A Comparative Analysis of the Membrane Binding and Remodeling Properties of Two Related Sorting Nexin Complexes Involved in Autophagy.

The sorting nexin (SNX) proteins, Atg20 and Atg24, are involved in nonselective autophagy, are necessary for efficient selective autophagy, and are required for the cytoplasm-to-vacuole transport pathway. However, the specific roles of these proteins in autophagy are not well understood. Atg20 and Atg24 each contain a Phox homology domain that facilitates phosphoinositide binding. They also each contain an SNX-Bin/Amphiphysin/Rvs domain that forms a cup-shaped dimer, capable of binding to curved membranes and remodeling those membranes in some cases. Atg20 and Atg24 form two distinct complexes, an Atg24/Atg24 homodimer and an Atg20/Atg24 heterodimer. Despite the presence of Atg24 in both complexes, it is currently unclear if these complexes have different membrane binding and remodeling properties. Therefore, in this study, we explored the membrane binding and shaping properties of these two dimeric complexes. We found that Atg24/Atg24 and Atg20/Atg24 have distinct membrane binding preferences. Both dimers recognized membranes containing phosphatidylinositol 3-phosphate [PI(3)P] and phosphatidylinositol 3,5-bisphosphate, but Atg20/Atg24 bound to a broader array of liposomes, including those lacking phosphorylated phosphatidylinositol. In addition, we discovered that while both complexes bound to autophagosomal-like liposomes containing at least 5% PI(3)P, Atg20/Atg24 was capable of binding to autophagosomal-like liposomes lacking PI(3)P. Lastly, we observed that the Atg20/Atg24 heterodimer tubulates PI(3)P-containing and autophagosomal-like liposomes, but the Atg24/Atg24 homodimer could not tubulate these liposomes. Our findings suggest that these two dimers contain distinct membrane binding and shaping properties.

A highly conserved glutamic acid in ALFY inhibits membrane binding to aid in aggregate clearance.

Autophagy-linked FYVE protein (ALFY) is a large, multidomain protein involved in the degradation of protein aggregates by selective autophagy. The C-terminal FYVE domain of ALFY has been shown to bind phosphatidylinositol 3-phosphate (PI(3)P); however, ALFY only partially colocalizes with other FYVE domains in cells. Thus, we asked if the FYVE domain of ALFY has distinct membrane binding properties compared to other FYVE domains and whether these properties might affect its function in vivo. We found that the FYVE domain of ALFY binds weakly to PI(3)P containing membranes in vitro. This weak binding is the result of a highly conserved glutamic acid within the membrane insertion loop in the FYVE domain of ALFY that is not present in any other human FYVE domain. In addition, not only does this glutamic acid reduce binding to membranes in vitro and inhibits its targeting to membranes in vivo, but it is also important for the ability of ALFY to clear protein aggregates.

The Third Coiled Coil Domain of Atg11 Is Required for Shaping Mitophagy Initiation Sites.

Selective autophagy is the capture of specific cytosolic contents in double-membrane vesicles that subsequently fuse with the vacuole or lysosome, thereby delivering cargo for degradation. Selective autophagy receptors (SARs) mark the cargo for degradation and, in yeast, recruit Atg11, the scaffolding protein for selective autophagy initiation. The mitochondrial protein Atg32 is the yeast SAR that mediates mitophagy, the selective autophagic capture of mitochondria. Atg11-Atg32 interactions concentrate Atg32 into puncta that are thought to represent sites of mitophagy initiation. However, it is unclear how Atg11 concentrates Atg32 to generate mitophagy initiation sites. We show here that the coiled coil 3 (CC3) domain of Atg11 is required for concentrating Atg32 into puncta. We determined the structure of the majority of the CC3, demonstrating that the CC3 forms a parallel homodimer whose dimer interface is formed by a small number of hydrophobic residues. We further show that the CC3 interface is not required for Atg11 dimerization but is required for shaping Atg32 into functional mitophagy initiation sites and for delivery of mitochondria to the vacuole. Our findings suggest that Atg11 self-interactions help concentrate SARs as a necessary precondition for cargo capture.

A pseudo-receiver domain in Atg32 is required for mitophagy.

