Bioluminescence for biological sensing in living mammals

Application and trend of bioluminescence imaging in metabolic syndrome research

Bioluminescence imaging is a non-invasive technology used to visualize physiological processes in animals and is useful for studying the dynamics of metabolic syndrome. Metabolic syndrome is a broad spectrum of diseases which are rapidly increasing in prevalence, and is closely associated with obesity, type 2 diabetes, nonalcoholic fatty liver disease, and circadian rhythm disorder. To better serve metabolic syndrome research, researchers have established a variety of animal models expressing luciferase, while also committing to finding more suitable luciferase promoters and developing more efficient luciferase-luciferin systems. In this review, we systematically summarize the applications of different models for bioluminescence imaging in the study of metabolic syndrome.

Live Imaging

Being able to vizualize a pathogen at a site of interaction with a host is an aesthetically appealing idea and the resulting images can be both informative as well as enjoyable to view. Moreover, the approaches used to derive these images can be powerful in terms of offering data unobtainable by other methods. In this article, we review three primary modalities for live imaging Borrelia spirochetes: whole animal imaging, intravital microscopy and live cell imaging. Each method has strengths and weaknesses, which we review, as well as specific purposes for which they are optimally utilized. Live imaging borriliae is a relatively recent development and there was a need of a review to cover the area. Here, in addition to the methods themselves, we also review areas of spirochete biology that have been significantly impacted by live imaging and present a collection of images associated with the forward motion in the field driven by imaging studies.

In Vivo Molecular Bioluminescence Imaging: New Tools and Applications

in vivo bioluminescence imaging (BLi) is an optical molecular imaging technique used to visualize molecular and cellular processes in health and diseases and to follow the fate of cells with high sensitivity using luciferase-based gene reporters. The high sensitivity of this technique arises from efficient photon production, followed by the reaction between luciferase enzymes and luciferin substrates. Novel discoveries and developments of luciferase reporters, substrates, and gene-editing techniques, and emerging fields of applications, promise a new era of deeper and more sensitive molecular imaging.

Systems biology through mouse imaging centers: experience and new directions

The completed sequencing of genomes has forced upon us the challenge of understanding how the detailed information in the genome gives rise to the specific characteristics--phenotype--of the individual. This is crucial for understanding not only normal development but also, from a medical perspective, the genetic basis of disease. Much of the mammalian genome-to-phenotype relationship will be worked out in the mouse, for which powerful genetic-manipulation tools are available. Mouse imaging combined with powerful statistical methods has a unique and growing role to play in phenotyping genetically modified mice. This review outlines the challenges for image-based phenotyping, summarizes the current state of three-dimensional imaging technologies for the mouse, and highlights new opportunities in systems biology that are opened by imaging mice.

A quantitative study of factors affecting in vivo bioluminescence imaging

In vivo bioluminescence imaging (BLI) has the advantages of high sensitivity and low background. By counting the number of photons emitted from a specimen, BLI can quantify biological events such as tumour growth, gene expression and drug response. The intensities and kinetics of the BL signal are affected by many factors and may confound the quantitative results acquired from consecutive imaging sessions or different specimens. We used three different mouse models of tumours to examine whether anaesthetics, positioning and tumour growth may affect the consistency of the BL signal. The results showed that BLI signal could be affected by different anaesthetics and repetitive positioning. Using the same anaesthetics produced consistent peak times, while other factors were held constant. However, as the tumours grew the peak times shifted and the time course of BL signals had different shapes, depending on the positioning of the mice. The data indicate that a carefully designed BLI experiment is required to generate optimal and consistent results.

Microglia are the major cellular source of inducible nitric oxide synthase during experimental herpes encephalitis

Although production of reactive nitrogen and reactive oxygen species (RNS and ROS) is a component of innate defense against viral infection, their overproduction in the brain may also lead to deleterious consequences. To investigate potential immunopathologic roles of oxidative stress during herpes encephalitis, the authors examined the expression kinetics of inducible nitric oxide synthase (iNOS) as well as heme oxygenase-1 (HO-1), a marker of oxidative stress, and evaluated infection-induced oxidative brain damage. Results from these studies showed that both iNOS and HO-1 gene expression were highly elevated in the brain within 7 days post infection (d.p.i.) and remained elevated through 21 d.p.i. Real-time bioluminescence imaging of HO-1 promoter-luciferase transgenic mice confirmed HO-1 promoter activity in the brains of HSV-1-infected animals within 3 d.p.i., which peaked between 5 and 7 d.p.i. Immunohistochemical staining for both 3-nitrotyrosine and 8-hydroxydeoxyguanosine (8-OH-dG), as well as quantitative assessment of 8-isoprostane levels, demonstrated the presence of viral infection-induced oxidative brain damage. In addition, when brain leukocytes obtained from animals with experimental herpes encephalitis were sorted using fluorescence-activated cell sorting (FACS) and the individual cell populations analyzed, CD45(int)/CD11b(+) resident microglia were found to be the major cellular source of iNOS expression.

