The scavenger receptor CD36 downmodulates the early inflammatory response while enhancing bacterial phagocytosis during pneumococcal pneumonia.

CD36 is a scavenger receptor that exhibits pleiotropic functions, including adhesion to thrombospondin, inhibition of angiogenesis, transport of long-chain fatty acids, and clearance of apoptotic cells. In addition, it has been implicated in the host immune response because it acts as a coreceptor for TLR2 and plays a role in Staphylococcus aureus infection. However, its role in other Gram-positive bacterial infections is unclear. In this study, using mice deficient in CD36, we sought to examine the role of CD36 in pneumococcal pneumonia, a major cause of morbidity and mortality worldwide. We show that CD36 is expressed on both alveolar macrophages and respiratory epithelial cells. Early in infection, CD36(-/-) mice have an exaggerated inflammatory response compared with wild-type littermate controls. In vitro studies using CD36(-/-) primary cells confirm the enhanced early inflammation in response to S. pneumoniae and its lipoteichoic acid, demonstrate that S. pneumoniae binds to cells via its phosphocholine residues, and suggest a role for CD36 in reducing inflammation induced by the phosphocholine residues of pneumococcal lipoteichoic acid. Later in infection, although CD36(-/-) mice exhibit impaired bacterial clearance, owing to a decreased capacity of CD36(-/-) macrophages to phagocytose S. pneumoniae, minor effects on mortality occur, in comparison with those in wild-type littermate control mice. These data show that CD36 contributes to the pulmonary host response during S. pneumoniae infection by virtue of its ability to act as a phagocytic receptor and as a modulator of the early innate immune response.

Myeloid PTEN promotes inflammation but impairs bactericidal activities during murine pneumococcal pneumonia.

Phosphatidylinositol 3-kinase has been described as an essential signaling component involved in the chemotactic cell influx that is required to eliminate pathogens. At the same time, PI3K was reported to modulate the immune response, thus limiting the magnitude of acute inflammation. The precise role of the PI3K pathway and its endogenous antagonist phosphatase and tensin homolog deleted on chromosome 10 (PTEN) during clinically relevant bacterial infections is still poorly understood. Utilizing mice lacking myeloid cell-specific PTEN, we studied the impact of PTEN on the immune response to Streptococcus pneumoniae. Survival analysis disclosed that PTEN-deficient mice displayed less severe signs of disease and prolonged survival. The inflammatory response to S. pneumoniae was greatly reduced in macrophages in vitro and in vivo. Unexpectedly, neutrophil influx to the lungs was significantly impaired in animals lacking myeloid-cell PTEN, whereas the additional observation of improved phagocytosis by alveolar macrophages lacking PTEN ultimately resulted in unaltered lung CFUs following bacterial infection. Together, the absence of myeloid cell-associated PTEN and consecutively enhanced PI3K activity dampened pulmonary inflammation, reduced neutrophil influx, and augmented phagocytic properties of macrophages, which ultimately resulted in decreased tissue injury and improved survival during murine pneumococcal pneumonia.

Inhibition of leukotriene receptors boosts neural progenitor proliferation.

Neural stem and progenitor cells serve as a reservoir for new neurons in the adult brain throughout lifetime. One of the critical steps determining the net production of new neurons is neural progenitor proliferation, which needs to be tightly controlled. Since inflammation has detrimental effects on neurogenesis and the 5-lipoxygenase/leukotriene pathway is involved in inflammatory processes, we investigated the effects of leukotrienes and montelukast, a small molecule inhibitor of the leukotriene receptors CysLT(1)R and GPR17, on neural stem and progenitor cell proliferation. We demonstrate expression of the leukotriene receptor GPR17 by neural progenitors and by neural stem cells. Stimulation with excess amounts of leukotrienes did not affect progenitor proliferation, whereas blockade of GPR17 with montelukast strongly elevated neural stem and progenitor proliferation, while maintaining their differentiation fate and potential. This effect was associated with increased ERK1/2 phosphorylation suggesting an involvement of the EGF signaling cascade. Based on our results, montelukast and the inhibition of the 5-LOX pathway might be potent candidates for future therapies employing neurogenesis to promote structural and functional improvement in neurodegeneration, neuropsychiatric disease and ageing.

The dark side of BrdU in neural stem cell biology: detrimental effects on cell cycle, differentiation and survival.

