NLRP3 selectively drives IL-1β secretion by Pseudomonas aeruginosa infected neutrophils and regulates corneal disease severity

Macrophages infected with Gram-negative bacteria expressing Type III secretion system (T3SS) activate the NLRC4 inflammasome, resulting in Gasdermin D (GSDMD)-dependent, but GSDME independent IL-1β secretion and pyroptosis. Here we examine inflammasome signaling in neutrophils infected with Pseudomonas aeruginosa strain PAO1 that expresses the T3SS effectors ExoS and ExoT. IL-1β secretion by neutrophils requires the T3SS needle and translocon proteins and GSDMD. In macrophages, PAO1 and mutants lacking ExoS and ExoT (ΔexoST) require NLRC4 for IL-1β secretion. While IL-1β release from ΔexoST infected neutrophils is also NLRC4-dependent, infection with PAO1 is instead NLRP3-dependent and driven by the ADP ribosyl transferase activity of ExoS. Genetic and pharmacologic approaches using MCC950 reveal that NLRP3 is also essential for bacterial killing and disease severity in a murine model of P. aeruginosa corneal infection (keratitis). Overall, these findings reveal a function for ExoS ADPRT in regulating inflammasome subtype usage in neutrophils versus macrophages and an unexpected role for NLRP3 in P. aeruginosa keratitis.

Immunity to pathogenic fungi in the eye

Fusarium, Aspergillus and Candida are important fungal pathogens that cause visual impairment and blindness in the USA and worldwide. This review will summarize the epidemiology and clinical features of corneal infections and discuss the immune and inflammatory responses that play an important role in clinical disease. In addition, we describe fungal virulence factors that are required for survival in infected corneas, and the activities of neutrophils in fungal killing, tissue damage and cytokine production.

Differential Roles for IL-1α and IL-1β in Pseudomonas aeruginosa Corneal Infection

Pseudomonas aeruginosa is an important cause of dermal, pulmonary, and ocular disease. Our studies have focused on P. aeruginosa infections of the cornea (keratitis) as a major cause of blinding microbial infections. The infection leads to an influx of innate immune cells, with neutrophils making up to 90% of recruited cells during early stages. We previously reported that the proinflammatory cytokines IL-1α and IL-1β were elevated during infection. Compared with wild-type (WT), infected Il1b-/- mice developed more severe corneal disease that is associated with impaired bacterial killing as a result of defective neutrophil recruitment. We also reported that neutrophils are an important source of IL-1α and IL-1β, which peaked at 24 h postinfection. To examine the role of IL-1α compared with IL-1β in P. aeruginosa keratitis, we inoculated corneas of C57BL/6 (WT), Il1a-/-, Il1b-/-, and Il1a-/-Il1b-/- (double-knockout) mice with 5 × 104 ExoS-expressing P. aeruginosa. Il1b-/- and double-knockout mice have significantly higher bacterial burden that was consistent with delayed neutrophil and monocyte recruitment to the corneas. Surprisingly, Il1a-/- mice had the opposite phenotype with enhanced bacteria clearance compared with WT mice. Although there were no significant differences in neutrophil recruitment, Il1a-/- neutrophils displayed a more proinflammatory transcriptomic profile compared to WT with elevations in C1q expression that likely caused the phenotypic differences observed. To our knowledge, our findings identify a novel, non-redundant role for IL-1α in impairing bacterial clearance.

Aspergillus fumigatus corneal infection is regulated by chitin synthases and by neutrophil-derived acidic mammalian chitinase

Aspergillus fumigatus is an important cause of pulmonary and systemic infections in immune compromised individuals, and of corneal ulcers and blindness in immune competent patients. To examine the role of chitin synthases in Aspergillus corneal infection, we analyzed Aspergillus mutants of chitin synthase family 1 and family 2, and found that compared with the parent strain, the quadruple mutants from both families were more readily killed by neutrophils in vitro, and that both also exhibited impaired hyphal growth in the cornea. Further, inhibition of chitin synthases using Nikkomycin Z enhanced neutrophil killing in vitro and in vivo in a murine model of A. fumigatus corneal infection. Acidic mammalian chitinase (AMCase) is mostly produced by macrophages in asthmatic lungs; however, we now demonstrate that neutrophils are a major source of AMCase, which inhibits hyphal growth. In A. fumigatus corneal infection, neutrophils are the major source of AMCase, and addition of AMCase inhibitors or adoptive transfer of neutrophils from AMCase^-/- mice resulted in impaired hyphal killing. Together, these findings identify chitin synthases as important fungal virulence factors and neutrophil-derived AMCase as an essential mediator of host defense.

