Iron deposits in the chronically inflamed central nervous system and contributes to neurodegeneration

Neurodegenerative disorders are characterized by the presence of inflammation in areas with neuronal cell death and a regional increase in iron that exceeds what occurs during normal aging. The inflammatory process accompanying the neuronal degeneration involves glial cells of the central nervous system (CNS) and monocytes of the circulation that migrate into the CNS while transforming into phagocytic macrophages. This review outlines the possible mechanisms responsible for deposition of iron in neurodegenerative disorders with a main emphasis on how iron-containing monocytes may migrate into the CNS, transform into macrophages, and die out subsequently to their phagocytosis of damaged and dying neuronal cells. The dying macrophages may in turn release their iron, which enters the pool of labile iron to catalytically promote formation of free-radical-mediated stress and oxidative damage to adjacent cells, including neurons. Healthy neurons may also chronically acquire iron from the extracellular space as another principle mechanism for oxidative stress-mediated damage. Pharmacological handling of monocyte migration into the CNS combined with chelators that neutralize the effects of extracellular iron occurring due to the release from dying macrophages as well as intraneuronal chelation may denote good possibilities for reducing the deleterious consequences of iron deposition in the CNS.     

Clearance of cerebral Aβ in Alzheimer’s disease: reassessing the role of microglia and monocytes

Deficiency in cerebral amyloid β-protein (Aβ) clearance is implicated in the pathogenesis of the common late-onset forms of Alzheimer’s disease (AD). Accumulation of misfolded Aβ in the brain is believed to be a net result of imbalance between its production and removal. This in turn may trigger neuroinflammation, progressive synaptic loss, and ultimately cognitive decline. Clearance of cerebral Aβ is a complex process mediated by various systems and cell types, including vascular transport across the blood–brain barrier, glymphatic drainage, and engulfment and degradation by resident microglia and infiltrating innate immune cells. Recent studies have highlighted a new, unexpected role for peripheral monocytes and macrophages in restricting cerebral Aβ fibrils, and possibly soluble oligomers. In AD transgenic (ADtg) mice, monocyte ablation or inhibition of their migration into the brain exacerbated Aβ pathology, while blood enrichment with monocytes and their increased recruitment to plaque lesion sites greatly diminished Aβ burden. Profound neuroprotective effects in ADtg mice were further achieved through increased cerebral recruitment of myelomonocytes overexpressing Aβ-degrading enzymes. This review summarizes the literature on cellular and molecular mechanisms of cerebral Aβ clearance with an emphasis on the role of peripheral monocytes and macrophages in Aβ removal.     

Netrins and netrin receptorsRID="†"ID="†" Review

The formation of precise connections between neurons and their targets during development is dependent on extracellular guidance cues that allow growing axons to navigate to their targets. One family of such guidance molecules. conserved across all species examined, is that of the netrin/UNC-6 proteins. Netrins act to both attract and repel the growing axons of a broad range of neuronal cell types during development and are also involved in controling neuronal cell migration. These actions are mediated by specific receptor complexes containing either the colorectal cancer (DCC) or neogenin protein, in the case of the attractive receptor, or UNC-5-related proteins, in the case of the repellent receptor. Recent work has identified a key role for intracellular cyclic nucleotide levels in regulating the nature of the response of the growing axon to netrins as either attractive or repulsive. Netrin-DCC signaling has also been shown to regulate cell death in epithelial cells in vitro, raising the interesting possibility that netrins may also regulate cell death in the developing nervous system.     

Regulation of nicotinic acetylcholine receptors by tyrosine kinases in the peripheral and central nervous system: same players, different roles

Nicotinic acetylcholine receptors (nAChRs) exist in many subtypes and are found in the peripheral and central nervous system where they mediate or modulate synaptic transmission. We review how tyrosine phosphorylation and kinases regulate muscle and neuronal nAChRs. Interestingly, although some of the same kinase players interact with the various receptor subtypes, the functional consequences are different. While concerted action of MuSK, Abl- and Src-family kinases (SFKs) regulates the synaptic distribution of nAChRs at the neuromuscular junction, SFKs activate heteromeric neuronal nAChRs in adrenal chromaffin cells, thereby enhancing catecholamine secretion. In contrast, the activity of homomeric neuronal nAChRs, as found in the hippocampus, is negatively regulated by tyrosine phosphorylation and SFKs. It appears that tyrosine kinases provide the means to regulate all nAChRs; but the functional consequences, even those caused by the same kinase family, are specific for each receptor subtype and location. Received 21 February 2006; received after revision 24 July 2006; accepted 30 August 2006     