5-Bromo-2'-deoxyuridin (BrdU) is frequently used in anaylsis of neural stem cell biology, in particular to label and to fate-map dividing cells. However, up to now, only a few studies have addressed the question as to whether BrdU labeling per se affects the cells to be investigated. Here, we focused on the potential impact of BrdU on neurosphere cultures derived from the adult rat brain and on proliferation of progenitors in vivo. In vitro, neurospheres were pulsed for 48 h with BrdU, and cell proliferation, cell cycle, differentiation, survival and adhesion properties were subsequently analyzed. BrdU inhibited the expansion of neural progenitors as assessed by MTS assay and increased the fraction of cells in the G0/G1-phase of the cell cycle. Moreover, BrdU increased cell death and dose-dependently induced adherence of NPCs. Cell adherence was accompanied by a reduced amount of active matrix-metalloproteinase-2 (MMP-2). Furthermore, BrdU repressed neuronal and oligodendroglial differentiation, whereas astroglial fate was not affected. In contrast to the in vitro situation, BrdU apparently did not influence endogenous proliferation of NPCs or neurogenesis in concentrations that are typically used for labeling of neural progenitors in vivo. Our results reveal so far uncharacterized effects of BrdU on adult NPCs. We conclude that, because of its ubiquitous use in stem cell biology, any potential effect of BrdU of NPCs has to be scrutinized prior to interpretation of data.

TREM-1 activation alters the dynamics of pulmonary IRAK-M expression in vivo and improves host defense during pneumococcal pneumonia.

Triggering receptor expressed on myeloid cells-1 (TREM-1) is an amplifier of TLR-mediated inflammation during bacterial infections. Thus far, TREM-1 is primarily associated with unwanted signs of overwhelming inflammation, rendering it an attractive target for conditions such as sepsis. Respiratory tract infections are the leading cause of sepsis, but the biological role of TREM-1 therein is poorly understood. To determine the function of TREM-1 in pneumococcal pneumonia, we first established TREM-1 up-regulation in infected lungs and human plasma together with augmented alveolar macrophage responsiveness toward Streptococcus pneumoniae. Mice treated with an agonistic TREM-1 Ab and infected with S. pneumoniae exhibited an enhanced early induction of the inflammatory response that was indirectly associated with lower levels of negative regulators of TLR signaling in lung tissue in vivo. Later in infection, TREM-1 engagement altered S. pneumoniae-induced IRAK-M (IL-1R-associated kinase-M) kinetics so as to promote the resolution of pneumonia and remarkably led to an accelerated elimination of bacteria and consequently improved survival. These data show that TREM-1 exerts a protective role in the innate immune response to a common bacterial infection and suggest that caution should be exerted in modulating TREM-1 activity during certain clinically relevant bacterial infections.

Blockade of chloride channels suppresses engulfment of microspheres in the microglial cell line, BV-2.

Microglial cells, monocyte-derived cells in the brain, phagocytose apoptotic and necrotic cells during neurodegenerative processes. As uptake of particles increases cellular volume and swelling-activated chloride channels participate in volume regulation, we investigated the phagocytotic capacity of microglial cells exposed to blockers of swelling-activated chloride channels. We visualized engulfment of hydrophobic polystyrenic microspheres (4 microm in diameter) in the microglial cell line, BV-2, using scanning electron microscopy and confocal laser microscopy. Microspheres instead of apoptotic cells were used because in scanning electron micrographic images, engulfed particles were clearly discriminated from attached ones. Exposure of BV-2 cells to the chloride channel blocker, flufenamic acid (200 microM) or NPPB (200 microM), eliminated uptake of microspheres almost completely. SITS (1 mM), which blocks chloride channels and to some extend K-Cl cotransporters (KCC), had only a moderate inhibiting impact on particle uptake. DIOA, a compound that inhibits KCC as well as chloride channels, did not inhibit particle uptake in BV-2 cells. Osmotic challenge by hypoosmotic saline (60% saline) elicited a swelling-activated chloride channel sensitive to SITS (1 mM) and flufenamic acid (200 microM). Because uptake of particles requires formation of engulfment pseudopodia, we hypothesize that engulfment pseudopodia are initially nothing but local swellings and that activation of swelling-activated chloride channels participates in the formation of these swellings.

Ultraviolet irradiation-induced apoptosis does not trigger nuclear fragmentation but translocation of chromatin from nucleus into cytoplasm in the microglial cell-line, BV-2.

