DAMPs Released From Injured Renal Tubular Epithelial Cells Activate Innate Immune Signals in Healthy Renal Tubular Epithelial Cells

Angiotensin-Converting Enzyme-Dependent Intrarenal Angiotensin II Contributes to CTP: Phosphoethanolamine Cytidylyltransferase Downregulation, Mitochondrial Membranous Disruption, and Reactive Oxygen Species Overgeneration in Diabetic Tubulopathy

Aims: The limited therapeutic options for diabetic tubulopathy (DT) in early diabetic kidney disease (DKD) reflect the difficulty of targeting renal tubular compartment. While renin-angiotensin-aldosterone system (RAS) inhibitors are commonly utilized in the management of DKD, how intrarenal RAS contributes to diabetic tubular injury is not fully understood. Mitochondrial disruption and reactive oxygen species (ROS) overgeneration have been involved in diabetic tubular injury. Herein, we aim to test the hypothesis that angiotensin-converting enzyme (ACE)-dependent intrarenal angiotensin II (AngII) disrupts tubular mitochondrial membranous homeostasis and causes excessive ROS generation in DT. Results: Mice suffered from renal tubular mitochondrial disruption and ROS overgeneration following high-fat diet/streptozocin-type 2 diabetic induction. Intrarenal AngII generation is ACE-dependent in DT. Local AngII accumulation in renal tissues was achieved by intrarenal artery injection. ACE-dependent intrarenal AngII-treated mice exhibit markedly elevated levels of makers of tubular injury. CTP: Phosphoethanolamine cytidylyltransferase (PCYT2), the primary regulatory enzyme for the biosynthesis of phosphatidylethanolamine, was enriched in renal tubules according to single-cell RNA sequencing. ACE-dependent intrarenal AngII-induced tubular membranous disruption, ROS overgeneration, and PCYT2 downregulation. The diabetic ambiance deteriorated the detrimental effect of ACE-dependent intrarenal AngII on renal tubules. Captopril, the ACE inhibitor (ACEI), showed efficiency in partially ameliorating ACE-dependent intrarenal AngII-induced tubular deterioration pre- and post-diabetic induction. Innovation and Conclusion: This study uncovers a critical role of ACE-dependent intrarenal AngII in mitochondrial membranous disruption, ROS overgeneration, and PCYT2 deficiency in diabetic renal tubules, providing novel insight into DT pathogenesis and ACEI-combined therapeutic targets. Antioxid. Redox Signal. 00, 000-000.

Nanoparticle-assisted Targeting Delivery Technologies for Preventing Organ Rejection

Although organ transplantation is a life-saving medical procedure, the challenge of posttransplant rejection necessitates safe and effective immune modulation strategies. Nanodelivery approaches may have the potential to overcome the limitations of small-molecule immunosuppressive drugs, achieving efficacious treatment options for transplant tolerance without compromising overall host immunity. This review highlights recent advances in biomaterial-assisted formulations and technologies for targeted nanodrug delivery with transplant organ- or immune cell-level precision for treating graft rejection after transplantation. We provide an overview of the mechanism of transplantation rejection, current clinically approved immunosuppressive drugs, and their relevant limitations. Finally, we discuss the targeting principles and advantages of organ- and immune cell-specific delivery technologies. The development of biomaterial-assisted novel therapeutic strategies holds considerable promise for treating organ rejection and clinical translation.

The Dual-specificity Phosphatase 3 (DUSP3): A Potential Target Against Renal Ischemia/Reperfusion Injury

Renal ischemia/reperfusion (I/R) injury is a common clinical challenge faced by clinicians in kidney transplantation. I/R is the leading cause of acute kidney injury, and it occurs when blood flow to the kidney is interrupted and subsequently restored. I/R impairs renal function in both short and long terms. Renal ischemic preconditioning refers to all maneuvers intended to prevent or attenuate ischemic damage. In this context, the present review focuses on the dual-specificity phosphatase 3 (DUSP3), also known as vaccinia H1-related phosphatase, an uncommon regulator of mitogen-activated protein kinase (MAPK) phosphorylation. DUSP3 has different biological functions: (1) it acts as a tumor modulator and (2) it is involved in the regulation of immune response, thrombosis, hemostasis, angiogenesis, and genomic stability. These functions occur either through MAPK-dependent or MAPK-independent mechanisms. DUSP3 genetic deletion dampens kidney damage and inflammation caused by I/R in mice, suggesting DUSP3 as a potential target for preventing renal I/R injury. Here, we discuss the putative role of DUSP3 in ischemic preconditioning and the potential mechanisms of such an attenuated inflammatory response via improved kidney perfusion and adequate innate immune response.

