Defective mitochondrial function by mutation in THICK ALEURONE 1 encoding a mitochondrion-targeted single-stranded DNA-binding protein leads to increased aleurone cell layers and improved nutrition in rice.

Cereal endosperm comprises an outer aleurone and an inner starchy endosperm. Although these two tissues have the same developmental origin, they differ in morphology, cell fate, and storage product accumulation, with the mechanism largely unknown. Here, we report the identification and characterization of rice thick aleurone 1 (ta1) mutant that shows an increased number of aleurone cell layers and increased contents of nutritional factors including proteins, lipids, vitamins, dietary fibers, and micronutrients. We identified that the TA1 gene, which is expressed in embryo, aleurone, and subaleurone in caryopses, encodes a mitochondrion-targeted protein with single-stranded DNA-binding activity named OsmtSSB1. Cytological analyses revealed that the increased aleurone cell layers in ta1 originate from a developmental switch of subaleurone toward aleurone instead of starchy endosperm in the wild type. We found that TA1/OsmtSSB1 interacts with mitochondrial DNA recombinase RECA3 and DNA helicase TWINKLE, and downregulation of RECA3 or TWINKLE also leads to ta1-like phenotypes. We further showed that mutation in TA1/OsmtSSB1 causes elevated illegitimate recombinations in the mitochondrial genome, altered mitochondrial morphology, and compromised energy supply, suggesting that the OsmtSSB1-mediated mitochondrial function plays a critical role in subaleurone cell-fate determination in rice.

Regeneration of Tooth with Allogenous, Autoclaved Treated Dentin Matrix with Dental Pulpal Stem Cells: An In Vivo Study.

INTRODUCTION: Biomaterials designed for tissue engineering should be nontoxic and nonimmunogenic and should achieve their intended functions. Treated dentin matrix (TDM), a bioactive extracellular matrix, is promising for tooth regeneration. However, the effect of sterilization on the surface properties of allogenous TDM in the animal model is unclear. METHODS: The biological characteristics and influences of dental pulp stem cells (DPSCs) with autoclaved TDM (a-TDM) were studied using scanning electron microscopy, immunofluorescence microscopy, immunohistochemistry, and reverse transcription polymerase chain reaction in vitro. In addition, a-TDM was implanted in a mouse model for 6 weeks and was a substrate with DPSCs for tooth reconstruction in a goat animal model in vivo. RESULTS: Allogenous a-TDM induced and supported DPSCs to develop new dentin pulp-like tissues, enamel dental pulp, and cementum periodontal complexes. Immunohistochemistry data showed that the markers dentin sialoprotein, ßⅢ-tubulin, dentin matrix protein 1, amelogenin, VIII factors, type I collagen, cementum-derived attachment protein, and scleraxis transcription factor were positive stained in toothlike tissue. CONCLUSIONS: Allogenous a-TDM served as an effective scaffold enabling DPSCs to proliferate and differentiate into a broad array of resident cells including odontoblasts, fibroblasts, vascular cells, and neural endings. Allogenous a-TDM with DPSCs can provide an ideal biomaterial for optimizing the regeneration of tooth material.

Neutrophil Extracellular Trap Killing Assay of Candida albicans.

Fungal pathogen Candida albicans is one of the top leading causes of overall healthcare-associated bloodstream infections worldwide. Neutrophil is the major effector cell to clear C. albicans infection. Our study showed that mouse neutrophils utilize two independent mechanisms to kill C. albicans: one is CR3 downstream NADPH oxidase-dependent mechanism that kills opsonized C. albicans; the other one is dectin-2-mediated NADPH oxidase-independent neutrophil extracellular trap (NET) that kills unopsonized C. albicans. Neutrophil killing of opsonized C. albicans requires phagocytosing the organism and production of reactive oxygen species production (ROS). Most existing protocols that assay for neutrophil killing of C. albicans requires a washing step after allowing neutrophils to phagocytose the organism. By definition, NET kills organisms extracellularly. Therefore, it is important to skip the washing step and add an optimal ratio of neutrophils and C. albicans to the wells. To demonstrate the effect of NET, it is necessary to compare killing ability of neutrophils treated with micrococcal nuclease (MNase), an enzyme that digests NET, to that treated with heat-inactivated MNase. MNase is also applied to release NET-bound fungal elements for counting. This protocol can be applied to assay NET killing of other biofilm-forming organisms.

Candida albicans triggers NADPH oxidase-independent neutrophil extracellular traps through dectin-2.

