Lauren Edgar

Heterogeneity of Scaffold Biomaterials in Tissue Engineering

Tissue engineering (TE) offers a potential solution for the shortage of transplantable organs and the need for novel methods of tissue repair. Methods of TE have advanced significantly in recent years, but there are challenges to using engineered tissues and organs including but not limited to: biocompatibility, immunogenicity, biodegradation, and toxicity. Analysis of biomaterials used as scaffolds may, however, elucidate how TE can be enhanced. Ideally, biomaterials should closely mimic the characteristics of desired organ, their function and their in vivo environments. A review of biomaterials used in TE highlighted natural polymers, synthetic polymers, and decellularized organs as sources of scaffolding. Studies of discarded organs supported that decellularization offers a remedy to reducing waste of donor organs, but does not yet provide an effective solution to organ demand because it has shown varied success in vivo depending on organ complexity and physiological requirements. Review of polymer-based scaffolds revealed that a composite scaffold formed by copolymerization is more effective than single polymer scaffolds because it allows copolymers to offset disadvantages a single polymer may possess. Selection of biomaterials for use in TE is essential for transplant success. There is not, however, a singular biomaterial that is universally optimal.

Regenerative immunology: the immunological reaction to biomaterials

Regenerative medicine promises to meet two of the most urgent needs of modern organ transplantation, namely immunosuppression‐free transplantation and an inexhaustible source of organs. Ideally, bioengineered organs would be manufactured from a patients own biomaterials—both cells and the supporting scaffolding materials in which cells would be embedded and allowed to mature to eventually regenerate the organ in question. While some groups are focusing on the feasibility of this approach, few are focusing on the immunogenicity of the scaffolds that are being developed for organ bioengineering purposes. This review will succinctly discuss progress in the understanding of immunological characteristics and behavior of different scaffolds currently under development, with emphasis on the extracellular matrix scaffolds obtained decellularized animal or human organs which seem to provide the ideal template for bioengineering purposes.

Tissue-Engineering Approaches to Restore Kidney Function

Kidney transplantation for the treatment of chronic kidney disease has established outcome and quality of life. However, its implementation is severely limited by a chronic shortage of donor organs; consequently, most candidates remain on dialysis and on the waiting list while accruing further morbidity and mortality. Furthermore, those patients that do receive kidney transplants are committed to a life-long regimen of immunosuppressive drugs that also carry significant adverse risk profiles. The disciplines of tissue engineering and regenerative medicine have the potential to produce alternative therapies which circumvent the obstacles posed by organ shortage and immunorejection. This review paper describes some of the most promising tissue-engineering solutions currently under investigation for the treatment of acute and chronic kidney diseases. The various stem cell therapies, whole embryo transplantation, and bioengineering with ECM scaffolds are outlined and summarized.

Kidney transplantation, bioengineering and regeneration: an originally immunology-based discipline destined to transition towards ad hoc organ manufacturing and repair

ABSTRACT Kidney transplantation (KT), as a modality of renal replacement therapy (RRT), has been shown to be both economically and functionally superior to dialysis for the treatment of end-stage renal disease (ESRD). Progress in KT is limited by two major barriers: a) a chronic and burgeoning shortage of transplantable organs and b) the need for chronic immunosuppression following transplantation. Although ground-breaking advances in transplant immunology have improved patient survival and graft durability, a new pathway of innovation is needed in order to overcome current obstacles. Regenerative medicine (RM) holds the potential to shift the paradigm in RRT, through organ bioengineering. Manufactured organs represent a potentially inexhaustible source of transplantable grafts that would bypass the need for immunosuppressive drugs by using autologous cells to repopulate extracellular matrix (ECM) scaffolds. This overview discusses the current status of renal transplantation while reviewing the most promising innovations in RM therapy as applied to RRT.

