The subventricular zone releases factors which can be protective in oxygen/glucose deprivation-induced cortical damage: an organotypic study

Perivascular invasion of primary human glioblastoma cells in organotypic human brain slices: human cells migrating in human brain

INTRODUCTION

Glioblastoma (GBM) is an aggressive primary brain cancer. Lack of effective therapy is related to its highly invasive nature. GBM invasion has been studied with reductionist systems that do not fully recapitulate the cytoarchitecture of the brain. We describe a human-derived brain organotypic model to study the migratory properties of GBM IDH-wild type ex vivo.

METHODS

Non-tumor brain samples were obtained from patients undergoing surgery (n = 7). Organotypic brain slices were prepared, and green fluorescent protein (GFP)-labeled primary human GBM IDH-wild type cells (GBM276, GBM612, GBM965) were placed on the organotypic slice. Migration was evaluated via microscopy and immunohistochemistry.

RESULTS

After placement, cells migrated towards blood vessels; initially migrating with limited directionality, sending processes in different directions, and increasing their speed upon contact with the vessel. Once merged, migration speed decreased and continued to decrease with time (p < 0.001). After perivascular localization, migration is limited along the blood vessels in both directions. The percentage of cells that contact blood vessels and then continue to migrate along the vessel was 92.5% (- 3.9/ + 2.9)% while the percentage of cells that migrate along the blood vessel and leave was 7.5% (- 2.9/ + 3.9) (95% CI, Clopper-Pearson (exact); n = 256 cells from six organotypic cultures); these percentages are significantly different from the random (50%) null hypothesis (z = 13.6; p < 10-7). Further, cells increase their speed in response to a decrease in oxygen tension from atmospheric normoxia (20% O2) to anoxia (1% O2) (p = 0.033).

CONCLUSION

Human organotypic models can accurately study cell migration ex vivo. GBM IDH-wild type cells migrate toward the perivascular space in blood vessels and their migratory parameters change once they contact vascular structures and under hypoxic conditions. This model allows the evaluation of GBM invasion, considering the human brain microenvironment when cells are removed from their native niche after surgery.

Pituitary Adenlylate Cyclase Activating Peptide Protects Adult Neural Stem Cells from a Hypoglycaemic milieu

Hypoglycaemia is a common side-effect of glucose-lowering therapies for type-2 diabetic patients, which may cause cognitive/neurological impairment. Although the effects of hypoglycaemia in the brain have been extensively studied in neurons, how hypoglycaemia impacts the viability of adult neural stem cells (NSCs) has been poorly investigated. In addition, the cellular and molecular mechanisms of how hypoglycaemia regulates NSCs survival have not been characterized. Recent work others and us have shown that the pituitary adenylate cyclase-activating polypeptide (PACAP) and the glucagon-like peptide-1 receptor (GLP-1R) agonist Exendin-4 stimulate NSCs survival against glucolipoapoptosis. The aim of this study was to establish an in vitro system where to study the effects of hypoglycaemia on NSC survival. Furthermore, we determine the potential role of PACAP and Exendin-4 in counteracting the effect of hypoglycaemia. A hypoglycaemic in vitro milieu was mimicked by exposing subventricular zone-derived NSC to low levels of glucose. Moreover, we studied the potential involvement of apoptosis and endoplasmic reticulum stress by quantifying protein levels of Bcl-2, cleaved caspase-3 and mRNA levels of CHOP. We show that PACAP via PAC-1 receptor and PKA activation counteracts impaired NSC viability induced by hypoglycaemia. The protective effect induced by PACAP correlated with endoplasmic reticulum stress, Exendin-4 was ineffective. The results show that hypoglycaemia decreases NSC viability and that this effect can be substantially counteracted by PACAP via PAC-1 receptor activation. The data supports a potential therapeutic role of PAC-1 receptor agonists for the treatment of neurological complications, based on neurogenesis impairment by hypoglycaemia.

Organotypic Cultures as a Model to Study Adult Neurogenesis in CNS Disorders

Neural regeneration resides in certain specific regions of adult CNS. Adult neurogenesis occurs throughout life, especially from the subgranular zone of hippocampus and the subventricular zone, and can be modulated in physiological and pathological conditions. Numerous techniques and animal models have been developed to demonstrate and observe neural regeneration but, in order to study the molecular and cellular mechanisms and to characterize multiple types of cell populations involved in the activation of neurogenesis and gliogenesis, investigators have to turn to in vitro models. Organotypic cultures best recapitulate the 3D organization of the CNS and can be explored taking advantage of many techniques. Here, we review the use of organotypic cultures as a reliable and well defined method to study the mechanisms of neurogenesis under normal and pathological conditions. As an example, we will focus on the possibilities these cultures offer to study the pathophysiology of diseases like Alzheimer disease, Parkinson's disease, and cerebral ischemia.

