The concept of intrinsic versus extrinsic apoptosis.

Regulated cell death is a vital and dynamic process in multicellular organisms that maintains tissue homeostasis and eliminates potentially dangerous cells. Apoptosis, one of the better-known forms of regulated cell death, is activated when cell-surface death receptors like Fas are engaged by their ligands (the extrinsic pathway) or when BCL-2-family pro-apoptotic proteins cause the permeabilization of the mitochondrial outer membrane (the intrinsic pathway). Both the intrinsic and extrinsic pathways of apoptosis lead to the activation of a family of proteases, the caspases, which are responsible for the final cell demise in the so-called execution phase of apoptosis. In this review, I will first discuss the most common types of regulated cell death on a morphological basis. I will then consider in detail the molecular pathways of intrinsic and extrinsic apoptosis, discussing how they are activated in response to specific stimuli and are sometimes overlapping. In-depth knowledge of the cellular mechanisms of apoptosis is becoming more and more important not only in the field of cellular and molecular biology but also for its translational potential in several pathologies, including neurodegeneration and cancer.

Nrf2 Promotes Inflammation in Early Myocardial Ischemia-Reperfusion via Recruitment and Activation of Macrophages.

Cardiomyocyte apoptosis in response to inflammation is a primary cause of myocardial ischemia-reperfusion injury (IRI). Nuclear factor erythroid 2 like 2 (Nrf2) reportedly plays an important role in myocardial IRI, but the underlying mechanism remains obscure. Expression data from the normal heart tissues of mice or heart tissues treated with reperfusion for 6 h after ischemia (IR6h) were acquired from the GEO database; changes in biological function and infiltrating immune cells were analyzed. The binding between the molecules was verified by chromatin immunoprecipitation sequencing. Based on confirmation that early myocardial ischemia-reperfusion (myocardial ischemia/reperfusion for 6 hours, IR6h) promoted myocardial apoptosis and inflammatory response, we found that Nrf2, cooperating with Programmed Cell Death 4, promoted transcription initiation of C-C Motif Chemokine Ligand 3 (Ccl3) in myocardial tissues of mice treated with IR6h. Moreover, Ccl3 contributed to the high signature score of C-C motif chemokine receptor 1 (Ccr1)-positive macrophages. The high signature score of Ccr1-positive macrophages leads to the release of pro-inflammatory factors interleukin 1 beta and interleukin 6. This study is the first to elucidate the damaging effect of Nrf2 via remodeling of the immune microenvironment in early myocardial ischemia-reperfusion, which provides us with new perspectives and treatment strategies for myocardial ischemia-reperfusion.

Essential role of TOSO/FAIM3 in intestinal IgM reverse transcytosis.

Secretory immunoglobulin A (SIgA) can travel to and from the lumen and transport antigen to subepithelial cells. However, IgM can also multimerize into functional secretory component-bound immunoglobulin. While it is already known that both SIgA and SIgM undergo transcytosis to be secreted at the mucosal surface, only SIgA has been shown to perform retrotranscytosis through microfold cells (M cells) of the Peyer's patch. Here, we investigate whether SIgM could also be taken up by M cells via retrotranscytosis. This transport involves FcµR binding at the apical membrane of M cells. We then demonstrate that SIgM can be exploited by SIgM-p24 (HIV-capsid protein) complexes during immunization in the nasal- or gut-associated lymphoid tissue (NALT or GALT), conferring efficient immune responses against p24. Our data demonstrate a mucosal function of SIgM, which could play a role in the regulation of mucosal immunity.

Faim knockout leads to gliosis and late-onset neurodegeneration of photoreceptors in the mouse retina.

