Cellular IAP1 regulates TRAIL-induced apoptosis in human fetal cortical neural progenitor cells

Influence of Perinatal Factors on Gene Expression of IAPs Family and Main Factors of Pluripotency: OCT4 and SOX2 in Human Breast Milk Stem Cells-A Preliminary Report

Due to their therapeutic potential, mesenchymal stem cells are the subject of intensive research on the use of their potential in the treatment of, among others, neurodegenerative diseases or immunological diseases. They are among the newest in the field of medicine. The presented study aimed to evaluate the expression of eight genes from the IAP family and the gene regulating IAP-XAF1-in stem cells derived from human milk, using the qPCR method. The relationships between the expression of genes under study and clinical data, such as maternal age, maternal BMI, week of pregnancy in which the delivery took place, bodyweight of the newborn, the number of pregnancies and deliveries, and the time elapsed since delivery, were also analyzed. The research was carried out on samples of human milk collected from 42 patients hospitalized in The Clinic of Obstetrics and Perinatology of the Independent Public Clinical Hospital No. 4, in Lublin. The conducted research confirmed the expression of the following genes in the tested material: NAIP, BIRC2, BIRC3, BIRC5, BIRC6, BIRC8, XIAP, XAF1, OCT4 and SOX2. Moreover, several dependencies of the expression of individual genes on the maternal BMI (BIRC5, XAF1 and NAIP), the time since childbirth (BIRC5, BIRC6, XAF1 and NAIP), the number of pregnancies and deliveries (BIRC2, BIRC5, BIRC6 and XAF1), the manner of delivery (XAF1 and OCT4), preterm labor (BIRC6 and NAIP) were demonstrated. Additionally, we found positive relationships between gene expression of BIRC7, BIRC8 and XAF1 and the main factors of pluripotency: SOX2 and OCT4. This work is the first to investigate the expression of genes from the IAPs family in mother's milk stem cells.

TRAIL receptor-induced features of epithelial-to-mesenchymal transition increase tumour phenotypic heterogeneity: potential cell survival mechanisms

The continuing efforts to exploit the death receptor agonists, such as the tumour necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), for cancer therapy, have largely been impaired by the anti-apoptotic and pro-survival signalling pathways leading to drug resistance. Cell migration, invasion, differentiation, immune evasion and anoikis resistance are plastic processes sharing features of the epithelial-to-mesenchymal transition (EMT) that have been shown to give cancer cells the ability to escape cell death upon cytotoxic treatments. EMT has recently been suggested to drive a heterogeneous cellular environment that appears favourable for tumour progression. Recent studies have highlighted a link between EMT and cell sensitivity to TRAIL, whereas others have highlighted their effects on the induction of EMT. This review aims to explore the molecular mechanisms by which death signals can elicit an increase in response heterogeneity in the metastasis context, and to evaluate the impact of these processes on cell responses to cancer therapeutics.

Increased Expression of BIRC2, BIRC3, and BIRC5 from the IAP Family in Mesenchymal Stem Cells of the Umbilical Cord Wharton's Jelly (WJSC) in Younger Women Giving Birth Naturally

The knowledge of factors affecting the viability as well as proliferation and therapeutic potential of perinatal stem cells is of great importance for the decisions concerning their collection, multiplication, and storing. The aim of this work is to evaluate the expression of the BIRC2, BIRC3, and BIRC5 genes at the level of transcription in mesenchymal stem cells derived from the umbilical cord Wharton's jelly. The study examined the relationship between the expression level of the studied genes and selected biophysical parameters of umbilical blood: pH, pCO₂, pO₂, and cHCO₃. Moreover, the relationship between the pregnant age, the type of delivery (natural delivery or cesarean section), and the level of expression of the BIRC2, BIRC3, and BIRC5 genes was assessed. The research was carried out on mesenchymal stem cells derived from the umbilical cord Wharton's jelly (WJSC) taken from 55 women immediately after delivery. Expression of the examined genes was assessed with the qPCR method using commercially available reagent kits. On the basis of the conducted research, it was demonstrated that WJSCs collected from younger women giving birth naturally, and in the acidic environment of the umbilical cord blood, are characterized by a higher expression of the BIRC2, BIRC3, and BIRC5 genes. It was shown that the expression of the BIRC2 and BIRC3 genes in Wharton's jelly mesenchymal stem cells declines with the mother's age. Our research suggests that stem cells collected from younger women giving birth naturally can be more resistant to apoptosis and show a more stem cell-like character, which can increase their therapeutic potential and clinical utility, but this conclusion needs to be approved in the next studies.