Chromatin condensation, decrease of nuclear volume, and nuclear fragmentation are key features of apoptosis (programmed cell death) in many eukaryotic cells. How chromatin is redistributed in a continuously shrinking nucleus is an intriguing question. To evaluate this interesting spatial problem, we studied the ultrastructural distribution of chromatin in distinct stages of apoptosis using the microglial cell-line, BV-2, as a model and UV irradiation as a trigger of apoptosis. During apoptosis, condensed chromatin accumulated initially at the nuclear periphery and, subsequently, occupied almost the entire nucleus. Surprisingly, nuclei did not fragmentize, but apoptotic cells showed condensed chromatin in the nucleus as well as in the nucleus-attached cytoplasm. During apoptosis, the nuclear envelope dilated and decreased in extension by formation of numerous electron lucent vesicles, which accumulated in the cytoplasm. Furthermore, we observed in BV-2 cells well-known apoptotic features, like increased caspase-3/7 activity and annexin V labeling, as well as a sequence of cell morphological alterations, including cell shrinkage, zeiosis, and formation of apoptotic bodies. Thus, our findings suggest that UV-induced chromatin degradation is not restricted to the nucleus but may also take place in the cytoplasm in BV-2 cells.

Cerebrolysin protects PC12 cells from CoCl2-induced hypoxia employing GSK3ß signaling.

Cerebrolysin (EVER Neuro Pharma GmbH, Austria) is a peptidergic drug indicated for clinical use in stroke, traumatic brain injury and dementia. The therapeutic effect of Cerebrolysin is thought to ensure from its neurotrophic activity, which shares some properties with naturally occurring neurotrophic factors. However, the exact mechanism of action of Cerebrolysin is yet to be fully deciphered. This study aimed to investigate the neuroprotective effect of Cerebrolysin in a widely used in vitro model of hypoxia-induced neuronal cytotoxicity, namely cobalt chloride (CoCl2)-treatment of PC12 cells. CoCl2-cytotoxicity was indicated by a reduced cell-diameter, cell shrinkage, increased pro-apoptotic Caspase-activities and a decreased metabolic activity. Cerebrolysin maintained the cell-diameter of CoCl2-treated naïve PC12 cells, decreased the activation of Caspase 3/7 in CoCl2-stressed naïve PC12 cells and restored the cells' metabolic activity in CoCl2-impaired naïve and differentiated PC12 cells. Cerebrolysin treatment also decreased the levels of superoxide observed after exposure to CoCl2. Investigating the mechanism of action, we could demonstrate that Cerebrolysin application to CoCl2-stressed PC12 cells increased the phosphorylation of GSK3ß, resulting in the inhibition of GSK3ß. This might become clinically relevant for Alzheimer's disease, since GSK3ß activity has been linked to the production of amyloid beta. Taken together, Cerebrolysin was found to have neuroprotective effects in CoCl2-induced cytotoxicity in PC12 cells.

Chroman-like cyclic prenylflavonoids promote neuronal differentiation and neurite outgrowth and are neuroprotective.

Flavonoids target a variety of pathophysiological mechanisms and are therefore increasingly considered as compounds encompassed with therapeutic potentials in diseases such as cancer, diabetes, arteriosclerosis, and neurodegenerative diseases and mood disorders. Hops (Humulus lupulus L.) is rich in flavonoids such as the flavanone 8-prenylnaringenin, which is the most potent phytoestrogen identified so far, and the prenylchalcone xanthohumol, which has potent tumor-preventive, anti-inflammatory and antiviral activities. In the present study, we questioned whether hops-derived prenylflavonoids and synthetic derivatives thereof act on neuronal precursor cells and neuronal cell lines to induce neuronal differentiation, neurite outgrowth and neuroprotection. Therefore, mouse embryonic forebrain-derived neural precursors and Neuro2a neuroblastoma-derived cells were stimulated with the prenylflavonoids of interest, and their potential to activate the promoter of the neuronal fate-specific doublecortin gene and to stimulate neuronal differentiation and neurite outgrowth was analyzed. In this screening, we identified highly "neuroactive" compounds, which we termed "enhancement of neuronal differentiation factors" (ENDFs). The most potent molecule, ENDF1, was demonstrated to promote neuronal differentiation of neural stem cells and neurite outgrowth of cultured dorsal root ganglion neurons and protected neuronal PC12 cells from cobalt chloride-induced as well as cholinergic neurons of the nucleus basalis of Meynert from deafferentation-induced cell death. The results indicate that hops-derived prenylflavonoids such as ENDFs might be powerful molecules to promote neurogenesis, neuroregeneration and neuroprotection in cases of chronic neurodegenerative diseases, acute brain and spinal cord lesion and age-associated cognitive impairments.

WAVE1 mediates suppression of phagocytosis by phospholipid-derived DAMPs.

