Bangladesh J Pharmacol. 2016; 11: S136-S143

Available Online: 10 March 2016 DOI: 10.3329/bjp.v11iS1.26845

A novel approach for locating mice brain regions of Cryptococcus neoformans CNS invasion

Chunting He, Qingfen Chen and Longkun Zhu

Department of Cell Biology and Medical Genetics/Center for Cell and Developmental Biology, School of Basic Medical Sciences, Fujian Medical University, Fuzhou 350 108, China.

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Abstract

Aim of this study was to locate the brain regions where Cryptococcus interact with brain cells and invade into brain. After 7 days of intratracheal inoculation of GFP-tagged Cryptococcus neoformans strains H99, serial cryosections (10 μm) from 3 C57 BL/6 J mice brains were imaged with immunofluorescence microscopy. GFP-tagged H99 were found in some brain regions such as primary motor cortex-secondary motor cortex, caudate putamen, stratum lucidum of hippocampus, field CA1 of hippocampus, dorsal lateral geniculate nucleus, lateral posterior thalamic nucleus, laterorostral part, lateral posterior thalamic nucleus, mediorostral part, retrosplenial agranular cortex, lateral area of secondary visual cortex, and lacunosum molecular layer of the hippocampus. The results will be very useful for further exploring the mechanism of C. neoformans infection of brain.


Introduction

Cryptococcus neoformans is an encapsulated fungal pathogen that can cause life-threatening infections of the central nervous system (CNS) in susceptible patients, mainly HIV+ individuals (Day et al., 2013; Eisenman et al., 2007; Hakim et al., 2000; Jarvis et al., 2009; Mitchell and Perfect, 1995; Mwaba et al., 2001; Park et al., 2009; Perfect et al., 2010; Powderly, 1993; Saag et al., 2000). C. neoformans are commonly acquired by inhalation (Day et al., 2013; Jarvis et al., 2009).

The mechanism of extrapulmonary dissemination to the CNS are not completely understood. The mouse model of experimental hematogenous meningoencephalitis was commonly used as an in vivo mode to investigate the mechanisms of C. neoformans penetration into the brain (Maruvada et al., 2012; Noverr et al., 2003).

Understanding the interactions between C. neoformans and brain cells is fundamental in exploring the mechanisms of the C. neoformans CNS infection. Brain capillaries can be the sites of the interaction of Cryptococcus with brain endothelial cells (Shi et al., 2010). However, brain regions where yeast cells interact with brain cells and invade into brain remain unclear.

Aim of this study was to locate the regions of brain invasion by Cryptococcus. We established a novel approach for locating the brain regions of C. neoformans CNS invasion in the mouse model of experimental hematogenous meningoencephalitis, which will be very useful for further exploring the mechanism of C. neoformans CNS infection.


Materials and Methods

Reagents

PECAM-1 (platelet/endothelial cell adhesion molecule-1) rat monoclonal antibody and p-cPLA2 rabbit polyclonal antibody were purchased from Santa Cruz Biotechnology (USA). Dylight 488 goat anti-Rat IgG was purchased from EarthOx Life Sciences (USA).

Cy3 goat anti-Rabbit IgG was purchased from Beyotime Biotechnology (China).

Yeast strains

C. neoformans strains H99 was purchased from ATCC. GFP-tagged H99 was generated by integration of plasmid containing GFP construct (a generous gift of Prof. Robin May, University of Birmingham, UK) into the genome of the H99 with a BioRad PDS-1000/He biolistic particle delivery system (Voelz et al., 2010).

Intratracheal inoculation

Mice (female; C57BL/6J mice; 10-12 weeks; 20-25 g) model of experimental meningitis was prepared by intratracheal inoculation of C. neoformans strains H99. Mice were anesthetized with intraperitoneal injection of 4% chloral hydrate at 50 mg/kg. A small incision was made in the skin over the trachea. A 30-gauge needle was attached to a tuberculin syringe. The needle was bent and inserted into the trachea, and 30 µL PBS (containing 105 CFU Cryptococcus) was delivered. The skin was sutured with a cyanoacrylate adhesive, and the mice recovered with no visible trauma (Noverr et al., 2003).