Small molecule ONC201 inhibits HIV-1 replication in macrophages via FOXO3a and TRAIL

Despite the success of antiretroviral therapy (ART), eradication of HIV-1 from brain reservoirs remains elusive. HIV-1 brain reservoirs include perivascular macrophages that are behind the blood-brain barrier and difficult to access by ART. Macrophages express transcription factor FOXO3a and the TNF superfamily cytokine TRAIL, which are known to target HIV-1-infected macrophages for viral inhibition. ONC201 is a novel and potent FOXO3a activator capable of inducing TRAIL. It can cross the blood-brain barrier, and has shown antitumor effects in clinical trials. We hypothesized that activation of FOXO3a/TRAIL by ONC201 will inhibit HIV-1 replication in macrophages. Using primary human monocyte-derived macrophages, we demonstrated that ONC201 dose-dependently decreased replication levels of both HIV-1 laboratory strain and primary strains as determined by HIV-1 reverse transcriptase activity assay. Consistent with data on HIV-1 replication, ONC201 also reduced intracellular and extracellular p24, viral RNA, and integrated HIV-1 DNA in infected macrophages. Blocking TRAIL or knockdown of FOXO3a with siRNA reversed ONC201-mediated HIV-1 suppression, suggesting that ONC201 inhibits HIV-1 through FOXO3a and TRAIL. The anti-HIV-1 effect of ONC201 was further validated in vivo in NOD/scid-IL-2Rgcnull mice. After intracranial injection of HIV-1-infected macrophages into the basal ganglia, we treated the mice daily with ONC201 through intraperitoneal injection for six days. ONC201 significantly decreased p24 levels in both the macrophages and the brain tissues, suggesting that ONC201 suppresses HIV-1 in vivo. Therefore, ONC201 can be a promising drug candidate to combat persistent HIV-1 infection in the brain.

Different effects of anesthetic isoflurane on caspase-3 activation and cytosol cytochrome c levels between mice neural progenitor cells and neurons

Commonly used anesthetic isoflurane has been reported to promote Alzheimer’s disease (AD) neuropathogenesis by inducing caspase-3 activation. However, the up-stream mechanisms of isoflurane’s effects remain largely to be determined. Specifically, there is a lack of a good model/system to elucidate the underlying mechanism of the isoflurane-induced caspase-3 activation. We therefore set out to assess and compare the effects of isoflurane on caspase-3 activation in neural progenitor cells (NPCs) and in primary neurons from wild-type (WT) and AD transgenic (Tg) mice. The NPCs and neurons were obtained, cultured and then treated with either 2% isoflurane or under control condition for 6 h. The NPCs or neurons were harvested at the end of the treatment and were subjected to Western blot analysis. Here we showed for the first time that the isoflurane treatment induced caspase-3 activation in neurons, but not in NPCs, from either WT or AD Tg mice. Consistently, the isoflurane treatment increased cytosol levels of cytochrome c, a potential up-stream mechanism of isoflurane-induced caspase-3 activation in the mice neurons, but not NPCs. Finally, the isoflurane treatment induced a greater casapse-3 activation in the neurons, but not the NPCs, from AD Tg mice as compared to the WT mice. These data demonstrated that investigation and comparison of isoflurane’s effects between mice NPCs and neurons would serve as a model/system to determine the underlying mechanism by which isoflurane induces caspase-3 activation. These findings would promote more research to investigate the effects of anesthetics on AD neuropathogenesis and the underlying mechanisms.

Molecular features of neural stem cells enable their enrichment using pharmacological inhibitors of survival-promoting kinases

Isolating a pure population of neural stem cells (NSCs) has been difficult since no exclusive surface markers have been identified for panning or FACS purification. Moreover, additional refinements for maintaining NSCs in culture are required, since NSCs generate a variety of neural precursors (NPs) as they proliferate. Here, we demonstrate that post-natal rat NPs express low levels of pro-apoptotic molecules and resist phosphatidylinositol 3'OH kinase and extracellular regulated kinase 1/2 inhibition as compared to late oligodendrocyte progenitors. Furthermore, maintaining subventricular zone precursors in LY294002 and PD98059, inhibitors of PI3K and ERK1/2 signaling, eliminated lineage-restricted precursors as revealed by enrichment for Nestin(+)/SOX-2(+) cells. The cells that survived formed neurospheres and 89% of these neurospheres were tripotential, generating neurons, astrocytes, and oligodendrocytes. Without this enrichment step, less than 50% of the NPs were Nestin(+)/SOX-2(+) and 42% of the neurospheres were tripotential. In addition, neurospheres enriched using this procedure produced 3-times more secondary neurospheres, supporting the conclusion that this procedure enriches for NSCs. A number of genes that enhance survival were more highly expressed in neurospheres compared to late oligodendrocyte progenitors. Altogether, these studies demonstrate that primitive neural precursors can be enriched using a relatively simple and inexpensive means that will facilitate cell replacement strategies using stem cells as well as other studies whose goal is to reveal the fundamental properties of primitive neural precursors.

