Ablation of C/EBP homologous protein attenuates renal fibrosis after ureteral obstruction by reducing autophagy and microtubule disruption

The pro-fibrotic role of autophagy in renal intrinsic cells: mechanisms and therapeutic potential in chronic kidney disease

Chronic kidney disease (CKD) represents a significant global public health burden, affecting over 10% of the world's population. Its high morbidity, multifactorial complications, and substantial mortality impose significant burdens on healthcare systems and patients, necessitating considerable investment in healthcare resources. Renal fibrosis (RF) is a key pathological feature and driver of CKD progression. Extensive research indicates that autophagy participates in the complete pathogenesis of RF. Under physiological conditions, autophagy is essential for maintaining renal cellular homeostasis. However, under pathological conditions, perhaps aberrant and sustained activation of autophagy contributes to oxidative stress, apoptosis, inflammation, etc. Ultimately, they accelerate the development of RF. The role of autophagy in RF is currently controversial. This review investigates the molecular mechanisms by which intrinsic renal cell autophagy contributes to RF across diverse disease models, suggesting that autophagy and its associated regulatory pathways represent potential diagnostic and therapeutic targets for CKD.

Endoplasmic Reticulum Stress-Mediated Cell Death in Renal Fibrosis

The endoplasmic reticulum (ER) is indispensable for maintaining normal life activities. Dysregulation of the ER function results in the accumulation of harmful proteins and lipids and the disruption of intracellular signaling pathways, leading to cellular dysfunction and eventual death. Protein misfolding within the ER disrupts its delicate balance, resulting in the accumulation of misfolded or unfolded proteins, a condition known as endoplasmic reticulum stress (ERS). Renal fibrosis, characterized by the aberrant proliferation of fibrotic tissue in the renal interstitium, stands as a grave consequence of numerous kidney disorders, precipitating a gradual decline in renal function. Renal fibrosis is a serious complication of many kidney conditions and is characterized by the overgrowth of fibrotic tissue in the glomerular and tubular interstitium, leading to the progressive failure of renal function. Studies have shown that, during the onset and progression of kidney disease, ERS causes various problems in the kidneys, a process that can lead to kidney fibrosis. This article elucidates the underlying intracellular signaling pathways modulated by ERS, delineating its role in triggering diverse forms of cell death. Additionally, it comprehensively explores a spectrum of potential pharmacological agents and molecular interventions aimed at mitigating ERS, thereby charting novel research avenues and therapeutic advancements in the management of renal fibrosis.

Arsenic exposure induced renal fibrosis via regulation of mitochondrial dynamics and the NLRP3-TGF-β1/SMAD signaling pathway

Environmental arsenic exposure is one of the major global public health problems. Studies have shown that arsenic exposure can cause renal fibrosis, but the underlying mechanism is still unclear. Integrating the in vivo and in vitro models, this study investigated the potential molecular pathways for arsenic-induced renal fibrosis. In this study, SD rats were treated with 0, 5, 25, 50, and 100 mg/L NaAsO2 for 8 weeks via drinking water, and HK2 cells were treated with different doses of NaAsO2 for 48 h. The in vivo results showed that arsenic content in the rats' kidneys increased as the dose increased. Body weight decreased and kidney coefficient increased at 100 mg/L. As a response to the elevated NaAsO2 dose, inflammatory cell infiltration, renal tubular injury, glomerular atrophy, tubulointerstitial hemorrhage, and fibrosis became more obvious indicated by HE and Masson staining. The kidney transcriptome profiles further supported the protein-protein interactions involved in NaAsO2-induced renal fibrosis. The in vivo results, in together with the in vitro experiments, have revealed that exposure to NaAsO2 disturbed mitochondrial dynamics, promoted mitophagy, activated inflammation and the TGF-β1/SMAD signaling pathway, and finally resulted in fibrosis. In summary, arsenic exposure contributed to renal fibrosis via regulating the mitochondrial dynamics and the NLRP3-TGF-β1/SMAD signaling axis. This study presented an adverse outcome pathway for the development of renal fibrosis due to arsenic exposure through drinking water.

Mitochondrial quality control in human health and disease

Mitochondria, the most crucial energy-generating organelles in eukaryotic cells, play a pivotal role in regulating energy metabolism. However, their significance extends beyond this, as they are also indispensable in vital life processes such as cell proliferation, differentiation, immune responses, and redox balance. In response to various physiological signals or external stimuli, a sophisticated mitochondrial quality control (MQC) mechanism has evolved, encompassing key processes like mitochondrial biogenesis, mitochondrial dynamics, and mitophagy, which have garnered increasing attention from researchers to unveil their specific molecular mechanisms. In this review, we present a comprehensive summary of the primary mechanisms and functions of key regulators involved in major components of MQC. Furthermore, the critical physiological functions regulated by MQC and its diverse roles in the progression of various systemic diseases have been described in detail. We also discuss agonists or antagonists targeting MQC, aiming to explore potential therapeutic and research prospects by enhancing MQC to stabilize mitochondrial function.