Actin dynamics in the regulation of endothelial barrier functions and neutrophil recruitment during endotoxemia and sepsis

Sepsis is a leading cause of death worldwide. Increased vascular permeability is a major hallmark of sepsis. Dynamic alterations in actin fiber formation play an important role in the regulation of endothelial barrier functions and thus vascular permeability. Endothelial integrity requires a delicate balance between the formation of cortical actin filaments that maintain endothelial cell contact stability and the formation of actin stress fibers that generate pulling forces, and thus compromise endothelial cell contact stability. Current research has revealed multiple molecular pathways that regulate actin dynamics and endothelial barrier dysfunction during sepsis. These include intracellular signaling proteins of the small GTPases family (e.g., Rap1, RhoA and Rac1) as well as the molecules that are directly acting on the actomyosin cytoskeleton such as myosin light chain kinase and Rho kinases. Another hallmark of sepsis is an excessive recruitment of neutrophils that also involves changes in the actin cytoskeleton in both endothelial cells and neutrophils. This review focuses on the available evidence about molecules that control actin dynamics and regulate endothelial barrier functions and neutrophil recruitment. We also discuss treatment strategies using pharmaceutical enzyme inhibitors to target excessive vascular permeability and leukocyte recruitment in septic patients.     

The role of VEGF receptors in angiogenesis; complex partnerships

Vascular endothelial growth factors (VEGFs) regulate blood and lymphatic vessel development and homeostasis but also have profound effects on neural cells. VEGFs are predominantly produced by endothelial, hematopoietic and stromal cells in response to hypoxia and upon stimulation with growth factors such as transforming growth factors, interleukins or platelet-derived growth factor. VEGFs bind to three variants of type III receptor tyrosine kinases, VEGF receptor 1, 2 and 3. Each VEGF isoform binds to a particular subset of these receptors giving rise to the formation of receptor homo- and heterodimers that activate discrete signaling pathways. Signal specificity of VEGF receptors is further modulated upon recruitment of coreceptors, such as neuropilins, heparan sulfate, integrins or cadherins. Here we summarize the knowledge accumulated since the discovery of these proteins more than 20 years ago with the emphasis on the signaling pathways activated by VEGF receptors in endothelial cells during cell migration, growth and differentiation. Received 15 September 2005; received after revision 11 November; accepted 24 November 2005     

Response of vascular mesenchymal stem/progenitor cells to hyperlipidemia

Hyperlipidemia is a risk factor for atherosclerosis that is characterized by lipid accumulation, inflammatory cell infiltration, and smooth muscle cell proliferation. It is well known that hyperlipidemia is a stimulator for endothelial dysfunction and smooth muscle cell migration during vascular disease development. Recently, it was found that vessel wall contains a variable number of mesenchymal stem cells (MSCs) that are quiescent in physiological conditions, but can be activated by a variety of stimuli, e.g., increased lipid level or hyperlipidemia. Vascular MSCs displayed characteristics of stem cells which can differentiate into several types of cells, e.g., smooth muscle cells, adipocytic, chondrocytic, and osteocytic lineages. In vitro, lipid loading can induce MSC migration and chemokines secretion. After MSC migration into the intima, they play an essential role in inflammatory response and cell accumulation during the initiation and progression of atherosclerosis. In addition, MSC transplantation has been explored as a therapeutic approach to treat atherosclerosis in animal models. In this review, we aim to summarize current progress in characterizing the identity of vascular MSCs and to discuss the mechanisms involved in the response of vascular stem/progenitor cells to lipid loading, as well as to explore therapeutic strategies for vascular diseases and shed new light on regenerative medicine.     

Galectins in cell growth and apoptosis

Fourteen members of the galectin family, proteins with conserved carbohydrate-recognition domains that bind β-galactoside, have been cloned and more are expected to be discovered in the near future. Many aspects of galectin biology have been thoroughly explored, and functional studies have implicated these proteins in cell growth, differentiation and apoptosis, in addition to cell adhesion, chemoattraction and cell migration. In some cases a galectin can either promote or suppress cell growth, depending on the cell types and doses used. Galectin-3 is the only member known so far to inhibit apoptosis, while galectin-1, -7 and -9 promote this cellular process. Galectins can act either extracellularly or intracellularly to exert effects on cell growth and apoptosis. RID="*" ID="*"Corresponding author.     

