Analysis of neurogenesis during experimental autoimmune encephalomyelitis reveals pitfalls of bioluminescence imaging

The Added Value of Longitudinal Imaging for Preclinical In Vivo Efficacy Testing of Therapeutic Compounds against Cerebral Cryptococcosis

Brain infections with Cryptococcus neoformans are associated with significant morbidity and mortality. Cryptococcosis typically presents as meningoencephalitis or fungal mass lesions called cryptococcomas. Despite frequent in vitro discoveries of promising novel antifungals, the clinical need for drugs that can more efficiently treat these brain infections remains. A crucial step in drug development is the evaluation of in vivo drug efficacy in animal models. This mainly relies on survival studies or postmortem analyses in large groups of animals, but these techniques only provide information on specific organs of interest at predefined time points. In this proof-of-concept study, we validated the use of noninvasive preclinical imaging to obtain longitudinal information on the therapeutic efficacy of amphotericin B or fluconazole monotherapy in meningoencephalitis and cryptococcoma mouse models. Bioluminescence imaging enabled the rapid in vitro and in vivo evaluation of drug efficacy, while complementary high-resolution anatomical information obtained by magnetic resonance imaging of the brain allowed a precise assessment of the extent of infection and lesion growth rates. We demonstrated a good correlation between both imaging readouts and the fungal burden in various organs. Moreover, we identified potential pitfalls associated with the interpretation of therapeutic efficacy based solely on postmortem studies, demonstrating the added value of this noninvasive dual imaging approach compared to standard mortality curves or fungal load endpoints. This novel preclinical imaging platform provides insights in the dynamic aspects of the therapeutic response and facilitates a more efficient and accurate translation of promising antifungal compounds from bench to bedside.

Bioluminescence imaging in mice with synthetic luciferin analogues

Luciferase enzymes from bioluminescent organisms can be expressed in mice, enabling these rodents to glow when treated with a corresponding luciferin substrate. Light emission occurs where the expression of the genetically-encoded luciferase overlaps with the biodistribution of the administered small molecule luciferin. Here we discuss differences between firefly luciferin analogues for bioluminescence imaging, focusing on transgenic and adeno-associated virus (AAV)-transduced mice.

Smad7 in intestinal CD4+ T cells determines autoimmunity in a spontaneous model of multiple sclerosis

Environmental triggers acting at the intestinal barrier are thought to contribute to the initiation of autoimmune disorders. The transforming growth factor beta inhibitor Smad7 determines the phenotype of CD4+ T cells. We hypothesized that Smad7 in intestinal CD4+ T cells controls initiation of opticospinal encephalomyelitis (OSE), a murine model of multiple sclerosis (MS), depending on the presence of gut microbiota. Smad7 was overexpressed or deleted in OSE CD4+ T cells to determine the effect on clinical progression, T cell differentiation, and T cell migration from the intestine to the central nervous system (CNS). Smad7 overexpression worsened the clinical course of OSE and increased CNS inflammation and demyelination. It favored expansion of intestinal CD4+ T cells toward an inflammatory phenotype and migration of intestinal CD4+ T cells to the CNS. Intestinal biopsies from MS patients revealed decreased transforming growth factor beta signaling with a shift toward inflammatory T cell subtypes. Smad7 in intestinal T cells might represent a valuable therapeutic target for MS to achieve immunologic tolerance in the intestine and suppress CNS inflammation.

Fingolimod for Irradiation-Induced Neurodegeneration

Background

Cranial irradiation is a common therapy for the treatment of brain tumors, but unfortunately patients suffer from side effects, particularly cognitive impairment, caused by neurodegenerative and neuroinflammatory mechanisms. Finding a therapeutic agent protecting hippocampal neurons would be beneficial. Fingolimod (FTY720), a sphingosine-1-phosphate receptor modulator approved for multiple sclerosis, is an immunosuppressant and known to enhance proliferation and differentiation of neuronal precursor cells (NPCs).

Objectives

To investigate whether pre-treatment with FTY720 protects NPCs in vitro and in vivo from irradiation-induced damage.

Methods

Neuronal precursor cells were isolated from E13 C57BL/6 wildtype mice, treated at day 0 of differentiation with FTY720 and irradiated on day 6 with 1 Gy. NPCs were analyzed for markers of cell death (PI, caspase-3), proliferation (Ki67), and differentiation (DCX, βIII-tubulin). Adult C57BL/6 wildtype mice were treated with FTY720 (1 mg/kg) and received a single dose of 6 Gy cranial irradiation at day 7. Using immunohistochemistry, we analyzed DCX and BrdU as markers of neurogenesis and Iba1, GFAP, and CD3 to visualize inflammation in the dentate gyrus (DG) and the subventricular zone (SVZ). B6(Cg)-Tyrc-2J/J DCX-luc reporter mice were used for bioluminescence imaging to evaluate the effect of FTY720 on neurogenesis in the DG and the spinal cord of naïve mice.

