Kidney regeneration and repair after transplantation

Cellular dynamics in pig-to-human kidney xenotransplantation

BACKGROUND

Xenotransplantation of genetically engineered porcine organs has the potential to address the challenge of organ donor shortage. Two cases of porcine-to-human kidney xenotransplantation were performed, yet the physiological effects on the xenografts and the recipients' immune responses remain largely uncharacterized.

METHODS

We performed single-cell RNA sequencing (scRNA-seq) and longitudinal RNA-seq analyses of the porcine kidneys to dissect xenotransplantation-associated cellular dynamics and xenograft-recipient interactions. We additionally performed longitudinal scRNA-seq of the peripheral blood mononuclear cells (PBMCs) to detect recipient immune responses across time.

FINDINGS

Although no hyperacute rejection signals were detected, scRNA-seq analyses of the xenografts found evidence of endothelial cell and immune response activation, indicating early signs of antibody-mediated rejection. Tracing the cells' species origin, we found human immune cell infiltration in both xenografts. Human transcripts in the longitudinal bulk RNA-seq revealed that human immune cell infiltration and the activation of interferon-gamma-induced chemokine expression occurred by 12 and 48 h post-xenotransplantation, respectively. Concordantly, longitudinal scRNA-seq of PBMCs also revealed two phases of the recipients' immune responses at 12 and 48-53 h. Lastly, we observed global expression signatures of xenotransplantation-associated kidney tissue damage in the xenografts. Surprisingly, we detected a rapid increase of proliferative cells in both xenografts, indicating the activation of the porcine tissue repair program.

CONCLUSIONS

Longitudinal and single-cell transcriptomic analyses of porcine kidneys and the recipient's PBMCs revealed time-resolved cellular dynamics of xenograft-recipient interactions during xenotransplantation. These cues can be leveraged for designing gene edits and immunosuppression regimens to optimize xenotransplantation outcomes.

FUNDING

This work was supported by NIH RM1HG009491 and DP5OD033430.

Renal regenerative capacity related to stem cell reserve in nephrectomized rats

PURPOSE

On the new era of stem cell therapy, the present experimental study was conducted to investigate renal regenerative capacity related to kidney stem cell reserve in different nephrectomy (Nx) models.

METHODS

Three- and eight-week-old rats (n = 168) were randomly divided into four groups to include control and three Nx subgroups (1/6 Nx, 1/2 Nx, and 5/6 Nx) (Fig. 1). On post-Nx days 15, 30 and 60, kidney specimens were obtained to determine renal regenerative capacity. The specimens were examined with immunofluorescence. CD90/CD105 and Ki-67 expressions were determined as stem cell and cellular proliferation markers, respectively. Fig. 1 Intraoperative photographs showing three different types of nephrectomies (unilateral total Nx has not been shown in 5/6 Nx group) RESULTS: CD90 and CD105 expressions were stronger in glomeruli, but Ki-67 expressions were present only in tubuli. When all Nx types and post-Nx days were considered, both 3- and 8-week-old rats undergone 5/6 Nx had the highest glomerular CD90 and CD105 double expressions. While the expressions gradually increased toward the day 60 in 3-weeks old rats, 8-week-old rats had almost stable double expressions. The strongest tubular Ki-67 expressions were seen in 5/6 Nx groups of both in 3- and 8-week-old rats. The expressions were strongest on day 15 and then gradually decreased. Ipsilateral 1/6 Nx groups had stronger Ki-67 expression than contralateral ones in both age groups.

CONCLUSIONS

Kidneys may pose a regenerative response to tissue/volume loss through its own CD90- and CD105-related stem cell reserve which mainly takes place in glomeruli and seems to have some interactions with Ki-67-related tubular proliferative process. This response supports that kidney stem cells may have a potential to overcome tissue/volume loss-related damage.

Genipin-crosslinked decellularized scaffold induces regeneration of defective rat kidneys

