Postconditioning protects renal fibrosis by attenuating oxidative stress-induced mitochondrial injury

Caffeic acid phenethyl ester restores mitochondrial homeostasis against peritoneal fibrosis induced by peritoneal dialysis through the AMPK/SIRT1 pathway

Increasing evidence suggests that peritoneal fibrosis induced by peritoneal dialysis (PD) is linked to oxidative stress. However, there are currently no effective interventions for peritoneal fibrosis. In the present study, we explored whether adding caffeic acid phenethyl ester (CAPE) to peritoneal dialysis fluid (PDF) improved peritoneal fibrosis caused by PD and explored the molecular mechanism. We established a peritoneal fibrosis model in Sprague-Dawley rats through intraperitoneal injection of PDF and lipopolysaccharide (LPS). Rats in the PD group showed increased peritoneal thickness, submesothelial collagen deposition, and the expression of TGFβ1 and α-SMA. Adding CAPE to PDF significantly inhibited PD-induced submesothelial thickening, reduced TGFβ1 and α-SMA expression, alleviated peritoneal fibrosis, and improved the peritoneal ultrafiltration function. In vitro, peritoneal mesothelial cells (PMCs) treated with PDF showed inhibition of the AMPK/SIRT1 pathway, mitochondrial membrane potential depolarization, overproduction of mitochondrial reactive oxygen species (ROS), decreased ATP synthesis, and induction of mesothelial-mesenchymal transition (MMT). CAPE activated the AMPK/SIRT1 pathway, thereby inhibiting mitochondrial membrane potential depolarization, reducing mitochondrial ROS generation, and maintaining ATP synthesis. However, the beneficial effects of CAPE were counteracted by an AMPK inhibitor and siSIRT1. Our results suggest that CAPE maintains mitochondrial homeostasis by upregulating the AMPK/SIRT1 pathway, which alleviates oxidative stress and MMT, thereby mitigating the damage to the peritoneal structure and function caused by PD. These findings suggest that adding CAPE to PDF may prevent and treat peritoneal fibrosis.

BRD4: an effective target for organ fibrosis

Fibrosis is an excessive wound-healing response induced by repeated or chronic external stimuli to tissues, significantly impacting quality of life and primarily contributing to organ failure. Organ fibrosis is reported to cause 45% of all-cause mortality worldwide. Despite extensive efforts to develop new antifibrotic drugs, drug discovery has not kept pace with the clinical demand. Currently, only pirfenidone and nintedanib are approved by the FDA to treat pulmonary fibrotic illness, whereas there are currently no available antifibrotic drugs for hepatic, cardiac or renal fibrosis. The development of fibrosis is closely related to epigenetic alterations. The field of epigenetics primarily studies biological processes, including chromatin modifications, epigenetic readers, DNA transcription and RNA translation. The bromodomain and extra-terminal structural domain (BET) family, a class of epigenetic readers, specifically recognizes acetylated histone lysine residues and promotes the formation of transcriptional complexes. Bromodomain-containing protein 4 (BRD4) is one of the most well-researched proteins in the BET family. BRD4 is implicated in the expression of genes related to inflammation and pro-fibrosis during fibrosis. Inhibition of BRD4 has shown promising anti-fibrotic effects in preclinical studies; however, no BRD4 inhibitor has been approved for clinical use. This review introduces the structure and function of BET proteins, the research progress on BRD4 in organ fibrosis, and the inhibitors of BRD4 utilized in fibrosis. We emphasize the feasibility of targeting BRD4 as an anti-fibrotic strategy and discuss the therapeutic potential and challenges associated with BRD4 inhibitors in treating fibrotic diseases.

Role of mitochondria in pathogenesis and therapy of renal fibrosis

Renal fibrosis, specifically tubulointerstitial fibrosis, represents the predominant pathological consequence observed in the context of progressive chronic kidney conditions. The pathogenesis of renal fibrosis encompasses a multifaceted interplay of mechanisms, including but not limited to interstitial fibroblast proliferation, activation, augmented production of extracellular matrix (ECM) components, and impaired ECM degradation. Notably, mitochondria, the intracellular organelles responsible for orchestrating biological oxidation processes in mammalian cells, assume a pivotal role within this intricate milieu. Mitochondrial dysfunction, when manifest, can incite a cascade of events, including inflammatory responses, perturbed mitochondrial autophagy, and associated processes, ultimately culminating in the genesis of renal fibrosis. This comprehensive review endeavors to furnish an exegesis of mitochondrial pathophysiology and biogenesis, elucidating the precise mechanisms through which mitochondrial aberrations contribute to the onset and progression of renal fibrosis. We explored how mitochondrial dysfunction, mitochondrial cytopathy and mitochondrial autophagy mediate ECM deposition and renal fibrosis from a multicellular perspective of mesangial cells, endothelial cells, podocytes, macrophages and fibroblasts. Furthermore, it succinctly encapsulates the most recent advancements in the realm of mitochondrial-targeted therapeutic strategies aimed at mitigating renal fibrosis.

