Interleukin-1α activation and localization in lipopolysaccharide-stimulated human monocytes and macrophages

Nuclear IL-1α Triggers Pyroptosis in Porcine Intramuscular Preadipocytes

Pigs are vital for meat production, and their intramuscular fat content significantly impacts pork quality and flavor. Using single-cell RNA sequencing (scRNA-seq) on porcine intramuscular fat, we found that adipose progenitor cells express highly inflammatory genes, including IL-1α, during adipogenic differentiation. IL-1α, a pro-inflammatory cytokine present in various cell types, can translocate to the nucleus via its nuclear localization sequence (NLS), yet its nuclear function remains unclear. By constructing an inactivated NLS carrier for IL-1α, we discovered that nuclear IL-1α promotes pyroptosis in porcine intramuscular adipocytes through the IRF2-NOCT-ROS pathway. This study reveals a novel role of nuclear IL-1α in pyroptosis regulation, providing insights into enhancing the intramuscular fat content and improving pork quality.

A new enzyme-linked immunosorbent assay system against the N-terminal propiece of interleukin-1α

Interleukin-1α (IL-1α) is produced inside cells in its precursor form (pIL-1α). Enzymatic cleavage yields mature (mIL-1α) and the propiece of IL-1α (ppIL-1α), which are thought to be localized in the nucleus, because of the presence of nuclear localizing signals. Studies of ppIL-1α function have been hampered by the lack of a ppIL-1α-specific antibody (Ab). In the present study, the authors generated anti-ppIL-1α Ab by using recombinant histidine-tagged ppIL-1α (His-ppIL-1α) as an immunogen. Rabbits were immunized with His-ppIL-1α, and affinity-purified Ab was obtained. Ab reactivity and specificity were examined by Western blotting. The antibody successfully recognized transfectant-derived green fluorescence protein (GFP)-tagged ppIL-1α but not GFP. A sandwich enzyme-linked immunosorbent assay (ELISA) system established by biotinylating the anti-ppIL-1α Ab successfully detected GFP-ppIL-1α. The Ab and ELISA system allows functional analysis of ppIL-1α and improves understanding of ppIL-1α.

A role for TNF-α in alveolar macrophage damage-associated molecular pattern release

Chronic beryllium disease (CBD) is a metal hypersensitivity/autoimmune disease in which damage-associated molecular patterns (DAMPs) promote a break in T cell tolerance and expansion of Be2+/self-peptide-reactive CD4+ T cells. In this study, we investigated the mechanism of cell death induced by beryllium particles in alveolar macrophages (AMs) and its impact on DAMP release. We found that phagocytosis of Be led to AM cell death independent of caspase, receptor-interacting protein kinases 1 and 3, or ROS activity. Before cell death, Be-exposed AMs secreted TNF-α that boosted intracellular stores of IL-1α followed by caspase-8-dependent fragmentation of DNA. IL-1α and nucleosomal DNA were subsequently released from AMs upon loss of plasma membrane integrity. In contrast, necrotic AMs released only unfragmented DNA and necroptotic AMs released only IL-1α. In mice exposed to Be, TNF-α promoted release of DAMPs and was required for the mobilization of immunogenic DCs, the expansion of Be-reactive CD4+ T cells, and pulmonary inflammation in a mouse model of CBD. Thus, early autocrine effects of particle-induced TNF-α on AMs led to a break in peripheral tolerance. This potentially novel mechanism may underlie the known relationship between fine particle inhalation, TNF-α, and loss of peripheral tolerance in T cell-mediated autoimmune disease and hypersensitivities.

Proteomic analysis of lipopolysaccharide activated human monocytes

Monocytes are key mediators of innate immunity and comprise an important cellular defence against invading pathogens. However, exaggerated or dysregulated monocyte activation can lead to severe immune-mediated pathology such as sepsis or chronic inflammatory diseases. Thus, detailed insight into the molecular mechanisms of monocyte activation is essential to understand monocyte-driven inflammatory pathologies. We therefore investigated the global protein changes in human monocytes during lipopolysaccharide (LPS) activation to mimic bacterial activation. Purified human monocytes were stimulated with LPS for 17 h and analyzed by state-of-the-art liquid chromatography tandem mass spectrometry (LC-MS/MS). The label-free quantitative proteome analysis identified 2746 quantifiable proteins of which 101 had a statistically significantly different abundance between LPS-stimulated cells and unstimulated controls. Additionally, 143 proteins were exclusively identified in either LPS stimulated cells or unstimulated controls. Functional annotation clustering demonstrated that LPS, most significantly, regulates proteasomal- and lysosomal proteins but in opposite directions. Thus, seven proteasome subunits were upregulated by LPS while 11 lysosomal proteins were downregulated. Both systems are critically involved in processing of proteins for antigen-presentation and together with LPS-induced regulation of CD74 and tapasin, our data suggest that LPS can skew monocytic antigen-presentation towards MHC class I rather than MHC class II. In summary, this study provides a sensitive high throughput protein analysis of LPS-induced monocyte activation and identifies several LPS-regulated proteins not previously described in the literature which can be used as a source for future studies.

