Mike Friedrich

STED-SPIM: Stimulated emission depletion improves sheet illumination microscopy resolution.

We demonstrate the first, to our knowledge, integration of stimulated emission depletion (STED) with selective plane illumination microscopy (SPIM). Using this method, we were able to obtain up to 60% improvements in axial resolution with lateral resolution enhancements in control samples and zebrafish embryos. The integrated STED-SPIM method combines the advantages of SPIM with the resolution enhancement of STED, and thus provides a method for fast, high-resolution imaging with >100 μm deep penetration into biological tissue.

Ultramicroscopy Reveals Axonal Transport Impairments in Cortical Motor Neurons at Prion Disease

The functional imaging of neuronal circuits of the central nervous system is crucial for phenotype screenings or investigations of defects in neurodegenerative disorders. Current techniques yield either low penetration depth, yield poor resolution, or are restricted by the age of the animals. Here, we present a novel ultramicroscopy protocol for fluorescence imaging and three-dimensional reconstruction in the central nervous system of adult mice. In combination with tracing as a functional assay for axonal transport, retrogradely labeled descending motor neurons were visualized with >4 mm penetration depth. The analysis of the motor cortex shortly before the onset of clinical prion disease revealed that >80% neurons have functional impairments in axonal transport. Our study provides evidence that prion disease is associated with severe axonal transport defects in the cortical motor neurons and suggests a novel mechanism for prion-mediated neurodegeneration.

Detection of single quantum dots in model organisms with sheet illumination microscopy

Single-molecule detection and tracking is important for observing biomolecule interactions in the microenvironment. Here we report selective plane illumination microscopy (SPIM) with single-molecule detection in living organisms, which enables fast imaging and single-molecule tracking and optical penetration beyond 300 microm. We detected single nanocrystals in Drosophila larvae and zebrafish embryo. We also report our first tracking of single quantum dots during zebrafish development, which displays a transition from flow to confined motion prior to the blastula stage. The new SPIM setup represents a new technique, which enables fast single-molecule imaging and tracking in living systems.

Impaired Axonal Transport in Motor Neurons Correlates with Clinical Prion Disease

Prion diseases are fatal neurodegenerative disorders causing motor dysfunctions, dementia and neuropathological changes such as spongiosis, astroglyosis and neuronal loss. The chain of events leading to the clinical disease and the role of distinct brain areas are still poorly understood. The role of nervous system integrity and axonal properties in prion pathology are still elusive. There is no evidence of both the functional axonal impairments in vivo and their connection with prion disease. We studied the functional axonal impairments in motor neurons at the onset of clinical prion disease using the combination of tracing as a functional assay for axonal transport with immunohistochemistry experiments. Well-established and novel confocal and ultramicroscopy techniques were used to image and quantify labeled neurons. Despite profound differences in the incubation times, 30% to 45% of neurons in the red nucleus of different mouse lines showed axonal transport impairments at the disease onset bilaterally after intracerebral prion inoculation and unilaterally—after inoculation into the right sciatic nerve. Up to 94% of motor cortex neurons also demonstrated transport defects upon analysis by alternative imaging methods. Our data connect axonal transport impairments with disease symptoms for different prion strains and inoculation routes and establish further insight on the development of prion pathology in vivo. The alterations in localization of the proteins involved in the retrograde axonal transport allow us to propose a mechanism of transport disruption, which involves Rab7-mediated cargo attachment to the dynein-dynactin pathway. These findings suggest novel targets for therapeutic and diagnostic approaches in the early stages of prion disease.

Myocardial aging as a T-cell–mediated phenomenon

Significance Aging is a risk factor for heart diseases, and it is also known to impact on several immunological processes. Nevertheless, most studies addressing the cardio-immune cross-talk have focused on juvenile rather than senescent animal models. In the present study, we addressed this gap and found that immunological activity contributes to myocardial aging. By using different lymphocyte-deficient animal models and heterochronic adoptive cell-transfer protocols, our study revealed a pivotal role for CD4+ T cells in mediating spontaneous local inflammation and mild organ dysfunction in aged hearts. These results might shed new light on the emerging field of “immunocardiology” because they reveal that spontaneous heart-directed immune responses arise even in the absence of previous myocardial tissue damage. In recent years, the myocardium has been rediscovered under the lenses of immunology, and lymphocytes have been implicated in the pathogenesis of cardiomyopathies with different etiologies. Aging is an important risk factor for heart diseases, and it also has impact on the immune system. Thus, we sought to determine whether immunological activity would influence myocardial structure and function in elderly mice. Morphological, functional, and molecular analyses revealed that the age-related myocardial impairment occurs in parallel with shifts in the composition of tissue-resident leukocytes and with an accumulation of activated CD4+ Foxp3− (forkhead box P3) IFN-γ+ T cells in the heart-draining lymph nodes. A comprehensive characterization of different aged immune-deficient mouse strains revealed that T cells significantly contribute to age-related myocardial inflammation and functional decline. Upon adoptive cell transfer, the T cells isolated from the mediastinal lymph node (med-LN) of aged animals exhibited increased cardiotropism, compared with cells purified from young donors or from other irrelevant sites. Nevertheless, these cells caused rather mild effects on cardiac functionality, indicating that myocardial aging might stem from a combination of intrinsic and extrinsic (immunological) factors. Taken together, the data herein presented indicate that heart-directed immune responses may spontaneously arise in the elderly, even in the absence of a clear tissue damage or concomitant infection. These observations might shed new light on the emerging role of T cells in myocardial diseases, which primarily affect the elderly population.

Mapping immune processes in intact tissues at cellular resolution.