Mitochondrial quality control in liver fibrosis: Epigenetic hallmarks and therapeutic strategies

BACKGROUND AND AIM

Mitochondrial quality control (MQC) plays a significant role in the progression of liver fibrosis, with key processes such as mitochondrial fission, fusion, mitophagy and biogenesis maintaining mitochondrial homeostasis. To understand the molecular mechanisms underlying epigenetic regulation of mitochondrial quality control in liver fibrosis, with the aim of uncovering novel therapeutic targets for treating, mitigating, and potentially reversing liver fibrosis, in light of the most recent advances in this field.

METHODS

We searched PubMed, Web of Science, and Scopus for published manuscripts using terms "mitochondrial quality control" "mitochondrial fission" "mitochondrial fusion" "mitochondrial biogenesis" "mitophagy" "liver fibrosis" "epigenetic regulation" "DNA methylation" "RNA methylation" "histone modification" and "non-coding RNA". Manuscripts were collated, studied and carried forward for discussion where appropriate.

RESULTS

Mitochondrial fission, fusion, biogenesis, and mitophagy regulate the homeostasis of mitochondria, and the imbalance of mitochondrial homeostasis can induce liver fibrosis. Epigenetic regulation, including DNA methylation, RNA methylation, histone modifications, and non-coding RNAs, plays a significant role in regulating the processes of mitochondrial homeostasis.

CONCLUSION

Mitochondrial quality control and epigenetic mechanisms are intricately linked to the pathogenesis of liver fibrosis. Understanding these molecular interactions provides insight into potential therapeutic strategies. Further research is necessary to translate these findings into clinical applications, with a focus on developing epigenetic drugs to ameliorate liver fibrosis by modulating MQC and epigenetic pathways.

A single administration of FGF2 after renal ischemia-reperfusion injury alleviates post-injury interstitial fibrosis

BACKGROUND

Despite lack of clinical therapy in acute kidney injury (AKI) or its progression to chronic kidney disease (CKD), administration of growth factors shows great potential in the treatment of renal repair and further fibrosis. At an early phase of AKI, administration of exogenous fibroblast growth factor 2 (FGF2) protects against renal injury by inhibition of mitochondrial damage and inflammatory response. Here, we investigated whether this treatment attenuates the long-term renal interstitial fibrosis induced by ischemia-reperfusion (I/R) injury.

METHODS

Unilateral renal I/R with contralateral nephrectomy was utilized as an in vivo model for AKI and subsequent CKD. Rats were randomly divided into four groups: Sham-operation group, I/R group, I/R-FGF2 group and FGF2-3D group. These groups were monitored for up to 2 months. Serum creatinine, inflammatory response and renal histopathology changes were detected to evaluate the role of FGF2 in AKI and followed renal interstitial fibrosis. Moreover, the expression of vimentin, α-SMA, CD31 and CD34 were examined.

RESULTS

Two months after I/R injury, the severity of renal interstitial fibrosis was significantly attenuated in both of I/R-FGF2 group and FGF2-3D group, compared with the I/R group. The protective effects of FGF2 administration were associated with the reduction of high-mobility group box 1 (HMGB1)-mediated inflammatory response, the inhibition of transforming growth factor beta (TGF-β1)/Smads signaling-induced epithelial-mesenchymal transition and the maintenance of peritubular capillary structure.

CONCLUSIONS

A single dose of exogenous FGF2 administration 1 h or 3 days after reperfusion inhibited renal fibrogenesis and thus blocked the transition of AKI to CKD. Our findings provided novel insight into the role of FGF signaling in AKI-to-CKD progression and underscored the potential of FGF-based therapy for this devastating disease.

Puerarin alleviated oxidative stress and ferroptosis during renal fibrosis induced by ischemia/reperfusion injury via TLR4/Nox4 pathway in rats

PURPOSE

To investigate the role of puerarin on renal fibrosis and the underlying mechanism in renal ischemia and reperfusion (I/R) model.