Purinergic signaling: a common pathway for neural and mesenchymal stem cell maintenance and differentiation

Extracellular ATP, related nucleotides and adenosine are among the earliest signaling molecules, operating in virtually all tissues and cells. Through their specific receptors, namely purinergic P1 for nucleosides and P2 for nucleotides, they are involved in a wide array of physiological effects ranging from neurotransmission and muscle contraction to endocrine secretion, vasodilation, immune response, and fertility. The purinergic system also participates in the proliferation and differentiation of stem cells from different niches. In particular, both mesenchymal stem cells (MSCs) and neural stem cells are endowed with several purinergic receptors and ecto-nucleotide metabolizing enzymes, and release extracellular purines that mediate autocrine and paracrine growth/proliferation, pro- or anti-apoptotic processes, differentiation-promoting effects and immunomodulatory actions. Here, we discuss the often opposing roles played by ATP and adenosine in adult neurogenesis in both physiological and pathological conditions, as well as in adipogenic and osteogenic MSC differentiation. We also focus on how purinergic ligands produced and released by transplanted stem cells can be regarded as ideal candidates to mediate the crosstalk with resident stem cell niches, promoting cell growth and survival, regulating inflammation and, therefore, contributing to local tissue homeostasis and repair.

FTY720 attenuates excitotoxicity and neuroinflammation

Background

FTY720 (fingolimod, Gilenya™), a structural analog of sphingosine-1-phosphate (S1P), is the first oral drug approved for treatment the relapsing-remitting form of multiple sclerosis (MS), and its efficacy has been related to induced lymphopenia and consequent immunosuppression via modulation of S1P₁ receptors (S1P₁R). However, due to its lipophilic nature, FTY720 crosses the blood brain barrier (BBB) and could act directly on neural cells. In this study, we investigated the effectiveness of FTY720 as a neuroprotective agent using in vitro and in vivo models of excitotoxic neuronal death and examined if FTY720 exerts a direct action on neurons, or/and an indirect modulation of inflammation-mediated neurodegeneration as a possible mechanism of neuroprotection.

Methods

Primary neuronal and organotypic cortical cultures were treated with N-methyl-D-aspartic acid (NMDA) to induce excitotoxic cell death (measured by lactate dehydrogenase (LDH) assay or propidium iodide uptake, respectively). The effects of FTY720 treatment (10, 100 and 1,000 nM) on neuronal survival were examined. As an in vivo model of neuronal death and inflammation, we used intracerebroventricular (icv) administration of kainic acid (KA; 0.5 μg/2 μl) in Sprague–Dawley rats. FTY720 was applied icv (1 μg/2 μl), together with KA, plus intraperitoneally (ip; 1 mg/kg) 24 h before, and daily, until sacrifice 3 days after icv. Rats were evaluated for neurological score, neuronal loss in CA3 hippocampal region and activation of microglia at the lesion site. In addition, we tested FTY720 as a modulator of microglia responses using microglial cell cultures activated with lipopolysaccharide (LPS) and its effects in stress signalling pathways using western blotting for p38 and JNK1/2 mitogen-activated protein kinases (MAPKs).

Results

FTY720 was able to reduce excitotoxic neuronal death in vitro. Moreover, in vivo repeated FTY720 administration attenuated KA-induced neurodegeneration and microgliosis at the CA3 lesion site. Furthermore, FTY720 negatively modulates p38 MAPK in LPS-activated microglia, whereas it had no effect on JNK1/2 activation.

Conclusions

These data support a role for FTY720 as a neuroprotective agent against excitotoxin-induced neuronal death and as a negative modulator of neuroinflammation by targeting the p38 MAPK stress signalling pathway in microglia.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0308-6) contains supplementary material, which is available to authorized users.