Results

FTY720 protected NPCs against irradiation induced cell death in vitro. Treatment with FTY720 dose-dependently reduced the number of PI⁺ cells 24 and 96 h after irradiation without effecting proliferation or neuronal differentiation. In vivo treatment resulted in a significant survival of DCX⁺ neurons in the DG and the SVZ 4 weeks after irradiation as well as a slight increase of proliferating cells. FTY720 inhibited microglia activation 24 h after X-ray exposure in the DG, while astrocyte activation was unaffected and no lymphocyte infiltrations were found. In naïve mice, FTY720 treatment for 4 weeks had no effect on neurogenesis.

Conclusion

FTY720 treatment of NPCs prior to X-ray exposure and of mice prior to cranial irradiation is neuroprotective. No effects on neurogenesis were found.

Sensitive bioluminescence imaging of fungal dissemination to the brain in mouse models of cryptococcosis

Cryptococcus neoformans is a leading cause of fungal brain infection, but the mechanism of dissemination and dynamics of cerebral infection following pulmonary disease are poorly understood. To address these questions, non-invasive techniques that can study the dynamic processes of disease development and progression in living animal models or patients are required. As such, bioluminescence imaging (BLI) has emerged as a powerful tool to evaluate the spatial and temporal distribution of infection in living animals. We aimed to study the time profile of the dissemination of cryptococcosis from the lung to the brain in murine models by engineering the first bioluminescent C. neoformans KN99α strain, expressing a sequence-optimized red-shifted luciferase. The high pathogen specificity and sensitivity of BLI was complemented by the three-dimensional anatomical information from micro-computed tomography (μCT) of the lung and magnetic resonance imaging (MRI) of the brain. These non-invasive imaging techniques provided longitudinal readouts on the spatial and temporal distribution of infection following intravenous, intranasal or endotracheal routes of inoculation. Furthermore, the imaging results correlated strongly with the fungal load in the respective organs. By obtaining dynamic and quantitative information about the extent and timing of brain infections for individual animals, we found that dissemination to the brain after primary infection of the lung is likely a late-stage event with a timeframe that is variable between animals. This novel tool in Cryptococcus research can aid the identification of host and pathogen factors involved in this process, and supports development of novel preventive or therapeutic approaches.

Summary: A novel combination of bioluminescence and anatomical imaging non-invasively identified the timeframe and extent of Cryptococcus neoformans dissemination to the brain in animal models of systemic and pulmonary fungal infection.

Localization of near-infrared labeled antibodies to the central nervous system in experimental autoimmune encephalomyelitis

Antibodies, including antibodies to the RNA binding protein heterogeneous nuclear ribonucleoprotein A1, have been shown to contribute to the pathogenesis of multiple sclerosis, thus it is important to assess their biological activity using animal models of disease. Near-infrared optical imaging of fluorescently labeled antibodies and matrix metalloproteinase activity were measured and quantified in an animal model of multiple sclerosis, experimental autoimmune encephalomyelitis. We successfully labeled, imaged and quantified the fluorescence signal of antibodies that localized to the central nervous system of mice with experimental autoimmune encephalomyelitis. Fluorescently labeled anti-heterogeneous nuclear ribonucleoprotein A1 antibodies persisted in the central nervous system of mice with experimental autoimmune encephalomyelitis, colocalized with matrix metalloproteinase activity, correlated with clinical disease and shifted rostrally within the spinal cord, consistent with experimental autoimmune encephalomyelitis being an ascending paralysis. The fluorescent antibody signal also colocalized with matrix metalloproteinase activity in brain. Previous imaging studies in experimental autoimmune encephalomyelitis analyzed inflammatory markers such as cellular immune responses, dendritic cell activity, blood brain barrier integrity and myelination, but none assessed fluorescently labeled antibodies within the central nervous system. This data suggests a strong association between autoantibody localization and disease. This system can be used to detect other antibodies that might contribute to the pathogenesis of autoimmune diseases of the central nervous system including multiple sclerosis.

