammopathy. Schnitzler syndrome shares strong clinicopathologic similarities with monogenic IL-1-mediated autoinflammatory disorders and is now considered an acquired adult-onset autoinflammatory disease. The spectacular effect of interleukin-1 inhibitors demonstrates the key role of this cytokine in the pathogenesis of the disease. However, the physiopathology of Schnitzler syndrome remains elusive, and the main question regarding the relationship between autoinflammatory features and monoclonal gammopathy is still unanswered. The purpose of this narrative review is to describe what is currently known about the pathogenesis of this peculiar disease, as well as to address its diagnosis and management.

Cordyceps militaris Solid Medium Extract Alleviates Lipoteichoic Acid-Induced MH-S Inflammation by Inhibiting TLR2/NF-κB/NLRP3 Pathways

The aim of this study was to investigate the inhibitory effects of Cordyceps militaris solid medium extract (CME) and cordycepin (COR) on LTA-induced inflammation in MH-S cells and their mechanisms of action. In this study, the establishment of an LTA-induced MH-S inflammation model was determined, the CCK-8 method was used to determine the safe concentration range for a drug for COR and CME, the optimal concentration of COR and CME to exert anti-inflammatory effects was further selected, and the expression of inflammatory factors of TNF-α, IL-1β, IL-18, and IL-6 was detected using ELISA. The relative expression of TNF-α, IL-1β, IL-18, IL-6, IL-10, TLR2 and MyD88 mRNA was detected using RT-PCR, and the IL-1β, IL-18, TLR2, MyD88, NF-κB p-p65, NLRP3, pro-caspase-1, Caspase-1 and ASC protein expression in the cells were detected using Western blot; immunofluorescence assay detected the expression of Caspase-1 in MH-S cells. The results revealed that both CME and COR inhibited the levels of IL-1β, IL-18, IL-6, and TNF-α in the supernatants of LTA-induced MH-S cells and the mRNA expression levels of IL-1β, IL-18, IL-6, TNF-α, TLR2 and MyD88, down-regulated the LTA-induced IL-1β, IL-18, TLR2 in MH-S cells, MyD88, NF-κB p-p65/p65, NLRP3, ASC, pro-caspase-1, and caspase-1 protein expression levels, and inhibited LTA-induced caspase-1 activation in MH-S cells. In conclusion, CME can play a therapeutic role in LTA-induced inflammation in MH-S cells via TLR2/NF-κB/NLRP3, and may serve as a potential drug for bacterial pneumonia caused by Gram-positive bacteria.

Potentilla paradoxa Nutt. Ethanol Extract Exhibits Anti-Inflammatory Effects by Suppression of the Src/NF-κB Signaling Pathway

Inflammation is an immune response that protects against harmful stimuli. However, severe inflammation can cause many diseases, such as diabetes, cancer, and arthritis. In this study, we examined the anti-inflammatory efficacy and mechanism of Potentilla paradoxa Nutt. ethanol extract (Pp-EE) as a new strategy for controlling the inflammatory response. Cellular activities and the molecular target of Pp-EE were identified in RAW264.7 cells and HEK293T cells. The effect of Pp-EE was analyzed using the Griess assay, the luciferase assay, reverse transcription-polymerase chain reaction, and Western blotting. To evaluate the in vivo effects, an HCl/EtOH-induced gastritis mouse model was used. NO production and pro-inflammatory gene (iNOS, COX-2, and TNF-α) mRNA levels were decreased by Pp-EE in a concentration-dependent manner without showing cytotoxicity. The activation of the transcription factor, particularly NF-κB, was effectively suppressed by Pp-EE. It was also found that Pp-EE directly inhibits the activation of Src in lipopolysaccharide (LPS)-treated RAW264.7 cells and in Src-overexpressed HEK293 cells by Western blotting analysis and cellular thermal shift assay. Experiments in the gastritis mouse model indicated that Pp-EE suppresses HCl/EtOH-induced gastric lesions, the expression levels of COX-2, IL-6, and TNF-α, and the phosphorylation of p65, p50, and Src. Taken together, these results suggest that Pp-EE can be applied as an anti-inflammatory remedy with a Src/NF-κB inhibitory property.

Focus on the Role of the NLRP3 Inflammasome in Multiple Sclerosis: Pathogenesis, Diagnosis, and Therapeutics

Neuroinflammation is initiated with an aberrant innate immune response in the central nervous system (CNS) and is involved in many neurological diseases. Inflammasomes are intracellular multiprotein complexes that can be used as platforms to induce the maturation and secretion of proinflammatory cytokines and pyroptosis, thus playing a pivotal role in neuroinflammation. Among the inflammasomes, the nucleotide-binding oligomerization domain-, leucine-rich repeat- and pyrin domain-containing 3 (NLRP3) inflammasome is well-characterized and contributes to many neurological diseases, such as multiple sclerosis (MS), Alzheimer's disease (AD), and ischemic stroke. MS is a chronic autoimmune disease of the CNS, and its hallmarks include chronic inflammation, demyelination, and neurodegeneration. Studies have demonstrated a relationship between MS and the NLRP3 inflammasome. To date, the pathogenesis of MS is not fully understood, and clinical studies on novel therapies are still underway. Here, we review the activation mechanism of the NLRP3 inflammasome, its role in MS, and therapies targeting related molecules, which may be beneficial in MS.