Extracellular matrix scaffolds as a platform for kidney regeneration

Chronic and end stage renal disease (ESRD) have reached pandemic levels and pose a substantial public health burden. Unfortunately, available therapies lack efficacy in preventing progression to its end stage phase. Regenerative medicine promises to restore function of diseased organs among which the kidney, through two possible approaches: firstly, the maximization of the innate ability of tissues to repair or regenerate following injury; secondly, the ex vivo bio-fabrication of the organ in question. When regenerative medicine is applied to the setting of chronic or ESRD, it is intuitive that endeavors to improve renal repair, promote nephrogenesis in damaged kidneys, or the de novo engineering of transplantable kidneys, could have a major impact on the current management of this pandemic. Among the different regenerative medicine technologies currently under development, cell-on-scaffold seeding technology (CSST) - involving cells seeded throughout supporting scaffold structures made from biomaterials - is the most favorable candidate in the context of realistic clinical application. In this review, we outline and describe current investigations taking place in the field of CSST as it pertains to the restoration of kidney function.

DCD and AKI Allografts Offer a Valuable Platform to Study Molecular Pathways Underlying Successful Adaptive Repair of the Kidney after Damage

Introduction Although the increased incidence of DGF in AKI/DCD recipients, DCD/AKI grafts typically recover and resume an excellent kidney function within one month from the surgery. Therefore, we hypothesize that comparative analysis of peripheral blood and renal allograft tissue throughout the initial 30 days of follow up after a kidney transplant will result in the identification and characterization of ongoing mechanisms of regeneration and repair (RR). Methods Peripheral blood was collected from kidney transplant (KT) patients immediately prior to transplant, immediately after transplant (for up to 5 consecutive days), twice weekly for the next 3 weeks, and at post-transplant day 30 following transplantation of living donor (LD, control group), DCD or AKI donor grafts. Total RNA was isolated from each patient sample and assayed on whole genome microarrays. Longitudinal gene expression was evaluated to identify molecular pathways and processes involved in the recovery phase following KT. Results Remarkably, comparative analysis of longitudinal peripheral blood gene expression between recipients of AKI/DCD vs. LD grafts revealed two significant gene clusters, representing a total of 141 genes that show a different expression profile between AKI/DCD and LD samples. The 77 transcripts that comprise cluster 1 show a significant over-representation of genes in several key biological pathways including mTOR signaling, Granzyme B Signaling, and Th1 and Th2 Activation and wnt Pathway. Immunological Disease is the top diseases and disorders category over-represented in this cluster. The second cluster of differentially-expressed genes (N=64) in the comparison between AKI/DCD and LD are significantly over-represented in Toll-like Receptor Signaling, Adrenergic signaling, and fMLP Signaling in neutrophils pathways. The most significant diseases and disorders category over-represented in the set of transcripts is Inflammatory Response. The 141 transcripts that are differentially expressed in the longitudinal comparison between LD and AKI/DCD include genes found to be different in LD vs AKI only (N=65), LD vs DCD only (N=63) and LD vs AKI + DCD. The 13 transcripts found to differentially-expressed in both DCD and AKI samples compared to LD may represent the most biologically relevant gene targets differentiating the two groups and warrant further investigation. Conclusions The pattern of gene expression in the peripheral blood of KT patients is significantly different, depending upon the source of donor graft. These markedly different expression patterns, particularly the coordinate elevation hundreds of expressed genes seen in DCD and AKI recipients beyond post-transplant day 1, provide further insight into mechanisms (and timing) of kidney RR that occurs following kidney transplantation.

Utility of extracellular matrix powders in tissue engineering

ABSTRACT Extracellular matrix (ECM) materials have had remarkable success as scaffolds in tissue engineering (TE) and as therapies for tissue injury whereby the ECM microenvironment promotes constructive remodeling and tissue regeneration. ECM powder and solubilized derivatives thereof have novel applications in TE and RM afforded by the capacity of these constructs to be dynamically modulated. The powder form allows for effective incorporation and penetration of reagents; hence, ECM powder is an efficacious platform for 3D cell culture and vehicle for small molecule delivery. ECM powder offers minimally invasive therapy for tissue injury and successfully treatment for wounds refractory to first-line therapies. Comminution of ECM and fabrication of powder-derived constructs, however, may compromise the biological integrity of the ECM. The current lack of optimized fabrication protocols prevents a more extensive and effective clinical application of ECM powders. Further study on methods of ECM powder fabrication and modification is needed.