(—)-Epigallocatechin-3-gallate interferes with mast cell adhesiveness, migration and its potential to recruit monocytes

Mast cells are multipotent effector cells of the immune system. They are able to induce and enhance angiogenesis via multiple pathways. (-)-Epigallocatechin-3-gallate (EGCG), a major component of green tea and a putative chemopreventive agent, was reported to inhibit tumor invasion and angiogenesis, processes that are essential for tumor growth and metastasis. Using the human mast cell line HMC-1 and commercial cDNA macroarrays, we evaluated the effect of EGCG on the expression of angiogenesis-related genes. Our data show that among other effects, EGCG treatment reduces expression of two integrins (alpha5 and beta3) and a chemokine (MCP1), resulting in a lower adhesion of mast cells associated with a decreased potential to produce signals eliciting monocyte recruitment. These effects on gene expression levels are functionally validated by showing inhibitory effects in adhesion, aggregation, migration and recruitment assays.     

Integrin and microtubule crosstalk in the regulation of cellular processes

Integrins engage components of the extracellular matrix, and in collaboration with other receptors, regulate signaling cascades that impact cell behavior in part by modulating the cell’s cytoskeleton. Integrins have long been known to function together with the actin cytoskeleton to promote cell adhesion, migration, and invasion, and with the intermediate filament cytoskeleton to mediate the strong adhesion needed for the maintenance and integrity of epithelial tissues. Recent studies have shed light on the crosstalk between integrin and the microtubule cytoskeleton. Integrins promote microtubule nucleation, growth, and stabilization at the cell cortex, whereas microtubules regulate integrin activity and remodeling of adhesion sites. Integrin-dependent stabilization of microtubules at the cell cortex is critical to the establishment of apical–basal polarity required for the formation of epithelial tissues. During cell migration, integrin-dependent microtubule stabilization contributes to front–rear polarity, whereas microtubules promote the turnover of integrin-mediated adhesions. This review focuses on this interdependent relationship and its impact on cell behavior and function.     

Reverse transendothelial cell migration in inflammation: to help or to hinder?

The endothelium provides a strong barrier separating circulating blood from tissue. It also provides a significant challenge for immune cells in the bloodstream to access potential sites of infection. To mount an effective immune response, leukocytes traverse the endothelial layer in a process known as transendothelial migration. Decades of work have allowed dissection of the mechanisms through which immune cells gain access into peripheral tissues, and subsequently to inflammatory foci. However, an often under-appreciated or potentially ignored question is whether transmigrated leukocytes can leave these inflammatory sites, and perhaps even return across the endothelium and re-enter circulation. Although evidence has existed to support “reverse” transendothelial migration for a number of years, it is only recently that mechanisms associated with this process have been described. Here we review the evidence that supports both reverse transendothelial migration and reverse interstitial migration within tissues, with particular emphasis on some of the more recent studies that finally hint at potential mechanisms. Additionally, we postulate the biological significance of retrograde migration, and whether it serves as an additional mechanism to limit pathology, or provides a basis for the dissemination of systemic inflammation.     

O death where is thy sting? Immunologic tolerance to apoptotic self

In higher organisms, innate scavenging cells maintain physiologic homeostasis by removal of the billions of apoptotic cells generated on a daily basis. Apoptotic cell removal requires efficient recognition and uptake by professional and non-professional phagocytic cells, which are governed by an array of soluble and apoptotic cell-integral signals resulting in immunologically silent clearance. While apoptosis is associated with profound suppression of adaptive and innate inflammatory immunity, we have only begun to scratch the surface in understanding how immunologic tolerance to apoptotic self manifest at either the molecular or cellular level. In the last 10 years, data has emerged implicating professional phagocytes, most notably stromal macrophages and CD8α⁺CD103⁺ dendritic cells, as critical in initiation of the regulatory cascade that will ultimately lead to long-term whole-animal immune tolerance. Importantly, recent work by our lab and others has shown that alterations in apoptotic cell perception by the innate immune system either by removal of critical phagocytic sentinels in secondary lymphoid organs or blockage of immunosuppressive pathways leads to pronounced inflammation with a breakdown of tolerance towards self. This challenges the paradigm that apoptotic cells are inherently immunosuppressive, suggesting that apoptotic cell tolerance is a “context-dependent” event.     