The organotypic longitudinal spinal cord slice culture for stem cell study

The objective of this paper is to describe in detail the method of organotypic longitudinal spinal cord slice culture and the scientific basis for its potential utility. The technique is based on the interface method, which was described previously and thereafter was modified in our laboratory. The most important advantage of the presented model is the preservation of the intrinsic spinal cord fiber tract and the ventrodorsal polarity of the spinal cord. All the processes occurring during axonal growth, regeneration, synapse formation, and myelination could be visualized while being cultured in vitro for up to 4-5 weeks after the slices had been isolated. Both pups and adult animals can undergo the same, equally efficient procedures when going by the protocol in question. The urgent need for an appropriate in vitro model for spinal cord regeneration results from a greater number of clinical trials concerning regenerative medicine in the spinal cord injury and from still insufficient knowledge of the molecular mechanisms involved in the neuroreparative processes. The detailed method of organotypic longitudinal spinal cord slice culture is accompanied by examples of its application to studying biological processes to which both the CNS inhabiting and grafted cells are subjected.

Extrasynaptic glutamate release through cystine/glutamate antiporter contributes to ischemic damage

During brain ischemia, an excessive release of glutamate triggers neuronal death through the overactivation of NMDA receptors (NMDARs); however, the underlying pathways that alter glutamate homeostasis and whether synaptic or extrasynaptic sites are responsible for excess glutamate remain controversial. Here, we monitored ischemia-gated currents in pyramidal cortical neurons in brain slices from rodents in response to oxygen and glucose deprivation (OGD) as a real-time glutamate sensor to identify the source of glutamate release and determined the extent of neuronal damage. Blockade of excitatory amino acid transporters or vesicular glutamate release did not inhibit ischemia-gated currents or neuronal damage after OGD. In contrast, pharmacological inhibition of the cystine/glutamate antiporter dramatically attenuated ischemia-gated currents and cell death after OGD. Compared with control animals, mice lacking a functional cystine/glutamate antiporter exhibited reduced anoxic depolarization and neuronal death in response to OGD. Furthermore, glutamate released by the cystine/glutamate antiporter activated extrasynaptic, but not synaptic, NMDARs, and blockade of extrasynaptic NMDARs reduced ischemia-gated currents and cell damage after OGD. Finally, PET imaging showed increased cystine/glutamate antiporter function in ischemic rats. Altogether, these data suggest that cystine/glutamate antiporter function is increased in ischemia, contributing to elevated extracellular glutamate concentration, overactivation of extrasynaptic NMDARs, and ischemic neuronal death.

Brain slices as models for neurodegenerative disease and screening platforms to identify novel therapeutics

Recent improvements in brain slice technology have made this biological preparation increasingly useful for examining pathophysiology of brain diseases in a tissue context. Brain slices maintain many aspects of in vivo biology, including functional local synaptic circuitry with preserved brain architecture, while allowing good experimental access and precise control of the extracellular environment, making them ideal platforms for dissection of molecular pathways underlying neuronal dysfunction. Importantly, these ex vivo systems permit direct treatment with pharmacological agents modulating these responses and thus provide surrogate therapeutic screening systems without recourse to whole animal studies. Virus or particle mediated transgenic expression can also be accomplished relatively easily to study the function of novel genes in a normal or injured brain tissue context.In this review we will discuss acute brain injury models in organotypic hippocampal and co-culture systems and the effects of pharmacological modulation on neurodegeneration. The review will also cover the evidence of developmental plasticity in these ex vivo models, demonstrating emergence of injury-stimulated neuronal progenitor cells, and neurite sprouting and axonal regeneration following pathway lesioning. Neuro-and axo-genesis are emerging as significant factors contributing to brain repair following many acute and chronic neurodegenerative disorders. Therefore brain slice models may provide a critical contextual experimental system to explore regenerative mechanisms in vitro.

An organotypic culture model to study nigro-striatal degeneration

Functional and reliable in vitro models of Parkinson's disease (PD) are valuable for studying mechanisms of dopaminergic degeneration before proceeding to animal testing. At present, all in vitro models involve substitute cell types and thus their direct relevance to PD is questionable. Here, we describe an organotypic culture model which conserves the 3D architecture of the nigro-striatal pathway, together with the subventricular zone and cerebral cortex, and recapitulates a specific pattern of dopaminergic degeneration which is the principal hallmark of PD. The organotypic culture is kept in vitro for up to 12 days and dopaminergic degeneration is induced by the simple cutting of dopaminergic fibers. This organotypic model represents a rapid and useful method (30 min/pup for preparation and up to 12 days of cultivation) to investigate in vitro the mechanisms underlying neuronal death and protection, as well as neurogenesis and repair after nigro-striatal neurodegeneration.

