Intravital Microscopy Research Articles

Removal of the endothelial surface layer via hyaluronidase does not modulate monocyte and neutrophil interactions with the glomerular endothelium.

The endothelial surface layer (ESL), a layer of macromolecules on the surface of endothelial cells, can both impede and facilitate leukocyte recruitment. However, its role in monocyte and neutrophil recruitment in glomerular capillaries is unknown. We used multiphoton intravital microscopy to examine monocyte and neutrophil behavior in the glomerulus following ESL disruption with hyaluronidase. Constitutive retention and migration of monocytes and neutrophils within the glomerular microvasculature was unaltered by hyaluronidase. Consistent with this, inhibition of the hyaluronan-binding molecule CD44 also failed to modulate glomerular trafficking of these immune cells. To investigate the contribution of the ESL during acute inflammation, we induced glomerulonephritis via in situ immune complex deposition. This resulted in increases in glomerular retention of monocytes and neutrophils but did not induce marked reduction in the glomerular ESL. Furthermore, hyaluronidase treatment did not modify the prolonged retention of monocytes and neutrophils in the acutely inflamed glomerular microvasculature. These observations indicate that, despite evidence that the ESL has the capacity to inhibit leukocyte-endothelial cell interactions while also containing adhesive ligands for immune cells, neither of these functions modulate trafficking of monocytes and neutrophils in steady-state or acutely-inflamed glomeruli.

Resolvin D1 prevents injurious neutrophil swarming in transplanted lungs

Neutrophils are the primary cell type involved in lung ischemia-reperfusion injury (IRI), which remains a frequent and morbid complication after organ transplantation. Endogenous lipid mediators that become activated during acute inflammation-resolution have gained increasing recognition for their protective role(s) in promoting the restoration of homeostasis, but their influence on early immune responses following transplantation remains to be uncovered. Resolvin D1, 7S,8R,17S-trihydroxy-4Z,9E,11E,13Z,15E,19Z-docosahexaenoic acid (RvD1), is a potent stereoselective mediator that exhibits proresolving and anti-inflammatory actions in the setting of tissue injury. Here, using metabololipidomics, we demonstrate that endogenous proresolving mediators including RvD1 are increased in human and murine lung grafts immediately following transplantation. In mouse grafts, we observe lipid mediator class switching early after reperfusion. We use intravital two-photon microscopy to reveal that RvD1 treatment significantly limits early neutrophil infiltration and swarming, thereby ameliorating early graft dysfunction in transplanted syngeneic lungs subjected to severe IRI. Through integrated analysis of single-cell RNA sequencing data of donor and recipient immune cells from lung grafts, we identify transcriptomic changes induced by RvD1. These results support a role for RvD1 as a potent modality for preventing early neutrophil-mediated tissue damage after lung IRI that may be therapeutic in the clinics.

Leishmania major drives host phagocyte death and cell-to-cell transfer depending on intracellular pathogen proliferation rate.

The virulence of intracellular pathogens relies largely on the ability to survive and replicate within phagocytes but also on release and transfer into new host cells. Such cell-to-cell transfer could represent a target for counteracting microbial pathogenesis. However, our understanding of the underlying cellular and molecular processes remains woefully insufficient. Using intravital 2-photon microscopy of caspase-3 activation in the Leishmania major-infected (L. major-infected) live skin, we showed increased apoptosis in cells infected by the parasite. Also, transfer of the parasite to new host cells occurred directly without a detectable extracellular state and was associated with concomitant uptake of cellular material from the original host cell. These in vivo findings were fully recapitulated in infections of isolated human phagocytes. Furthermore, we observed that high pathogen proliferation increased cell death in infected cells, and long-term residency within an infected host cell was only possible for slowly proliferating parasites. Our results therefore suggest that L. major drives its own dissemination to new phagocytes by inducing host cell death in a proliferation-dependent manner.

