Diminished Immune Response and Elevated Abundance in Gut Microbe Dubosiella in Mouse Models of Chronic Colitis with GBP5 Deficiency.

Guanylate binding protein 5 (GBP5) is an emerging immune component that has been increasingly recognized for its involvement in autoimmune diseases, particularly inflammatory bowel disease (IBD). IBD is a complex disease involving inflammation of the gastrointestinal tract. Here, we explored the functional significance of GBP5 using Gbp5 knockout mice and wildtype mice exposed to dextran sulfate sodium (DSS) to generate chronic colitis model. We found that Gbp5 deficiency protected mice from DSS-induced chronic colitis. Transcriptome analysis of colon tissues showed reduced immune responses in Gbp5 knockout mice compared to those in corresponding wildtype mice. We further observed that after repeated DSS exposure, the gut microbiota was altered, both in wildtype mice and Gbp5 knockout mice; however, the gut microbiome health index was higher in the Gbp5 knockout mice. Notably, a probiotic murine commensal bacterium, Dubosiella, was predominantly enriched in these knockout mice. Our findings suggest that GBP5 plays an important role in promoting inflammation and dysbiosis in the intestine, the prevention of which might therefore be worth exploring in regards to IBD treatment.

HBS1L deficiency causes retinal dystrophy in a child and in a mouse model associated with defective development of photoreceptor cells.

Inherited retinal diseases encompass a genetically diverse group of conditions caused by variants in genes critical to retinal function, including handful of ribosome-associated genes. This study focuses on the HBS1L gene, which encodes for the HBS1-like translational GTPase that is crucial for ribosomal rescue. We have reported a female child carrying biallelic HBS1L variants, manifesting with poor growth and neurodevelopmental delay. Here, we describe the ophthalmologic findings in the patient and in Hbs1ltm1a/tm1a hypomorph mice and describe the associated microscopic and molecular perturbations. The patient has impaired visual function, showing dampened amplitudes of a- and b-waves in both rod- and cone-mediated responses. Hbs1ltm1a/tm1a mice exhibited profound thinning of the entire retina, specifically of the outer photoreceptor layer, due to extensive photoreceptor cell apoptosis. Loss of Hbs1l resulted in comprehensive proteomic alterations by mass spectrometry analysis, with an increase in the levels of 169 proteins and a decrease in the levels of 480 proteins, including rhodopsin (Rho) and peripherin 2 (Prph2). Gene Ontology biological process and gene set enrichment analyses reveal that the downregulated proteins are primarily involved in phototransduction, cilium assembly and photoreceptor cell development. These findings underscore the importance of ribosomal rescue proteins in maintaining retinal health, particularly in photoreceptor cells.

Knockdown of GBP1 inhibits BCG-induced apoptosis in macrophage RAW 264.7 cells via p38/JNK pathway.

Alveolar macrophage apoptosis induced by Mycobacterium tuberculosis (Mtb) plays a significant role in mediating the pathogenesis of tuberculosis. There is growing evidence that guanylate-binding proteins (GBPs) are associated with different pathological processes such as microbial infection. However, it remains unclear whether GBPs can regulate the apoptosis of macrophages induced by Mtb. In this study, we investigated the potential effect of GBP1 on RAW 264.7 cell apoptosis during Bacillus Calmette-Guerin (BCG) infection. The results demonstrated that BCG could induce macrophage apoptosis and GBP1 upregulation. In addition, we explored the role of GBP1 in regulating BCG-induced RAW 264.7 cell apoptosis using small interfering RNAs targeting GBP1. The results showed that knockdown of GBP1 could attenuate BCG-induced apoptosis in RAW 264.7 cells. Moreover, we found that GBP1 knockdown decreased the levels of cleaved-Caspase 3 and cleaved-PARP-1, while decreased those of cleaved-Caspase 9, BAX, Cytochrome C and APAF1. These findings imply that GBP1 knockdown can prevent BCG-induced apoptosis through an endogenous apoptosis pathway. In addition, the mitochondrial membrane potential of macrophages was significantly increased after BCG infection, and GBP1 knockdown could alleviate this phenomenon. Furthermore, downregulation of GBP1 also attenuated BCG-induced accumulation of reactive oxygen species in macrophages. Mechanistically, GBP1 suppressed the phosphorylation of the target molecules in p38/JNK pathway, thus regulating the apoptosis of BGC-infected macrophages. Collectively, these findings reveal a significant role of GBP1 in mediating cell apoptosis in macrophages infected with BCG, and the molecular mechanism underlying its suppressive effect on BCG-induced apoptosis.