Clearance of invading pathogens is essential to preventing overwhelming inflammation and sepsis that are symptomatic of bacterial peritonitis. Macrophages participate in this innate immune response by engulfing and digesting pathogens, a process called phagocytosis. Oxidized phospholipids (OxPL) are danger-associated molecular patterns (DAMPs) generated in response to infection that can prevent the phagocytic clearance of bacteria. We investigated the mechanism underlying OxPL action in macrophages. Exposure to OxPL induced alterations in actin polymerization, resulting in spreading of peritoneal macrophages and diminished uptake of E. coli. Pharmacological and cell-based studies showed that an anchored pool of PKA mediates the effects of OxPL. Gene silencing approaches identified the A-kinase anchoring protein (AKAP) WAVE1 as an effector of OxPL action in vitro. Chimeric Wave1(-/-) mice survived significantly longer after infection with E. coli and OxPL treatment in vivo. Moreover, we found that endogenously generated OxPL in human peritoneal dialysis fluid from end-stage renal failure patients inhibited phagocytosis via WAVE1. Collectively, these data uncover an unanticipated role for WAVE1 as a critical modulator of the innate immune response to severe bacterial infections.

Mesenchymal stem cells prime proliferating adult neural progenitors toward an oligodendrocyte fate.

Oligodendrogenesis encompasses lineage specification of neural progenitor cells (NPCs) and differentiation into oligodendrocytes that ultimately culminates in the myelination of central nervous system axons. Each individual process must be tightly regulated by extracellular and cell-intrinsic mechanisms, whose identities are barely understood. We had previously demonstrated that soluble factors derived from rat mesenchymal stem cells (MSCs) induce oligodendrogenesis in differentiating adult NPCs under differentiation conditions. However, since lineage specification predominantly occurs in proliferating progenitors and not necessarily during early differentiation, we investigated if soluble factors derived from MSCs are able to prime NPCs to the oligodendroglial fate already under proliferation conditions. Therefore, we analyzed the effects of a 3 weeks stimulation of adult NPCs under proliferation conditions with conditioned media derived from MSCs (MSC-CM) in terms of cell morphology, proliferation, cell-specific marker expression profile, response to growth factor withdrawal (GFW), cell-lineage restriction, and expression of glial fate determinants. While MSC-CM did not affect the proliferation rate of NPCs, it boosted the formation of 2', 3'-cyclic-nucleotide-3'-phosphodieesterase (CNPase)- and myelin basic protein-expressing oligodendrocytes after GFW, even when cells were exposed to an astrogenic milieu. Moreover, it reinforced the proper development of oligodendrocytes, since it ensured a sustained expression of the functional marker CNPase. Finally, the presence of MSC-CM reduced the anti-oligodendrogenic determinant Id2 in proliferating NPCs, thus increasing the relative proportion of the pro-oligodendrogenic factor Olig2 expression. In summary, MSCs prime proliferating progenitors and, thus, reinforce cell fate choice and accelerate differentiation toward the oligodendrocyte lineage. The present findings underscore the potential use of MSCs in cell therapies for remyelination such as in multiple sclerosis and spinal cord injury. Moreover, they urge the identification of the oligodendrogenic activity(ies) derived from MSCs to develop novel molecular therapies for demyelinating diseases.

Identity, fate and potential of cells grown as neurospheres: species matters.

It is commonly accepted that adult neurogenesis and gliogenesis follow the same principles through the mammalian class. However, it has been reported that neurogenesis might differ between species, even from the same order, like in rodents. Currently, it is not known if neural stem/progenitor cells (NSPCs) from various species differ in their cell identity and potential. NSPCs can be expanded ex vivo as neurospheres (NSph), a model widely used to study neurogenesis in vitro. Here we demonstrate that rat (r) and mouse (m) NSph display different cell identities, differentiation fate, electrophysiological function and tumorigenic potential. Adult rNSph consist mainly of oligodendroglial progenitors (OPCs), which after repeated passaging proliferate independent of mitogens, whereas adult mNSph show astroglial precursor-like characteristics and retain their mitogen dependency. Most of the cells in rNSph express OPC markers and spontaneously differentiate into oligodendrocytes after growth factor withdrawal. Electrophysiological analysis confirmed OPC characteristics. mNSph have different electrophysiological properties, they express astrocyte precursor markers and spontaneously differentiate primarily into astrocytes. Furthermore, rNSph have the potential to differentiate into oligodendrocytes and astrocytes, whereas mNSph are restricted to the astrocytic lineage. The phenotypic differences between rNSph and mNSph were not due to a distinct response to species specific derived growth factors and are probably not caused by autocrine mechanisms. Our findings suggest that NSph derived from adult rat and mouse brains display different cell identities. Thus, results urge for caution when data derived from NSph are extrapolated to other species or to the in vivo situation, especially when aimed towards the clinical use of human NSph.