METHODS

Rats were intraperitoneally injected with puerarin (50 or 100 mg/kg) per day for one week before renal I/R. The level of renal collagen deposition and interstitial fibrosis were observed by hematoxylin and eosin and Sirius Red staining, and the expression of α-smooth muscle actin (α-SMA) was examined by immunohistochemical staining. The ferroptosis related factors and TLR4/Nox4-pathway-associated proteins were detected by Western blotting.

RESULTS

Puerarin was observed to alleviate renal collagen deposition, interstitial fibrosis and the α-SMA expression induced by I/R. Superoxide dismutase (SOD) activities and glutathione (GSH) level were decreased in I/R and hypoxia/reoxygenation (H/R), whereas malondialdehyde (MDA) and Fe2+ level increased. However, puerarin reversed SOD, MDA, GSH and Fe2+ level changes induced by I/R and H/R. Besides, Western blot indicated that puerarin inhibited the expression of ferroptosis related factors in a dose-dependent manner, which further demonstrated that puerarin had the effect to attenuate ferroptosis. Moreover, the increased expression of TLR/Nox4-pathway-associated proteins were observed in I/R and H/R group, but puerarin alleviated the elevated TLR/Nox4 expression.

CONCLUSIONS

Our results suggested that puerarin inhibited oxidative stress and ferroptosis induced by I/R and, thus, delayed the progression of renal fibrosis, providing a new target for the treatment of renal fibrosis.

Chitosan oligosaccharide alleviates renal fibrosis through reducing oxidative stress damage and regulating TGF-β1/Smads pathway

Renal fibrosis (RF) is the common pathway for a variety of chronic kidney diseases that progress to end-stage renal disease. Chitosan oligosaccharide (COS) has been identified as possessing many health functions. However, it is not clear whether COS can prevent RF. The purpose of this paper was to explore the action and mechanism of COS in alleviating RF. First, an acute unilateral ureteral obstruction operation (UUO) in male BALB/c mice was performed to induce RF, and COS or fosinopril (positive control drug) were administered for 7 consecutive days. Data from our experiments indicated that COS treatment can significantly alleviate kidney injury and decrease the levels of blood urea nitrogen (BUN) and serum creatinine (SCr) in the UUO mouse model. More importantly, our results show that COS can reduce collagen deposition and decrease the expression of fibrosis proteins, such as collagen IV, fibronectin, collagen I, α-smooth muscle actin (α-SMA) and E-cadherin, ameliorating experimental renal fibrosis in vivo. In addition, we also found that COS suppressed oxidative stress and inflammation in RF model mice. Further studies indicated that the mechanism by which COS alleviates renal fibrosis is closely related to the regulation of the TGF-β1/Smad pathway. COS has a therapeutic effect on ameliorating renal fibrosis similar to that of the positive control drug fosinopril. Taken together, COS can alleviate renal fibrosis induced by UUO by reducing oxidative stress damage and regulating the TGF-β1/Smad pathway.

Autophagy in renal fibrosis: Protection or promotion?

Autophagy is a process that degrades endogenous cellular protein aggregates and damaged organelles via the lysosomal pathway to maintain cellular homeostasis and energy production. Baseline autophagy in the kidney, which serves as a quality control system, is essential for cellular metabolism and organelle homeostasis. Renal fibrosis is the ultimate pathological manifestation of progressive chronic kidney disease. In several experimental models of renal fibrosis, different time points, stimulus intensities, factors, and molecular mechanisms mediating the upregulation or downregulation of autophagy may have different effects on renal fibrosis. Autophagy occurring in a single lesion may also exert several distinct biological effects on renal fibrosis. Thus, whether autophagy prevents or facilitates renal fibrosis remains a complex and challenging question. This review explores the different effects of the dual regulatory function of autophagy on renal fibrosis in different renal fibrosis models, providing ideas for future work in related basic and clinical research.

Drp1-mediated mitochondrial fission promotes carbon tetrachloride-induced hepatic fibrogenesis in mice

Background

Mitochondrial dynamics is essential for the maintenance of healthy mitochondrial network. Emerging evidence suggests that mitochondrial dysfunction is closely linked to the pathogenesis of hepatic fibrogenesis following chronic liver injury. However, the role of dynamin-related protein 1 (Drp1)-mediated mitochondrial fission in the context of liver fibrosis remains unclear.

