Delivery of EPC embedded in HA-hydrogels for treatment of acute kidney injury

In Situ Tissue Regeneration of Renal Tissue Induced by Collagen Hydrogel Injection

Host stem/progenitor cells can be mobilized and recruited to a target location using biomaterials, and these cells may be used for in situ tissue regeneration. The objective of this study was to investigate whether host biologic resources could be used to regenerate renal tissue in situ. Collagen hydrogel was injected into the kidneys of normal mice, and rat kidneys that had sustained ischemia/reperfusion injury. After injection, the kidneys of both animal models were examined up to 4 weeks for host tissue response. The infiltrating host cells present within the injection regions expressed renal stem/progenitor cell markers, PAX‐2, CD24, and CD133, as well as mesenchymal stem cell marker, CD44. The regenerated renal structures were identified by immunohistochemistry for renal cell specific markers, including synaptopodin and CD31 for glomeruli and cytokeratin and neprilysin for tubules. Quantitatively, the number of glomeruli found in the injected regions was significantly higher when compared to normal regions of renal cortex. This phenomenon occurred in normal and ischemic injured kidneys. Furthermore, the renal function after ischemia/reperfusion injury was recovered after collagen hydrogel injection. These results demonstrate that introduction of biomaterials into the kidney is able to facilitate the regeneration of glomerular and tubular structures in normal and injured kidneys. Such an approach has the potential to become a simple and effective treatment for patients with renal failure. Stem Cells Translational Medicine2018;7:241–250

Concise Reviews: Stem Cells and Kidney Regeneration: An Update

Significant progress has been made to advance stem cell products as potential therapies for kidney diseases: various kinds of stem cells can restore renal function in preclinical models of acute and chronic kidney injury. Nonetheless this literature contains contradictory results, and for this reason, we focus this review on reasons for apparent discrepancies in the literature, because they contribute to difficulty in translating renal regenerative therapies. Differences in methodologies used to derive and culture stem cells, even those from the same source, in addition to the lack of standardized renal disease animal models (both acute and chronic), are important considerations underlying contradictory results in the literature. We propose that harmonized rigorous protocols for characterization, handling, and delivery of stem cells in vivo could significantly advance the field, and present details of some suggested approaches to foster translation in the field of renal regeneration. Our goal is to encourage coordination of methodologies (standardization) and long‐lasting collaborations to improve protocols and models to lead to reproducible, interpretable, high‐quality preclinical data. This approach will certainly increase our chance to 1 day offer stem cell therapeutic options for patients with all‐too‐common renal diseases. Stem Cells Translational Medicine2019;8:82–92

The use of hydrogels for cell-based treatment of chronic kidney disease

Chronic kidney disease (CKD) is a major and growing public health concern with increasing incidence and prevalence worldwide. The therapeutic potential of stem cell therapy, including mesenchymal stem cells (MSCs) and endothelial progenitor cells (EPCs) holds great promise for treatment of CKD. However, there are significant bottlenecks in the clinical translation due to the reduced number of transplanted cells and the duration of their presence at the site of tissue damage. Bioengineered hydrogels may provide a route of cell delivery to enhance treatment efficacy and optimise the targeting effectiveness while minimising any loss of cell function. In this review, we highlight the advances in stem cell therapy targeting kidney disease and discuss the emerging role of hydrogel delivery systems to fully realise the potential of adult stem cells as a regenerative therapy for CKD in humans. MSCs and EPCs mediate kidney repair through distinct paracrine effects. As a delivery system, hydrogels can prolong these paracrine effects by improving retention at the site of injury and protecting the transplanted cells from the harsh inflammatory microenvironment. We also discuss the features of a hydrogel, which may be tuned to optimise the therapeutic potential of encapsulated stem cells, including cell-adhesive epitopes, material stiffness, nanotopography, modes of gelation and degradation and the inclusion of bioactive molecules. This review concludes with a discussion of the challenges to be met for the widespread clinical use of hydrogel delivery system of stem cell therapy for CKD.

Endothelial Progenitor Cells and Kidney Diseases

Endothelial progenitor cells (EPC) are bone marrow derived or tissue-resident cells that play major roles in the maintenance of vascular integrity and repair of endothelial damage. Although EPCs may be capable of directly engrafting and regenerating the endothelium, the most important effects of EPCs seem to be depended on paracrine effects. In recent studies, specific microvesicles and mRNAs have been found to mediate the pro-angiogenic and regenerative effects of EPCs on endothelium. EPC counts have important prognostic implications in cardiovascular diseases (CVD). Uremia and inflammation are associated with lower EPC counts which probably contribute to increased CVD risks in patients with chronic kidney disease. Beneficial effects of the EPC therapies have been shown in studies performed on different models of CVD and kidney diseases such as acute and chronic kidney diseases and glomerulonephritis. However, lack of a clear definition and specific marker of EPCs is the most important problem causing difficulties in interpretation of the results of the studies investigating EPCs.