Objective: The purpose of this study was to improve the performance of decellularized renal scaffolds by the genipin crosslinking method to facilitate the regeneration of tissues and cells and provide better conditions for the regeneration and repair of defective kidneys. Methods: SD rats were randomly divided into three groups: normal group, uncrosslinked scaffold group and genipin-crosslinked scaffold group. Hematoxylin eosin, Masson and immunofluorescence staining was used to observe the histomorphological characteristics of the kidneys in each group. The preservation of the renal vascular structure in the three groups was observed by vascular casting. A collagenase degradation assay was used to detect the antidegradation ability of the kidney in the three groups. CCK8 assays were used to test the in vitro biocompatibility of the scaffolds. The lower 1/3 of the rat left kidney was excised, and the defect was filled with decellularized renal scaffolds to observe the effect of scaffold implantation on the regenerative ability of the defective kidney. Results: Histological images showed that the genipin-crosslinked scaffold did not destroy the structure of the scaffold, and the collagen fibers in the scaffold was more regular, and the outline of the glomerulus was clearer than uncrosslinked scaffold. The results of casting showed that the vascular structure of genipin-crosslinked scaffold was still intact. The anti-degradation ability test showed that the anti-degradation ability of genipin-crosslinked scaffold was significantly higher than that of the uncrosslinked scaffold. Cell culture experiments showed that the genipin-crosslinked scaffold had no cytotoxicity and promoted cell proliferation to some extent. In vivo scaffold transplantation experiments further demonstrated that the genipin-crosslinked scaffold had better anti-degradation and anti-inflammatory ability. Conclusion: Genipin-crosslinked rat kidney scaffold complemented kidney defects in rats can enhance scaffold-induced kidney regeneration and repair.

Expanding the Non-Invasive Diagnosis of Acute Rejection in Kidney Transplants Through Detection of Donor-Derived DNA in Urine: Proof-of-Concept Study

Background

Approximately 10%-20% of kidney transplant (KT) recipients suffer from acute rejection (AR); thus, sensitive and accurate monitoring of allograft status is recommended. We evaluated the clinical utility of donor-derived DNA (dd-DNA) detection in the urine of KT recipients as a non-invasive means for diagnosing AR.

Methods

Urine samples serially collected from 39 KT recipients were tested for 39 single-nucleotide variant loci selected according to technical criteria (i.e., high minor allele frequency and low analytical error) using next-generation sequencing. The fraction of dd-DNA was calculated and normalized by the urine creatinine (UCr) level (%dd-DNA/UCr). The diagnostic performance of %dd-DNA/UCr for AR was assessed by ROC curve analysis.

Results

There was an increasing trend of %dd-DNA/UCr in the AR group before subsequent graft injury, which occurred before (median of 52 days) histological rejection. The serum creatinine (SCr) level differed significantly between the AR and non-AR groups at two and four months of follow-up, whereas %dd-DNA/UCr differed between the groups at six months of follow-up. The combination of %dd-DNA/UCr, SCr, and spot urine protein (UPtn)/UCr showed high discriminating power, with an area under the ROC curve of 0.93 (95% confidence interval: 0.81-1.00) and a high negative predictive value of 100.0%.

Conclusions

Although the dd-DNA-based test cannot eliminate the need for biopsy, the high negative predictive value of this marker could increase the prebiopsy probability of detecting treatable injury to make biopsy an even more effective diagnostic tool.

Advances in the Knowledge about Kidney Decellularization and Repopulation

End-stage renal disease (ESRD) is characterized by the progressive deterioration of renal function that may compromise different tissues and organs. The major treatment indicated for patients with ESRD is kidney transplantation. However, the shortage of available organs, as well as the high rate of organ rejection, supports the need for new therapies. Thus, the implementation of tissue bioengineering to organ regeneration has emerged as an alternative to traditional organ transplantation. Decellularization of organs with chemical, physical, and/or biological agents generates natural scaffolds, which can serve as basis for tissue reconstruction. The recellularization of these scaffolds with different cell sources, such as stem cells or adult differentiated cells, can provide an organ with functionality and no immune response after in vivo transplantation on the host. Several studies have focused on improving these techniques, but until now, there is no optimal decellularization method for the kidney available yet. Herein, an overview of the current literature for kidney decellularization and whole-organ recellularization is presented, addressing the pros and cons of the actual techniques already developed, the methods adopted to evaluate the efficacy of the procedures, and the challenges to be overcome in order to achieve an optimal protocol.

In vivo regeneration of renal vessels post whole decellularized kidneys transplantation

Nearly 50 million patients in China live with end-stage renal disease (ESRD), and only about 4000 patients may receive kidney transplantation. The purpose of this study was to investigate regeneration of renal vessels post whole decellularized kidneys transplantation in vivo. We decellularized kidneys of donor rats by perfusing a detergent through the abdominal aorta, yielding feasible extracellular matrix, confirmed for acellularity before transplantation. Based on the concept of using the body as a bioreactor, we orthotopically transplanted the kidney and ureter scaffolds in recipient rats, and found the regeneration of vessels including artery and vein in the renal sinus following a spontaneous recanalization. Although the findings only represent an initial step toward the ultimate goal of the generation of fully functional kidneys in vivo, these findings suggest that the body itself, as the bioreactor, is a viable strategy for kidney regeneration.