Fas Apoptotic Inhibitory Molecule protein (FAIM) is a death receptor antagonist and an apoptosis regulator. It encodes two isoforms, namely FAIM-S (short) and FAIM-L (long), both with significant neuronal functions. FAIM-S, which is ubiquitously expressed, is involved in neurite outgrowth. In contrast, FAIM-L is expressed only in neurons and it protects them from cell death. Interestingly, FAIM-L is downregulated in patients and mouse models of Alzheimer's disease before the onset of neurodegeneration, and Faim transcript levels are decreased in mouse models of retinal degeneration. However, few studies have addressed the role of FAIM in the central nervous system, yet alone the retina. The retina is a highly specialized tissue, and its degeneration has proved to precede pathological mechanisms of neurodegenerative diseases. Here we describe that Faim depletion in mice damages the retina persistently and leads to late-onset photoreceptor death in older mice. Immunohistochemical analyses showed that Faim knockout (Faim-/- ) mice present ubiquitinated aggregates throughout the retina from early ages. Moreover, retinal cells released stress signals that can signal to Müller cells, as shown by immunofluorescence and qRT-PCR. Müller cells monitor retinal homeostasis and trigger a gliotic response in Faim-/- mice that becomes pathogenic when sustained. In this regard, we observed pronounced vascular leakage at later ages, which may be caused by persistent inflammation. These results suggest that FAIM is an important player in the maintenance of retinal homeostasis, and they support the premise that FAIM is a plausible early marker for late photoreceptor and neuronal degeneration.

Programmed cell death 5 improves skeletal muscle insulin resistance by inhibiting IRS-1 ubiquitination through stabilization of MDM2.

AIMS: Insulin resistance is defined as the decreased sensitivity of tissues and organs to insulin and it is the main pathological basis of metabolic syndrome. PDCD5 is widely expressed in tissues including skeletal muscle and liver, but its exact function and the role in insulin resistance has not been studied. The present study is to explore the effect of PDCD5 on insulin resistance in skeletal muscle, the largest target organ of insulin, and its mechanism. MATERIALS AND METHODS: Mice were fed with high-fat diet to establish obesity model. C2C12 myoblasts differentiated into myotubes and then were treated with palmitate to induce insulin resistance. Gain-of-function and loss-of-function experiments were performed by infecting C2C12 with adenovirus containing PDCD5 cDNA or PDCD5 shRNA. KEY FINDINGS: PDCD5 protein was first increased and then decreased in the skeletal muscle from high-fat diet induced obese mice and consistently in palmitate induced insulin resistance C2C12 myotubes. Overexpression of PDCD5 in C2C12 cells did not affect the sensitivity to insulin but inhibited the palmitate induced insulin resistance, while knockdown of PDCD5 aggravated the insulin resistance. Mechanistically, PDCD5 interacted with ubiquitin ligase MDM2; overexpression of PDCD5 decreased MDM2 protein level, inhibited the increased interaction of MDM2 with IRS-1 and the degradation of IRS-1 by palmitate stimulation. SIGNIFICANCE: PDCD5 is upregulated during the early stage of insulin resistance in skeletal muscle. The increased PDCD5 inhibits IRS-1 ubiquitination, increases the stability of IRS-1 by interacting with and degrading MDM2, thus providing a protective effect on insulin resistance in skeletal muscle.

Loss of apoptosis repressor with caspase recruitment domain (ARC) worsens high fat diet-induced hyperglycemia in mice.

Apoptosis repressor with caspase recruitment domain (ARC) is an endogenous inhibitor of cell death signaling that is expressed in insulin-producing ß cells. ARC has been shown to reduce ß-cell death in response to diabetogenic stimuli in vitro, but its role in maintaining glucose homeostasis in vivo has not been fully established. Here we examined whether loss of ARC in FVB background mice exacerbates high fat diet (HFD)-induced hyperglycemia in vivo over 24 weeks. Prior to commencing 24-week HFD, ARC-/- mice had lower body weight than wild type (WT) mice. This body weight difference was maintained until the end of the study and was associated with decreased epididymal and inguinal adipose tissue mass in ARC-/- mice. Non-fasting plasma glucose was not different between ARC-/- and WT mice prior to HFD feeding, and ARC-/- mice displayed a greater increase in plasma glucose over the first 4 weeks of HFD. Plasma glucose remained elevated in ARC-/- mice after 16 weeks of HFD feeding, at which time it had returned to baseline in WT mice. Following 24 weeks of HFD, non-fasting plasma glucose in ARC-/- mice returned to baseline and was not different from WT mice. At this final time point, no differences were observed between genotypes in plasma glucose or insulin under fasted conditions or following intravenous glucose administration. However, HFD-fed ARC-/- mice exhibited significantly decreased ß-cell area compared to WT mice. Thus, ARC deficiency delays, but does not prevent, metabolic adaptation to HFD feeding in mice, worsening transient HFD-induced hyperglycemia.