Methods and Results

In this study, C57BL/6 mice were used to establish a model of liver fibrosis via oral gavage with CCl4 treatment for 8 weeks. Furthermore, mitochondrial fission intervention experiments were achieved by the mitochondrial division inhibitor 1 (Mdivi-1). The results demonstrated that chronic CCl4 exposure resulted in severe hepatic fibrogenesis and mitochondrial damage. By contrast, pharmacological inhibition of mitochondrial division by Mdivi-1 substantially reduced the changes of mitochondrial dynamics and finally prevented the deposition of extracellular matrix proteins. Mechanistically, excessive mitochondrial fission may activate hepatic stellate cells through RIPK1-MLKL-dependent hepatocyte death, which ultimately promotes liver fibrosis.

Conclusion

Our study imply that inhibiting Drp1-mediated mitochondrial fission attenuates CCl4-induced liver fibrosis and may serve as a therapeutic target for retarding progression of chronic liver disease.

Mitophagy induced by UMI-77 preserves mitochondrial fitness in renal tubular epithelial cells and alleviates renal fibrosis

Renal fibrosis is the final common outcome of chronic kidney disease (CKD), which remains a huge challenge due to a lack of targeted treatment. Growing evidence suggests that during the process of CKD, the integrity and function of mitochondria in renal tubular epithelial cells (TECs) are generally impaired and strongly connected with the progression of renal fibrosis. Mitophagy, a selective form of autophagy, could remove aberrant mitochondria to maintain mitochondrial homeostasis. Deficiency of mitophagy has been reported to aggravate renal fibrosis. However, whether induction of mitophagy could alleviate renal fibrosis has not been stated. In this study, we explored the effect of mitophagy activation by UMI-77, a compound recently verified to induce mitophagy, on murine CKD model of unilateral ureteral obstruction (UUO) in vivo and TECs in vitro. In UUO mice, we found the changes of mitochondrial damage, ROS production, transforming growth factor (TGF)-β1/Smad pathway activation, as well as epithelial-mesenchymal transition phenotype and renal fibrosis, and these changes were ameliorated by mitophagy enhancement using UMI-77. Moreover, TEC apoptosis, nuclear factor (NF)-κB signaling activation, and interstitial inflammation after UUO were significantly mitigated by augmented mitophagy. Then, we found UMI-77 could effectively and safely induce mitophagy in TECs in vitro, and reduced TGF-β1/Smad signaling and downstream profibrotic responses in TGF-β1-treated TECs. These changes were restored by a mitophagy inhibitor. In conclusion, we demonstrated that mitophagy activation protected against renal fibrosis through improving mitochondrial fitness, downregulating TGF-β1/Smad signaling and alleviating TEC injuries and inflammatory infiltration in kidneys.

Fluorofenidone Inhibits UUO/IRI-Induced Renal Fibrosis by Reducing Mitochondrial Damage

Objective

Mitochondrial damage contributes to extracellular matrix (ECM) deposition and renal fibrosis. In this study, we aimed (1) to investigate whether fluorofenidone (AKF-PD) can attenuate mitochondrial damage in two renal fibrosis models: unilateral ureteral obstruction (UUO) and renal ischemia-reperfusion injury (IRI), and (2) to explore the underlying mechanism.

Method

Mitochondrial damage and renal lesions were analyzed in the UUO and IRI models. Mitochondrial energy metabolism, mitochondrial biogenesis, and oxidative stress were measured to assess the effect of AKF-PD on mitochondrial damage and to explore the underlying mechanism. In addition, HK-2 cells were stimulated with TGF-β with and without AKF-PD. The mitochondrial morphology, mtROS, ATP contents, and redox-related proteins were then examined.

Results

In both UUO and IRI models, AKF-PD relieved renal fibrosis, maintained mitochondrial structure, and increased mitochondrial DNA copy numbers. The protection was associated with (1) sustaining mitochondrial energy metabolism, evident by elevations of tricarboxylic acid (TCA) cycle enzymes and mitochondrial respiratory chain complexes; (2) improving mitochondrial biogenesis with increases of TFAM, NRF1, PGC-1α, and SIRT1; and (3) reducing mitochondrial oxidative stress likely via regulating SOD2, SIRT3, and NOX4 expressions. In HK-2 cells treated with TGF-β, AKF-PD protected mitochondria along with improving mitochondrial morphology, enhancing ATP production, reducing mtROS, and regulating SOD2, SIRT3, and NOX4 expression.

Conclusion

We demonstrate that AKF-PD inhibited renal fibrosis at least in part via protecting mitochondria from damages developed in the UUO and IRI models. The mitochondrial protection was associated with sustaining mitochondrial energy metabolism, improving mitochondrial biogenesis, and reducing mitochondrial oxidative stress. This research verified the protective effect of AKF-PD on mitochondria in the UUO and IRI models and elaborated the underlying mechanism.

