Neuronally differentiated macula densa cells regulate tissue remodeling and regeneration in the kidney.

Tissue regeneration is limited in several organs, including the kidney, contributing to the high prevalence of kidney disease globally. However, evolutionary and physiological adaptive responses and the presence of renal progenitor cells suggest an existing remodeling capacity. This study uncovered endogenous tissue remodeling mechanisms in the kidney that were activated by the loss of body fluid and salt and regulated by a unique niche of a minority renal cell type called the macula densa (MD).

Serial intravital imaging captures dynamic and functional endothelial remodeling with single-cell resolution.

Endothelial cells are important in the maintenance of healthy blood vessels and in the development of vascular diseases. However, the origin and dynamics of endothelial precursors and remodeling at the single-cell level have been difficult to study in vivo owing to technical limitations. Therefore, we aimed to develop a direct visual approach to track the fate and function of single endothelial cells over several days and weeks in the same vascular bed in vivo using multiphoton microscopy (MPM) of transgenic Cdh5-Confetti mice and the kidney glomerulus as a model.

A new view of macula densa cell microanatomy.

Although macula densa (MD) cells are chief regulatory cells in the nephron with unique microanatomical features, they have been difficult to study in full detail due to their inaccessibility and limitations in earlier microscopy techniques. The present study used a new mouse model with a comprehensive imaging approach to visualize so far unexplored microanatomical features of MD cells, their regulation, and functional relevance. MD-GFP mice with conditional and partial induction of green fluorescent protein (GFP) expression, which specifically and intensely illuminated only single MD cells, were used with fluorescence microscopy of fixed tissue and live MD cells in vitro and in vivo with complementary electron microscopy of the rat, rabbit, and human kidney.

Essential role and therapeutic targeting of the glomerular endothelial glycocalyx in lupus nephritis.

Lupus nephritis (LN) is a major organ complication and cause of morbidity and mortality in patients with systemic lupus erythematosus (SLE). There is an unmet medical need for developing more efficient and specific, mechanism-based therapies, which depends on improved understanding of the underlying LN pathogenesis. Here we present direct visual evidence from high-power intravital imaging of the local kidney tissue microenvironment in mouse models showing that activated memory T cells originated in immune organs and the LN-specific robust accumulation of the glomerular endothelial glycocalyx played central roles in LN development.

Novel fluorescence techniques to quantitate renal cell biology.

Fluorescence microscopy techniques are powerful tools to study tissue dynamics, cellular function and biology both in vivo and in vitro. These tools allow for functional assessment and quantification along with qualitative analysis, thus providing a comprehensive understanding of various cellular processes under normal physiological and disease conditions. The main focus of this chapter is the recently developed method of serial intravital multiphoton microscopy that has helped shed light on the dynamic alterations of the spatial distribution and fate of single renal cells or cell populations and their migration patterns in the same tissue region over several days in response to various stimuli within the living kidney.

Aldosterone induces albuminuria via matrix metalloproteinase-dependent damage of the endothelial glycocalyx.

Aldosterone contributes to end-organ damage in heart failure and chronic kidney disease. Mineralocorticoid-receptor inhibitors limit activation of the receptor by aldosterone and slow disease progression, but side effects, including hyperkalemia, limit their clinical use. Damage to the endothelial glycocalyx (a luminal biopolymer layer) has been implicated in the pathogenesis of endothelial dysfunction and albuminuria, but to date no one has investigated whether the glomerular endothelial glycocalyx is affected by aldosterone.

The macula densa prorenin receptor is essential in renin release and blood pressure control.

The prorenin receptor (PRR) was originally proposed to be a member of the renin-angiotensin system (RAS); however, recent work questioned their association. The present paper describes a functional link between the PRR and RAS in the renal juxtaglomerular apparatus (JGA), a classic anatomical site of the RAS. PRR expression was found in the sensory cells of the JGA, the macula densa (MD), and immunohistochemistry-localized PRR to the MD basolateral cell membrane in mouse, rat, and human kidneys.

Prasugrel suppresses development of lithium-induced nephrogenic diabetes insipidus in mice.

Previously, we localized ADP-activated P2Y receptor (R) in rodent kidney and showed that its blockade by clopidogrel bisulfate (CLPD) attenuates lithium (Li)-induced nephrogenic diabetes insipidus (NDI). Here, we evaluated the effect of prasugrel (PRSG) administration on Li-induced NDI in mice. Both CLPD and PRSG belong to the thienopyridine class of ADP receptor antagonists.

Just Look! Intravital Microscopy as the Best Means to Study Kidney Cell Death Dynamics.

Kidney cell death plays a key role in the progression of life-threatening renal diseases, such as acute kidney injury and chronic kidney disease. Injured and dying epithelial and endothelial cells take part in complex communication with the innate immune system, which drives the progression of cell death and the decrease in renal function. To improve our understanding of kidney cell death dynamics and its impact on renal disease, a study approach is needed that facilitates the visualization of renal function and morphology in real time.

Intravital imaging in the kidney.

Purpose Of Review: The review aims to provide a brief summary and evaluation of the current state of research that uses multiphoton fluorescence microscopy for intravital kidney imaging.