DeSUMOylation of Apoptosis Inhibitor 5 by Avibirnavirus VP3 Supports Virus Replication.

SUMOylation is a reversible posttranslational modification involved in the regulation of diverse biological processes. Growing evidence suggests that virus infection can interfere with the SUMOylation system. In the present study, we discovered that apoptosis inhibitor 5 (API5) is a SUMOylated protein. Amino acid substitution further identified that Lys404 of API5 was the critical residue for SUMO3 conjugation. Moreover, we found that Avibirnavirus infectious bursal disease virus (IBDV) infection significantly decreased SUMOylation of API5. In addition, our results further revealed that viral protein VP3 inhibited the SUMOylation of API5 by targeting API5 and promoting UBC9 proteasome-dependent degradation through binding to the ubiquitin E3 ligase TRAF3. Furthermore, we revealed that wild-type but not K404R mutant API5 inhibited IBDV replication by enhancing MDA5-dependent IFN-ß production. Taken together, our data demonstrate that API5 is a UBC9-dependent SUMOylated protein and deSUMOylation of API5 by viral protein VP3 aids in viral replication. IMPORTANCE Apoptosis inhibitor 5 (API5) is a nuclear protein initially identified for its antiapoptotic function. However, so far, posttranslational modification of API5 is unclear. In this study, we first identified that API5 K404 can be conjugated by SUMO3, and Avibirnavirus infectious bursal disease virus (IBDV) infection significantly decreased SUMOylation of API5. Mechanically, viral protein VP3 directly interacts with API5 and inhibits SUMOylation of API5. Additionally, the cellular E3 ligase TNF receptor-associated factor 3 (TRAF3) is employed by VP3 to facilitate UBC9 proteasome-dependent degradation, leading to the reduction of API5 SUMOylation. Moreover, our data reveal that SUMOylation of API5 K404 promotes MDA5-dependent beta interferon (IFN-ß) induction, and its deSUMOylation contributes to IBDV replication. This work highlights a critical role of conversion between SUMOylation and deSUMOylation of API5 in regulating viral replication.

Murine Irgm Paralogs Regulate Nonredundant Functions To Execute Host Defense to Toxoplasma gondii.

Gamma interferon (IFN-γ)-induced immunity-related GTPases (IRGs) confer cell-autonomous immunity to the intracellular protozoan pathogen Toxoplasma gondii. Effector IRGs are loaded onto the Toxoplasma-containing parasitophorous vacuole (PV), where they recruit ubiquitin ligases, ubiquitin-binding proteins, and IFN-γ-inducible guanylate-binding proteins (Gbps), prompting PV lysis and parasite destruction. Host cells lacking the regulatory IRGs Irgm1 and Irgm3 fail to load effector IRGs, ubiquitin, and Gbps onto the PV and are consequently defective for cell-autonomous immunity to Toxoplasma. However, the role of the third regulatory IRG, Irgm2, in cell-autonomous immunity to Toxoplasma has remained unexplored. Here, we report that Irgm2 unexpectedly plays a limited role in the targeting of effector IRGs, ubiquitin, and Gbps to the Toxoplasma PV. Instead, Irgm2 is instrumental in the decoration of PVs with γ-aminobutyric acid receptor-associated protein-like 2 (GabarapL2). Cells lacking Irgm2 are as defective for cell-autonomous host defense to Toxoplasma as pan-Irgm-/- cells lacking all three Irgm proteins, and Irgm2-/- mice succumb to Toxoplasma infections as readily as pan-Irgm-/- mice. These findings demonstrate that, relative to Irgm1 and Irgm3, Irgm2 plays a distinct but critically important role in host resistance to Toxoplasma.

AKTIP interacts with ESCRT I and is needed for the recruitment of ESCRT III subunits to the midbody.