Longitudinal tracking of acute kidney injury reveals injury propagation along the nephron

Acute kidney injury (AKI) is an important risk factor for chronic kidney disease (CKD), but the underlying mechanisms of failed tubule repair and AKI-CKD transition are incompletely understood. In this study, we aimed for dynamic tracking of tubule injury and remodeling to understand if focal injury upon AKI may spread over time. Here, we present a model of AKI, in which we rendered only half of the kidney ischemic. Using serial intravital 2-photon microscopy and genetic identification of cycling cells, we tracked dynamic tissue remodeling in post- and non-ischemic kidney regions simultaneously and over 3 weeks. Spatial and temporal analysis of cycling cells relative to initial necrotic cell death demonstrated pronounced injury propagation and expansion into non-necrotic tissue regions, which predicted tubule atrophy with epithelial VCAM1 expression. In summary, our longitudinal analyses of tubule injury, remodeling, and fate provide important insights into AKI pathology.

Targeted Nanocarriers Co-Opting Pulmonary Intravascular Leukocytes for Drug Delivery to the Injured Brain.

Ex vivo-loaded white blood cells (WBC) can transfer cargo to pathological foci in the central nervous system (CNS). Here we tested affinity ligand driven in vivo loading of WBC in order to bypass the need for ex vivo WBC manipulation. We used a mouse model of acute brain inflammation caused by local injection of tumor necrosis factor alpha (TNF-α). We intravenously injected nanoparticles targeted to intercellular adhesion molecule 1 (anti-ICAM/NP). We found that (A) at 2 h, >20% of anti-ICAM/NP were localized to the lungs; (B) of the anti-ICAM/NP in the lungs >90% were associated with leukocytes; (C) at 6 and 22 h, anti-ICAM/NP pulmonary uptake decreased; (D) anti-ICAM/NP uptake in brain increased up to 5-fold in this time interval, concomitantly with migration of WBCs into the injured brain. Intravital microscopy confirmed transport of anti-ICAM/NP beyond the blood-brain barrier and flow cytometry demonstrated complete association of NP with WBC in the brain (98%). Dexamethasone-loaded anti-ICAM/liposomes abrogated brain edema in this model and promoted anti-inflammatory M2 polarization of macrophages in the brain. In vivo targeted loading of WBC in the intravascular pool may provide advantages of coopting WBC predisposed to natural rapid mobilization from the lungs to the brain, connected directly via conduit vessels.

Improvement of hemodynamics in mesenteric microcirculation in septic shock rats by anisodamine and anisodine

Anisodamine and anisodine have been used in treatment of septic shock, but the underlying mechanism are still unclear. In the present study, the effects of anisodamine hydrobromide (Ani HBr) and anisodine hydrobromide (AT3) on the mesenteric hemodynamics in septic shock rats were performed. The rat model of septic shock was established by intravenous tail vein injection of 5 ​mg/kg lipopolysaccharide (LPS), and then treated with Ani HBr, AT3, racemic anisodine (Race Ani) or atropine (ATP). The mesenteric microcirculation was observed using the intravital microscopy. Then, the flow pattern of the microcirculation, leukocytes dynamics and the plasma levels of cytokines tumor necrosis factor (TNF)-α and interleukin-6 (IL-6) were analyzed. Compared with the control rats, reduced mean arterial pressure, increased heart rate, and slow microcirculatory blood flow was found in septic shock rats. The main abnormal flow patterns were intermittent and reciprocating motions. Ani HBr, AT3, Race Ani and ATP elevated the mean arterial pressure and reduced heart rate in septic shock rats. Ani HBr and AT3 not only restored the velocity of microcirculatory blood flow and improved the microcirculatory flow patterns, but also suppressed the LPS-induced leukocyte-endothelium interaction and releases of TNF-α and IL-6. Therefore, Ani HBr and AT3 improves hemodynamics in both macro- and microcirculation, which provide a novel experimental basis for exploring the mechanobiological mechanisms in septic shock.

High-Dose Vitamin C Alleviates Pancreatic Necrosis by Inhibiting Platelet Activation Through the CXCL12/CXCR4 Pathway in Severe Acute Pancreatitis.

