The angiotensin II receptors type 1 and 2 modulate astrocytes and their crosstalk with microglia and neurons in an in vitro model of ischemic stroke.

BACKGROUND: Astrocytes are the most abundant cell type of the central nervous system and are fundamentally involved in homeostasis, neuroprotection, and synaptic plasticity. This regulatory function of astrocytes on their neighboring cells in the healthy brain is subject of current research. In the ischemic brain we assume disease specific differences in astrocytic acting. The renin-angiotensin-aldosterone system regulates arterial blood pressure through endothelial cells and perivascular musculature. Moreover, astrocytes express angiotensin II type 1 and 2 receptors. However, their role in astrocytic function has not yet been fully elucidated. We hypothesized that the angiotensin II receptors impact astrocyte function as revealed in an in vitro system mimicking cerebral ischemia. Astrocytes derived from neonatal wistar rats were exposed to telmisartan (angiotensin II type 1 receptor-blocker) or PD123319 (angiotensin II type 2 receptor-blocker) under normal conditions (control) or deprivation from oxygen and glucose. Conditioned medium (CM) of astrocytes was harvested to elucidate astrocyte-mediated indirect effects on microglia and cortical neurons. RESULT: The blockade of angiotensin II type 1 receptor by telmisartan increased the survival of astrocytes during ischemic conditions in vitro without affecting their proliferation rate or disturbing their expression of S100A10, a marker of activation. The inhibition of the angiotensin II type 2 receptor pathway by PD123319 resulted in both increased expression of S100A10 and proliferation rate. The CM of telmisartan-treated astrocytes reduced the expression of pro-inflammatory mediators with simultaneous increase of anti-inflammatory markers in microglia. Increased neuronal activity was observed after treatment of neurons with CM of telmisartan- as well as PD123319-stimulated astrocytes. CONCLUSION: Data show that angiotensin II receptors have functional relevance for astrocytes that differs in healthy and ischemic conditions and effects surrounding microglia and neuronal activity via secretory signals. Above that, this work emphasizes the strong interference of the different cells in the CNS and that targeting astrocytes might serve as a therapeutic strategy to influence the acting of glia-neuronal network in de- and regenerative context.

Glia from the central and peripheral nervous system are differentially affected by paclitaxel chemotherapy via modulating their neuroinflammatory and neuroregenerative properties.

Glia are critical players in defining synaptic contacts and maintaining neuronal homeostasis. Both astrocytes as glia of the central nervous system (CNS), as well as satellite glial cells (SGC) as glia of the peripheral nervous system (PNS), intimately interact with microglia, especially under pathological conditions when glia regulate degenerative as well as regenerative processes. The chemotherapeutic agent paclitaxel evokes peripheral neuropathy and cognitive deficits; however, the mechanisms underlying these diverse clinical side effects are unclear. We aimed to elucidate the direct effects of paclitaxel on the function of astrocytes, microglia, and SGCs, and their glia-glia and neuronal-glia interactions. After intravenous application, paclitaxel was present in the dorsal root ganglia of the PNS and the CNS of rodents. In vitro, SGC enhanced the expression of pro-inflammatory factors and reduced the expression of neurotrophic factor NT-3 upon exposure to paclitaxel, resulting in predominantly neurotoxic effects. Likewise, paclitaxel induced a switch towards a pro-inflammatory phenotype in microglia, exerting neurotoxicity. In contrast, astrocytes expressed neuroprotective markers and increasingly expressed S100A10 after paclitaxel exposure. Astrocytes, and to a lesser extent SGCs, had regulatory effects on microglia independent of paclitaxel exposure. Data suggest that paclitaxel differentially modulates glia cells regarding their (neuro-) inflammatory and (neuro-) regenerative properties and also affects their interaction. By elucidating those processes, our data contribute to the understanding of the mechanistic pathways of paclitaxel-induced side effects in CNS and PNS.

Osteopontin regulates proliferation, migration, and survival of astrocytes depending on their activation phenotype.

The glycoprotein osteopontin is highly upregulated in central nervous system (CNS) disorders such as ischemic stroke. Osteopontin regulates cell growth, cell adhesion, homeostasis, migration, and survival of various cell types. Accordingly, osteopontin is considered an essential regulator of regeneration and repair in the ischemic milieu. Astrocytes are the most abundant cells in the CNS and play significant roles in health and disease. Astrocytes are involved in homeostasis, promote neuroprotection, and regulate synaptic plasticity. Upon activation, astrocytes may adopt different phenotypes, termed A1 and A2. The direct effects of osteopontin on astrocytes, especially in distinct activation states, are yet unknown. The current study aimed to elucidate the impact of osteopontin on resting and active astrocytes. We established an inflammatory in vitro model of activated (A1) primary astrocytes derived from neonatal wistar rats by exposure to a distinct combination of proinflammatory cytokines. To model ischemic stroke in vitro, astrocytes were subjected to oxygen and glucose deprivation (OGD) in the presence or absence of osteopontin. Osteopontin modulated the activation phenotype by attenuating A1- and restoring A2-marker expression without compromising the active astrocytes' immunocompetence. Osteopontin promoted the proliferation of active and the migration of resting astrocytes. Following transient OGD, osteopontin mitigated the delayed ongoing death of primary astrocytes, promoting their survival. Data suggest that osteopontin differentially regulates essential functions of resting and active astrocytes and confirm a significant regulatory role of osteopontin in an in vitro ischemia model. Furthermore, the data suggest that osteopontin constitutes a promising target for experimental therapies modulating neuroregeneration and repair.

