Transglutaminase 2 Prevents Premature Senescence and Promotes Osteoblastic Differentiation of Mesenchymal Stem Cells through NRF2 Activation.

Transglutaminase 2 (TG2) is a multifunctional enzyme that exhibits transamidase, GTPase, kinase, and protein disulfide isomerase (PDI) activities. Of these, transamidase-mediated modification of proteins regulates apoptosis, differentiation, inflammation, and fibrosis. TG2 is highly expressed in mesenchymal stem cells (MSCs) compared with differentiated cells, suggesting a role of TG2 specific for MSC characteristics. In this study, we report a new function of TG2 in the regulation of MSC redox homeostasis. During in vitro MSC expansion, TG2 is required for cell proliferation and self-renewal by preventing premature senescence but has no effect on the expression of surface antigens and oxidative stress-induced cell death. Moreover, induction of differentiation upregulates TG2 that promotes osteoblastic differentiation. Molecular analyses revealed that TG2 mediates tert-butylhydroquinone, but not sulforaphane, -induced nuclear factor erythroid 2-related factor 2 (NRF2) activation in a transamidase activity-independent manner. Differences in the mechanism of action between two NRF2 activators suggest that PDI activity of TG2 may be implicated in the stabilization of NRF2. The role of TG2 in the regulation of antioxidant response was further supported by transcriptomic analysis of MSC. These results indicate that TG2 is a critical enzyme in eliciting antioxidant response in MSC through NRF2 activation, providing a target for optimizing MSC manufacturing processes to prevent premature senescence.

Double-Stranded RNA Enhances Matrix Metalloproteinase-1 and -13 Expressions through TLR3-Dependent Activation of Transglutaminase 2 in Dermal Fibroblasts.

UV-irradiation induces the secretion of double-stranded RNA (dsRNA) derived from damaged noncoding RNAs in keratinocytes, which enhance the expression of matrix metalloproteinases (MMP) in non-irradiated dermal fibroblasts, leading to dysregulation of extracellular matrix homeostasis. However, the signaling pathway responsible for dsRNA-induced MMP expression has not been fully understood. Transglutaminase 2 (TG2) is an enzyme that modifies substrate proteins by incorporating polyamine or crosslinking of proteins, thereby regulating their functions. In this study, we showed that TG2 mediates dsRNA-induced MMP-1 expression through NF-κB activation. Treatment of poly(I:C), a synthetic dsRNA analogue binding to toll-like receptor 3 (TLR3), generates ROS, which in turn activates TG2 in dermal fibroblast. Subsequently, TG2 activity enhances translocation of p65 into the nucleus, where it augments transcription of MMP. We confirmed these results by assessing the level of MMP expression in Tlr3-/-, TG2-knockdowned and Tgm2-/- dermal fibroblasts after poly(I:C)-treatment. Moreover, treatment with quercetin showed dose-dependent suppression of poly(I:C)-induced MMP expression. Furthermore, ex vivo cultured skin from Tgm2-/- mice exhibited a significantly reduced level of MMP mRNA compared with those from wild-type mice. Our results indicate that TG2 is a critical regulator in dsRNA-induced MMP expression, providing a new target and molecular basis for antioxidant therapy in preventing collagen degradation.

Transglutaminase 2 crosslinks the glutathione S-transferase tag, impeding protein-protein interactions of the fused protein.

Glutathione S-transferase (GST) from Schistosoma japonicum has been widely used as a tag for affinity purification and pulldown of fusion proteins to detect protein-protein interactions. However, the reliability of this technique is undermined by the formation of GST-fused protein aggregates after incubation with cell lysates. It remains unknown why this aggregation occurs. Here, we demonstrate that the GST tag is a substrate of transglutaminase 2 (TG2), which is a calcium-dependent enzyme that polyaminates or crosslinks substrate proteins. Mutation analysis identified four glutamine residues in the GST tag as polyamination sites. TG2-mediated modification of the GST tag caused aggregate formation but did not affect its glutathione binding affinity. When incubated with cell lysates, GST tag aggregation was dependent on cellular TG2 expression levels. A GST mutant in which four glutamine residues were replaced with asparagine (GST4QN) exhibited a glutathione binding affinity similar to that of wild-type GST and could be purified by glutathione affinity chromatography. Moreover, the use of GST4QN as a tag reduced fused p53 aggregation and enhanced the induction of p21 transcription and apoptosis in cells treated with 5-fluorouracil (5-FU). These results indicated that TG2 interferes with the protein-protein interactions of GST-fused proteins by crosslinking the GST tag; therefore, a GST4QN tag could improve the reproducibility and reliability of GST pulldown experiments.