Global Rhes knockout in the Q175 Huntington's disease mouse model.

Huntington's disease (HD) results from an expansion mutation in the polyglutamine tract in huntingtin. Although huntingtin is ubiquitously expressed in the body, the striatum suffers the most severe pathology. Rhes is a Ras-related small GTP-binding protein highly expressed in the striatum that has been reported to modulate mTOR and sumoylation of mutant huntingtin to alter HD mouse model pathogenesis. Reports have varied on whether Rhes reduction is desirable for HD. Here we characterize multiple behavioral and molecular endpoints in the Q175 HD mouse model with genetic Rhes knockout (KO). Genetic RhesKO in the Q175 female mouse resulted in both subtle attenuation of Q175 phenotypic features, and detrimental effects on other kinematic features. The Q175 females exhibited measurable pathogenic deficits, as measured by MRI, MRS and DARPP32, however, RhesKO had no effect on these readouts. Additionally, RhesKO in Q175 mixed gender mice deficits did not affect mTOR signaling, autophagy or mutant huntingtin levels. We conclude that global RhesKO does not substantially ameliorate or exacerbate HD mouse phenotypes in Q175 mice.

Involvement of the Protein Ras Homolog Enriched in the Striatum, Rhes, in Dopaminergic Neurons' Degeneration: Link to Parkinson's Disease.

Rhes is one of the most interesting genes regulated by thyroid hormones that, through the inhibition of the striatal cAMP/PKA pathway, acts as a modulator of dopamine neurotransmission. Rhes mRNA is expressed at high levels in the dorsal striatum, with a medial-to-lateral expression gradient reflecting that of both dopamine D2 and adenosine A2A receptors. Rhes transcript is also present in the hippocampus, cerebral cortex, olfactory tubercle and bulb, substantia nigra pars compacta (SNc) and ventral tegmental area of the rodent brain. In line with Rhes-dependent regulation of dopaminergic transmission, data showed that lack of Rhes enhanced cocaine- and amphetamine-induced motor stimulation in mice. Previous studies showed that pharmacological depletion of dopamine significantly reduces Rhes mRNA levels in rodents, non-human primates and Parkinson's disease (PD) patients, suggesting a link between dopaminergic innervation and physiological Rhes mRNA expression. Rhes protein binds to and activates striatal mTORC1, and modulates L-DOPA-induced dyskinesia in PD rodent models. Finally, Rhes is involved in the survival of mouse midbrain dopaminergic neurons of SNc, thus pointing towards a Rhes-dependent modulation of autophagy and mitophagy processes, and encouraging further investigations about mechanisms underlying dysfunctions of the nigrostriatal system.

IRGM1 links mitochondrial quality control to autoimmunity.

Mitochondrial abnormalities have been noted in lupus, but the causes and consequences remain obscure. Autophagy-related genes ATG5, ATG7 and IRGM have been previously implicated in autoimmune disease. We reasoned that failure to clear defective mitochondria via mitophagy might be a foundational driver in autoimmunity by licensing mitochondrial DNA-dependent induction of type I interferon. Here, we show that mice lacking the GTPase IRGM1 (IRGM homolog) exhibited a type I interferonopathy with autoimmune features. Irgm1 deletion impaired the execution of mitophagy with cell-specific consequences. In fibroblasts, mitochondrial DNA soiling of the cytosol induced cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING)-dependent type I interferon, whereas in macrophages, lysosomal Toll-like receptor 7 was activated. In vivo, Irgm1-/- tissues exhibited mosaic dependency upon nucleic acid receptors. Whereas salivary and lacrimal gland autoimmune pathology was abolished and lung pathology was attenuated by cGAS and STING deletion, pancreatic pathology remained unchanged. These findings reveal fundamental connections between mitochondrial quality control and tissue-selective autoimmune disease.

