Mitochondrial Damage and Activation of the STING Pathway Lead to Renal Inflammation and Fibrosis

TBK1-Zyxin signaling controls tumor-associated macrophage recruitment to mitigate antitumor immunity

Mechanical control is fundamental for cellular localization within a tissue, including for tumor-associated macrophages (TAMs). While the innate immune sensing pathways cGAS-STING and RLR-MAVS impact the pathogenesis and therapeutics of malignant diseases, their effects on cell residency and motility remain incompletely understood. Here, we uncovered that TBK1 kinase, activated by cGAS-STING or RLR-MAVS signaling in macrophages, directly phosphorylates and mobilizes Zyxin, a key regulator of actin dynamics. Under pathological conditions and in STING or MAVS signalosomes, TBK1-mediated Zyxin phosphorylation at S143 facilitates rapid recruitment of phospho-Zyxin to focal adhesions, leading to subsequent F-actin reorganization and reduced macrophage migration. Intratumoral STING-TBK1-Zyxin signaling was evident in TAMs and critical in antitumor immunity. Furthermore, myeloid-specific or global disruption of this signaling decreased the population of CD11b+ F4/80+ TAMs and promoted PD-1-mediated antitumor immunotherapy. Thus, our findings identify a new biological function of innate immune sensing pathways by regulating macrophage tissue localization, thus providing insights into context-dependent mitigation of antitumor immunity.

cGAS/STING signalling pathway in senescence and oncogenesis

The cGAS/STING signaling pathway is a crucial component of the innate immune system, playing significant roles in sensing cytosolic DNA, regulating cellular senescence, and contributing to oncogenesis. Recent advances have shed new lights into the molecular mechanisms governing pathway activation in multiple pathophysiological settings, the indispensable roles of cGAS/STING signaling in cellular senescence, and its context-dependent roles in cancer development and suppression. This review summarizes current knowledge related to the biology of cGAS/STING signaling pathway and its participations into senescence and oncogenesis. We further explore the clinical implications and therapeutic potential for cGAS/STING targeted therapies, and faced challenges in the field. With a focus on molecular mechanisms and emerging pharmacological targets, this review underscores the importance of future studies to harness the therapeutic potential of the cGAS/STING pathway in treating senescence-related disorders and cancer. Advanced understanding of the regulatory mechanisms of cGAS/STING signaling, along with the associated deregulations in diseases, combined with the development of new classes of cGAS/STING modulators, hold great promises for creating novel and effective therapeutic strategies. These advancements could address current treatment challenges and unlock the full potential of cGAS/STING in treating senescence-related disorders and oncogenesis.

Mitophagy deficiency activates stimulator of interferon genes activation and aggravates pathogenetic cardiac remodeling

Stimulator of interferon genes (STING) has recently been found to play a crucial role in cardiac sterile inflammation and dysfunction. The role of stimulator of interferon genes (STING) in cardiac sterile inflammation and dysfunction has been recently discovered. This study aims to examine the involvement of STING in pathological cardiac remodeling and the mechanisms that govern the activation of the STING pathway. To investigate this, transverse aortic constriction (TAC) was performed on STING knockout mice to induce pressure overload-induced cardiac remodeling. Subsequently, cardiac function, remodeling, and inflammation levels were evaluated. The STING pathway was found to be activated in the pressure overload-stressed heart and angiotensin II (Ang II)-stimulated cardiac fibroblasts. Loss of STING expression led to a significant reduction in inflammatory responses, mitochondrial fragmentation, and oxidative stress in the heart, resulting in attenuated cardiac remodeling and dysfunction. Furthermore, the exacerbation of pressure overload-induced STING-mediated inflammation and pathological cardiac remodeling was observed when mitophagy was suppressed through the silencing of Parkin, an E3 ubiquitin ligase. Taken together, these findings indicate that STING represents a newly identified and significant molecule implicated in the process of pathological cardiac remodeling and that mitophagy is an upstream mechanism that regulates STING activation. Targeting STING may therefore provide a novel therapeutic strategy for pathological cardiac remodeling and heart failure.

Recent advancements in cGAS-STING activation, tumor immune evasion, and therapeutic implications

The cGAS-STING signaling pathway is indeed a pivotal component of the immune system and serve as a crucial link between innate and adaptive immune responses. STING is involved in the cellular response to pathogen invasion and DNA damage, and which has important consequences for host defense mechanisms and cancer regulation. Ongoing research aiming to modulate the cGAS-STING pathway for improved clinical outcomes in cancer and autoimmune diseases is underway. Indeed, the interaction between the cGAS-STING pathway and immune evasion mechanisms is a complex and critical aspect of cancer biology. Pathogens and various host factors can exploit this pathway to reduce the effectiveness of cancer therapies, particularly immunotherapies. Thus, immunotherapies or combination therapies may assist in overcoming the immune suppression and improving clinical outcomes. This review explores recent advancements in understanding the cGAS-STING signaling pathway, with particular emphasis on its activation mechanisms and role in tumor immune evasion. The dual role of the pathway in boosting immune responses while simultaneously enabling tumors to evade the immune system makes it a crucial target for innovative cancer treatment approaches.Please confirm if the author names are presented accurately and in the correct sequence (given name, middle name/initial, family name). Author 2 Given name: [Md Mazedul] Last name [Islam], Author 3 Given name: [Mst Rubaiat Nazneen] Last name [Akhand] and Author 5 Given name: [Md Rashedunnabi] Last name [Akanda]. Also, kindly confirm the details in the metadata are correct.AQ1: Here Author 4 given name: [Byung-Yong] Last name [Park] is missing. Metadata are correct.

Dapagliflozin attenuates AKI to CKD transition in diabetes by activating SIRT3/PGC1-α signaling and alleviating aberrant metabolic reprogramming

BACKGROUND

Patients with diabetes are prone to acute kidney injury (AKI) with a high mortality rate, poor prognosis, and a higher risk of progression to chronic kidney disease than non-diabetic patients.

METHODS

Streptozotocin (STZ)-treated type 1 and db/db type 2 diabetes model were established, AKI model was induced in mice by ischemia-reperfusion injury(IRI). Mouse proximal tubular cell cells were subjected to high glucose and hypoxia-reoxygenation in vitro. Transcriptional RNA sequencing was performed for clustering analysis and target gene screening. Renal structural damage was determined by histological staining, whereas creatinine and urea nitrogen levels were used to measure renal function.

RESULTS

Deteriorated renal function and renal tissue damage were observed in AKI mice with diabetic background. RNA sequencing showed a decrease in fatty acid oxidation (FAO) pathway and an increase in abnormal glycolysis. Treatment with Dapa, Sitagliptin(a DPP-4 inhibitor)and insulin reduced blood glucose levels in mice, and improved renal function. However, Dapa had a superior therapeutic effect and alleviated aberrant FAO and glycosis. Dapa reduced cellular death in cultured cells under high glucose hypoxia-reoxygenation conditions, alleviated FAO dysfunction, and reduced abnormal glycolysis. RNA sequencing showed that SIRT3 expression was reduced in diabetic IRI, which was largely restored by Dapa intervention. 3-TYP, a SIRT3 inhibitor, reversed the renal protective effects of Dapa and mediated abnormal FAO and glycolysis in mice and tubular cells.