To complete mitosis, the bridge that links the two daughter cells needs to be cleaved. This step is carried out by the endosomal sorting complex required for transport (ESCRT) machinery. AKTIP, a protein discovered to be associated with telomeres and the nuclear membrane in interphase cells, shares sequence similarities with the ESCRT I component TSG101. Here we present evidence that during mitosis AKTIP is part of the ESCRT machinery at the midbody. AKTIP interacts with the ESCRT I subunit VPS28 and forms a circular supra-structure at the midbody, in close proximity with TSG101 and VPS28 and adjacent to the members of the ESCRT III module CHMP2A, CHMP4B and IST1. Mechanistically, the recruitment of AKTIP is dependent on MKLP1 and independent of CEP55. AKTIP and TSG101 are needed together for the recruitment of the ESCRT III subunit CHMP4B and in parallel for the recruitment of IST1. Alone, the reduction of AKTIP impinges on IST1 and causes multinucleation. Our data altogether reveal that AKTIP is a component of the ESCRT I module and functions in the recruitment of ESCRT III components required for abscission.

A dynamic Dab2 keeps myosin VI stably on track.

Myosins are actin-based motor proteins known to perform a variety of different mechanical tasks in cells including transporting cargo, generating tension, and linking the cytoskeleton and membrane. Myosins that function as transporters often form complexes with adaptor proteins and vesicular membranes, making it unclear how they transport their cargo through the actin cytoskeletal network. Rai et al. now use single-molecule kinetics, FRET, and DNA origami scaffolds that mimic motor-adaptor complexes to reveal that the myosin VI-Dab2 complex, which is held together weakly and turns over rapidly, can facilitate processive transport without disruption of the cytoskeleton.

Roles of Interferon Induced Protein with Tetratricopeptide Repeats (IFIT) Family in Cancer.

The Interferon-induced protein with tetratricopeptide repeats (IFIT) family is an important component of the antiviral immune response. There are currently four known IFIT family members in humans, namely IFIT1, IFIT2, IFIT3 and IFIT5. Recent discoveries have brought attention to the significant roles of IFITs in cancer. This review summarises current knowledge on the biological roles of different IFIT proteins in various types of malignant neoplasm, and highlights the potential use of these molecules as cancer biomarkers and prognostic factors.

Metformin regulates the Th17/Treg balance by glycolysis with TIGAR in hepatic ischemia-reperfusion injury.

The balance of Th17/Treg plays an important role in hepatic ischemia-reperfusion (I/R) injury. Glycolysis and glutaminolysis for energy metabolism governs the differentiate of CD 4+ T-cells to Th17/Treg. Metformin can regulate glucose metabolism in the liver, but its protective effect on I/R liver injury and its effect on Th17/Treg balancestill unknown. In this study, the I/R liver injury rat model and the primary hepatocyte hypoxia/reoxygenation injury model were established. The biochemical indexes, inflammatory factor indexes, Th17/Treg balance and energy metabolism were evaluated. RNA-seq and gene knockout cells were used to investigated the target protein of metformin. The results showed that metformin could effectively improve liver injury caused by I/R, significantly inhibit the glycolysis, improve the Th17/Treg balance, and inhibit the expression of inflammatory factors. RNA-seq results showed that TIGAR was a possible regulatory site of metformin. However, the protective effect and the regulating effect of Th17/Treg balance by metformin in TIGAR knock-out cells were disappeared. In conclusion, metformin could regulate TIGAR inhibit glycolysis then regulate Th17/Treg balance, inhibit the release of liver inflammatory factors, and finally play a role in inhibiting the occurrence of liver injury caused by ischemia-reperfusion.

Intact TP-53 function is essential for sustaining durable responses to BH3-mimetic drugs in leukemias.