Autophagy, a double-edged sword for oral tissue regeneration

BACKGROUND

Oral health is of fundamental importance to maintain systemic health in humans. Stem cell-based oral tissue regeneration is a promising strategy to achieve the recovery of impaired oral tissue. As a highly conserved process of lysosomal degradation, autophagy induction regulates stem cell function physiologically and pathologically. Autophagy activation can serve as a cytoprotective mechanism in stressful environments, while insufficient or over-activation may also lead to cell function dysregulation and cell death.

AIM OF REVIEW

This review focuses on the effects of autophagy on stem cell function and oral tissue regeneration, with particular emphasis on diverse roles of autophagy in different oral tissues, including periodontal tissue, bone tissue, dentin pulp tissue, oral mucosa, salivary gland, maxillofacial muscle, temporomandibular joint, etc. Additionally, this review introduces the molecular mechanisms involved in autophagy during the regeneration of different parts of oral tissue, and how autophagy can be regulated by small molecule drugs, biomaterials, exosomes/RNAs or other specific treatments. Finally, this review discusses new perspectives for autophagy manipulation and oral tissue regeneration.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Overall, this review emphasizes the contribution of autophagy to oral tissue regeneration and highlights the possible approaches for regulating autophagy to promote the regeneration of human oral tissue.

Nicotinamide N-Methyl Transferase as a Predictive Marker of Tubular Fibrosis in CKD

Purpose

Chronic kidney disease (CKD) progression is complex. There are not standardized methods for predicting the prognosis of CKD. Nicotinamide N-methyltransferase (NNMT) has been shown to be associated with renal fibrosis. This study aimed to validate NNMT as a prognostic biomarker of progressive CKD.

Patients and Methods

We explored the relationship between NNMT expression and CKD-related outcome variables using the NephroseqV5 and GEO databases. Additionally, a validation set of 37 CKD patients was enrolled to measure the correlation between NNMT expression levels and CKD outcomes. Furthermore, single-cell RNA sequencing data and the Human Protein Atlas were reanalyzed to investigate the expression specificity of NNMT in the kidney. Finally, to detect the status of NNMT expression with tubular fibrosis in vivo, we constructed a unilateral ureteral obstruction (UUO) mouse treated with an NNMT inhibitor.

Results

Analyzing the datasets showed that NNMT was expressed mainly in proximal tubule compartments. And patients with high NNMT expression levels had a significantly lower overall survival rate compared to those with low NNMT expression levels (P = 0.013). NNMT was independent of prognosis factors in the multivariate Cox regression model, and the AUCs for CKD progression at 1, 3, and 5 years were 0.849, 0.775, and 0.877, respectively. Pathway enrichment analysis indicated that NNMT regulates the biological processes of tubulointerstitial fibrosis (TIF). In the validation group, NNMT levels were significantly higher in the CKD group combined with interstitial fibrosis. In vivo, NNMT was a high expression in the UUO group, peaking at postoperative day 21. Treatment with an NNMT inhibitor improved renal tubular interstitial fibrosis, and expression levels of FN, α-SMA, VIM, and TGF-β1 were decreased compared with UUO (P < 0.05).

Conclusion

NNMT was expressed mainly in tubular renal compartments, and associated with CKD prognosis. It holds potential as a diagnostic biomarker for tubular fibrosis in CKD.

Research progress on endoplasmic reticulum homeostasis in kidney diseases

The endoplasmic reticulum (ER) plays important roles in biosynthetic and metabolic processes, including protein and lipid synthesis, Ca²⁺ homeostasis regulation, and subcellular organelle crosstalk. Dysregulation of ER homeostasis can cause toxic protein accumulation, lipid accumulation, and Ca²⁺ homeostasis disturbance, leading to cell injury and even death. Accumulating evidence indicates that the dysregulation of ER homeostasis promotes the onset and progression of kidney diseases. However, maintaining ER homeostasis through unfolded protein response, ER-associated protein degradation, autophagy or ER-phagy, and crosstalk with other organelles may be potential therapeutic strategies for kidney disorders. In this review, we summarize the recent research progress on the relationship and molecular mechanisms of ER dysfunction in kidney pathologies. In addition, the endogenous protective strategies for ER homeostasis and their potential application for kidney diseases have been discussed.

Epoxyeicosatrienoic acid administration or soluble epoxide hydrolase inhibition attenuates renal fibrogenesis in obstructive nephropathy

