Intravital multiphoton microscopy as a tool for studying renal physiology and pathophysiology

Lrpap1 (RAP) Inhibits Proximal Tubule Clathrin Mediated and Clathrin Independent Endocytosis, Ameliorating Renal Aminoglycoside Nephrotoxicity

Key Points

Proximal tubule endocytosis of toxins often leads to nephrotoxicity. Inhibition of endocytosis with receptor-associated protein may serve as a clinical approach to reduce or eliminate kidney damage from a potential nephrotoxin.

Background

Proximal tubules (PTs) are exposed to many exogenous and endogenous nephrotoxins that pass through the glomerular filter. This includes many small molecules, such as aminoglycoside and myeloma light chains. These filtered molecules are rapidly endocytosed by the PTs and lead to nephrotoxicity.

Methods

To investigate whether inhibition of PT uptake of filtered toxins can reduce toxicity, we evaluated the ability of Lrpap1 or receptor-associated protein (RAP) to prevent PT endocytosis. Munich Wistar Frömter rats were used since both glomerular filtration and PT uptake can be visualized and quantified. The injury model chosen was the well-established gentamicin-induced toxicity, which leads to significant reductions in GFR and serum creatinine increases. CKD was induced with a right uninephrectomy and left 40-minute pedicle clamp. Rats had 8 weeks to recover and to stabilize GFR and proteinuria. Multiphoton microscopy was used to evaluate endocytosis in vivo and serum creatinine, and 24-hour creatinine clearances were used to evaluate kidney functional changes.

Results

Studies showed that preadministration of RAP significantly inhibited both albumin and dextran endocytosis in outer cortical PTs. Importantly, this inhibition was found to be rapidly reversible with time. RAP was also found to be an excellent inhibitor of PT gentamicin endocytosis. Finally, gentamicin administration for 6 days resulted in significant elevation of serum creatinine in vehicle-treated rats, but not in those receiving daily infusion of RAP before gentamicin.

Conclusions

This study provides a model for the potential use of RAP to prevent, in a reversible manner, PT endocytosis of potential nephrotoxins, thus protecting the kidney from damage.

Capturing effects of blood flow on the transplanted decellularized nephron with intravital microscopy

Organ decellularization creates cell-free, collagen-based extracellular matrices that can be used as scaffolds for tissue engineering applications. This technique has recently gained much attention, yet adequate scaffold repopulation and implantation remain a challenge. Specifically, there still needs to be a greater understanding of scaffold responses post-transplantation and ways we can improve scaffold durability to withstand the in vivo environment. Recent studies have outlined vascular events that limit organ decellularization/recellularization scaffold viability for long-term transplantation. However, these insights have relied on in vitro/in vivo approaches that need enhanced spatial and temporal resolutions to investigate such issues at the microvascular level. This study uses intravital microscopy to gain instant feedback on their structure, function, and deformation dynamics. Thus, the objective of this study was to capture the effects of in vivo blood flow on the decellularized glomerulus, peritubular capillaries, and tubules after autologous and allogeneic orthotopic transplantation into rats. Large molecular weight dextran molecules labeled the vasculature. They revealed substantial degrees of translocation from glomerular and peritubular capillary tracks to the decellularized tubular epithelium and lumen as early as 12 h after transplantation, providing real-time evidence of the increases in microvascular permeability. Macromolecular extravasation persisted for a week, during which the decellularized microarchitecture was significantly and comparably compromised and thrombosed in both autologous and allogeneic approaches. These results indicate that in vivo multiphoton microscopy is a powerful approach for studying scaffold viability and identifying ways to promote scaffold longevity and vasculogenesis in bioartificial organs.

Defining the Intravital Renal Disposition of Fluorescence-Quenched Exenatide

Despite the understanding that renal clearance is pivotal for driving the pharmacokinetics of numerous therapeutic proteins and peptides, the specific processes that occur following glomerular filtration remain poorly defined. For instance, sites of catabolism within the proximal tubule can occur at the brush border, within lysosomes following endocytosis, or even within the tubule lumen itself. The objective of the current study was to address these limitations and develop methodology to study the kidney disposition of a model therapeutic protein. Exenatide is a peptide used to treat type 2 diabetes mellitus. Glomerular filtration and ensuing renal catabolism have been shown to be its principal clearance pathway. Here, we designed and validated a Förster resonance energy transfer-quenched exenatide derivative to provide critical information on the renal handling of exenatide. A combination of in vitro techniques was used to confirm substantial fluorescence quenching of intact peptide that was released upon proteolytic cleavage. This evaluation was then followed by an assessment of the in vivo disposition of quenched exenatide directly within kidneys of living rats via intravital two-photon microscopy. Live imaging demonstrated rapid glomerular filtration and identified exenatide metabolism occurred within the subapical regions of the proximal tubule epithelia, with subsequent intracellular trafficking of cleaved fragments. These results provide a novel examination into the real-time, intravital disposition of a protein therapeutic within the kidney and offer a platform to build upon for future work.