Candida albicans is one of the top leading causes of healthcare-associated bloodstream infection. Neutrophil extracellular traps (NET) are known to capture and kill pathogens. It is reported that opsonized C. albicans-triggered NETosis is NADPH oxidase-dependent. We discovered a NADPH oxidase-independent NETosis pathway in neutrophil response to unopsonized C. albicans. While CR3 engagement with opsonized C. albicans triggered NET, dectin-2 recognized unopsonized C. albicans and mediated NET formation. Engagement of dectin-2 activated the downstream Syk-Ca2+-PKCδ-protein arginine deiminase 4 (PAD4) signaling pathway which modulated nuclear translocation of neutrophil elastase (NE), histone citrullination and NETosis. In a C. albicans peritonitis model we observed Ki67+Ly6G+ NETotic cells in the peritoneal exudate and mesenteric tissues within 3 h of infection. Treatment with PAD4 inhibitor GSK484 or dectin-2 deficiency reduced % Ki67+Ly6G+ cells and the intensity of Ki67 in peritoneal neutrophils. Employing DNA digestion enzyme micrococcal nuclease, GSK484 as well as dectin-2-deficient mice, we further showed that dectin-2-mediated PAD4-dependent NET formation in vivo restrained the spread of C. albicans from the peritoneal cavity to kidney. Taken together, this study reveals that unopsonized C. albicans evokes NADPH oxidase-independent NETosis through dectin-2 and its downstream signaling pathway and dectin-2-mediated NET helps restrain fungal dissemination.

Human dendritic cell-specific ICAM-3-grabbing non-integrin downstream signaling alleviates renal fibrosis via Raf-1 activation in systemic candidiasis.

We generated a human dendritic cell-specific ICAM-3-grabbing non-integrin (DC-SIGN) transgenic mouse in which renal tubular epithelial cells expressed DC-SIGN. The transgenic mice were infected with Candida albicans intravenously to study how DC-SIGN expression affected the pathogenesis of systemic candidiasis. We discovered that, while C. albicans infection induced renal fibrosis in both transgenic and littermate control mice, the transgenic mice had significantly lower levels of Acta2, Col1a2, Col3a1, and Col4a1 mRNA transcripts compared to the controls. KIM-1, an emerging biomarker for kidney injury, along with Tnf, Il6, and Tgfb1 transcripts, were lower in infected transgenic mice, and yet, the levels of Il10 remained comparable to the controls. While renal CD45+ infiltrating cells were the source of Tnf, Il6, and Il10, LTL+ renal proximal tubular epithelial cells were TGF-ß1 producers in both infected transgenic and littermate controls. DC-SIGN-expressing tubular epithelial cells produced less TGF-ß1 in response to C. albicans infection. In vivo experiments demonstrated that renal proximal tubular epithelial cell production of TGF-ß1 was key to C. albicans-induced renal fibrosis and injury. Infection of transgenic mice induced a marked increase of phosphorylated Raf-1 and p38 in the kidney. However, ERK1/2 and JNK phosphorylation was more pronounced in the infected-littermate controls. Interestingly, treating the infected transgenic mice with a Raf-1 inhibitor increased the levels of the Tgfb1, Kim1, and Acta2 transcripts. These results indicate that DC-SIGN signaling, through activation of Raf-1 and p38 and suppression of JNK and ERK1/2 phosphorylation, reduces TGF-ß1 production and C. albicans-induced renal fibrosis. Our study reveals for the first time the effect of DC-SIGN expression on C. albicans-induced renal fibrosis.

NLRX1 Facilitates Histoplasma capsulatum-Induced LC3-Associated Phagocytosis for Cytokine Production in Macrophages.