Epoxyeicosatrienoic acids (EETs) are arachidonic acid metabolites with biological effects, including antiapoptotic, anti-inflammatory, and antifibrotic functions. Soluble epoxide hydrolase (sEH)-mediated hydrolysis of EETs to dihydroxyeicosatrienoic acids (DHETs) attenuates these effects. Recent studies have demonstrated that inhibition of sEH prevents renal tubulointerstitial fibrosis and inflammation in the chronic kidney disease model. Given the pathophysiological role of the EET pathway in chronic kidney disease, we investigated if administration of EET regioisomers and/or sEH inhibition will promote antifibrotic and renoprotective effects in renal fibrosis following unilateral ureteral obstruction (UUO). EETs administration abolished tubulointerstitial fibrogenesis, as demonstrated by reduced fibroblast activation and collagen deposition after UUO. The inflammatory response was prevented as demonstrated by decreased neutrophil and macrophage infiltration and expression of cytokines in EET-administered UUO kidneys. EET administration and/or sEH inhibition significantly reduced M1 macrophage markers, whereas M2 macrophage markers were highly upregulated. Furthermore, UUO-induced oxidative stress, tubular injury, and apoptosis were all downregulated following EET administration. Combined EET administration and sEH inhibition, however, had no additive effect in attenuating inflammation and renal interstitial fibrogenesis after UUO. Taken together, our findings provide a mechanistic understanding of how EETs prevent kidney fibrogenesis during obstructive nephropathy and suggest EET treatment as a potential therapeutic strategy to treat fibrotic diseases.NEW & NOTEWORTHY Epoxyeicosatrienoic acids (EETs) are cytochrome P-450-dependent antihypertensive and anti-inflammatory derivatives of arachidonic acid, which are highly abundant in the kidney and considered renoprotective. We found that EET administration and/or soluble epoxide hydrolase inhibition significantly attenuates oxidative stress, renal cell death, inflammation, macrophage differentiation, and fibrogenesis following unilateral ureteral obstruction. Our findings provide a mechanistic understanding of how EETs prevent kidney fibrogenesis during obstructive nephropathy and suggest that EET treatment may be a potential therapeutic strategy to treat fibrotic diseases.

Inhibition of RIP1-RIP3-mediated necroptosis attenuates renal fibrosis via Wnt3α/β-catenin/GSK-3β signaling in unilateral ureteral obstruction

Renal fibrosis represents the final common outcome of chronic kidney disease of virtually any etiology. However, the mechanism underlying the evolution of renal fibrosis remains to be addressed. This study sought to clarify whether RIP1-RIP3-mediated necroptosis is involved in renal fibrosis via Wnt3α/β-catenin/GSK-3β signaling in vitro and in a rat model of unilateral ureteral obstruction (UUO). Rats with UUO were administered RIP inhibitors (necrostatin-1 or GSK872) or β-catenin/TCF inhibitor ICG-001 daily for 7 consecutive days. UUO caused significant renal tubular necrosis and overexpression of RIP1-RIP3-MLKL axis proteins, and was accompanied by activation of the NLRP3 inflammasome and renal fibrosis. Oxidative stress caused by UUO was closely associated with endoplasmic reticulum stress and mitochondrial dysfunction, which resulted in apoptotic cell death via Wnt3α/β-catenin/GSK-3β signaling. All of these effects were abolished by an RIP inhibitor (necrostatin-1 or GSK872) or ICG-001. In H2O2-treated HK-2 cells, both RIP inhibitor and ICG-001 decreased intracellular reactive oxygen species production and apoptotic cells, but increased cell viability. Activated Wnt3α/β-catenin/GSK-3β signaling was decreased by either RIP inhibitor or ICG-001. Our findings suggest that RIP1-RIP3-mediated necroptosis contributes to the development of renal fibrosis via Wnt3α/β-catenin/GSK-3β signaling in UUO and may be a therapeutic target for protection against renal scarring of other origins.

CCAAT/Enhancer-Binding Proteins in Fibrosis: Complex Roles Beyond Conventional Understanding

CCAAT/enhancer-binding proteins (C/EBPs) are a family of at least six identified transcription factors that contain a highly conserved basic leucine zipper domain and interact selectively with duplex DNA to regulate target gene expression. C/EBPs play important roles in various physiological processes, and their abnormal function can lead to various diseases. Recently, accumulating evidence has demonstrated that aberrant C/EBP expression or activity is closely associated with the onset and progression of fibrosis in several organs and tissues. During fibrosis, various C/EBPs can exert distinct functions in the same organ, while the same C/EBP can exert distinct functions in different organs. Modulating C/EBP expression or activity could regulate various molecular processes to alleviate fibrosis in multiple organs; therefore, novel C/EBPs-based therapeutic methods for treating fibrosis have attracted considerable attention. In this review, we will explore the features of C/EBPs and their critical functions in fibrosis in order to highlight new avenues for the development of novel therapies targeting C/EBPs.

Investigation into the effect and mechanism of dapagliflozin against renal interstitial fibrosis based on transcriptome and network pharmacology

BACKGROUND

Renal interstitial fibrosis (RIF) is the final pathway for chronic kidney diseases (CKD) to end-stage renal disease (ESRD). Dapagliflozin, a selective inhibitor of the sodium glucose co-transporter 2, reduced the risk of renal events in non-diabetic CKD patients in the DAPA-CKD trial. However, the effect and mechanism of dapagliflozin on RIF are not very clear. Currently, we evaluate the effects of dapagliflozin on RIF and systematically explore its mechanism.