Intravital microscopy datasets examining key nephron segments of transplanted decellularized kidneys

This study contains intravital microscopy (IVM) data examining the microarchitecture of acellular kidney scaffolds. Acellular scaffolds are cell-free collagen-based matrices derived from native organs that can be used as templates for regenerative medicine applications. This data set contains in vivo assays that evaluate the effectiveness of decellularization and how these acellular nephron compartments perform in the post-transplantation environment. Qualitative and quantitative assessments of scaffold DNA concentrations, tissue fluorescence signals, and structural and functional integrities of decellularized tubular and peritubular capillary segments were acquired and compared to the native (non-transplanted) organ. Cohorts of 2–3-month-old male Sprague Dawley rats were used: non-transplanted (n = 4), transplanted day 0 (n = 4), transplanted day 1 (n = 4), transplanted day 2 (n = 4), and transplanted day 7 (n = 4). Micrographs and supporting measurements are provided to illustrate IVM processes used to perform this study and are publicly available in a data repository to assist scientific reproducibility and extend the use of this powerful imaging application to analyze other scaffold systems. Measurements(s) DNA quantification • tissue fluorescence • microvascular leakage • tubular and peritubular capillary integrity Technology Type(s) intravital microscopy • multiphoton microscopy • UV-visible spectroscopy Sample Characterization(s) rats • native and decellularized kidneys

Atrial Natriuretic Peptide and the Epithelial Sodium Channel Contribute to Spinal Cord Injury-Induced Polyuria in Mice

Polyuria is found in patients with spinal cord injury (SCI). However, the underlying cellular and molecular mechanism is unknown. Here, we show that mice had elevated urine for 7 days after T10 contusion. Using multi-photon confocal microscopy, we performed intra-vital imaging experiments to evaluate water reabsorption in kidney tubules by examining fluorescent intensity in the lumen of the distal tubule from live mice. The data show that SCI significantly reduced the concentrating function of kidney tubules. The reduced water reabsorption appears to be mediated by atrial natriuretic peptide (ANP) because SCI increased the expression levels of both ANP and natriuretic peptide receptor A (NPR-A) in the kidney cortex. Our patch-clamp single-channel recordings from split-open distal tubules show that SCI decreased the activity of the epithelial sodium channel (ENaC). Western blot combined with confocal microscopy data show that the levels of 70 kD γ-ENaC, which is an active isoform because of proteolytic cleavage, were significantly reduced in distal tubule principal cells. An NPR-A inhibitor (A71915) given intravenously eliminated the effects of SCI on ENaC and polyuria. These data together with previous studies suggest that SCI causes polyuria, probably by reducing ENaC activity through elevating ANP and NPR-A. Further investigation of the signal transduction pathways may provide useful information for discovering an efficient drug to treat SCI-induced polyuria.

Intravital Imaging with Two-Photon Microscopy: A Look into the Kidney

Fluorescence microscopy has represented a crucial technique to explore the cellular and molecular mechanisms in the field of biomedicine. However, the conventional one-photon microscopy exhibits many limitations when living samples are imaged. The new technologies, including two-photon microscopy (2PM), have considerably improved the in vivo study of pathophysiological processes, allowing the investigators to overcome the limits displayed by previous techniques. 2PM enables the real-time intravital imaging of the biological functions in different organs at cellular and subcellular resolution thanks to its improved laser penetration and less phototoxicity. The development of more sensitive detectors and long-wavelength fluorescent dyes as well as the implementation of semi-automatic software for data analysis allowed to gain insights in essential physiological functions, expanding the frontiers of cellular and molecular imaging. The future applications of 2PM are promising to push the intravital microscopy beyond the existing limits. In this review, we provide an overview of the current state-of-the-art methods of intravital microscopy, focusing on the most recent applications of 2PM in kidney physiology.

