Novel light microscopy imaging techniques in nephrology

Super-resolution imaging for monitoring cytoskeleton dynamics

The cytoskeleton is a key cellular structure that is important in the control of cellular movement, structure, and sensing. To successfully image the individual cytoskeleton components, high resolution and super-resolution fluorescence imaging methods are needed. This review covers the three basic cytoskeletal elements and the relative benefits and drawbacks of fixed versus live cell imaging before moving on to recent studies using high resolution and super-resolution techniques. The techniques covered include the near-diffraction limited imaging methods of confocal microscopy and TIRF microscopy and the super-resolution fluorescence imaging methods of STORM, PALM, and STED.

Increased capillary branching contributes to angiotensin type 1 receptor blocker (ARB)-induced regression of sclerosis

Chronic kidney disease is characterized by progressive glomerulosclerosis and tubulointerstitial fibrosis. High-dose angiotensin type 1 receptor blocker (ARB) or angiotensin-converting enzyme inhibitor can induce regression of existing glomerulosclerosis, at least in part by decreasing matrix accumulation. However, the potential mechanisms of remodeling of capillary loops remain obscure. This study aimed to determine whether capillary branching was augmented in glomeruli with ARB-induced regression of sclerosis. Three-dimensional confocal images were assessed by graph theory analysis to explore the topology of the glomerular capillary network. Compared with normal glomeruli, glomeruli of rats with progressive sclerosis were enlarged but had a significantly reduced number of capillary segments and capillary branch points and decreased complexity of the glomerular network. In contrast, in rats with regression of sclerosis induced by ARB, glomerular enlargement was due to a significantly increased number of glomerular capillary segments and capillary branch points and restored complexity of the capillary network. These data support the theory that capillary growth contributes to regression of sclerosis and is mediated at least in part by ARB-induced increased complexity and branching of capillary segments.

Pharmacophotonics: utilizing multi-photon microscopy to quantify drug delivery and intracellular trafficking in the kidney

The recent introduction of multi-photon microscopy coupled with advances in optics, computer sciences and the available fluorophores used to label molecules of interest have empowered investigators to study the dynamic events within the functioning kidney at cellular and subcellular levels. This emerging technique, with improved spatial and temporal resolution and sensitivity, enables investigators to follow the cell specific uptake of large and small molecules, determine the mode of cellular uptake, intracellular trafficking and drug metabolism in complex heterogeneous organs such as the kidney over time. Repeat determinations over seconds to hours to days allow for multiple observations within the same animal, thereby minimizing animal use and inter-animal variability. This can be particularly useful for preclinical studies. Furthermore, the ability to obtain volumetric data (3-D) makes quantitative 4-D (time) analysis possible. Finally, up to three fluorophores can be visualized simultaneously allowing for three different or interactive processes to be observed and resolved.

Image processing software for 3D light microscopy

Advances in microscopy now enable researchers to easily acquire multi-channel three-dimensional (3D) images and 3D time series (4D). However, processing, analyzing, and displaying this data can often be difficult and time- consuming. We discuss some of the software tools and techniques that are available to accomplish these tasks.

Intravital multiphoton microscopy of dynamic renal processes

Recent advances in microscopy and optics, computer sciences, and the available fluorophores used to label molecules of interest have empowered investigators to utilize intravital two-photon microscopy to study the dynamic events within the functioning kidney. This emerging technique enables investigators to follow functional and structural alterations with subcellular resolution within the same field of view over seconds to weeks. This approach invigorates the validity of data and facilitates analysis and interpretation as trends are more readily determined when one is more closely monitoring indicative physiological parameters. Therefore, in this review we emphasize how specific approaches will enable studies into glomerular permeability, proximal tubule endocytosis, and microvascular function within the kidney. We attempt to show how visual data can be quantified, thus allowing enhanced understanding of the process under study. Finally, emphasis is given to the possible future opportunities of this technology and its present limitations.