Bacterial Outer Membrane Vesicle-Mediated Cytosolic Delivery of Flagellin Triggers Host NLRC4 Canonical Inflammasome Signaling.

Bacteria-released components can modulate host innate immune response in the absence of direct host cell-bacteria interaction. In particular, bacteria-derived outer membrane vesicles (OMVs) were recently shown to activate host caspase-11-mediated non-canonical inflammasome pathway via deliverance of OMV-bound lipopolysaccharide. However, further precise understanding of innate immune-modulation by bacterial OMVs remains elusive. Here, we present evidence that flagellated bacteria-released OMVs can trigger NLRC4 canonical inflammasome activation via flagellin delivery to the cytoplasm of host cells. Salmonella typhimurium-derived OMVs caused a robust NLRC4-mediated caspase-1 activation and interleukin-1ß secretion in macrophages in an endocytosis-dependent, but guanylate-binding protein-independent manner. Notably, OMV-associated flagellin is crucial for Salmonella OMV-induced inflammasome response. Flagellated Pseudomonas aeruginosa-released OMVs consistently promoted robust NLRC4 inflammasome activation, while non-flagellated Escherichia coli-released OMVs induced NLRC4-independent non-canonical inflammasome activation leading to NLRP3-mediated interleukin-1ß secretion. Flagellin-deficient Salmonella OMVs caused a weak interleukin-1ß production in a NLRP3-dependent manner. These findings indicate that Salmonella OMV triggers NLRC4 inflammasome activation via OMV-associated flagellin in addition to a mild induction of non-canonical inflammasome signaling via OMV-bound lipopolysaccharide. Intriguingly, flagellated Salmonella-derived OMVs induced more rapid inflammasome response than flagellin-deficient Salmonella OMV and non-flagellated Escherichia coli-derived OMVs. Supporting these in vitro results, Nlrc4-deficient mice showed significantly reduced interleukin-1ß production after intraperitoneal challenge with Salmonella-released OMVs. Taken together, our results here propose that NLRC4 inflammasome machinery is a rapid sensor of bacterial OMV-bound flagellin as a host defense mechanism against bacterial pathogen infection.

Role of Gate-16 and Gabarap in Prevention of Caspase-11-Dependent Excess Inflammation and Lethal Endotoxic Shock.

Sepsis is a life-threating multi-organ disease induced by host innate immunity to pathogen-derived endotoxins including lipopolysaccharide (LPS). Direct sensing of LPS by caspase-11 activates inflammasomes and causes lethal sepsis in mice. Inhibition of caspase-11 inflammasomes is important for the prevention of LPS-induced septic shock; however, whether a caspase-11 inflammasome-specific suppressive mechanism exists is unclear. Here we show that deficiency of GABARAP autophagy-related proteins results in over-activation of caspase-11 inflammasomes but not of canonical inflammasomes. Gate-16-/-Gabarap-/- macrophages exhibited elevated guanylate binding protein 2 (GBP2)-dependent caspase-11 activation and inflammatory responses. Deficiency of GABARAPs resulted in formation of GBP2-containing aggregates that promote IL-1ß production. High mortality after low dose LPS challenge in Gate-16-/-Gabarap-/- mice primed with poly(I:C) or polymicrobial sepsis was ameliorated by compound GBP2 deficiency. These results reveal a critical function of Gate-16 and Gabarap to suppress GBP2-dependent caspase-11-induced inflammation and septic shock.

Irgm1-deficiency leads to myeloid dysfunction in colon lamina propria and susceptibility to the intestinal pathogen Citrobacter rodentium.