Molecular imaging of novel cell- and viral-based therapies

Drugs, surgery, and radiation are the traditional modalities of therapy in medicine. To these are being added new therapies based on cells and viruses or their derivatives. In these novel therapies, a cell or viral vector acts as a drug in its own right, altering the host or a disease process to bring about healing. Most of these advances originate from the significant recent advances in molecular medicine, but some have been around for some time. Blood transfusions and cowpox vaccinations are part of the history of medicine...but nevertheless are examples of cell- and viral-based therapies. This article focuses on the modern molecular incarnations of these therapies, and specifically on how imaging is used to track and guide these novel agents. We survey the literature dealing with imaging these new cell and viral particle therapies and provide a framework for understanding publications in this area. Leading technology of gene modifications are the fundamental modifications applied to make these new therapies amenable to imaging.

Apigenin decreases hemin-mediated heme oxygenase-1 induction

Hemin is a strong inducer of heme oxygenase-1 (HO-1) expression in vitro and in vivo. Whereas moderate overexpression of HO-1 is protective against oxidative stress, uncontrolled levels of HO-1 can be detrimental. Therefore, we evaluated the effects of apigenin (APG), a flavonoid involved in a number of phosphorylation pathways and also known to inhibit inducible genes, such as iNOS and COX-2, on HO-1 expression. Incubation of mouse embryonic fibroblasts with APG (5--40 microM) decreased hemin-induced HO-1 protein and mRNA expression. APG also reduced the induction of HO-1 promoter activity, as assessed by bioluminescence imaging, in NIH3T3 cells transfected with the 15-kb HO-1 promoter fused with the reporter gene luciferase (HO-1-luc). Furthermore, through the use of specific inhibitors, APG's effect was found to be unrelated to its PKC, CK 2, PI 3 K, p38, or ERK inhibitory activities. Quercetin (10--40 microM), also a flavonoid, also inhibited hemin-induced HO-1 expression. Additionally, in vivo studies using HO-1-luc transgenic mice showed that APG (50 mg/kg) decreased hemin-induced HO activity and HO-1 protein expression in the liver. These results suggest that hemin-induced HO-1 expression can be attenuated by flavonoids, such as APG.

Assessment of pancreatic islet mass after islet transplantation using in vivo bioluminescence imaging

BACKGROUND

Pancreatic islet transplantation is an emerging therapy for type 1 diabetes, but it is difficult to assess islets after transplantation and thus to design interventions to improve islet survival.

METHODS

To image and quantify islets, the authors transplanted luciferase-expressing murine or human islets (by adenovirus-mediated gene transfer) into the liver or beneath the renal capsule of immunodeficient mice and quantified the in vivo bioluminescence imaging (BLI) of mice using a cooled charge-coupled device camera and digital photon-counting image analysis. To account for variables that are independent of islet mass such as transplant site, animal positioning, and wound healing, the BLI of transplanted islets was calibrated against measurement of luminescence of an implanted bead emitting a constant light intensity.

RESULTS

BLI of mice bearing islet transplants was seen in the expected anatomic location, was stable for more than 8 weeks after transplantation, and correlated with the number of islets transplanted into the liver or kidney. BLI of the luminescent bead and of transplanted islets in the kidney was approximately four times greater than when transplanted in the liver, indicating that photon emission is dependent on optical absorption of generated light and thus light source location.

CONCLUSION

In vivo BLI allows for quantitative, serial measurements of pancreatic islet mass after transplantation and should be useful in assessing interventions to sustain or increase islet survival of transplanted islets.

Novel bidirectional vector strategy for amplification of therapeutic and reporter gene expression

Molecular imaging methods have previously been employed to image tissue-specific reporter gene expression by a two-step transcriptional amplification (TSTA) strategy. We have now developed a new bidirectional vector system, based on the TSTA strategy, that can simultaneously amplify expression for both a target gene and a reporter gene, using a relatively weak promoter. We used the synthetic Renilla luciferase (hrl) and firefly luciferase (fl) reporter genes to validate the system in cell cultures and in living mice. When mammalian cells were transiently cotransfected with the GAL4-responsive bidirectional reporter vector and various doses of the activator plasmid encoding the GAL4-VP16 fusion protein, pSV40-GAL4-VP16, a high correlation (r(2) = 0.95) was observed between the expression levels of both reporter genes. Good correlations (r(2) = 0.82 and 0.66, respectively) were also observed in vivo when the transiently transfected cells were implanted subcutaneously in mice or when the two plasmids were delivered by hydrodynamic injection and imaged. This work establishes a novel bidirectional vector approach utilizing the TSTA strategy for both target and reporter gene amplification. This validated approach should prove useful for the development of novel gene therapy vectors, as well as for transgenic models, allowing noninvasive imaging for indirect monitoring and amplification of target gene expression.