Developmental HCN channelopathy results in decreased neural progenitor proliferation and microcephaly in mice.

The development of the cerebral cortex relies on the controlled division of neural stem and progenitor cells. The requirement for precise spatiotemporal control of proliferation and cell fate places a high demand on the cell division machinery, and defective cell division can cause microcephaly and other brain malformations. Cell-extrinsic and -intrinsic factors govern the capacity of cortical progenitors to produce large numbers of neurons and glia within a short developmental time window. In particular, ion channels shape the intrinsic biophysical properties of precursor cells and neurons and control their membrane potential throughout the cell cycle. We found that hyperpolarization-activated cyclic nucleotide-gated cation (HCN) channel subunits are expressed in mouse, rat, and human neural progenitors. Loss of HCN channel function in rat neural stem cells impaired their proliferation by affecting the cell-cycle progression, causing G1 accumulation and dysregulation of genes associated with human microcephaly. Transgene-mediated, dominant-negative loss of HCN channel function in the embryonic mouse telencephalon resulted in pronounced microcephaly. Together, our findings suggest a role for HCN channel subunits as a part of a general mechanism influencing cortical development in mammals.

Uncovering an Optic Nerve Sheath Meningioma Using 68Ga-DOTATATE PET/CT.

ABSTRACT: A 56-year-old woman was initially diagnosed with optic neuritis. However, several "red flags" were present: older age at presentation, no multiple sclerosis suspicious findings on MRI, and negative oligoclonal bands. 68Ga-DOTATATE PET/CT confirmed the differential diagnosis of an optic sheath meningioma. Our case stresses the value of the somatostatin receptor ligand PET/CT in patients with suspected optic neuritis if the diagnostic workup does not support immune-mediated pathogenesis.

[Dysphagia in Multiple Sclerosis - an underestimated symptom?] / Dysphagie bei Multipler Sklerose ­ ein unterschätztes Symptom?

BACKGROUND: It is estimated that 240,000 people suffer from multiple sclerosis in Germany. In addition to sensory, motor, vegetative, and neuropsychological functional deficits, dysphagia is a highly relevant and disabling, although not well studied symptom of MS. OBJECTIVES: The purpose of this article is to provide an overview of the scientific background, increase awareness of the symptoms of dysphagia, and to introduce diagnostic tools for its management, overall aiming at alleviating symptoms of dysphagia in persons with MS, and improving their quality of life. METHODS: A structured literature review was conducted of what is currently known on the development, manifestation, diagnosis and treatment options for MS-related dysphagia. Due to the lack of class 1 evidence, in particular for diagnosis and treatment options of dysphagia, also smaller studies or pilot projects were included and discussed in this review. RESULTS: Data from imaging methods such as Flexible Endoscopic Evaluation of Swallowing and Videofluoroscopic Swallowing Evaluation enabled the diagnosis. There was a high variablity in the reported frequency of dysphagia in published studies, largely related to differences in methodology to evaluate the swallowing (from 38 % up to 81 %). Overall, dysphagia as a symptom of multiple sclerosis was underestimated at the patient and the physician level. According to current data from the German MS register, specific treatments were only carried out in 30% of the affected patients.

The impact of hyperpolarization-activated cyclic nucleotide-gated (HCN) and voltage-gated potassium KCNQ/Kv7 channels on primary microglia function.