Single nephron glomerular filtration rate measured by linescan multiphoton microscopy compared to conventional micropuncture

Renal micropuncture, which requires the direct access to the renal tubules, has for long time been the technique of choice to measure the single nephron glomerular filtration rate (SNGFR) in animal models. This approach is challenging by virtue of complex animal preparation and numerous technically difficult steps. The introduction of intravital multiphoton microscopy (MPM) offers another approach to the measure of the SNGFR by mean of the high laser-tissue penetration and the optical sectioning capacity. Previous MPM studies measuring SNGFR in vivo relied on fast full-frame acquisition during the filtration process obtainable with high performance resonant scanners. In this study, we describe an innovative linescan–based MPM method. The new method can discriminate SNGFR variations both in conditions of low and high glomerular filtration, and shows results comparable to conventional micropuncture both for rats and mice. Moreover, this novel approach has improved spatial and time resolution and is faster than previous methods, thus enabling the investigation of SNGFR from more tubules and improving options for data-analysis.

Albumin Uptake and Processing by the Proximal Tubule: Physiologic, Pathologic and Therapeutic Implications

For nearly 50 years the proximal tubule (PT) has been known to reabsorb, process, and either catabolize or transcytose albumin from the glomerular filtrate. Innovative techniques and approaches have provided insights into these processes. Several genetic diseases, nonselective PT cell defects, chronic kidney disease (CKD), and acute PT injury lead to significant albuminuria, reaching nephrotic range. Albumin is also known to stimulate PT injury cascades. Thus, the mechanisms of albumin reabsorption, catabolism, and transcytosis are being reexamined with the use of techniques that allow for novel molecular and cellular discoveries. Megalin, a scavenger receptor, cubilin, amnionless, and Dab2 form a nonselective multireceptor complex that mediates albumin binding and uptake and directs proteins for lysosomal degradation after endocytosis. Albumin transcytosis is mediated by a pH-dependent binding affinity to the neonatal Fc receptor (FcRn) in the endosomal compartments. This reclamation pathway rescues albumin from urinary losses and cellular catabolism, extending its serum half-life. Albumin that has been altered by oxidation, glycation, or carbamylation or because of other bound ligands that do not bind to FcRn traffics to the lysosome. This molecular sorting mechanism reclaims physiological albumin and eliminates potentially toxic albumin. The clinical importance of PT albumin metabolism has also increased as albumin is now being used to bind therapeutic agents to extend their half-life and minimize filtration and kidney injury. The purpose of this review is to update and integrate evolving information regarding the reabsorption and processing of albumin by proximal tubule cells including discussion of genetic disorders and therapeutic considerations.

Multiphoton imaging of melanoma 3D models with plasmonic nanocapsules

We report the synthesis of plasmonic nanocapsules and the cellular responses they induce in 3D melanoma models for their perspective use as a photothermal therapeutic agent. The wall of the nanocapsules is composed of polyelectrolytes. The inner part is functionalized with discrete gold nanoislands. The cavity of the nanocapsules contains a fluorescent payload to show their ability for loading a cargo. The nanocapsules exhibit simultaneous two-photon luminescent, fluorescent properties and X-ray contrasting ability. The average fluorescence lifetime (τ) of the nanocapsules measured with FLIM (0.3 ns) is maintained regardless of the intracellular environment, thus proving their abilities for bioimaging of models such as 3D spheroids with a complex architecture. Their multimodal imaging properties are exploited for the first time to study tumorspheres cellular responses exposed to the nanocapsules. Specifically, we studied cellular uptake, toxicity, intracellular fate, generation of reactive oxygen species, and effect on the levels of hypoxia by using multi-photon and confocal laser scanning microscopy. Because of the high X-ray attenuation and atomic number of the gold nanostructure, we imaged the nanocapsule-cell interactions without processing the sample. We confirmed maintenance of the nanocapsules' geometry in the intracellular milieu with no impairment of the cellular ultrastructure. Furthermore, we observed the lack of cellular toxicity and no alteration in oxygen or reactive oxygen species levels. These results in 3D melanoma models contribute to the development of these nanocapsules for their exploitation in future applications as agents for imaging-guided photothermal therapy. STATEMENT OF SIGNIFICANCE: The novelty of the work is that our plasmonic nanocapsules are multimodal. They are responsive to X-ray and to multiphoton and single-photon excitation. This allowed us to study their interaction with 2D and 3D cellular structures and specifically to obtain information on tumor cell parameters such as hypoxia, reactive oxygen species, and toxicity. These nanocapsules will be further validated as imaging-guided photothermal probes.