CONCLUSION

Our study provides experimental evidence for the use of Dapa as a means to reduce diabetic AKI by ameliorating metabolic reprogramming in renal tubular cells.

Cannabinoid receptor 2 plays a key role in renal fibrosis through inhibiting lipid metabolism in renal tubular cells

AIMS

Renal fibrosis is a common feature in various chronic kidney diseases (CKD). Tubular cell damage is a main characterization which results from dysregulated fatty acid oxidation (FAO) and lipid accumulation. Cannabinoid Receptor 2 (CB2) contributes to renal fibrosis, however, its role in FAO dysregulation in tubular cells is not clarified. In this study, we found CB2 plays a detrimental role in lipid metabolism in tubular cells.

METHODS

CB2 knockout mice were adopted to establish a folic acid-induced nephropathy (FAN) model. CB2-induced FAO dysfunction, lipid deposition, and fibrogenesis were assessed in vivo and vitro. To explore molecular mechanisms, β-catenin inhibitors and peroxisome proliferator-activated receptor alpha (PPARα) activators were also used in CB2-overexpressed cells. The mediative role of β-catenin in CB2-inhibited PPARα and peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) activation was analyzed.

RESULTS

CB2 activates β-catenin signaling, resulting in the suppression of PPARα/PGC-1α axis. This decreased FAO functions and led to lipid droplet formation in tubular cells. CB2 gene ablation effectively mitigated FAO dysfunction, lipid deposition and uremic toxins accumulation in FAN mice, consequently retarding renal fibrosis. Additionally, inhibition to β-catenin or PPARα activation could greatly inhibit lipid accumulation and fibrogenesis induced by CB2.

CONCLUSIONS

This study highlights CB2 disrupts FAO in tubular cells through β-catenin activation and subsequent inhibition on PPARα/PGC-1α activity. Targeted inhibition on CB2 offers a perspective therapeutic strategy to fight against renal fibrosis.

HAO2 protects from proximal tubular cells injured in rats with chronic kidney disease by promoting fatty acid metabolic processes

The complex pathogenesis of kidney disease is closely related to the diversity of kidney intrinsic cells. In this study, single-cell transcriptome sequencing technology was used to sequence and analyze blood and kidney tissue cells in normal control rats and rats with chronic kidney disease (CKD), focusing on key cell populations and functional enrichment to explore the pathogenesis of CKD. Oil red O staining and enzyme-linked immunosorbent assay (ELISA) were used to detect lipid droplets and free fatty acid (FFA). Quantitative real-time polymerase chain reaction (RT-PCR), western blot (WB) were used to verify the differential gene hydroxyacid oxidase 2 (HAO2) and fatty acid metabolic process in tissue to ensure the reliability of single-cell sequencing results. We successfully established a single-cell transcriptome atlas of blood and kidney tissue in rats with CKD, which were annotated into 14 cell subsets (MPCs, PT, Tc, DCT, B-IC, A-IC, CNT, ALOH, BC, Neu, Endo, Pla, NKT, Baso) according to marker gene, and the integrated single-cell atlas of rats showed a significant increase and decrease of MPCs and PTs in the CKD group, respectively. Functional analysis found extensive enrichment of metabolic-related pathways in PT cells, includes fatty acid metabolic process, cellular amino acid metabolic process and generation of precursor metabolites and energy. Immunohistochemical experiments determined that the differential gene HAO2 was localized in the renal tubules, and its expression was significantly reduced in CKD group compared with control, and oil red O staining showed that lipid droplets increased in the CKD group, after overexpression of HAO2 the lipid droplets was inhibited. ELISA assay showed that ATP content decreased in the CKD group and FFA increased in the CKD group. Moreover, the mitochondrial membrane potential of the cells in the OE-HAO2 group was significantly increased compared with OE-NC. The acyl-CoA oxidase 1(ACOX1), peroxisome proliferator-activated receptor alpha (PPARα), peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) were decreased in the CKD group, while genes and proteins were increased after overexpression of HAO2, and the AMP-activated protein kinase (AMPK) phosphorylated proteins were increased, the acetyl-CoA carboxylase (ACC) phosphorylated proteins were decreased, reversely. Therefore, HAO2 may be an important regulator of fatty acid metabolic processes in CKD, and overexpression of HAO2 can enhance fatty acid metabolism by promoting fatty acid oxidation (FAO) pathway.

METTL3-Mediated N 6 -Methyladenosine mRNA Modification and cGAS-STING Pathway Activity in Kidney Fibrosis

Background

Chemical modifications on RNA profoundly affect RNA function and regulation. m6A, the most abundant RNA modification in eukaryotes, plays a pivotal role in diverse cellular processes and disease mechanisms. However, its importance is understudied in human CKD samples regarding its influence on pathological mechanisms.

Methods

Liquid chromatography–tandem mass spectrometry and methylated RNA immunoprecipitation sequencing were used to examine alterations in m6A levels and patterns in CKD samples. Overexpression of the m6A writer METTL3 in cultured kidney tubular cells was performed to confirm the effect of m6A in tubular cells and explore the biological functions of m6A modification on target genes. In addition, tubule-specific deletion of Mettl3 (Ksp-Cre Mettl3f/f) mice and antisense oligonucleotides inhibiting Mettl3 expression were used to reduce m6A modification in an animal kidney disease model.

Results

By examining 127 human CKD samples, we observed a significant increase in m6A modification and METTL3 expression in diseased kidneys. Epitranscriptomic analysis unveiled an enrichment of m6A modifications in transcripts associated with the activation of inflammatory signaling pathways, particularly the cyclic guanosine monophosphate–AMP synthase (cGAS)-stimulator of IFN genes (STING) pathway. m6A hypermethylation increased mRNA stability in cGAS and STING1 as well as elevated the expression of key proteins within the cGAS-STING pathway. Both the tubule-specific deletion of Mettl3 and the use of antisense oligonucleotides to inhibit Mettl3 expression protected mice from inflammation, reduced cytokine expression, decreased immune cell recruitment, and attenuated kidney fibrosis.

Conclusions

Our research revealed heightened METTL3-mediated m6A modification in fibrotic kidneys, particularly enriching the cGAS-STING pathway. This hypermethylation increased mRNA stability for cGAS and STING1, leading to sterile inflammation and fibrosis.

