The Presence of Urinary Renal Progenitor Cells in Stable Kidney Transplant Recipients Anticipates Allograft Deterioration

Severe ischemia-reperfusion injury induces epigenetic inactivation of LHX1 in kidney progenitor cells after kidney transplantation

Severe ischemia-reperfusion injury (IRI) causes acute and chronic kidney allograft damage. As therapeutic interventions to reduce damage are limited yet, research on how to promote kidney repair has gained significant interest. To address this question, we performed genome-wide transcriptome and epigenome profiling in progenitor cells isolated from the urine of deceased (severe IRI) and living (mild IRI) donor human kidney transplants and identified LIM homeobox-1 (LHX1) as an epigenetically regulated gene whose expression depends on the IRI severity. Using a mouse model of IRI, we observed a relationship between IRI severity, LHX1 promoter hypermethylation, and LHX1 gene expression. Using functional studies, we confirmed that LHX1 expression is involved in the proliferation of epithelial tubular cells and podocyte differentiation from kidney progenitor cells. Our results provide evidence that severe IRI may reduce intrinsic mechanisms of kidney repair through epigenetic signaling.

Modeled microgravity unravels the roles of mechanical forces in renal progenitor cell physiology

BACKGROUND

The glomerulus is a highly complex system, composed of different interdependent cell types that are subjected to various mechanical stimuli. These stimuli regulate multiple cellular functions, and changes in these functions may contribute to tissue damage and disease progression. To date, our understanding of the mechanobiology of glomerular cells is limited, with most research focused on the adaptive response of podocytes. However, it is crucial to recognize the interdependence between podocytes and parietal epithelial cells, in particular with the progenitor subset, as it plays a critical role in various manifestations of glomerular diseases. This highlights the necessity to implement the analysis of the effects of mechanical stress on renal progenitor cells.

METHODS

Microgravity, modeled by Rotary Cell Culture System, has been employed as a system to investigate how renal progenitor cells respond to alterations in the mechanical cues within their microenvironment. Changes in cell phenotype, cytoskeleton organization, cell proliferation, cell adhesion and cell capacity for differentiation into podocytes were analyzed.

RESULTS

In modeled microgravity conditions, renal progenitor cells showed altered cytoskeleton and focal adhesion organization associated with a reduction in cell proliferation, cell adhesion and spreading capacity. Moreover, mechanical forces appeared to be essential for renal progenitor differentiation into podocytes. Indeed, when renal progenitors were exposed to a differentiative agent in modeled microgravity conditions, it impaired the acquisition of a complex podocyte-like F-actin cytoskeleton and the expression of specific podocyte markers, such as nephrin and nestin. Importantly, the stabilization of the cytoskeleton with a calcineurin inhibitor, cyclosporine A, rescued the differentiation of renal progenitor cells into podocytes in modeled microgravity conditions.

CONCLUSIONS

Alterations in the organization of the renal progenitor cytoskeleton due to unloading conditions negatively affect the regenerative capacity of these cells. These findings strengthen the concept that changes in mechanical cues can initiate a pathophysiological process in the glomerulus, not only altering podocyte actin cytoskeleton, but also extending the detrimental effect to the renal progenitor population. This underscores the significance of the cytoskeleton as a druggable target for kidney diseases.

Urine-Derived Renal Epithelial Cells (URECs) from Transplanted Kidneys as a Promising Immunomodulatory Cell Population