Protective effects of hsp70 in inflammation

Inflammation results from the recruitement to a given tissue or organ and the activation of leucocytes, among which the monocytes-macrophages play a major role. These phagocytic cells produce high levels of reactive oxygen species (ROS) as well as cytokines. Whereas both ROS and cytokines have the potential to regulate the expression of heat shock (HS)/stress proteins (HSP), it appears that these proteins in turn have the ability to protect cells and tissues from the deleterious effects of inflammation. The mechanisms by which such protection occurs include prevention of ROS-induced DNA strand breaks and lipid peroxidation as well as protection from mitochondrial structure and function. In vivo, HS protects organs against a number of lesions associated with the increased production of ROS and/or cytokines. In an animal model for adult respiratory distress syndrome, an acute pulmonary inflammatory condition, HS completely prevented mortality. HSP (hsp70 in particular) may also exert protective effects in the immune system by contributing to the processing and presentation of bacterial and tumoral antigens. The analysis of the expression of hsp70 may prove of diagnostic and prognostic value in inflammatory conditions and therapeutical applications are being considered.     

Leukocyte recruitment in atherosclerosis: Potential targets for therapeutic approaches?

Atherosclerosis is a complex inflammatory disease involving cellular migration and interaction. Vascular injury in response to different cardiovascular risk factors enhances endothelial dysfunction, which in turn promotes the expression of inflammatory markers and transendothelial leukocyte migration. Recruitment of leukocytes from the blood stream into the vessel intima is a crucial step for the development of the disease. Recent findings have highlighted the role of chemokines, chemokine receptors, adhesion molecules, and gap junctions in this process by acting as chemoattractant, adhesive, or intercellular communication molecules. In this short review, we summarize new data concerning the different steps from leukocyte arrest to transendothelial migration and discuss potential new therapeutic approaches concerning these processes. Received 15 March 2006; received after revision 19 May 2006; accepted 13 June 2006     

Bioassay for hamster macrophage chemotaxis: application to study particle-lung interactions

Attraction of lung macrophages to particle deposition sites has been demonstrated in different animal species. We reported a threefold increase of the number of macrophages to occur within 40 min after polystyrene particle deposition in hamster airways [Geiser et al. (1994) Am. J. Respir. Cell Mol. Biol. 160: 594–603]. Complement-derived chemotactic activity is one of the mechanisms postulated for macrophage recruitment. It was the aim of this study to test whether complement-derived chemotactic activity is involved in the rapid recruitment of macrophages to the site of deposited polystyrene particles in hamster airways. We first developed an in vitro cell migration assay for hamster macrophages to assess complement-derived chemotaxis. Second, the bronchoalveolar lavage fluids (BALF) of four hamsters that had inhaled aerosols of polystyrene microspheres were tested for chemotactic activity by this bioassay and compared with BALF of four sham-exposed hamsters. Chemotactic response of macrophages was found toward complement-activated hamster serum, whereas macrophage migration was not increased toward BALF of particle and sham-exposed hamsters. In contrast, macrophage migration to BALF of both groups was reduced by 1.6-fold. Thus, the stimulus for macrophage recruitment to the site of deposited polystyrene particles in hamster airways could not be demonstrated using this bioassay. Received 10 September 1997; received after revision 24 November 1997; accepted 10 December 1997     

Myosin regulation in the migration of tumor cells and leukocytes within a three-dimensional collagen matrix

The migration of cells is a complex regulatory process which results in the generation of motor forces through the reorganization of the cytoskeleton. Here we present a comparative study of the expression and involvement of myosin in the regulation of the physiological migration of leukocytes and the pathological migration of tumor cells. We show that the involvement of myosin in the migration is distinct in these two cell types. In leukocytes, the activity of non-muscle myosin II is essential for both the spontaneous (matrix-induced) migration and the migration induced by ligands to G protein-coupled receptors, i.e. chemokines and neurotransmitters. In contrast, spontaneous tumor cell migration is largely independent of non-muscle myosin II activity, whereas the norepinephrine-induced migration is completely inhibited by either direct inhibition of non-muscle myosin II or of the kinases phosphorylating the myosin light chain, namely ROCK or the calcium/calmodulin-dependent myosin light-chain kinase.Received 31 August 2004; accepted 26 October 2004     

