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. 2023 Mar 31;13(1):5289.
doi: 10.1038/s41598-023-31747-w.

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

Affiliations

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

Peter R Corridon. Sci Rep. .

Abstract

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.

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Conflict of interest statement

The author declares no competing interests.

Figures

Figure 1
Figure 1
Illustrations of the autologous and allogeneic orthotopic transplantation schema and IVM process. (A) Left-radical nephrectomies were first conducted to obtain kidneys with intact segments of renal arteries, veins, and ureters. Each native kidney was then decellularized and transplanted back into its respective recipient or implanted into another uninephrectomized recipient. (B) A schematic illustrating the intravital imaging process used to visualize live transplanted or native kidneys. As outlined in the literature, anesthetized rats with exteriorized (native or transplanted) kidneys were placed in a 50 mm glass-bottom dish, filled with saline, and set above the stage of an inverted microscope with a Nikon × 60 1.2-NA water-immersion objective. A 25-gauge butterfly needle was inserted into the dilated tail vein and attached to a syringe containing injectates. The heating pad was placed directly over the animal to maintain the core temperature.
Figure 2
Figure 2
An evaluation of the decellularization process using biochemical assays. (A) An image of a whole rat kidney with its renal artery cannulated for perfusion-based decellularization. (B) The kidney, after 4 h of perfusion with SDS, illustrates its transition from a solid to a translucent structure. (C) The fully decellularized kidney is shown after 8 h of SDS perfusion. (D) The kidney after its subsequent perfusion with PBS. (E) A plot presenting the low level of remnant DNA in the scaffold after decellularization. (F) A graph highlighting the effective removal of SDS from the scaffold and its low residual concentration. Non-parametric evaluations conducted using Kruskal–Wallis detected significant declines in DNA and SDS concentrations after decellularization (*p < 0.001).
Figure 3
Figure 3
An evaluation of the decellularization process using IVM. (A) Images obtained from a native (non-transplanted) kidney show the nuclear stain’s vibrant presence. (B) Image from a transplanted decellularized kidney showing the absence of Hoechst 33342 labeling and comparing green autofluorescence signals gathered from native (non-transplanted) and transplanted decellularized kidneys. (C) Image obtained from a native kidney that presents only distal (DT) and proximal (PT) tubular compartments and peritubular vascular tracks (V). (D) Intravital micrograph identifying decellularized tubular (T) and vascular compartments. It should be noted that the decellularization process made it difficult to differentiate between tubular segments. (E) Image obtained from a native kidney that captured the Bowman’s space (BS) and glomerular capillaries (GC), the S1 segment of the proximal tubule compartment (S1), and peritubular vasculature. (F) Image of a scaffold kidney highlighted the decellularized glomerular and tubular segments. (G) Comparison of relative blue pseudo-color fluorescence intensity from native and decellularized scaffolds. (H) Comparison of relative green pseudo-color fluorescence intensity from native and decellularized scaffolds. Non-parametric evaluations conducted using the Kruskal–Wallis test detected significant reductions in both the normalized blue (*p < 0.001) and green (**p < 0.001) pseudo-color fluorescence observed after decellularization. Scale bars represent 20 µm.
Figure 4
Figure 4
In vivo assessment of microvascular leakage in decellularized nephrons directly after injection of the dextran. (A) 1 min, (B) 2 min, and (C) 5 min segments of time-series images taken across 5 min from a live native kidney display the proper confinement of large molecular weight dextrans within the peritubular vasculature (V) and characteristic autofluorescence levels within proximal and distal tubules and nuclear staining with Hoechst 33422 (arrows). (D) 1 min, (E) 2 min, and (F) 3 min images time-points obtained from transplanted acellular scaffold also display the confinement of large molecular weight dextrans within the peritubular vasculature (V) and substantially reduced autofluorescence levels within the tubules, and absence of nuclear staining. Tubular lumens are highlighted by (L). Scale bars represent 20 µm. (G) A graphical representation of green pseudo-color fluorescence variations outlining relatively constant and elevated fluorescence levels within the vasculature, compared to the much lower signals recorded in the tubular lumen and epithelium. (H) A similar graphical representation of the variations in green pseudo-color fluorescence levels observed in decellularized kidneys shows the rising level and FITC fluorescent within the vasculature compared to lower signals recorded in the tubular lumen and epithelium. The data presented in this figure highlight events recorded from autologous transplantation and are comparable to those observed in allogeneic cases.
Figure 5
Figure 5
Disruptions to scaffold integrity during a week after transplantation and estimations of blood extravasation from various decellularized renal compartments, rouleaux density, glomerular hypertrophy, and velocity within the microvasculature. (A) An image taken from a decellularized kidney that displays the decellularized autofluorescence before the introduction of FITC (this is the same imaging field shown in Fig. 3F. (B) An image taken from a decellularized kidney 12 h after transplantation illustrates substantial and inhomogeneous levels of dye translocation (arrowheads) between luminal, epithelial, and interstitial compartments. (C) Image taken from a decellularized kidney 24 h after transplantation presents the accumulation of the translocated dextran (arrowheads) and blebs within the Bowman’s capsule, interstitium, and tubules. (D) Image taken from a transplanted decellularized kidney 1 week (168 h) after transplantation provides evidence of rouleaux (dashed oval within the vasculature) and bleb/vesicle (arrows within the Bowman’s space and tubular lumen) formation that accompanied dye extrusion from breached decellularized glomerular capillary tracks to occlude this enlarged glomerulus completely. Graphs examining the degree of FITC dye translocated within (E) the Bowman’s space, (F) tubular epithelium, (G) tubular lumen, (H) interstitial space, (I) peritubular capillary endothelium, as well as (J) rouleaux density and (K) glomerular diameter, during the 168-h measurement period. (L) In vivo assessment of velocity within the microcirculation of native kidneys and transplanted acellular scaffolds. Scale bars represent 20 µm. The data presented in this figure highlight events recorded from autologous transplantation and are comparable to those observed in allogeneic cases (see Supplemental Fig. 1). *p < 0.05. Among all the examined cases, the Kruskal–Wallis test only supported the retention of the null hypothesis (p = 0.82) for the data recorded in plot (G).
Figure 6
Figure 6
A proposed simplified view of dextran extravasation from the decellularized vasculature and translocation to the extravascular space. This model presents the large molecular weight, 150-kDa FITC, dye’s entry into the decellularized nephron vasculature via the afferent arteriole. The vascular marker then progresses through the decellularized glomerulus, where it can be filtered into the Bowman’s space and enter the tubular lumen. This unregulated process can potentially induce significant dynamic and static pressures to facilitate bilateral dye translocation between tubular epithelium, interstitium, and peritubular endothelium. The original image of the glomerulus was adapted with permission from https://www.lecturio.com/concepts/glomerular-filtration/.

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