Sara Tassi

ATP is released by monocytes stimulated with pathogen-sensing receptor ligands and induces IL-1β and IL-18 secretion in an autocrine way

IL-1β and IL-18 are crucial mediators of inflammation, and a defective control of their release may cause serious diseases. Yet, the mechanisms regulating IL-1β and IL-18 secretion are partially undefined. Both cytokines are produced as inactive cytoplasmic precursors. Processing to the active form is mediated by caspase-1, which is in turn activated by the multiprotein complex inflammasome. Here, we show that in primary human monocytes microbial components acting on different pathogen-sensing receptors and the danger-associated molecule uric acid are all competent to induce maturation and secretion of IL-1β and IL-18 through a process that involves as a first event the extracellular release of endogenous ATP. ATP release is followed by autocrine stimulation of the purinergic receptors P2X7. Indeed, antagonists of the P2X7 receptor (P2X7R), or treatment with apyrase, prevent IL-1β and IL-18 maturation and secretion triggered by the different stimuli. At variance, blocking P2X7R activity has no effects on IL-1β secretion by monocytes carrying a mutated inflammasome that does not require exogenous ATP for activation. P2X7R engagement is followed by K+ efflux and activation of phospholipase A2. Both events are required for processing and secretion induced by all of the stimuli. Thus, stimuli acting on different pathogen-sensing receptors converge on a common pathway where ATP externalization is the first step in the cascade of events leading to inflammasome activation and IL-1β and IL-18 secretion.

The pattern of response to anti-interleukin-1 treatment distinguishes two subsets of patients with systemic-onset juvenile idiopathic arthritis

OBJECTIVE To assess the clinical response to interleukin-1 (IL-1) blockade and in vitro IL-1beta and IL-18 secretion in patients with systemic-onset juvenile idiopathic arthritis (JIA). METHODS Twenty-two patients with systemic-onset JIA were treated with the IL-1 receptor antagonist (IL-1Ra) anakinra. Monocytes from 18 patients and 20 healthy donors were activated by different Toll-like receptor ligands. Intracellular and secreted IL-1beta and IL-18 were analyzed by Western blotting and enzyme-linked immunosorbent assay. RESULTS Ten patients with systemic-onset JIA exhibited a dramatic response to anakinra and were classified as complete responders. Eleven patients had an incomplete response or no response, and 1 patient could not be classified in terms of response. Compared with patients who had an incomplete response or no response, complete responders had a lower number of active joints (P = 0.02) and an increased absolute neutrophil count (P = 0.02). In vitro IL-1beta and IL-18 secretion in response to various stimuli was not increased and was independent of treatment efficacy. Likewise, secretion of IL-1Ra by monocytes from patients with systemic-onset JIA was not impaired. An overall low level of IL-1beta secretion upon exposure to exogenous ATP was observed, unrelated to treatment responsiveness or disease activity. CONCLUSION Two subsets of systemic-onset JIA can be identified according to patient response to IL-1 blockade. The 2 subsets appear to be characterized by some distinct clinical features. In vitro secretion of IL-1beta and IL-18 by monocytes from patients with systemic-onset JIA is not increased and is independent of both treatment outcome and disease activity.

Clinical Presentation and Pathogenesis of Cold-Induced Autoinflammatory Disease in a Family With Recurrence of an NLRP12 Mutation