Inhibition of SRC family kinases facilitates anti-CTLA4 immunotherapy in head and neck squamous cell carcinoma

The immune system plays a critical role in the establishment, development, and progression of head and neck squamous cell carcinoma (HNSCC). As treatment with single-immune checkpoint agent results in a lower response rate in patients, it is important to investigate new strategies to maintain favorable anti-tumor immune response. Herein, the combination immunotherapeutic value of CTLA4 blockade and SFKs inhibition was assessed in transgenic HNSCC mouse model. Our present work showed that tumor growth was not entirely controlled when HNSCC model mice were administered anti-CTLA4 chemotherapeutic treatment. Moreover, it was observed that Src family kinases (SFKs) were hyper-activated and lack of anti-tumor immune responses following anti-CTLA4 chemotherapeutic treatment. We hypothesized that activation of SFKs is a mechanism of anti-CTLA4 immunotherapy resistance. We, therefore, carried out combined drug therapy using anti-CTLA4 mAbs and an SFKs’ inhibitor, dasatinib. As expected, dasatinib and anti-CTLA4 synergistically inhibited tumor growth in Tgfbr1/Pten 2cKO mice. Furthermore, dasatinib and anti-CTLA4 combined to reduce the number of myeloid-derived suppressor cells and Tregs, increasing the CD8⁺ T cell-to-Tregs ratio. We also found that combining dasatinib with anti-CTLA4 therapy significantly attenuated the expression of p-STAT3^Y705 and Ki67 in tumoral environment. These results suggest that combination therapy with SFKs inhibitors may be a useful therapeutic approach to increase the efficacy of anti-CTLA4 immunotherapy in HNSCC.     

Neutrophilic granulocytosis following lead acetate in female mice

Summary Lead induces an abrupt neutrophilic granulocytosis with the peak response detected 4 days after treatment. Using the incorporation of tritiated thymidine as an index of neutrophil production, autoradiographic analysis revealed that only about 16% of the total neutrophil increase is associated with a stimulatory effect on production. The remainder of the increase appears to be linked to the panhistotoxic action of lead, promoting migration of neutrophils from reserve sites in the wake of tissue damage.     

Dietary vitamin E does not protect from endotoxin-induced hepatic microvascular dysfunction

Starting from the concept that lipopolysaccharide (LPS)-associated hepatotoxicity involves the action of reactive oxygen species, the present study was conducted to test whether vitamin E, a lipophilic antioxidant, prevents LPS-induced hepatic microvascular dysfunction and liver injury. Fifty-two rats were divided into three groups and fed diets containing 0 (n=16), 75 (n=18) or 8000 mg (n=18) α-tocopherol acetate/kg food for four weeks. At 1 h and 6 h after intravenous LPS-exposure (10 mg/kg E. coli LPS) hepatic microvascular response and liver injury were assessed by the analysis of Kupffer cell phagocytic activity, leukocyte-endothelial cell interaction and nutritive sinusoidal perfusion (intravital fluorescence epi- illumination technique) as well as bile flow, serum liver enzyme activities and tissue histomorphology. In animals fed with 75 mg vitamin E/kg (standard diet), LPS caused hepatic Kupffer cell activation (increased phagocytic activity) and hepatic microvascular leukocyte activation, with stasis in sinusoids and adherence in postsinusoidal venules (1 h) followed by leukocytic infiltration into tissue (6 h) and progredient sinusoidal perfusion failure (6 h). Hepatic microvascular injury was accompanied by reduced bile flow and enhanced liver enzyme release. Vitamin E-enriched diet (8000 mg/kg) and even vitamin E-deficient diet did not significantly affect LPS-induced hepatic microvascular cell activation and perfusion failure. Thus, we conclude, that vitamin E is not effective to protect from endotoxin-induced hepatic microvascular dysfunction. Received 7 November 1996; received after revision 30 December 1996; accepted 20 January 1997     

Neutrophilic granulocytosis following lead acetate in female mice

Lead induces an abrupt neutrophilic granulocytosis with the peak response detected 4 days after treatment. Using the incorporation of tritiated thymidine as an index of neutrophil production, autoradiographic analysis revealed that only about 16% of the total neutrophil increase is associated with a stimulatory effect on production. The remainder of the increase appears to be linked to the panhistotoxic action of lead, promoting migration of neutrophils from reserve sites in the wake of tissue damage.