An injectable collagen/poly(γ-glutamic acid) hydrogel as a scaffold of stem cells and α-lipoic acid for enhanced protection against renal dysfunction

We have developed a collagen/γ-PGA hydrogel as an injectable scaffold for use in MSC-based therapy against renal dysfunction.

Periosteum tissue engineering in an orthotopic in vivo platform

The periosteum plays a critical role in bone homeostasis and regeneration. It contains a vascular component that provides vital blood supply to the cortical bone and an osteogenic niche that acts as a source of bone-forming cells. Periosteal grafts have shown promise in the regeneration of critical size defects, however their limited availability restricts their widespread clinical application. Only a small number of tissue-engineered periosteum constructs (TEPCs) have been reported in the literature. A current challenge in the development of appropriate TEPCs is a lack of pre-clinical models in which they can reliably be evaluated. In this study, we present a novel periosteum tissue engineering concept utilizing a multiphasic scaffold design in combination with different human cell types for periosteal regeneration in an orthotopic in vivo platform. Human endothelial and bone marrow mesenchymal stem cells (BM-MSCs) were used to mirror both the vascular and osteogenic niche respectively. Immunohistochemistry showed that the BM-MSCs maintained their undifferentiated phenotype. The human endothelial cells developed into mature vessels and connected to host vasculature. The addition of an in vitro engineered endothelial network increased vascularization in comparison to cell-free constructs. Altogether, the results showed that the human TEPC (hTEPC) successfully recapitulated the osteogenic and vascular niche of native periosteum, and that the presented orthotopic xenograft model provides a suitable in vivo environment for evaluating scaffold-based tissue engineering concepts exploiting human cells.

Postischemic microvasculopathy and endothelial progenitor cell-based therapy in ischemic AKI: update and perspectives

Acute kidney injury (AKI) dramatically increases mortality of hospitalized patients. Incidences have been increased in recent years. The most frequent cause is transient renal hypoperfusion or ischemia which induces significant tubular cell dysfunction/damage. In addition, two further events take place: interstitial inflammation and microvasculopathy (MV). The latter evolves within minutes to hours postischemia and may result in permanent deterioration of the peritubular capillary network, ultimately increasing the risk for chronic kidney disease (CKD) in the long term. In recent years, our understanding of the molecular/cellular processes responsible for acute and sustained microvasculopathy has increasingly been expanded. The methodical approaches for visualizing impaired peritubular blood flow and increased vascular permeability have been optimized, even allowing the depiction of tissue abnormalities in a three-dimensional manner. In addition, endothelial dysfunction, a hallmark of MV, has increasingly been recognized as an inductor of both vascular malfunction and interstitial inflammation. In this regard, so-called regulated necrosis of the endothelium could potentially play a role in postischemic inflammation. Endothelial progenitor cells (EPCs), represented by at least two major subpopulations, have been shown to promote vascular repair in experimental AKI, not only in the short but also in the long term. The discussion about the true biology of the cells continues. It has been proposed that early EPCs are most likely myelomonocytic in nature, and thus they may simply be termed proangiogenic cells (PACs). Nevertheless, they reliably protect certain types of tissues/organs from ischemia-induced damage, mostly by modulating the perivascular microenvironment in an indirect manner. The aim of the present review is to summarize the current knowledge on postischemic MV and EPC-mediated renal repair.

Experimental renal progenitor cells: repairing and recreating kidneys?

Strategies to facilitate repair or generate new nephrons are exciting prospects for acute and chronic human renal disease. Repair of kidney injury involves not just local mechanisms but also mobilisation of progenitor/stem cells from intrarenal niches, including papillary, tubular and glomerular locations. Diverse markers characterise these unique cells, often including CD24 and CD133. Extrarenal stem cells may also contribute to repair, with proposed roles in secreting growth factors, transfer of microvesicles and exosomes and immune modulation. Creating new nephrons from stem cells is beginning to look feasible in mice in which kidneys can be dissociated into single cells and will then generate mature renal structures when recombined. The next step is to identify the correct human markers for progenitor cells from the fetus or mature kidney with similar potential to form new kidneys. Intriguingly, development can continue in vivo: whole foetal kidneys and recombined organs engraft, develop a blood supply and grow when xenotransplanted, and there are new advances in decellularised scaffolds to promote differentiation. This is an exciting time for human kidney repair and regeneration. Many of the approaches and techniques are in their infancy and based on animal rather than human work, but there is a rapid pace of discovery, and we predict that therapies based on advances in this field will come into clinical practice in the next decade.