Mitochondria are targeted for degradation by mitophagy, a selective form of autophagy. In Saccharomyces cerevisiae, mitophagy is dependent on the autophagy receptor, Atg32, an outer mitochondrial membrane protein. Once activated, Atg32 recruits the autophagy machinery to mitochondria, facilitating mitochondrial capture in phagophores, the precursors to autophagosomes. However, the mechanism of Atg32 activation remains poorly understood. To investigate this crucial step in mitophagy regulation, we examined the structure of Atg32. We have identified a structured domain in Atg32 that is essential for the initiation of mitophagy, as it is required for the proteolysis of the C-terminal domain of Atg32 and the subsequent recruitment of Atg11. The solution structure of this domain was determined by NMR spectroscopy, revealing that Atg32 contains a previously undescribed pseudo-receiver (PsR) domain. Our data suggests that the PsR domain of Atg32 regulates Atg32 activation and the initiation of mitophagy. ABBREVIATIONS: AIM: Atg8-interacting motif; GFP: green fluorescent protein; LIR: LC3-interacting region; NMR: nuclear magnetic resonance; NOESY: nuclear Overhauser effect spectroscopy; PDB: protein data bank; PsR: pseudo-receiver; RMSD: root-mean-square deviation.

Isolation, Purification, and Culture of Primary Murine Sensory Neurons.

Cultured primary neurons have been of extraordinary value for the study of neuronal anatomy, cell biology, and physiology. While use of neuronal cell lines has ease and utility, there are often caveats that arise due to their mitotic nature. This methods article presents detailed methodology for the preparation, purification, and culture of adult murine sensory neurons for the study of herpes simplex virus lytic and latent infections. While virology is the application for our laboratory, these cultures also have broad utility for neurobiologists and cell biologists. While these primary cultures have been highly informative, the methodology is challenging to many investigators. Through publication of this highly detailed protocol, it is our hope that the use of this culture system can spread in the field to allow more rapid progress in furthering our understanding of neurotropic virus infection.

Correction to: Isolation, Purification, and Culture of Primary Murine Sensory Neurons.

In chapter 15, section 2.3, the unit "180 µg/ml mouse laminin in HBSS. Prepare 150 µl per coverslip" is corrected to "18 µg/ml mouse laminin in HBSS. Prepare 150 µl per coverslip."

Neuronal IFN signaling is dispensable for the establishment of HSV-1 latency.

IFN responses control acute HSV infection, but their role in regulating HSV latency is poorly understood. To address this we used mice lacking IFN signaling specifically in neural tissues. These mice supported a higher acute viral load in nervous tissue and delayed establishment of latency. While latent HSV-1 genome copies were equivalent, ganglia from neuronal IFN signaling-deficient mice unexpectedly supported reduced reactivation. IFNß promoted survival of primary sensory neurons after infection with HSV-1, indicating a role for IFN signaling in sustaining neurons. We observed higher levels of latency associated transcripts (LATs) per HSV genome in mice lacking neuronal IFN signaling, consistent with a role for IFN in regulating LAT expression. These data show that neuronal IFN signaling modulates the expression of LAT and may conserve the pool of neurons available to harbor latent HSV-1 genome. The data also show that neuronal IFN signaling is dispensable for the establishment of latency.

Herpes Simplex Virus and Interferon Signaling Induce Novel Autophagic Clusters in Sensory Neurons.

UNLABELLED: Herpes simplex virus 1 (HSV-1) establishes lifelong infection in the neurons of trigeminal ganglia (TG), cycling between productive infection and latency. Neuronal antiviral responses are driven by type I interferon (IFN) and are crucial to controlling HSV-1 virulence. Autophagy also plays a role in this neuronal antiviral response, but the mechanism remains obscure. In this study, HSV-1 infection of murine TG neurons triggered unusual clusters of autophagosomes, predominantly in neurons lacking detectable HSV-1 antigen. Treatment of neurons with IFN-ß induced a similar response, and cluster formation by infection or IFN treatment was dependent upon an intact IFN-signaling pathway. The autophagic clusters were decorated with both ISG15, an essential effecter of the antiviral response, and p62, a selective autophagy receptor. The autophagic clusters were not induced by rapamycin or starvation, consistent with a process of selective autophagy. While clusters were triggered by other neurotropic herpesviruses, infection with unrelated viruses failed to induce this response. Following ocular infection in vivo, clusters formed exclusively in the infected ophthalmic branch of the TG. Taken together, our results show that infection with HSV and antiviral signaling in TG neurons produce an unorthodox autophagic response. This autophagic clustering is associated with antiviral signaling, the presence of viral genome, and the absence of HSV protein expression and may therefore represent an important neuronal response to HSV infection and the establishment of latency. IMPORTANCE: Herpes simplex virus type 1 (HSV-1) is a ubiquitous virus and a significant cause of morbidity and some mortality. It is the causative agent of benign cold sores, but it can also cause blindness and life-threatening encephalitis. The success of HSV-1 is largely due to its ability to establish lifelong latent infections in neurons and to occasionally reactivate. The exact mechanisms by which neurons defend against virus infection is poorly understood, but such defense is at least partially mediated by autophagy, an intracellular pathway by which pathogens and other unwanted cargoes are degraded. The study demonstrates and investigates a new autophagic structure that appears to be specific to the interaction between neurotropic herpesviruses and murine primary sensory neurons. This work may therefore have important implications for our understanding of latency and reactivation.

