STAT3 activation and c-FOS expression in the brain following peripheral administration of bacterial DNA

Prognostic and therapeutic potential of STAT3: Opportunities and challenges in targeting HPV-mediated cervical carcinogenesis

Cervical cancer (CaCx) ranks as the fourth most prevalent cancer among women globally. Persistent infection of high-risk human papillomaviruses (HR-HPVs) is major etiological factor associated with CaCx. Signal Transducer and Activator of Transcription 3 (STAT3), a prominent member of the STAT family, has emerged as independent oncogenic driver. It is a target of many oncogenic viruses including HPV. How STAT3 influences HPV viral gene expression or gets affected by HPV is an area of active investigation. A better understanding of host-virus interaction will provide a prognostic and therapeutic window for CaCx control and management. In this comprehensive review, we delve into carcinogenic role of STAT3 in development of HPV-induced CaCx. With an emphasis on fascinating interplay between STAT3 and HPV genome, the review explores the diverse array of opportunities and challenges associated with this field to harness the prognostic and therapeutic potential of STAT3 in CaCx.

Calcitonin Gene-Related Peptide-Induced Phosphorylation of STAT3 in Arcuate Neurons Is a Link in the Metabolic Benefits of Portal Glucose

INTRODUCTION

Intestinal gluconeogenesis (IGN) exerts metabolic benefits in energy homeostasis via the neural sensing of portal glucose.

OBJECTIVE

The aim of this work was to determine central mechanisms involved in the effects of IGN on the control of energy homeostasis.

METHODS

We investigated the effects of glucose infusion into the portal vein, at a rate that mimics IGN, in conscious wild-type, leptin-deficient Ob/Ob and calcitonin gene-related peptide (CGRP)-deficient mice.

RESULTS

We report that portal glucose infusion decreases food intake and plasma glucose and induces in the hypothalamic arcuate nucleus (ARC) the phosphorylation of STAT3, the classic intracellular messenger of leptin signaling. This notably takes place in POMC-expressing neurons. STAT3 phosphorylation does not require leptin, since portal glucose effects are observed in leptin-deficient Ob/Ob mice. We hypothesized that the portal glucose effects could require CGRP, a neuromediator previously suggested to suppress hunger. In line with this hypothesis, neither the metabolic benefits nor the phosphorylation of STAT3 in the ARC take place upon portal glucose infusion in CGRP-deficient mice. Moreover, intracerebroventricular injection of CGRP activates hypothalamic phosphorylation of STAT3 in mice, and CGRP does the same in hypothalamic cells. Finally, no metabolic benefit of dietary fibers (known to depend on the induction of IGN), takes place in CGRP-deficient mice.

CONCLUSIONS

CGRP-induced phosphorylation of STAT3 in the ARC is part of the neural chain determining the hunger-modulating and glucose-lowering effects of IGN/portal glucose.

Circumventricular Organs and Parasite Neurotropism: Neglected Gates to the Brain?

Circumventricular organs (CVOs), neural structures located around the third and fourth ventricles, harbor, similarly to the choroid plexus, vessels devoid of a blood-brain barrier (BBB). This enables them to sense immune-stimulatory molecules in the blood circulation, but may also increase chances of exposure to microbes. In spite of this, attacks to CVOs by microbes are rarely described. It is here highlighted that CVOs and choroid plexus can be infected by pathogens circulating in the bloodstream, providing a route for brain penetration, as shown by infections with the parasites Trypanosoma brucei. Immune responses elicited by pathogens or systemic infections in the choroid plexus and CVOs are briefly outlined. From the choroid plexus trypanosomes can seed into the ventricles and initiate accelerated infiltration of T cells and parasites in periventricular areas. The highly motile trypanosomes may also enter the brain parenchyma from the median eminence, a CVO located at the base of the third ventricle, by crossing the border into the BBB-protected hypothalamic arcuate nuclei. A gate may, thus, be provided for trypanosomes to move into brain areas connected to networks of regulation of circadian rhythms and sleep-wakefulness, to which other CVOs are also connected. Functional imbalances in these networks characterize human African trypanosomiasis, also called sleeping sickness. They are distinct from the sickness response to bacterial infections, but can occur in common neuropsychiatric diseases. Altogether the findings lead to the question: does the neglect in reporting microbe attacks to CVOs reflect lack of awareness in investigations or of gate-opening capability by microbes?