Complement C3 opsonization of Chlamydia trachomatis facilitates uptake in human monocytes

Chlamydia trachomatis is an obligate intracellular bacterium that causes severe infections, which can lead to infertility and ectopic pregnancy. Although both innate and adaptive immune responses are elicited during chlamydial infection the bacterium succeeds to evade host defense mechanisms establishing chronic infections. Thus, studying the host-pathogen interaction during chlamydial infection is of importance to understand how C. trachomatis can cause chronic infections. Both the complement system and monocytes play essential roles in anti-bacterial defense, and, therefore, we investigated the interaction between the complement system and the human pathogens C. trachomatis D and L2. Complement competent serum facilitated rapid uptake of both chlamydial serovars into monocytes. Using immunoelectron microscopy, we showed that products of complement C3 were loosely deposited on the bacterial surface in complement competent serum and further characterization demonstrated that the deposited C3 product was the opsonin iC3b. Using C3-depleted serum we confirmed that complement C3 facilitates rapid uptake of chlamydiae into monocytes in complement competent serum. Complement facilitated uptake did not influence intracellular survival of C. trachomatis or C. trachomatis-induced cytokine secretion. Hence, C. trachomatis D and L2 activate the complement system leading to chlamydial opsonization by iC3b and subsequent phagocytosis, activation and bacterial elimination by human monocytes.

Propiece IL-1α facilitates the growth of acute T-lymphocytic leukemia cells through the activation of NF-κB and SP1

Interleukin 1α (IL-1α) is a pro-inflammatory cytokine that possesses multiple immune-regulatory functions. It is mainly expressed as the cell-associated form and not actively secreted in healthy tissues. The intracellular IL-1α has been shown to be a chromatin-associated cytokine and can affect transcription. There are spontaneous expressions of IL-1α in acute lymphocytic leukemia (ALL) blasts. However, the role of nuclear-localized IL-1α in ALL is not clear. Here we showed that overexpression of the nuclear form of IL-1α (propiece IL-1α) could promote proliferation and reduce apoptosis of T-ALL cells. It also increased the ALL cells’ resistance to low serum concentration and cisplatin treatment. In vivo growth of the T-ALL cells overexpressing the propiece IL-1α were also enhanced compared to the control cells. Microarray analysis revealed many changes in gene expressions related to cell growth and stress, including a group of metallothionein genes. Moreover, the expressions of transcription factors, NFκB and specific protein 1 (SP1), were up-regulated by propiece IL-1α. Propiece IL-1α could bind to the promoter of SP1 and a binding sequence logo was identified. Therefore, nuclear expression of propiece IL-1α can facilitate the growth of T-ALL cells possibly through the activation of NFκB and SP1.

Pseudomonas aeruginosa Induced Airway Epithelial Injury Drives Fibroblast Activation: A Mechanism in Chronic Lung Allograft Dysfunction

Bacterial infections after lung transplantation cause airway epithelial injury and are associated with an increased risk of developing bronchiolitis obliterans syndrome. The damaged epithelium is a source of alarmins that activate the innate immune system, yet their ability to activate fibroblasts in the development of bronchiolitis obliterans syndrome has not been evaluated. Two epithelial alarmins were measured longitudinally in bronchoalveolar lavages from lung transplant recipients who developed bronchiolitis obliterans syndrome and were compared to stable controls. In addition, conditioned media from human airway epithelial cells infected with Pseudomonas aeruginosa was applied to lung fibroblasts and inflammatory responses were determined. Interleukin-1 alpha (IL-1α) was increased in bronchoalveolar lavage of lung transplant recipients growing P. aeruginosa (11.5 [5.4-21.8] vs. 2.8 [0.9-9.4] pg/mL, p < 0.01) and was significantly elevated within 3 months of developing bronchiolitis obliterans syndrome (8.3 [1.4-25.1] vs. 3.6 [0.6-17.1] pg/mL, p < 0.01), whereas high mobility group protein B1 remained unchanged. IL-1α positively correlated with elevated bronchoalveolar lavage IL-8 levels (r(2)  = 0.6095, p < 0.0001) and neutrophil percentage (r(2)  = 0.25, p = 0.01). Conditioned media from P. aeruginosa infected epithelial cells induced a potent pro-inflammatory phenotype in fibroblasts via an IL-1α/IL-1R-dependent signaling pathway. In conclusion, we propose that IL-1α may be a novel therapeutic target to limit Pseudomonas associated allograft injury after lung transplantation.