BACKGROUND: Microglia are essential to maintain cell homeostasis in the healthy brain and are activated after brain injury. Upon activation, microglia polarize towards different phenotypes. The course of microglia activation is complex and depends on signals in the surrounding milieu. Recently, it has been suggested that microglia respond to ion currents, as a way of regulating their activity and function. METHODS AND RESULTS: Under the hypothesis that HCN and KCNQ/Kv7 channels impact on microglia, we studied primary rat microglia in the presence or absence of specific pharmacological blockade or RNA silencing. Primary microglia expressed the subunits HCN1-4, Kv7.2, Kv7.3, and Kv7.5. The expression of HCN2, as well as Kv7.2 and Kv7.3, varied among different microglia phenotypes. The pharmacological blockade of HCN channels by ZD7288 resulted in cell depolarization with slowly rising intracellular calcium levels, leading to enhanced survival and reduced proliferation rates of resting microglia. Furthermore, ZD7288 treatment, as well as knockdown of HCN2 RNA by small interfering RNA, resulted in an attenuation of later microglia activation-both towards the anti- and pro-inflammatory phenotype. However, HCN channel inhibition enhanced the phagocytic capacity of IL4-stimulated microglia. Blockade of Kv7/KCNQ channel by XE-991 exclusively inhibited the migratory capacity of resting microglia. CONCLUSION: These observations suggest that the HCN current contributes to various microglia functions and impacts on the course of microglia activation, while the Kv7/KCNQ channels affect microglia migration. Characterizing the role of HCN channels in microglial functioning may offer new therapeutic approaches for targeted modulation of neuroinflammation as a hallmark of various neurological disorders.

Crosstalk between stressed brain cells: direct and indirect effects of ischemia and aglycemia on microglia.

BACKGROUND: In cerebral ischemia, microglia have a dichotomous role in keeping the balance between pro- and anti-inflammatory mediators to avoid deleterious chronic inflammation and to leverage repair processes. METHODS: We examined functional and inflammatory markers in primary rat microglia in vitro after oxygen-glucose deprivation (OGD) or glucose deprivation (aglycemia). We then investigated the preconditioning effect of OGD or aglycemia upon a subsequent strong inflammatory stimulus, here lipopolysaccharides (LPS). Moreover, an "in vitro brain model" of neurons and glia, differentiated from primary rat neural stem cells, was exposed to OGD or aglycemia. Conditioned medium (CM) of this neuronal/glial co-culture was then used to condition microglia, followed by LPS as a "second hit." RESULTS: OGD or aglycemia at sublethal doses did not significantly affect microglia function, including the expression of inflammatory markers. However, preconditioning with either OGD or aglycemia led to a decreased pro-inflammatory response to a subsequent stimulus with LPS. Interestingly, the anti-inflammatory markers IGF-1 and IL-10 were additionally reduced after such preconditioning, while expression of CD206 remained unaffected. Treatment with CM from the neuronal/glial co-culture alone did not affect the expression of inflammatory markers in microglia. In contrast, treatment with CM increased the expression of both pro- and anti-inflammatory markers in microglia upon a second hit with LPS. Interestingly, this effect could be attenuated in microglia treated with CM from neuronal/glia co-cultures preconditioned with OGD or aglycemia. CONCLUSIONS: Data suggest specific and distinct microglia signatures in response to metabolic stress. While metabolic stress directly and indirectly applied to microglia did not mitigate their subsequent response to inflammation, preconditioning with metabolic stress factors such as OGD and aglycemia elicited a decreased inflammatory response to a subsequent inflammation stimulus.

Transcranial Current Stimulation Alters the Expression of Immune-Mediating Genes.

Despite its extensive use in clinical studies, the molecular mechanisms underlying the effects of transcranial direct current stimulation (tDCS) remain to be elucidated. We previously described subacute effects of tDCS on immune- and stem cells in the rat brain. To investigate the more immediate effects of tDCS regulating those cellular responses, we treated rats with a single session of either anodal or cathodal tDCS, and analyzed the gene expression by microarray; sham-stimulated rats served as control. Anodal tDCS increased expression of several genes coding for the major histocompatibility complex I (MHC I), while cathodal tDCS increased the expression of the immunoregulatory protein osteopontin (OPN). We confirmed the effects of gene upregulation by immunohistochemistry at the protein level. Thus, our data show a novel mechanism for the actions of tDCS on immune- and inflammatory processes, providing a target for future therapeutic studies.

Substrate elasticity induces quiescence and promotes neurogenesis of primary neural stem cells-A biophysical in vitro model of the physiological cerebral milieu.

In the brain, neural stem cells (NSC) are tightly regulated by external signals and biophysical cues mediated by the local microenvironment or "niche." In particular, the influence of tissue elasticity, known to fundamentally affect the function of various cell types in the body, on NSC remains poorly understood. We, accordingly, aimed to characterize the effects of elastic substrates on critical NSC functions. Primary rat NSC were grown as monolayers on polydimethylsiloxane- (PDMS-) based gels. PDMS-coated cell culture plates, simulating the physiological microenvironment of the living brain, were generated in various degrees of elasticity, ranging from 1 to 50 kPa; additionally, results were compared with regular glass plates as usually used in cell culture work. Survival of NSC on the PDMS-based substrates was unimpaired. The proliferation rate on 1 kPa PDMS decreased by 45% compared with stiffer PMDS substrates of 50 kPa (p < 0.05) whereas expression of cyclin-dependent kinase inhibitor 1B/p27Kip1 increased more than two fold (p < 0.01), suggesting NSC quiescence. NSC differentiation was accelerated on softer substrates and favored the generation of neurons (42% neurons on 1 kPa PDMS vs. 25% on 50 kPa PDMS; p < 0.05). Neurons generated on 1 kPa PDMS showed 29% longer neurites compared with those on stiffer PDMS substrates (p < 0.05), suggesting optimized neuronal maturation and an accelerated generation of neuronal networks. Data show that primary NSC are significantly affected by the mechanical properties of their microenvironment. Culturing NSC on a substrate of brain-like elasticity keeps them in their physiological, quiescent state and increases their neurogenic potential.