LTBP4 affects renal fibrosis by influencing angiogenesis and altering mitochondrial structure

Transforming growth factor beta (TGFβ) signalling regulates extracellular matrix accumulation known to be essential for the pathogenesis of renal fibrosis; latent transforming growth factor beta binding protein 4 (LTBP4) is an important regulator of TGFβ activity. To date, the regulation of LTBP4 in renal fibrosis remains unknown. Herein, we report that LTBP4 is upregulated in patients with chronic kidney disease and fibrotic mice kidneys created by unilateral ureteral obstruction (UUO). Mice lacking the short LTBP4 isoform (Ltbp4S-/-) exhibited aggravated tubular interstitial fibrosis (TIF) after UUO, indicating that LTBP4 potentially protects against TIF. Transcriptomic analysis of human proximal tubule cells overexpressing LTBP4 revealed that LTBP4 influences angiogenic pathways; moreover, these cells preserved better mitochondrial respiratory functions and expressed higher vascular endothelial growth factor A (VEGFA) compared to wild-type cells under hypoxia. Results of the tube formation assay revealed that additional LTBP4 in human umbilical vein endothelial cell supernatant stimulates angiogenesis with upregulated vascular endothelial growth factor receptors (VEGFRs). In vivo, aberrant angiogenesis, abnormal mitochondrial morphology and enhanced oxidative stress were observed in Ltbp4S-/- mice after UUO. These results reveal novel molecular functions of LTBP4 stimulating angiogenesis and potentially impacting mitochondrial structure and function. Collectively, our findings indicate that LTBP4 protects against disease progression and may be of therapeutic use in renal fibrosis.

Restoration of afferent arteriolar autoregulatory behavior in ischemia-reperfusion injury in rat kidneys

Renal autoregulation is critical in maintaining stable renal blood flow (RBF) and glomerular filtration rate (GFR). Renal ischemia-reperfusion (IR)-induced kidney injury is characterized by reduced RBF and GFR. The mechanisms contributing to renal microvascular dysfunction in IR have not been fully determined. We hypothesized that increased reactive oxygen species (ROS) contributed to impaired renal autoregulatory capability in IR rats. Afferent arteriolar autoregulatory behavior was assessed using the blood-perfused juxtamedullary nephron preparation. IR was induced by 60 min of bilateral renal artery occlusion followed by 24 h of reperfusion. Afferent arterioles from sham rats exhibited normal autoregulatory behavior. Stepwise increases in perfusion pressure caused pressure-dependent vasoconstriction to 65 ± 3% of baseline diameter (13.2 ± 0.4 μm) at 170 mmHg. In contrast, pressure-mediated vasoconstriction was markedly attenuated in IR rats. Baseline diameter averaged 11.7 ± 0.5 µm and remained between 90% and 101% of baseline over 65-170 mmHg, indicating impaired autoregulatory function. Acute antioxidant administration (tempol or apocynin) to IR kidneys for 20 min increased baseline diameter and improved autoregulatory capability, such that the pressure-diameter profiles were indistinguishable from those of sham kidneys. Furthermore, the addition of polyethylene glycol superoxide dismutase or polyethylene glycol-catalase to the perfusate blood also restored afferent arteriolar autoregulatory responsiveness in IR rats, indicating the involvement of superoxide and/or hydrogen peroxide. IR elevated mRNA expression of NADPH oxidase subunits and monocyte chemoattractant protein-1 in renal tissue homogenates, and this was prevented by tempol pretreatment. These results suggest that ROS accumulation, likely involving superoxide and/or hydrogen peroxide, impairs renal autoregulation in IR rats in a reversible fashion.NEW & NOTEWORTHY Renal ischemia-reperfusion (IR) leads to renal microvascular dysfunction manifested by impaired afferent arteriolar autoregulatory efficiency. Acute administration of scavengers of reactive oxygen species, polyethylene glycol-superoxide dismutase, or polyethylene glycol-catalase following renal IR restored afferent arteriolar autoregulatory capability in IR rats, indicating that renal IR led to reversible impairment of afferent arteriolar autoregulatory capability. Intervention with antioxidant treatment following IR may improve outcomes in patients by preserving renovascular autoregulatory function and potentially preventing the progression to chronic kidney disease after acute kidney injury.