Recent Findings: Direct visualization of the glomerular filter, proximal and distal tubule segments, and the renal vasculature in the living, intact kidney in zebrafish, mouse, and rat models with high temporal and spatial resolution provided new insights into the function of the normal and diseased kidney. New technical developments in fluorescence excitation and detection, in combination with transgenic animal models for cell function and fate mapping, and serial imaging of the same glomerulus in the same animal over several days further advanced the field of nephrology research, and the understanding of disease mechanisms.

An ectopic renin-secreting adrenal corticoadenoma in a child with malignant hypertension.

A previously healthy 7-year-old male presented with hypertensive emergency, hypokalemia, and elevated plasma renin activity and aldosterone levels. There was no evidence of virilization or cushingoid features. MRI of the abdomen revealed a large (5 × 5 × 3 cm) peripherally enhancing, heterogeneous mass arising from the left adrenal gland.

Clopidogrel attenuates lithium-induced alterations in renal water and sodium channels/transporters in mice.

Lithium (Li) administration causes deranged expression and function of renal aquaporins and sodium channels/transporters resulting in nephrogenic diabetes insipidus (NDI). Extracellular nucleotides (ATP/ADP/UTP), via P2 receptors, regulate these transport functions. We tested whether clopidogrel bisulfate (CLPD), an antagonist of ADP-activated P2Y(12) receptor, would affect Li-induced alterations in renal aquaporins and sodium channels/transporters.

Novel in vivo techniques to visualize kidney anatomy and function.

Intravital imaging using multiphoton microscopy (MPM) has become an increasingly popular and widely used experimental technique in kidney research over the past few years. MPM allows deep optical sectioning of the intact, living kidney tissue with submicron resolution, which is unparalleled among intravital imaging approaches. MPM has solved a long-standing critical technical barrier in renal research to study several complex and inaccessible cell types and anatomical structures in vivo in their native environment.

Intravital imaging of podocyte calcium in glomerular injury and disease.

Intracellular calcium ([Ca²⁺]i) signaling mediates physiological and pathological processes in multiple organs, including the renal podocyte; however, in vivo podocyte [Ca²⁺]i dynamics are not fully understood. Here we developed an imaging approach that uses multiphoton microscopy (MPM) to directly visualize podocyte [Ca²⁺]i dynamics within the intact kidneys of live mice expressing a fluorescent calcium indicator only in these cells. [Ca²⁺]i was at a low steady-state level in control podocytes, while Ang II infusion caused a minor elevation.

The absence of intrarenal ACE protects against hypertension.

Activation of the intrarenal renin-angiotensin system (RAS) can elicit hypertension independently from the systemic RAS. However, the precise mechanisms by which intrarenal Ang II increases blood pressure have never been identified. To this end, we studied the responses of mice specifically lacking kidney angiotensin-converting enzyme (ACE) to experimental hypertension.

Effects of ACE inhibition and ANG II stimulation on renal Na-Cl cotransporter distribution, phosphorylation, and membrane complex properties.

The renal distal tubule Na-Cl cotransporter (NCC) reabsorbs <10% of the filtered Na(+) but is a key control point for blood pressure regulation by angiotensin II (ANG II), angiotensin-converting enzyme inhibitors (ACEI), and thiazide diuretics. This study aimed to determine whether NCC phosphorylation (NCCp) was regulated by acute (20-30 min) treatment with the ACEI captopril (12 μg/min × 20 min) or by a sub-pressor dose of ANG II (20 ng·kg(-1)·min(-1)) in Inactin-anesthetized rats. By immuno-EM, NCCp was detected exclusively in or adjacent to apical plama membranes (APM) in controls and after ACEI or ANG II treatment, while NCC total was detected in both APM and subapical cytoplasmic vesicles (SCV) in all conditions.

Metabolic control of renin secretion.

One emerging topic in renin-angiotensin system (RAS) research is the direct local control of renin synthesis and release by endogenous metabolic intermediates. During the past few years, our laboratory has characterized the localization and signaling of the novel metabolic receptor GPR91 in the normal and diabetic kidney and established GPR91 as a new, direct link between high glucose and RAS activation in diabetes. GPR91 (also called SUCNR1) binds tricarboxylic acid (TCA) cycle intermediate succinate which can rapidly accumulate in the local tissue environment when energy supply and demand are out of balance.

AT1A angiotensin receptors in the renal proximal tubule regulate blood pressure.

Hypertension affects more than 1.5 billion people worldwide but the precise cause of elevated blood pressure (BP) cannot be determined in most affected individuals. Nonetheless, blockade of the renin-angiotensin system (RAS) lowers BP in the majority of patients with hypertension.

Angiotensin II stimulates trafficking of NHE3, NaPi2, and associated proteins into the proximal tubule microvilli.

Angiotensin II (ANG II) stimulates proximal tubule (PT) sodium and water reabsorption. We showed that treating rats acutely with the angiotensin-converting enzyme inhibitor captopril decreases PT salt and water reabsorption and provokes rapid redistribution of the Na(+)/H(+) exchanger isoform 3 (NHE3), Na(+)/Pi cotransporter 2 (NaPi2), and associated proteins out of the microvilli. The aim of the present study was to determine whether acute ANG II infusion increases the abundance of PT NHE3, NaPi2, and associated proteins in the microvilli available for reabsorbing NaCl.