LC3-associated phagocytosis (LAP) is an emerging non-canonical autophagy process that bridges signaling from pattern-recognition receptors (PRRs) to autophagic machinery. LAP formation results in incorporation of lipidated LC3 into phagosomal membrane (termed LAPosome). Increasing evidence reveals that LAP functions as an innate defense mechanism against fungal pathogens. However, the molecular mechanism involved and the consequence of LAP in regulating anti-fungal immune response remain largely unexplored. Here we show that Histoplasma capsulatum is taken into LAPosome upon phagocytosis by macrophages. Interaction of H. capsulatum with Dectin-1 activates Syk and triggers subsequent NADPH oxidase-mediated reactive oxygen species (ROS) response that is involved in LAP induction. Inhibiting LAP induction by silencing LC3α/ß or treatment with ROS inhibitor impairs the activation of MAPKs-AP-1 pathway, thereby reduces macrophage proinflammatory cytokine response to H. capsulatum. Additionally, we unravel the importance of NLRX1 in fungus-induced LAP. NLRX1 facilitates LAP by interacting with TUFM which associates with autophagic proteins ATG5-ATG12 for LAPosome formation. Macrophages from Nlrx1-/- mice or TUFM-silenced cells exhibit reduced LAP induction and LAP-mediated MAPKs-AP-1 activation for cytokine response to H. capsulatum. Furthermore, inhibiting ROS production in Nlrx1-/- macrophages almost completely abolishes H. capsulatum-induced LC3 conversion, indicating that both Dectin-1/Syk/ROS-dependent pathway and NLRX1-TUFM complex-dependent pathway collaboratively contribute to LAP induction. Our findings reveal new pathways underlying LAP induction by H. capsulatum for macrophage cytokine response.

Cell Intrinsic Galectin-3 Attenuates Neutrophil ROS-Dependent Killing of Candida by Modulating CR3 Downstream Syk Activation.

Invasive candidiasis is a leading cause of nosocomial bloodstream infection. Neutrophils are the important effector cells in host resistance to candidiasis. To investigate the modulation of neutrophil fungicidal function will advance our knowledge on the control of candidiasis. While recombinant galectin-3 enhances neutrophil phagocytosis of Candida, we found that intracellular galectin-3 downregulates neutrophil fungicidal functions. Co-immunoprecipitation and immunofluorescence staining reveal that cytosolic gal3 physically interacts with Syk in neutrophils after Candida stimulation. Gal3-/- neutrophils have higher level of Syk activation as well as greater abilities to generate reactive oxygen species (ROS) and kill Candida than gal3+/+ cells. While galectin-3 deficiency modulates neutrophil and macrophage activation and the recruitment of monocytes and dendritic cells, the deficiency does not affect the numbers of infiltrating neutrophils or macrophages. Galectin-3 deficiency ameliorates systemic candidiasis by reducing fungal burden, renal pathology, and mortality. Adoptive transfer experiments demonstrate that cell intrinsic galectin-3 negatively regulates neutrophil effector functions against candidiasis. Reducing galectin-3 expression or activity by siRNA or gal3 inhibitor TD139 enhances human neutrophil ROS production. Mice treated with TD139 have enhanced ability to clear the fungus. Our work unravels the mechanism by which galectin-3 regulates Syk-dependent neutrophil fungicidal functions and raises the possibility that blocking gal3 in neutrophils may be a promising therapeutic strategy for treating systemic candidiasis.

CR3 and Dectin-1 Collaborate in Macrophage Cytokine Response through Association on Lipid Rafts and Activation of Syk-JNK-AP-1 Pathway.

Collaboration between heterogeneous pattern recognition receptors (PRRs) leading to synergistic coordination of immune response is important for the host to fight against invading pathogens. Although complement receptor 3 (CR3) and Dectin-1 are major PRRs to detect fungi, crosstalk between these two receptors in antifungal immunity is largely undefined. Here we took advantage of Histoplasma capsulatum which is known to interact with both CR3 and Dectin-1 and specific particulate ligands to study the collaboration of CR3 and Dectin-1 in macrophage cytokine response. By employing Micro-Western Array (MWA), genetic approach, and pharmacological inhibitors, we demonstrated that CR3 and Dectin-1 act collaboratively to trigger macrophage TNF and IL-6 response through signaling integration at Syk kinase, allowing subsequent enhanced activation of Syk-JNK-AP-1 pathway. Upon engagement, CR3 and Dectin-1 colocalize and form clusters on lipid raft microdomains which serve as a platform facilitating their cooperation in signaling activation and cytokine production. Furthermore, in vivo studies showed that CR3 and Dectin-1 cooperatively participate in host defense against disseminated histoplasmosis and instruct adaptive immune response. Taken together, our findings define the mechanism of receptor crosstalk between CR3 and Dectin-1 and demonstrate the importance of their collaboration in host defense against fungal infection.

Galectin-3 modulates Th17 responses by regulating dendritic cell cytokines.