Inflammatory transcription factors as activation markers and functional readouts in immune-to-brain communication

Immune-to-brain communication pathways involve humoral mediators, including cytokines, central modulation by neuronal afferents and immune cell trafficking to the brain. During systemic inflammation these pathways contribute to mediating brain-controlled sickness symptoms including fever. Experimentally, activation of these signaling pathways can be mimicked and studied when injecting animals with pathogen associated molecular patterns (PAMPS). One central component of the brain inflammatory response, which leads, for example, to fever induction, is transcriptional activation of brain cells via cytokines and PAMPS. We and others have studied the spatiotemporal activation and the physiological significance of transcription factors for the induction of inflammation within the brain and the manifestation of fever. Evidence has revealed a role of nuclear factor (NF)κB in the initiation, signal transducer and activator of transcription (STAT)3 in the maintenance and NF-interleukin (IL)6 in the maintenance or even termination of brain-inflammation and fever. Moreover, psychological stressors, such as exposure to a novel environment, leads to increased body core temperature and genomic NF-IL6-activation, suggesting a potential use of NF-IL6-immunohistochemistry as a multimodal brain cell activation marker and a role for NF-IL6 for differential brain activity. In addition, the nutritional status, as reflected by circulating levels of the cytokine-like hormone leptin, influence immune-to-brain communication and age-dependent changes in LPS-induced fever. Overall, transcription factors remain therapeutically important targets for the treatment of brain-inflammation and fever induction during infectious/non-infectious inflammatory and psychological stress. However, the exact physiological role and significance of these transcription factors requires to be further investigated.

Toll-like receptor 9 plays a key role in the autonomic cardiac and baroreflex control of arterial pressure

The crosstalk between the immune and the autonomic nervous system may impact the cardiovascular function. Toll-like receptors are components of the innate immune system and play developmental and physiological roles. Toll-like receptor 9 (TLR9) is involved in the pathogenesis of cardiovascular diseases, such as hypertension and heart failure. Since such diseases are commonly accompanied by autonomic imbalance and lower baroreflex sensitivity, we hypothesized that TLR9 modulates cardiac autonomic and baroreflex control of arterial pressure (AP). Toll-like receptor 9 knockout (TLR9 KO) and wild-type (WT) mice were implanted with catheters into carotid artery and jugular vein and allowed to recover for 3 days. After basal recording of AP, mice received methyl-atropine or propranolol. AP and pulse interval (PI) variability were evaluated in the time and frequency domain (spectral analysis), as well as by multiscale entropy. Spontaneous baroreflex was studied by sequence technique. Behavioral and cardiovascular responses to fear-conditioning stress were also evaluated. AP was similar between groups, but TLR9 KO mice exhibited lower basal heart rate (HR). AP variability was not different, but PI variability was increased in TLR9 KO mice. The total entropy was higher in TLR9 KO mice. Moreover, baroreflex function was found higher in TLR9 KO mice. Atropine-induced tachycardia was increased in TLR9 KO mice, whereas the propranolol-induced bradycardia was similar to WT mice. TLR9 KO mice exhibit increased behavioral and decreased tachycardia responses to fear-conditioning stress. In conclusion, our findings suggest that TLR9 may negatively modulate cardiac vagal tone and baroreflex in mice.

Intraperitoneal and subcutaneous injections of the TLR9 agonist ODN 1668 in rats: brain inflammatory responses are related to peripheral IL-6 rather than interferons

Subcutaneous or intraperitoneal administration of Toll-like receptor (TLR)-9 agonist, ODN 1668 caused moderate fever and anorexia. In comparison to stimulation of other intracellular TLRs, activation of TLR9 did not result in pronounced peripheral induction of interferons, but rather induced interleukin-6. Expression of cytokines (TNFα, IL-1β) and inducible forms of enzymes for prostaglandin E2 synthesis occurred in the brain, in conjunction with a moderate activation of the transcription factors STAT3 and NF-IL6 in brain endothelial cells. The lack of a septic-like state in ODN 1668-treated rats reinforces the therapeutic value of this drug.