Understanding the spatiotemporal changes of cellular and molecular events within an organism is crucial to elucidate the complex immune processes involved in infections, autoimmune disorders, transplantation, and neoplastic transformation and metastasis. Here we introduce a novel multicolor light sheet fluorescence microscopy (LSFM) approach for deciphering immune processes in large tissue specimens on a single-cell level in 3 dimensions. We combined and optimized antibody penetration, tissue clearing, and triple-color illumination to create a method for analyzing intact mouse and human tissues. This approach allowed us to successfully quantify changes in expression patterns of mucosal vascular addressin cell adhesion molecule-1 (MAdCAM-1) and T cell responses in Peyers patches following stimulation of the immune system. In addition, we employed LSFM to map individual T cell subsets after hematopoietic cell transplantation and detected rare cellular events. Thus, we present a versatile imaging technology that should be highly beneficial in biomedical research.

Thrombopoiesis is spatially regulated by the bone marrow vasculature

In mammals, megakaryocytes (MKs) in the bone marrow (BM) produce blood platelets, required for hemostasis and thrombosis. MKs originate from hematopoietic stem cells and are thought to migrate from an endosteal niche towards the vascular sinusoids during their maturation. Through imaging of MKs in the intact BM, here we show that MKs can be found within the entire BM, without a bias towards bone-distant regions. By combining in vivo two-photon microscopy and in situ light-sheet fluorescence microscopy with computational simulations, we reveal surprisingly slow MK migration, limited intervascular space, and a vessel-biased MK pool. These data challenge the current thrombopoiesis model of MK migration and support a modified model, where MKs at sinusoids are replenished by sinusoidal precursors rather than cells from a distant periostic niche. As MKs do not need to migrate to reach the vessel, therapies to increase MK numbers might be sufficient to raise platelet counts.Megakaryocyte maturation is thought to occur as the cells migrate from a vessel-distant (endosteal) niche to the vessel within the bone. Here, the authors show that megakaryocytes represent largely sessile cells in close contact with the vasculature and homogeneously distributed in the bone marrow.

Oncostatic effects of fluoxetine in experimental colon cancer models

Colon cancer is one of the most common tumors in the human population. Recent studies have shown a reduced risk for colon cancer in patients given the antidepressant fluoxetine (FLX). The exact mechanism by which FLX might protect from colon cancer remains however controversial. Here, FLX reduced the development of different colon tumor xenografts, as well as proliferation in hypoxic tumor areas within them. FLX treatment also decreased microvessel numbers in tumors. Although FLX did not increase serum and tumor glucose levels as much as the colon chemotherapy gold standard Fluorouracil did, lactate levels were significantly augmented within tumors by FLX treatment. The gene expression of the MCT4 lactate transporter was significantly downregulated. Total protein amounts from the third and fifth mitochondrial complexes were significantly decreased by FLX in tumors. Cell culture experiments revealed that FLX reduced the mitochondrial membrane potential significantly and disabled the reactive oxygen species production of the third mitochondrial complex. Furthermore, FLX arrested hypoxic colon tumor cells in the G0/G1 phase of the cell-cycle. The expression of key cell-cycle-related checkpoint proteins was enhanced in cell culture and in vivo experiments. Therefore, we suggest FLX impairs energy generation, cell cycle progression and proliferation in tumor cells, especially under condition of hypoxia. This then leads to reduced microvessel formation and tumor shrinkage in xenograft models.

Axial resolution beyond the diffraction limit of a sheet illumination microscope with stimulated emission depletion.

Abstract. Planar illumination imaging allows for illumination of the focal plane orthogonal to the imaging axis in various light forms and is advantageous for high optical sectioning, high imaging speed, low light exposure, and inherently deeper imaging penetration into small organisms and tissue sections. The drawback of the technique is the low inherent resolution, which can be overcome by the incorporation of a dual-sheet stimulated emission depletion (STED) beam to the planar illumination excitation. Our initiative is the implementation of STED into the planar illumination microscope for enhanced resolution. We demonstrate some of our implementations. The depletion of STED in the microscope follows an inverse square root saturation for up to 2.5-fold axial resolution improvements with both high and low numerical aperture imaging objectives.

Image‐based modeling and scoring of Howell–Jolly Bodies in human erythrocytes

The spleen selectively removes cells with intracellular inclusions, for example, detached nuclear fragments in circulating erythrocytes, called Howell–Jolly Bodies (HJBs). With absent or deficient splenic function HJBs appear in the peripheral blood and can be used as a simple and non‐invasive risk‐indicator for fulminant potentially life‐threatening infection after spleenectomy. However, it is still under debate whether counting of the rare HJBs is a reliable measure of splenic function. Investigating HJBs in premature erythrocytes from patients during radioiodine therapy gives about 10 thousand times higher HJB counts than in blood smears. However, we show that there is still the risk of false‐positive results by unspecific nuclear remnants in the prepared samples that do not originate from HJBs, but from cell debris residing above or below the cell. Therefore, we present a method to improve accuracy of image‐based tests that can be performed even in non‐specialized medical institutions. We show how to selectively label HJB‐like clusters in human blood samples and how to only count those that are undoubtedly inside the cell. We found a “critical distance” dcrit referring to a relative HJB‐Cell distance that true HJBs do not exceed. To rule out false‐positive counts we present a simple inside‐outside‐rule based on dcrit—a robust threshold that can be easily assessed by combining conventional 2D imaging and straight‐forward image analysis. Besides data based on fluorescence imaging, simulations of randomly distributed HJB‐like objects on realistically modelled cell objects demonstrate the risk and impact of biased counting in conventional analysis.