Intravital Multiphoton Microscopy as a Tool for Studying Renal Physiology, Pathophysiology and Therapeutics

Intravital multiphoton microscopy has empowered investigators to study dynamic cell and subcellular processes in vivo within normal and disease organs. Advances in hardware, software, optics, transgenics and fluorescent probe design and development have enabled new quantitative approaches to create a disruptive technology pioneering advances in understanding of normal biology, disease pathophysiology and therapies. Offering superior spatial and temporal resolution with high sensitivity, investigators can follow multiple processes simultaneously and observe complex interactions between different cell types, intracellular organelles, proteins and track molecules for cellular uptake, intracellular trafficking, and metabolism in a cell specific fashion. The technique has been utilized in the kidney to quantify multiple dynamic processes including capillary flow, permeability, glomerular function, proximal tubule processes and determine the effects of diseases and therapeutic mechanisms. Limitations include the depth of tissue penetration with loss of sensitivity and resolution due to scattered emitted light. Tissue clearing technology has virtually eliminated penetration issues for fixed tissue studies. Use of multiphoton microscopy in preclinical animal models offers distinct advantages resulting in new insights into physiologic processes and the pathophysiology and treatment of diseases.

Pericyte-mediated constriction of renal capillaries evokes no-reflow and kidney injury following ischaemia

Acute kidney injury is common, with ~13 million cases and 1.7 million deaths/year worldwide. A major cause is renal ischaemia, typically following cardiac surgery, renal transplant or severe haemorrhage. We examined the cause of the sustained reduction in renal blood flow ('no-reflow'), which exacerbates kidney injury even after an initial cause of compromised blood supply is removed. Adult male Sprague-Dawley rats, or NG2-dsRed male mice were used in this study. After 60 min kidney ischaemia and 30-60 min reperfusion, renal blood flow remained reduced, especially in the medulla, and kidney tubule damage was detected as Kim-1 expression. Constriction of the medullary descending vasa recta and cortical peritubular capillaries occurred near pericyte somata, and led to capillary blockages, yet glomerular arterioles and perfusion were unaffected, implying that the long-lasting decrease of renal blood flow contributing to kidney damage was generated by pericytes. Blocking Rho kinase to decrease pericyte contractility from the start of reperfusion increased the post-ischaemic diameter of the descending vasa recta capillaries at pericytes, reduced the percentage of capillaries that remained blocked, increased medullary blood flow and reduced kidney injury. Thus, post-ischaemic renal no-reflow, contributing to acute kidney injury, reflects pericytes constricting the descending vasa recta and peritubular capillaries. Pericytes are therefore an important therapeutic target for treating acute kidney injury.

Renal Normothermic Machine Perfusion: The Road Toward Clinical Implementation of a Promising Pretransplant Organ Assessment Tool

The increased utilization of high-risk renal grafts for transplantation requires optimization of pretransplant organ assessment strategies. Current decision-making methods to accept an organ for transplantation lack overall predictive power and always contain an element of subjectivity. Normothermic machine perfusion (NMP) creates near-physiological conditions, which might facilitate a more objective assessment of organ quality before transplantation. NMP is rapidly gaining popularity, with various transplant centers developing their own NMP protocols and renal viability criteria. However, to date, no validated sets of on-pump viability markers exist nor are there unified NMP protocols. This review provides a critical overview of the fundamentals of current renal NMP protocols and proposes a framework to approach further development of ex vivo organ evaluation. We also comment on the potential logistical implications of routine clinical use of NMP, which is a more complex procedure compared with static cold storage or even hypothermic machine perfusion.

Immune cell behaviour and dynamics in the kidney - insights from in vivo imaging

The actions of immune cells within the kidney are of fundamental importance in kidney homeostasis and disease. In disease settings such as acute kidney injury, anti-neutrophil cytoplasmic antibody-associated vasculitis, lupus nephritis and renal transplant rejection, immune cells resident within the kidney and those recruited from the circulation propagate inflammatory responses with deleterious effects on the kidney. As in most forms of inflammation, intravital imaging - particularly two-photon microscopy - has been critical to our understanding of immune cell responses in the renal microvasculature and interstitium, enabling visualization of immune cell dynamics over time rather than statically. These studies have demonstrated differences in the recruitment and function of these cells from those in more conventional vascular beds, and provided a wealth of information on the actions of blood-borne immune cells such as neutrophils, monocytes and T cells, as well as kidney-resident mononuclear phagocytes, in a range of diseases affecting different kidney compartments. In particular, in vivo imaging has furthered our understanding of leukocyte function within the glomerulus in acute glomerulonephritis, and in the tubulointerstitium and interstitial microvasculature during acute kidney injury and following transplantation, revealing mechanisms of immune surveillance, antigen presentation and inflammation in the kidney.