Sepsis Associated Encephalopathy

Sepsis associated encephalopathy (SAE) is a common but poorly understood neurological complication of sepsis. It is characterized by diffuse brain dysfunction secondary to infection elsewhere in the body without overt CNS infection. The pathophysiology of SAE is complex and multifactorial including a number of intertwined mechanisms such as vascular damage, endothelial activation, breakdown of the blood brain barrier, altered brain signaling, brain inflammation, and apoptosis. Clinical presentation of SAE may range from mild symptoms such as malaise and concentration deficits to deep coma. The evaluation of cognitive dysfunction is made difficult by the absence of any specific investigations or biomarkers and the common use of sedation in critically ill patients. SAE thus remains diagnosis of exclusion which can only be made after ruling out other causes of altered mentation in a febrile, critically ill patient by appropriate investigations. In spite of high mortality rate, management of SAE is limited to treatment of the underlying infection and symptomatic treatment for delirium and seizures. It is important to be aware of this condition because SAE may present in early stages of sepsis, even before the diagnostic criteria for sepsis can be met. This review discusses the diagnostic approach to patients with SAE along with its epidemiology, pathophysiology, clinical presentation, and differential diagnosis.

Postacute ischemia vascular endothelial growth factor transfer by transferrin-targeted liposomes attenuates ischemic brain injury after experimental stroke in rats

Our objective was to achieve the enhanced delivery of vascular endothelial growth factor (VEGF) to ischemically disordered brain through transferrin-coupled liposomes (Tf-PLs) via intravenous administration, and to observe the effect of Tf-VEGF-PLs on ischemic brain neuroprotection and angiogenesis. Cerebral VEGF overexpression was achieved with Tf-PLs by intravenous injection 48 hr after an acute stroke. β-Galactosidase expression was monitored; saline was injected as a control. The success of postischemic gene transduction was confirmed by β-galactosidase staining and by increased VEGF mRNA and protein in ischemic brain. Vascular density, neurological recovery, and ischemic area calculation were performed to evaluate the effect of Tf-VEGF-PLs. The positive expression of β-galactosidase indirectly indicated that VEGF was successfully delivered into brain by Tf-VEGF-PLs. VEGF mRNA in the Tf-VEGF-PL group 24 hr after injection was significantly higher than in the control group (p < 0.05). Western blot analysis showed that postischemic Tf-VEGF-PLs resulted in increased VEGF protein levels compared with VEGF-PLs and saline-administered rats (p < 0.05) 48 hr after administration. At 21 days after drug injection, we observed a significant decrease in infarct volume and better neurological function in the Tf-VEGF-PL-treated group, compared with the VEGF-PL group. FITC-dextran marking showed increased vascular density in the penumbra of Tf-VEGF-PL-treated hemispheres (245,873.9, number of microvessels per field) compared with that in VEGF-PL-treated hemispheres (139,801.3) or saline-treated hemispheres (102,175.5) (p < 0.05). The remainder of the cerebral blood flow after ischemia in the Tf-VEGF-PL group was significantly more than in the control groups (0.35 vs. 0.29, 0.21; p < 0.05). We conclude that the VEGF gene can be delivered noninvasively into the brain by Tf-VEGF-PLs. Postischemic treatment with Tf-VEGF-PLs effectively promoted neuroprotection and vascular regeneration in the chronic stage of cerebral infarction.

Systemic infection and inflammation in acute CNS injury and chronic neurodegeneration: underlying mechanisms

We have all at some time experienced the non-specific symptoms that arise from being ill following a systemic infection. These symptoms, such as fever, malaise, lethargy and loss of appetite are often referred to as "sickness behavior" and are a consequence of systemically produced pro-inflammatory mediators. These inflammatory mediators signal to the brain, leading to activation of microglial cells, which in turn, signal to neurons to induce adaptive metabolic and behavioral changes. In normal healthy persons this response is a normal part of our defense, to protect us from infection, to maintain homeostasis and causes no damage to neurons. However, in animals and patients with chronic neurodegenerative disease, multiple sclerosis, stroke and even during normal aging, systemic inflammation leads to inflammatory responses in the brain, an exaggeration of clinical symptoms and increased neuronal death. These observations imply that, as the population ages and the number of individuals with CNS disorders increases, relatively common systemic infections and inflammation will become significant risk factors for disease onset or progression. In this review we discuss the underlying mechanisms responsible for sickness behavior induced by systemic inflammation in the healthy brain and how they might be different in individuals with CNS pathology.

