Label-Free Imaging and Optical Characterization of Tissues Based on Autofluorescence

From Cell Populations to Molecular Complexes: Multiplexed Multimodal Microscopy to Explore p53-53BP1 Molecular Interaction

Surpassing the diffraction barrier revolutionized modern fluorescence microscopy. However, intrinsic limitations in statistical sampling, the number of simultaneously analyzable channels, hardware requirements, and sample preparation procedures still represent an obstacle to its widespread diffusion in applicative biomedical research. Here, we present a novel pipeline based on automated multimodal microscopy and super-resolution techniques employing easily available materials and instruments and completed with open-source image-analysis software developed in our laboratory. The results show the potential impact of single-molecule localization microscopy (SMLM) on the study of biomolecules' interactions and the localization of macromolecular complexes. As a demonstrative application, we explored the basis of p53-53BP1 interactions, showing the formation of a putative macromolecular complex between the two proteins and the basal transcription machinery in situ, thus providing visual proof of the direct role of 53BP1 in sustaining p53 transactivation function. Moreover, high-content SMLM provided evidence of the presence of a 53BP1 complex on the cell cytoskeleton and in the mitochondrial space, thus suggesting the existence of novel alternative 53BP1 functions to support p53 activity.

Optical imaging of the small intestine immune compartment across scales

The limitations of 2D microscopy constrain our ability to observe and understand tissue-wide networks that are, by nature, 3-dimensional. Optical projection tomography (OPT) enables the acquisition of large volumes (ranging from micrometres to centimetres) in various tissues. We present a multi-modal workflow for the characterization of both structural and quantitative parameters of the mouse small intestine. As proof of principle, we evidence its applicability for imaging the mouse intestinal immune compartment and surrounding mucosal structures. We quantify the volumetric size and spatial distribution of Isolated Lymphoid Follicles (ILFs) and quantify the density of villi throughout centimetre-long segments of intestine. Furthermore, we exhibit the age and microbiota dependence for ILF development, and leverage a technique that we call reverse-OPT for identifying and homing in on regions of interest. Several quantification capabilities are displayed, including villous density in the autofluorescent channel and the size and spatial distribution of the signal of interest at millimetre-scale volumes. The concatenation of 3D imaging with reverse-OPT and high-resolution 2D imaging allows accurate localisation of ROIs and adds value to interpretations made in 3D. Importantly, OPT may be used to identify sparsely-distributed regions of interest in large volumes whilst retaining compatibility with high-resolution microscopy modalities, including confocal microscopy. We believe this pipeline to be approachable for a wide-range of specialties, and to provide a new method for characterisation of the mouse intestinal immune compartment.

Label-free, fast, 2-photon volume imaging of the organization of neurons and glia in the enteric nervous system

The enteric nervous system (ENS), sometimes referred to as a "second brain" is a quasi-autonomous nervous system, made up of interconnected plexuses organized in a mesh-like network lining the gastrointestinal tract. Originally described as an actor in the regulation of digestion, bowel contraction, and intestinal secretion, the implications of the ENS in various central neuropathologies has recently been demonstrated. However, with a few exceptions, the morphology and pathologic alterations of the ENS have mostly been studied on thin sections of the intestinal wall or, alternatively, in dissected explants. Precious information on the three-dimensional (3-D) architecture and connectivity is hence lost. Here, we propose the fast, label-free 3-D imaging of the ENS, based on intrinsic signals. We used a custom, fast tissue-clearing protocol based on a high refractive-index aqueous solution to increase the imaging depth and allow us the detection of faint signals and we characterized the autofluorescence (AF) from the various cellular and sub-cellular components of the ENS. Validation by immunofluorescence and spectral recordings complete this groundwork. Then, we demonstrate the rapid acquisition of detailed 3-D image stacks from unlabeled mouse ileum and colon, across the whole intestinal wall and including both the myenteric and submucosal enteric nervous plexuses using a new spinning-disk two-photon (2P) microscope. The combination of fast clearing (less than 15 min for 73% transparency), AF detection and rapid volume imaging [less than 1 min for the acquisition of a z-stack of 100 planes (150*150 μm) at sub-300-nm spatial resolution] opens up the possibility for new applications in fundamental and clinical research.