Molecular Pathways Underlying Adaptive Repair of the Injured Kidney: Novel Donation After Cardiac Death and Acute Kidney Injury Platforms

OBJECTIVE To test the hypothesis that gene expression profiling in peripheral blood from patients who have undergone kidney transplantation (KT) will provide mechanistic insights regarding graft repair and regeneration. BACKGROUND Renal grafts obtained from living donors (LD) typically function immediately, whereas organs from donation after cardiac death (DCD) or acute kidney injury (AKI) donors may experience delayed function with eventual recovery. Thus, recipients of LD, DCD, and AKI kidneys were studied to provide a more complete understanding of the molecular basis for renal recovery. METHODS Peripheral blood was collected from LD and DCD/AKI recipients before transplant and throughout the first 30 days thereafter. Total RNA was isolated and assayed on whole genome microarrays. RESULTS Comparison of longitudinal gene expression between LD and AKI/DCD revealed 2 clusters, representing 141 differentially expressed transcripts. A subset of 11 transcripts was found to be differentially expressed in AKI/DCD versus LD. In all recipients, the most robust gene expression changes were observed in the first day after transplantation. After day 1, gene expression profiles differed depending upon the source of the graft. In patients receiving LD grafts, the expression of most genes did not remain markedly elevated beyond the first day post-KT. In the AKI/DCD groups, elevations in gene expression were maintained for at least 5 days post-KT. In all recipients, the pattern of coordinate gene overexpression subsided by 28 to 30 days. CONCLUSIONS Gene expression in peripheral blood of AKI/DCD recipients offers a novel platform to understand the potential mechanisms and timing of kidney repair and regeneration after transplantation.

Tissue Bioengineering in Transplantation

Organ transplantation has emerged in recent decades as one of the most effective modalities for the treatment of end-stage organ disease. Over 100,000 transplants are performed worldwide each year; however, the supply has not been able to keep up with increasing demand. Furthermore, transplant recipients are committed to a lifelong regimen of brutal immunosuppressive medications that themselves carry significant side effect profiles, influencing clinical outcomes. Recent advances in the fields of tissue engineering and regenerative medicine are beginning to offer alternative solutions that could potentially improve the longevity, functionality, and biocompatibility profiles of transplants. Decellularization technology to produce extracellular matrix scaffolds represents one of the most promising strategies currently under investigation. Such methods can produce bioengineered, transplantable organs using autologous cells that would bypass the need for immunosuppression and its associated side effects. Furthermore, bioengineering strategies in general are not bound by supply constraints imposed by organ donation.

Converging Organ Transplantation Towards Regenerative Medicine

In recent decades, organ transplantation has proven itself a landmark success for the treatment of end-stage organ failure. In light of such dramatic success, the demand for transplantable organs continues to rise at an extraordinary rate while the supply has reached a virtual plateau. Waiting lists have reached alarming levels with patients enduring significant morbidity and mortality in hopes of eventually receiving a transplant. On the other hand, patients who do go on to receive life-saving transplants are consigned to a lifelong regimen of brutal immunosuppressive protocols, which themselves carry harmful side-effect profiles. The present trajectory of organ bioengineering and regeneration (OBR) indicates a potential to dramatically alter the discipline of organ transplantation. Modern techniques in OBR allow for the manufacture of relatively simple organs using autologous cellular material, which would avoid evoking immune response and thereby bypass the need for immunosuppressive protocols. The ideal end product of current investigations would be the fabrication of an autograft-equivalent for clinical application by using cells obtained from the patient in need of a transplant. Such an achievement would represent an immunosuppression-free state, a laborious yet fruitless pursuit that has persisted since the early days of the transplant era. Furthermore, an optimized protocol for the biofabrication of transplantable organs using methods in OBR could theoretically generate an inexhaustible supply and thus provide a solution to the chronic shortage suffered by end-stage patients on the waiting list today. The incorporation of OBR approaches and methodologies into the modern practice of transplantation could plausibly represent a major paradigm shift for the field given the advantages described above.