Bioluminescence imaging visualizes osteopontin-induced neurogenesis and neuroblast migration in the mouse brain after stroke

Background

Osteopontin (OPN), an acidic phosphoglycoprotein, is upregulated in the brain after cerebral ischemia. We previously reported that OPN supports migration, survival, and proliferation of neural stem cells (NSC) in primary cell culture, as well as their differentiation into neurons. We here analyzed the effects of OPN on neuroblasts in vivo in the context of cerebral ischemia.

Methods

Transgenic mice expressing luciferase under the control of the neuroblast-specific doublecortin (DCX)-promoter, allowing visualization of neuroblasts in vivo using bioluminescence imaging (BLI), were injected with OPN intracerebroventricularly while control mice were injected with vehicle buffer. To assess the effects of OPN after ischemia, additional mice were subjected to photothrombosis and injected with either OPN or vehicle.

Results

OPN enhanced the migration of neuroblasts both in the healthy brain and after ischemia, as quantified by BLI in vivo. Moreover, the number of neural progenitors was increased following OPN treatment, with the maximum effect on the second day after OPN injection into the healthy brain, and 14 days after OPN injection following ischemia. After ischemia, OPN quantitatively promoted the endogenous, ischemia-induced neuroblast expansion, and additionally recruited progenitors from the contralateral hemisphere.

Conclusions

Our results strongly suggest that OPN constitutes a promising substance for the targeted activation of neurogenesis in ischemic stroke.

[18F]FSPG-PET reveals increased cystine/glutamate antiporter (xc-) activity in a mouse model of multiple sclerosis

BACKGROUND

The cystine/glutamate antiporter (xc-) has been implicated in several neurological disorders and, specifically, in multiple sclerosis (MS) as a mediator of glutamate excitotoxicity and proinflammatory immune responses. We aimed to evaluate an xc-specific positron emission tomography (PET) radiotracer, (4S)-4-(3-[¹⁸F]fluoropropyl)-L-glutamate ([¹⁸F]FSPG), for its ability to allow non-invasive monitoring of xc- activity in a mouse model of MS.

METHODS

Experimental autoimmune encephalomyelitis (EAE) was induced in C57BL/6 mice by subcutaneous injection of myelin oligodendrocyte glycoprotein (MOG_35-55) peptide in complete Freund's adjuvant (CFA) followed by pertussis toxin. Control mice received CFA emulsion and pertussis toxin without MOG peptide, while a separate cohort of naïve mice received no treatment. PET studies were performed to investigate the kinetics and distribution of [¹⁸F]FSPG in naïve, control, pre-symptomatic, and symptomatic EAE mice, compared to ¹⁸F-fluorodeoxyglucose ([¹⁸F]FDG). After final PET scans, each mouse was perfused and radioactivity in dissected tissues was measured using a gamma counter. Central nervous system (CNS) tissues were further analyzed using ex vivo autoradiography or western blot. [¹⁸F]FSPG uptake in human monocytes, and T cells pre- and post-activation was investigated in vitro.

RESULTS

[¹⁸F]FSPG was found to be more sensitive than [¹⁸F]FDG at detecting pathological changes in the spinal cord and brain of EAE mice. Even before clinical signs of disease, a small but significant increase in [¹⁸F]FSPG signal was observed in the spinal cord of EAE mice compared to controls. This increase in PET signal became more pronounced in symptomatic EAE mice and was confirmed by ex vivo biodistribution and autoradiography. Likewise, in the brain of symptomatic EAE mice, [¹⁸F]FSPG uptake was significantly higher than controls, with the largest changes observed in the cerebellum. Western blot analyses of CNS tissues revealed a significant correlation between light chain of xc- (xCT) protein levels, the subunit of xc- credited with its transporter activity, and [¹⁸F]FSPG-PET signal. In vitro [¹⁸F]FSPG uptake studies suggest that both activated monocytes and T cells contribute to the observed in vivo PET signal.

CONCLUSION

These data highlight the promise of [¹⁸F]FSPG-PET as a technique to provide insights into neuroimmune interactions in MS and the in vivo role of xc- in the development and progression of this disease, thus warranting further investigation.

Animal models of multiple sclerosis: Focus on experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is a chronic, progressive disorder of the central nervous system (CNS) that affects more than two million people worldwide. Several animal models resemble MS pathology; the most employed are experimental autoimmune encephalomyelitis (EAE) and toxin- and/or virus-induced demyelination. In this review we will summarize our knowledge on the utility of different animal models in MS research. Although animal models cannot replicate the complexity and heterogeneity of the MS pathology, they have proved to be useful for the development of several drugs approved for treatment of MS patients. This review focuses on EAE because it represents both clinical and pathological features of MS. During the past decades, EAE has been effective in illuminating various pathological processes that occur during MS, including inflammation, CNS penetration, demyelination, axonopathy, and neuron loss mediated by immune cells.