An Effective Method to Reduce Residual Lithium on LiNi0.8Co0.1Mn0.1O2 Cathode Material Using a Reducing Agent.

Among the various cathode materials used in LIBs (Lithium ion batteries), nickel rich cathode materials have attracted an increasing amount of interest due to their high capacity, relatively low cost, and low toxicity when compared to LiCoO2. However, these materials always contain a large amount of residual lithium compounds such as LiOH and Li2CO3. The presence of lithium residues is undesirable because the oxidation of these compounds results in the formation of Li2O and CO2 gas at higher voltages, which lowers the coulombic efficiency between the charge and discharge capacities during cycling. In this study, using LiNi0.8Co0.1Mn0.1O2 as a starting material, a surface-modified cathode material was obtained by using reducing agent. The reducing agent not only plays the role of reducing the oxide conversion energy but also suppresses the side reaction with the electrolyte due to the surface modification. Residual lithium present on the cathode material surface was reduced from 11,702 ppm to 8,658 ppm, resulting in improved high temperature cycle performance and impedance characteristics.

Glutathione dynamics determine the therapeutic efficacy of mesenchymal stem cells for graft-versus-host disease via CREB1-NRF2 pathway.

Glutathione (GSH), the most abundant nonprotein thiol functioning as an antioxidant, plays critical roles in maintaining the core functions of mesenchymal stem cells (MSCs), which are used as a cellular immunotherapy for graft-versus-host disease (GVHD). However, the role of GSH dynamics in MSCs remains elusive. Genome-wide gene expression profiling and high-throughput live-cell imaging assays revealed that CREB1 enforced the GSH-recovering capacity (GRC) of MSCs through NRF2 by directly up-regulating NRF2 target genes responsible for GSH synthesis and redox cycling. MSCs with enhanced GSH levels and GRC mediated by CREB1-NRF2 have improved self-renewal, migratory, anti-inflammatory, and T cell suppression capacities. Administration of MSCs overexpressing CREB1-NRF2 target genes alleviated GVHD in a humanized mouse model, resulting in improved survival, decreased weight loss, and reduced histopathologic damages in GVHD target organs. Collectively, these findings demonstrate the molecular and functional importance of the CREB1-NRF2 pathway in maintaining MSC GSH dynamics, determining therapeutic outcomes for GVHD treatment.

Keratinocyte transglutaminase 2 promotes CCR6+ γδT-cell recruitment by upregulating CCL20 in psoriatic inflammation.

Keratinocyte-derived cytokines and chemokines amplify psoriatic inflammation by recruiting IL-17-producing CCR6+ γδT-cells and neutrophils. The expression of these cytokines and chemokines mainly depends on NF-κB activity; however, the pathway that activates NF-κB in response to triggering factors is poorly defined. Here, we show that transglutaminase 2 (TG2), previously reported to elicit a TH17 response by increasing IL-6 expression in a mouse model of lung fibrosis, mediates the upregulation of cytokines and chemokines by activating NF-κB in imiquimod (IMQ)-treated keratinocytes. TG2-deficient mice exhibited reduced psoriatic inflammation in skin treated with IMQ but showed systemic immune responses similar to wild-type mice. Experiments in bone marrow (BM) chimeric mice revealed that TG2 is responsible for promoting psoriatic inflammation in non-BM-derived cells. In keratinocytes, IMQ treatment activated TG2, which in turn activated NF-κB signaling, leading to the upregulation of IL-6, CCL20, and CXCL8 and increased leukocyte migration, in vitro. Consequently, TG2-deficient mice showed markedly decreased CCR6+ γδT-cell and neutrophil infiltration in IMQ-treated skin. Moreover, TG2 levels were higher in psoriatic skin than in normal skin and correlated with IL-6, CXCL8, and CCL20 levels. Therefore, these results indicate that keratinocyte TG2 acts as a critical mediator in the amplification of psoriatic inflammation.

Transglutaminase 2 mediates hypoxia-induced selective mRNA translation via polyamination of 4EBPs.

