Neutrophil and Macrophage NADPH Oxidase 2 Differentially Control Responses to Inflammation and to Aspergillus fumigatus in Mice

Aspergillus fumigatus is an important opportunistic fungal pathogen and causes invasive pulmonary aspergillosis in conditions with compromised innate antifungal immunity, including chronic granulomatous disease, which results from inherited deficiency of the superoxide-generating leukocyte NADPH oxidase 2 (NOX2). Derivative oxidants have both antimicrobial and immunoregulatory activity and, in the context of A. fumigatus, contribute to both fungal killing and dampening inflammation induced by fungal cell walls. As the relative roles of macrophage versus neutrophil NOX2 in the host response to A. fumigatus are incompletely understood, we studied mice with conditional deletion of NOX2. When NOX2 was absent in alveolar macrophages as a result of LysM-Cre-mediated deletion, germination of inhaled A. fumigatus conidia was increased. Reducing NOX2 activity specifically in neutrophils via S100a8 (MRP8)-Cre also increased fungal burden, which was inversely proportional to the level of neutrophil NOX2 activity. Moreover, diminished NOX2 in neutrophils synergized with corticosteroid immunosuppression to impair lung clearance of A. fumigatus. Neutrophil-specific reduction in NOX2 activity also enhanced acute inflammation induced by inhaled sterile fungal cell walls. These results advance understanding into cell-specific roles of NOX2 in the host response to A. fumigatus. We show that alveolar macrophage NOX2 is a nonredundant effector that limits germination of inhaled A. fumigatus conidia. In contrast, reducing NOX2 activity only in neutrophils is sufficient to enhance inflammation to fungal cell walls as well as to promote invasive A. fumigatus. This may be relevant in clinical settings with acquired defects in NOX2 activity due to underlying conditions, which overlap risk factors for invasive aspergillosis.

Derivation of extra-embryonic and intra-embryonic macrophage lineages from human pluripotent stem cells

Tissue-resident macrophages are increasingly recognized as important determinants of organ homeostasis, tissue repair, remodeling and regeneration. Although the ontogeny and function of tissue-resident macrophages has been identified as distinct from postnatal hematopoiesis, the inability to specify, in vitro, similar populations that recapitulate these developmental waves has limited our ability to study their function and potential for regenerative applications. We took advantage of the concept that tissue-resident macrophages and monocyte-derived macrophages originate from distinct extra-embryonic and definitive hematopoietic lineages to devise a system to generate pure cultures of macrophages that resemble tissue-resident or monocyte-derived subsets. We demonstrate that human pluripotent stem cell-derived extra-embryonic-like and intra-embryonic-like hematopoietic progenitors differentiate into morphologically, transcriptionally and functionally distinct macrophage populations. Single-cell RNA sequencing of developing and mature cultures uncovered distinct developmental trajectories and gene expression programs of macrophages derived from extra-embryonic-like and intra-embryonic-like hematopoietic progenitors. These findings establish a resource for the generation of human tissue resident-like macrophages to study their specification and function under defined conditions and to explore their potential use in tissue engineering and regenerative medicine applications.

LysMD3 is a type II membrane protein without an role in the response to a range of pathogens

Germline-encoded receptors recognizing common pathogen-associated molecular patterns are a central element of the innate immune system and play an important role in shaping the host response to infection. Many of the innate immune molecules central to these signaling pathways are evolutionarily conserved. LysMD3 is a novel molecule containing a putative peptidoglycan-binding domain that has orthologs in humans, mice, zebrafish, flies, and worms. We found that the lysin motif (LysM) of LysMD3 is likely related to a previously described peptidoglycan-binding LysM found in bacteria. Mouse LysMD3 is a type II integral membrane protein that co-localizes with GM130+ structures, consistent with localization to the Golgi apparatus. We describe here two lines of mLysMD3-deficient mice for in vivo characterization of mLysMD3 function. We found that mLysMD3-deficient mice were born at Mendelian ratios and had no obvious pathological abnormalities. They also exhibited no obvious immune response deficiencies in a number of models of infection and inflammation. mLysMD3-deficient mice exhibited no signs of intestinal dysbiosis by 16S analysis or alterations in intestinal gene expression by RNA sequencing. We conclude that mLysMD3 contains a LysM with cytoplasmic orientation, but we were unable to define a physiological role for the molecule in vivo.