STING Promotes the Progression of ADPKD by Regulating Mitochondrial Function, Inflammation, Fibrosis, and Apoptosis

Autosomal dominant polycystic kidney disease (ADPKD) is a predominant genetic disease, which is caused by mutations in PKD genes and is associated with DNA damage in cystic cells. The intrinsic stimulator of interferon genes (STING) pathway is crucial for recognizing damaged DNA in the cytosol, triggering the expression of inflammatory cytokines to activate defense mechanisms. However, the precise roles and mechanisms of STING in ADPKD remain elusive. In this study, we show that Pkd1 mutant mouse kidneys show upregulation of STING, which is stimulated by the DNAs of nuclear and mitochondrial origin. The activation of STING promotes cyst growth through increasing (1) the activation of NF-κB in Pkd1 mutant cells and (2) the recruitment of macrophages in the interstitial and peri-cystic regions in Pkd1 mutant mouse kidneys via NF-κB mediating the upregulation of TNF-α and MCP-1. Targeting STING with its specific inhibitor C-176 delays cyst growth in an early-stage aggressive Pkd1 conditional knockout mouse model and a milder long-lasting Pkd1 mutant mouse model. Targeting STING normalizes mitochondrial structure and function, decreases the formation of micronuclei, induces Pkd1 mutant renal epithelial cell death via p53 signaling, and decreases renal fibrosis in Pkd1 mutant mouse kidneys. These results support that STING is a novel therapeutic target for ADPKD treatment.

APC and ZBTB2 May Mediate M2 Macrophage Infiltration to Promote the Development of Renal Fibrosis: A Bioinformatics Analysis

Background and Purpose: The continuous accumulation of M2 macrophages may potentially contribute to the development of kidney fibrosis in chronic kidney disease (CKD). The purpose of this study was to analyze the infiltration of M2 macrophages in uremic patients and to seek new strategies to slow down the progression of renal fibrosis. Methods: We conducted a comprehensive search for expression data pertaining to uremic samples within the Gene Expression Omnibus (GEO) database, encompassing the time frame from 2010 to 2022. Control and uremic differentially expressed genes (DEGs) were identified. Immune cell infiltration was investigated by CIBERSORT and modules associated with M2 macrophage infiltration were identified by weighted gene coexpression network analysis (WGCNA). Consistent genes were identified using the least absolute shrinkage and selection operator (LASSO) and selection and visualization of the most relevant features (SVM-RFE) methods to search for overlapping genes. Receiver operating characteristic (ROC) curves were examined for the diagnostic value of candidate genes. Quantitative real-time PCR (qPCR) examined the expression levels of candidate genes obtained from uremic patients in M2 macrophage. Results: A total of 1298 DEGs were identified within the GSE37171 dataset. Significant enrichment of DEGs was observed in 20 biological processes (BP), 19 cellular components (CC), 6 molecular functions (MF), and 70 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. CIBERSORT analysis observed a significant increase in B-cell memory, dendritic cell activation, M0, M1, M2, and plasma cell numbers in uremic samples. We identified the 10 most interrelated genes. In particular, adenomatous polyposis coli (APC) and zinc finger and BTB structural domain 2 (ZBTB2) were adversely associated with the infiltration of M2 macrophages. Importantly, the expression levels of APC and ZBTB2 were far lower in M2 macrophages from uremic patients than those in healthy individuals. Conclusion: The development of renal fibrosis may be the result of M2 macrophage infiltration promoted by APC and ZBTB2.

Fibrosis uncovered: ADAMTS12 cuts to the core of extracellular matrix drama

Fibrosis is a common manifestation of most progressive and degenerative diseases, with myofibroblast activation and matrix accumulation playing a key role. In this issue of the JCI, Hoeft et al. identify the important role of ADAMTS12 in fibroblast activation. ADAMTS12, a secreted protein, is involved in extracellular matrix (ECM) remodeling, cell signaling, and inflammation. ADAMTS12 facilitates proteolysis by cleaving various substrates such as ECM components, which are vital for cellular signaling and remodeling. Additionally, it modulates cell-matrix interactions, influencing cell adhesion and migration, and plays an important role in the inflammatory processes. Understanding the role of ADAMTS12 offers potential therapeutic insights for targeting fibrosis in progressive diseases.

Unveiling the role of mtDNA in Liver-Kidney Crosstalk: Insights from trichloroethylene hypersensitivity syndrome

In specific pathological conditions, addressing liver injury may yield favorable effects on renal function through the phenomenon of liver-kidney crosstalk. Mitochondrial DNA (mtDNA) possesses the capability to trigger downstream pathways of inflammatory cytokines, ultimately leading to immune-mediated organ damage. Consequently, understanding the intricate molecular mechanisms governing mtDNA involvement in diseases characterized by liver-kidney crosstalk is of paramount significance. This study seeks to elucidate the role of mtDNA in conditions marked by liver-kidney crosstalk. In previous clinical cases, it has been observed that patients with Trichloroethylene Hypersensitivity Syndrome (TCE-HS) who experience severe liver injury often also exhibit renal injury. In this study, patients diagnosed with trichloroethylene hypersensitivity syndrome were recruited from Shenzhen Occupational Disease Control Center. And Balb/c mice were treated with trichloroethylene. The correlation between liver and kidney injuries in patients with TCE-HS was assessed using Enzyme-Linked Immunosorbent Assay (ELISA). Alterations in mtDNA levels were examined in mouse hepatocytes, red blood cells (RBCs), and renal tubular epithelial cells utilizing immunofluorescence and PCR techniques. TCE-sensitized mice exhibited a significant increase in reactive oxygen species (ROS) and the opening of the mitochondrial permeability transition pore in hepatocytes, resulting in the release of mtDNA. Furthermore, heightened levels of mtDNA and Toll-like Receptor 9 (TLR9) expression were observed in RBCs. Additional experiments demonstrated elevated expression of TLR9 and its downstream mediator MyD88 in renal tubule epithelial cells of TCE-sensitized mice. In vitro investigations confirmed that mtDNA activates the TLR9 pathway in TCMK-1 cells. Collectively, these results suggest that mtDNA released from mitochondrial damage in hepatocytes is carried by RBCs to renal tubular epithelial cells and mediates inflammatory injury in renal tubular epithelial cells through activation of the TLR9 receptor.