A model of ischemia-induced neuroblast activation in the adult subventricular zone

We have developed a rat brain organotypic culture model, in which tissue slices contain cortex-subventricular zone-striatum regions, to model neuroblast activity in response to in vitro ischemia. Neuroblast activation has been described in terms of two main parameters, proliferation and migration from the subventricular zone into the injured cortex. We observed distinct phases of neuroblast activation as is known to occur after in vivo ischemia. Thus, immediately after oxygen/glucose deprivation (6–24 hours), neuroblasts reduce their proliferative and migratory activity, whereas, at longer time points after the insult (2 to 5 days), they start to proliferate and migrate into the damaged cortex. Antagonism of ionotropic receptors for extracellular ATP during and after the insult unmasks an early activation of neuroblasts in the subventricular zone, which responded with a rapid and intense migration of neuroblasts into the damaged cortex (within 24 hours). The process is further enhanced by elevating the production of the chemoattractant SDf-1α and may also be boosted by blocking the activation of microglia. This organotypic model which we have developed is an excellent in vitro system to study neurogenesis after ischemia and other neurodegenerative diseases. Its application has revealed a SOS response to oxygen/glucose deprivation, which is inhibited by unfavorable conditions due to the ischemic environment. Finally, experimental quantifications have allowed us to elaborate a mathematical model to describe neuroblast activation and to develop a computer simulation which should have promising applications for the screening of drug candidates for novel therapies of ischemia-related pathologies.

Region-specific tolerance criteria for the living brain

Computational models of traumatic brain injury (TBI) can predict injury-induced brain deformation. However, predicting the biological consequences (i.e. cell death or dysfunction) of induced brain deformation requires tolerance criteria. Here, we present a tolerance criterion for the cortex which exhibits important differences from that of the hippocampus. Organotypic slice cultures of the rat cortex, which maintain tissue architecture and cell content consistent with that in vivo, were mechanically injured with an in vitro model described previously. Cultures were stretched equibiaxially up to 0.35 Lagrangian strain at strain rates up to 50 s(-1). Cell death was quantified at 1, 2, 3, and 4 days following injury. Statistical analysis (repeated measures ANOVA) showed that all three factors (Strain, Strain Rate, and Time post-injury) significantly affected cell death. An equation describing cell death as a function of the significant parameters was then fit to the data. Compared to the hippocampus, the cortex was less vulnerable to stretch-induced injury and demonstrated a strain threshold below 0.20. Strain rate was also a significant factor for cortical but not hippocampal cell death. Cortical cell death began at an earlier time point than in the hippocampus, with cell death evident at 1 day post-injury versus 3 days in the hippocampus. In conclusion, different regions of the brain respond differently to identical mechanical stimuli, and this difference should be incorporated into finite element models of TBI if they are to more accurately predict in vivo consequences of TBI.

Preservation of glial cytoarchitecture from ex vivo human tumor and non-tumor cerebral cortical explants: A human model to study neurological diseases

For the human brain, in vitro models that accurately represent what occurs in vivo are lacking. Organotypic models may be the closest parallel to human brain tissue outside of a live patient. However, this model has been limited primarily to rodent-derived tissue. We present an organotypic model to maintain intraoperatively collected human tumor and non-tumor explants ex vivo for a prolonged period of time ( approximately 11 days) without any significant changes to the tissue cytoarchitecture as evidenced through immunohistochemistry and electron microscopy analyses. The ability to establish and reliably predict the cytoarchitectural changes that occur with time in an organotypic model of tumor and non-tumor human brain tissue has several potential applications including the study of cell migration on actual tissue matrix, drug toxicity on neural tissue and pharmacological treatment for brain cancers, among others.

Glucose metabolism in the late preterm infant

Prematurity and low birth weight are important determinants of neonatal morbidity and mortality. A rising trend of preterm births is caused by an increase in the birth rate of near-term infants. Near-term infants are defined as infants of 34 to 36 6/7 weeks gestation. It is dangerous to assume that the incidence of hypoglycemia in the later preterm infant is similar to the infant born at full term. Although current methods for assessing effects of hypoglycemia are imperfect, the injury to central nervous system depends on the degree of prematurity, presence of intrauterine growth restriction (IUGR), intrauterine compromise, genotype, blood flow, metabolic rate, and availability of other substrates. Therefore, early recognition of glucose metabolic abnormalities pertaining to late preterm infants is essential to provide appropriate and timely interventions in the newborn nursery. Although many of the investigations have targeted full-term infants, premature infants inclusive of the extremely low birth weight infants and the intrauterine growth-restricted infants, adequately powered studies restricted to only the late preterm infants are required and need future consideration.