Regrow or Repair: An Update on Potential Regenerative Therapies for the Kidney

5-Hydroxytryptamine 1F Receptor Agonist Lasmiditan Differentially Regulates Successful Repair and Failed Repair Genes in a Mouse Model of Acute Kidney Injury

Increasing evidence substantiates the role of mitochondrial dysfunction, inflammation, fibrosis, and cell senescence in the onset and progression of acute kidney injury (AKI) to chronic kidney disease . The underlying governing cellular and transcriptional events, however, are not fully understood. Recently, the key factors that regulate successful and failed repair states in the proximal tubule have been identified at a single-cell resolution following bilateral ischemia-reperfusion (I/R) in a mouse model of AKI. Previously, our group showed that treatment with the FDA-approved selective 5-hydroxytryptamine receptor 1F agonist lasmiditan following AKI induces mitochondrial biogenesis , restores renal mitochondrial function, and increases renal and vascular recovery in vivo. Here, we assessed the effect of lasmiditan on transcriptional and translational changes that are responsible for successful repair, injury, and failed repair states in the renal cortex following I/R-induced AKI. Increased levels of successful repair genes such as acyl-coA synthase medium-chain family member 2a, low-density lipoprotein receptor-related protein 2, solute carrier family 5 member 12, and hepatocyte nuclear factor 4 alpha were observed with 6 and 12 days of lasmiditan treatment following AKI compared to vehicle control. While 6 days of lasmiditan treatment had no effect on failed repair genes, the administration of lasmiditan for 12 days decreased the levels of vascular cell adhesion protein 1, tumor necrosis factor α, and interleukin-1β, which drive maladaptive repair. These data reveal that lasmiditan treatment post-AKI differentially regulates successful and failed repair gene expression in the renal cortex, likely contributing to the restoration of renal function and providing a potential targeted therapeutic pathway for the treatment of AKI.

Fibroblast expression of transmembrane protein smoothened governs microenvironment characteristics after acute kidney injury

The smoothened (Smo) receptor facilitates hedgehog signaling between kidney fibroblasts and tubules during acute kidney injury (AKI). Tubule-derived hedgehog is protective in AKI, but the role of fibroblast-selective Smo is unclear. Here, we report that Smo-specific ablation in fibroblasts reduced tubular cell apoptosis and inflammation, enhanced perivascular mesenchymal cell activities, and preserved kidney function after AKI. Global proteomics of these kidneys identified extracellular matrix proteins, and nidogen-1 glycoprotein in particular, as key response markers to AKI. Intriguingly, Smo was bound to nidogen-1 in cells, suggesting that loss of Smo could affect nidogen-1 accessibility. Phosphoproteomics revealed that the 'AKI protector' Wnt signaling pathway was activated in these kidneys. Mechanistically, nidogen-1 interacted with integrin β1 to induce Wnt in tubules to mitigate AKI. Altogether, our results support that fibroblast-selective Smo dictates AKI fate through cell-matrix interactions, including nidogen-1, and offers a robust resource and path to further dissect AKI pathogenesis.

Neuronally differentiated macula densa cells regulate tissue remodeling and regeneration in the kidney

Tissue regeneration is limited in several organs, including the kidney, contributing to the high prevalence of kidney disease globally. However, evolutionary and physiological adaptive responses and the presence of renal progenitor cells suggest an existing remodeling capacity. This study uncovered endogenous tissue remodeling mechanisms in the kidney that were activated by the loss of body fluid and salt and regulated by a unique niche of a minority renal cell type called the macula densa (MD). Here, we identified neuronal differentiation features of MD cells that sense the local and systemic environment and secrete angiogenic, growth, and extracellular matrix remodeling factors, cytokines and chemokines, and control resident progenitor cells. Serial intravital imaging, MD nerve growth factor receptor and Wnt mouse models, and transcriptome analysis revealed cellular and molecular mechanisms of these MD functions. Human and therapeutic translation studies illustrated the clinical potential of MD factors, including CCN1, as a urinary biomarker and therapeutic target in chronic kidney disease. The concept that a neuronally differentiated key sensory and regulatory cell type responding to organ-specific physiological inputs controls local progenitors to remodel or repair tissues may be applicable to other organs and diverse tissue-regenerative therapeutic strategies.