Selective targeting of BCL-2 with the BH3-mimetic venetoclax has been a transformative treatment for patients with various leukemias. TP-53 controls apoptosis upstream of where BCL-2 and its prosurvival relatives, such as MCL-1, act. Therefore, targeting these prosurvival proteins could trigger apoptosis across diverse blood cancers, irrespective of TP53 mutation status. Indeed, targeting BCL-2 has produced clinically relevant responses in blood cancers with aberrant TP-53. However, in our study, TP53-mutated or -deficient myeloid and lymphoid leukemias outcompeted isogenic controls with intact TP-53, unless sufficient concentrations of BH3-mimetics targeting BCL-2 or MCL-1 were applied. Strikingly, tumor cells with TP-53 dysfunction escaped and thrived over time if inhibition of BCL-2 or MCL-1 was sublethal, in part because of an increased threshold for BAX/BAK activation in these cells. Our study revealed the key role of TP-53 in shaping long-term responses to BH3-mimetic drugs and reconciled the disparate pattern of initial clinical response to venetoclax, followed by subsequent treatment failure among patients with TP53-mutant chronic lymphocytic leukemia or acute myeloid leukemia. In contrast to BH3-mimetics targeting just BCL-2 or MCL-1 at doses that are individually sublethal, a combined BH3-mimetic approach targeting both prosurvival proteins enhanced lethality and durably suppressed the leukemia burden, regardless of TP53 mutation status. Our findings highlight the importance of using sufficiently lethal treatment strategies to maximize outcomes of patients with TP53-mutant disease. In addition, our findings caution against use of sublethal BH3-mimetic drug regimens that may enhance the risk of disease progression driven by emergent TP53-mutant clones.

The BAX-binding protein MOAP1 associates with LC3 and promotes closure of the phagophore.

MOAP1 (modulator of apoptosis 1) is a BAX-binding protein tightly regulated by the ubiquitin-proteasome system. Apoptotic stimuli stabilize MOAP1 protein and facilitate its interaction with BAX to promote apoptosis. Here we show that in contrast to being resistant to apoptotic stimuli, MOAP1-deficient cells are hypersensitive to cell death mediated by starvation rendered by EBSS treatment. MOAP1-deficient cells exhibited impairment in macroautophagy/autophagy signaling induced by EBSS. Mechanistic analysis revealed that MOAP1-deficient cells had no notable defect in the recruitment of the pre-autophagosomal phosphatidylinositol-3-phosphate (PtdIns3P)-binding proteins, ZFYVE1/DFCP1 and WIPI2, nor in the LC3 lipidation mechanism regulated by the ATG12-ATG5-ATG16L1 complex upon EBSS treatment. Interestingly, MOAP1 is required for facilitating efficient closure of phagophore in the EBSS-treated cells. Analysis of LC3-positive membrane structures using Halo-tagged LC3 autophagosome completion assay showed that predominantly unclosed phagophore rather than closed autophagosome was present in the EBSS-treated MOAP1-deficient cells. The autophagy substrate SQSTM1/p62, which is normally contained within the enclosed autophagosome under EBSS condition, was also highly sensitive to degradation by proteinase K in the absence of MOAP1. MOAP1 binds LC3 and the binding is critically dependent on a LC3-interacting region (LIR) motif detected at its N-terminal region. Re-expression of MOAP1, but not its LC3-binding defective mutant, MOAP1-LIR, in the MOAP1-deficient cells, restored EBSS-induced autophagy. Together, these observations suggest that MOAP1 serves a distinct role in facilitating autophagy through interacting with LC3 to promote efficient phagophore closure during starvation.Abbreviations: CQ: Chloroquine; EBSS: Earle's Balanced Salt Solution; GABARAP: Gamma-Amino Butyric Acid Receptor Associated Protein; IF: Immunofluorescence; IP: Immunoprecipitation; LAMP1: Lysosomal-Associated Membrane Protein 1; LIR: LC3-Interacting Region; MAP1LC3/LC3: Microtubule Associated Protein 1 Light Chain 3; MEF: Mouse Embryonic Fibroblast; MOAP1: Modulator of Apoptosis 1; PE: Phosphatidylethanolamine; PtdIns3K: class III PtdIns3K complex I; PtdIns3P: Phosphatidylinositol-3-phosphate; STX17: Syntaxin 17; ULK1: unc-51 like autophagy activating kinase 1.

Conversion of the death inhibitor ARC to a killer activates pancreatic ß cell death in diabetes.