Hexane extract from Polygonum multiflorum attenuates glutamate-induced apoptosis in primary cultured cortical neurons

ETHNOPHARMACOLOGICAL RELEVANCE

Polygonum multiflorum has traditionally had wide use as an anti-aging treatment in East Asian countries. We investigated the neuroprotective effects of Polygonum multiflorum against glutamate-induced neurotoxicity with a focus on the anti-apoptotic mechanism in primary cultured cortical neurons.

MATERIAL AND METHODS

Cell viability, cytotoxicity, morphological, flow cytometry, Western blot, and caspase activity assays were performed for examination of the neuroprotective effects of active hexane extract from Polygonum multiflorum (HEPM).

RESULTS

Pretreatment with HEPM resulted in significantly decreased glutamate-induced neurotoxicity in a concentration-dependent manner and also resulted in drastically inhibited glutamate-induced apoptosis. Treatment with HEPM resulted in decreased expression of glutamate-induced death receptor (DR)4, and enhanced expression of glutamate-attenuated anti-apoptotic proteins, including Bcl-2, XIAP, and cIAP-1, and slightly reduced glutamate-induced cleavage of Bid. In addition, treatment with HEPM resulted in suppressed glutamate-induced activation of caspase-8, caspase-9, and caspase-3, and, subsequently, decreased degradation of poly(ADP-ribose) polymerase, β-catenin, and phospholipase Cγ1 protein, which are downstream targets of activated caspase-3.

CONCLUSIONS

The results of this study demonstrated that HEPM exerts a neuroprotective effect against glutamate-induced neurotoxicity via inhibition of apoptosis. This protection may be mediated through suppression of DR4 and up-regulation of Bcl-2, XIAP, and cIAP-1, as well as inhibition of caspase activation, resulting in prevention of apoptosis of cortical neurons.

Ischemic preconditioning reduces neurovascular damage after hypoxia-ischemia via the cellular inhibitor of apoptosis 1 in neonatal brain

BACKGROUND AND PURPOSE

The neurovascular unit is a major target of hypoxia-ischemia (HI) injury in the neonatal brain. Although neurons are the cellular target of ischemic preconditioning (IP), vessel tolerance also contributes greatly to protection. Nerves and vessels cross-talk and use common signals during development. Cellular inhibitor of apoptosis 1 (cIAP1) is an important regulator that inhibits apoptosis. This study hypothesized that cIAP1 is a shared molecule underlying IP-mediated neurovascular protection against HI in the neonatal brain.

METHODS

In vivo IP was induced by 2-hour reversible occlusion of right carotid artery 24 hours before HI on postpartum day 7 in rat pups. In vitro oxygen-glucose deprivation (OGD) preconditioning was established in SH-SY5Y neuronal cells and in human microvascular endothelial cell-1 vascular endothelial cells. cIAP1 expression was inhibited by cIAP1 small interfering RNA in vivo or by lentivirus-mediated short hairpin RNA in vitro, or was upregulated by the lentiviral expression system.

RESULTS

IP reduced apoptosis, selectively increased cIAP1 in neurons and vascular endothelial cells, and provided long-term neuroprotection against HI. Intracerebroventricular delivery of cIAP1 small interfering RNA significantly attenuated IP-mediated cIAP1 upregulation and neuroprotection in vivo. In vitro, OGD preconditioning induced cIAP1 and protected against OGD cell death in SH-SY5Y neuronal and human microvascular endothelial cells-1. Knockdown of cIAP1 by lentivirus-mediated short hairpin RNA decreased the protective effect of OGD preconditioning in SH-SY5Y and human microvascular endothelial cell-1, whereas overexpression of cIAP1 by lentivirus protected against OGD in these cells.

CONCLUSIONS

cIAP1 is a shared molecule underlying IP-induced protection in neurons and vascular endothelial cells against HI in the neonatal brain.