FGF21 and autophagy coordinately counteract kidney disease progression during aging and obesity

Chronic kidney disease (CKD) has reached epidemic proportions worldwide, partly due to the increasing population of elderly and obesity. Macroautophagy/autophagy counteracts CKD progression, whereas autophagy is stagnated owing to lysosomal overburden during aging and obesity, which promotes CKD progression. Therefore, for preventing CKD progression during aging and obesity, it is important to elucidate the compensation mechanisms of autophagy stagnation. We recently showed that FGF21 (fibroblast growth factor 21), which is a prolongevity and metabolic hormone, is induced by autophagy deficiency in kidney proximal tubular epithelial cells (PTECs); however, its pathophysiological role remains uncertain. Here, we investigated the interplay between FGF21 and autophagy and the direct contribution of endogenous FGF21 in the kidney during aging and obesity using PTEC-specific fgf21- and/or atg5-deficient mice at 24 months (aged) or under high-fat diet (obese) conditions. PTEC-specific FGF21 deficiency in young mice increased autophagic flux due to increased demand of autophagy, whereas fgf21-deficient aged or obese mice exacerbated autophagy stagnation due to severer lysosomal overburden caused by aberrant autophagy. FGF21 was robustly induced by autophagy deficiency, and aged or obese PTEC-specific fgf21- and atg5-double deficient mice deteriorated renal histology compared with atg5-deficient mice. Mitochondrial function was severely disturbed concomitant with exacerbated oxidative stress and downregulated TFAM (transcription factor A, mitochondrial) in double-deficient mice. These results indicate that FGF21 is robustly induced by autophagy disturbance and protects against CKD progression during aging and obesity by alleviating autophagy stagnation and maintaining mitochondrial homeostasis, which will pave the way to a novel treatment for CKD.

Rilparencel (Renal Autologous Cell Therapy-REACT®) for Chronic Kidney Disease and Type 1 and Type 2 Diabetes: Phase 2 Trial Design Evaluating Bilateral Kidney Dosing and Redosing Triggers

INTRODUCTION

Autologous cell-based therapies (CBT) to treat chronic kidney disease (CKD) with diabetes are novel and can potentially preserve renal function and decelerate disease progression. CBT dosing schedules are in early development and may benefit from individual bilateral organ dosing and kidney-dependent function to improve efficacy and durability. The objective of this open-label, phase 2 randomized controlled trial (RCT) is to evaluate participants' responses to rilparencel (Renal Autologous Cell Therapy-REACT®) following bilateral percutaneous kidney injections into the kidney cortex with a prescribed dosing schedule versus redosing based on biomarker triggers.

METHODS

Eligible participants with type 1 or 2 diabetes and CKD, eGFR 20-50 mL/min/1.73 m2, urine albumin-to-creatinine ratio (UACR) 30-5,000 mg/g, hemoglobin >10 g/dL, and glycosylated hemoglobin <10% were enrolled. After a percutaneous kidney biopsy and bioprocessing ex vivo expansion of selected renal cells, participants were randomized 1:1 into two cohorts determined by the dosing scheme. Cohort 1 receives 2 cell injections, one in each kidney 3 months apart, and cohort 2 receives one injection and the second dose only if there is a sustained eGFR decline of ≥20 mL/min/1.73 m2 and/or UACR increase of ≥30% and ≥30 mg/g, confirmed by re-testing.

CONCLUSION

The trial is fully enrolled with fifty-three participants. Cell injections and follow-up clinical visits are ongoing. This multicenter phase 2 RCT is designed to investigate the efficacy and safety of rilparencel with bilateral kidney dosing and compare two injection schedules with the potential of preserving or improving kidney function and delaying kidney disease progression among patients with stages 3a-4 CKD with diabetes.