The encephalopathy in sepsis

Brain dysfunction is a severe complication of sepsis with an incidence ranging from 9% to 71% that is associated with increased morbidity and mortality. Its diagnosis relies mainly on neurologic examination with clinical manifestations ranging from confusion to coma. An electroencephalogram, somatosensory evoked potentials, and measurement of plasma S-100b protein and neuron-specific enolase can be useful for the detection of brain dysfunction. Brain MRI can identify brain lesions such as cerebral infarction, posterior reversible encephalopathy syndrome, and leukoencephalopathy. The mechanism of sepsis-associated encephalopathy involves inflammatory and non-inflammatory processes that affect endothelial cells, glial cells, and neurons and induce blood-brain barrier breakdown, derangements of intracellular metabolism, and cell death. Specific treatments for sepsis-associated encephalopathy need to be developed. Currently, treatment is mainly the management of sepsis.

Macrophage-activating lipopeptide-2 (MALP-2) induces a localized inflammatory response in rats resulting in activation of brain sites implicated in fever

Macrophage-activating lipopeptide-2 (MALP-2) has been identified as the pathogen-associated molecular pattern of Mycoplasma fermentans, which causes stimulation of the innate immune system through the activation of the heterodimeric Toll-like receptors (TLRs) 2 and 6. Based on the reported protective effects of MALP-2 on healing of skin wounds, the central goal of this study was to evaluate the capacity of MALP-2 to induce a localized inflammatory response in an established model of a subcutaneous air pouch. Injections of MALP-2 into the pouch caused fever and some components of sickness behavior in rats. At the subcutaneous site of localized inflammation, a massive formation of tumor necrosis factor-alpha (TNF), interleukin-6 (IL-6), and prostaglandin E2 (PGE2) could be demonstrated in response to injections of MALP-2. Moderate amounts of IL-6 and PGE2 seemed to enter the systemic circulation of MALP-2-treated rats. The IL-6, which appeared in the blood after injection of MALP-2 into the air pouch was sufficient to cause a direct activation of brain cells in areas which lack a complete blood-brain barrier, namely in the sensory circumventricular organs (sCVOs), the organum vasculosum laminae terminalis (OVLT), the subfornical organ (SFO), and the area postrema (AP). The stimulation of cells at these brain sites was revealed by demonstration of a nuclear translocation of the transcription factor STAT3 (signal transducer and activator of transcription 3). Corresponding to the circulating levels of IL-6, the nuclear STAT3 activation of cells within the sCVOs was much less pronounced after local subcutaneous when compared to systemic treatment with MALP-2. In conclusion, cells within the subcutaneous compartment are activated by the TLR2/6 agonist MALP-2. Fever and sickness behavior induced by injection of MALP-2 into subcutaneous tissue may, in part, be mediated by a spillover of IL-6 from the subcutaneous site of inflammation into the blood to cause activation of brain sites which are implicated in the manifestation of these illness responses.

STAT3 and COX-2 activation in the guinea-pig brain during fever induced by the Toll-like receptor-3 agonist polyinosinic:polycytidylic acid

Intra-arterial injections of synthetic double-stranded RNA (polyinosinic:polycytidylic acid, PIPC) at a dose of 500 microg/kg evoked pronounced fever in guinea-pigs. PIPC-induced fever could be antagonized by treatment with the non-selective cyclooxygenase (COX) inhibitor diclofenac and was, in part, attenuated by the administration of the selective COX-2-inhibitor nimesulide (dose: 5 mg/kg for both COX inhibitors). We further investigated whether direct activation of brain cells during PIPC-induced fever could be demonstrated. Using radioactive in situ hybridization, we demonstrated that treatment with PIPC resulted in an upregulation of COX-2 and interleukin-1 beta mRNA in the guinea-pig brain. Thus, COX-2-specific hybridization signals seemed to be mainly associated with brain blood vessels. Intra-arterial injections of PIPC further induced the pronounced nuclear translocation of the transcription factor STAT3 in the endothelium of various fore- and hindbrain areas and in the meninges. In brain structures that lacked a tight blood-brain barrier, i.e. the sensory circumventricular organs (area postrema, vascular organ of laminae terminalis, subfornical organ), the astrocytes and a population of still undetermined cellular phenotype also showed marked STAT3 activation in response to PIPC. The Toll-like receptor-3 agonist PIPC therefore caused a similar activation of brain cells as that reported for other experimental models of systemic inflammation.