Atlas of Circadian Metabolism Reveals System-wide Coordination and Communication between Clocks

Metabolic diseases are often characterized by circadian misalignment in different tissues, yet how altered coordination and communication among tissue clocks relate to specific pathogenic mechanisms remains largely unknown. Applying an integrated systems biology approach, we performed 24-hr metabolomics profiling of eight mouse tissues simultaneously. We present a temporal and spatial atlas of circadian metabolism in the context of systemic energy balance and under chronic nutrient stress (high-fat diet [HFD]). Comparative analysis reveals how the repertoires of tissue metabolism are linked and gated to specific temporal windows and how this highly specialized communication and coherence among tissue clocks is rewired by nutrient challenge. Overall, we illustrate how dynamic metabolic relationships can be reconstructed across time and space and how integration of circadian metabolomics data from multiple tissues can improve our understanding of health and disease.

Neutrophil Caspase-11 Is Required for Cleavage of Caspase-1 and Secretion of IL-1β in Aspergillus fumigatus Infection

Neutrophils are an important source of IL-1β secretion in bacterial infections, where they infiltrate affected tissues in log-fold higher numbers than macrophages. Neutrophils also have functional NLRP3 and NLRC4 inflammasomes that can process pro-IL-1β to the bioactive 17-kDa form. In the current study, we examined the role of IL-1β in response to corneal infection with the filamentous fungus Aspergillus fumigatus and found that neutrophils were the predominant source of bioactive IL-1β in the cornea. We also observed that caspase-11^-/- mice exhibit the same susceptibility phenotype as IL-1β^-/-, ASC^-/-, NLRP3^-/-, and caspase-1^-/- mice, with impaired neutrophil recruitment to infected corneas and increased hyphal growth. We further demonstrate that caspase-11 is required for caspase-1 activation and IL-1β processing during infection. In vitro, we show that caspase-11 is regulated by the common type I IFN receptor (IFNAR) through JAK-STAT signaling and that caspase-11 is required for speck formation and caspase-1 activity. Aspergillus spores (conidia) stimulate IL-1β processing and secretion in neutrophils activation of Dectin-1 and signaling through the Raf1 kinase/MEKK rather than the spleen tyrosine kinase pathway. Collectively, these findings reveal unexpected regulation of IL-1β production by neutrophils in response to pathogenic fungi.

Protein Deiminase 4 and CR3 Regulate Aspergillus fumigatus and β-Glucan-Induced Neutrophil Extracellular Trap Formation, but Hyphal Killing Is Dependent Only on CR3

Neutrophil extracellular trap (NET) formation requires chromatin decondensation before nuclear swelling and eventual extracellular release of DNA, which occurs together with nuclear and cytoplasmic antimicrobial proteins. A key mediator of chromatin decondensation is protein deiminase 4 (PAD4), which catalyzes histone citrullination. In the current study, we examined the role of PAD4 and NETosis following activation of neutrophils by A. fumigatus hyphal extract or cell wall β-glucan (curdlan) and found that both induced NET release by human and murine neutrophils. Also, using blocking antibodies to CR3 and Dectin-1 together with CR3-deficient CD18-/- and Dectin-1-/- murine neutrophils, we found that the β-glucan receptor CR3, but not Dectin-1, was required for NET formation. NETosis was also dependent on NADPH oxidase production of reactive oxygen species (ROS). Using an antibody to citrullinated histone 3 (H3Cit) as an indicator of PAD4 activity, we show that β-glucan stimulated NETosis occurs in neutrophils from C57BL/6, but not PAD4-/- mice. Similarly, a small molecule PAD4 inhibitor (GSK484) blocked NET formation by human neutrophils. Despite these observations, the ability of PAD4-/- neutrophils to release calprotectin and kill A. fumigatus hyphae was not significantly different from C57BL/6 neutrophils, whereas CD18-/- neutrophils exhibited an impaired ability to perform both functions. We also detected H3Cit in A. fumigatus infected C57BL/6, but not PAD4-/- corneas; however, we found no difference between C57BL/6 and PAD4-/- mice in either corneal disease or hyphal killing. Taken together, these findings lead us to conclude that although PAD4 together with CR3-mediated ROS production is required for NET formation in response to A. fumigatus, PAD4-dependent NETosis is not required for A. fumigatus killing either in vitro or during infection.

Comparative Circadian Metabolomics Reveal Differential Effects of Nutritional Challenge in the Serum and Liver

Diagnosis and therapeutic interventions in pathological conditions rely upon clinical monitoring of key metabolites in the serum. Recent studies show that a wide range of metabolic pathways are controlled by circadian rhythms whose oscillation is affected by nutritional challenges, underscoring the importance of assessing a temporal window for clinical testing and thereby questioning the accuracy of the reading of critical pathological markers in circulation. We have been interested in studying the communication between peripheral tissues under metabolic homeostasis perturbation. Here we present a comparative circadian metabolomic analysis on serum and liver in mice under high fat diet. Our data reveal that the nutritional challenge induces a loss of serum metabolite rhythmicity compared with liver, indicating a circadian misalignment between the tissues analyzed. Importantly, our results show that the levels of serum metabolites do not reflect the circadian liver metabolic signature or the effect of nutritional challenge. This notion reveals the possibility that misleading reads of metabolites in circulation may result in misdiagnosis and improper treatments. Our findings also demonstrate a tissue-specific and time-dependent disruption of metabolic homeostasis in response to altered nutrition.