1001 lights: luciferins, luciferases, their mechanisms of action and applications in chemical analysis, biology and medicine

Bioluminescence (BL) is a spectacular phenomenon involving light emission by live organisms. It is caused by the oxidation of a small organic molecule, luciferin, with molecular oxygen, which is catalysed by the enzyme luciferase. In nature, there are approximately 30 different BL systems, of which only 9 have been studied to various degrees in terms of their reaction mechanisms. A vast range of in vitro and in vivo analytical techniques have been developed based on BL, including tests for different analytes, immunoassays, gene expression assays, drug screening, bioimaging of live organisms, cancer studies, the investigation of infectious diseases and environmental monitoring. This review aims to cover the major existing applications for bioluminescence in the context of the diversity of luciferases and their substrates, luciferins. Particularly, the properties and applications of d-luciferin, coelenterazine, bacterial, Cypridina and dinoflagellate luciferins and their analogues along with their corresponding luciferases are described. Finally, four other rarely studied bioluminescent systems (those of limpet Latia, earthworms Diplocardia and Fridericia and higher fungi), which are promising for future use, are also discussed.

Effects of Environmental Enrichment on Doublecortin and BDNF Expression along the Dorso-Ventral Axis of the Dentate Gyrus

Adult hippocampal neurogenesis (AHN) in the dentate gyrus is known to respond to environmental enrichment, chronic stress, and many other factors. The function of AHN may vary across the septo-temporal axis of the hippocampus, as different subdivisions are responsible for different functions. The dorsal pole regulates cognitive-related behaviors, while the ventral pole mediates mood-related responses through the hypothalamic-pituitary-adrenal (HPA) axis. In this study, we investigate different methods of quantifying the effect of environmental enrichment on AHN in the dorsal and ventral parts of the dentate gyrus (dDG and vDG). To this purpose, 11-week-old female CD-1 mice were assigned for 8 days to one of two conditions: the Environmental Enrichment (E) group received (i) running wheels, (ii) larger cages, (iii) plastic tunnels, and (iv) bedding with male urine, while the Control (C) group received standard housing. Dorsal CA (Cornu Ammonis) and DG regions were larger in the E than the C animals. Distance run linearly predicted the volume of the dorsal hippocampus, as well as of the intermediate and ventral CA regions. In the dDG, the amount of Doublecortin (DCX) immunoreactivity was significantly higher in E than in C mice. Surprisingly, this pattern was the opposite in the vDG (C > E). Real-time PCR measurement of Dcx mRNA and DCX protein analysis using ELISA showed the same pattern. Brain Derived Neurotrophic Factor (BDNF) immunoreactivity and mRNA displayed no difference between E and C, suggesting that upregulation of DCX was not caused by changes in BDNF levels. BDNF levels were higher in vDG than in dDG, as measured by both methods. Bdnf expression in vDG correlated positively with the distance run by individual E mice. The similarity in the patterns of immunoreactivity, mRNA and protein for differential DCX expression and for BDNF distribution suggests that the latter two methods might be effective tools for more rapid quantification of AHN.

In vivo bioluminescence imaging of neurogenesis - the role of the blood brain barrier in an experimental model of Parkinson's disease

Bioluminescence imaging in transgenic mice expressing firefly luciferase in Doublecortin⁺ (Dcx) neuroblasts might serve as a powerful tool to study the role of neurogenesis in models of brain injury and neurodegeneration using non-invasive, longitudinal in vivo imaging. Therefore, we aimed to use BLI in B6(Cg)-Tyrc-2J/J Dcx-Luc (Doublecortin-Luciferase, Dcx-Luc) mice to investigate its suitability to assess neurogenesis in a unilateral injection model of Parkinson's disease. We further aimed to assess the blood brain barrier leakage associated with the intranigral 6-OHDA injection to evaluate its impact on substrate delivery and bioluminescence signal intensity. Two weeks after lesion, we observed an increase in bioluminescence signal in the ipsilateral hippocampal region in both, 6-OHDA and vehicle injected Dcx-Luc mice. At the same time, no corresponding increase in Dcx⁺ neuroblast numbers could be observed in the dentate gyrus of C57Bl6 mice. Blood brain barrier leakage was observed in the hippocampal region and in the degenerating substantia nigra of C57Bl6 mice in vivo using T1 weighted Magnetic Resonance Imaging with Gadovist^® and ex vivo using Evans Blue Fluorescence Reflectance Imaging and mouse Immunoglobulin G staining. Our data suggests a BLI signal dependency on blood brain barrier permeability, underlining a major pitfall of substrate/tracer dependent imaging in invasive disease models.