Strategies of Conditional Gene Expression in Myocardium

The use of specialized reporter genes to monitor real-time, tissue-specific transgene expression in animal models offers an opportunity to circumvent current limitations associated with the establishment of transgenic mouse models. The Cre-loxP and the tetracycline (Tet)-inducible systems are useful methods of conditional gene expression that allow spatial (cell-type-specific) and temporal (inducer-dependent) control. Most often, the alpha-myosin heavy chain (alpha-MHC) promoter is used in these inducible systems to restrict expression of reporter genes and transgenes to the myocardium. An overview of each inducible system is described, along with suggested reporter genes for real-time, noninvasive imaging in the myocardium. Effective gene delivery of the inducible gene expression system is carried out by lentiviral vectors, which offer high transduction efficiency, long-term transgene expression, and low immunogenicity. This chapter outlines the packaging of myocardium-specific inducible expression systems into lentiviral vectors, in which a transgene and a reporter gene are transduced into cardiomyocytes. In doing so, transgene and reporter expression can be monitored/tracked with bioluminescence imaging (BLI) and positron emission tomography (PET).

Photodynamic therapy: a new antimicrobial approach to infectious disease?

Photodynamic therapy (PDT) employs a non-toxic dye, termed a photosensitizer (PS), and low intensity visible light which, in the presence of oxygen, combine to produce cytotoxic species. PDT has the advantage of dual selectivity, in that the PS can be targeted to its destination cell or tissue and, in addition, the illumination can be spatially directed to the lesion. PDT has previously been used to kill pathogenic microorganisms in vitro, but its use to treat infections in animal models or patients has not, as yet, been much developed. It is known that Gram-(-) bacteria are resistant to PDT with many commonly used PS that will readily lead to phototoxicity in Gram-(+) species, and that PS bearing a cationic charge or the use of agents that increase the permeability of the outer membrane will increase the efficacy of killing Gram-(-) organisms. All the available evidence suggests that multi-antibiotic resistant strains are as easily killed by PDT as naive strains, and that bacteria will not readily develop resistance to PDT. Treatment of localized infections with PDT requires selectivity of the PS for microbes over host cells, delivery of the PS into the infected area and the ability to effectively illuminate the lesion. Recently, there have been reports of PDT used to treat infections in selected animal models and some clinical trials: mainly for viral lesions, but also for acne, gastric infection by Helicobacter pylori and brain abcesses. Possible future clinical applications include infections in wounds and burns, rapidly spreading and intractable soft-tissue infections and abscesses, infections in body cavities such as the mouth, ear, nasal sinus, bladder and stomach, and surface infections of the cornea and skin.

Imaging of light emission from the expression of luciferases in living cells and organisms: a review

Luciferases are enzymes that emit light in the presence of oxygen and a substrate (luciferin) and which have been used for real-time, low-light imaging of gene expression in cell cultures, individual cells, whole organisms, and transgenic organisms. Such luciferin-luciferase systems include, among others, the bacterial lux genes of terrestrial Photorhabdus luminescens and marine Vibrio harveyi bacteria, as well as eukaryotic luciferase luc and ruc genes from firefly species (Photinus) and the sea pansy (Renilla reniformis), respectively. In various vectors and in fusion constructs with other gene products such as green fluorescence protein (GFP; from the jellyfish Aequorea), luciferases have served as reporters in a number of promoter search and targeted gene expression experiments over the last two decades. Luciferase imaging has also been used to trace bacterial and viral infection in vivo and to visualize the proliferation of tumour cells in animal models.

In vivo imaging of gene expression:

With the ability to readily engineer genes, create knock-in and knock-out models of human disease, and replace and insert genes in clinical trials of gene therapy, it has become clear that imaging will play a critical role in these fields. Imaging is particularly helpful in recording temporal and spatial resolution of gene expression in vivo, determining vector distribution, and, ultimately, understanding endogenous gene expression during disease development. While endeavors are under way to image targets ranging from DNA to entire phenotypes in vivo, this short review focuses on in vivo imaging of gene expression with magnetic resonance and optical techniques.