Identification of Differentially Expressed Genes in Cold Storage-associated Kidney Transplantation

BACKGROUND

Although it is acknowledged that ischemia-reperfusion injury is the primary pathology of cold storage-associated kidney transplantation, its underlying mechanism is not well elucidated.

METHODS

To extend the understanding of molecular events and mine hub genes posttransplantation, we performed bulk RNA sequencing at different time points (24 h, day 7, and day 14) on a murine kidney transplantation model with prolonged cold storage (10 h).

RESULTS

In the present study, we showed that genes related to the regulation of apoptotic process, DNA damage response, cell cycle/proliferation, and inflammatory response were steadily elevated at 24 h and day 7. The upregulated gene profiling delicately transformed to extracellular matrix organization and fibrosis at day 14. It is prominent that metabolism-associated genes persistently took the first place among downregulated genes. The gene ontology terms of particular note to enrich are fatty acid oxidation and mitochondria energy metabolism. Correspondingly, the key enzymes of the above processes were the products of hub genes as recognized. Moreover, we highlighted the proximal tubular cell-specific increased genes at 24 h by combining the data with public RNA-Seq performed on proximal tubules. We also focused on ferroptosis-related genes and fatty acid oxidation genes to show profound gene dysregulation in kidney transplantation.

CONCLUSIONS

The comprehensive characterization of transcriptomic analysis may help provide diagnostic biomarkers and therapeutic targets in kidney transplantation.

Targeting Kidney Inflammation After Brain Death and Cold Storage: Investigating the Potential of an NLRP3 Inflammasome Inhibitor (MCC950) for Preconditioning Donor Kidneys

BACKGROUND

Brain death (BD) and cold storage (CS) are critical factors that induce inflammation in donor kidneys, compromising organ quality. We investigated whether treating kidneys from BD rats with an inflammasome Nod-like receptor family pyrin domain containing 3 (NLRP3) inhibitor (MCC950) followed by CS could reduce kidney inflammation.

METHODS

BD rats were assigned to MCC950-treated or nontreated (NT) groups. Kidneys were evaluated immediately before CS (T0) and after 12 h (T12) and 24 h (T24) of CS. Mean arterial pressure, serum creatinine, gene/protein expression, and histology were evaluated.

RESULTS

At T0, MCC950 treatment did not affect mean arterial pressure but tended to reduce serum creatinine and ameliorated the histological score of acute tubular necrosis. However, MCC950 reduced NLRP3, caspase-1, interleukin (IL)-1β, IL-6, Kim-1, nuclear factor kappa B, tumor necrosis factor alpha, and caspase-3 gene expression while increasing IL-10 cytokine gene expression. After 12 h of CS, only the expression of the NLRP3 and caspase-1 genes decreased, and after 24 h of CS, no further changes in the gene expression profile were observed. The levels of the inflammasome proteins NLRP3, caspase-1, and IL-1β consistently decreased across all time points (T0, T12, and T24).

CONCLUSIONS

These findings suggest that MCC950 treatment holds promise for mitigating the proinflammatory state observed in kidneys after BD and CS.

[High STING expression exacerbates renal ischemia-reperfusion injury in mice by regulating the TLR4/NF-κB/NLRP3 pathway and promoting inflammation and apoptosis]

OBJECTIVE

To investigate renal expression level of STING in mice with renal ischemia-reperfusion injury (IRI) and its regulatory role in IRI.