Long-term effects of autoimmune CNS inflammation on adult hippocampal neurogenesis

Neurogenesis is a well-characterized phenomenon within the dentate gyrus (DG) of the adult hippocampus. Aging and chronic degenerative disorders have been shown to impair hippocampal neurogenesis, but the consequence of chronic inflammation remains controversial. In this study the chronic experimental autoimmune encephalomyelitis (EAE) mouse model of multiple sclerosis was used to investigate the long-term effects of T cell-mediated central nervous system inflammation on hippocampal neurogenesis. 5-Bromodeoxyuridine (BrdU)-labeled subpopulations of hippocampal cells in EAE and control mice (coexpressing GFAP, doublecortin, NeuN, calretinin, and S100) were quantified at the recovery phase, 21 days after BrdU administration, to estimate alterations on the rate and differentiation pattern of the neurogenesis process. The core features of EAE mice DG are (i) elevated number of newborn (BrdU+) cells indicating vigorous proliferation, which in the long term subsided; (ii) enhanced migration of newborn cells into the granule cell layer; (iii) increased level of immature neuronal markers (including calretinin and doublecortin); (iv) trending decrease in the percentage of newborn mature neurons; and (v) augmented gliogenesis and differentiation of newborn neural precursor cells (NPCs) to mature astrocytes (BrdU+/S100+). Although the inflammatory environment in the brain of EAE mice enhances the proliferation of hippocampal NPCs, in the long term neurogenesis is progressively depleted, giving prominence to gliogenesis. The discrepancy between the high number of immature cells and the low number of mature newborn cells could be the result of a caused defect in the maturation pathway. © 2016 Wiley Periodicals, Inc.

Tomographic brain imaging with nucleolar detail and automatic cell counting

Brain tissue evaluation is essential for gaining in-depth insight into its diseases and disorders. Imaging the human brain in three dimensions has always been a challenge on the cell level. In vivo methods lack spatial resolution, and optical microscopy has a limited penetration depth. Herein, we show that hard X-ray phase tomography can visualise a volume of up to 43 mm³ of human post mortem or biopsy brain samples, by demonstrating the method on the cerebellum. We automatically identified 5,000 Purkinje cells with an error of less than 5% at their layer and determined the local surface density to 165 cells per mm² on average. Moreover, we highlight that three-dimensional data allows for the segmentation of sub-cellular structures, including dendritic tree and Purkinje cell nucleoli, without dedicated staining. The method suggests that automatic cell feature quantification of human tissues is feasible in phase tomograms obtained with isotropic resolution in a label-free manner.

The feasibility of in vivo imaging of infiltrating blood cells for predicting the functional prognosis after spinal cord injury

After a spinal cord injury (SCI), a reliable prediction of the potential functional outcome is essential for determining the optimal treatment strategy. Despite recent advances in the field of neurological assessment, there is still no satisfactory methodology for predicting the functional outcome after SCI. We herein describe a novel method to predict the functional outcome at 12 hours after SCI using in vivo bioluminescence imaging. We produced three groups of SCI mice with different functional prognoses: 50 kdyn (mild), 70 kdyn (moderate) and 90 kdyn (severe). Only the locomotor function within 24 hours after SCI was unable to predict subsequent functional recovery. However, both the number of infiltrating neutrophils and the bioluminescence signal intensity from infiltrating blood cells were found to correlate with the severity of the injury at 12 hours after SCI. Furthermore, a strong linear relationship was observed among the number of infiltrating neutrophils, the bioluminescence signal intensity, and the severity of the injury. Our findings thus indicate that in vivo bioluminescence imaging is able to accurately predict the long-term functional outcome in the hyperacute phase of SCI, thereby providing evidence that this imaging modality could positively contribute to the future development of tailored therapeutic approaches for SCI.

Luciferins behave like drugs

The light emission chemistry of firefly luciferase can be harnessed to reveal otherwise invisible biological processes occurring in the brains of live animals. Though powerful, the need for the luciferase substrate D-luciferin to traverse the blood-brain barrier poses limitations on the sensitivity and interpretation of these experiments. In this Viewpoint, we discuss bioluminescent imaging probes for the enzyme fatty acid amide hydrolase (FAAH) and the broader implications for optical imaging and drug delivery in the brain.