IRGM and its mouse orthologue Irgm1 are dynamin-like proteins that regulate vesicular remodeling, intracellular microbial killing, and pathogen immunity. IRGM dysfunction is linked to inflammatory bowel disease (IBD), and while it is thought that defective intracellular killing of microbes underscores IBD susceptibility, studies have yet to address how IRGM/Irgm1 regulates immunity to microbes relevant to intestinal inflammation. Here we find that loss of Irgm1 confers marked susceptibility to Citrobacter rodentium, a noninvasive intestinal pathogen that models inflammatory responses to intestinal bacteria. Irgm1-deficient mice fail to control C. rodentium outgrowth in the intestine, leading to systemic pathogen spread and host mortality. Surprisingly, susceptibility due to loss of Irgm1 function was not linked to defective intracellular killing of C. rodentium or exaggerated inflammation, but was instead linked to failure to remodel specific colon lamina propria (C-LP) myeloid cells that expand in response to C. rodentium infection and are essential for C. rodentium immunity. Defective immune remodeling was most striking in C-LP monocytes, which were successfully recruited to the infected C-LP, but subsequently underwent apoptosis. Apoptotic susceptibility was induced by C. rodentium infection and was specific to this setting of pathogen infection, and was not apparent in other settings of intestinal inflammation. These studies reveal a novel role for Irgm1 in host defense and suggest that deficiencies in survival and remodeling of C-LP myeloid cells that control inflammatory intestinal bacteria may underpin IBD pathogenesis linked to IRGM dysfunction.

Transglutaminase 2 limits the extravasation and the resultant myocardial fibrosis associated with factor XIII-A deficiency.

BACKGROUND AND AIMS: Transglutaminase (TG) 2 and Factor (F) XIII-A have both been implicated in cardiovascular protection and repair. This study was designed to differentiate between two competing hypotheses: that TG2 and FXIII-A mediate these functions in mice by fulfilling separate roles, or that they act redundantly in this respect. METHODS: Atherosclerosis was assessed in brachiocephalic artery plaques of fat-fed mixed strain apolipoprotein (Apo)e deficient mice that lacked either or both transglutaminases. Cardiac fibrosis was assessed both in the mixed strain mice and also in C57BL/6J Apoe expressing mice lacking either or both transglutaminases. RESULTS: No difference was found in the density of buried fibrous caps within brachiocephalic plaques from mice expressing or lacking these transglutaminases. Cardiac fibrosis developed in both Apoe/F13a1 double knockout and F13a1 single knockout mice, but not in Tgm2 knockout mice. However, concomitant Tgm2 knockout markedly increased fibrosis, as apparent in both Apoe/Tgm2/F13a1 knockout and Tgm2/F13a1 knockout mice. Amongst F13a1 knockout and Tgm2/F13a1 knockout mice, the extent of fibrosis correlated with hemosiderin deposition, suggesting that TG2 limits the extravasation of blood in the myocardium, which in turn reduces the pro-fibrotic stimulus. The resulting fibrosis was interstitial in nature and caused only minor changes in cardiac function. CONCLUSIONS: These studies confirm that FXIII-A and TG2 fulfil different roles in the mouse myocardium. FXIII-A protects against vascular leakage while TG2 contributes to the stability or repair of the vasculature. The protective function of TG2 must be considered when designing clinical anti-fibrotic therapies based upon FXIII-A or TG2 inhibition.

Mitochondrial fission regulates germ cell differentiation by suppressing ROS-mediated activation of Epidermal Growth Factor Signaling in the Drosophila larval testis.

Mitochondria are essential organelles that have recently emerged as hubs for several metabolic and signaling pathways in the cell. Mitochondrial morphology is regulated by constant fusion and fission events to maintain a functional mitochondrial network and to remodel the mitochondrial network in response to external stimuli. Although the role of mitochondria in later stages of spermatogenesis has been investigated in depth, the role of mitochondrial dynamics in regulating early germ cell behavior is relatively less-well understood. We previously demonstrated that mitochondrial fusion is required for germline stem cell (GSC) maintenance in the Drosophila testis. Here, we show that mitochondrial fission is also important for regulating the maintenance of early germ cells in larval testes. Inhibition of Drp1 in early germ cells resulted in the loss of GSCs and spermatogonia due to the accumulation of reactive oxygen species (ROS) and activation of the EGFR pathway in adjacent somatic cyst cells. EGFR activation contributed to premature germ cell differentiation. Our data provide insights into how mitochondrial dynamics can impact germ cell maintenance and differentiation via distinct mechanisms throughout development.

The Crohn's Disease Risk Factor IRGM Limits NLRP3 Inflammasome Activation by Impeding Its Assembly and by Mediating Its Selective Autophagy.