METHODS

C57BL/6 mice were divided into sham operation group, IRI (induced by clamping the renal artery) model group, IRI+DMSO treatment group, and IRI+SN-011 treatment group. Serum creatinine and blood urea nitrogen of the mice were analyzed, and pathological changes in the renal tissue were assessed with PAS staining. RT-qPCR, ELISA, Western blotting, and immunohistochemistry were used to detect the expression levels of STING, KIM-1, Bcl-2, Bax, caspase-3, TLR4, P65, NLRP3, caspase-1, CD68, MPO, IL-1β, IL-6, and TNF-α in the renal tissues. In the cell experiment, HK-2 cells exposed to hypoxia-reoxygenation (H/R) were treated with DMSO or SN-011, and cellular STING expression levels and cell apoptosis were analyzed using RT-qPCR, Western blotting or flow cytometry.

RESULTS

In C57BL/6 mice, renal IRI induced obvious renal tissue damage, elevation of serum creatinine and blood urea nitrogen levels and renal expression levels of KIM-1, STING, TLR4, P65, NLRP3, caspase-1, caspase-3, Bax, CD68, MPO, IL-1β, IL-6, and TNF-α, and reduction of Bcl-2 expression level. Treatment of the mouse models with SN-011 for inhibiting STING expression significantly alleviated these changes. In HK-2 cells, H/R exposure caused significant elevation of cellular STING expression and obviously increased cell apoptosis rate, which was significantly lowered by treatment with SN-011.

CONCLUSION

Renal STING expression is elevated in mice with renal IRI to exacerbate renal injury by regulating the TLR4/NF-κB/NLRP3 pathway and promoting inflammation and apoptosis in the renal tissues.

LncRNA HMOX1 alleviates renal ischemia-reperfusion-induced ferroptotic injury via the miR-3587/HMOX1 axis

Emerging evidence suggests that long non-coding RNAs (lncRNAs) play significant roles in renal ischemia reperfusion (RIR) injury. However, the specific mechanisms by which lncRNAs regulate ferroptosis in renal tubular epithelial cells remain largely unknown. The objective of this study was to investigate the biological function of lncRNA heme oxygenase 1 (lnc-HMOX1) in RIR and its potential molecular mechanism. Our findings demonstrated that the expression of HMOX1-related lnc-HMOX1 was reduced in renal tubular epithelial cells treated with hypoxia-reoxygenation (HR). Furthermore, the over-expression of lnc-HMOX1 mitigated ferroptotic injury in renal tubular epithelial cells in vivo and in vitro. Mechanistically, lnc-HMOX1, as a competitive endogenous RNA (ceRNA), promoted the expression of HMOX1 by sponging miR-3587. Furthermore, the inhibition of HMOX1 effectively impeded the aforementioned effects exerted by lnc-HMOX1. Ultimately, the inhibitory or mimic action of miR-3587 reversed the promoting or refraining influence of silenced or over-expressed lnc-HMOX1 on ferroptotic injury during HR. In summary, our findings contribute to a comprehensive comprehension of the mechanism underlying ferroptotic injury mediated by lnc-HMOX1 during RIR. Significantly, we identified a novel lnc-HMOX1-miR-3587-HMOX1 axis, which holds promise as a potential therapeutic target for RIR injury.

Human pulmonary microvascular endothelial cells respond to DAMPs from injured renal tubular cells

Acute kidney injury (AKI) causes distant organ dysfunction through yet unknown mechanisms, leading to multiorgan failure and death. The lungs are one of the most common extrarenal organs affected by AKI, and combined lung and kidney injury has a mortality as high as 60%-80%. One mechanism that has been implicated in lung injury after AKI involves molecules released from injured kidney cells (DAMPs, or damage-associated molecular patterns) that promote a noninfectious inflammatory response by binding to pattern recognition receptors (PRRs) constitutively expressed on the pulmonary endothelium. To date there are limited data investigating the role of PRRs and DAMPs in the pulmonary endothelial response to AKI. Understanding these mechanisms holds great promise for therapeutics aimed at ameliorating the devastating effects of AKI. In this study, we stimulate primary human microvascular endothelial cells with DAMPs derived from injured primary renal tubular epithelial cells (RTECs) as an ex-vivo model of lung injury following AKI. We show that DAMPs derived from injured RTECs cause activation of Toll-Like Receptor and NOD-Like Receptor signaling pathways as well as increase human primary pulmonary microvascular endothelial cell (HMVEC) cytokine production, cell signaling activation, and permeability. We further show that cytokine production in HMVECs in response to DAMPs derived from RTECs is reduced by the inhibition of NOD1 and NOD2, which may have implications for future therapeutics. This paper adds to our understanding of PRR expression and function in pulmonary HMVECs and provides a foundation for future work aimed at developing therapeutic strategies to prevent lung injury following AKI.

