Exosomes derived from calcium oxalate-treated macrophages promote apoptosis of HK-2 cells by promoting autophagy

Cell death‑related molecules and targets in the progression of urolithiasis (Review)

Urolithiasis is a high‑incidence disease caused by calcium oxalate (mainly), uric acid, calcium phosphate, struvite, apatite, cystine and other stones. The development of kidney stones is closely related to renal tubule cell damage and crystal adhesion and aggregation. Cell death, comprising the core steps of cell damage, can be classified into various types (i.e., apoptosis, ferroptosis, necroptosis and pyroptosis). Different crystal types, concentrations, morphologies and sizes cause tubular cell damage via the regulation of different forms of cell death. Oxidative stress caused by high oxalate or crystal concentrations is considered to be a precursor to a variety of types of cell death. In addition, complex crosstalk exists among numerous signaling pathways and their key molecules in various types of cell death. Urolithiasis is considered a metabolic disorder, and tricarboxylic acid cycle‑related molecules, such as citrate and succinate, are closely related to cell death and the inhibition of stone development. However, a literature review of the associations between kidney stone development, metabolism and various types of cell death is currently lacking, at least to the best of our knowledge. Thus, the present review summarizes the major advances in the understanding of regulated cell death and urolithiasis progression.

Regulation of regulated cell death by extracellular vesicles in acute kidney injury and chronic kidney disease

The imbalance between proliferation and death of kidney resident cells is a crucial factor in the development of acute or chronic renal dysfunction. Acute kidney injury (AKI) is often associated with the rapid loss of tubular epithelial cells (TECs). Sustained injury leads to the loss of glomerular endothelial cells (GECs) and podocytes, which is a key mechanism in the pathogenesis of glomerular diseases. This irreversible damage resulting from progressive cell loss eventually leads to deterioration of renal function characterized by glomerular compensatory hypertrophy, tubular degeneration, and renal fibrosis. Regulated cell death (RCD), which involves a cascade of gene expression events with tight structures, plays a certain role in regulating kidney health by determining the fate of kidney resident cells. Under pathological conditions, cells in the nephron have been demonstrated to constitutively release extracellular vesicles (EVs) which act as messengers that specifically interact with recipient cells to regulate their cell death process. For therapeutic intervention, exogenous EVs have exhibited great potential for the prevention and treatment of kidney disease by modulating RCD, with enhanced effects through engineering modification. Based on the functional role of EVs, this review comprehensively explores the regulation of RCD by EVs in AKI and chronic kidney disease (CKD), with emphasis on pathogenesis and therapeutic intervention.

Ambra1 in exosomes secreted by HK-2 cells damaged by supersaturated oxalate induce mitophagy and autophagy-ferroptosis in normal HK-2 cells to participate in the occurrence of kidney stones

Injury to the renal tubular epithelium has emerged as a leading factor underlying the formation of kidney stones. Indeed, epithelial cell damage contributes to the adherence and aggregation of crystals, thereby accelerating the formation of renal stones. Meanwhile, exosomes play an instrumental role in cellular communication, including DNA, RNA, mRNA, etc. In this study, homogenous cells were treated with exosomes derived from damaged cells in an attempt to establish "positive feedback" of cell damage, and the desired results were achieved. To begin, a serum-free medium and supersaturated concentrations of oxalate were added to the HK-2 cell line, and then exosomes were isolated from the two groups for analysis and comparison, and the autophagy-related gene Ambra1 (autophagy and beclin-1 regulator 1) was detected. Subsequently, normal HK-2 cells were treated with exosomes, and the related indexes of autophagy, ferroptosis and mitophagy were determined. Thereafter, Ambra1 was knocked down in exosome-derived HK-2 cells, resulting in the down-regulation of Ambra1 expression in exosomes produced by HK-2 cells following oxalate intervention. Thereafter, the ability of exosomes to stimulate autophagy, mitophagy and ferroptosis was re-evaluated in HK-2 cells after Ambra1 knockdown. The results corroborated that exosomes secreted by oxalate-treated HK-2 can directly elevate autophagy, ferroptosis and mitophagy levels in normal cells, and this effect was significantly mitigated following Ambra1 knockdown within exosomes. Meanwhile, exosomes-induced autophagy and ferroptosis were alleviated after knockdown of beclin-1 in recipient HK-2 cells. These results further suggest that beclin-1 plays a critical role in the process of exosome-induced autophagy-ferroptosis.