Objective NLRP12 mutations have been described in patients affected with peculiar autoinflammatory symptoms. This study was undertaken to characterize NLRP12 mutations in patients with autoinflammatory syndromes, particularly a novel missense mutation, p.D294E, affecting a protein sequence crucial for ATP binding, which was identified in a Caucasian family with familial cold-induced autoinflammatory syndrome in some family members. Methods Fifty patients were tested for NLRP12 mutations. A Caucasian family with the p.D294E missense mutation of NLRP12 in some family members was clinically characterized. In vitro analysis of the effects of the mutation on NF-κB activity was performed in HEK 293 cells after cotransfection of the cells with a luciferase NF-κB–responsive element and mutant or wild-type (WT) NLRP12 expression plasmids. NF-κB activity was also evaluated 24 hours after stimulation with tumor necrosis factor α in monocytes from individual family members carrying the mutation. Furthermore, secretion of interleukin-1β (IL-1β), production of reactive oxygen species (ROS), and activation of antioxidant systems in patient and healthy donor monocytes, under resting conditions and after stimulation with pathogen-associated molecular patterns (PAMPs), were also assessed. Results In the family assessed, the p.D294E mutation segregated in association with a particular sensitivity to cold exposure (especially arthralgias and myalgia), but not always with an inflammatory phenotype (e.g., urticarial rash or fever). In vitro, the mutant protein maintained the same inhibitory activity as that shown by WT NLRP12. Consistently, NLRP12-mutated monocytes showed neither increased levels of p65-induced NF-κB activity nor higher secretion of IL-1β. However, the kinetics of PAMP-induced IL-1β secretion were significantly accelerated, and high production of ROS and up-regulation of antioxidant systems were demonstrated. Conclusion Even with a variable range of associated manifestations, the extreme sensitivity to cold represents the main clinical hallmark in an individual carrying the p.D294E mutation of the NLRP12 gene. Although regulation of NF-κB activity is not affected in patients, redox alterations and accelerated secretion of IL-1β are associated with this mild autoinflammatory phenotype.

Altered redox state of monocytes from cryopyrin-associated periodic syndromes causes accelerated IL-1β secretion

In healthy monocytes, Toll-like receptor (TLR) engagement induces production of reactive oxygen species (ROS), followed by an antioxidant response involved in IL-1β processing and secretion. Markers of the antioxidant response include intracellular thioredoxin and extracellular release of reduced cysteine. Cryopyrin-associated periodic syndromes (CAPS) are autoinflammatory diseases in which Nod-like receptor family pyrin domain–containing 3 (NLRP3) gene mutations lead to increased IL-1β secretion. We show in a large cohort of patients that IL-1β secretion by CAPS monocytes is much faster than that by healthy monocytes. This accelerated kinetics is caused by alterations in the basal redox state, as well as in the redox response to TLR triggering displayed by CAPS monocytes. Indeed, unstimulated CAPS monocytes are under a mild oxidative stress, with elevated levels of both ROS and antioxidants. The redox response to LPS is quickened, with early generation of the reducing conditions favoring IL-1β processing and secretion, and then rapidly exhausted. Therefore, secretion of IL-1β is accelerated, but reaches a plateau much earlier than in healthy controls. Pharmacologic inhibition of the redox response hinders IL-1β release, confirming the functional link between redox impairment and altered kinetics of secretion. Monocytes from patients with juvenile idiopathic arthritis display normal kinetics of redox response and IL-1β secretion, excluding a role of chronic inflammation in the alterations observed in CAPS. We conclude that preexisting redox alterations distinct from CAPS monocytes anticipate the pathogen-associated molecular pattern molecule–induced generation of the reducing environment favorable to inflammasome activation and IL-1β secretion.

DAMPs and inflammatory processes: the role of redox in the different outcomes

Inflammation is deeply entangled with redox modulation. Triggering of PRRs on inflammatory cells induces ROS generation. As a consequence, activated cells mount antioxidant responses to counteract the possible harmful effects of oxidation. Therefore, when repair is completed, homeostasis is restored. Here, we describe some recent results showing that an exuberant antioxidant response to pro–oxidant inflammatory stimuli modifies not only the intra– but also the extracellular redox and contributes to the outcome of the inflammatory process. In particular, the role of redox modulation in IL–1β secretion, in B lymphocyte differentiation to plasma cells, and in tumor progression will be discussed, and the potential consequences of extracellular redox alterations on DAMP activity will be considered.

Pathogen-Induced Interleukin-1β Processing and Secretion Is Regulated by a Biphasic Redox Response

In this study, we show that IL-1β processing and secretion induced by pathogen-associated molecular pattern (PAMP) molecules in human monocytes is regulated by a biphasic redox event including a prompt oxidative stress and a delayed antioxidant response. Namely, PAMPs induce an early generation of reactive oxygen species (ROS) followed by increase of intracellular thioredoxin and release of reduced cysteine: this antioxidant phase is paralleled by secretion of mature IL-1β. ROS production and antioxidant response are both required, because either inhibitors of NADPH oxidase and of thioredoxin reductase impair IL-1β secretion. These inhibitors also hinder cysteine release and consequently prevent reduction of the extracellular medium: addition of exogenous reducing agents restores IL-1β secretion. Not only silencing of thioredoxin, but also of the ROS scavenger superoxide dismutase 1 results in inhibition of IL-1β secretion. Thus, PAMP-induced ROS trigger an antioxidant response involving intracellular redox enzymes and release of cysteine, ultimately required for IL-1β processing and secretion.