Bidirectional pressure: a mini review of ventilator-lung-kidney interactions

Acute kidney injury and respiratory failure that requires mechanical ventilation are both common complications of critical illnesses. Failure of either of these organ systems also increases the risk of failure to the other. As a result, there is a high incidence of patients with concomitant acute kidney injury and the need for mechanical ventilation, which has a devasting impact on intensive care unit outcomes, including mortality. Despite decades of research into the mechanisms of ventilator-lung-kidney interactions, several gaps in knowledge remain and current treatment strategies are primarily supportive. In this review, we outline our current understanding of the mechanisms of acute kidney injury due to mechanical ventilation including a discussion of; 1) The impact of mechanical ventilation on renal perfusion, 2) activation of neurohormonal pathways by positive pressure ventilation, and 3) the role of inflammatory mediators released during ventilator induced lung injury. We also provide a review of the mechanisms by which acute kidney injury increases the risk of respiratory failure. Next, we outline a summary of the current therapeutic approach to preventing lung and kidney injury in the critically ill, including fluid and vasopressor management, ventilator strategies, and treatment of acute kidney injury. Finally, we conclude with a discussion outlining opportunities for novel investigations that may provide a rationale for new treatment approaches.

Traditional Chinese Medicine and renal regeneration: experimental evidence and future perspectives

Repair of acute kidney injury (AKI) is a typical example of renal regeneration. AKI is characterized by tubular cell death, peritubular capillary (PTC) thinning, and immune system activation. After renal tubule injury, resident renal progenitor cells, or renal tubule dedifferentiation, give rise to renal progenitor cells and repair the damaged renal tubule through proliferation and differentiation. Mesenchymal stem cells (MSCs) also play an important role in renal tubular repair. AKI leads to sparse PTC, affecting the supply of nutrients and oxygen and indirectly aggravating AKI. Therefore, repairing PTC is important for the prognosis of AKI. The activation of the immune system is conducive for the body to clear the necrotic cells and debris generated by AKI; however, if the immune activation is too strong or lengthy, it will cause damage to renal tubule cells or inhibit their repair. Macrophages have been shown to play an important role in the repair of kidney injury. Traditional Chinese medicine (TCM) has unique advantages in the treatment of AKI and a series of studies have been conducted on the topic in recent years. Herein, the role of TCM in promoting the repair of renal injury and its molecular mechanism is discussed from three perspectives: repair of renal tubular epithelial cells, repair of PTC, and regulation of macrophages to provide a reference for the treatment and mechanistic research of AKI.

Crosstalk between proximal tubular epithelial cells and other interstitial cells in tubulointerstitial fibrosis after renal injury

The energy needs of tubular epithelial components, especially proximal tubular epithelial cells (PTECs), are high and they heavily depend on aerobic metabolism. As a result, they are particularly vulnerable to various injuries caused by factors such as ischemia, proteinuria, toxins, and elevated glucose levels. Initial metabolic and phenotypic changes in PTECs after injury are likely an attempt at survival and repair. Nevertheless, in cases of recurrent or prolonged injury, PTECs have the potential to undergo a transition to a secretory state, leading to the generation and discharge of diverse bioactive substances, including transforming growth factor-β, Wnt ligands, hepatocyte growth factor, interleukin (IL)-1β, lactic acid, exosomes, and extracellular vesicles. By promoting fibroblast activation, macrophage recruitment, and endothelial cell loss, these bioactive compounds stimulate communication between epithelial cells and other interstitial cells, ultimately worsening renal damage. This review provides a summary of the latest findings on bioactive compounds that facilitate the communication between these cellular categories, ultimately leading to the advancement of tubulointerstitial fibrosis (TIF).