Several large-scale genome-wide association studies genetically linked IRGM to Crohn's disease and other inflammatory disorders in which the IRGM appears to have a protective function. However, the mechanism by which IRGM accomplishes this anti-inflammatory role remains unclear. Here, we reveal that IRGM/Irgm1 is a negative regulator of the NLRP3 inflammasome activation. We show that IRGM expression, which is increased by PAMPs, DAMPs, and microbes, can suppress the pro-inflammatory responses provoked by the same stimuli. IRGM/Irgm1 negatively regulates IL-1ß maturation by suppressing the activation of the NLRP3 inflammasome. Mechanistically, we show that IRGM interacts with NLRP3 and ASC and hinders inflammasome assembly by blocking their oligomerization. Further, IRGM mediates selective autophagic degradation of NLRP3 and ASC. By suppressing inflammasome activation, IRGM/Irgm1 protects from pyroptosis and gut inflammation in a Crohn's disease experimental mouse model. This study for the first time identifies the mechanism by which IRGM is protective against inflammatory disorders.

CCP1 promotes mitochondrial fusion and motility to prevent Purkinje cell neuron loss in pcd mice.

A perplexing question in neurodegeneration is why different neurons degenerate. The Purkinje cell degeneration (pcd) mouse displays a dramatic phenotype of degeneration of cerebellar Purkinje cells. Loss of CCP1/Nna1 deglutamylation of tubulin accounts for pcd neurodegeneration, but the mechanism is unknown. In this study, we modulated the dosage of fission and fusion genes in a Drosophila melanogaster loss-of-function model and found that mitochondrial fragmentation and disease phenotypes were rescued by reduced Drp1. We observed mitochondrial fragmentation in CCP1 null cells and in neurons from pcd mice, and we documented reduced mitochondrial fusion in cells lacking CCP1. We examined the effect of tubulin hyperglutamylation on microtubule-mediated mitochondrial motility in pcd neurons and noted markedly reduced retrograde axonal transport. Mitochondrial stress promoted Parkin-dependent turnover of CCP1, and CCP1 and Parkin physically interacted. Our results indicate that CCP1 regulates mitochondrial motility through deglutamylation of tubulin and that loss of CCP1-mediated mitochondrial fusion accounts for the exquisite vulnerability of Purkinje neurons in pcd mice.

Transglutaminase 2 programs differentiating acute promyelocytic leukemia cells in all-trans retinoic acid treatment to inflammatory stage through NF-κB activation.

Differentiation syndrome (DS) is a life-threatening complication arising during retinoid treatment of acute promyelocytic leukemia (APL). Administration of all-trans retinoic acid leads to significant changes in gene expression, among the most induced of which is transglutaminase 2, which is not normally expressed in neutrophil granulocytes. To evaluate the pathophysiological function of transglutaminase 2 in the context of immunological function and disease outcomes, such as excessive superoxide anion, cytokine, and chemokine production in differentiated NB4 cells, we used an NB4 transglutaminase knock-out cell line and a transglutaminase inhibitor, NC9, which inhibits both transamidase- and guanosine triphosphate-binding activities, to clarify the contribution of transglutaminase to the development of potentially lethal DS during all-trans retinoic acid treatment of APL. We found that such treatment not only enhanced cell-surface expression of CD11b and CD11c but also induced high-affinity states; atypical transglutaminase 2 expression in NB4 cells activated the nuclear factor kappa (κ)-light-chain-enhancer of the activated B-cell pathway, driving pathogenic processes with an inflammatory cascade through the expression of numerous cytokines, including tumor necrosis factor alpha (TNF-α), interleukin 1 beta (IL-1ß), and monocyte chemoattractant protein 1. NC9 decreased the amount of transglutaminase 2, p65/RelA, and p50 in differentiated NB4 cells and their nuclei, leading to attenuated inflammatory cytokine synthesis. NC9 significantly inhibits transglutaminase 2 nuclear translocation but accelerates its proteasomal breakdown. This study demonstrates that transglutaminase 2 expression induced by all-trans retinoic acid treatment reprograms inflammatory signaling networks governed by nuclear factor κ-light-chain-enhancer of activated B-cell activation, resulting in overexpression of TNF-α and IL-1ß in differentiating APL cells, suggesting that atypically expressed transglutaminase 2 is a promising target for leukemia treatment.