Proteolytic processing of SDF-1α by matrix metalloproteinase-2 impairs CXCR4 signaling and reduces neural progenitor cell migration

Neural stem cells and neural progenitor cells (NPCs) exist throughout life and are mobilized to replace neurons, astrocytes and oligodendrocytes after injury. Stromal cell-derived factor 1 (SDF-1, now named CXCL12) and its receptor CXCR4, an α-chemokine receptor, are critical for NPC migration into damaged areas of the brain. Our previous studies demonstrated that immune activated and/or HIV-1-infected human monocyte-derived-macrophages (MDMs) induced a substantial increase of SDF-1 production by human astrocytes. However, matrix metalloproteinase (MMP)-2, a protein up-regulated in HIV-1-infected macrophages, is able to cleave four amino acids from the N-terminus of SDF-1, resulting in a truncated SDF-1(5-67). In this study, we investigate the diverse signaling and function induced by SDF-1α and SDF-1(5-67) in human cortical NPCs. SDF-1(5-67) was generated by incubating human recombinant SDF-1α with MMP-2 followed by protein determination via mass spectrometry, Western blotting and ELISA. SDF-1α induced time-dependent phosphorylation of extracellular signal-regulated kinases (ERK) 1/2, Akt-1, and diminished cyclic adenosine monophosphate (cAMP). In contrast, SDF-1(5-67) failed to induce these signaling. SDF-1α activation of CXCR4 induced migration of NPCs, an effect that is dependent on ERK1/2 and Akt-1 pathways; whereas SDF-1(5-67) failed to induce NPC migration. This observation provides evidence that MMP-2 may affect NPC migration through post-translational processing of SDF-1α.

CXCL12 enhances human neural progenitor cell survival through a CXCR7- and CXCR4-mediated endocytotic signaling pathway

Chemokine CXCL12 is widely expressed in the central nervous system and essential for the proper functioning of human neural progenitor cells (hNPCs). Although CXCL12 is known to function through its receptor CXCR4, recent data have suggested that CXCL12 binds to chemokine receptor CXCR7 with higher affinity than to CXCR4. However, little is known about the function of CXCR7 in hNPCs. Using a primary hNPC culture system, we demonstrated that CXCL12 promotes hNPC survival in the events of camptothecin-induced apoptosis or growth factor deprivation, and that this effect requires both CXCR7 and CXCR4. Through fluorescence-activated cell sorting analysis and immunocytochemistry, we determined that CXCR7 is mainly localized in the early endosome, while CXCR4 is more broadly expressed at the cell surface and on both early and recycling endosomes. Furthermore, we found that endocytosis is required for the prosurvival function of CXCL12. Using dual-color total internal reflection fluorescence microscopy and immunoprecipitation, we demonstrated that CXCR7 quickly trafficks to plasma membrane in mediating CXCL12 endocytosis and colocalizes with CXCR4 after CXCL12 treatment. Investigating the molecular mechanisms, we found that ERK1/2 endocytotic signaling pathway is essential for hNPC survival upon apoptotic challenges. Consistent with these findings, a significantly higher number of apoptotic NPCs were found in the developing brain of CXCR7 knockout mice. In conclusion, CXCL12 protects hNPCs from apoptotic challenges through CXCR7- and CXCR4-mediated endocytotic signaling. Since survival of hNPCs is important for neurogenesis, CXCR7 may become a new therapeutic target to properly regulate critical processes of brain development.

Suppression of apoptosis inhibitor c-FLIP selectively eliminates breast cancer stem cell activity in response to the anti-cancer agent, TRAIL

INTRODUCTION

It is postulated that breast cancer stem cells (bCSCs) mediate disease recurrence and drive formation of distant metastases - the principal cause of mortality in breast cancer patients. Therapeutic targeting of bCSCs, however, is hampered by their heterogeneity and resistance to existing therapeutics. In order to identify strategies to selectively remove bCSCs from breast cancers, irrespective of their clinical subtype, we sought an apoptosis mechanism that would target bCSCs yet would not kill normal cells. Suppression of the apoptosis inhibitor cellular FLICE-Like Inhibitory Protein (c-FLIP) partially sensitizes breast cancer cells to the anti-cancer agent Tumour Necrosis Factor-Related Apoptosis Inducing Ligand (TRAIL). Here we demonstrate in breast cancer cell lines that bCSCs are exquisitely sensitive to the de-repression of this pro-apoptotic pathway, resulting in a dramatic reduction in experimental metastases and the loss of bCSC self-renewal.