Post-ischemic inactivation of HIF prolyl hydroxylases in endothelium promotes maladaptive kidney repair by inducing glycolysis

Ischemic acute kidney injury (AKI) is common in hospitalized patients and increases the risk for chronic kidney disease (CKD). Impaired endothelial cell (EC) functions are thought to contribute in AKI to CKD transition, but the underlying mechanisms remain unclear. Here, we identify a critical role for endothelial oxygen sensing prolyl hydroxylase domain (PHD) enzymes 1-3 in regulating post-ischemic kidney repair. In renal endothelium, we observed compartment-specific differences in the expression of the three PHD isoforms in both mice and humans. We found that post-ischemic concurrent inactivation of endothelial PHD1, PHD2, and PHD3 but not PHD2 alone promoted maladaptive kidney repair characterized by exacerbated tissue injury, fibrosis, and inflammation. Single-cell RNA-seq analysis of the post-ischemic endothelial PHD1, PHD2 and PHD3 deficient (PHDTiEC) kidney revealed an endothelial glycolytic transcriptional signature, also observed in human kidneys with severe AKI. This metabolic program was coupled to upregulation of the SLC16A3 gene encoding the lactate exporter monocarboxylate transporter 4 (MCT4). Strikingly, treatment with the MCT4 inhibitor syrosingopine restored adaptive kidney repair in PHDTiEC mice. Mechanistically, MCT4 inhibition suppressed pro-inflammatory EC activation reducing monocyte-endothelial cell interaction. Our findings suggest avenues for halting AKI to CKD transition based on selectively targeting the endothelial hypoxia-driven glycolysis/MCT4 axis.

An integrated organoid omics map extends modeling potential of kidney disease

Kidney organoids are a promising model to study kidney disease, but their use is constrained by limited knowledge of their functional protein expression profile. Here, we define the organoid proteome and transcriptome trajectories over culture duration and upon exposure to TNFα, a cytokine stressor. Older organoids increase deposition of extracellular matrix but decrease expression of glomerular proteins. Single cell transcriptome integration reveals that most proteome changes localize to podocytes, tubular and stromal cells. TNFα treatment of organoids results in 322 differentially expressed proteins, including cytokines and complement components. Transcript expression of these 322 proteins is significantly higher in individuals with poorer clinical outcomes in proteinuric kidney disease. Key TNFα-associated protein (C3 and VCAM1) expression is increased in both human tubular and organoid kidney cell populations, highlighting the potential for organoids to advance biomarker development. By integrating kidney organoid omic layers, incorporating a disease-relevant cytokine stressor and comparing with human data, we provide crucial evidence for the functional relevance of the kidney organoid model to human kidney disease.

How to Best Protect Kidneys for Transplantation-Mechanistic Target

The increasing number of patients on the kidney transplant waiting list underlines the need to expand the donor pool and improve kidney graft utilization. By protecting kidney grafts adequately from the initial ischemic and subsequent reperfusion injury occurring during transplantation, both the number and quality of kidney grafts could be improved. The last few years have seen the emergence of many new technologies to abrogate ischemia-reperfusion (I/R) injury, including dynamic organ preservation through machine perfusion and organ reconditioning therapies. Although machine perfusion is gradually making the transition to clinical practice, reconditioning therapies have not yet progressed from the experimental setting, pointing towards a translational gap. In this review, we discuss the current knowledge on the biological processes implicated in I/R injury and explore the strategies and interventions that are being proposed to either prevent I/R injury, treat its deleterious consequences, or support the reparative response of the kidney. Prospects to improve the clinical translation of these therapies are discussed with a particular focus on the need to address multiple aspects of I/R injury to achieve robust and long-lasting protective effects on the kidney graft.

The "3Ds" of Growing Kidney Organoids: Advances in Nephron Development, Disease Modeling, and Drug Screening

A kidney organoid is a three-dimensional (3D) cellular aggregate grown from stem cells in vitro that undergoes self-organization, recapitulating aspects of normal renal development to produce nephron structures that resemble the native kidney organ. These miniature kidney-like structures can also be derived from primary patient cells and thus provide simplified context to observe how mutations in kidney-disease-associated genes affect organogenesis and physiological function. In the past several years, advances in kidney organoid technologies have achieved the formation of renal organoids with enhanced numbers of specialized cell types, less heterogeneity, and more architectural complexity. Microfluidic bioreactor culture devices, single-cell transcriptomics, and bioinformatic analyses have accelerated the development of more sophisticated renal organoids and tailored them to become increasingly amenable to high-throughput experimentation. However, many significant challenges remain in realizing the use of kidney organoids for renal replacement therapies. This review presents an overview of the renal organoid field and selected highlights of recent cutting-edge kidney organoid research with a focus on embryonic development, modeling renal disease, and personalized drug screening.