GRP78/IRE1 and cGAS/STING pathway crosstalk through CHOP facilitates iodoacetic acid-mediated testosterone decline

Iodoacetic acid (IAA) is an emerging unregulated iodinated disinfection byproduct with high toxicity and widespread exposure. IAA has potential reproductive toxicity and could damage male reproduction. However, the underlying mechanisms and toxicological targets of IAA on male reproductive impairment are still unclear, and thus Sprague-Dawley rats and Leydig cells were used in this work to decode these pending concerns. Results showed that after IAA exposure, the histomorphology and ultrastructure of rat testes were abnormally changed, numbers of Leydig cells were reduced, the hypothalamic-pituitary-testis (HPT) axis was disordered, and testosterone biosynthesis was inhibited. Proteomics analyses displayed that oxidative stress, endoplasmic reticulum stress, and steroid hormone biosynthesis were involved in IAA-caused reproductive injury. Antioxidant enzymes were depleted, while levels of ROS, MDA, 8-OHdG, and γ-H2A.X were increased by IAA. IAA triggered oxidative stress and DNA damage, and then activated the GRP78/IRE1/XBP1s and cGAS/STING/NF-κB pathways in Leydig cells. The two signaling pathways constructed an interactive network by synergistically regulating the downstream transcription factor CHOP, which in turn directly bound to and negatively modulated steroidogenic StAR, finally refraining testosterone biosynthesis in Leydig cells. Collectively, IAA as a reproductive toxicant has anti-androgenic effects, and the GRP78/IRE1 and cGAS/STING pathway crosstalk through CHOP facilitates IAA-mediated testosterone decline.

Visualization of intracellular ATP dynamics in different nephron segments under pathophysiological conditions using the kidney slice culture system

ATP depletion plays a central role in the pathogenesis of kidney diseases. Recently, we reported spatiotemporal intracellular ATP dynamics during ischemia reperfusion (IR) using GO-ATeam2 mice systemically expressing an ATP biosensor. However, observation from the kidney surface did not allow visualization of deeper nephrons or accurate evaluation of ATP synthesis pathways. Here, we established a novel ATP imaging system using slice culture of GO-ATeam2 mouse kidneys, evaluated the ATP synthesis pathway, and analyzed intracellular ATP dynamics using an ex vivo IR-mimicking model and a cisplatin nephropathy model. Proximal tubules (PTs) were found to be strongly dependent on oxidative phosphorylation (OXPHOS) using the inhibitor oligomycin A, whereas podocytes relied on both OXPHOS and glycolysis using phloretin an active transport inhibitor of glucose. We also confirmed that an ex vivo IR-mimicking model could recapitulate ATP dynamics in vivo; ATP recovery in PTs after reoxygenation varied depending on anoxic time length, whereas ATP in distal tubules (DTs) recovered well even after long-term anoxia. After cisplatin administration, ATP levels in PTs decreased first, followed by a decrease in DTs. An organic cation transporter 2 inhibitor, cimetidine, suppressed cisplatin uptake in kidney slices, leading to better ATP recovery in PTs, but not in DTs. Finally, we confirmed that a mitochondria protection reagent (Mitochonic Acid 5) delayed the cisplatin-induced ATP decrease in PTs. Thus, our novel system may provide new insights into the energy dynamics and pathogenesis of kidney disease.

Uremic Toxin Receptor AhR Facilitates Renal Senescence and Fibrosis via Suppressing Mitochondrial Biogenesis

Retention of metabolic end-products in the bodily fluids of patients with chronic kidney disease (CKD) may lead to uremia. The uremic toxin indoxyl sulfate (IS), a tryptophan metabolite, is an endogenous ligand of aryl hydrocarbon receptor (AhR). It is clarified that the upregulation and activation of AhR by IS in tubular epithelial cells (TECs) promote renal senescence and fibrosis. Renal TEC-specific knockout of AhR attenuates renal senescence and fibrosis, as well as the suppression of PGC1α-mediated mitochondrial biogenesis in ischemia reperfusion (IR)- or IS-treated CKD mice kidneys. Overexpression of peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC1α) attenuates IS-induced cell senescence and extracellular matrix production in cultured TECs. Mechanistically, AhR is able to interact with PGC1α and promotes the ubiquitin degradation of PGC1α via its E3 ubiquitin ligase activity. In summary, the elevation and activation of AhR by the accumulated uremic toxins in the progression of CKD accelerate renal senescence and fibrosis by suppressing mitochondrial biogenesis via promoting ubiquitination and proteasomal degradation of PGC1α.

Disrupted mitochondrial transcription factor A expression promotes mitochondrial dysfunction and enhances ocular surface inflammation by activating the absent in melanoma 2 inflammasome

PURPOSE

Severe dry eye disease causes ocular surface damage, which is highly associated with mitochondrial dysfunction. Mitochondrial transcription factor A (TFAM) is essential for packaging mitochondrial DNA (mtDNA) and is crucial for maintaining mitochondrial function. Herein, we aimed to explore the effect of a decreased TFAM expression on ocular surface damage.

METHODS

Female C57BL/6 mice were induced ocular surface injury by topical administrating benzalkonium chloride (BAC). Immortalized human corneal epithelial cells (HCECs) were stimulated by tert-butyl hydroperoxide (t-BHP) to create oxidative stress damage. HCECs with TFAM knockdown were established. RNA sequencing was employed to analyze the whole-genome expression. Mitochondrial changes were measured by transmission electron microscopy, Seahorse metabolic flux analysis, mitochondrial membrane potential, and mtDNA copy number. TFAM expression and inflammatory cytokines were determined using RT-qPCR, immunohistochemistry, immunofluorescence, and immunoblotting.

RESULTS

In both the corneas of BAC-treated mice and t-BHP-induced HCECs, we observed impaired TFAM expression, accompanied by mitochondrial structure and function defects. TFAM downregulation in HCECs suppressed mitochondrial respiratory capacity, reduced mtDNA content, induced mtDNA leakage into the cytoplasm, and led to inflammation. RNA sequencing revealed the absent in melanoma 2 (AIM2) inflammasome was activated in the corneas of BAC-treated mice. The AIM2 inflammasome activation was confirmed in TFAM knockdown HCECs. TFAM knockdown in t-BHP-stimulated HCECs aggravated mitochondrial dysfunction and the AIM2 inflammasome activation, thereby further triggering the secretion of inflammatory factors such as interleukin (IL) -1β and IL-18.

CONCLUSIONS

TFAM reduction impaired mitochondrial function, activated AIM2 inflammasome and promoted ocular surface inflammation, revealing an underlying molecular mechanism for ocular surface disorders.

LONP1 alleviates ageing-related renal fibrosis by maintaining mitochondrial homeostasis

Mitochondrial dysfunction is a pivotal event contributing to the development of ageing-related kidney disorders. Lon protease 1 (LONP1) has been reported to be responsible for ageing-related renal fibrosis; however, the underlying mechanism(s) of LONP1-driven kidney ageing with respect to mitochondrial disturbances remains to be further explored. The level of LONP1 was tested in the kidneys of aged humans and mice. Renal fibrosis and mitochondrial quality control were confirmed in the kidneys of aged mice. Effects of LONP1 silencing or overexpression on renal fibrosis and mitochondrial quality control were explored. In addition, N6-methyladenosine (m6A) modification and methyltransferase like 3 (METTL3) levels, the relationship between LONP1 and METTL3, and the impacts of METTL3 overexpression on mitochondrial functions were confirmed. Furthermore, the expression of insulin-like growth factor 2 mRNA binding protein 2 (IGF2BP2) and the regulatory effects of IGF2BP2 on LONP1 were confirmed in vitro. LONP1 expression was reduced in the kidneys of aged humans and mice, accompanied by renal fibrosis and mitochondrial dysregulation. Overexpression of LONP1 alleviated renal fibrosis and maintained mitochondrial homeostasis, while silencing of LONP1 had the opposite effect. Impaired METTL3-m6A signalling contributed at least in part to ageing-induced LONP1 modification, reducing subsequent degradation in an IGF2BP2-dependent manner. Moreover, METTL3 overexpression alleviated proximal tubule cell injury, preserved mitochondrial stability, inhibited LONP1 degradation, and protected mitochondrial functions. LONP1 mediates mitochondrial function in kidney ageing and that targeting LONP1 may be a potential therapeutic strategy for improving ageing-related renal fibrosis.