METHODS

Suppression c-FLIP was performed by siRNA (FLIPi) in four breast cancer cell lines and by conditional gene-knockout in murine mammary glands. Sensitivity of these cells to TRAIL was determined by complementary cell apoptosis assays, including a novel heterotypic cell assay, while tumour-initiating potential of cancer stem cell subpopulations was determined by mammosphere cultures, aldefluor assay and in vivo transplantation.

RESULTS

Genetic suppression of c-FLIP resulted in the partial sensitization of TRAIL-resistant cancer lines to the pro-apoptotic effects of TRAIL, irrespective of their cellular phenotype, yet normal mammary epithelial cells remained refractory to killing. While 10% to 30% of the cancer cell populations remained viable after TRAIL/FLIPi treatment, subsequent mammosphere and aldefluor assays demonstrated that this pro-apoptotic stimulus selectively targeted the functional bCSC pool, eliminating stem cell renewal. This culminated in an 80% reduction in primary tumours and a 98% reduction in metastases following transplantation. The recurrence of residual tumour initiating capacity was consistent with the observation that post-treated adherent cultures re-acquired bCSC-like properties in vitro. Importantly however this recurrent bCSC activity was attenuated following repeated TRAIL/FLIPi treatment.

CONCLUSIONS

We describe an apoptotic mechanism that selectively and repeatedly removes bCSC activity from breast cancer cell lines and suggest that a combined TRAIL/FLIPi therapy could prevent metastatic disease progression in a broad range of breast cancer subtypes.

The role of tumor necrosis factor receptor superfamily members in mammalian brain development, function and homeostasis

Tumor necrosis factor receptor superfamily (TNFRSF) members were initially identified as immunological mediators, and are still commonly perceived as immunological molecules. However, our understanding of the diversity of TNFRSF members' roles in mammalian physiology has grown significantly since the first discovery of TNFRp55 (TNFRSF1) in 1975. In particular, the last decade has provided evidence for important roles in brain development, function and the emergent field of neuronal homeostasis. Recent evidence suggests that TNFRSF members are expressed in an overlapping regulated pattern during neuronal development, participating in the regulation of neuronal expansion, growth, differentiation and regional pattern development. This review examines evidence for non-immunological roles of TNFRSF members in brain development, function and maintenance under normal physiological conditions. In addition, several aspects of brain function during inflammation will also be described, when illuminating and relevant to the non-immunological role of TNFRSF members. Finally, key questions in the field will be outlined.

HIV-1-infected and immune-activated macrophages induce astrocytic differentiation of human cortical neural progenitor cells via the STAT3 pathway

Diminished adult neurogenesis is considered a potential mechanism in the pathogenesis of HIV-1-associated dementia (HAD). In HAD, HIV-1-infected and immune-activated brain mononuclear phagocytes (MP; perivascular macrophages and microglia) drive central nervous system (CNS) inflammation and may alter normal neurogenesis. We previously demonstrated HIV-1-infected and lipopolysaccharide (LPS) activated monocyte-derived macrophages (MDM) inhibit human neural progenitor cell (NPC) neurogenesis, while enhancing astrogliogenesis through the secretion of the inflammatory cytokines such as tumor necrosis factor-alpha (TNF-α), in vitro and in vivo. Here we further test the hypothesis that HIV-1-infected/activated MDM promote NPC astrogliogenesis via activation of the transcription factor signal transducer and activator of transcription 3 (STAT3), a critical factor for astrogliogenesis. Our results show that LPS-activated MDM-conditioned medium (LPS-MCM) and HIV-infected/LPS-activated MDM-conditioned medium (LPS+HIV-MCM) induced Janus kinase 1 (Jak1) and STAT3 activation. Induction of the Jak-STAT3 activation correlated with increased glia fibrillary acidic protein (GFAP) expression, demonstrating an induction of astrogliogenesis. Moreover, STAT3-targeting siRNA (siSTAT3) decreased MCM-induced STAT3 activation and NPC astrogliogenesis. Furthermore, inflammatory cytokines (including IL-6, IL-1β and TNF-α) produced by LPS-activated and/or HIV-1-infected MDM may contribute to MCM-induced STAT3 activation and astrocytic differentiation. These observations were confirmed in severe combined immunodeficient (SCID) mice with HIV-1 encephalitis (HIVE). In HIVE mice, siRNA control (without target sequence, sicon) pre-transfected NPCs injected with HIV-1-infected MDM showed more astrocytic differentiation and less neuronal differentiation of NPCs as compared to NPC injection alone. siSTAT3 abrogated HIV-1-infected MDM-induced astrogliogenesis of injected NPCs. Collectively, these observations demonstrate that HIV-1-infected/activated MDM induces NPC astrogliogenesis through the STAT3 pathway. This study generates important data elucidating the role of brain inflammation in neurogenesis and may provide insight into new therapeutic strategies for HAD.