Loss of insulin-secreting pancreatic ß cells through apoptosis contributes to the progression of type 2 diabetes, but underlying mechanisms remain elusive. Here, we identify a pathway in which the cell death inhibitor ARC paradoxically becomes a killer during diabetes. While cytoplasmic ARC maintains ß cell viability and pancreatic architecture, a pool of ARC relocates to the nucleus to induce ß cell apoptosis in humans with diabetes and several pathophysiologically distinct mouse models. ß cell death results through the coordinate downregulation of serpins (serine protease inhibitors) not previously known to be synthesized and secreted by ß cells. Loss of the serpin α1-antitrypsin from the extracellular space unleashes elastase, triggering the disruption of ß cell anchorage and subsequent cell death. Administration of α1-antitrypsin to mice with diabetes prevents ß cell death and metabolic abnormalities. These data uncover a pathway for ß cell loss in type 2 diabetes and identify an FDA-approved drug that may impede progression of this syndrome.

GABARAP suppresses EMT and breast cancer progression via the AKT/mTOR signaling pathway.

Few studies have focused on γ-aminobutyric acid type A (GABAA) receptor-associated protein (GABARAP) in tumor progression. We investigated the expression and importance of GABARAP in breast cancer. We analyzed the expression of GABARAP and its relationship with clinicopathological features and prognosis (TCGA). To explain the role and potential mechanism of GABARAP in regulating tumor development, we performed acquisition and loss of function experiments using cell lines and models of mouse xenotransplantation. We found that GABARAP inhibited proliferation, migration and invasion in vitro and in vivo. Notably, low levels of GABARAP induced the epithelial-mesenchymal transition (EMT). Low levels of GABARAP increased p-AKT and p-mTOR levels, and a specific AKT pathway inhibitor reversed the downregulation of GABARAP-induced tumor progression. GABARAP negatively correlated with advanced clinicopathological features in clinical specimens, such as tumor size and TNM stage. Notably, patients with low GABARAP levels had a poor prognosis. Immunohistochemistry (IHC) revealed that GABARAP expression negatively correlated with matrix metalloproteinase (MMP) 2 and MMP14. Conclusively, these data indicate that GABARAP suppresses the malignant behaviors of breast cancer likely via the AKT/mTOR pathway. The targeting of GABARAP may improve the certainty of diagnosis and treatment strategies for breast cancer.

Different roles of BAG3 in cardiac physiological hypertrophy and pathological remodeling.

Heart failure is one of the leading causes of death worldwide. A stimulated heart undergoes either adaptive physiological hypertrophy, which can maintain a normal heart function, or maladaptive pathological remodeling, which can deteriorate heart function. These 2 kinds of remodeling often co-occur at the early stages of many heart diseases and have important effects on cardiac function. The Bcl2-associated athanogene 3 (BAG3) protein is highly expressed in the heart and has many functions. However, it is unknown how BAG3 is regulated and what its function is during physiological hypertrophy and pathological remodeling. We generated tamoxifen-induced, heart-specific heterozygous and homozygous BAG3 knockout mouse models (BAG3 protein level decreased by approximately 40% and 80% in the hearts after tamoxifen administration). BAG3 knockout models were subjected to swimming training or phenylephrine (PE) infusion to induce cardiac physiological hypertrophy and pathological remodeling. Neonatal rat ventricular cardiomyocytes (NRVCs) were used to study BAG3 functions and mechanisms in vitro. We found that BAG3 was upregulated in physiological hypertrophy and in pathological remodeling both in vivo and in vitro. Heterozygous or homozygous knockout BAG3 in mouse hearts and knockdown of BAG3 in the NRVCs blunted physiological hypertrophy and aggravated pathological remodeling, while overexpression of BAG3 promoted physiological hypertrophy and inhibited pathological remodeling in NRVCs. Mechanistically, BAG3 overexpression in NRVCs promoted physiological hypertrophy by activating the protein kinase B (AKT)/mammalian (or mechanistic) target of rapamycin (mTOR) pathway. BAG3 knockdown in NRVCs aggravated pathological remodeling through activation of the calcineurin/nuclear factor of activated T cells 2 (NFATc2) pathway. Because BAG3 has a dual role in cardiac remodeling, heart-specific regulation of BAG3 may be an effective therapeutic strategy to protect against deterioration of heart function and heart failure caused by many heart diseases.

KLF11 protects against abdominal aortic aneurysm through inhibition of endothelial cell dysfunction.