Metabolism and bioenergetics in the pathophysiology of organ fibrosis

Fibrosis is the tissue scarring characterized by excess deposition of extracellular matrix (ECM) proteins, mainly collagens. A fibrotic response can take place in any tissue of the body and is the result of an imbalanced reaction to inflammation and wound healing. Metabolism has emerged as a major driver of fibrotic diseases. While glycolytic shifts appear to be a key metabolic switch in activated stromal ECM-producing cells, several other cell types such as immune cells, whose functions are intricately connected to their metabolic characteristics, form a complex network of pro-fibrotic cellular crosstalk. This review purports to clarify shared and particular cellular responses and mechanisms across organs and etiologies. We discuss the impact of the cell-type specific metabolic reprogramming in fibrotic diseases in both experimental and human pathology settings, providing a rationale for new therapeutic interventions based on metabolism-targeted antifibrotic agents.

BCAT1 alleviates early brain injury by inhibiting ferroptosis through PI3K/AKT/mTOR/GPX4 pathway after subarachnoid hemorrhage

Regulation of the redox system by branched-chain amino acid transferase 1 (BCAT1) is of great significance in the occurrence and development of diseases, but the relationship between BCAT1 and subarachnoid hemorrhage (SAH) is still unknown. Ferroptosis, featured by iron-dependent lipid peroxidation accompanied by the depletion of glutathione peroxidase 4 (GPX4), has been implicated in the pathological process of early brain injury after subarachnoid hemorrhage. This study established SAH model by endovascular perforation and adding oxyhemoglobin (Hb) to HT22 cells and delved into the mechanism of BCAT1 in SAH-induced ferroptotic neuronal cell death. It was found that SAH-induced neuronal ferroptosis could be inhibited by BCAT1 overexpression (OE) in rats and HT22 cells, and BCAT1 OE alleviated neurological deficits and cognitive dysfunction in rats after SAH. In addition, the effect of BCAT1 could be reversed by the Ly294002, a specific inhibitor of the PI3K pathway. In summary, our present study indicated that BCAT1 OE alleviated early brain injury EBI after SAH by inhibiting neuron ferroptosis via activation of PI3K/AKT/mTOR pathway and the elevation of GPX4. These results suggested that BCAT1 was a promising therapeutic target for subarachnoid hemorrhage.

mtDNA amplifies beryllium sulfate-induced inflammatory responses via the cGAS-STING pathway in 16HBE cells

Beryllium sulfate (BeSO4) can cause inflammation through the mechanism, which has not been elucidated. Mitochondrial DNA (mtDNA) is a key contributor of inflammation. With mitochondrial damage, released mtDNA can bind to specific receptors (e.g., cGAS) and then activate related pathway to promote inflammatory responses. To investigate the mechanism of mtDNA in BeSO4-induced inflammatory response in 16HBE cells, we established the BeSO4-induced 16HBE cell inflammation model and the ethidium bromide (EB)-induced ρ016HBE cell model to detect the mtDNA content, oxidative stress-related markers, mitochondrial membrane potential, the expression of the cGAS-STING pathway, and inflammation-related factors. Our results showed that BeSO4 caused oxidative stress, decline of mitochondrial membrane potential, and the release of mtDNA into the cytoplasm of 16HBE cells. In addition, BeSO4 induced inflammation in 16HBE cells by activating the cGAS-STING pathway. Furthermore, mtDNA deletion inhibited the expression of cGAS-STING pathway, IL-10, TNF-α, and IFN-β. This study revealed a novel mechanism of BeSO4-induced inflammation in 16HBE cells, which contributes to the understanding of the molecular mechanism of beryllium and its compounds-induced toxicity.

Experimental Type 2 diabetes and lipotoxicity-associated neuroinflammation involve mitochondrial DNA-mediated cGAS/STING axis: implication of Type-1 interferon response in cognitive impairment

Type-1 IFN (interferon)-associated innate immune response is increasingly getting attention in neurodegenerative and metabolic diseases like type 2 diabetes (T2DM). However, its significance in T2DM/lipotoxicity-induced neuroglia changes and cognitive impairment is missing. The present study aims to evaluate the involvement of cGAS (cyclic GMP-AMP synthase)-STING (stimulator of interferon gene), IRF3 (interferon regulatory factor-3), TBK (TANK binding kinase)-mediated Type-1 IFN response in the diabetic brain, and lipotoxicity (palmitate-bovine serum albumin conjugate/PA-BSA)-induced changes in cells (neuro2a and BV2). T2DM was induced in C57/BL6 mice by feeding on a high-fat diet (HFD, 60% Kcal) for 16 weeks and injecting a single dose of streptozotocin (100 mg/kg, i.p) in the 12th week. Plasma biochemical parameter analysis, neurobehavioral assessment, protein expression, and quantitative polymerase chain reaction study were carried out to decipher the hypothesis. T2DM-associated metabolic and lipotoxic stress led to mitochondrial impairment causing leakage of mtDNA to the cytoplasm further commencing cGAS activation and its downstream signaling. The diseased hippocampus and cortex showed decreased expression of synaptophysin (p < 0.01) and PSD-95 (p < 0.01, p < 0.05) with increased expression of cGAS (p < 0.001), p-STING (p < 0.001), p-STAT1 (signal transducer and activator of transcription) (p < 0.01), and IFN-β (p < 0.001) compared to normal control. The IFN-β/p-STAT1-mediated microglia activation was executed employing a conditioned media approach. C-176, a selective STING inhibitor, alleviated cGAS/p-STING/IFN-β expression and proinflammatory microglia/M1-associated markers (CD16 expression, CXCL10, TNF-α, IL-1β mRNA fold change) in the diabetic brain. The present study suggests Type-1IFN response may result in neuroglia dyshomeostasis affecting normal brain function. Alleviating STING signaling has the potential to protect T2DM-associated central ailment.