Kidney transplantation is a lifesaving procedure for patients with end-stage kidney disease (ESKD). Organs derived from donation after cardiac death (DCD) are constantly increasing; however, DCD often leads to ischaemia-reperfusion (IR) and Acute Kidney Injury (AKI) events. These phenomena increase kidney cell turnover to replace damaged cells, which are voided in urine. Urine-derived renal epithelial cells (URECs) are rarely present in the urine of healthy subjects, and their loss has been associated with several kidney disorders. The present study aimed to characterize the phenotype and potential applications of URECs voided after transplant. The results indicate that URECs are highly proliferating cells, expressing several kidney markers, including markers of kidney epithelial progenitor cells. Since the regulation of the immune response is crucial in organ transplantation and new immunoregulatory strategies are needed, UREC immunomodulatory properties were investigated. Co-culture with peripheral blood mononuclear cells (PBMCs) revealed that URECs reduced PBMC apoptosis, inhibited lymphocyte proliferation, increased T regulatory (Treg) cells and reduced T helper 1 (Th1) cells. URECs from transplanted patients represent a promising cell source for the investigation of regenerative processes occurring in kidneys, and for cell-therapy applications based on the regulation of the immune response.

In-vitro and in-vivo biocompatibility of dECM-alginate as a promising candidate in cell delivery for kidney regeneration

In this study, kidney decellularized extracellular matrix (dECM) and alginate (ALG) hybrid injectable hydrogel, with the purpose of delivering progenitor cells for tissue engineering, were prepared by using a physical crosslinking method in a CaCl₂ solution with high porosity for the exchange of nutrition and waste. In addition, the physical appearance and surface morphology of the hydrogel were investigated using optical and scanning electron microscopy, respectively. The functional groups of the dECM/ALG xerogels was examined via Fourier transform infrared spectroscopy. The biocompatibility of dECM/ALG xerogels was examined in-vitro using renal progenitor cells obtained from adult rat kidney. Enhanced biocompatibility and significant hemostatic behavior was noticed. Furthermore, the in-vivo biocompatibility of dECM/ALG hydrogel with progenitor cells was determined in the deep renal cortex for 7 and 21 days, in order to assess the foreign body reaction and inflammatory response. Early-stage glomerulus-like structure and dense linear cell network-like phenomenon were noticed. Loading of progenitor cells together with hydrogel enhances the cell density obviously due to cell migration from host and form a pattern. The desired early stage in-vivo response to progenitor cell-laden dECM/ALG hydrogel plays a potential role in kidney regeneration long term.

Urinary mRNA Expression of Glomerular Podocyte Markers in Glomerular Disease and Renal Transplant

The research of novel markers in urinary samples, for the description of renal damage, is of high interest, and several works demonstrated the value of urinary mRNA quantification for the search of events related to renal disease or affecting the outcome of transplant kidneys. In the present pilot study, a comparison of the urine mRNA expression of specific podocyte markers among patients who had undergone clinical indication to renal transplanted (RTx, n = 20) and native (N, n = 18) renal biopsy was performed. The aim of this work was to identify genes involved in podocytes signaling and cytoskeletal regulation (NPHS1, NPHS2, SYNPO, WT1, TRPC6, GRM1, and NEUROD) in respect to glomerular pathology. We considered some genes relevant for podocytes signaling and for the function of the glomerular filter applying an alternative normalization approach. Our results demonstrate the WT1 urinary mRNA increases in both groups and it is helpful for podocyte normalization. Furthermore, an increase in the expression of TRPC6 after all kinds of normalizations was observed. According to our data, WT1 normalization might be considered an alternative approach to correct the expression of urinary mRNA. In addition, our study underlines the importance of slit diaphragm proteins involved in calcium disequilibrium, such as TRPC6.