Galectin-3 is a ß-galactoside-binding animal lectin with diverse functions, including regulation of T helper (Th) 1 and Th2 responses. Current data indicate that galectin-3 expressed in dendritic cells (DCs) may be contributory. Th17 cells have emerged as critical inducers of tissue inflammation in autoimmune disease and important mediators of host defense against fungal pathogens, although little is known about galectin-3 involvement in Th17 development. We investigated the role of galectin-3 in the induction of Th17 immunity in galectin-3-deficient (gal3(-/-)) and gal3(+/+) mouse bone marrow-derived DCs. We demonstrate that intracellular galectin-3 negatively regulates Th17 polarization in response to the dectin-1 agonist curdlan (a ß-glucan present on the cell wall of fungal species) and lipopolysaccharide, agents that prime DCs for Th17 differentiation. On activation of dectin-1, gal3(-/-) DCs secreted higher levels of the Th17-axis cytokine IL-23 compared with gal3(+/+) DCs and contained higher levels of activated c-Rel, an NF-κB subunit that promotes IL-23 expression. Levels of active Raf-1, a kinase that participates in downstream inhibition of c-Rel binding to the IL23A promoter, were impaired in gal3(-/-) DCs. Modulation of Th17 by galectin-3 in DCs also occurred in vivo because adoptive transfer of gal3(-/-) DCs exposed to Candida albicans conferred higher Th17 responses and protection against fungal infection. We conclude that galectin-3 suppresses Th17 responses by regulating DC cytokine production.

Galectin-3 negatively regulates dendritic cell production of IL-23/IL-17-axis cytokines in infection by Histoplasma capsulatum.

Galectin-3 (gal3) is known for its immunoregulatory functions in infectious, autoimmune, and inflammatory diseases. However, little is known about its regulatory role in the host's IL-17A response to infection. Using a mouse model of histoplasmosis in which both Th1 and Th17 responses contribute to fungal clearance, we investigated how gal3 regulates IL-17A responses. Our study showed that Histoplasma infection induced gal3(-/-) dendritic cells to produce significantly higher levels of IL-23, TGF-ß1, and IL-1ß than did gal3(+/+) cells. Infected by the same inoculum of Histoplasma, gal3(-/-) mice had lower fungal burden and produced higher levels of IL-23/IL-17-axis cytokines and lower levels of IL-12 and IFN-γ. Additionally, there was an increase in Th17 cells and a reduction in Th1 cells in infected gal3(-/-) mice. In vitro Th1/Th17-skewing experiments excluded the intrinsic effect of gal3 on Th cell differentiation. Although neutrophils from both gal3(+/+) and gal3(-/-) mice produced IL-17A upon IL-23 stimulation, their contribution to IL-17A production was greater in gal3(-/-) mice than in gal3(+/+) mice. Compared with gal3(+/+) dendritic cells, adoptive transfer of gal3(-/-) dendritic cells resulted in production of significantly higher levels of IL-17-axis cytokines and reduced fungal burden. It appears that reduced fungal burden and preferential IL-17A response in gal3(-/-) mice by both Th17 cells and neutrophils were the result of preferential production of IL-23/IL-17-axis cytokines by dendritic cells. Our study showed that gal3 negatively regulates IL-17A responses through inhibition of IL-23/IL-17-axis cytokine production by dendritic cells.

Distinct roles of complement receptor 3, Dectin-1, and sialic acids in murine macrophage interaction with Histoplasma yeast.

The yeast cells of dimorphic fungal pathogen Histoplasma reside primarily within the macrophages of an infected host; the interaction between the yeast and macrophage has a profound impact on host defense against the fungus. We used blocking antibodies and saccharides to identify the receptors that participate in the phagocytosis of and the cytokine response to Histoplasma. The phagocytosis and cytokine response results show that sialic acids on the macrophages were involved in the interaction between macrophages and Histoplasma. CR3, although not the only receptor involved, was responsible for phagocytosis and cytokine response. It is unclear which receptors other than CR3 are responsible for phagocytosis, but we did rule out the participation of TLR2, TLR4, MR, DC-SIGN/SIGNR1, FcgammaR, VLA-5, and Dectin-1. Even though Dectin-1 did not participate in phagocytosis, it collaborated with CR3 in the cytokine response to Histoplasma, suggesting that in the presence of phagocytic receptors, Histoplasma triggers cytokine signals through Dectin-1. Moreover, macrophage phagocytosis of and cytokine response to Histoplasma are Syk kinase-dependent. Our study delineated the distinct roles of CR3, Dectin-1, and sialic acids in the interaction with Histoplasma and suggested that multiple receptor use might be important to host defense against Histoplasma.