New Endothelial Mechanisms in Glomerular (Patho)biology and Proteinuria Development Captured by Intravital Multiphoton Imaging

In the past two decades, intravital imaging using multiphoton microscopy has provided numerous new visual and mechanistic insights into glomerular biology and disease processes including the function of glomerular endothelial cells (GEnC), podocytes, and the development of proteinuria. Although glomerular endothelial injury is known to precede podocyte damage in several renal diseases, the primary role of GEnCs in proteinuria development received much less attention compared to the vast field of podocyte pathobiology. Consequently, our knowledge of GEnC mechanisms in glomerular diseases is still emerging. This review highlights new visual clues on molecular and cellular mechanisms of GEnCs and their crosstalk with podocytes and immune cells that were acquired recently by the application of multiphoton imaging of the intact glomerular microenvironment in various proteinuric disease models. New mechanisms of glomerular tissue remodeling and regeneration are discussed based on results of tracking the fate and function of individual GEnCs using serial intravital multiphoton imaging over several days and weeks. The three main topics of this review include (i) the role of endothelial injury and microthrombi in podocyte detachment and albumin leakage via hemodynamic and mechanical forces, (ii) the alterations of the endothelial surface layer (glycocalyx) and its interactions with circulating immune cells in lupus nephritis, and (iii) the structural and functional remodeling and regeneration of GEnCs in hypertension, diabetes, and other experimental injury conditions. By the comprehensive visual portrayal of GEnCs and the many other contributing glomerular cell types, this review emphasizes the complexity of pathogenic mechanisms that result in proteinuria development.

Kidney intercalated cells are phagocytic and acidify internalized uropathogenic Escherichia coli

Kidney intercalated cells are involved in acid-base homeostasis via vacuolar ATPase expression. Here we report six human intercalated cell subtypes, including hybrid principal-intercalated cells identified from single cell transcriptomics. Phagosome maturation is a biological process that increases in biological pathway analysis rank following exposure to uropathogenic Escherichia coli in two of the intercalated cell subtypes. Real time confocal microscopy visualization of murine renal tubules perfused with green fluorescent protein expressing Escherichia coli or pHrodo Green E. coli BioParticles demonstrates that intercalated cells actively phagocytose bacteria then acidify phagolysosomes. Additionally, intercalated cells have increased vacuolar ATPase expression following in vivo experimental UTI. Taken together, intercalated cells exhibit a transcriptional response conducive to the kidney's defense, engulf bacteria and acidify the internalized bacteria. Intercalated cells represent an epithelial cell with characteristics of professional phagocytes like macrophages.

The Indiana O'Brien Center for Advanced Renal Microscopic Analysis

The Indiana O'Brien Center for Advanced Microscopic Analysis is a National Institutes of Health (NIH) P30-funded research center dedicated to the development and dissemination of advanced methods of optical microscopy to support renal researchers throughout the world. The Indiana O'Brien Center was founded in 2002 as an NIH P-50 project with the original goal of helping researchers realize the potential of intravital multiphoton microscopy as a tool for understanding renal physiology and pathophysiology. The center has since expanded into the development and implementation of large-scale, high-content tissue cytometry. The advanced imaging capabilities of the center are made available to renal researchers worldwide via collaborations and a unique fellowship program. Center outreach is accomplished through an enrichment core that oversees a seminar series, an informational website, and a biennial workshop featuring hands-on training from members of the Indiana O'Brien Center and imaging experts from around the world.

In Vivo Assessment of Size-Selective Glomerular Sieving in Transplanted Human Induced Pluripotent Stem Cell-Derived Kidney Organoids

BACKGROUND

The utility of kidney organoids in regenerative medicine will rely on the functionality of the glomerular and tubular structures in these tissues. Recent studies have demonstrated the vascularization and subsequent maturation of human pluripotent stem cell-derived kidney organoids after renal subcapsular transplantation. This raises the question of whether the glomeruli also become functional upon transplantation.

METHODS

We transplanted kidney organoids under the renal capsule of the left kidney in immunodeficient mice followed by the implantation of a titanium imaging window on top of the kidney organoid. To assess glomerular function in the transplanted human pluripotent stem cell-derived kidney tissue 1, 2, and 3 weeks after transplantation, we applied high-resolution intravital multiphoton imaging through the imaging window during intravenous infusion of fluorescently labeled low and high molecular mass dextran molecules or albumin.