METHODS AND RESULTS

Firstly, unilateral ureteral obstruction (UUO) mouse model was established to evaluate effects of dapagliflozin on RIF, and results demonstrated dapagliflozin improved renal function and RIF of UUO mice independent of blood glucose control. Subsequently, transcriptome analysis was performed to explore the potential mechanism of dapagliflozin against RIF, which exhibited the therapeutic effect of dapagliflozin on RIF may be achieved through multiple pathways regulation. Then we verified the potential mechanisms with molecular biology methods, and found that dapagliflozin treatment significantly alleviated inflammation, apoptosis, oxidative stress and mitochondrial injury in kidneys of UUO mice. Furthermore, network pharmacology analysis was used to investigate the potential targets of dapagliflozin against RIF. Moreover, we also applied molecular docking and molecular dynamics simulation to predict the specific binding sites and binding capacity of dapagliflozin and hub target.

CONCLUSIONS

Dapagliflozin had therapeutic effect on RIF independent of blood glucose control, and the protective effects probably mediated by multiple pathways and targets regulation.

Molecular mechanisms and physiological functions of autophagy in kidney diseases

Autophagy is a highly conserved cellular progress for the degradation of cytoplasmic contents including micromolecules, misfolded proteins, and damaged organelles that has recently captured attention in kidney diseases. Basal autophagy plays a pivotal role in maintaining cell survival and kidney homeostasis. Accordingly, dysregulation of autophagy has implicated in the pathologies of kidney diseases. In this review, we summarize the multifaceted role of autophagy in kidney aging, maladaptive repair, tubulointerstitial fibrosis and discuss autophagy-related drugs in kidney diseases. However, uncertainty still remains as to the precise mechanisms of autophagy in kidney diseases. Further research is needed to clarify the accurate molecular mechanism of autophagy in kidney diseases, which will facilitate the discovery of a promising strategy for the prevention and treatment of kidney diseases.

Proximal tubule cyclophilin D mediates kidney fibrogenesis in obstructive nephropathy

The proximal tubule (PT) is highly vulnerable to acute injury, including ischemic insult and nephrotoxins, and chronic kidney injury. It has been established that PT injury is a primary cause of the development of chronic kidney disease, but the underlying molecular mechanism remains to be defined. Here, we tested whether PT cyclophilin D (CypD), a mitochondrial matrix protein, is a critical factor to cause kidney fibrosis progression. To define the role of CypD in kidney fibrosis, we used an established mouse model for kidney fibrosis: the unilateral ureteral obstruction (UUO) model in global and PT-specific CypD knockout (KO). Global CypD KO blunted kidney fibrosis progression with inhibition of myofibroblast activation and fibrosis. UUO-induced tubular atrophy was suppressed in kidneys of global CypD KO but not tubular dilation or apoptotic cell death. PT cell cycle arrest was highly increased in wild-type UUO kidneys but was markedly attenuated in global CypD KO UUO kidneys. The number of macrophages and neutrophils was less in UUO kidneys of global CypD KO than those of wild-type kidneys. Proinflammatory and profibrotic factors were all inhibited in global CypD KO. In line with those of global CypD KO, PT-specific CypD KO also blunted kidney fibrosis progression, along with less tubular atrophy, renal parenchymal loss, cell cycle arrest in PT, and inflammation, indicating a critical role for PT CypD in fibrogenesis. Collectively, our data demonstrate that CypD in the PT is a critical factor contributing to kidney fibrosis in UUO, providing a new paradigm for mitochondria-targeted therapeutics of fibrotic diseases.NEW & NOTEWORTHY It has been established that renal proximal tubule (PT) injury is a primary cause of the development of chronic kidney disease, but the underlying molecular mechanism remains to be defined. Here, we show that cyclophilin D, a mitochondrial matrix protein, in the PT causes kidney fibrogenesis in obstructive nephropathy. Our data suggest that targeting PT cyclophilin D could be beneficial to prevent fibrosis progression.

Redox signaling pathways in unilateral ureteral obstruction (UUO)-induced renal fibrosis

Unilateral ureteral obstruction (UUO) is an experimental rodent model that mimics renal fibrosis associated with obstructive nephropathy in an accelerated manner. After UUO, the activation of the renin-angiotensin system (RAS), nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOXs) and mitochondrial dysfunction lead to reactive oxygen species (ROS) overproduction in the kidney. ROS are secondary messengers able to induce post-translational modifications (PTMs) in redox-sensitive proteins, which activate or deactivate signaling pathways. Therefore, in UUO, it has been proposed that ROS overproduction causes changes in said pathways promoting inflammation, oxidative stress, and apoptosis that contribute to fibrosis development. Furthermore, mitochondrial metabolism impairment has been associated with UUO, contributing to renal damage in this model. Although ROS production and oxidative stress have been studied in UUO, the development of renal fibrosis associated with redox signaling pathways has not been addressed. This review focuses on the current information about the activation and deactivation of signaling pathways sensitive to a redox state and their effect on mitochondrial metabolism in the fibrosis development in the UUO model.