Mitochondrial dysfunction in kidney stones and relief of kidney stones after reducing mtROS

Mitochondria are essential organelles because they generate the energy required for cellular functions. Kidney stones, as one of the most common urological diseases, have garnered significant attention. In this study, we first collected peripheral venous blood from patients with kidney stones and used qRT-PCR to detect mitochondrial DNA (mtDNA) copy number as a means of assessing mitochondrial function in these patients. Subsequently, through Western blotting, qPCR, immunofluorescence, immunohistochemistry, and transmission electron microscopy, we examined whether calcium oxalate crystals could cause mitochondrial dysfunction in the kidney in both in vitro and in vivo. We then examined the intersection of the DEGs obtained by transcriptome sequencing of the mouse kidney stone model with mitochondria-related genes, and performed KEGG and GO analyses on the intersecting genes. Finally, we administered the mitochondrial ROS scavenger Mito-Tempo in vivo and observed its effects. Our findings revealed that patients with kidney stones had a reduced mtDNA copy number in their peripheral venous blood compared to the control group, suggesting mitochondrial dysfunction in this population. This conclusion was further validated through in vitro and in vivo experiments. Enrichment analyses revealed that the intersecting genes were closely related to metabolism. We observed that after mitochondrial function was preserved, the deposition of calcium oxalate crystals decreased, and the kidney damage and inflammation caused by them were also alleviated. Our research indicates that kidney stones can cause mitochondrial dysfunction. After clearing mtROS, the damage and inflammation caused by kidney stones are reversed, providing new insights into the prevention and treatment of kidney stones.

Case-inspired exploration of renin mutations in autosomal dominant tubulointerstitial kidney disease: not all paths lead to the endoplasmic reticulum

BACKGROUND

Autosomal dominant tubulointerstitial kidney disease (ADTKD) results from mutations in various genes, including REN, UMOD, MUC1, and HNF1B. ADTKD due to REN mutations (ADTKD-REN) is often characterized as a proteinopathy that triggers the endoplasmic reticulum stress (ERS) cascade, potentially sharing similarities with ADTKD-UMOD and ADTKD-MUC1 at the cellular level. This study, inspired by a patient harboring a W17R mutation, investigates ERS activation by this mutation alongside two other renin variants, W10R and L381P.

METHODS

We established stable cell lines expressing both wild-type and mutated renin forms (W17R, W10R, and L381P). Using luciferase reporter assays, RT-qPCR, and confocal microscopy, we evaluated ERS activation, determined the cellular localization of the renin variants, and characterized the mitochondrial network in the W17R line.

RESULTS

The L381P line exhibited ERS activation, including transcriptional upregulation of MANF and CRELD2. No ERS activation was observed in the W17R line, while the W10R line exhibited intermediate characteristics. Notably, the W17R variant was misrouted to the mitochondria resulting in changes of the mitochondrial network organisation.

CONCLUSIONS

ERS activation is not a universal response to different renin mutations in ADTKD-REN. The pathogenesis of the W17R mutation may involve mitochondrial dysfunction rather than the ER pathway, albeit further research is needed to substantiate this hypothesis fully. Testing CRELD2 and MANF as targeted therapy markers for a specific subgroup of ADTKD-REN patients is recommended. Additionally, fludrocortisone treatment has shown efficacy in stabilizing the renal function of our patient over a four-year period without significant side effects.

PAR2-mediated cellular senescence promotes inflammation and fibrosis in aging and chronic kidney disease

Cellular senescence contributes to inflammatory kidney disease via the secretion of inflammatory and profibrotic factors. Protease-activating receptor 2 (PAR2) is a key regulator of inflammation in kidney diseases. However, the relationship between PAR2 and cellular senescence in kidney disease has not yet been described. In this study, we found that PAR2-mediated metabolic changes in renal tubular epithelial cells induced cellular senescence and increased inflammatory responses. Using an aging and renal injury model, PAR2 expression was shown to be associated with cellular senescence. Under in vitro conditions in NRK52E cells, PAR2 activation induces tubular epithelial cell senescence and senescent cells showed defective fatty acid oxidation (FAO). Cpt1α inhibition showed similar senescent phenotype in the cells, implicating the important role of defective FAO in senescence. Finally, we subjected mice lacking PAR2 to aging and renal injury. PAR2-deficient kidneys are protected from adenine- and cisplatin-induced renal fibrosis and injury, respectively, by reducing senescence and inflammation. Moreover, kidneys lacking PAR2 exhibited reduced numbers of senescent cells and inflammation during aging. These findings offer fresh insights into the mechanisms underlying renal senescence and indicate that targeting PAR2 or FAO may be a promising therapeutic approach for managing kidney injury.

Mesenchymal stem cell-derived extracellular vesicles ameliorate renal interstitial fibrosis via the miR-13474/ADAM17 axis

Renal interstitial fibrosis (RIF) is a prevalent consequence of chronic renal diseases, characterized by excessive extracellular matrix (ECM) deposition. A Disintegrin and Metalloprotease 17 (ADAM17), a transmembrane metalloproteinase, plays a central role in driving renal fibrosis progression by activating Notch 1 protein and the downstream TGF-β signaling pathway. Our study investigated potential therapeutic interventions for renal fibrosis, focusing on human umbilical cord mesenchymal stem cell-derived extracellular vesicles (hucMSC-EVs). We found that hucMSC-EVs inhibit ADAM17, thereby impeding renal fibrosis progression. Analysis of hucMSC-EVs miRNA profiles revealed significant enrichment of miR-13474, which effectively targeted and inhibited ADAM17 mRNA expression, subsequently suppressing Notch1 activation, TGF-β signaling, and collagen deposition. Overexpression of miR-13474 enhanced hucMSC-EVs' inhibitory effect on renal fibrosis, while its downregulation abolished this protective effect. Our findings highlight the efficacy of hucMSC-EVs overexpressing miR-13474 in mitigating renal fibrosis via ADAM17 targeting. These insights offer potential therapeutic strategies for managing renal fibrosis.

Diabetes mellitus-Progress and opportunities in the evolving epidemic

Diabetes, a complex multisystem metabolic disorder characterized by hyperglycemia, leads to complications that reduce quality of life and increase mortality. Diabetes pathophysiology includes dysfunction of beta cells, adipose tissue, skeletal muscle, and liver. Type 1 diabetes (T1D) results from immune-mediated beta cell destruction. The more prevalent type 2 diabetes (T2D) is a heterogeneous disorder characterized by varying degrees of beta cell dysfunction in concert with insulin resistance. The strong association between obesity and T2D involves pathways regulated by the central nervous system governing food intake and energy expenditure, integrating inputs from peripheral organs and the environment. The risk of developing diabetes or its complications represents interactions between genetic susceptibility and environmental factors, including the availability of nutritious food and other social determinants of health. This perspective reviews recent advances in understanding the pathophysiology and treatment of diabetes and its complications, which could alter the course of this prevalent disorder.