Viral infection and neural stem/progenitor cell's fate: implications in brain development and neurological disorders

Viral infections in the prenatal (during pregnancy) and perinatal period have been a common cause of brain malformation. Besides the immediate neurological dysfunctions, virus infections may critically affect CNS development culminating in long-term cognitive deficits. Most of these neurotropic viruses are most damaging at a critical stage of the host, when the brain is in a dynamic stage of development. The neuropathology can be attributed to the massive neuronal loss induced by the virus as well as lack of CNS repair owing to a deficit in the neural stem/progenitor cell (NSPC) pool or aberrant formation of new neurons from NSPCs. Being one of the mitotically active populations in the post natal brain, the NSPCs have emerged as the potential targets of neurotropic viruses. The NSPCs are self-renewing and multipotent cells residing in the neurogenic niches of the brain, and, therefore, hampering the developmental fate of these cells may adversely affect the overall neurogenesis pattern. A number of neurotropic viruses utilize NSPCs as their cellular reservoirs and often establish latent and persistent infection in them. Both HIV and Herpes virus infect NSPCs over long periods of time and reactivation of the virus may occur later in life. The virus infected NSPCs either undergoes cell cycle arrest or impaired neuronal or glial differentiation, all of which leads to impaired neurogenesis. The disturbances in neurogenesis and CNS development following neurotropic virus infections have direct implications in the viral pathogenesis and long-term neurobehavioral outcome in infected individuals.

Unilateral blood flow decrease induces bilateral and symmetric responses in the immature brain

The effects of hemodynamic changes in the developing brain have yet to be fully understood. The aim of this study was to explore the relationship between perturbations of the cerebral blood flow in the developing brain via unilateral hypoperfusion in P7 rats. As expected, nuclear caspase-3 (casp3) cleavage and DNA fragmentation were detected at 48 hours after stroke in the injured cortex. Surprisingly, casp3 was also cleaved in the contralateral cortex, although without cell death markers. Delayed (48 hours) casp3 cleavage without DNA fragmentation was also identified after unilateral common carotid artery occlusion, both in the hypoperfused cortex and the unaffected cortex, producing mirror images. Upstream calpain activation, caspase-2 cleavage, and mitochondrial cytochrome c release initiated casp3 cleavage, but did not produce preconditioning. The neuronal marker NeuN co-localized with cleaved casp3 in cortical layers II-III and VI and with gaba-amino butyric acid in layer III. Indeed, collateral supply was provided from the opposite side during carotid artery occlusion but not after reperfusion, and the number of cleaved casp3-positive cells significantly negatively correlated with the common carotid artery immediate reperfusion percentage. In summary, unilateral hypoperfusion, while insufficient to induce cell death, may active bilateral and symmetric casp3 in the P7 rat brain. Additionally, the opposite healthy hemisphere is altered due to the injury and thus should not be used as an internal control.

Type I interferons and interferon regulatory factors regulate TNF-related apoptosis-inducing ligand (TRAIL) in HIV-1-infected macrophages

TNF-related apoptosis-inducing ligand (TRAIL) is a member of the TNF family that participates in HIV-1 pathogenesis through the depletion of CD4+ T cells. TRAIL is expressed on the cell membrane of peripheral immune cells and can be cleaved into a soluble, secreted form. The regulation of TRAIL in macrophages during HIV-1 infection is not completely understood. In this study, we investigated the mechanism(s) of TRAIL expression in HIV-1-infected macrophages, an important cell type in HIV-1 pathogenesis. A human monocyte-derived macrophage (MDM) culture system was infected with macrophage-tropic HIV-1_ADA, HIV-1_JR-FL, or HIV-1_BAL strains. TRAIL, predominantly the membrane-bound form, increased following HIV-1 infection. We found that HIV-1 infection also induced interferon regulatory factor (IRF)-1, IRF-7 gene expression and signal transducers and activators of transcription 1 (STAT1) activation. Small interfering RNA knockdown of IRF-1 or IRF-7, but not IRF-3, reduced STAT1 activation and TRAIL expression. Furthermore, the upregulation of IRF-1, IRF-7, TRAIL, and the activation of STAT1 by HIV-1 infection was reduced by the treatment of type I interferon (IFN)-neutralizing antibodies. In addition, inhibition of STAT1 by fludarabine abolished IRF-1, IRF-7, and TRAIL upregulation. We conclude that IRF-1, IRF-7, type I IFNs, and STAT1 form a signaling feedback loop that is critical in regulating TRAIL expression in HIV-1-infected macrophages.