The Role of Autophagy in Anti-Cancer and Health Promoting Effects of Cordycepin

Cordycepin is an adenosine derivative isolated from Cordyceps sinensis, which has been used as an herbal complementary and alternative medicine with various biological activities. The general anti-cancer mechanisms of cordycepin are regulated by the adenosine A3 receptor, epidermal growth factor receptor (EGFR), mitogen-activated protein kinases (MAPKs), and glycogen synthase kinase (GSK)-3β, leading to cell cycle arrest or apoptosis. Notably, cordycepin also induces autophagy to trigger cell death, inhibits tumor metastasis, and modulates the immune system. Since the dysregulation of autophagy is associated with cancers and neuron, immune, and kidney diseases, cordycepin is considered an alternative treatment because of the involvement of cordycepin in autophagic signaling. However, the profound mechanism of autophagy induction by cordycepin has never been reviewed in detail. Therefore, in this article, we reviewed the anti-cancer and health-promoting effects of cordycepin in the neurons, kidneys, and the immune system through diverse mechanisms, including autophagy induction. We also suggest that formulation changes for cordycepin could enhance its bioactivity and bioavailability and lower its toxicity for future applications. A comprehensive understanding of the autophagy mechanism would provide novel mechanistic insight into the anti-cancer and health-promoting effects of cordycepin.

Potential Therapeutic Targets for Cisplatin-Induced Kidney Injury: Lessons from Other Models of AKI and Fibrosis

The effectiveness of cisplatin, a mainstay in the treatment of many solid organ cancers, is hindered by dose-limiting nephrotoxicity. Cisplatin causes AKI in 30% of patients. Patients who do not develop AKI by clinical standards during treatment are still at risk for long-term decline in kidney function and the development of CKD. The connection between AKI and CKD has become increasingly studied, with renal fibrosis a hallmark of CKD development. To prevent both the short- and long-term effects of cisplatin, researchers must use models that reflect both types of pathology. Although a lot is known about cisplatin-induced AKI, very little is known about the mechanisms by which repeated low levels of cisplatin lead to fibrosis development. In this review, strategies used in various rodent models to prevent kidney injury, its progression to fibrosis, or both, are examined to gain mechanistic insights and identify potential therapeutic targets for cisplatin-induced kidney pathologies. Reviewing the results from these models highlights the diverse and highly complex role of cell death, cell senescence, endoplasmic reticulum stress, autophagy, and immune cell activation in acute and chronic kidney injuries. The use of several models of kidney injury is needed for development of agents that will prevent all aspects of cisplatin-induced kidney injury.

Mitochondrial quality control in kidney injury and repair

Mitochondria are essential for the activity, function and viability of eukaryotic cells and mitochondrial dysfunction is involved in the pathogenesis of acute kidney injury (AKI) and chronic kidney disease, as well as in abnormal kidney repair after AKI. Multiple quality control mechanisms, including antioxidant defence, protein quality control, mitochondrial DNA repair, mitochondrial dynamics, mitophagy and mitochondrial biogenesis, have evolved to preserve mitochondrial homeostasis under physiological and pathological conditions. Loss of these mechanisms may induce mitochondrial damage and dysfunction, leading to cell death, tissue injury and, potentially, organ failure. Accumulating evidence suggests a role of disturbances in mitochondrial quality control in the pathogenesis of AKI, incomplete or maladaptive kidney repair and chronic kidney disease. Moreover, specific interventions that target mitochondrial quality control mechanisms to preserve and restore mitochondrial function have emerged as promising therapeutic strategies to prevent and treat kidney injury and accelerate kidney repair. However, clinical translation of these findings is challenging owing to potential adverse effects, unclear mechanisms of action and a lack of knowledge of the specific roles and regulation of mitochondrial quality control mechanisms in kidney resident and circulating cell types during injury and repair of the kidney.

Emodin-induced autophagic cell death hinders epithelial-mesenchymal transition via regulation of BMP-7/TGF-β1 in renal fibrosis

We aim to explore the effects of emodin and its mechanisms on renal fibrosis (RF). We firstly modeled adriamycin-induced rat RF with unilateral nephrectomy. In vivo and in vitro pharmacological experiments were performed in this study. The presence of collagen deposition was detected by Masson staining. To verify whether emodin attenuates RF by monitoring autophagy, the immunohistochemistry staining for autophagy protein LC3B was performed. We conducted western blot to detect the expression of the autophagy-related proteins in EMT in vitro model after treating with emotin and BMP-7. In vivo, we demonstrated that emodin could improve renal dysfunction and decrease pathological damage of the kidney by activation of autophagy and inhibition of EMT. Upregulation of BMP-7 was recorded in the RF rats subjected to emodin treatment. In vitro studies, emodin has the capacity of reversing EMT and activating autophagy, and emodin could regulate the expression of BMP-7. The results revealed that the attenuation of EMT by emodin could be blocked after the inhibition of BMP-7 and suppression of autophagy. Our findings demonstrated that emodin alleviates EMT during RF by actuating autophagy through BMP-7, suggesting a role of BMP-7 in RF treatment and prevention.