Platelet activation in the early stage of pancreatitis is the key step developing into pancreatic necrosis. Studies suggested that vitamin C (Vit C) can inhibit platelet activity by targeting CXCL12/CXCR4 pathway. High-dose Vit C were showed to reduce pancreatic necrosis in severe acute pancreatitis (SAP) but the mechanism remains unclear. Here we speculate high-dose Vit C reduce pancreatic necrosis by inhibiting platelet activation through downregulating CXCL12/CXCR4 pathway. The pancreatic microcirculation of rats was observed by intravital microscopy. The platelet activity of SAP rats treated with or without high-dose Vit C was analyzed by platelet function test. Besides, the activity of platelets preincubated with high-dose Vit C or vehicle from SAP patients was also evaluated. Then, the TFA (CXCR4 agonist) and rCXCL12 were used to neutralize the effect of high-dose Vit C in SAP rats treated with high-dose Vit C. Meanwhile, the levels of enzymes and inflammatory cytokines in rat plasma, and rats' pancreatic histopathology and mortality were assessed. Platelets from animals and patients with SAP are more sensitive to agonists and are more easily activated. Administration of high-dose Vit C significantly ameliorated excessive activation of platelets in SAP rats, ultimately increasing the microvessel density and inducing microthrombus and blood stasis; these results were consistent with clinical sample analysis. Moreover, high-dose Vit C significantly inhibited the release of amylase, lipase, TNF-α, and IL-6 in SAP rat plasma, reducing pancreatic damage and the mortality of SAP rats. However, using TFA and rCXCL12 significantly reversed the effect of high-dose Vit C on excessive activation of platelets, aggravating microcirculation impairment and pancreatic damage. The present study suggests that high-dose Vit C can ameliorate pancreatic necrosis by improving microcirculation disorders of SAP. For the first time, the underlying mechanism is related with inhibiting platelet activation through the CXCL12/CXCR4 pathway.

Streamlined Intravital Imaging Approach for Long-Term Monitoring of Epithelial Tissue Dynamics on an Inverted Confocal Microscope.

Understanding normal and aberrant in vivo cell behaviors is necessary to develop clinical interventions to thwart disease initiation and progression. It is therefore critical to optimize imaging approaches that facilitate the observation of cell dynamics in situ, where tissue structure and composition remain unperturbed. The epidermis is the body's outermost barrier, as well as the source of the most prevalent human cancers, namely cutaneous skin carcinomas. The accessibility of skin tissue presents a unique opportunity to monitor epithelial and dermal cell behaviors in intact animals using noninvasive intravital microscopy. Nevertheless, this sophisticated imaging approach has primarily been achieved using upright multiphoton microscopes, which represent a significant barrier for entry for most investigators. This study presents a custom-designed, 3D-printed microscope stage insert suitable for use with inverted confocal microscopes, streamlining the long-term intravital imaging of ear skin in live transgenic mice. We believe this versatile invention, which may be customized to fit the inverted microscope brand and model of choice and adapted to image additional organ systems, will prove invaluable to the greater scientific research community by significantly enhancing the accessibility of intravital microscopy. This technological advancement is critical for bolstering our understanding of live cell dynamics in normal and disease contexts.

Improving flat fluorescence microscopy in scattering tissue through deep learning strategies.

Intravital microscopy in small animals growingly contributes to the visualization of short- and long-term mammalian biological processes. Miniaturized fluorescence microscopy has revolutionized the observation of live animals' neural circuits. The technology's ability to further miniaturize to improve freely moving experimental settings is limited by its standard lens-based layout. Typical miniature microscope designs contain a stack of heavy and bulky optical components adjusted at relatively long distances. Computational lensless microscopy can overcome this limitation by replacing the lenses with a simple thin mask. Among other critical applications, Flat Fluorescence Microscope (FFM) holds promise to allow for real-time brain circuits imaging in freely moving animals, but recent research reports show that the quality needs to be improved, compared with imaging in clear tissue, for instance. Although promising results were reported with mask-based fluorescence microscopes in clear tissues, the impact of light scattering in biological tissue remains a major challenge. The outstanding performance of deep learning (DL) networks in computational flat cameras and imaging through scattering media studies motivates the development of deep learning models for FFMs. Our holistic ray-tracing and Monte Carlo FFM computational model assisted us in evaluating deep scattering medium imaging with DL techniques. We demonstrate that physics-based DL models combined with the classical reconstruction technique of the alternating direction method of multipliers (ADMM) perform a fast and robust image reconstruction, particularly in the scattering medium. The structural similarity indexes of the reconstructed images in scattering media recordings were increased by up to 20% compared with the prevalent iterative models. We also introduce and discuss the challenges of DL approaches for FFMs under physics-informed supervised and unsupervised learning.