Abdominal aortic aneurysm (AAA) is a life-threatening degenerative vascular disease. Endothelial cell (EC) dysfunction is implicated in AAA. Our group recently demonstrated that Krüppel-like factor 11 (KLF11) plays an essential role in maintaining vascular homeostasis, at least partially through inhibition of EC inflammatory activation. However, the functions of endothelial KLF11 in AAA remain unknown. Here we found that endothelial KLF11 expression was reduced in the ECs from human aneurysms and was time dependently decreased in the aneurysmal endothelium from both elastase- and Pcsk9/AngII-induced AAA mouse models. KLF11 deficiency in ECs markedly aggravated AAA formation, whereas EC-selective KLF11 overexpression markedly inhibited AAA formation. Mechanistically, KLF11 not only inhibited the EC inflammatory response but also diminished MMP9 expression and activity and reduced NADPH oxidase 2-mediated production of reactive oxygen species in ECs. In addition, KLF11-deficient ECs induced smooth muscle cell dedifferentiation and apoptosis. Overall, we established endothelial KLF11 as a potentially novel factor protecting against AAA and a potential target for intervention in aortic aneurysms.

Structure, regulation, and biological functions of TIGAR and its role in diseases.

TIGAR (TP53-induced glycolysis and apoptosis regulator) is the downstream target gene of p53, contains a functional sequence similar to 6-phosphofructose kinase/fructose-2, 6-bisphosphatase (PFKFB) bisphosphatase domain. TIGAR is mainly located in the cytoplasm; in response to stress, TIGAR is translocated to nucleus and organelles, including mitochondria and endoplasmic reticulum to regulate cell function. P53 family members (p53, p63, and p73), some transcription factors (SP1 and CREB), and noncoding miRNAs (miR-144, miR-885-5p, and miR-101) regulate the transcription of TIGAR. TIGAR mainly functions as fructose-2,6-bisphosphatase to hydrolyze fructose-1,6-diphosphate and fructose-2,6-diphosphate to inhibit glycolysis. TIGAR in turn facilitates pentose phosphate pathway flux to produce nicotinamide adenine dinucleotide phosphate (NADPH) and ribose, thereby promoting DNA repair, and reducing intracellular reactive oxygen species. TIGAR thus maintains energy metabolism balance, regulates autophagy and stem cell differentiation, and promotes cell survival. Meanwhile, TIGAR also has a nonenzymatic function and can interact with retinoblastoma protein, protein kinase B, nuclear factor-kappa B, hexokinase 2, and ATP5A1 to mediate cell cycle arrest, inflammatory response, and mitochondrial protection. TIGAR might be a potential target for the prevention and treatment of cardiovascular and neurological diseases, as well as cancers.

Involvement of the NLRC4 inflammasome in promoting retinal ganglion cell death in an acute glaucoma mouse model.

PURPOSE: To explore the role of nucleotide-binding oligomerization domain-like receptors (NLRs) family caspase-activation and the recruitment domain containing 4 (NLRC4) inflammasome in retinal ganglion cell (RGC) injury induced by an acute glaucoma mouse model. METHOD: A mouse model of acute ocular hypertension, which can lead to retinal ischemia-reperfusion (I/R) injury, was established. The expression level of NLRC4 was detected by polymerase chain reaction and western blotting. Localized expression of NLRC4 was detected by examining immunofluorescence in eyeball sections. Intravitreal adeno-associated virus 2(AAV2) administration was used to knockdown retinal Nlrc4. Fluoro-Gold labeled RGCs and TdT-mediated dUTP nick end labeling were used to evaluate the survival and apoptosis of RGCs. Tlr4-/- mice were utilized to explore whether NLRC4 inflammasome is influenced by Toll-like receptor4 (TLR4). RESULTS: NLRC4, expressed in RGCs and microglial cells, was actively involved in mouse retinal I/R injury. Knockdown of Nlrc4 using an AAV2 vector caused an obvious reduction in the generation of IL-1ß led by the rapidly elevated intraocular pressure, and thereby improved the RGC survival. In addition, activation of the NLRC4 inflammasome could influence the phosphorylation of p38 and Jun N-terminal kinase, which was largely dependent on TLR4 signaling. CONCLUSION: Our study demonstrated the role of NLRC4 inflammasome in promoting RGC damage in mouse retinal I/R injury. Inhibition of NLRC4 might be leveraged as a potential therapeutic target in glaucomatous retinopathy.