Kidney bioengineering in regenerative medicine: An emerging therapy for kidney disease

The prevalence of end-stage renal disease is emerging as a serious worldwide public health problem because of the shortage of donor organs and the need to take lifelong immunosuppressive medication in patients who receive a transplanted kidney. Recently, tissue bioengineering of decellularization and recellularization scaffolds has emerged as a novel strategy for organ regeneration, and we review the critical technologies supporting these methods. We present a summary of factors associated with experimental protocols that may shed light on the future development of kidney bioengineering and we discuss the cell sources and bioreactor techniques applied to the recellularization process. Finally, we review some artificial renal engineering technologies and their future prospects, such as kidney on a chip and the application of three-dimensional and four-dimensional printing in kidney tissue engineering.

Influence of a modified preservation solution in kidney transplantation: A comparative experimental study in a porcine model

BACKGROUND/OBJECTIVE

Currently, due to lack of optimal donors, more marginal organs are transplanted. Therefore, there is a high interest to ameliorate preischemic organ preservation, especially for critical donor organs. In this regard, a new histidine-tryptophane ketoglutarate (HTK-N) solution has been designed and its protective efficacy was compared with the standard preservation solutions-University of Wisconsin solution and standard HTK or Custodiol (Bretschneider's solution).

METHODS

Seventy-two landrace pigs were included into the study, as donors and recipients. The donor kidneys were perfused during explantation with cold University of Wisconsin solution (n = 12), standard HTK (n = 12), or HTK-N solutions (n = 12), kept in the respective preservation solution at 4°C for 30 hours, implanted in the recipient pigs, and reperfused. The pigs survived in daily control for 7 days. The serum creatinine and blood urea nitrogen were assessed in pre- and postreperfusion phase on the 3^rd day and 7^th day posttransplantation. Additionally, tissue samples were taken to analyze the histopathological degree of tubular injury and regeneration before and after reperfusion.

RESULTS

The three preservation groups were comparable in age, body weight, and hemodynamic parameters. According to statistical proof, they differed in none of the control parameters.

CONCLUSION

Although the new preservation HTK solution is in several points a well-thought-out modification of the standard HTK solution, its preservation efficacy, at least for kidney preservation in a pig model for 30 hours, seems to be comparable to the current used solutions. A real advantage, however, could be confirmed in clinical settings, where marginal organs may influence the clinical outcome.

Current achievements and future perspectives in whole-organ bioengineering

Irreversible end-stage organ failure represents one of the leading causes of death, and organ transplantation is currently the only curative solution. Donor organ shortage and adverse effects of immunosuppressive regimens are the major limiting factors for this definitive practice. Recent developments in bioengineering and regenerative medicine could provide a solid base for the future creation of implantable, bioengineered organs. Whole-organ detergent-perfusion protocols permit clinicians to gently remove all the cells and at the same time preserve the natural three-dimensional framework of the native organ. Several decellularized organs, including liver, kidney, and pancreas, have been created as a platform for further successful seeding. These scaffolds are composed of organ-specific extracellular matrix that contains growth factors important for cellular growth and function. Macro- and microvascular tree is entirely maintained and can be incorporated in the recipient's vascular system after the implant. This review will emphasize recent achievements in the whole-organ scaffolds and at the same time underline complications that the scientific community has to resolve before reaching a functional bioengineered organ.

The proteome of postsurgical pancreatic juice

OBJECTIVE

This study aimed to evaluate the proteome of the pancreatic juice after pancreatectomy.

METHODS

Pancreatic juice samples were obtained during surgery and the postoperative period. Proteins were identified by mass spectrometry-based protein quantification technology and compared with published data of the nonoperated pancreas. Subgroup analyses were done in patients with pancreatic ductal adenocarcinoma (PDAC) receiving neoadjuvant chemotherapy and in smokers.

RESULTS

Five hundred eighteen proteins were identified in the postoperative pancreatic juice, encompassing all of the main organ functions. Sixty-seven of these were also present in the published data of the nonoperated pancreas and 7 of these had significant variation of concentration after surgery. Growth factors that have been described in postsurgical regeneration of the liver were not found to be overexpressed, whereas clusterin did, confirming the finding of previous experimental studies on pancreatic regeneration. Several proteins involved in immunomodulation and organ functions were differently expressed, depending on PDAC, neoadjuvant therapy, and smoking.

CONCLUSIONS

The proteome of the pancreas after surgical resection contains factors related to all main organ functions, changes over time, and is different in patients with PDAC receiving neoadjuvant therapy and in smokers. The pancreas reacts to the surgical trauma by producing proteins that protect the organ and stimulate the restoration of its function.