Exogenous pancreatic kininogenase protects against renal fibrosis in rat model of unilateral ureteral obstruction

Tissue kallikrein has protective function against various types of injury. In this study, we investigated whether exogenous pancreatic kininogenase (PK) conferred renoprotection in a rat model of unilateral ureteral obstruction (UUO) and H₂O₂-treated HK-2 cells in vitro. SD rats were subjected to UUO surgery, then PK (7.2 U/g per day, ip) was administered for 7 or 14 days. After the treatment, rats were euthanized; the obstructed kidneys were harvested for further examination. We found that PK administration significantly attenuated interstitial inflammation and fibrosis, and downregulated the expression of proinflammatory (MCP-1, TLR-2, and OPN) and profibrotic (TGF-β1 and CTGF) cytokines in obstructed kidney. UUO-induced oxidative stress, closely associated with excessive apoptotic cell death and autophagy via PI3K/AKT/FoxO1a signaling, which were abolished by PK administration. We further showed that PK administration increased the expression of bradykinin receptors 1 and 2 (B1R and B2R) mRNA and the production of NO and cAMP in kidney tissues. Coadministration with either B1R antagonist (des-Arg9-[Leu8]-bradykinin) or B2R antagonist (icatibant) abrogated the renoprotective effects of PK, and reduced the levels of NO and cAMP in obstructed kidney. In H₂O₂-treated HK-2 cells, addition of PK (6 pg/mL) significantly decreased ROS production, regulated the expression of oxidant and antioxidant enzymes, suppressed the expression of TGF-β1 and MCP-1, and inhibited cell apoptosis. Our data demonstrate that PK treatment protects against the progression of renal fibrosis in obstructed kidneys.

MiR-22-3p inhibits fibrotic cataract through inactivation of HDAC6 and increase of α-tubulin acetylation

OBJECTIVES

Fibrotic cataract, including posterior capsule opacification (PCO) and anterior subcapsular cataract (ASC), renders millions of people visually impaired worldwide. However, the underlying mechanism remains poorly understood. Here, we report a miRNA-based regulatory pathway that controls pathological fibrosis of lens epithelium.

MATERIALS AND METHODS

Expression of miR-22-3p and histone deacetylase 6 (HDAC6) in normal and PCO patient samples were measured by qPCR. Human lens epithelial explants were treated with TGF-β2 in the presence or absence of miR-22-3p mimics or inhibitor. Cell proliferation was determined by MTS assay, and migration was tested by transwell assay. Expression of HDAC6 and EMT-related molecules were analysed by Western blot, qPCR and immunocytochemical experiments.

RESULTS

We identify miR-22-3p as a downregulated miRNA targeting HDAC6 in LECs during lens fibrosis and TGF-β2 treatment. Mechanistically, gain- and loss-of-function experiments in human LECs and lens epithelial explants reveal that miR-22-3p prevents proliferation, migration and TGF-β2 induced EMT of LECs via targeting HDAC6 and thereby promoting α-tubulin acetylation. Moreover, pharmacological targeting of HDAC6 deacetylase with Tubacin prevents fibrotic opaque formation through increasing α-tubulin acetylation under TGF-β2 stimulated conditions in both human lens epithelial explants and the whole rat lenses.

CONCLUSIONS

These findings suggest that miR-22-3p prevents lens fibrotic progression by targeting HDAC6 thereby promoting α-tubulin acetylation. The 'miR-22-HDAC6-α-tubulin (de)acetylation' signalling axis may be therapeutic targets for the treatment of fibrotic cataract.

Autophagy in kidney homeostasis and disease

Autophagy is a conserved lysosomal pathway for the degradation of cytoplasmic components. Basal autophagy in kidney cells is essential for the maintenance of kidney homeostasis, structure and function. Under stress conditions, autophagy is altered as part of the adaptive response of kidney cells, in a process that is tightly regulated by signalling pathways that can modulate the cellular autophagic flux - mammalian target of rapamycin, AMP-activated protein kinase and sirtuins are key regulators of autophagy. Dysregulated autophagy contributes to the pathogenesis of acute kidney injury, to incomplete kidney repair after acute kidney injury and to chronic kidney disease of varied aetiologies, including diabetic kidney disease, focal segmental glomerulosclerosis and polycystic kidney disease. Autophagy also has a role in kidney ageing. However, questions remain about whether autophagy has a protective or a pathological role in kidney fibrosis, and about the precise mechanisms and signalling pathways underlying the autophagy response in different types of kidney cells and across the spectrum of kidney diseases. Further research is needed to gain insights into the regulation of autophagy in the kidneys and to enable the discovery of pathway-specific and kidney-selective therapies for kidney diseases and anti-ageing strategies.