Hypoxia selectively enhances mRNA translation despite suppressed mammalian target of rapamycin complex 1 activity, contributing to gene expression reprogramming that promotes metastasis and survival of cancer cells. Little is known about how this paradoxical control of translation occurs. Here, we report a new pathway that links hypoxia to selective mRNA translation. Transglutaminase 2 (TG2) is a hypoxia-inducible factor 1-inducible enzyme that alters the activity of substrate proteins by polyamination or crosslinking. Under hypoxic conditions, TG2 polyaminated eukaryotic translation initiation factor 4E (eIF4E)-bound eukaryotic translation initiation factor 4E-binding proteins (4EBPs) at conserved glutamine residues. 4EBP1 polyamination enhances binding affinity for Raptor, thereby increasing phosphorylation of 4EBP1 and cap-dependent translation. Proteomic analyses of newly synthesized proteins in hypoxic cells revealed that TG2 activity preferentially enhanced the translation of a subset of mRNA containing G/C-rich 5'UTRs but not upstream ORF or terminal oligopyrimidine motifs. These results indicate that TG2 is a critical regulator in hypoxia-induced selective mRNA translation and provide a promising molecular target for the treatment of cancers.

Competitive Binding of Magnesium to Calcium Binding Sites Reciprocally Regulates Transamidase and GTP Hydrolysis Activity of Transglutaminase 2.

Transglutaminase 2 (TG2) is a Ca2+-dependent enzyme, which regulates various cellular processes by catalyzing protein crosslinking or polyamination. Intracellular TG2 is activated and inhibited by Ca2+ and GTP binding, respectively. Although aberrant TG2 activation has been implicated in the pathogenesis of diverse diseases, including cancer and degenerative and fibrotic diseases, the structural basis for the regulation of TG2 by Ca2+ and GTP binding is not fully understood. Here, we produced and analyzed a Ca2+-containing TG2 crystal, and identified two glutamate residues, E437 and E539, as Ca2+-binding sites. The enzymatic analysis of the mutants revealed that Ca2+ binding to these sites is required for the transamidase activity of TG2. Interestingly, we found that magnesium (Mg2+) competitively binds to the E437 and E539 residues. The Mg2+ binding to these allosteric sites enhances the GTP binding/hydrolysis activity but inhibits transamidase activity. Furthermore, HEK293 cells transfected with mutant TG2 exhibited higher transamidase activity than cells with wild-type TG2. Cells with wild-type TG2 showed an increase in transamidase activity under Mg2+-depleted conditions, whereas cells with mutant TG2 were unaffected. These results indicate that E437 and E539 are Ca2+-binding sites contributing to the reciprocal regulation of transamidase and GTP binding/hydrolysis activities of TG2 through competitive Mg2+ binding.

Novel Composition of Co-Free LiNi0.875-xMn0.125AlxO2 Cathode Materials.

Ni-rich LiNi1-xMnxO2 cathode materials have attracted widespread interest as promising alternative cathode materials owing to their higher capacity, lower cost, and lower toxicity compared to those of LiCoO2. Therefore, we designed herein a LiNi0.875Mn0.125O2 positive electrode material. However, as the Ni content increases, the materials suffer from an extensive phase transition during the de-lithiation process owing to the low-bond strength of Ni (391.6 kJ mol-1) and Mn (402 kJ mol-1). In this study, Al-doped LiNi0.875-xMn0.125AlxO2 (x= 0, 0.05, 0.1) was synthesized using the coprecipitation method. Al had a higher bond strength (512 kJ mol-1) between oxygen and metal ions compared to that of Ni and Mn ions. Additionally, Al is usually stabilized in the form of Al3+. Therefore, the increased bond strength decreased the electrostatic repulsion with oxygen during the de-lithiation process and prevented cation mixing by stabilizing the Ni ion's valence, thereby resulting in increased structural stability. X-ray diffraction (XRD) was used to characterize their structures and calculate the cation mixing value. The electrochemical properties showed that LiNi0.775Mn0.125Al0.1O2 exhibited the high capacity retention of 97.1% after 30 cycles at 1 C at 55 °C.

Effect of PEDOT:PSS (Poly(3,4-ethylenedioxythiophene)-polystyrenesulfonate) Coating on Nanostructured Cobalt-Free LiNi0.9Mn0.1O2 Layered Oxide Cathode Materials for Lithium-Ion Battery.