Overexpression of sirtuin 1 attenuates calcium oxalate-induced kidney injury by promoting macrophage polarization

Sirtuin 1 (SIRT1) protein is involved in macrophage differentiation, while NOTCH signaling affects inflammation and macrophage polarization. Inflammation and macrophage infiltration are typical processes that accompany kidney stone formation. However, the role and mechanism of SIRT1 in renal tubular epithelial cell injury caused by calcium oxalate (CaOx) deposition and the relationship between SIRT1 and the NOTCH signaling pathway in this urological disorder are unclear. This study investigated whether SIRT1 promotes macrophage polarization to inhibit CaOx crystal deposition and reduce renal tubular epithelial cell injury. Public single-cell sequencing data, RT-qPCR, immunostaining approaches, and Western blotting showed decreased SIRT1 expression in macrophages treated with CaOx or exposed to kidney stones. Macrophages overexpressing SIRT1 differentiated towards the anti-inflammatory M2 phenotype, significantly inhibiting apoptosis and alleviating injury in the kidneys of mice with hyperoxaluria. Conversely, decreased SIRT1 expression in CaOx-treated macrophages triggered Notch signaling pathway activation, promoting macrophage polarization towards the pro-inflammatory M1 phenotype. Our results suggest that SIRT1 promotes macrophage polarization towards the M2 phenotype by repressing the NOTCH signaling pathway, which reduces CaOx crystal deposition, apoptosis, and damage in the kidney. Therefore, we propose SIRT1 as a potential target for preventing disease progression in patients with kidney stones.

Metabolic changes in kidney stone disease

Kidney stone disease (KSD) is one of the earliest medical diseases known, but the mechanism of its formation and metabolic changes remain unclear. The formation of kidney stones is a extensive and complicated process, which is regulated by metabolic changes in various substances. In this manuscript, we summarized the progress of research on metabolic changes in kidney stone disease and discuss the valuable role of some new potential targets. We reviewed the influence of metabolism of some common substances on stone formation, such as the regulation of oxalate, the release of reactive oxygen species (ROS), macrophage polarization, the levels of hormones, and the alternation of other substances. New insights into changes in substance metabolism changes in kidney stone disease, as well as emerging research techniques, will provide new directions in the treatment of stones. Reviewing the great progress that has been made in this field will help to improve the understanding by urologists, nephrologists, and health care providers of the metabolic changes in kidney stone disease, and contribute to explore new metabolic targets for clinical therapy.

Exosome-mediated crosstalk between epithelial cells amplifies the cell injury cascade in CaOx stone formation

BACKGROUND

Calcium oxalate (CaOx) stone disease is found worldwide. To explore the role of exosomes as a mediator of intercellular crosstalk during CaOx stone formation, we conducted this study, which may provide a new insight into the treatment and prevention of CaOx stones.

METHODS

Exosomes derived from HK2 cells with (EXO(S)) or without (EXO(C))CaOx crystal stimulation were cocultured with normal tubular epithelial cells and subcapsularly injected into rat kidneys. Then, oxidative stress levels, the MAPK signalling pathway and osteogenic changes were detected via qPCR, Western blotting, immunofluorescence and immunohistochemical staining. In vivo fluorescence imaging and exosome internalization assays showed the absorption and utilization of exosomes.

RESULTS

EXO(S) increased the reactive oxygen species (ROS) level and activated the expression of BMP2, OPN and OCN via the MAPK/P-38 pathway both in vivo and in vitro. In vivo experiments showed that preinjection of EXO(S) aggravated, while preinjection of EXO(C) ameliorated, these effects. Crystal depositions were significantly increased in SD rats injected with GAM when they were preinjected with EXO(S), and these effects could be reversed after preinjection with EXO(C).

CONCLUSION

Our study revealed that exosome-mediated intercellular crosstalk could accelerate the formation of CaOx stones by promoting oxidative stress and the osteogenic cascade in normal tubular epithelial cells. HK2 cells stimulated with CaOx crystals released more exosomal miR-223-3p and S100A8 comparing with normal HK2 cells. These exosomes derived from HK2 cells stimulated with CaOx (EXO(S)) could amplify the oxidative stress and osteogenic changes via MAPK/P-38 pathway, which finally led to the formation of Randall's plaque.