Lasmiditan promotes recovery from acute kidney injury through induction of mitochondrial biogenesis

Acute kidney injury (AKI) involves rapid loss of renal function and occurs in 8-16% of hospitalized patients. AKI can be induced by drugs, sepsis, and ischemia-reperfusion (I/R). Hallmarks of AKI include mitochondrial and microvasculature dysfunction as well as renal tubular injury. There is currently no available therapeutic for AKI. Previously, our group identified that serotonin (5-HT)1F receptor agonism with lasmiditan accelerated endothelial cell recovery and induced mitochondrial biogenesis (MB) in vitro. We hypothesized that lasmiditan, a Federal Drug Administration-approved drug, would induce MB and improve microvascular and renal function in a mouse model of AKI. Male mice were subjected to renal I/R and treated with lasmiditan (0.3 mg/kg) or vehicle beginning 24 h after injury and then daily until euthanasia at 6 or 12 days. Serum creatinine was measured to estimate glomerular filtration rate. The renal cortex was assessed for mitochondrial density, vascular permeability and integrity, tubular damage, and interstitial fibrosis. Lasmiditan increased mitochondrial number (1.4-fold) in renal cortices. At 6 days, serum creatinine decreased 41% in the I/R group and 72% with lasmiditan. At 6 or 12 days, kidney injury molecule-1 increased in the I/R group and decreased 50% with lasmiditan. At 12 days, interstitial fibrosis decreased with lasmiditan by 50% and collagen type 1 by 38%. Evan's blue dye leakage increased 2.5-fold in the I/R group and was restored with lasmiditan. The tight junction proteins zonula occludens-1, claudin-2, and claudin-5 decreased in the I/R group and recovered with lasmiditan. At 6 or 12 days, peroxisome proliferator-activated receptor-γ coactivator-1α and electron transport chain complexes increased only with lasmiditan. In conclusion, lasmiditan treatment beginning AKI induces MB, attenuated vascular and tubular injury, decreased interstitial fibrosis, and lowered serum creatinine. Given that lasmiditan is a Federal Drug Administration-approved drug, these preclinical data support repurposing lasmiditan as a therapeutic for AKI.NEW & NOTEWORTHY AKI pathology involves a rapid decline in kidney function and occurs in 8-16% of hospitalized patients. There is currently no therapeutic for AKI. AKI results in mitochondria dysfunction, microvasculature injury, and loss of renal tubular function. In an I/R-induced AKI mouse model, treatment with the FDA-approved 5-HT1F receptor-selective agonist lasmiditan induced mitochondrial biogenesis, improved vascular integrity, reduced fibrosis, and reduced proximal tubule damage. These data support repurposing lasmiditan for the treatment of AKI.

Urinary single-cell sequencing captures kidney injury and repair processes in human acute kidney injury

Acute kidney injury (AKI) is a major health issue, the outcome of which depends primarily on damage and reparative processes of tubular epithelial cells. Mechanisms underlying AKI remain incompletely understood, specific therapies are lacking and monitoring the course of AKI in clinical routine is confined to measuring urine output and plasma levels of filtration markers. Here we demonstrate feasibility and potential of a novel approach to assess the cellular and molecular dynamics of AKI by establishing a robust urine-to-single cell RNA sequencing (scRNAseq) pipeline for excreted kidney cells via flow cytometry sorting. We analyzed 42,608 single cell transcriptomes of 40 urine samples from 32 patients with AKI and compared our data with reference material from human AKI post-mortem biopsies and published mouse data. We demonstrate that tubular epithelial cells transcriptomes mirror kidney pathology and reflect distinct injury and repair processes, including oxidative stress, inflammation, and tissue rearrangement. We also describe an AKI-specific abundant urinary excretion of adaptive progenitor-like cells. Thus, single cell transcriptomics of kidney cells excreted in urine provides noninvasive, unprecedented insight into cellular processes underlying AKI, thereby opening novel opportunities for target identification, AKI sub-categorization, and monitoring of natural disease course and interventions.