Immunofluorescence

After 7 days of intratracheal inoculation of C. neoformans, mouse chest was cut open, and mouse was perfused with a mammalian Ringer's solution by transcardiac perfusion through a 23-gauge needle inserted into the left ventricle of the heart under the perfusion pressure of about 100 mmHg for 20 min. The brains were removed and put in liquid nitrogen. Serial cryosections (10 μm) were incubated overnight with a monoclonal rat anti-PECAM-1 primary antibody and/or a polyclonal rabbit anti-p-cPLA2 primary antibody. Afterward, sections were incubated with Dylight 488 goat Anti-Rat IgG secondary antibody and/or Cy3 goat anti-Rabbit IgG secondary antibody. Slides were imaged with a confocal microscopy (Leica TCS SP5).


Results

In this study, the mouse model of experimental hematogenous meningoencephalitis was prepared by intratracheal inoculation of GFP-tagged C. neoformans H99 (Figure 1AB). After 7 days of the inoculation, serial cryosections from 3 mice brains were imaged with fluorescence microscopy for locating regions of brain invasion by C. neoformans. GFP-tagged H99 were found in some brain regions such as primary motor cortex-secondary motor cortex (M1-M2), caudate putamen (CPu), stratum lucidum of hippocampus (SLu), field CA1 of hippocampus (CA1), dorsal lateral geniculate nucleus (DLG), lateral posterior thalamic nucleus, laterorostral part (LPLR), lateral posterior thalamic nucleus, mediorostral part (LPMR), retrosplenial agranular cortex (RSA), lateral area of secondary visual cortex (V2L), and lacunosum molecular layer of the hippocampus (LMol) (Figure 1C and D). Furthermore, immunofluorescent imaging for specific regions in Figure 1C and D are showed respectively in Figure 2 (CPu, M1-M2, RSA-V2L), Figure 3 (DLG, LMol, SLu), and Figure 4 (CA1).

Some evidence from human cases and experimental animal models of C. neoformans meningoencephalitis indicate that cerebral capillaries are the portal of C. neoformans invasion into the brain (Chang et al., 2004 ; Chretien et al., 2002; Lee et al., 1996; Neuville et al., 2002; Shi et al., 2010). In this study, PECAM-1 (platelet/endothelial cell adhesion molecule-1), a marker of brain vessel endothelial cells, was stained with immunofluorescent antibody to show microvasculature, which enable us to locate both C. neoformans and vasculature.

Our results have showed that C. neoformans invaded into hippocampal regions such as LMol and SLu (Figure 3) after 7 days of intratracheal inoculation. Our previous work showed that host cytosolic phospholipase A2α (cPLA2) contributes to group B Streptococcus penetration of the blood-brain barrier (BBB) (Maruvada et al., 2011). However, the role of cPLA2 in C. neoformans CNS infection remains unclear. cPLA2 had been showed to be involved in Aβ-dependent deficits of learning and memory in a mouse model of Alzheimer's disease (Sanchez-Mejia et al., 2008). Therefore, it will be very interesting to examine whether the cPLA2 in hippocampus is involved in C. neoformans invasion and resulting memory impairment of cryptococcal meningoencephalitis. We have found that cPLA2 is extensively active in hippocampus CA1 (Figure 4). The disappearance of p-cPLA2 positive cells in infected areas indicated that C. neoformans invasion into CA1 cause the damage of the tissue in this region (Figure 4). Although more evidence need for clarifying the role of cPLA2 in C. neoformans CNS infection, the preliminary experiment has showed that this approach will be very useful for future studies of C. neoformans CNS infection.


Discussion

Approaches of traditional histology had been used to study the CNS invasion by C. neoformans. Experiments were designed to characterize the anatomical site where C. neoformans crossed the BBB after intravenous injection of Cryptococcus. However, during a natural infection Cryptococcus are gradually released from the lung and enter the blood stream in limited numbers (Shi et al., 2012). Previous study showed that yeasts were observed in or next to the cortical capillaries of the brain and cerebellum and that no yeast cells were observed in the choroid plexus after intravenous inoculation. In this study, mice model of CNS infection was prepared by intratracheal inoculation, which is more close to natural infection as compared with intravenous inoculation. We provided the first evidence that several important brain regions were infected by C. neoformans after 7 days of intratracheal inoculation.