Genetic ablation of tau mitigates cognitive impairment induced by type 1 diabetes

Patients affected by diabetes show an increased risk of developing Alzheimer disease (AD). Similarly, patients with AD show impaired insulin function and glucose metabolism. However, the underlying molecular mechanisms connecting these two disorders are still not well understood. Herein, we investigated the microtubule-associated protein tau as a new link between AD and diabetes. To determine whether diabetes causes cognitive decline by a tau-dependent mechanism, we treated non-transgenic (Ntg) and tau-knockout mice with streptozotocin, causing type 1 diabetes-like disease (T1D). Interestingly, although induction of T1D in Ntg mice led to cellular and behavioral deficits, it did not do so in tau-knockout mice. Thus, data suggest that tau is a fundamental mediator of the induction of cognitive impairments in T1D. Tau dysregulation, which causes a reduction in synaptic protein levels, may be responsible for the cognitive decline observed in Ntg streptozotocin-treated mice. Concomitantly, we demonstrate the novel finding that depletion of endogenous tau mitigates behavioral impairment and synaptic deficits induced in T1D-like mice. Overall, our data reveal that tau is a key molecular factor responsible for the induction of cognitive deficits observed in T1D and represents a potential therapeutic target for diabetes and patients with AD.

Correction of CNS defects in the MPSII mouse model via systemic enzyme replacement therapy

Mucopolysaccharidosis type II (MPSII), or Hunter syndrome, is a devastating disorder associated with a shortened life expectancy. Patients affected by MPSII have a variety of symptoms that affect all organs of the body and may include progressive cognitive impairment. MPSII is due to inactivity of the enzyme iduronate-2-sulfatase (IDS), which results in the accumulation of storage material in the lysosomes, such as dermatan and heparan sulfates, with consequent cell degeneration in all tissues including, in the severe phenotype, neurodegeneration in the central nervous system (CNS). To date, the only treatment available is systemic infusion of IDS, which ameliorates exclusively certain visceral defects. Therefore, it is important to simultaneously treat the visceral and CNS defects of the MPSII patients. Here, we have developed enzyme replacement therapy (ERT) protocols in a mouse model that allow the IDS to reach the brain, with the substantial correction of the CNS phenotype and of the neurobehavioral features. Treatments were beneficial even in adult and old MPSII mice, using relatively low doses of infused IDS over long intervals. This study demonstrates that CNS defects of MPSII mice can be treated by systemic ERT, providing the potential for development of an effective treatment for MPSII patients.

Comparative genomics reveals a functional thyroid-specific element in the far upstream region of the PAX8 gene

Background

The molecular mechanisms leading to a fully differentiated thyrocite are still object of intense study even if it is well known that thyroglobulin, thyroperoxidase, NIS and TSHr are the marker genes of thyroid differentiation. It is also well known that Pax8, TTF-1, Foxe1 and Hhex are the thyroid-enriched transcription factors responsible for the expression of the above genes, thus are responsible for the differentiated thyroid phenotype. In particular, the role of Pax8 in the fully developed thyroid gland was studied in depth and it was established that it plays a key role in thyroid development and differentiation. However, to date the bases for the thyroid-enriched expression of this transcription factor have not been unraveled yet. Here, we report the identification and characterization of a functional thyroid-specific enhancer element located far upstream of the Pax8 gene.

Results

We hypothesized that regulatory cis-acting elements are conserved among mammalian genes. Comparison of a genomic region extending for about 100 kb at the 5'-flanking region of the mouse and human Pax8 gene revealed several conserved regions that were tested for enhancer activity in thyroid and non-thyroid cells. Using this approach we identified one putative thyroid-specific regulatory element located 84.6 kb upstream of the Pax8 transcription start site. The in silico data were verified by promoter-reporter assays in thyroid and non-thyroid cells. Interestingly, the identified far upstream element manifested a very high transcriptional activity in the thyroid cell line PC Cl3, but showed no activity in HeLa cells. In addition, the data here reported indicate that the thyroid-enriched transcription factor TTF-1 is able to bind in vitro and in vivo the Pax8 far upstream element, and is capable to activate transcription from it.

Conclusions

Results of this study reveal the presence of a thyroid-specific regulatory element in the 5' upstream region of the Pax8 gene. The identification of this regulatory element represents the first step in the investigation of upstream regulatory mechanisms that control Pax8 transcription during thyroid differentiation and are relevant to further studies on Pax8 as a candidate gene for thyroid dysgenesis.