Mitochondrial dysfunction in fibrotic diseases

Although fibrosis is a common pathological feature of most end-stage organ diseases, its pathogenesis remains unclear. There is growing evidence that mitochondrial dysfunction contributes to the development and progression of fibrosis. The heart, liver, kidney and lung are highly oxygen-consuming organs that are sensitive to mitochondrial dysfunction. Moreover, the fibrotic process of skin and islet is closely related to mitochondrial dysfunction as well. This review summarized emerging mechanisms related to mitochondrial dysfunction in different fibrotic organs and tissues above. First, it highlighted the important elucidation of mitochondria morphological changes, mitochondrial membrane potential and structural damage, mitochondrial DNA (mtDNA) damage and reactive oxidative species (ROS) production, etc. Second, it introduced the abnormality of mitophagy and mitochondrial transfer also contributed to the fibrotic process. Therefore, with gaining the increasing knowledge of mitochondrial structure, function, and origin, we could kindle a new era for the diagnostic and therapeutic strategies of many fibrotic diseases based on mitochondrial dysfunction.

Imbalance in mitochondrial dynamics induced by low PGC-1α expression contributes to hepatocyte EMT and liver fibrosis

An imbalance in mitochondrial dynamics induced by oxidative stress may lead to hepatocyte epithelial mesenchymal transition (EMT) and liver fibrosis. However, the underlying molecular mechanisms have not been fully elucidated. This study investigated the role of mitochondrial dynamics in hepatocyte EMT and liver fibrosis using an in vitro human (L-02 cells, hepatic cell line) and an in vivo mouse model of liver fibrosis. Findings showed that oxidative stress-induced mitochondrial DNA damage was associated with abnormal mitochondrial fission and hepatocyte EMT. The reactive oxygen species (ROS) scavengers apocynin and mito-tempo effectively attenuated carbon tetrachloride (CCl4)-induced abnormal mitochondrial fission and liver fibrosis. Restoring mitochondrial biogenesis attenuated hepatocyte EMT. Oxidative stress-induced abnormal hepatocyte mitochondrial fission events by a mechanism that involved the down regulation of PGC-1α. PGC-1α knockout mice challenged with CCl4 had increased abnormal mitochondrial fission and more severe liver fibrosis than wild type mice. These results indicate that PGC-1α has a protective role in oxidative stress-induced-hepatocyte EMT and liver fibrosis.

Adiponectin in renal fibrosis

Renal fibrosis is an inevitable consequence of parenchymal scarring and is the common final pathway that mediates almost all progressive renal diseases. Adiponectin, a hormone produced by adipose tissue, possesses potent anti-insulin, anti-inflammatory, and anti-fibrotic properties. Reportedly, adiponectin serves as an important messenger that facilitates complex interactions between adipose tissue and other metabolically related organs. In recent years, a growing body of evidence supports adiponectin involvement in renal fibrosis. These studies provide a deeper understanding of the molecular mechanism of action of adiponectin in renal fibrosis and also offer a potential preventive and therapeutic target for renal fibrosis. In this review, the physiological role of adiponectin is briefly introduced, and then the mechanism of adiponectin-mediated renal fibrosis and the related signaling pathways are described. Finally, we summarize the findings regarding the clinical value of adiponectin in renal fibrotic diseases and prospected its application potential.

Underlying Histopathology Determines Response to Oxidative Stress in Cultured Human Primary Proximal Tubular Epithelial Cells

Proximal tubular epithelial cells (PTEC) are key players in the progression of kidney diseases. PTEC studies to date have primarily used mouse models and transformed human PTEC lines. However, the translatability of these models to human kidney disease has been questioned. In this study, we investigated the phenotypic and functional response of human primary PTEC to oxidative stress, an established driver of kidney disease. Furthermore, we examined the functional contribution of the underlying histopathology of the cortical tissue used to generate our PTEC. We demonstrated that human primary PTEC from both histologically ‘normal’ and ‘diseased’ cortical tissue responded to H₂O₂-induced oxidative stress with significantly elevated mitochondrial superoxide levels, DNA damage, and significantly decreased proliferation. The functional response of ‘normal’ PTEC to oxidative stress mirrored the reported pathogenesis of human kidney disease, with significantly attenuated mitochondrial function and increased cell death. In contrast, ‘diseased’ PTEC were functionally resistant to oxidative stress, with maintenance of mitochondrial function and cell viability. This selective survival of ‘diseased’ PTEC under oxidizing conditions is reminiscent of the in vivo persistence of maladaptive PTEC following kidney injury. We are now exploring the impact that these differential PTEC responses have in the therapeutic targeting of oxidative stress pathways.