Efficient gene delivery targeted to the brain using a transferrin‐conjugated polyethyleneglycol‐modified polyamidoamine dendrimer

The blood-brain barrier (BBB) poses great difficulties for gene delivery to the brain. To circumvent the BBB, we investigated a novel brain-targeting gene vector based on the nanoscopic high-branching dendrimer, polyamidoamine (PAMAM), in vitro and in vivo. Transferrin (Tf) was selected as a brain-targeting ligand conjugated to PAMAM via bifunctional polyethyleneglycol (PEG), yielding PAMAM-PEG-Tf. UV and nuclear magnetic resonance (NMR) spectroscopy were used to evaluate the synthesis of vectors. The characteristics and biodistribution of gene vectors were evaluated by fluorescent microscopy, flow cytometry, and a radiolabeling method. The transfection efficiency of vector/DNA complexes in brain capillary endothelial cells (BCECs) was evaluated by fluorescent microscopy and determination of luciferase activity. The potency of vector/DNA complexes was evaluated by using frozen sections and measuring tissue luciferase activity in Balb/c mice after i.v. administration. UV and NMR results demonstrated the successful synthesis of PAMAM-PEG-Tf. This vector showed a concentration-dependent manner in cellular uptake study and a 2.25-fold brain uptake compared with PAMAM and PAMAM-PEG in vivo. Transfection efficiency of PAMAM-PEG-Tf/DNA complex was much higher than PAMAM/DNA and PAMAM-PEG/DNA complexes in BCECs. Results of tissue expression experiments indicated the widespread expression of an exogenous gene in mouse brain after i.v. administration. With a PAMAM/DNA weight ratio of 10:1, the brain gene expression of the PAMAM-PEG-Tf/DNA complex was approximately 2-fold higher than that of the PAMAM/DNA and PAMAM-PEG/DNA complexes. These results suggested that PAMAM-PEG-Tf can be exploited as a potential nonviral gene vector targeting to brain via noninvasive administration.

Neural-immune interface in the rat area postrema

The area postrema functions as one interface between the immune system and the brain. Immune cells within the area postrema express immunoreactivity for the pro-inflammatory cytokine, interleukin-1beta following challenge with immune stimulants, including lipopolysaccharide (from bacterial cell walls). As a circumventricular organ, the area postrema accesses circulating immune-derived mediators, but also receives direct primary viscerosensory signals via the vagus nerve. Neurons in the area postrema contribute to central autonomic network neurocircuitry implicated in brain-mediated host defense responses. These experiments were directed toward clarifying relationships between immune cells and neurons in the area postrema, with a view toward potential mechanisms by which they may communicate. We used antisera directed toward markers indicating microglia (CR3/CD11b; OX-42), resident macrophages (CD163; ED-2), or dendritic cell-like phenotypes (major histocompability complex class II; OX-6), in area postrema sections from lipopolysaccharide-treated rats processed for light, laser scanning confocal, and electron microscopy. Lipopolysaccharide treatment induced interleukin-1beta-like immunoreactivity in immune cells that either associated with the vasculature (perivascular cells, a subtype of macrophage) or associated with neuronal elements (dendritic-like, and unknown phenotype). Electron microscopic analysis revealed that some immune cells, including interleukin-1beta-positive cells, evinced membrane apposition with neuronal elements, including dendrites and terminals, that could derive from inputs to the area postrema such as vagal sensory fibers, or intrinsic area postrema neurons. This arrangement provides an anatomical substrate by which immune cells could directly and specifically influence individual neurons in the area postrema, that may support the induction and/or maintenance of brain responses to inflammation.