Among cobalt-free layered oxides, Li(Ni1-xMnx)O2 (x ≤0.5) (LNMO) shows high reversible capacity, good cycling performance and thermal stability, and has relatively low cost and toxicity due to the absence of cobalt. In this study, we synthesized LNMO cathode materials having a porous fiber shape with primary particles that had an average diameter of about 328 nm. The prepared LNMO has an increased surface area, on which side reactions between the electrolyte and cathode material occur. Therefore, we coated the conductive polymer PEDOT:PSS to solve the problems that may arise. The coated LNMO exhibited a reversible capacity of 128.03 mAh g-1, and 87.1% capacity retention, at a current density of 0.1 C, for up to 30 cycles. It showed a better performance than uncoated LNMO. The process used in this study can be proposed as a new synthesis method for cobalt-free layered oxide materials.

Monitoring Glutathione Dynamics and Heterogeneity in Living Stem Cells.

Glutathione (GSH) is a major antioxidant in cells, and plays vital roles in the cellular defense against oxidants and in the regulation of redox signals. In a previous report, we demonstrated that stem cell function is critically affected by heterogeneity and dynamic changes in cellular GSH concentration. Here, we present a detailed protocol for the monitoring of GSH concentration in living stem cells using FreSHtracer, a real-time GSH probe. We describe the steps involved in monitoring GSH concentration in single living stem cells using confocal microscopy and flow cytometry. These methods are simple, rapid, and quantitative, and able to demonstrate intracellular GSH concentration changes in real time. We also describe the application of FreSHtracer to the sorting of stem cells according to their GSH content using flow cytometry. Typically, microscopic or flow cytometric analyses of FreSHtracer and MitoFreSHtracer signals in living stem cells take ~2~3 h, and the fractionation of stem cells into subpopulations on the basis of cellular GSH levels takes 3~4.5 h. This method could be applied to almost every kind of mammalian cell with minor modifications to the protocol described here.

Novel Core-Shell-Type Design of Na0.5[Li0.5(Ni0.8Co0.1Mn0.1)1-x(Ni0.5 Co0.1Mn0.4)x]O2 Cathode Material for Sodium-Ion Batteries.

High-nickel cathode materials possess several disadvantages such as poor cycle performance and thermal instability resulting from the side reaction with the electrolyte that occurs during cycling. In order to improve the cycle performance and thermal stability of the Na0.5[Li0.5(Ni0.8Co0.1Mn0.1)]O2 (core), we synthesized the core-shell structure of Na0.5[Li0.5(Ni0.8Co0.1Mn0.1)1-x(Ni0.5Co0.1Mn0.4)x]O2. The results of energy-dispersive X-ray spectroscopy (EDS) line analysis showed that the core of the high-nickel NCM precursor and the shell of the low-nickel NCM precursor were successfully synthesized as two phases. The core-shell cathode material shows a small capacity loss after 30 cycles (capacity retention=60.78%) compared with the core cathode material (capacity retention = 48.57%). The results of differential scanning calorimetry (DSC) show that the 4.6 V charged core-shell cathode material has a large exothermic peak at 297.4 °C, and the low reaction releases 246.1 J·g-1 of heat. The core-shell cathode material shows improved electrochemical performance and is a thermally stable material for use as a cathode material for sodium-ion batteries.

Real-Time Monitoring of Glutathione in Living Cells Reveals that High Glutathione Levels Are Required to Maintain Stem Cell Function.

The core functions of stem cells (SCs) are critically regulated by their cellular redox status. Glutathione is the most abundant non-protein thiol functioning as an antioxidant and a redox regulator. However, an investigation into the relationship between glutathione-mediated redox capacity and SC activities is hindered by lack of probe. Here, we demonstrate that cyanoacrylamide-based coumarin derivatives are ratiometric probes suitable for the real-time monitoring of glutathione levels in living SCs. These probes revealed that glutathione levels are heterogeneous among subcellular organelles and among individual cells and show dynamic changes and heterogeneity in repopulating SCs depending on oxidative stress or culture conditions. Importantly, a subpopulation of SCs with high glutathione levels exhibited increased stemness and migration activities in vitro and showed improved therapeutic efficiency in treating asthma. Our results indicate that high glutathione levels are required for maintaining SC functions, and monitoring glutathione dynamics and heterogeneity can advance our understanding of the cellular responses to oxidative stress.

Inhibition of erythropoiesis by Smad6 in human cord blood hematopoietic stem cells.