CXCL12 increases human neural progenitor cell proliferation through Akt-1/FOXO3a signaling pathway

CXCL12, a ligand for the chemokine receptor CXCR4, is well known in mediating neural progenitor cell (NPC) migration during neural development. However, the effects of CXCL12 on human NPC proliferation and its associated signaling pathways remain unclear. The transcription factor, FOXO3a, a downstream target of Akt-1, is critical for cell cycle control and may also play an important role in regulating NPC proliferation. In this study, we found that CXCL12 promotes human NPC proliferation as determined by the proliferation marker Ki67 and BrdU incorporation. This CXCL12-mediated NPC proliferation was associated with an increase in Akt-1 and FOXO3a phosphorylation in a time- and dose-dependent manner. The CXCR4 antagonist (T140) or inhibitors for G proteins (Pertussis toxin) and phosphoinositide 3-kinase (PI3K) (LY294002) abolished CXCL12-mediated NPC proliferation and phosphorylation of Akt-1 and FOXO3a. The roles of Akt-1 and FOXO3a in CXCL12-mediated NPC proliferation were further investigated by using adenoviral over-expression in NPCs. Over-expression of dominant-negative Akt-1 or wild-type FOXO3a in NPC abrogated CXCL12-mediated proliferation. These data suggest that CXCL12-mediated NPC proliferation is reliant upon the phosphorylation of Akt-1 and FOXO3a and gives insight to an essential role of CXCL12 in neurogenesis. Understanding this mechanism may facilitate the development of novel therapeutic targets for NPC proliferation during neurogenesis.

Neural progenitor cell death is induced by extracellular ATP via ligation of P2X7 receptor

Neural progenitor cells (NPCs) are capable of self-renewal and differentiation into neurons, astrocytes and oligodendrocytes, and have been used to treat several animal models of CNS disorders. In the present study, we show that the P2X7 purinergic receptor (P2X7R) is present on NPCs. In NPCs, P2X7R activation by the agonists extracellular ATP or benzoyl ATP triggers opening of a non-selective cationic channel. Prolonged activation of P2X7R with these nucleotides leads to caspase independent death of NPCs. P2X7R ligation induces NPC lysis/necrosis demonstrated by cell membrane disruption accompanied with loss of mitochondrial membrane potential. In most cells that express P2X7R, sustained stimulation with ATP leads to the formation of a non-selective pore allowing the entry of solutes up to 900 Da, which are reportedly involved in P2X7R-mediated cell lysis. Surprisingly, activation of P2X7R in NPCs causes cell death in the absence of pore formation. Our data support the notion that high levels of extracellular ATP in inflammatory CNS lesions may delay the successful graft of NPCs used to replace cells and repair CNS damage.

Cellular repair of CNS disorders: an immunological perspective

Cellular repair is a promising strategy for treating central nervous system (CNS) disorders. Several strategies have been contemplated including replacement of neurons or glia that have been lost due to injury or disease, use of cellular grafts to modify or augment the functions of remaining neurons and/or use of cellular grafts to protect neural tissue by local delivery of growth or trophic factors. Depending on the specific disease target, there may be one or many cell types that could be considered for therapy. In each case, an additional variable must be considered--the role of the immune system in both the injury process itself and in the response to incoming cells. Cellular transplants can be roughly categorized into autografts, allografts and xenografts. Despite the immunological privilege of the CNS, allografts and xenografts can elicit activation of the innate and adaptive immune system. In this article, we evaluate the various effects that immune cells and signals may have on the survival, proliferation, differentiation and migration/integration of transplanted cells in therapeutic approaches to CNS injury and disease.

HIV-1-infected and/or immune-activated macrophage-secreted TNF-alpha affects human fetal cortical neural progenitor cell proliferation and differentiation