CD103 Regulates Dermal Regulatory T Cell Motility and Interactions with CD11c-Expressing Leukocytes to Control Skin Inflammation.

Dermal regulatory T cells (Tregs) are essential for maintenance of skin homeostasis and control of skin inflammatory responses. In mice, Tregs in the skin are characterized by high expression of CD103, the αE integrin. Evidence indicates that CD103 promotes Treg retention within the skin, although the mechanism underlying this effect is unknown. The main ligand of CD103, E-cadherin, is predominantly expressed by cells in the epidermis. However, because Tregs are predominantly located within the dermis, the nature of the interactions between E-cadherin and CD103-expressing Tregs is unclear. In this study, we used multiphoton intravital microscopy to examine the contribution of CD103 to Treg behavior in resting and inflamed skin of mice undergoing oxazolone-induced contact hypersensitivity. Inhibition of CD103 in uninflamed skin did not alter Treg behavior, whereas 48 h after inducing contact hypersensitivity by oxazolone challenge, CD103 inhibition increased Treg migration. This coincided with E-cadherin upregulation on infiltrating myeloid leukocytes in the dermis. Using CD11c-enhanced yellow fluorescent protein (EYFP) × Foxp3-GFP dual-reporter mice, inhibition of CD103 was found to reduce Treg interactions with dermal dendritic cells. CD103 inhibition also resulted in increased recruitment of effector CD4+ T cells and IFN-γ expression in challenged skin and resulted in reduced glucocorticoid-induced TNFR-related protein expression on Tregs. These results demonstrate that CD103 controls intradermal Treg migration, but only at later stages in the inflammatory response, when E-cadherin expression in the dermis is increased, and provide evidence that CD103-mediated interactions between Tregs and dermal dendritic cells support regulation of skin inflammation.

354-OR: Attenuation of Obesity-Induced Vascular Inflammation by microRNA-485 in Endothelial Cells

Obesity induced endothelial dysfunction contributes to the vascular inflammation. MicroRNAs (miRNAs) are implicated in the epigenetic regulation of inflammatory pathways. However, relevant miRNAs in the microvasculature, and their relation to chronic inflammation and metabolic dysfunction are poorly understood. Using micro-RNA Seq approach to profile microRNAs from the endothelial cells (ECs) of brown adipose tissue (BAT) of mice with diet-induced obesity (DIO), we identified microRNA- 485-5p (miR-485-5p) as one of the most differentially regulated miRNA. MiR-485-5p was rapidly induced in ECs in response to TNFα, highly enriched in the BAT vascular endothelium of mice with DIO, and was increased by 1.97 fold in human plasma samples with obesity. MiR-485-5p inhibition decreased TNF-α-induced NF-kB-responsive adhesion molecules VCAM-1 (32.6%) and ICAM-1 (34.7%) and phosphorylation of IKBα in ECs in vitro. Gain and loss-of-function studies revealed that neutralization of miR-485-5p potently inhibited leukocyte adhesion to EC monolayers by 20.8% while the overexpression had the opposite effects. Mechanistically, miR-485-5p inhibited the expression of its target gene PCF11 (~40.3%), a polyadenylation factor subunit, an effect that increased VCAM-1 (2.51 fold) and ICAM-1 (1.43 fold) expression as well as leukocyte adhesion to EC monolayers by 18.6% in vitro. Systemic neutralization of miR-485-5p in mice decreased leukocyte adhesion and rolling by 55.1% and 46.7% respectively by intravital microscopy. Finally, systemic delivery of LNA-anti-miR-485-5p inhibitor resulted in improved glucose and insulin tolerance and energy expenditure in mice with DIO while decreasing Ly6Chigh proinflammatory monocytes in blood as measured by FACS. Our findings indicate that miR-485-5p plays a key regulatory role in controlling vascular inflammation in diet-induced obesity, an effect that could be exploited for therapeutic intervention in obesity-induced chronic inflammation. Disclosure F.Bestepe: None. P.F.O'tierney-ginn: None. P.Alcaide: None. I.Z.Jaffe: None. B.Icli: None. R.Pal-ghosh: None. C.Fritsche: None. K.Lakhotiya: None. S.Smolgovsky: None. J.Weston: None. A.Stepanian: None. F.Alvarado: None. P.Catalano: None. Funding American Diabetes Association (1-16-JDF-046 to B.I.); National Institutes of Health (HL149999)