For intravital imaging of C. neoformans CNS invasion, the yeast cells can be labeled with fluorescent dyes (Shi et al., 2010). However, the yeast cell will lose the fluorescent label when it multiplies. Consequently, it will be hard to track the C. neoformans if it begins to replicate. To overcome this disadvantage, we generated GFP-tagged H99 by integration of plasmid containing GFP construct into the genome of the H99. In in vitro models, GFP-tagged Cryptococcus had been used for automated analysis of cryptococcal macrophage parasitism (Voelz et al., 2010) and for the study of interaction between yeast and human brain microvascular endothelial cell (Huang et al., 2011). In our in vivo model of this study, using of GFP-tagged H99 enable us to track and locate the regions of brain invasion by C. neoformans after 7 days of intratracheal inoculation of Cryptococcus.

In addition, this approach also provides some other advantages: Firstly, GFP-tagged Cryptococcus in serial cryosections are readily visualized via fluorescence microscopy. Secondly, brain structures such as vasculature that are morphologically distinguishable from Cryptococcus can both be stained as the same color in fluorescence imaging, which save one light path for fluorescence imaging of other molecular. Thirdly, all cell nucleus DNA can be stained with DAPI as blue color, and any tissue damage (disappearance of blue) is readily detected.

As an example of using this approach in study of CNS infection, we have showed that the molecular such as cPLA2 can be stained with fluorescence dyes and can be visualized by fluorescence microscopy to examine the role of this molecular in CNS infection. In fact, most fluorescence microscopes can have four light path used for fluorescence imaging. In this approach, GFP-tagged H99 and PECAM-1 (green) and DAPI (blue) occupy two light path, and there are two other light path leave for fluorescence imaging of two other molecular. If gene knockout or transgene mice are used in the model, up to three or four molecular that may be involved in CNS infection can be examined in the same experimental model, which will make this approach a valuable research tool in the field of C. neoformans CNS infection.


Conclusion

We provided the first evidence that several important brain regions were infected by C. neoformans after 7 days of intratracheal inoculation, which will be very useful for further exploring the mechanism of C. neoformans CNS infection.

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Ethical Issue

All animal experiments were approved by the Ethics Committee of Fujian Medical University, China.


Conflict of Interest

We declare that we have no conflict of interest.


Acknowledgement

This work was supported by grant from the National Natural Science Foundation of China (No. 81171115). The authors thank Prof. Robin C. May, University of Birmingham, UK for a generous gift of plasmid containing GFP construct


References

Chang YC, Stins MF, McCaffery MJ, Miller GF, Pare DR, Dam T, Paul-Satyaseela M, Kim KS, Kwon-Chung KJ. Cryptococcal yeast cells invade the central nervous system via trans-cellular penetration of the blood-brain barrier. Infect Immun. 2004; 72: 4985-95.

Chretien F, Lortholary O, Kansau I, Neuville S, Gray F, Dromer F. Pathogenesis of cerebral Cryptococcus neoformans infection after fungemia. J Infectious Dis. 2002; 186: 522-30.

Day JN, Chau TT, Wolbers M, Mai PP, Dung NT, Mai NH, Phu NH, Nghia HD, Phong ND, Thai CQ, Thai le H, Chuong LV, Sinh DX, Duong VA, Hoang TN, Diep PT, Campbell JI, Sieu TP, Baker SG, Chau NV, Hien TT, Lalloo DG, Farrar JJ. Combination antifungal therapy for Cryptococcal meningitis. New Engl J Med. 2013; 368: 1291-302.

Eisenman HC, Casadevall A, McClelland EE. New insights on the pathogenesis of invasive Cryptococcus neoformans infection. Curr Infect Dis Reports. 2007; 9: 457-64.

Hakim JG, Gangaidzo IT, Heyderman RS, Mielke J, Mushangi E, Taziwa A, Robertson VJ, Musvaire P, Mason PR. Impact of HIV infection on meningitis in Harare, Zimbabwe: A prospective study of 406 predominantly adult patients. AIDS (London, England). 2000; 14: 1401-07.

Huang SH, Long M, Wu CH, Kwon-Chung KJ, Chang YC, Chi F, Lee S, Jong A. Invasion of Cryptococcus neoformans into human brain microvascular endothelial cells is mediated through the lipid rafts-endocytic pathway via the dual specificity tyrosine phosphorylation-regulated kinase 3 (DYRK3). J Biol Chem. 2011; 286: 34761-69.