Chronic Kidney Allograft Disease: New Concepts and Opportunities

Chronic kidney disease (CKD) is increasing in most countries and kidney transplantation is the best option for those patients requiring renal replacement therapy. Therefore, there is a significant number of patients living with a functioning kidney allograft. However, progressive kidney allograft functional deterioration remains unchanged despite of major advances in the field. After the first post-transplant year, it has been estimated that this chronic allograft damage may cause a 5% graft loss per year. Most studies focused on mechanisms of kidney graft damage, especially on ischemia-reperfusion injury, alloimmunity, nephrotoxicity, infection and disease recurrence. Thus, therapeutic interventions focus on those modifiable factors associated with chronic kidney allograft disease (CKaD). There are strategies to reduce ischemia-reperfusion injury, to improve the immunologic risk stratification and monitoring, to reduce calcineurin-inhibitor exposure and to identify recurrence of primary renal disease early. On the other hand, control of risk factors for chronic disease progression are particularly relevant as kidney transplantation is inherently associated with renal mass reduction. However, despite progress in pathophysiology and interventions, clinical advances in terms of long-term kidney allograft survival have been subtle. New approaches are needed and probably a holistic view can help. Chronic kidney allograft deterioration is probably the consequence of damage from various etiologies but can be attenuated by kidney repair mechanisms. Thus, besides immunological and other mechanisms of damage, the intrinsic repair kidney graft capacity should be considered to generate new hypothesis and potential therapeutic targets. In this review, the critical risk factors that define CKaD will be discussed but also how the renal mechanisms of regeneration could contribute to a change chronic kidney allograft disease paradigm.

Molecular Mechanisms of Renal Progenitor Regulation: How Many Pieces in the Puzzle?

Kidneys of mice, rats and humans possess progenitors that maintain daily homeostasis and take part in endogenous regenerative processes following injury, owing to their capacity to proliferate and differentiate. In the glomerular and tubular compartments of the nephron, consistent studies demonstrated that well-characterized, distinct populations of progenitor cells, localized in the parietal epithelium of Bowman capsule and scattered in the proximal and distal tubules, could generate segment-specific cells in physiological conditions and following tissue injury. However, defective or abnormal regenerative responses of these progenitors can contribute to pathologic conditions. The molecular characteristics of renal progenitors have been extensively studied, revealing that numerous classical and evolutionarily conserved pathways, such as Notch or Wnt/β-catenin, play a major role in cell regulation. Others, such as retinoic acid, renin-angiotensin-aldosterone system, TLR2 (Toll-like receptor 2) and leptin, are also important in this process. In this review, we summarize the plethora of molecular mechanisms directing renal progenitor responses during homeostasis and following kidney injury. Finally, we will explore how single-cell RNA sequencing could bring the characterization of renal progenitors to the next level, while knowing their molecular signature is gaining relevance in the clinic.

Renal progenitor cells modulated by angiotensin II receptor blocker (ARB) medication and differentiation towards podocytes in anti-thy1.1 nephritis

Background

Mesangial proliferative glomerulonephritis (MsPGN) is an epidemic disease with increasing occurrence. As important as mesangial cells, podocytes are key innate cells for MsPGN prognosis and recovery. Renal progenitor cells, located at the urinary pole (UP) of Bowman’s capsule (BC), could alleviate kidney injury through their capacity to differentiate into podocytes.

Methods

Seventy-two male rats were categorized randomly into the sham (n=24), untreated Thy-1 (n=24) and losartan-treated (n=24) groups. We administered vehicle or losartan (50 mg/kg by gavage) daily to treat rats with anti-thy1.1 nephritis, an ideal model to simulate human MsPGN. Two weeks after the intravenous injection of antibody, urinary protein and blood samples were analyzed, pathological changes were examined, the number of podocytes was determined, and renal progenitor cells were studied.

Results

Anti-thy1.1 nephritis was significantly alleviated after losartan treatment, as reported previously and as expected. Compared with the untreated Thy-1 group, the number of podocytes in the losartan group increased, and the area of renal progenitor cells significantly increased. The protein expression of components of the p-ERK pathway was determined during the development of renal progenitor cells differentiating into podocytes.

Conclusions

The data in this paper show the direct glomerular cell action of angiotensin II receptor blocker (ARB) treatment in improving outcomes in anti-thy1.1 nephritis. The positive effects of ARB medication on anti-thy1.1 nephritis were due to an increase in the number of renal epithelial progenitor cells (defined as PECs that expressed only stem cell markers without podocyte proteins).