Two-photon Laser Scanning Microscopy Imaging Research Articles

Microvascular permeability of skeletal muscle after eccentric contraction-induced muscle injury: in vivo imaging using two-photon laser scanning microscopy.

Via modulation of endothelial integrity and vascular permeability in response to damage, skeletal muscle microvessels play a crucial permissive role in tissue leukocyte invasion. However, direct visual evidence of altered microvascular permeability of skeletal muscle has not been technically feasible, impairing mechanistic understanding of these responses. Two-photon laser scanning microscopy (TPLSM) allows three-dimensional in vivo imaging of skeletal muscle microcirculation. We hypothesized that the regulation of microvascular permeability in vivo is temporally related to acute inflammatory and regenerative processes following muscle injury. To test our hypothesis, tibialis anterior muscles of anesthetized male Wistar rats were subjected to eccentric contractions (ECCs) via electrical stimulation. The skeletal muscle microcirculation was imaged by an intravenously infused fluorescent dye (rhodamine B isothiocyanate-dextran) to assess microvascular permeability via TPLSM 1, 3, and 7 days after ECC. Immunohistochemistry on serial muscle sections was performed to determine the proportion of VEGF-A-positive muscle fibers in the damaged muscle. Compared with control rats, the volumetrically determined interstitial leakage of fluorescent dye (5.1 ± 1.4, 5.3 ± 1.2 vs. 0.51 ± 0.14 μm3 × 106; P < 0.05, days 1 and 3, respectively, vs. control) and percentage of VEGF-A-positive fibers in the damaged muscle (10 ± 0.4%, 22 ± 1.1% vs. 0%; days 1 and 3, respectively, vs. control) were significantly higher on days 1 and 3 after ECC. The interstitial leakage volume returned to control by day 7. These results suggest that microvascular hyperpermeability assessed by in vivo TPLSM imaging is associated with ECC-induced muscle damage and increased VEGF expression. NEW & NOTEWORTHY This investigation employed a novel in vivo imaging technique for skeletal muscle microcirculation using two-photon laser scanning microscopy that enabled microvascular permeability to be assessed by four-dimensional image analysis. By combining in vivo imaging and histological analysis, we found the temporal profile of microvascular hyperpermeability to be related to that of eccentric contraction-induced skeletal muscle injury and pronounced novel myocyte VEGF expression.

Skeletal Muscle Microvascular Permeability After Eccentric Contraction-Induced Muscle Injury

Within injured skeletal muscle the capillary bed plays a crucial role in leukocyte invasion through modulations of the endothelial integrity, associated with increased permeability. However, direct observation of altered microvascular permeability and compromised capillary integrity has not been technically feasible. Two-photon laser scanning microscopy (TPLSM) allows three-dimensional in vivo imaging which, given the depth of penetration and high resolution of TPLSM, will facilitate measurement of microvascular leakage. PURPOSE: We hypothesized that the regulation of capillary permeability in vivo, as assessed by real-time TPLSM, is temporally related to acute inflammatory and regenerative processes following muscle injury. METHODS: Tibialis anterior muscles of anesthetized male Wistar rats (n=57) were subjected to eccentric contractions (ECC) via electrical stimulation. The skeletal muscle microcirculation was imaged by an intravenously infused fluorescent dye (rhodamine b isothiocyanate dextran, molecular weight 70,000 Daltons) to assess microvascular permeability via TPLSM 1, 3 and 7 days after ECC. Immunohistochemistry on serial muscle sections was performed to determine the percentage of VEGF-A positive muscle fibers in the damaged muscle. RESULTS: Compared with non-ECC control, the volumetrically-determined interstitial leakage of fluorescent dye had increased significantly on days 1 and 3 post-ECC (5.1±1.4, 5.3±1.2 vs. 0.51±0.14 μm3x106, P<0.05 respectively days 1 and 3 vs. control). However, by post-ECC day 7 interstitial leakage had returned to control values. Damaged muscle fibers were evident on days 1 and 3 (% damaged muscle fiber: 11.7±4.7, 48.4±12.4% vs. 0% P<0.05 respectively days 1 and 3 vs. control). Percentage of VEGF-A positive muscle fiber in damaged muscle fiber was significantly higher on days 1 and 3 compared to control (24.9±9.8, 39.3±16.7 vs. 0%, P<0.05 respectively days 1 and 3 vs. control). Regenerated skeletal muscle fibers were found only at 7 days post- ECC. CONCLUSION:In vivo TPLSM imaging represents a powerful investigative technique for skeletal muscle microcirculatory research. Microvascular hyperpermeability is associated with ECC-induced muscle damage and increased VEGF expression.