Mitochondrial dysfunction and endoplasmic reticulum stress in the promotion of fibrosis in obstructive nephropathy induced by unilateral ureteral obstruction

Obstructive nephropathy favors the progression to chronic kidney disease (CKD), a severe health problem worldwide. The unilateral ureteral obstruction (UUO) model is used to study the development of fibrosis. Impairment of renal mitochondria plays a crucial role in several types of CKD and has been strongly related to fibrosis onset. Nevertheless, in the UUO model, the impairment of mitochondria, their relationship with endoplasmic reticulum (ER) stress induction and the participation of both to induce the fibrotic process remain unclear. In this review, we summarize the current information about mitochondrial bioenergetics, redox dynamics, mitochondrial mass, and biogenesis alterations, as well as the relationship of these mitochondrial alterations with ER stress and their participation in fibrotic processes in UUO models. Early after obstruction, there is metabolic reprogramming related to mitochondrial fatty acid β-oxidation impairment, triggering lipid deposition, oxidative stress, (calcium) Ca²⁺ dysregulation, and a reduction in mitochondrial mass and biogenesis. Mitochondria and the ER establish a pathological feedback loop that promotes the impairment of both organelles by ER stress pathways and Ca²⁺ levels dysregulation. Preserving mitochondrial and ER function can prevent or at least delay the fibrotic process and loss of renal function. However, deeper understanding is still necessary for future clinically-useful therapies.

Self-eating: friend or foe? The emerging role of autophagy in fibrotic diseases

Fibrosis occurs in most human organs including the liver, lung, heart and kidney, and is crucial for the progression of most chronic diseases. As an indispensable catabolic process for intracellular quality control and homeostasis, autophagy occurs in most mammalian cells and is implicated in many biological processes including fibrogenesis. Although advances have been made in understanding autophagy process, the potential role of autophagy in fibrotic diseases remains controversial and has recently attracted a great deal of attention. In the current review, we summarize the commonalities of autophagy affecting different types of fibrosis in different organs, including the liver, lung, heart, and kidney as well as in cystic fibrosis, systematically outline the contradictory results and highlight the distinct role of autophagy during the various stages of fibrosis. In summary, the exact role autophagy plays in fibrogenesis depends on specific cell types and different stimuli, and identifying and evaluating the pathogenic contribution of autophagy in fibrogenesis will promote the discovery of novel therapeutic strategies for the clinical management of these fibrotic diseases.

Atf6α impacts cell number by influencing survival, death and proliferation

Background

A growing body of literature suggests the cell–intrinsic activity of Atf6α during ER stress responses has implications for tissue cell number during growth and development, as well as in adult biology and tumorigenesis [1]. This concept is important, linking the cellular processes of secretory protein synthesis and endoplasmic reticulum stress response with functional tissue capacity and organ size. However, the field contains conflicting observations, especially notable in secretory cell types like the pancreatic beta cell.

Scope of review

Here we summarize current knowledge of the basic biology of Atf6α, along with the pleiotropic roles Atf6α plays in cell life and death decisions and possible explanations for conflicting observations. We include studies investigating the roles of Atf6α in cell survival, death and proliferation using well-controlled methodology and specific validated outcome measures, with a focus on endocrine and metabolic tissues when information was available.

Major conclusions

The net outcome of Atf6α on cell survival and cell death depends on cell type and growth conditions, the presence and degree of ER stress, and the duration and intensity of Atf6α activation. It is unquestioned that Atf6α activity influences the cell fate decision between survival and death, although opposite directions of this outcome are reported in different contexts. Atf6α can also trigger cell cycle activity to expand tissue cell number through proliferation. Much work remains to be done to clarify the many gaps in understanding in this important emerging field.

Salvianolic acid B attenuates epithelial-mesenchymal transition in renal fibrosis rats through activating Sirt1-mediated autophagy

Renal fibrosis is a kind of progressive kidney disease leading to end-stage renal damage. Epithelial-mesenchymal transition (EMT) is one of the crucial features of renal fibrosis. Salvianolic acid B (SalB), isolated from traditional Chinese medicine Radix Salviae miltiorrhizae, has been proved to be suitable for renal protection. The aims of this study are to investigate the pharmacological effects of SalB on renal fibrosis and explore the underlying mechanisms. In vivo, our study showed that SalB could improve kidney dysfunction and reduce the expression of EMT-related proteins, including fibronectin (FN), α-smooth muscle actin (α-SMA) and transforming growth factor-β (TGF-β). In addition, SalB activated autophagy and up-regulated the expression of Sirt1. In vitro, our study showed that SalB reversed EMT in TGF-β1-induced human kidney proximal tubular epithelial cells (HK-2 cells). Further mechanism studies showed that the inhibition of Sirt1 and autophagy could reverse the protective effect of SalB on the EMT process in TGF-β1-induced HK-2 cells. Taken together, this study demonstrated that SalB attenuates EMT in the process of renal fibrosis through activating Sirt1-mediated autophagy, and Sirt1 could be a key target for treatment of renal fibrosis.