Targeted echogenic and anti-inflammatory polymeric prodrug nanoparticles for the management of renal ischemia/reperfusion injury

Ischemia/reperfusion (IR) injury is an inevitable pathological event occurring when blood is resupplied to the tissues after a period of ischemia. One of major causes of IR injury is the overproduction of reactive oxygen species (ROS) including hydrogen peroxide (H2O2), which mediates the expression of various inflammatory cytokines to exacerbate tissue damages. The overproduced H2O2 could therefore serve as a diagnostic and therapeutic biomarker of IR injury. In this study, poly(boronated methacrylate) (pBMA) nanoparticles were developed as nanotheranostic agents for renal IR injury, which not only generate CO2 bubbles to enhance the ultrasound contrast but also provide potent preventive effects in a H2O2-triggered manner. The surface of pBMA nanoparticles was decorated with taurodeoxycholic acid (TUDCA) that binds P-selectin overexpressed in inflamed tissues. In the mouse model of renal IR injury, TUDCA-coated pBMA (T-pBMA) nanoparticles preferentially accumulated in the injured kidney and markedly enhanced the ultrasound contrast. T-pBMA nanoparticles also effectively prevented renal IR injury by scavenging H2O2 and suppressing the expression of inflammatory cytokines. Treatment progress of IR injury could be also monitored by echogenic T-pBMA nanoparticles. Given their targeting ability, excellent H2O2-responsiveness, anti-inflammatory activity and H2O2-triggered echogenicity, T-pBMA nanoparticles have excellent translational potential for the management of various H2O2-related diseases including IR injury.

The Reparative Roles of IL-33

When discovered in the early 2000s, interleukin-33 (IL-33) was characterized as a potent driver of type 2 immunity and implicated in parasite clearance, as well as asthma, allergy, and lung fibrosis. Yet research in other models has since revealed that IL-33 is a highly pleiotropic molecule with diverse functions. These activities are supported by elusive release mechanisms and diverse expression of the IL-33 receptor, STimulation 2 (ST2), on both immune and stromal cells. Interestingly, IL-33 also supports type 1 immune responses during viral and tumor immunity and after allogeneic hematopoietic stem cell transplantation. Yet the IL-33-ST2 axis is also critical to the establishment of systemic homeostasis and tissue repair and regeneration. Despite these recent findings, the mechanisms by which IL-33 governs the balance between immunity and homeostasis or can support both effective repair and pathogenic fibrosis are poorly understood. As such, ongoing research is trying to understand the potential reparative and regulatory versus pro-inflammatory and pro-fibrotic roles for IL-33 in transplantation. This review provides an overview of the emerging regenerative role of IL-33 in organ homeostasis and tissue repair as it relates to transplantation immunology. It also outlines the known impacts of IL-33 in commonly transplanted solid organs and covers the envisioned roles for IL-33 in ischemia-reperfusion injury, rejection, and tolerance. Finally, we give a comprehensive summary of its effects on different cell populations involved in these processes, including ST2 + regulatory T cells, innate lymphoid cell type 2, as well as significant myeloid cell populations.

Molecular Mechanisms of Cellular Injury and Role of Toxic Heavy Metals in Chronic Kidney Disease

Chronic kidney disease (CKD) is a progressive disease that affects millions of adults every year. Major risk factors include diabetes, hypertension, and obesity, which affect millions of adults worldwide. CKD is characterized by cellular injury followed by permanent loss of functional nephrons. As injured cells die and nephrons become sclerotic, remaining healthy nephrons attempt to compensate by undergoing various structural, molecular, and functional changes. While these changes are designed to maintain appropriate renal function, they may lead to additional cellular injury and progression of disease. As CKD progresses and filtration decreases, the ability to eliminate metabolic wastes and environmental toxicants declines. The inability to eliminate environmental toxicants such as arsenic, cadmium, and mercury may contribute to cellular injury and enhance the progression of CKD. The present review describes major molecular alterations that contribute to the pathogenesis of CKD and the effects of arsenic, cadmium, and mercury on the progression of CKD.