Oxidative Stress in the Pathogenesis and Evolution of Chronic Kidney Disease: Untangling Ariadne's Thread

Amplification of oxidative stress is present since the early stages of chronic kidney disease (CKD), holding a key position in the pathogenesis of renal failure. Induction of renal pro-oxidant enzymes with excess generation of reactive oxygen species (ROS) and accumulation of dityrosine-containing protein products produced during oxidative stress (advanced oxidation protein products—AOPPs) have been directly linked to podocyte damage, proteinuria, and the development of focal segmental glomerulosclerosis (FSGS) as well as tubulointerstitial fibrosis. Vascular oxidative stress is considered to play a critical role in CKD progression, and ROS are potential mediators of the impaired myogenic responses of afferent renal arterioles in CKD and impaired renal autoregulation. Both oxidative stress and inflammation are CKD hallmarks. Oxidative stress promotes inflammation via formation of proinflammatory oxidized lipids or AOPPs, whereas activation of nuclear factor κB transcription factor in the pro-oxidant milieu promotes the expression of proinflammatory cytokines and recruitment of proinflammatory cells. Accumulating evidence implicates oxidative stress in various clinical models of CKD, including diabetic nephropathy, IgA nephropathy, polycystic kidney disease as well as the cardiorenal syndrome. The scope of this review is to tackle the issue of oxidative stress in CKD in a holistic manner so as to provide a future framework for potential interventions.

Beraprost sodium mitigates renal interstitial fibrosis through repairing renal microvessels

Beraprost sodium (BPS), as a prostacyclin analog, plays a significant role in various diseases based on its antiplatelet and vasodilation functions. However, its regulation and role in chronic kidney disease (CKD) still remain elusive. Here, we determined whether BPS could alleviate renal interstitial fibrosis, and improve the renal function and its therapeutic mechanism. In vitro, BPS increased angiogenesis in the HUVECs incubated with BPS detected by tube formation assay and repair damaged endothelial cell-cell junctions induced by hypoxia. In vivo, mice were randomly assigned to a sham-operation group (sham), a unilateral ureteral obstruction group (UUO), and a BPS intragastrical administration group (BPS), and sacrificed at days 3 and 7 post-surgery (six in each group). In UUO model, tissue hypoxia, renal inflammation, oxidative stress, and fibrotic lesions were detected by q-PCR and Western blot techniques and peritubular capillaries (PTCs) injury was detected by a novel technique of fluorescent microangiography (FMA) and analyzed by MATLAB software. Meanwhile, we identified cells undergoing endothelial cell-to-myofibroblast transition by the coexpression of endothelial cell (CD31) and myofibroblast (a-SMA) markers in the obstructed kidney. In contrast, BPS protected against interstitial fibrosis and substantially reduced the number of endothelial cell-to-myofibroblast transition cells. In conclusion, our data indicate the potent therapeutic of BPS in mitigating fibrosis through repairing renal microvessels and suppressing endothelial-mesenchymal transition (EndMT) progression after inhibiting inflammatory and oxidative stress effects. KEY MESSAGES: BPS could improve renal recovery through anti-inflammatory and anti-oxidative pathways. BPS could mitigate fibrosis through repairing renal microvessels and suppressing endothelial-mesenchymal transition (EndMT).

Effect of eNOS on Ischemic Postconditioning-Induced Autophagy against Ischemia/Reperfusion Injury in Mice

Autophagy is involved in the development of numerous illnesses, including ischemia/reperfusion (I/R). Endothelial nitric oxide synthase (eNOS) participates in the protective effects of ischemic postconditioning (IPostC). However, it remains unclear whether eNOS-mediated autophagy serves as a critical role in IPostC in the hearts of mice, in protecting against I/R injury. In the present study, the hearts of mice with left anterior descending coronary artery ligation were studied as I/R models. H9c2 cells underwent exposure to hypoxia/reoxygenation (H/R) and were examined as in vitro model. IPostC reduced mice myocardial infarct size and improved the structure of the heart. IPostC increased the formation of autophagosomes and increased the phosphorylation of eNOS and adenosine monophosphate-activated protein kinase (AMPK). Autophagy and eNOS inhibition suppressed the cardioprotective effects of IPostC. AMPK or eNOS inhibition abolished the improvement effect of IPostC on autophagy. AMPK inhibition decreased eNOS phosphorylation in the heart. Additionally, H9c2 cells suffering hypoxia were used as in vitro model. Autophagy or eNOS inhibition abolished the protective effects of hypoxic postconditioning (HPostC) against H/R injury. AMPK and eNOS inhibition/knockout decreased autophagic activity in the HPostC group. These results indicated that IPostC protects the heart against I/R injury, partially via promoting AMPK/eNOS-mediated autophagy.