Mycobacterium tuberculosis Requires Regulation of ESX-5 Secretion for Virulence in Irgm1-Deficient Mice.

The Mycobacterium tuberculosis type VII secretion system ESX-5, which has been implicated in virulence, is activated at the transcriptional level by the phosphate starvation-responsive Pst/SenX3-RegX3 signal transduction system. Deletion of pstA1, which encodes a Pst phosphate transporter component, causes constitutive activation of the response regulator RegX3, hypersecretion of ESX-5 substrates and attenuation in the mouse infection model. We hypothesized that constitutive activation of ESX-5 secretion causes attenuation of the ΔpstA1 mutant. To test this, we uncoupled ESX-5 from regulation by RegX3. Using electrophoretic mobility shift assays, we defined a RegX3 binding site in the esx-5 locus. Deletion or mutation of the RegX3 binding site reversed hypersecretion of the ESX-5 substrate EsxN by the ΔpstA1 mutant and abrogated induction of EsxN secretion in response to phosphate limitation by wild-type M. tuberculosis The esx-5 RegX3 binding site deletion (ΔBS) also suppressed attenuation of the ΔpstA1 mutant in Irgm1-/- mice. These data suggest that constitutive ESX-5 secretion sensitizes M. tuberculosis to an immune response that still occurs in Irgm1-/- mice. However, the ΔpstA1 ΔBS mutant remained attenuated in both NOS2-/- and C57BL/6 mice, suggesting that factors other than ESX-5 secretion also contribute to attenuation of the ΔpstA1 mutant. In addition, a ΔpstA1 ΔesxN mutant lacking the hypersecreted ESX-5 substrate EsxN remained attenuated in Irgm1-/- mice, suggesting that ESX-5 substrates other than EsxN cause increased susceptibility to host immunity. Our data indicate that while M. tuberculosis requires ESX-5 for virulence, it tightly controls secretion of ESX-5 substrates to avoid elimination by host immune responses.

Active Zone Proteins RIM1αß Are Required for Normal Corticostriatal Transmission and Action Control.

Dynamic regulation of synaptic transmission at cortical inputs to the dorsal striatum is considered critical for flexible and efficient action learning and control. Presynaptic mechanisms governing the properties and plasticity of glutamate release from these inputs are not fully understood, and the corticostriatal synaptic processes that support normal action learning and control remain unclear. Here we show in male and female mice that conditional deletion of presynaptic proteins RIM1αß (RIM1) from excitatory cortical neurons impairs corticostriatal synaptic transmission in the dorsolateral striatum. Key forms of presynaptic G-protein-coupled receptor-mediated short- and long-term striatal plasticity are spared following RIM1 deletion. Conditional RIM1 KO mice show heightened novelty-induced locomotion and impaired motor learning on the accelerating rotarod. They further show heightened self-paced instrumental responding for food and impaired learning of a habitual instrumental response strategy. Together, these findings reveal a selective role for presynaptic RIM1 in neurotransmitter release at prominent basal ganglia synapses, and provide evidence that RIM1-dependent processes help to promote the refinement of skilled actions, constrain goal-directed behaviors, and support the learning and use of habits.SIGNIFICANCE STATEMENT Our daily functioning hinges on the ability to flexibly and efficiently learn and control our actions. How the brain encodes these capacities is unclear. Here we identified a selective role for presynaptic proteins RIM1αß in controlling glutamate release from cortical inputs to the dorsolateral striatum, a brain structure critical for action learning and control. Behavioral analysis of mice with restricted genetic deletion of RIM1αß further revealed roles for RIM1αß-dependent processes in the learning and refinement of motor skills and the balanced expression of goal-directed and habitual actions.

HflX protein protects Escherichia coli from manganese stress.