Intravital imaging of neutrophil recruitment in intestinal ischemia-reperfusion injury

BackgroundNeutrophils are known to be key players in innate immunity. Activated neutrophils induce local inflammation, which results in pathophysiologic changes during intestinal ischemia-reperfusion injury (IRI). However, most studies have been based on static assessments, and few have examined real-time intravital neutrophil recruitment. We herein report a method for imaging and evaluating dynamic changes in the neutrophil recruitment in intestinal IRI using two-photon laser scanning microscopy (TPLSM). MethodsLysM-eGFP mice were subjected to 45 min of warm intestinal ischemia followed by reperfusion. Mice received an intravenous injection of tetramethylrhodamine isothiocyanate-labeled albumin to visualize the microvasculature. Using a time-lapse TPLSM technique, we directly observed the behavior of neutrophils in intestinal IRI. ResultsWe were able to image all layers of the intestine without invasive surgical stress. At low-magnification, the number of neutrophils per field of view continued to increase for 4 h after reperfusion. High-magnification images revealed the presence or absence of blood circulation. At 0–2 h after reperfusion, rolling and adhesive neutrophils increased along the vasculature. At 2–4 h after reperfusion, the irregularity of crypt architecture and transmigration of neutrophils were observed in the lamina propria. Furthermore, TPLSM imaging revealed the villus height, the diameters of the crypt, and the number of infiltrating neutrophils in the crypt. In the IRI group, the villus height 4 h after reperfusion was significantly shorter than in the control group. ConclusionsTPLSM imaging revealed the real-time neutrophil recruitment in intestinal IRI. Z-stack imaging was useful for evaluating pathophysiological changes in the intestinal wall.

Noninvasive molecular ultrasound monitoring of vessel healing after intravascular surgical procedures in a preclinical setup.

Cardiovascular interventions induce damage to the vessel wall making antithrombotic therapy inevitable until complete endothelial recovery. Without a method to accurately determine the endothelial status, many patients undergo prolonged anticoagulation therapy, denying them any invasive medical procedures, such as surgical operations and dental interventions. Therefore, we aim to introduce molecular ultrasound imaging of the vascular cell adhesion molecule (VCAM)-1 using targeted poly-n-butylcyanoacrylate microbubbles (MB(VCAM-1)) as an easy accessible method to monitor accurately the reendothelialization of vessels. ApoE(-/-) mice were fed with an atherogenic diet for 1 and 12 weeks and subsequently, endothelial denudation was performed in the carotid arteries using a guidewire. Molecular ultrasound imaging was performed at different time points after denudation (1, 3, 7, and 14 days). An increased MB(VCAM-1) binding after 1 day, a peak after 3 days, and a decrease after 7 days was found. After 12 weeks of diet, MB(VCAM-1) binding also peaked after 3 days but remained high until 7 days, indicating a delay in endothelial recovery. Two-photon laser scanning microscopy imaging of double fluorescence staining confirmed the exposure of VCAM-1 on the superficial layer after arterial injury only during the healing phase. After complete reendothelialization, VCAM-1 expression persisted in the subendothelial layer but was not reachable for the MBV(CAM-1) anymore. Molecular ultrasound imaging with MB(VCAM-1) is promising to assess vascular damage and to monitor endothelial recovery after arterial interventions. Thus, it may become an important diagnostic tool supporting the development of adequate therapeutic strategies to personalize anticoagulant and anti-inflammatory therapy after cardiovascular intervention.