305-OR: Short-Term Hyperglycemia Impacts Mouse Skeletal Muscle in a Sex-Specific Manner

Cardiorespiratory Fitness (CRF) a universal predictor of cardiovascular and all-cause mortality, is lower in people with diabetes. Skeletal muscle is a key determinant of CRF, in particular mitochondrial content, function and oxygen extraction. Hyperglycemia is implicated in the dysfunction of microvascular blood flow. Our previous work demonstrated lower mitochondrial density/fiber and capillary mean flow velocity (MFV) with 4 weeks of hyperglycemia in males and females. Treadmill running resulted in greater capillary MFV and mitochondrial density in only hyperglycemic females. We hypothesize that along with alterations in mitochondrial density and blood flow, there is a disruption in skeletal muscle mitochondrial function with hyperglycemia, and that these parameters will respond to nitrite (NO2-) treatment in a sex-specific manner. We used a model of short-term hyperglycemia with tamoxifen inducible β-cell deletion of glucokinase. Two weeks after induction, blood flow in the gastrocnemius (gastroc) was measured using intravital microscopy, and the gastroc was collected from male (M) and female (F) mice with blood glucose >400mg/dl (HG) and euglycemic controls (EG). A subset of mice received NO2- treatment for 1-2 weeks prior to gastroc measurements. Immunofluorescence imaging of gastroc were analyzed for expression of COX1 (mitochondrial marker), Dystrophin (muscle fiber sarcolemma boundary), and CD31 (capillary marker). Mitochondrial respiration was measured in gastroc fibers using Oroboros O2k. Mitochondrial respiration was lower in HG compared to EG (p<0.0009), but only respiration in M appeared to respond to NO2- treatment (p=0.0252). No difference was observed in mitochondrial density in EG versus HG. Capillary MFV was greater with HG and mitigated by NO2-treatment. NO2- targets mitochondrial function by improving capillary blood flow, but only in males. Our combined data sets suggest HG-associated mitochondrial defects need to be treated in a sex-specific manner. Disclosure N.A.Hulett: None. L.Knaub: None. G.Pott: None. D.Ramirez: None. A.Johnston: None. R.L.Scalzo: None. J.E.B.Reusch: Advisory Panel; Medtronic. Funding U.S. Department of Veterans Affairs (BX002046, CX001532); National Institutes of Health (P30DK116073, 5T32AG000279-20)

Ductular reaction-associated neutrophils promote biliary epithelium proliferation in chronic liver disease

Ductular reaction expansion is associated with poor prognosis in patients with advanced liver disease. However, the mechanisms promoting biliary cell proliferation are largely unknown. Here, we identify neutrophils as drivers of biliary cell proliferation and the defective wound-healing response. The intrahepatic localization of neutrophils was evaluated in patients with chronic liver disease. Neutrophil dynamics were analyzed by intravital microscopy and neutrophil-labeling assays in DDC-treated mice. Neutrophil depletion or inhibition of recruitment was achieved using a Ly6g antibody or a CXCR1/2 inhibitor, respectively. Mice deficient in PAD4 (peptidyl arginine deiminase 4) and ELANE/NE (neutrophil elastase) were used to investigate the mechanisms underlying ductular reaction expansion. In this study we describe a population of ductular reaction-associated neutrophils (DRANs), which are in direct contact with biliary epithelial cells in chronic liver diseases and whose numbers increased in parallel with disease progression. We show that DRANs are immobilized at the site of ductular reaction for a prolonged period of time. In addition, liver neutrophils display a unique phenotypic and transcriptomic profile, showing a decreased phagocytic capacity and increased oxidative burst. Depletion of neutrophils or inhibition of their recruitment reduces DRANs and the expansion of ductular reaction, while mitigating liver fibrosis and angiogenesis. Mechanistically, neutrophils deficient in PAD4 and ELANE abrogate neutrophil-induced biliary cell proliferation, thus indicating the role of neutrophil extracellular traps and elastase release in ductular reaction expansion. Overall, our study reveals the accumulation of DRANs as a hallmark of advanced liver disease and a potential therapeutic target to mitigate ductular reaction and the maladaptive wound-healing response. Our results indicate that neutrophils are highly plastic and can have an extended lifespan. Moreover, we identify a new role of neutrophils as triggers of expansion of the biliary epithelium. Overall, the results of this study indicate that ductular reaction-associated neutrophils (or DRANs) are new players in the maladaptive tissue-healing response in chronic liver injury and may be a potential target for therapeutic interventions to reduce ductular reaction expansion and promote tissue repair in advanced liver disease.