The rate of interleukin-1beta secretion in different myeloid cells varies with the extent of redox response to Toll-like receptor triggering.

Human myeloid cells activate the NLRP3 inflammasome and secrete interleukin (IL)-1β in response to various Toll-like receptor (TLR) ligands, but the rate of secretion is much higher in primary human monocytes than in cultured macrophages or THP-1 cells. The different myeloid cells also display different redox status under resting conditions and redox response to TLR activation. Resting monocytes display a balanced redox state, with low production of reactive oxygen species (ROS) and antioxidants. TLR engagement induces an effective redox response with increased ROS generation followed by a sustained antioxidant response, parallelled by efficient IL-1β secretion. Drugs blocking ROS production or the antioxidant response prevent the secretion of mature IL-1β but not the biosynthesis of pro-IL-1β, indicating that redox remodeling is responsible for IL-1β processing and release. Unlike monocytes, THP-1 cells and cultured macrophages have up-regulated antioxidant systems that buffer the oxidative hit provided by TLR triggering and suppress the consequent redox response. This aborted redox remodeling is paralleled by low efficiency IL-1β processing and secretion. High doses (5 mm) of H2O2 overcome the high antioxidant capacity of THP-1 cells, restore an efficient redox response, and increase the rate of IL-1β secretion. Together these data indicate that a tightly controlled redox homeostasis in resting cells is a prerequisite for a robust redox response to TLR ligands, in turn necessary for the efficient inflammasome activation. Inflammasome activation by bacterial DNA is not modulated by redox responses, suggesting that redox-dependent regulation of IL-1β secretion is restricted to some inflammasomes including NLRP3 but excluding AIM-2.

Deficient production of IL-1 receptor antagonist and IL-6 coupled to oxidative stress in cryopyrin-associated periodic syndrome monocytes

Objective To determine whether dysregulated production of cytokines downstream of interleukin (IL)-1 participates in the pathophysiology of cryopyrin-associated periodic syndromes (CAPS). Methods Primary monocytes from patients with CAPS, unstimulated or after stimulation with lipopolysaccharide (LPS) and other Toll-like receptor (TLR) agonists, were examined for signs of stress and production of IL-1β, IL-1 receptor antagonist (IL-1Ra) and IL-6 in comparison with monocytes from patients with autoimmune diseases and from healthy donors. Results Unstimulated CAPS monocytes showed mild signs of stress including elevated levels of reactive oxygen species and fragmented mitochondria. Stress signs were worsened by TLR stimulation and eventually led to protein synthesis inhibition with strong impairment of production of cytokines downstream of IL-1, such as IL-1Ra and IL-6. These defects were not detected in monocytes from autoimmune patients and healthy donors. Conclusions The stress state of LPS-stimulated CAPS monocytes and the consequent inhibition of translation are likely to be responsible for the impaired production of IL-1Ra and IL-6. The deficient secretion of these cytokines coupled with increased IL-1β release explains the severity of the IL-1-related clinical manifestations and the predominant implication of innate immunity in CAPS.

ABCA2 is a marker of neural progenitors and neuronal subsets in the adult rodent brain.

The notion that the ATP‐binding cassette transporter‐A2 (ABCA2) may be involved in brain sterol homeostasis and is associated with early onset Alzheimers disease led us to explore its neural expression. Our data support and extend the previous reports on ABCA2 expression by oligodendrocytes. They evidence that ABCA2 (i) is located in intracellular vesicles, identified in transfected cells as lysosome‐related organelles only partially overlapping with classical endolysosomes; (ii) is a marker of neural progenitors as it is expressed in the subventricular zone of the lateral ventricle and the dentate gyrus of the hippocampal formation, sites of continual neurogenesis in the adult brain, and in nestin+ cells differentiated in vitro from embryonic stem cells; (iii) persists, in the adult rodent brain, in a subset of GABAergic and glutamatergic neurons. Considering that the latter are targets of Alzheimers lesions, these data provide a new rationale to explore the neuropathological consequences of ABCA2 functional dysregulations.