Microvesicles of pregnant women receiving low molecular weight heparin improve trophoblast function.

INTRODUCTION: Microvesicles including exosomes and microparticles, participate in the placental-maternal crosstalk in normal pregnancies and gestational vascular complications (GVC). Low molecular weight heparin (LMWH) is known to reduce the risk of placenta-mediated pregnancy complications. This study was aimed to characterize microvesicles of pregnant women receiving LMWH and explore microvesicle involvement in trophoblast and endothelial cell function. MATERIALS AND METHODS: Microvesicles were isolated from blood samples obtained from non-pregnant women, healthy pregnant women (HP) and pregnant woman treated with LMWH. Microvesicle protein contents were assessed by protein array and ELISA. Microvesicle effects on early stage trophoblasts, term trophoblasts and endothelial cell migration, angiogenesis and apoptosis were evaluated. RESULTS: Microvesicles derived from the group treated with LMWH contained higher levels of several proangiogenic proteins compared to those of HP women. Exposure of endothelial cells to circulating microvesicles derived from HP and LMWH treated groups induced significantly higher cell migration and branch tube formation compared to untreated cells. The effect of microvesicles from HP- and LMWH groups on early-stage trophoblast migration was similar. Microvesicles derived from these two study groups significantly decreased early-stage trophoblast apoptosis, while microvesicles derived from the HP-group (but not from the LMWH-group) significantly increased the term trophoblast apoptosis (TUNEL assay) compared to untreated cells. CONCLUSION: Therapy with LMWH affects patients' microvesicle content, leading to normalization of invasion, angiogenesis activity and survival of endothelial and trophoblast cells in vitro. The effects of LMWH on microvesicles may point to an additional mechanism of heparin action in high-risk pregnancy.

The differential interferon responses of two strains of Stat1-deficient mice do not alter susceptibility to HSV-1 and VSV in vivo.

Stat1 is a pivotal transcription factor for generation of the interferon (IFN)-dependent antiviral response. Two Stat1 knockout mouse lines have been previously generated, one deleted the N-terminal domain (ΔNTD) and one in the DNA-binding domain (ΔDBD). These widely-used strains are assumed interchangeable, and both are highly susceptible to various pathogens. In this study, primary cells derived from ΔNTD mice were shown to be significantly more responsive to IFN, and established an antiviral state with greater efficiency than cells derived from ΔDBD mice, following infection with vesicular stomatitis virus and herpes simplex virus type-1. Also, while mice from both strains succumbed rapidly and equally to virus infection, ΔDBD mice supported significantly higher replication in brains and livers than ΔNTD mice. Endpoint-type experimental comparisons of these mouse strains are therefore misleading in failing to indicate important differences in virus replication and innate response.

Microvesicles of women with gestational hypertension and preeclampsia affect human trophoblast fate and endothelial function.