Drp1-regulated PARK2-dependent mitophagy protects against renal fibrosis in unilateral ureteral obstruction

Mitophagy is a principle mechanism to degrade damaged mitochondria through PARK2-dependent or PARK2-independent pathway. Mitophagy has been identified to play an important role in acute kidney disease, whereas its role in renal fibrosis remains ill-defined. We sought to investigate the involvement and regulation of mitophagy in renal tubular epithelial cell(RTEC) injury and renal fibrosis after unilateral ureteral obstruction(UUO). Mitochondrial damageand mitochondrial reactive oxygen species (ROS) production was increased in kidney after obstruction of the left ureter. Mitophagy was increased in kidneys following UUO and HK-2 cells under hypoxia exposure, assessed by electron microscopy of mitophagosome, colocalization of MitotrackerRed-stained mitochondria and LC3 staining. The upregulation of PINK1, PARK2, and LC3 II in mitochondrial fraction was observed in the obstructed kidney and hypoxia-exposed HK-2 cells. Pink1 or Park2 gene deletion markedly increased mtROS production, mitochondrial damage, TGFβ1 expression in RTEC, and renal fibrosis in UUO. Mitochondrial recruitment of Drp1 was also induced after UUO. The Drp1 inhibitor, Mdivi-1, decreased mitochondrial PINK1, PARK2 and LC3II level, increased mtROS production both in vivo and in vitro, activated TGFβ1-Smad2/3 signaling in HK-2 cells under hypoxia and worsened renal fibrosis following UUO. The upregulation of TGFβ1 signaling in hypoxia-treated HK-2 cells due to PINK1 or PARK2 silencing, or worsened renal fibrosis after UUO due to Pink1-or Park2-KO mice was rescued by mitoTEMPO, a mitochondria-targeted antioxidant. The findings of this study suggest that Drp1-regulated PARK2-dependent mitophagy plays a critical role in hypoxia-induced renal tubular epithelial cell injury and renal fibrosis in UUO.

Thrombospondin 1 and Its Diverse Roles as a Regulator of Extracellular Matrix in Fibrotic Disease

Thrombospondin 1 (TSP1) is a matricellular extracellular matrix protein that has diverse roles in regulating cellular processes important for the pathogenesis of fibrotic diseases. We will present evidence for the importance of TSP1 control of latent transforming growth factor beta activation in renal fibrosis with an emphasis on diabetic nephropathy. Other functions of TSP1 that affect renal fibrosis, including regulation of inflammation and capillary density, will be addressed. Emerging roles for TSP1 N-terminal domain regulation of collagen matrix assembly, direct effects of TSP1-collagen binding, and intracellular functions of TSP1 in mediating endoplasmic reticulum stress responses in extracellular matrix remodeling and fibrosis, which could potentially affect renal fibrogenesis, will also be discussed. Finally, we will address possible strategies for targeting TSP1 functions to treat fibrotic renal disease.

Inhibition of eIF2α dephosphorylation accelerates pterostilbene-induced cell death in human hepatocellular carcinoma cells in an ER stress and autophagy-dependent manner

Hepatocellular carcinoma (HCC) is the one of the most common cancers worldwide. Because the side effects of current treatments are severe, new effective therapeutic strategies are urgently required. Pterostilbene (PT), a natural analogue of resveratrol, has diverse pharmacologic activities, including antioxidative, anti-inflammatory and antiproliferative activities. Here we demonstrated that PT inhibits HCC cell growth without the induction of apoptosis in an endoplasmic reticulum (ER) stress- and autophagy-dependent manner. Mechanistic studies indicated that the combination of salubrinal and PT modulates ER stress-related autophagy through the phospho-eukaryotic initiation factor 2α/activating transcription factor-4/LC3 pathway, leading to a further inhibition of eIF2α dephosphorylation and the potentiation of cell death. An in vivo xenograft analysis revealed that PT significantly reduced tumour growth in mice with a SK-Hep-1 tumour xenograft. Taken together, our results yield novel insights into the pivotal roles of PT in ER stress- and autophagy-dependent cell death in HCC cells.

Inhibition of HDAC6 activity in kidney diseases: a new perspective

Histone deacetylase 6 (HDAC6), a cytoplasmic enzyme that plays important roles in many biological processes, is one isoform of a family of HDAC enzymes that catalyse the removal of functional acetyl groups from proteins. HDAC6 stands out from the other members of this family because it almost exclusively deacetylates cytoplasmic proteins and exerts deacetylation-independent effects, which has led to the successful development of relatively isoform-specific inhibitors of its enzymatic action. Numerous studies have recently demonstrated that HDAC6 expression and activity are increased in kidney disease, such as autosomal dominant polycystic kidney disease (ADPKD), renal fibrosis, and acute kidney injury (AKI), among others. Moreover, HDAC6 inhibitors have been investigated for use in treating these diseases. In fact, HDAC6 inhibitors effectively limit the progression of kidney diseases, suggesting that targeting HDAC6 may provide a novel treatment approach. However, the primary challenge in developing HDAC6-targeted therapies is understanding how the renoprotective effect of NDAC6 inhibitors can be selectively harnessed. Here, we discuss the unique function of HDAC6 and recapitulate the alluring potential of its inhibitors in kidney diseases.