Jarvis JN, Lawn SD, Vogt M, Bangani N, Wood R, Harrison TS. Screening for Cryptococcal antigenemia in patients accessing an antiretroviral treatment program in South Africa. Clin Infect Dis. 2009; 48: 856-62.

Lee SC, Casadevall A, Dickson DW. Immunohistochemical localization of capsular polysaccharide antigen in the central nervous system cells in Cryptococcal meningoencephalitis. Am J Pathol. 1996; 148: 1267-74.

Maruvada R, Zhu L, Pearce D, Sapirstein A, Kim KS. Host cytosolic phospholipase A(2)alpha contributes to group B Streptococcus penetration of the blood-brain barrier. Infect Immun. 2011; 79: 4088-93.

Maruvada R, Zhu L, Pearce D, Zheng Y, Perfect J, Kwon-Chung KJ, Kim KS. Cryptococcus neoformans phospholipase B1 activates host cell Rac1 for traversal across the blood-brain barrier. Cell Microbiol. 2012; 14: 1544-53.

Mitchell TG, Perfect JR. Cryptococcosis in the era of AIDS- 100 years after the discovery of Cryptococcus neoformans. Clin Microbiol Rev. 1995; 8: 515-48.

Mwaba P, Mwansa J, Chintu C, Pobee J, Scarborough M, Portsmouth S, Zumla A. Clinical presentation, natural history, and cumulative death rates of 230 adults with primary Cryptococcal meningitis in Zambian AIDS patients treated under local conditions. Postgraduate Med J. 2001; 77: 769-73.

Neuville S, Dromer F, Chretien F, Gray F, Lortholary O. [Physiopathology of meningoencephalitis caused by Cryptococcus neoformans]. Annales de Med interne. 2002; 153: 323-28.

Noverr MC, Cox GM, Perfect JR, Huffnagle GB. Role of PLB1 in pulmonary inflammation and Cryptococcal eicosanoid production. Infect Immun. 2003; 71: 1538-47.

Park BJ, Wannemuehler KA, Marston BJ, Govender N, Pappas PG, Chiller TM. Estimation of the current global burden of Cryptococcal meningitis among persons living with HIV/AIDS. AIDS (London, England). 2009; 23: 525-30.

Perfect JR, Dismukes WE, Dromer F, Goldman DL, Graybill JR, Hamill RJ, Hamill RJ, Harrison TS, Larsen RA, Lortholary O, Nguyen MH, Pappas PG, Powderly WG, Singh N, Sobel JD, Sorrell TC. Clinical practice guidelines for the management of Cryptococcal disease: 2010 update by the Infectious Diseases Society of America. Clin Infect Dis. 2010; 50: 291-322.

Powderly WG. Cryptococcal meningitis and AIDS. Clin Infect Dis. 1993; 17: 837-42.

Saag MS, Graybill RJ, Larsen RA, Pappas PG, Perfect JR, Powderly WG, Sobel JD, Dismukes WE. Practice guidelines for the management of Cryptococcal disease. Clin Infect Dis. 2000; 30: 710-18.

Sanchez-Mejia RO, Newman JW, Toh S, Yu GQ, Zhou Y, Halabisky B, Cisse M, Scearce-Levie K, Cheng IH, Gan L, Palop JJ, Bonventre JV, Mucke L. Phospholipase A2 reduction ameliorates cognitive deficits in a mouse model of Alzheimer's disease. Nat Neurosci. 2008; 11: 1311-18.

Shi M, Colarusso P, Mody CH. Real-time in vivo imaging of fungal migration to the central nervous system. Cell Microbiol. 2012; 14: 1819-27.

Shi M, Li SS, Zheng C, Jones GJ, Kim KS, Zhou H, Kubes P, Mody CH. Real-time imaging of trapping and urease-dependent transmigration of Cryptococcus neoformans in mouse brain. J Clin Invest. 2010; 120: 1683-93.

Voelz K, Johnston SA, Rutherford JC, May RC. Automated analysis of Cryptococcal macrophage parasitism using GFP-tagged cryptococci. PloS one. 2010; 5: e15968.