Imaging the time course, morphology, neuronal tissue compression, and resolution of cerebral microhemorrhages in mice using intravital two-photon microscopy: insights into arteriolar, capillary, and venular origin.

Cerebral microhemorrhages (CMHs, microbleeds), a manifestation of age-related cerebral small vessel disease, contribute to the pathogenesis of cognitive decline and dementia in older adults. Histological studies have revealed that CMHs exhibit distinct morphologies, which may be attributed to differences in intravascular pressure and the size of the vessels of origin. Our study aimed to establish a direct relationship between the size/morphology of CMHs and the size/anatomy of the microvessel of origin. To achieve this goal, we adapted and optimized intravital two-photon microscopy-based imaging methods to monitor the development of CMHs in mice equipped with a chronic cranial window upon high-energy laser light-induced photodisruption of a targeted cortical arteriole, capillary, or venule. We assessed the time course of extravasation of fluorescently labeled blood and determined the morphology and size/volume of the induced CMHs. Our findings reveal striking similarities between the bleed morphologies observed in hypertension-induced CMHs in models of aging and those originating from different targeted vessels via multiphoton laser ablation. Arteriolar bleeds, which are larger (> 100μm) and more widely dispersed, are distinguished from venular bleeds, which are smaller and exhibit a distinct diffuse morphology. Capillary bleeds are circular and smaller (< 10μm) in size. Our study supports the concept that CMHs can occur at any location in the vascular tree, and that each type of vessel produces microbleeds with a distinct morphology. Development of CMHs resulted in immediate constriction of capillaries, likely due to pericyte activation and constriction of precapillary arterioles. Additionally, tissue displacement observed in association with arteriolar CMHs suggests that they can affect an area with a radius of ~ 50μm to ~ 100μm, creating an area at risk for ischemia. Longitudinal imaging of CMHs allowed us to visualize reactive astrocytosis and bleed resolution during a 30-day period. Our study provides new insights into the development and morphology of CMHs, highlighting the potential clinical implications of differentiating between the types of vessels involved in the pathogenesis of CMHs. This information may help in the development of targeted interventions aimed at reducing the risk of cerebral small vessel disease-related cognitive decline and dementia in older adults.

Nicotine and Microvascular Responses in Skeletal Muscle from Acute Exposure to Cigarettes and Vaping.

Despite claims of safety or harm reduction for electronic cigarettes (E-cig) use (also known as vaping), emerging evidence indicates that E-cigs are not likely safe, or necessarily safer than traditional cigarettes, when considering the user's risk of developing vascular dysfunction/disease. E-cigs are different from regular cigarettes in that E-cig devices are highly customizable, and users can change the e-liquid composition (such as the base solution, flavors, and nicotine level). Since the effects of E-cigs on the microvascular responses in skeletal muscle are poorly understood, we used intravital microscopy with an acute (one-time 10 puff) exposure paradigm to evaluate the individual components of e-liquid on vascular tone and endothelial function in the arterioles of the gluteus maximus muscle of anesthetized C57Bl/6 mice. Consistent with the molecular responses seen with endothelial cells, we found that the peripheral vasoconstriction response was similar between mice exposed to E-cig aerosol or cigarette smoke (i.e., 3R4F reference cigarette); this response was not nicotine dependent, and endothelial cell-mediated vasodilation was not altered within this acute exposure paradigm. We also report that, regardless of the base solution component [i.e., vegetable glycerin (VG)-only or propylene glycol (PG)-only], the vasoconstriction responses were the same in mice with inhalation exposure to 3R4F cigarette smoke or E-cig aerosol. Key findings from this work reveal that some component other than nicotine, in inhaled smoke or aerosol, is responsible for triggering peripheral vasoconstriction in skeletal muscle, and that regardless of one's preference for an E-cig base solution composition (i.e., ratio of VG-to-PG), the acute physiological response to blood vessels appears to be the same. The data suggest that vaping is not likely to be 'safer' than smoking towards blood vessels and can be expected to produce and/or result in the same adverse vascular health outcomes associated with smoking cigarettes.