Microvesicles shedding from cell membrane affect inflammation, apoptosis, and angiogenesis. We hypothesize that microvesicles of women with gestational vascular complications reflect pathophysiological state of the patients and affect their endothelial and trophoblast cell function. Microvesicles of healthy pregnant women, women with gestational hypertension, mild, or severe preeclampsia/toxemia, were characterized, and their effects on early-stage or term trophoblasts and endothelial cells were evaluated using apoptosis, migration, and tube formation assays. Patient subgroups differed significantly only in proteinuria levels, therefore their microvesicles were assessed as 1 group, demonstrating higher levels of inflammatory and angiogenic proteins compared with those of healthy pregnant women. In endothelial cells, microvesicles of healthy pregnant women reduced caspase 3/7 activity, increased migration, and induced tube formation. These processes were suppressed by microvesicles of women with gestational vascular complications. In early-stage trophoblasts, microvesicles of healthy pregnant women decreased apoptosis compared with untreated cells (6±5% versus 13.8±5.8%; P<0.001) and caspase 3/7 activity and induced higher migration (39.7±10.1 versus 20.3±8.3 mm2; P<0.001). This effect was mediated through extracellular signal-regulated kinase pathway. Conversely, microvesicles of women with gestational vascular complications increased term trophoblast apoptosis compared with cells exposed to microvesicles of healthy pregnant women (15.1±3.3% versus 6.5±2.1%; P<0.001) and inhibited early-stage trophoblasts migration (21.4±18.5 versus 39.7±10.1 mm2; P<0.001). In conclusion, microvesicle content and effects on endothelial and trophoblast cells vary according to the physiological/pathological state of a pregnant woman. Microvesicles seem to play a pivotal role in the course of pregnancy, which could potentially result in gestational vascular complications.

Fibroblast growth factor-2 is required for vasa vasorum plexus stability in hypercholesterolemic mice.

OBJECTIVE: Vasa vasorum are angiogenic in advanced stages of human atherosclerosis and hypercholesterolemic mouse models. Fibroblast growth factor-2 (FGF-2) is the predominant angiogenic growth factor in the adventitia and plaque of hypercholesterolemic low-density lipoprotein receptor-deficient/apolipoprotein B(100/100) mice (DKO). FGF-2 seems to play a role in the formation of a distinct vasa vasorum network. This study examined the vasa vasorum structure and its relationship to FGF-2. METHODS AND RESULTS: DKO mice treated with saline, antiangiogenic recombinant plasminogen activator inhibitor-1(23) (rPAI-1(23)), or soluble FGF receptor 1 were perfused with fluorescein-labeled Lycopersicon esculentum lectin. Confocal images of FGF-2-probed descending aorta adventitia show that angiogenic vasa vasorum form a plexus-like network in saline-treated DKO similar to the FGF-2 pattern of distribution. Mice treated with rPAI-1(23) and soluble FGF receptor 1 lack a plexus; FGF-2 and vasa vasorum density and area are significantly reduced. A perlecan/FGF-2 complex is critical for plexus stability. Excess plasmin produced in rPAI-1(23)-treated DKO mice degrades perlecan and destabilizes the plexus. Plasmin activity and plaque size measured in DKO and DKO/plasminogen activator inhibitor-1(-)(/-) mice demonstrate that elevated plasmin activity contributes to reduced plaque size. CONCLUSIONS: An FGF-2/perlecan complex is required for vasa vasorum plexus stability. Elevated plasmin activity plays a significant inhibitory role in vasa vasorum plexus and plaque development.

Characterization of negatively charged phospholipids and cell origin of microparticles in women with gestational vascular complications.

INTRODUCTION: Gestational vascular complications (GVC) are a major cause of maternal and fetal morbidity which can be potentially reduced by LMWH. Microparticles (MPs) are involved in thrombosis and inflammation. However, characterization and role of MPs in GVC have not been elucidated. MATERIALS AND METHODS: MPs were isolated from non-pregnant women, healthy pregnant women, women with GVC (hypertension or preeclamptic toxemia (PET)) and women with a history of pregnancy complications who were treated with LMWH. MP count, cell origin and expression of negatively charged phospholipids were evaluated. RESULTS: Total numbers of MPs were similar in the study cohorts, with a non-significant trend toward an increase in the pregnant groups, while percentage of MPs bearing negatively charged phospholipids was significantly reduced in all the pregnancy groups. Endothelial CD144-MPs were elevated in the GVC groups compared to the healthy pregnant cohort. Endothelial CD31+/CD41-MPs were decreased in the LMWH group compared to women with PET. Percentage of placental trophoblast MPs was similar in all pregnancy groups and platelet MPs were reduced in healthy pregnant compared to non-pregnant women. Notably, percent of MPs bearing negatively charged phospholipids correlated only with platelet MPs, but not with endothelial, trophoblast or leukocyte MPs. CONCLUSION(S): Presence of negatively charged phospholipids cannot be considered universal characteristics of MPs in pregnancy. MPs may reflect the vascular injury characterizing GVC pathology.