Bone morphogenetic proteins (BMPs) that belong to the transforming growth factor-ß (TGF-ß) superfamily cytokines, play crucial roles in hematopoiesis. However, roles of Smad6 in hematopoiesis remained unknown in contrast to the other inhibitory Smad (I-Smad), Smad7. Here we show that Smad6 inhibits erythropoiesis in human CD34(+) cord blood hematopoietic stem cells (HSCs). Smad6 was specifically expressed in CD34(+) cord blood HSCs, which was correlated with the expression of BMP2/4/6/7 and BMP type I receptor (BMPRI). BMP-specific receptor-regulated Smads (R-Smads), Smad1 and Smad5 in cooperation with Smad4 induced transcription of the Smad6 gene. Instead of affecting cell cycle, apoptosis, self-renewal, and stemness of CD34(+) cells, Smad6 knockdown enhanced, whereas Smad6 overexpression suppressed erythropoiesis in stem cell culture and colony formation assay. Consistently, Smad6 suppressed the expression of the genes essential for erythropoiesis, such as Kruppel-like factor 1 (erythroid) (KLF1/EKLF) and GATA binding protein 2 (GATA-2). Promoter analyses showed that Smad6 repressed Smad5/4-induced transcription of the Klf1 gene. Thus, our data suggest that Smad6 indirectly maintains stemness by preventing spontaneous erythropoiesis in HSCs.

Combined effects of hematopoietic progenitor cell mobilization from bone marrow by granulocyte colony stimulating factor and AMD3100 and chemotaxis into the brain using stromal cell-derived factor-1α in an Alzheimer's disease mouse model.

Transplantation of bone marrow-derived stem cells (BMSCs) has been suggested as a potential therapeutic approach to prevent neurodegenerative diseases, but it remains problematic due to issues of engraftment, potential toxicities, and other factors. An alternative strategy is pharmacological-induced recruitment of endogenous BMSCs into an injured site by systemic administration of growth factors or chemokines. Therefore, the aim of this study was to examine the effects of therapy involving granulocyte colony stimulating factor (G-CSF)/AMD3100 (CXCR4 antagonist) and stromal cell-derived factor-1α (SDF-1α) on endogenous BM-derived hematopoietic progenitor cell (BM-HPC) recruitment into the brain of an Alzheimer's disease (AD) mouse model. To mobilize BM-HPCs, G-CSF was injected intraperitoneally and boosted by AMD3100. Simultaneously, these mice received an intracerebral injection with SDF-1α to induce migration of mobilized BM-HPCs into brain. We found that the memory deficit in the AD mice was significantly improved by these treatments, but amyloid ß deposition was unchanged. Interestingly, microglial activation was increased with alternative activation of microglia to a neuroprotective phenotype. Furthermore, by generating an amyloid precursor protein/presenilin 1-green fluorescent protein (GFP) chimeric mouse, we ascertained that the GFP positive microglia identified in the brain were BM-derived. Additionally, increased hippocampal neurogenesis and improved memory was observed in mice receiving combined G-CSF/AMD3100 and SDF-1α, but not in controls or animals receiving each treatment alone. These results suggest that SDF-1α is an effective adjuvant in inducing migration into brain of the endogenous BM-HPCs, mobilized by G-CSF/AMD3100, and that the two can act synergistically to produce a therapeutic effect. This approach warrants further investigation as a potential therapeutic option for the treatment of AD patients in the future.

The therapeutic potential of human umbilical cord blood-derived mesenchymal stem cells in Alzheimer's disease.

The neuropathological hallmarks of Alzheimer's disease (AD) include the presence of extracellular amyloid-beta peptide (Abeta) in the form of amyloid plaques in the brain parenchyma and neuronal loss. The mechanism associated with neuronal death by amyloid plaques is unclear but oxidative stress and glial activation has been implicated. Human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) are being scrutinized as a potential therapeutic tool to prevent various neurodegenerative diseases including AD. However, the therapeutic impact of hUCB-MSCs in AD has not yet been reported. Here we undertook in vitro work to examine the potential impact of hUCB-MSCs treatment on neuronal loss using a paradigm of cultured hippocampal neurons treated with Abeta. We confirmed that hUCB-MSCs co-culture reduced the hippocampal apoptosis induced by Abeta treatment. Moreover, in an acute AD mouse model to directly test the efficacy of hUCB-MSCs treatment on AD-related cognitive and neuropathological outcomes, we demonstrated that markers of glial activation, oxidative stress and apoptosis levels were decreased in AD mouse brain. Interestingly, hUCB-MSCs treated AD mice demonstrated cognitive rescue with restoration of learning/memory function. These data suggest that hUCB-MSCs warrant further investigation as a potential therapeutic agent in AD.