Neurogenesis, tied to the proliferation, migration and differentiation of neural progenitor cells (NPC) is affected during neurodegenerative diseases, but how neurogenesis is affected during HIV-1 associated dementia (HAD) has not been fully addressed. Here we test the hypothesis that HIV-1-infected and/or immune-activated brain macrophages affect NPC proliferation and differentiation through the regulation of cytokines. We showed that human monocyte-derived macrophages (MDM) conditioned medium (MCM) induces a dose dependent increase in NPC proliferation. Conditioned media from lipopolysaccharide (LPS)-activated MDM (LPS-MCM) or HIV-infected MCM (HIV-MCM) induced a profound increase in NPC proliferation. HIV-infected and LPS-activated MCM (HIV+LPS-MCM) induced the most robust increase in NPC proliferation. Moreover, LPS-MCM and HIV+LPS-MCM decreased beta-III-tubulin and increased GFAP expression, demonstrating an induction of gliogenesis and inhibition of neurogenesis. The increase of NPC proliferation and gliogenesis correlated with increases in production of TNF-alpha by infected/activated MDM. Although both IL-1beta and TNF-alpha induced NPC proliferation and gliogenesis, these effects were only partially abrogated by soluble TNF-alpha receptors R1 and R2 (TNF-R1R2), but not by the IL-1 receptor antagonist (IL-1ra). This indicated that the HIV-1-infected/LPS-activated MCM-mediated effects were, in part, through TNF-alpha. These observations were confirmed in severe combined immunodeficient (SCID) mice with HIV-1 encephalitis (HIVE). In these HIVE mice, NPC injected with HIV-infected MDM showed more astrocyte differentiation and less neuronal differentiation compared to NPC injection alone. These observations demonstrated that HIV-1-infected and immune-activated MDM could affect neurogenesis through induction of NPC proliferation, inhibition of neurogenesis, and activation of gliogenesis.

Survivin and heat shock protein 25/27 colocalize with cleaved caspase-3 in surviving reactive astrocytes following excitotoxicity to the immature brain

Following immature excitotoxic brain damage, distinct patterns of caspase activation have been described in neurons and glial cells. Neuronal cells show activation of the mitochondrial apoptosis pathway, caspase-3 cleavage and apoptotic cell death, while reactive astrocytes show caspase-3 cleavage that is not always correlated with enzymatic protease activity and does not generally terminate in cell death. Accordingly, the aim of the present study was to evaluate the astrocytic colocalization of cleaved caspase-3 and several anti-apoptotic proteins of the inhibitor of apoptosis proteins family (IAPs), such as survivin and cellular inhibitor of apoptosis-2 (cIAP-2), and the heat shock proteins (HSPs) family, Hsp25/27 and Hsc70/Hsp70, which can all prevent caspases from cleaving their substrates. At several survival times ranging from 4 h to 14 days after cortical excitotoxic damage induced by N-methyl-d-aspartate (NMDA) injection at postnatal day 9 in rat pups, single and double immunohistochemical techniques were performed in free floating cryostat sections and sections were analyzed by confocal microscopy. Our results show that survivin and Hsp25/27 are primarily expressed in reactive astrocytes of the damaged cortex and the adjacent white matter. In addition, both molecules strongly colocalize with cleaved caspase-3. Survivin is primarily located in the nucleus, like cleaved caspase-3; while Hsp25/27 is cytoplasmic but very frequently found in cells showing nuclear caspase-3. cIAP-2 was mostly found in damaged neurons but also in some glial scar reactive astrocytes and showed fewer correlation with caspase-3. Hsc70/Hsp70 was only expressed in injured neurons and did not correlate with caspase-3. Thus, we conclude that primarily survivin and Hsp25/27 may participate in the inhibition of cleaved caspase-3 in reactive astrocytes and may be involved in protecting astrocytes after injury.

The signaling and apoptotic effects of TNF-related apoptosis-inducing ligand in HIV-1 associated dementia

HIV-1 Associated Dementia (HAD) develops during progressive HIV-1 infection and is characterized by cognitive impairments, behavioral disorders and potential progressive motor abnormality. Abnormal inflammation within the central nervous system (CNS), activation of macrophage/microglia and involvement of proinflammatory cytokines have been suggested as primary factors in the pathogenesis of HAD. Impairment of neuronal function and neuronal cell death are believed to be the end pathophysiological result of HAD. TNF-related apoptosis-inducing ligand (TRAIL), a member of the TNF family of cytokines, was suggested to participate in apoptotic cell death during HAD. As a death ligand, TRAIL was originally thought to target only tumor cells. TRAIL is not typically present in CNS; however, emerging data show that TRAIL can be induced by immune stimuli on macrophage and microglia, major disease effector cells during HAD. Upregulated TRAIL may then cause neuronal apoptosis through direct interaction with TRAIL receptors on neurons or through macrophage death-mediated release of neurotoxins. In this review, we summarize the pivotal role of TRAIL in HAD and TRAIL-initiated intracellular death cascades that culminate in neuronal apoptosis as observed in HAD.