Scaffolds from surgically removed kidneys as a potential source of organ transplantation

End stage renal disease (ESRD) is a common disease, which relates to nearly 600 million people in the total population. What is more, it seems to be a crucial problem from the epidemiological point of view. These facts lead to a further necessity of renal replacement therapy development connected with rising expenditures for the health care system. The aim of kidney tissue engineering is to develop and innovate methods of obtaining renal extracellular matrix (ECM) scaffolds derived from kidney decellularization. Recently, progress has been made towards developing a functional kidney graft in vitro on demand. In fact, decellularized tissues constitute ideal natural scaffolds, due to the preservation of native ECM architecture, as well as of cell-ECM binding domains critical in promoting cell attachment, migration, and proliferation. One of the potential sources of the natural scaffolds is the kidney, which cannot be transplanted immediately after excision.

Kidney regeneration: Where we are and future perspectives

In 2012, about 16487 people received kidney transplants in the United States, whereas 95022 candidates were on the waiting list by the end of the year. Despite advances in renal transplant immunology, approximately 40% of recipients will die or lose graft within 10 years. The limitations of current therapies for renal failure have led researchers to explore the development of modalities that could improve, restore, or replace the renal function. The aim of this paper is to describe a reasonable approach for kidney regeneration and review the current literature regarding cell sources and mechanisms to develop a bioengineering kidney. Due to kidneys peculiar anatomy, extracellular matrix based scaffolds are rational starting point for their regeneration. The perfusion of detergents through the kidney vasculature is an efficient method for delivering decellularizing agents to cells and for removing of cellular material from the tissue. Many efforts have focused on the search of a reliable cell source to provide enrichment for achieving stable renal cell systems. For an efficient bioengineered kidney, these cells must be attached to the organ and then maturated into the bioractors, which simulates the human body environment. A functional bioengineered kidney is still a big challenge for scientists. In the last ten years we have got many improvements on the field of solid organ regeneration; however, we are still far away from the main target. Currently, regenerative centers worldwide have been striving to find feasible strategies to develop bioengineered kidneys. Cell-scaffold technology gives hope to end-stage renal disease patients who struggle with morbidity and mortality due to extended periods on dialysis or immunosupression. The potential of bioengineered organ is to provide a reliable source of organs, which can be refunctionalized and transplanted.

Decellularized kidney scaffold-mediated renal regeneration

Renal regeneration approaches offer great potential for the treatment of chronic kidney disease, but their availability remains limited by the clinical challenges they pose. In the present study, we used continuous detergent perfusion to generate decellularized (DC) rat kidney scaffolds. The scaffolds retained intact vascular trees and overall architecture, along with significant concentrations of various cytokines, but lost all cellular components. To evaluate its potential in renal function recovery, DC scaffold tissue was grafted onto partially nephrectomized rat kidneys. An increase of renal size was found, and regenerated renal parenchyma cells were observed in the repair area containing the grafted scaffold. In addition, the number of nestin-positive renal progenitor cells was markedly higher in scaffold-grafted kidneys compared to controls. Moreover, radionuclide scan analysis showed significant recovery of renal functions at 6 weeks post-implantation. Our results provide further evidence to show that DC kidney scaffolds could be used to promote renal recovery in the treatment of chronic kidney disease.

Lung regeneration and translational implications of the postpneumonectomy model

Lung regeneration research is yielding data with increasing translational value. The classical models of lung development, postnatal alveolarization, and postpneumonectomy alveolarization have contributed to a broader understanding of the cellular participants including stem-progenitor cells, cell-cell signaling pathways, and the roles of mechanical deformation and other physiologic factors that have the potential to be modulated in human and animal patients. Although recent information is available describing the lineage fate of lung fibroblasts, genetic fate mapping, and clonal studies are lacking in the study of lung regeneration and deserve further examination. In addition to increasing knowledge concerning classical alveolarization (postnatal, postpneumonectomy), there is increasing evidence for remodeling of the adult lung after partial pneumonectomy. Though limited in scope, compelling data have emerged describing restoration of lung tissue mass in the adult human and in large animal models. The basis for this long-term adaptation to pneumonectomy is poorly understood, but investigations into mechanisms of lung regeneration in older animals that have lost their capacity for rapid re-alveolarization are warranted, as there would be great translational value in modulating these mechanisms. In addition, quantitative morphometric analysis has progressed in conjunction with developments in advanced imaging, which allow for longitudinal and nonterminal evaluation of pulmonary regenerative responses in animals and humans. This review focuses on the cellular and molecular events that have been observed in animals and humans after pneumonectomy because this model is closest to classical regeneration in other mammalian systems and has revealed several new fronts of translational research that deserve consideration.