The effects of cGAS-STING inhibition in liver disease, kidney disease, and cellular senescence

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway is one of the fundamental mechanisms of the body's defense, which responds to the abnormal presence of double-stranded DNA in the cytoplasm to establish an effective natural immune response. In addition to detecting microbial infections, the cGAS pathway may be triggered by any cytoplasmic DNA, which is absent from the normal cytoplasm, and only conditions such as senescence and mitochondrial stress can lead to its leakage and cause sterile inflammation. A growing body of research has shown that the cGAS-STING pathway is strongly associated with sterile inflammation. In this study, we reviewed the regulatory mechanisms and biological functions of the cGAS-STING pathway through its involvement in aseptic inflammation in liver disease, kidney disease, and cellular senescence.

Inhibition of PKC-δ retards kidney fibrosis via inhibiting cGAS-STING signaling pathway in mice

Kidney fibrosis is considered to be the ultimate aggregation pathway of chronic kidney disease (CKD), but its underlying mechanism remains elusive. Protein kinase C-delta (PKC-δ) plays critical roles in the control of growth, differentiation, and apoptosis. In this study, we found that PKC-δ was highly upregulated in human biopsy samples and mouse kidneys with fibrosis. Rottlerin, a PKC-δ inhibitor, alleviated unilateral ureteral ligation (UUO)-induced kidney fibrosis, inflammation, VDAC1 expression, and cGAS-STING signaling pathway activation. Adeno-associated virus 9 (AAV9)-mediated VDAC1 silencing or VBIT-12, a VDAC1 inhibitor, attenuated renal injury, inflammation, and activation of cGAS-STING signaling pathway in UUO mouse model. Genetic and pharmacologic inhibition of STING relieved renal fibrosis and inflammation in UUO mice. In vitro, hypoxia resulted in PKC-δ phosphorylation, VDAC1 oligomerization, and activation of cGAS-STING signaling pathway in HK-2 cells. Inhibition of PKC-δ, VDAC1 or STING alleviated hypoxia-induced fibrotic and inflammatory responses in HK-2 cells, respectively. Mechanistically, PKC-δ activation induced mitochondrial membrane VDAC1 oligomerization via direct binding VDAC1, followed by the mitochondrial DNA (mtDNA) release into the cytoplasm, and subsequent activated cGAS-STING signaling pathway, which contributed to the inflammation leading to fibrosis. In conclusion, this study has indicated for the first time that PKC-δ is an important regulator in kidney fibrosis by promoting cGAS-STING signaling pathway which mediated by VDAC1. PKC-δ may be useful for treating renal fibrosis and subsequent CKD.

Role of the Innate Immune Response in Glomerular Disease Pathogenesis: Focus on Podocytes

Accumulating evidence indicates that inflammatory and immunologic processes play a significant role in the development and progression of glomerular diseases. Podocytes, the terminally differentiated epithelial cells, are crucial for maintaining the integrity of the glomerular filtration barrier. Once injured, podocytes cannot regenerate, leading to progressive proteinuric glomerular diseases. However, emerging evidence suggests that podocytes not only maintain the glomerular filtration barrier and are important targets of immune responses but also exhibit many features of immune-like cells, where they are involved in the modulation of the activity of innate and adaptive immunity. This dual role of podocytes may lead to the discovery and development of new therapeutic targets for treating glomerular diseases. This review aims to provide an overview of the innate immunity mechanisms involved in podocyte injury and the progression of proteinuric glomerular diseases.

Lycopene Protects against Atrazine-Induced Kidney STING-Dependent PANoptosis through Stabilizing mtDNA via Interaction with Sam50/PHB1

Atrazine (ATR) is a widely used herbicide worldwide that can cause kidney damage in humans and animals by accumulation in water and soil. Lycopene (LYC), a carotenoid with numerous biological activities, plays an important role in kidney protection due to its potent antioxidant and anti-inflammatory effects. The current study sought to investigate the role of interactions between mtDNA and the cGAS-STING signaling pathway in LYC mitigating PANoptosis and inflammation in kidneys induced by ATR exposure. In our research, 350 mice were orally administered LYC (5 mg/kg BW/day) and ATR (50 or 200 mg/kg BW/day) for 21 days. Our results reveal that ATR exposure induces a decrease in mtDNA stability, resulting in the release of mtDNA into the cytoplasm through the mPTP pore and the BAX pore and the mobilization of the cGAS-STING pathway, thereby inducing renal PANoptosis and inflammation. LYC can inhibit the above changes caused by ATR. In conclusion, LYC inhibited ATR exposure-induced histopathological changes, renal PANoptosis, and inflammation by inhibiting the cGAS-STING pathway. Our results demonstrate the positive role of LYC in ATR-induced renal injury and provide a new therapeutic target for treating renal diseases in the clinic.

The key role of altered tubule cell lipid metabolism in kidney disease development

Kidney epithelial cells have very high energy requirements, which are largely met by fatty acid oxidation. Complex changes in lipid metabolism are observed in patients with kidney disease. Defects in fatty acid oxidation and increased lipid uptake, especially in the context of hyperlipidemia and proteinuria, contribute to this excess lipid build-up and exacerbate kidney disease development. Recent studies have also highlighted the role of increased de novo lipogenesis in kidney fibrosis. The defect in fatty acid oxidation causes energy starvation. Increased lipid uptake, synthesis, and lower fatty acid oxidation can cause toxic lipid build-up, reactive oxygen species generation, and mitochondrial damage. A better understanding of these metabolic processes may open new treatment avenues for kidney diseases by targeting lipid metabolism.

The role of the cGAS-STING pathway in metabolic diseases

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway is a critical innate immune pathway primarily due to its vital DNA sensing mechanism in pathogen defence. Recent research advances have shown that excessive activation or damage to the cGAS-STING pathway can exacerbate chronic inflammatory responses, playing a significant role in metabolic dysfunction and aging, leading to the development of related diseases such as obesity, osteoporosis, and neurodegenerative diseases. This article reviews the structure and biological functions of the cGAS-STING signaling pathway and discusses in detail how this pathway regulates the occurrence and development of metabolic and age-related diseases. Additionally, this article introduces potential small molecule drugs targeting cGAS and STING, aiming to provide new research perspectives for studying the pathogenesis and treatment of metabolic-related diseases.

CD36 deletion prevents white matter injury by modulating microglia polarization through the Traf5-MAPK signal pathway

BACKGROUND

White matter injury (WMI) represents a significant etiological factor contributing to neurological impairment subsequent to Traumatic Brain Injury (TBI). CD36 receptors are recognized as pivotal participants in the pathogenesis of neurological disorders, including stroke and spinal cord injury. Furthermore, dynamic fluctuations in the phenotypic polarization of microglial cells have been intimately associated with the regenerative processes within the injured tissue following TBI. Nevertheless, there is a paucity of research addressing the impact of CD36 receptors on WMI and microglial polarization. This investigation aims to elucidate the functional role and mechanistic underpinnings of CD36 in modulating microglial polarization and WMI following TBI.