Three-dimensional imaging and analysis of pathological tissue samples with de novo generation of citrate-based fluorophores

Two-dimensional (2D) histopathology based on the observation of thin tissue slides is the current paradigm in diagnosis and prognosis. However, labeling strategies in conventional histopathology are limited in compatibility with 3D imaging combined with tissue clearing techniques. Here, we present a rapid and efficient volumetric imaging technique of pathological tissues called 3D tissue imaging through de novo formation of fluorophores, or 3DNFC, which is the integration of citrate-based fluorogenic reaction DNFC and tissue clearing techniques. 3DNFC markedly increases the fluorescence intensity of tissues by generating fluorophores on nonfluorescent amino-terminal cysteine and visualizes the 3D structure of the tissues to provide their anatomical morphology and volumetric information. Furthermore, the application of 3DNFC to pathological tissue achieves the 3D reconstruction for the unbiased analysis of diverse features of the disorders in their natural context. We suggest that 3DNFC is a promising volumetric imaging method for the prognosis and diagnosis of pathological tissues.

Dose Fractionation During Puberty Is More Detrimental to Mammary Gland Development Than an Equivalent Acute Dose of Radiation Exposure

PURPOSE

Computed tomographic (CT) scans in adolescents have increased dramatically in recent years. However, the effects of cumulative low-dose exposures on the development of radiation sensitive organs, such as the mammary gland, is unknown. The purpose of this work was to define the effects of dose rate on mammary organ formation during puberty, an especially sensitive window in mammary development. We used a fractionated low-dose x-ray exposure to mimic multiple higher dose CT scans, and we hypothesized that fractionated exposure would have less of an effect on the number of mammary gland defects compared with an acute exposure.

METHODS AND MATERIALS

Female mice were subjected to fractionated low-dose x-ray exposure (10 cGy/d for 5 days), acute x-ray exposure (1 × 50 cGy), or sham exposure. As the wide genetic diversity in humans can play a role in a person's response to irradiation, 2 genetically diverse mouse strains differing in radiation sensitivity (BALB/c-sensitive; C57BL/6-resistant) were used to investigate the role of genetic background on the magnitude of the effect.

RESULTS

Unexpectedly, our data reveal that multiple low-dose exposures produce greater immune and mammary defects for weeks after exposure compared with controls. The most pronounced defects being increased ductal branching in both strains and a greater percentage of terminal end buds in the BALB/c strain of mice exposed to fractionated radiation compared with sham. Radiation-induced defects near the terminal end bud were also increased in both strains.

CONCLUSIONS

The findings suggest that fractionated low-dose exposures are potentially more damaging to organ development compared with an equivalent, single acute exposure and that genetic background is an important parameter modifying the severity of these effects.

Whole-Section Tumor Micro-Architecture Analysis by a Two-Dimensional Phasor-Based Approach Applied to Polarization-Dependent Second Harmonic Imaging

Second Harmonic Generation (SHG) microscopy has gained much interest in the histopathology field since it allows label-free imaging of tissues simultaneously providing information on their morphology and on the collagen microarchitecture, thereby highlighting the onset of pathologies and diseases. A wide request of image analysis tools is growing, with the aim to increase the reliability of the analysis of the huge amount of acquired data and to assist pathologists in a user-independent way during their diagnosis. In this light, we exploit here a set of phasor-parameters that, coupled to a 2-dimensional phasor-based approach (μMAPPS, Microscopic Multiparametric Analysis by Phasor projection of Polarization-dependent SHG signal) and a clustering algorithm, allow to automatically recover different collagen microarchitectures in the tissues extracellular matrix. The collagen fibrils microscopic parameters (orientation and anisotropy) are analyzed at a mesoscopic level by quantifying their local spatial heterogeneity in histopathology sections (few mm in size) from two cancer xenografts in mice, in order to maximally discriminate different collagen organizations, allowing in this case to identify the tumor area with respect to the surrounding skin tissue. We show that the “fibril entropy” parameter, which describes the tissue order on a selected spatial scale, is the most effective in enlightening the tumor edges, opening the possibility of their automatic segmentation. Our method, therefore, combined with tissue morphology information, has the potential to become a support to standard histopathology in diseases diagnosis.