Alpha-lipoic acid suppresses Nε-(carboxymethyl) lysine-induced epithelial mesenchymal transition in HK-2 human renal proximal tubule cells

N^ε-(carboxymethyl) lysine (CML) plays causal roles in diabetic complications. In the present study, we investigated whether CML-induced HIF-1α accumulation and epithelial-mesenchymal transition (EMT) in HK-2 renal proximal tubular epithelial cells. Treatment with CML-BSA increased reactive oxygen species (ROS) production reduced the mitochondrial membrane potential and induced mitochondrial fragmentation. Pre-treatment of cells with antioxidant, α-lipoic acid, normalised the ROS production and restored the mitochondrial membrane potential. These changes were accompanied with morphological changes of epithelial mesenchymal transition. CML-BSA increased the protein level of hypoxia-inducible factor-1α (HIF-1α), and the EMT-associated transcription factor, TWIST. These effects were reversed by α-lipoic acid. CML-BSA increased the protein levels of mesenchymal-specific markers, including vimentin, α-smooth muscle actin, which were alleviated by pre-treatment with α-lipoic acid. Our data suggest that CML-BSA induces EMT through a ROS/HIF-1α/TWIST-dependent mechanism, and that α-lipoic acid may alleviate the CML-induced EMT in renal tubular cells.

Inhibition of heparanase protects against chronic kidney dysfunction following ischemia/reperfusion injury

Renal ischemia/reperfusion (I/R) injury occurs in patients undergoing renal transplantation and with acute kidney injury and is responsible for the development of chronic allograft dysfunction as characterized by parenchymal alteration and fibrosis. Heparanase (HPSE), an endoglycosidase that regulates EMT and macrophage polarization, is an active player in the biological response triggered by ischemia/reperfusion (I/R) injury. I/R was induced in vivo by clamping left renal artery for 30 min in wt C57BL/6J mice. Animals were daily treated and untreated with Roneparstat (an inhibitor of HPSE) and sacrificed after 8 weeks. HPSE, fibrosis, EMT-markers, inflammation and oxidative stress were evaluated by biomolecular and histological methodologies together with the evaluation of renal histology and measurement of renal function parameters. 8 weeks after I/R HPSE was upregulated both in renal parenchyma and plasma and tissue specimens showed clear evidence of renal injury and fibrosis. The inhibition of HPSE with Roneparstat-restored histology and fibrosis level comparable with that of control. I/R-injured mice showed a significant increase of EMT, inflammation and oxidative stress markers but they were significantly reduced by treatment with Roneparstat. Finally, the inhibition of HPSE in vivo almost restored renal function as measured by BUN, plasma creatinine and albuminuria. The present study points out that HPSE is actively involved in the mechanisms that regulate the development of renal fibrosis arising in the transplanted organ as a consequence of ischemia/reperfusion damage. HPSE inhibition would therefore constitute a new pharmacological strategy to reduce acute kidney injury and to prevent the chronic pro-fibrotic damage induced by I/R.

Activation of autophagy contributes to the renoprotective effect of postconditioning on acute kidney injury and renal fibrosis

Ischemia/Reperfusion injury contributes to acute kidney injury (AKI) and subsequent chronic kidney disease (CKD) including renal fibrosis. Autophagy is a cytoplasmic components degradation pathway that has complex function in the development of various diseases such as fibrosis in kidney. Our previous work demonstrated that postconditioning (POC) showed excellent therapeutic effect on renal fibrosis via inhibiting the overproduction of reactive oxygen species (ROS) after reperfusion. But the connection of autophagy and POC in the renoprotective effect remains unclear. Here, we defined the relevance of autophagy and POC in the protective effect on AKI and subsequent renal fibrosis. We found that at two days after I/R injury, POC largely reduced renal tubular epithelial cell apoptosis and improved renal function; autophagy was significantly activated in kidneys of the POC rats. At two months after reperfusion, the I/R injury rats displayed severe renal fibrosis and epithelial-mesenchymal transition (EMT), whereas these were remarkably attenuated in the POC treated rats. Overall, our results demonstrated that POC could reduce renal damage and attenuate the degree of EMT after I/R injury via enhanced activation of autophagy.