Cerebral hemodynamic response to acute hyperoxia in awake mice

Cerebral hemodynamic response to acute hyperoxia was investigated in awake mice. Using laser-Doppler flowmetry (LDF), baseline cerebral blood flow (CBF) and the cerebrovascular responses to whisker stimulation were measured in awake mice during normoxia and hyperoxia. Using two-photon laser scanning microscopy (TPLSM), the changes in cortical microvasculature were measured during normoxia and hyperoxia. During hyperoxia (PaO2=482.3±19.7mmHg), baseline CBF was 6.8% lower than normoxia (PaO2=97.3±6.0mmHg). The degree of increase in CBF evoked by whisker stimulation was greater during hyperoxia (18.1±5.0%) than normoxia (13.1±3.5%) (P<0.05). TPLSM imaging of the somatosensory cortex showed vasconstriction in arterioles and capillaries during hyperoxia. Since the effective diffusivity for oxygen in the capillary bed might decrease by hyperoxia due to a decrease in capillary blood volume according to Hyder׳s model, an increase in the cerebral metabolic rate of oxygen utilization by neural activation during hyperoxia might need a greater increase in CBF as compared with normoxia. The hemodynamic response to neural activation could be modified by acute hyperoxia due to modification of the relation between changes in CBF and oxygen consumption by neural activation.

In vivo real-time imaging of chemotherapy response on the liver metastatic tumor microenvironment using multiphoton microscopy

Invivo real-time visualization of chemotherapy response at the cellular level provides us with direct evidence of what happens on the tumor microenvironment of metastatic organs. We imaged the response of metastatic tumor cells and host stromal cells to chemotherapeutics on liver metastatic xenografts in living mice using intravital two-photon laser scanning microscopy (TPLSM). Red fluorescent protein-expressing human colorectal cancer cells (HT29) was inoculated to the spleen of green fluorescent protein-expressing nude mice. 5-Fluorouracil or irinotecan was intraperitoneally administered after the formation of macroscopic liver metastases. Intravital TPLSM was performed at multiple time-points for time-series imaging of liver metastatic xenografts in the same mice. Under the 1st TPLSM, HT29 cells were visualized in hepatic sinusoids at the single cell level. Liver metastatic nodules consisting of viable cancer cells and surrounding stroma with tumor vessels were visualized under the 2nd TPLSM. After chemotherapy, tumor cell fragmentation, condensation, swelling and intracellular vacuoles were observed under the 3rd TPLSM. There was no obvious morphological difference in tumor response between these chemotherapeutics. Time-series intravital TPLSM imaging on the metastatic tumor xenografts may be useful for screening and evaluating new chemotherapeutics with less interindividual variability.

Intravital imaging of gastrointestinal diseases in preclinical models using two-photon laser scanning microscopy

Two-photon laser scanning microscopy (TPLSM), relying on two-photon excitation restricted to the focal plane, has become the gold standard in biomedical research because of its ability to produce high-resolution, higher penetrating imaging of biological materials over an extended duration without an significant photobleaching. Intravital (in vivo) imaging using TPLSM for intra-abdominal organs has long been a technical challenge because of the difficulty of achieving high-quality and higher magnification imaging with acceptable cardiac and respiratory motion artifacts. A method of intravital TPLSM was developed using an organ-stabilizing system for imaging the intra-abdominal organs of green fluorescent protein transgenic mice. This method was further refined for the time-series imaging of intra-abdominal organs in the same mouse model using intravital TPLSM. These procedures allow the observation of not only a single cell or tissue microenvironment at a higher penetrating depth for a longer period of time but also to observe the same organ of the same mouse at multiple time points in preclinical models. This report presents the general principles and properties of TPLSM for biomedical research. In addition, the methods and the usefulness of time-series intravital TPLSM imaging for preclinical gastrointestinal diseases is discussed.

Infection-Induced Regulation of Natural Killer Cells by Macrophages and Collagen at the Lymph Node Subcapsular Sinus

Infection leads to heightened activation of natural killer (NK) cells, a process that likely involves direct cell-to-cell contact, but how this occurs in vivo is poorly understood. We have used two-photon laser-scanning microscopy in conjunction with Toxoplasma gondii mouse infection models to address this question. We found that after infection, NK cells accumulated in the subcapsular region of the lymph node, where they formed low-motility contacts with collagen fibers and CD169(+) macrophages. We provide evidence that interactions with collagen regulate NK cell migration, whereas CD169(+) macrophages increase the activation state of NK cells. Interestingly, a subset of CD169(+) macrophages that coexpress the inflammatory monocyte marker Ly6C had the most potent ability to activate NK cells. Our data reveal pathways through which NK cell migration and function are regulated after infection and identify an important accessory cell population for activation of NK cell responses in lymph nodes.

