Analysis of the three dimensional structure of the kidney glomerulus capillary network

Abstract

The capillary network of the kidney glomerulus filters small molecules from the blood. The glomerular 3D structure should help to understand its function, but it is poorly characterized. We therefore devised a new approach in which an automated tape collecting microtome (ATUM) was used to collect 0.5 μm thick serial sections from fixed mouse kidneys. The sections were imaged by scanning electron microscopy at ~ 50 nm/pixel resolution. With this approach, 12 glomeruli were reconstructed at an x–y–z resolution ~ 10 × higher than that of paraffin sections. We found a previously undescribed no-cross zone between afferent and efferent branches on the vascular pole side; connections here would allow blood to exit without being adequately filtered. The capillary diameters throughout the glomerulus appeared to correspond with the amount of blood flow within them. The shortest path (minimum number of branches to travel from afferent to efferent arterioles) is relatively independent of glomerular size and is present primarily on the vascular pole size. This suggests that new branches and longer paths form on the urinary pole side. Network analysis indicates that the glomerular network does not form by repetitive longitudinal splitting of capillaries. Thus the 3D structure of the glomerular capillary network provides useful information with which to understand glomerular function. Other tissue structures in the body may benefit from this new three dimensional approach.

Emerging Insights into Glomerular Vascular Pole and Microcirculation

“…The idea of a shunt pathway (Trueta or Oxford shunt), suggested to connect afferent and efferent arterioles and redistribute blood flow away from glomerular capillaries, has been definitively rejected in recent electron microscopy reconstruction from serial sections and graph analysis of mouse glomeruli. These investigations demonstrate a “no cross zone” between afferent and efferent arterioles with no detectable “shunt” vessels 16 . Nonetheless, these studies show (Figure 1) within each glomerular tuft (which has 75–250 nodes or brunching points) a shorter pathway of eight to 12 nodes between the afferent and efferent arterioles 16 .…”

“…Different variations of this question have long been vexing, as Steinhausen et al 24 describe. In all examined glomeruli, the shorter path crossed the intraglomerular mesangial stalk, 16 raising the possibility that the intrinsic pulsatile contractility of mesangial cells could regulate the extent of open/closed states of the shorter path. Could the oscillatory pattern of chloride ion concentration ([Cl − ]) at the luminal side of the macula densa trigger commensurate contraction-relaxation cycles of mesangial cells, the oscillating pattern of deformation of glomerular capillaries, and thus glomerular perfusion?…”

“…According to Terasaki et al , 16 this shorter circuit represents a developmental primordium of the glomerular tuft, which undergoes eventual vasculogenic or angiogenic sprouting, giving rise to the rich network of glomerular capillaries. Shorter path patency could regulate the proportion of blood flowing toward the deeper bifurcating glomerular capillaries to undergo filtration in the glomerular capillary tuft.…”

Three-Dimensional Architecture of Glomerular Endothelial Cells Revealed by FIB-SEM Tomography

“…The serial ultrathin sections on the base substrate are physically stable and repeatedly observable by SEM. Terasaki et al (2020) visualized the 3D architecture of a normal glomerular capillary system by array tomography using an ATUMtome, which automatically collects serial ultrathin sections on a tape base ( Hayworth et al, 2014 ). This method will be useful for evaluating 3D pathologic alterations of the glomerular capillary system, such as the hilar neovascularization in diabetic nephropathy ( Min and Yamanaka, 1993 ; Osterby et al, 1999 ) and the reorganization of the capillary system in mesangioproliferative glomerulonephritis ( Kriz et al, 2003 ; Notoya et al, 2003 ; Ichimura et al, 2006 ).…”

Computational Identification and 3D Morphological Characterization of Renal Glomeruli in Optically Cleared Murine Kidneys

“…In rodents, a technique has been established for the extraction of intact glomeruli from renal tissue, but was not associated with techniques allowing the 3D structural characterization of the isolated glomeruli [3,8]. 3D glomerular structure has been reconstructed from glomerulus serial 2D sectional images taken by electron microscopy and photonic microscopy [9,10]. Recently, MRI has been performed on mice to count the glomeruli and calculate their volume from 3D images [11].…”