Intravital imaging of three different microvascular beds in SARS-CoV-2–infected mice

AbstractSevere acute respiratory syndrome coronavirus–2 (SARS-CoV-2) enters the respiratory tract, where it infects the alveoli epithelial lining. However, patients have sequelae that extend well beyond the alveoli into the pulmonary vasculature and, perhaps, beyond to the brain and other organs. Because of the dynamic events within blood vessels, histology does not report platelet and neutrophil behavior. Because of the rapid nontranscriptional response of these cells, neither single-cell RNA sequencing nor proteomics report robustly on their critical behaviors. We used intravital microscopy in level-3 containment to examine the pathogenesis of SARS-CoV-2 within 3 organs in mice expressing human angiotensin converting enzyme 2 (ACE-2) ubiquitously (CAG-AC-70) or on epithelium (K18-promoter). Using a neon-green SARS-CoV-2, we observed both the epithelium and endothelium infected in AC70 mice but only the epithelium in K18 mice. There were increased neutrophils in the microcirculation but not in the alveoli of the lungs of AC70 mice. Platelets formed large aggregates in the pulmonary capillaries. Despite only neurons being infected within the brain, profound neutrophil adhesion forming the nidus of large platelet aggregates were observed in the cerebral microcirculation, with many nonperfused microvessels. Neutrophils breached the brain endothelial layer associated with a significant disruption of the blood-brain-barrier. Despite ubiquitous ACE-2 expression, CAG-AC-70 mice had very small increases in blood cytokine, no increase in thrombin, no infected circulating cells, and no liver involvement suggesting limited systemic effects. In summary, our imaging of SARS-CoV-2–infected mice gave direct evidence that there is a significant perturbation locally in the lung and brain microcirculation induced by local viral infection leading to increased local inflammation and thrombosis in these organs.

Short-wavelength excitation two-photon intravital microscopy of endogenous fluorophores.

The noninvasive two-photon excitation autofluorescence imaging of cellular and subcellular structure and dynamics in live tissue could provide critical in vivo information for biomedical studies. However, the two-photon microscopy of short-wavelength endogenous fluorophores, such as tryptophan and hemoglobin, is extremely limited due to the lack of suitable imaging techniques. In this study, we developed a short-wavelength excitation time- and spectrum-resolved two-photon microscopy system. A 520-nm femtosecond fiber laser was used as the excitation source, and a time-correlated single-photon counting module connected with a spectrograph was used to provide time- and spectrum-resolved detection capability. The system was specially designed for measuring ultraviolet and violet-blue fluorescence signals and thus was very suitable for imaging short-wavelength endogenous fluorophores. Using the system, we systematically compared the fluorescence spectra and fluorescence lifetimes of short-wavelength endogenous fluorophores, including the fluorescent molecules tyrosine, tryptophan, serotonin (5-HT), niacin (vitamin B3), pyridoxine (vitamin B6), and NADH and the protein group (keratin, elastin, and hemoglobin). Then, high-resolution three-dimensional (3D) label-free imaging of different biological tissues, including rat esophageal tissue, rat oral cheek tissue, and mouse ear skin, was performed in vivo or ex vivo. Finally, we conducted time-lapse imaging of leukocyte migration in the lipopolysaccharide injection immunization model and a mechanical trauma immunization model. The results indicate that the system can specifically characterize short-wavelength endogenous fluorophores and provide noninvasive label-free 3D visualization of fine structures and dynamics in biological systems. The microscopy system developed here can empower more flexible imaging of endogenous fluorophores and provide a novel method for the 3D monitoring of biological events in their native environment.

Aging modulates homeostatic leukocyte trafficking to the peritoneal cavity in a sex-specific manner.