Aspergillus fumigatus Copper Export Machinery and Reactive Oxygen Intermediate Defense Counter Host Copper-Mediated Oxidative Antimicrobial Offense

The Fenton-chemistry-generating properties of copper ions are considered a potent phagolysosome defense against pathogenic microbes, yet our understanding of underlying host/microbe dynamics remains unclear. We address this issue in invasive aspergillosis and demonstrate that host and fungal responses inextricably connect copper and reactive oxygen intermediate (ROI) mechanisms. Loss of the copper-binding transcription factor AceA yields an Aspergillus fumigatus strain displaying increased sensitivity to copper and ROI in vitro, increased intracellular copper concentrations, decreased survival in challenge with murine alveolar macrophages (AMΦs), and reduced virulence in a non-neutropenic murine model. ΔaceA survival is remediated by dampening of host ROI (chemically or genetically) or enhancement of copper-exporting activity (CrpA) in A. fumigatus. Our study exposes a complex host/microbe multifactorial interplay that highlights the importance of host immune status and reveals key targetable A. fumigatus counter-defenses.

Neurologic abnormalities in mouse models of the lysosomal storage disorders mucolipidosis II and mucolipidosis III γ

UDP-GlcNAc:lysosomal enzyme N-acetylglucosamine-1-phosphotransferase is an α₂β₂γ₂ hexameric enzyme that catalyzes the synthesis of the mannose 6-phosphate targeting signal on lysosomal hydrolases. Mutations in the α/β subunit precursor gene cause the severe lysosomal storage disorder mucolipidosis II (ML II) or the more moderate mucolipidosis III alpha/beta (ML III α/β), while mutations in the γ subunit gene cause the mildest disorder, mucolipidosis III gamma (ML III γ). Here we report neurologic consequences of mouse models of ML II and ML III γ. The ML II mice have a total loss of acid hydrolase phosphorylation, which results in depletion of acid hydrolases in mesenchymal-derived cells. The ML III γ mice retain partial phosphorylation. However, in both cases, total brain extracts have normal or near normal activity of many acid hydrolases reflecting mannose 6-phosphate-independent lysosomal targeting pathways. While behavioral deficits occur in both models, the onset of these changes occurs sooner and the severity is greater in the ML II mice. The ML II mice undergo progressive neurodegeneration with neuronal loss, astrocytosis, microgliosis and Purkinje cell depletion which was evident at 4 months whereas ML III γ mice have only mild to moderate astrocytosis and microgliosis at 12 months. Both models accumulate the ganglioside GM2, but only ML II mice accumulate fucosylated glycans. We conclude that in spite of active mannose 6-phosphate-independent targeting pathways in the brain, there are cell types that require at least partial phosphorylation function to avoid lysosomal dysfunction and the associated neurodegeneration and behavioral impairments.

The role of human ribosomal proteins in the maturation of rRNA and ribosome production

Production of ribosomes is a fundamental process that occurs in all dividing cells. It is a complex process consisting of the coordinated synthesis and assembly of four ribosomal RNAs (rRNA) with about 80 ribosomal proteins (r-proteins) involving more than 150 nonribosomal proteins and other factors. Diamond Blackfan anemia (DBA) is an inherited red cell aplasia caused by mutations in one of several r-proteins. How defects in r-proteins, essential for proliferation in all cells, lead to a human disease with a specific defect in red cell development is unknown. Here, we investigated the role of r-proteins in ribosome biogenesis in order to find out whether those mutated in DBA have any similarities. We depleted HeLa cells using siRNA for several individual r-proteins of the small (RPS6, RPS7, RPS15, RPS16, RPS17, RPS19, RPS24, RPS25, RPS28) or large subunit (RPL5, RPL7, RPL11, RPL14, RPL26, RPL35a) and studied the effect on rRNA processing and ribosome production. Depleting r-proteins in one of the subunits caused, with a few exceptions, a decrease in all r-proteins of the same subunit and a decrease in the corresponding subunit, fully assembled ribosomes, and polysomes. R-protein depletion, with a few exceptions, led to the accumulation of specific rRNA precursors, highlighting their individual roles in rRNA processing. Depletion of r-proteins mutated in DBA always compromised ribosome biogenesis while affecting either subunit and disturbing rRNA processing at different levels, indicating that the rate of ribosome production rather than a specific step in ribosome biogenesis is critical in patients with DBA.