The ribosome-binding GTPase HflX is required for manganese homeostasis in E. coli. While under normal conditions ΔhflX cells behave like wild type E. coli with respect to growth pattern and morphology, deletion of hflX makes E. coli cells extremely sensitive to manganese, characterized by arrested cell growth and filamentation. Here we demonstrate that upon complementation by hflX, manganese stress is relieved. In phenotypic studies done in a manganese-rich environment, ΔhflX cells were highly sensitive to antibiotics that bind the penicillin binding protein 3 (PBP3), suggesting that the manganese stress led to impaired peptidoglycan biosynthesis. An irregular distribution of dark bands of constriction along filaments, delocalization of the dark bands from midcell towards poles and subpoles, lack of septum formation and arrested cell division were observed in ΔhflX cells under manganese stress. However, chromosome replication and segregation of nucleoids were unaffected under these conditions, as observed from confocal microscopy imaging and FACS studies. We conclude that absence of HflX leads to manganese accumulation in E. coli cells, affecting cell septum formation, probably by modulating the activity of the cell division protein PBP3 (FtsI), a major component of the divisome apparatus. We propose that HflX acts as a gatekeeper, regulating the influx of manganese into the cell.

DRG2 Deficiency Causes Impaired Microtubule Dynamics in HeLa Cells.

The developmentally regulated GTP binding protein 2 (DRG2) is involved in the control of cell growth and differentiation. Here, we demonstrate that DRG2 regulates microtubule dynamics in HeLa cells. Analysis of live imaging of the plus-ends of microtubules with EB1-EGFP showed that DRG2 deficiency (shDRG2) significantly reduced the growth rate of HeLa cells. Depletion of DRG2 increased 'slow and long-lived' subpopulations, but decreased 'fast and short-lived' subpopulations of microtubules. Microtubule polymerization inhibitor exhibited a reduced response in shDRG2 cells. Using immunoprecipitation, we show that DRG2 interacts with tau, which regulates microtubule polymerization. Collectively, these data demonstrate that DRG2 may aid in affecting microtubule dynamics in HeLa cells.

Detection and identification of potential transglutaminase 2 substrates in the mouse renal glomeruli.

The glomerulus primarily comprises mesangial cells, glomerular microvascular endothelial cells, and podocytes. IgA nephropathy is the most common primary glomerulonephritis worldwide and has a risk of progression to end-stage renal disease. IgA nephropathy is characterized by predominant IgA deposition in the glomerular mesangial area, where TG2 is significantly enhanced. Therefore, identification of glomerular TG2 substrates is the first step in elucidating the role of TG2 as a crosslinking enzyme during disease progression. To clarify potential glomerular TG2 substrates, and to establish a procedure for substrate identification, we attempted to identify those molecules using normal mouse glomeruli. Extracts from mouse glomerular and non-glomerular fractions were treated with our established biotin-labeled substrate peptide, which specifically crosslinks to the lysine-donor substrates depending on TG2 activity. Peptide-incorporated proteins were then purified using avidin resin and identified via mass spectrometry. In parallel, we performed the identification using corresponding samples from TG2 knockout mice. Consequently, potential TG2 substrates were separately identified in glomerular and non-glomerular fractions. They were mainly identified as novel TG2 substrates and partly include the well-known substrates. These results potentially provide novel insights into the mechanism underlying IgA nephropathy and may help elucidate the physiological functions of TG2.

Microglial transglutaminase-2 drives myelination and myelin repair via GPR56/ADGRG1 in oligodendrocyte precursor cells.

In the central nervous system (CNS), myelin formation and repair are regulated by oligodendrocyte (OL) lineage cells, which sense and integrate signals from their environment, including from other glial cells and the extracellular matrix (ECM). The signaling pathways that coordinate this complex communication, however, remain poorly understood. The adhesion G protein-coupled receptor ADGRG1 (also known as GPR56) is an evolutionarily conserved regulator of OL development in humans, mice, and zebrafish, although its activating ligand for OL lineage cells is unknown. Here, we report that microglia-derived transglutaminase-2 (TG2) signals to ADGRG1 on OL precursor cells (OPCs) in the presence of the ECM protein laminin and that TG2/laminin-dependent activation of ADGRG1 promotes OPC proliferation. Signaling by TG2/laminin to ADGRG1 on OPCs additionally improves remyelination in two murine models of demyelination. These findings identify a novel glia-to-glia signaling pathway that promotes myelin formation and repair, and suggest new strategies to enhance remyelination.