RESULTS

After vascularization, glomerular structures in the organoid displayed dextran and albumin size selectivity across their glomerular filtration barrier. We also observed evidence of proximal tubular dextran reuptake.

CONCLUSIONS

Our results demonstrate that human pluripotent stem cell-derived glomeruli can develop an appropriate barrier function and discriminate between molecules of varying size. These characteristics together with tubular presence of low molecular mass dextran provide clear evidence of functional filtration. This approach to visualizing glomerular filtration function will be instrumental for translation of organoid technology for clinical applications as well as for disease modeling.

Advances in fluorescence microscopy techniques to study kidney function

Fluorescence microscopy, in particular immunofluorescence microscopy, has been used extensively for the assessment of kidney function and pathology for both research and diagnostic purposes. The development of confocal microscopy in the 1950s enabled imaging of live cells and intravital imaging of the kidney; however, confocal microscopy is limited by its maximal spatial resolution and depth. More recent advances in fluorescence microscopy techniques have enabled increasingly detailed assessment of kidney structure and provided extraordinary insights into kidney function. For example, nanoscale precise imaging by rapid beam oscillation (nSPIRO) is a super-resolution microscopy technique that was originally developed for functional imaging of kidney microvilli and enables detection of dynamic physiological events in the kidney. A variety of techniques such as fluorescence recovery after photobleaching (FRAP), fluorescence correlation spectroscopy (FCS) and Förster resonance energy transfer (FRET) enable assessment of interaction between proteins. The emergence of other super-resolution techniques, including super-resolution stimulated emission depletion (STED), photoactivated localization microscopy (PALM), stochastic optical reconstruction microscopy (STORM) and structured illumination microscopy (SIM), has enabled functional imaging of cellular and subcellular organelles at ≤50 nm resolution. The deep imaging via emission recovery (DIVER) detector allows deep, label-free and high-sensitivity imaging of second harmonics, enabling assessment of processes such as fibrosis, whereas fluorescence lifetime imaging microscopy (FLIM) enables assessment of metabolic processes.

Combined Structural and Functional Imaging of the Kidney Reveals Major Axial Differences in Proximal Tubule Endocytosis

BACKGROUND

The kidney proximal convoluted tubule (PCT) reabsorbs filtered macromolecules via receptor-mediated endocytosis (RME) or nonspecific fluid phase endocytosis (FPE); endocytosis is also an entry route for disease-causing toxins. PCT cells express the protein ligand receptor megalin and have a highly developed endolysosomal system (ELS). Two PCT segments (S1 and S2) display subtle differences in cellular ultrastructure; whether these translate into differences in endocytotic function has been unknown.

METHODS

To investigate potential differences in endocytic function in S1 and S2, we quantified ELS protein expression in mouse kidney PCTs using real-time quantitative polymerase chain reaction and immunostaining. We also used multiphoton microscopy to visualize uptake of fluorescently labeled ligands in both living animals and tissue cleared using a modified CLARITY approach.

RESULTS

Uptake of proteins by RME occurs almost exclusively in S1. In contrast, dextran uptake by FPE takes place in both S1 and S2, suggesting that RME and FPE are discrete processes. Expression of key ELS proteins, but not megalin, showed a bimodal distribution; levels were far higher in S1, where intracellular distribution was also more polarized. Tissue clearing permitted imaging of ligand uptake at single-organelle resolution in large sections of kidney cortex. Analysis of segmented tubules confirmed that, compared with protein uptake, dextran uptake occurred over a much greater length of the PCT, although individual PCTs show marked heterogeneity in solute uptake length and three-dimensional morphology.

CONCLUSIONS

Striking axial differences in ligand uptake and ELS function exist along the PCT, independent of megalin expression. These differences have important implications for understanding topographic patterns of kidney diseases and the origins of proteinuria.

Characterization of Blood Volume Space and Mitochondrial Activity in Functional Renal Cells

Renal function can become compromised in the event of shock, leading to acute kidney injury (AKI). As a result, microcirculatory dysfunction and disruption of oxygen homeostastis is observed, which leads to a shift in mitochondrial bioenergetics. These events can be studied by assessing the functionality in healthy, normal states and diseased states. Characterization of the spatial heterogeneity of mitochondrial activity and capillary blood volume space in healthy renal cells was performed using intravital multi-photon microscopy. The developed metrics that were used for depiction and quantification of the physiologic normal state can be applied to a diseased state, allowing the extent of microcirculatory dysfunction to be observed and evaluated.