Epigenetic memory contributing to the pathogenesis of AKI-to-CKD transition

Epigenetic memory, which refers to the ability of cells to retain and transmit epigenetic marks to their daughter cells, maintains unique gene expression patterns. Establishing programmed epigenetic memory at each stage of development is required for cell differentiation. Moreover, accumulating evidence shows that epigenetic memory acquired in response to environmental stimuli may be associated with diverse diseases. In the field of kidney diseases, the “memory” of acute kidney injury (AKI) leads to progression to chronic kidney disease (CKD); epidemiological studies show that patients who recover from AKI are at high risk of developing CKD. The underlying pathological processes include nephron loss, maladaptive epithelial repair, inflammation, and endothelial injury with vascular rarefaction. Further, epigenetic alterations may contribute as well to the pathophysiology of this AKI-to-CKD transition. Epigenetic changes induced by AKI, which can be recorded in cells, exert long-term effects as epigenetic memory. Considering the latest findings on the molecular basis of epigenetic memory and the pathophysiology of AKI-to-CKD transition, we propose here that epigenetic memory contributing to AKI-to-CKD transition can be classified according to the presence or absence of persistent changes in the associated regulation of gene expression, which we designate “driving” memory and “priming” memory, respectively. “Driving” memory, which persistently alters the regulation of gene expression, may contribute to disease progression by activating fibrogenic genes or inhibiting renoprotective genes. This process may be involved in generating the proinflammatory and profibrotic phenotypes of maladaptively repaired tubular cells after kidney injury. “Priming” memory is stored in seemingly successfully repaired tubular cells in the absence of detectable persistent phenotypic changes, which may enhance a subsequent transcriptional response to the second stimulus. This type of memory may contribute to AKI-to-CKD transition through the cumulative effects of enhanced expression of profibrotic genes required for wound repair after recurrent AKI. Further understanding of epigenetic memory will identify therapeutic targets of future epigenetic intervention to prevent AKI-to-CKD transition.

Identifying Common Molecular Mechanisms in Experimental and Human Acute Kidney Injury

Acute kidney injury (AKI) is a highly prevalent, heterogeneous syndrome, associated with increased short- and long-term mortality. A multitude of different factors cause AKI including ischemia, sepsis, nephrotoxic drugs, and urinary tract obstruction. Upon injury, the kidney initiates an intrinsic repair program that can result in adaptive repair with regeneration of damaged nephrons and functional recovery of epithelial activity, or maladaptive repair and persistence of damaged epithelial cells with a characteristic proinflammatory, profibrotic molecular signature. Maladaptive repair is linked to disease progression from AKI to chronic kidney disease. Despite extensive efforts, no therapeutic strategies provide consistent benefit to AKI patients. Since kidney biopsies are rarely performed in the acute injury phase in humans, most of our understanding of AKI pathophysiology is derived from preclinical AKI models. This raises the question of how well experimental models of AKI reflect the molecular and cellular mechanisms underlying human AKI? Here, we provide a brief overview of available AKI models, discuss their strengths and limitations, and consider important aspects of the AKI response in mice and humans, with a particular focus on the role of proximal tubule cells in adaptive and maladaptive repair.

Generation of chimeric kidneys using progenitor cell replacement: Oshima Award Address 2021

It is believed that the development of new renal replacement therapy (RRT) will increase treatment options for end-stage kidney disease and help reduce the mismatch between supply and demand. Technological advancement in the development of kidney organoids derived from pluripotent stem cells and xenotransplantation using porcine kidneys has been accelerated by a convergence of technological innovations, including the discovery of induced pluripotent stem cells and genome editing, and improvement of analysis techniques such as single-cell ribonucleic acid sequencing. Given the difficulty associated with kidney regeneration, hybrid kidneys are studied as an innovative approach that involves the use of stem cells to generate kidneys, with animal fetal kidneys used as a scaffold. Hybrid kidney technology entails the application of local chimerism for the generation of chimeric kidneys from exogenous renal progenitor cells by borrowing complex nephrogenesis programs from the developmental environment of heterologous animals. Hybrid kidneys can also utilize the urinary tract and bladder tissue of animal fetuses for urine excretion. Generating nephrons from syngeneic stem cells to increase self-cell ratio in xeno-tissues can reduce the risk of xeno-rejection. We showed that nephrons can be generated by ablation of host nephron progenitor cells (NPCs) in the nephron development region of animals and replacing them with exogenous NPCs. This progenitor cell replacement is the basis of hybrid kidney regeneration from progenitor cells using chimera technology. The goal of xeno-regenerative medicine using hybrid kidneys is to overcome serious organ shortage.