The plasticity of primary microglia and their multifaceted effects on endogenous neural stem cells in vitro and in vivo.

BACKGROUND: Microglia-the resident immune cells of the brain-are activated after brain lesions, e.g., cerebral ischemia, and polarize towards a classic "M1" pro-inflammatory or an alternative "M2" anti-inflammatory phenotype following characteristic temporo-spatial patterns, contributing either to secondary tissue damage or to regenerative responses. They closely interact with endogenous neural stem cells (NSCs) residing in distinct niches of the adult brain. The current study aimed at elucidating the dynamics of microglia polarization and their differential effects on NSC function. RESULTS: Primary rat microglia in vitro were polarized towards a M1 phenotype by LPS, or to a M2 phenotype by IL4, while simultaneous exposure to LPS plus IL4 resulted in a hybrid phenotype expressing both M1- and M2-characteristic markers. M2 microglia migrated less but exhibit higher phagocytic activity than M1 microglia. Defined mediators switched microglia from one polarization state to the other, a process more effective when transforming M2 microglia towards M1 than vice versa. Polarized microglia had differential effects on the differentiation potential of NSCs in vitro and in vivo, with M1 microglia promoting astrocytogenesis, while M2 microglia supported neurogenesis. Regardless of their polarization, microglia inhibited NSC proliferation, increased NSC migration, and accelerated NSC differentiation. CONCLUSION: Overall, this study shed light on the complex conditions governing microglia polarization and the effects of differentially polarized microglia on critical functions of NSCs in vitro and in vivo. Refining the understanding of microglia activation and their modulatory effects on NSCs is likely to facilitate the development of innovative therapeutic concepts supporting the innate regenerative capacity of the brain.

Osteopontin directly modulates cytokine expression of primary microglia and increases their survival.

Osteopontin (OPN) is constitutively expressed in the brain and upregulated during neuroinflammation, e.g., focal cerebral ischemia. In OPN-deficient mice, microglia are deregulated after ischemia, but specific OPN-effects on microglia remain elusive. Primary microglia were cultured in the presence or absence of OPN. The survival of microglia under stress conditions was dose-dependently increased by OPN. Lipopolysaccharides (LPS)-induced release of nitric oxide (NO), TNF-α, and IL-6, as well as expression of inducible Nitric Oxide Synthase (iNOS), were attenuated by OPN. Data suggest that OPN modulates microglia function by shifting their inflammatory profile towards a neutral anti-inflammatory phenotype.

Minocycline mitigates the gliogenic effects of proinflammatory cytokines on neural stem cells.

Mobilizing endogenous neural stem cells (NSCs) in the adult brain is designed to enhance the brain's regenerative capacity after cerebral lesions, e.g., as a result of stroke. Cerebral ischemia elicits neuroinflammatory processes affecting NSCs in multiple ways, the precise mechanisms of which currently remain elusive. An inhibitory effect of minocycline on microglia activation, a hallmark of postischemic neuroinflammation, has already been demonstrated in clinical trials, showing minocycline to be safe and potentially effective in ischemic stroke. Here we investigate the direct effects of minocycline and of proinflammatory cytokines on the differentiation potential of NSCs in vitro and in vivo. Primary fetal rat NSCs were treated with minocycline plus a combination of the proinflammatory cytokines tumor necrosis factor-α, interleukin 1ß, and interleukin 6. The differentiation fate of NSCs was assessed immunocytochemically. To investigate the effects of minocycline and inflammation in vivo, minocycline or lipopolysaccharides were injected intraperitoneally into adult rats, with subsequent immunohistochemistry. Minocycline alone did not affect the differentiation potential of NSCs in vivo or in vitro. In contrast, proinflammatory cytokines accelerated the differentiation of NSCs, promoting an astrocytic fate while inhibiting neurogenesis in vitro and in vivo. It is interesting to note that minocycline counteracted this cytokine-induced rapid astrocytic differentiation and restored the neurogenic and oligodendrogliogenic potential of NSCs. Data suggest that minocycline antagonizes the rapid glial differentiation induced by proinflammatory cytokines following cerebral ischemia but without having a direct effect on the differentiation potential of NSCs. Thus, minocycline constitutes a promising drug for stroke research, counteracting the detrimental effects of postischemic neuroinflammation in multiple ways.