Exosomal transfer of microRNA-590-3p between renal tubular epithelial cells after renal ischemia-reperfusion injury regulates autophagy by targeting TRAF6

BACKGROUND

Acute kidney injury (AKI) is a common complication in patients, especially elderly patients, who undergo cardiac surgery with cardiopulmonary bypass. Studies have indicated a protective role of autophagy in AKI. However, the mechanisms underlying the regulatory effect of autophagy in AKI among patients undergoing cardiac surgeries are poorly understood. In this study, we aimed to test the hypothesis that exosomal microRNAs (miRNAs) regulate autophagy in tubular epithelial cells after AKI.

METHODS

Plasma exosomal RNA was extracted from young and elderly AKI patients undergoing cardiac surgery, and the miRNAs expression during the perioperative period were analyzed using next-generation sequencing. The screened miRNAs and their target genes were subjected to gene oncology function and Kyoto Encyclopedia of Genes and Genome enrichment analyses. Renal tubular epithelial cell line (HK-2 cells) was cultured and hypoxia/reoxygenation (H/R) model was established, which is an in vitro renal ischemia/reperfusion (I/R) model. We used Western blot analysis, cell viability assay, transfection, luciferase assay to investigate the mechanisms underlying the observed increases in the levels of renal I/R injury-mediated exosomal miRNAs and their roles in regulating HK-2 cells autophagy.

RESULTS

miR-590-3p was highly enriched in the plasma exosomes of young AKI patients after cardiac surgery. Increased levels of miR-590-3p led to the increases in the expression of autophagy marker proteins, including Beclin-1 and microtubule associated protein 1 light chain 3 beta (LC3II), and prolonged the autophagic response in HK-2 cells after H/R treatment. These effects were achieved mainly via increases in the exosomal miR-590-3p levels, and the tumor necrosis factor receptor-associated factor 6 protein was shown to play a key role in I/R injury-mediated autophagy induction.

CONCLUSION

Exosomes released from HK-2 cells after renal I/R injury regulate autophagy by transferring miR-590-3p in a paracrine manner, which suggests that increasing the miR-590-3p levels in HK-2 cell-derived exosomes may increase autophagy and protect against kidney injury after renal I/R injury.

The role of autophagy in calcium oxalate kidney stone: A systematic review of the literature

Background: Calcium oxalate kidney stone is one of the common diseases in the urinary system and has a high recurrence rate. Currently, the pathogenesis of kidney stone and the methods to prevent recurrence are still being investigated. Autophagy, as an event of cellular self-repair, has received attention in the field of kidney stone in recent years. In some current studies, autophagy has shown destructiveness and protectiveness in the pathogenesis of kidney stone. The inhibition or promotion of autophagy may be a key target for future kidney stone therapy. This systematic literature review discusses the function of autophagy in kidney stone pathogenesis in the context of current research and synthesizes the evidence analysis to provide a basis for new future therapies.

Method: We systematically reviewed the literature during September 2021 according to the Preferred Reporting Items for Systematic Evaluation and Meta-Analysis (PRISMA) guidelines. Articles on studying the role of autophagy in the pathogenesis of calcium oxalate kidney stone were extracted from PubMed, MEDLINE, Embase and Scopus, including in vivo versus in vitro experiments. The study topic, language and publication date were not restricted. Two authors (Li and Zhou) searched and screened the literature.

Results: We screened 18 articles from the 33 collected articles, of which 6 conducted in vitro cellular studies, four conducted animal studies, eight conducted cellular studies with animal studies, and five studied human specimens. In early studies, the literature generally concluded that autophagy is deleterious in the development of kidney stone. In 2020, the idea of the protectiveness of autophagy associated with kidney stone was first proposed and focused on targeting transcription factor EB. In addition, the interaction of autophagy with other cellular events and the regulation of signaling molecules are focused on in this paper.

Conclusion: This systematic review provides advances in research on the role of autophagy in renal calculi. The current studies suggest that both upregulation and downregulation of autophagy may ameliorate injury in kidney stone models. The authors prefer the upregulation of autophagy as a future research direction for kidney stone treatment.