Novel in vivo techniques to visualize kidney anatomy and function

Abstract

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. Comprehensive and quantitative kidney structure and function MPM studies helped our better understanding of the cellular and molecular mechanisms of the healthy and diseased kidney. This review summarizes recent in vivo MPM studies with a focus on the glomerulus and the filtration barrier, although select, glomerulus-related renal vascular and tubular functions are also mentioned. The latest applications of serial MPM of the same glomerulus in vivo, in the intact kidney over several days, during the progression of glomerular disease are discussed. This visual approach, in combination with genetically encoded fluorescent markers of cell lineage, has helped to track the fate and function (e.g. cell calcium changes) of single podocytes during the development of glomerular pathologies, and provided visual proof for the highly dynamic rather than static nature of the glomerular environment. Future intravital imaging applications have the promise to further push the limits of optical microscopy, and to advance our understanding of the mechanisms of kidney injury. Also, MPM will help to study new mechanisms of tissue repair and regeneration, a cutting edge area of kidney research.

Combined use of electron microscopy and intravital imaging captures morphological and functional features of podocyte detachment

“…The present study confirmed the presence and passage of albumin-containing vesicles in the Bowman’s space in the rat PAN model. A recent report documented the rupture of albumin-containing pseudocysts that resulted in the emptying of the high albumin-containing cyst fluid into the Bowman’s space and downstream the nephron [25]. Albumin endocytosis by injured podocytes and the rupture of albumin-containing large pseudocysts are likely alternative mechanisms of albumin leakage through the GFB that contribute to the development of albuminuria.…”

Intravital imaging of the kidney

“…1A). Because of strong light scattering, deeper live imaging is currently limited as compared to other organs such as the brain, where less scattering species are present [1,18,19]. Improving imaging depth can be achieved with: 1) an increment in laser power, 2) the use of a high numerical aperture of the objective lens with matched refractive indices of the sample and immersion medium, 3) a long free working distance (e.g., Olympus objectives: XLPLanN 25x/1.05W MP, UPlanSApo 30x/1.05 Silicon oil, XLUMPlanFI 20x/0.95 W), 4) longer excitation wavelength as achieved with an optical parametric oscillator [20,21].…”

Drug discovery in focal and segmental glomerulosclerosis

“…Notwithstanding these limitations, some groups have been successful in deriving assays that might mimic some of the mechanistic processes associated with proteinuric disease 38, 39 and that can be used for drug screening purposes 40 . It will be interesting to determine if high throughput imaging system of podocyte function in vivo can be developed, and the scientific progress of this technique has been reviewed elsewhere 41 .…”