Aging is associated with exacerbated systemic inflammation (inflammaging) and the progressive loss of immune system function (immunosenescence). Leukocyte migration is necessary for effective immunity; however, dysregulated trafficking of leukocytes into tissue contributes to inflammaging and the development of age-related inflammatory diseases. Aging modulates leukocyte trafficking under inflammatory conditions; however, whether aging modulates leukocyte trafficking under homeostatic conditions remains to be elucidated. Although immune responses are evidently sexually dimorphic, limited studies have investigated the effect of sex on age-related changes to leukocyte trafficking processes. Here, we investigated age-related and sex-specific changes to the leukocyte populations within the peritoneal cavity of young (3-mo), middle-aged (18-mo) and old (21-mo) male and female wild-type mice in the steady state. We found an age-related increase in the number of leukocytes within the peritoneal cavity of female mice, predominantly B cells, which may reflect increased trafficking through this tissue with age. This was accompanied by an increased inflammatory environment within the aged cavity, including increased levels of chemoattractants, including B cell chemoattractants CXCL13 and CCL21, soluble adhesion molecules, and proinflammatory cytokines, which was more pronounced in aged female mice. Intravital microscopy techniques revealed altered vascular structure and increased vascular permeability within the peritoneal membrane of aged female mice, which may support increased leukocyte trafficking to the cavity with age. Together, these data indicate that aging affects homeostatic leukocyte trafficking processes in a sex-specific fashion.

BIOL-08. RADIATION DRIVES METASTASIS IN MEDULLOBLASTOMA THROUGH AN INFLAMMATORY PROCESS

Abstract Current treatment for medulloblastoma is comprised of surgery, radiotherapy (RT) and/or chemotherapy. Although the primary tumor is controlled with this approach, recurrent metastatic disease is ubiquitously fatal. However, little is known about the biology of metastatic recurrences in medulloblastoma. In the present study, we observe across 3 non-overlapping cohorts of infant medulloblastoma that patients recur locally without focal RT and metastatically after focal RT. Using 3 independent murine flank xenograft medulloblastoma models, we found that the incidence of leptomeningeal metastasis was significantly increased in mice that received RT compared to sham controls. We have also found a significant increase in viable circulating tumor cells after RT. Our multi-omics (bulk RNA-seq, scRNA-seq and proteo/phosphoproteomics) approach using immunocompetent sporadic medulloblastoma models treated with RT showed activation of the innate inflammatory response through the overexpression of chemokines, cytokines and activation of immune cell types. In situ analysis of protein expression after RT showed a gradual increase in the abundance of macrophages, neutrophils and dendritic cells after RT, suggesting increased permeability and cell trafficking across the blood brain barrier. Applying live intravital microscopy using a low molecular weight vascular dye (150kDa), we observed a striking increase in blood vessel permeability in RT vs sham-treated brain tumors. Our observations support a model where RT drives metastasis through inflammation. To test this, we applied lipopolysaccharide (LPS), an inflammation inducing treatment, to a sporadic murine medulloblastoma model which significantly increased the metastatic burden. We then treated a xenograft model with dexamethasone in combination with RT, which resulted in total abrogation of metastatic dissemination compared to RT alone. Collectively, our findings suggest that while external beam irradiation is an effective and essential treatment for medulloblastoma, it may facilitate metastatic dissemination through an inflammation-induced process. These findings can help inform potential approaches to prevent disseminated relapsed disease.

Laser Ablation and Intravital Microscopy to Study Intestinal Remodeling.

Investigating intestinal recovery in vivo is an exquisite technical challenge. A lack of longitudinal imaging protocols has prevented deeper insights into the cell and tissue scale dynamics that orchestrate intestinal regeneration. Here, we describe an intravital microscopy method that locally induces tissue damage at the single crypt scale and follows the regenerative response of the intestinal epithelium in living mice. Single crypts or larger intestinal fields were ablated by a high-intensity multiphoton infrared laser in a time- and space-controlled manner. Subsequent long-term repetitive intravital imaging enabled the tracking of the damaged areas over time and allowed for the monitoring of crypt dynamics during tissue recovery over a period of multiple weeks. Crypt remodeling events such as crypt fission, fusion, and disappearance were observed in the neighboring tissue upon laser-induced damage. This protocol enables the study of crypt dynamics both in homeostatic and pathophysiological settings, such as aging and tumor initiation.