In vivo real-time imaging of tumor microcirculatory alterations in colorectal liver metastatic xenografts by chemotherapy using multiphoton microscopy.

e21053 Background: Tumor endothelium is a distinct target for anticancer treatments of metastatic colorectal cancer. Various chemotherapeutics themselves have anti-angiogenic effects on tumor microenvironment by targeting proliferative endothelial cells during tumor angiogenesis. In this study, we imaged the dynamics of tumor microcirculation of colorectal liver metastasis in living mice in vivo real-time using two-photon laser scanning microscopy (TPLSM), and evaluated the microcirculatory alterations in tumor microenvironment by chemotherapy. Methods: Red fluorescent protein expressing human colorectal cancer cell line (HT29) was inoculated to the spleen of green fluorescent protein expressing nude mice. 5-fluorouracil or irinotecan was administered three times a week for more than three weeks for metronomic scheduling. Intravital TPLSM was performed at multiple time points for time-series imaging of liver metastatic xenografts in the same mice. The alterations in tumor microcirculation during chemotherapy was evaluated by measuring blood flows at tumor vessels of colorectal liver metastasis and hepatic sinusoids of adjacent normal liver. Results: At the first TPLSM imaging, the blood flow, as determined from the movement of platelets, was heterogeneous and non-directional in the tumor vessels of liver metastatic xenografts. The blood flow was relatively slower in tumor vessels than normal hepatic sinusoids. At the second TPLSM imaging after chemotherapy, platelet aggregation was observed in tumor vessels of the same mice. Aggregated platelets were frequently adhered to the tumor endothelium, suggesting tumor vessel damage or intratumoral coagulation abnormality by chemotherapy. There was no difference in chemotherapeutics with regard to these findings. Conclusions: Intravital TPLSM imaging of tumor microcirculation at metastatic tumor xenografts is a useful tool to evaluate anti-angiogenic drugs in preclinical models.

Two-photon microscopy of cortical NADH fluorescence intensity changes: correcting contamination from the hemodynamic response

Quantification of nicotinamide adenine dinucleotide (NADH) changes during functional brain activation and pathological conditions provides critical insight into brain metabolism. Of the different imaging modalities, two-photon laser scanning microscopy (TPLSM) is becoming an important tool for cellular-resolution measurements of NADH changes associated with cellular metabolic changes. However, NADH fluorescence emission is strongly absorbed by hemoglobin. As a result, in vivo measurements are significantly affected by the hemodynamics associated with physiological and pathophysiological manipulations. We model NADH fluorescence excitation and emission in TPLSM imaging based on precise maps of cerebral microvasculature. The effects of hemoglobin optical absorption and optical scattering from red blood cells, changes in blood volume and hemoglobin oxygen saturation, vessel size, and location with respect to imaging location are explored. A simple technique for correcting the measured NADH fluorescence intensity changes is provided, with the utilization of a parallel measurement of a physiologically inert fluorophore. The model is applied to TPLSM measurements of NADH fluorescence intensity changes in rat somatosensory cortex during mild hypoxia and hyperoxia. The general approach of the correction algorithm can be extended to other TPLSM measurements, where changes in the optical properties of the tissue confound physiological measurements, such as the detection of calcium dynamics.

Intravital imaging of DSS-induced cecal mucosal damage in GFP-transgenic mice using two-photon microscopy