Arabidopsis SMG7 protein is required for exit from meiosis

Meiosis consists of two nuclear divisions that are separated by a short interkinesis. Here we show that the SMG7 protein, which plays an evolutionarily conserved role in nonsense-mediated RNA decay (NMD) in animals and yeast, is essential for the progression from anaphase to telophase in the second meiotic division in Arabidopsis. Arabidopsis SMG7 is an essential gene, the disruption of which causes embryonic lethality. Plants carrying a hypomorphic smg7 mutation exhibit an elevated level of transcripts containing premature stop codons. This suggests that the role of SMG7 in NMD is conserved in plants. Furthermore, hypomorphic smg7 alleles render mutant plants sterile by causing an unusual cell-cycle arrest in anaphase II that is characterized by delayed chromosome decondensation and aberrant rearrangement of the meiotic spindle. The smg7 phenotype was mimicked by exposing meiocytes to the proteasome inhibitor MG115. Together, these data indicate that SMG7 counteracts cyclin-dependent kinase (CDK) activity at the end of meiosis, and reveal a novel link between SMG7 and regulation of the meiotic cell cycle.

Telomere dynamics and fusion of critically shortened telomeres in plants lacking DNA ligase IV

In the absence of the telomerase, telomeres undergo progressive shortening and are ultimately recruited into end-to-end chromosome fusions via the non-homologous end joining (NHEJ) double-strand break repair pathway. Previously, we showed that fusion of critically shortened telomeres in Arabidopsis proceeds with approximately the same efficiency in the presence or absence of KU70, a key component of NHEJ. Here we report that DNA ligase IV (LIG4) is also not essential for telomere joining. We observed only a modest decrease (3-fold) in the frequency of chromosome fusions in triple tert ku70 lig4 mutants versus tert ku70 or tert. Sequence analysis revealed that, relative to tert ku70, chromosome fusion junctions in tert ku70 lig4 mutants contained less microhomology and less telomeric DNA. These findings argue that the KU-LIG4 independent end-joining pathway is less efficient and mechanistically distinct from KU-independent NHEJ. Strikingly, in all the genetic backgrounds we tested, chromosome fusions are initiated when the shortest telomere in the population reaches approximately 1 kb, implying that this size represents a critical threshold that heralds a detrimental structural transition. These data reveal the transitory nature of telomere stability, and the robust and flexible nature of DNA repair mechanisms elicited by telomere dysfunction.

Cells depleted for RPS19, a protein associated with Diamond Blackfan Anemia, show defects in 18S ribosomal RNA synthesis and small ribosomal subunit production

The gene encoding the small subunit ribosomal protein 19 (RPS19) is mutated in about 25% of cases of the bone marrow failure syndrome Diamond Blackfan Anemia (DBA), a childhood disease characterized by failure of red cell production. In these cases DBA is inherited as an autosomal dominant trait and RPS19 haploinsufficiency is thought to cause the disease. To study the molecular pathogenesis of DBA we used siRNA to decrease the level of RPS19 in two human cell lines, HeLa cells and U-2 OS osteosarcoma cells. Cells with reduced RPS19 levels showed a dramatic reduction in the amounts of small 40S ribosome subunits and mature 80S ribosomes and an excess of large 60S subunits. These cells were defective in 18S rRNA production and accumulated 21S and 20S nuclear pre-rRNA molecules, suggesting that RPS19 is required for specific steps in rRNA processing. RPS19 depletion produced a reduction in steady-state levels of RPS6 and RPS16 via a post-transcriptional mechanism while the levels of RPL7 and RPL26 were unaltered, indicating that levels of ribosomal proteins are determined by subunit assembly. This has interesting implications for the pathogenesis of DBA suggesting that deficiency of any of the RPS proteins might have a similar effect and thus may be responsible for causing DBA. Finally in cell lines from DBA patients with mutations we find increased levels of 21S rRNA precursors but no abnormality in the ribosome profile on sucrose gradients or in the steady-state levels of RPS19 suggesting that some cells can partially compensate for the loss of one allele of RPS19. We conclude that defects in ribosome biogenesis may underlie the pathology of Diamond Blackfan Anemia.