Two-photon laser-scanning microscopy (TPLSM) is a powerful diagnostic tool for real-time, high-resolution structural imaging. However, obtaining high-quality in vivo TPLSM images of intra-abdominal organs remains technically challenging. An organ-stabilizing system was applied to high-quality TPLSM imaging. Real-time imaging of visceral organs, such as the liver, spleen, kidney and intestine, of transgenic green fluorescent protein (GFP) mice was performed in vivo using TPLSM. The bacterial translocation model using dextran sodium sulfate (DSS)-induced colitis was also investigated in prepared GFP mice following simple surgery. This allowed the capture of morphological real images using in vivo TPLSM. Immunohistochemical analysis of ZO-1 was performed to support the morphological findings of TPLSM. We established an organ-stabilizing system to evaluate the real-time imaging of visceral organs in actin-GFP transgenic mice using in vivo TPLSM. DSS-induced colitis showed irregularity of crypt architecture, disappearance of crypts, inflammatory cell infiltration and increased rolling of white blood cells along the vasculature. In addition, the intercellular distance of mucosal cells in the crypt and vascular endothelial cells in the intestinal wall was increased in the intestinal mucosa during DSS colitis. In DSS colitis, there was remarkable loss of mucosal and vascular endothelial ZO-1 expression, as could be seen by a decrease in ZO-1 staining. In conclusion, our observations suggested the possibility that our TPLSM imaging system can be used to clarify the pathophysiological changes in various diseases using longitudinal studies of microscopic changes in the same animal over long periods of time.

Arterial radius estimation from microscopic data using a new algorithm for circle parameter estimation

We develop and test a new method for automatic determination of vessel wall diameters from image stacks obtained using two-photon laser scanning microscopy (TPLSM) on viable arteries in perfusion flow chambers. To this extent, a new method is proposed for estimating the parameters of a circle describing the inner diameter of the blood vessels. The new method is based on the Hough transform and the observation that three points that are not colinear uniquely define a circle. By only storing the estimated center location, the computational and memory costs of the Hough transform can be greatly reduced. We test the algorithm on 20 images and compare the result with a ground-truth established by human volunteers and a standard least-squares technique. With errors of 3 to 5%, the algorithm enables accurate estimation of the vessel diameters from image stacks containing only small parts of the vessel cross section. Combined with TPLSM imaging of anatomical vessel wall properties, potentially, the algorithm enables the correlation of structural and functional properties of large intact arteries simultaneously, without requirements for additional experiments.

Two-photon laser scanning microscopy imaging of intact spinal cord and cerebral cortex reveals requirement for CXCR6 and neuroinflammation in immune cell infiltration of cortical injury sites

The mouse spinal cord is an important site for autoimmune and injury models. Skull thinning surgery provides a minimally invasive window for microscopy of the mouse cerebral cortex, but there are no parallel methods for the spinal cord. We introduce a novel, facile and inexpensive method for two-photon laser scanning microscopy of the intact spinal cord in the mouse by taking advantage of the naturally accessible intervertebral space. These are powerful methods when combined with gene-targeted mice in which endogenous immune cells are labeled with green fluorescent protein (GFP). We first demonstrate that generation of the intervertebral window does not elicit a reaction of GFP + microglial cells in CX3CR1 gfp/+ mice. We next demonstrate a distinct rostrocaudal migration of GFP + immune cells in the spinal cord of CXCR6 gfp/+ mice during active experimental autoimmune encephalomyelitis (EAE). Interestingly, infiltration of the cerebral cortex by GFP + cells in these mice required three conditions: EAE induction, cortical injury and expression of CXCR6 on immune cells.

Donor Islet Endothelial Cells Participate in Formation of Functional Vessels Within Pancreatic Islet Grafts

Pancreatic islet transplantation has emerged as a therapy for type 1 diabetes and is today performed using both freshly isolated and cultured islets. Islet blood vessels are disrupted during islet isolation; therefore, proper revascularization of the transplanted islets is of great importance for islet graft function and survival. We have studied intraislet endothelial cells after islet isolation, during islet culture, and following islet transplantation. By isolating islets from the transgenic Tie2-GFP (green fluorescent protein) mouse, characterized by an endothelial cell-specific expression of GFP, living endothelial cells could be studied in intact islets utilizing two-photon laser-scanning microscopy (TPLSM). Intraislet endothelial cells were found to survive islet transplantation but to rapidly disappear during islet culture. By transplanting freshly isolated Tie2-GFP islets and applying a novel ex vivo model for simultaneous perfusion and TPLSM imaging of the graft-bearing kidneys, GFP fluorescent endothelial cells were found to extensively contribute to vessels within the islet graft vasculature. Real-time imaging of the flow through the islet graft vasculature confirmed that the donor-derived vessels were functionally integrated. Hence, intraislet endothelial cells have the capability of participating in revascularization of pancreatic islets subsequent to transplantation. Therefore, preservation of intraislet endothelial cell mass may improve long-term graft function.