METHODS

TBI models were induced in murine subjects via controlled cortical impact (CCI). The spatiotemporal patterns of CD36 expression were examined through quantitative polymerase chain reaction (qPCR), Western blot analysis, and immunofluorescence staining. The extent of white matter injury was assessed via transmission electron microscopy, Luxol Fast Blue (LFB) staining, and immunofluorescence staining. Transcriptome sequencing was employed to dissect the molecular mechanisms underlying CD36 down-regulation and its influence on white matter damage. Microglial polarization status was ascertained using qPCR, Western blot analysis, and immunofluorescence staining. In vitro, a Transwell co-culture system was employed to investigate the impact of CD36-dependent microglial polarization on oligodendrocytes subjected to oxygen-glucose deprivation (OGD).

RESULTS

Western blot and qPCR analyses revealed that CD36 expression reached its zenith at 7 days post-TBI and remained sustained at this level thereafter. Immunofluorescence staining exhibited robust CD36 expression in astrocytes and microglia following TBI. Genetic deletion of CD36 ameliorated TBI-induced white matter injury, as evidenced by a reduced SMI-32/MBP ratio and G-ratio. Transcriptome sequencing unveiled differentially expressed genes enriched in processes linked to microglial activation, regulation of neuroinflammation, and the TNF signaling pathway. Additionally, bioinformatics analysis pinpointed the Traf5-p38 axis as a critical signaling pathway. In vivo and in vitro experiments indicated that inhibition of the CD36-Traf5-MAPK axis curtailed microglial polarization toward the pro-inflammatory phenotype. In a Transwell co-culture system, BV2 cells treated with LPS + IFN-γ exacerbated the damage of post-OGD oligodendrocytes, which could be rectified through CD36 knockdown in BV2 cells.

CONCLUSIONS

This study illuminates that the suppression of CD36 mitigates WMI by constraining microglial polarization towards the pro-inflammatory phenotype through the down-regulation of the Traf5-MAPK signaling pathway. Our findings present a potential therapeutic strategy for averting neuroinflammatory responses and ensuing WMI damage resulting from TBI.

WWP2 Regulates Renal Fibrosis and the Metabolic Reprogramming of Profibrotic Myofibroblasts

Key Points

WWP2 expression is elevated in the tubulointerstitium of fibrotic kidneys and contributes to CKD pathogenesis and progression. WWP2 uncouples the profibrotic activation and cell proliferation in renal myofibroblasts. WWP2 controls mitochondrial respiration in renal myofibroblasts through the metabolic regulator peroxisome proliferator-activated receptor gamma coactivator 1-alpha.

Background

Renal fibrosis is a common pathologic end point in CKD that is challenging to reverse, and myofibroblasts are responsible for the accumulation of a fibrillar collagen–rich extracellular matrix. Recent studies have unveiled myofibroblasts' diversity in proliferative and fibrotic characteristics, which are linked to different metabolic states. We previously demonstrated the regulation of extracellular matrix genes and tissue fibrosis by WWP2, a multifunctional E3 ubiquitin–protein ligase. Here, we investigate WWP2 in renal fibrosis and in the metabolic reprograming of myofibroblasts in CKD.

Methods

We used kidney samples from patients with CKD and WWP2 -null kidney disease mice models and leveraged single-cell RNA sequencing analysis to detail the cell-specific regulation of WWP2 in fibrotic kidneys. Experiments in primary cultured myofibroblasts by bulk-RNA sequencing, chromatin immunoprecipitation sequencing, metabolomics, and cellular metabolism assays were used to study the metabolic regulation of WWP2 and its downstream signaling.

Results

The tubulointerstitial expression of WWP2 was associated with fibrotic progression in patients with CKD and in murine kidney disease models. WWP2 deficiency promoted myofibroblast proliferation and halted profibrotic activation, reducing the severity of renal fibrosis in vivo . In renal myofibroblasts, WWP2 deficiency increased fatty acid oxidation and activated the pentose phosphate pathway, boosting mitochondrial respiration at the expense of glycolysis. WWP2 suppressed the transcription of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), a metabolic mediator of fibrotic response, and pharmacologic inhibition of PGC-1α partially abrogated the protective effects of WWP2 deficiency on myofibroblasts.

Conclusions

WWP2 regulates the metabolic reprogramming of profibrotic myofibroblasts by a WWP2-PGC-1α axis, and WWP2 deficiency protects against renal fibrosis in CKD.

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.

Therapeutic landscape in systemic lupus erythematosus: mtDNA activation of the cGAS-STING pathway

Mitochondrial DNA (mtDNA) serves as a pivotal immune stimulus in the immune response. During stress, mitochondria release mtDNA into the cytoplasm, where it is recognized by the cytoplasmic DNA receptor cGAS. This activation initiates the cGAS-STING-IRF3 pathway, culminating in an inflammatory response. The cGAS-STING pathway has emerged as a critical mediator of inflammatory responses in microbial infections, stress, autoimmune diseases, chronic illnesses, and tissue injuries. Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by connective tissue involvement across various bodily systems. Its hallmark is the production of numerous autoantibodies, which prompt the immune system to target and damage the body's own tissues, resulting in organ and tissue damage. Increasing evidence implicates the cGAS-STING pathway as a significant contributor to SLE pathogenesis. This article aims to explore the role of the mtDNA-triggered cGAS-STING pathway and its mechanisms in SLE, with the goal of providing novel insights for clinical interventions.

Mitochondrial DNA release and sensing in innate immune responses

Mitochondria are pleiotropic organelles central to an array of cellular pathways including metabolism, signal transduction, and programmed cell death. Mitochondria are also key drivers of mammalian immune responses, functioning as scaffolds for innate immune signaling, governing metabolic switches required for immune cell activation, and releasing agonists that promote inflammation. Mitochondrial DNA (mtDNA) is a potent immunostimulatory agonist, triggering pro-inflammatory and type I interferon responses in a host of mammalian cell types. Here we review recent advances in how mtDNA is detected by nucleic acid sensors of the innate immune system upon release into the cytoplasm and extracellular space. We also discuss how the interplay between mtDNA release and sensing impacts cellular innate immune endpoints relevant to health and disease.

Serine synthesis controls mitochondrial biogenesis in macrophages

Mitochondrial dysfunction is the pivotal driving factor of multiple inflammatory diseases, and targeting mitochondrial biogenesis represents an efficacious approach to ameliorate such dysfunction in inflammatory diseases. Here, we demonstrated that phosphoglycerate dehydrogenase (PHGDH) deficiency promotes mitochondrial biogenesis in inflammatory macrophages. Mechanistically, PHGDH deficiency boosts mitochondrial reactive oxygen species (mtROS) by suppressing cytoplasmic glutathione synthesis. mtROS provokes hypoxia-inducible factor-1α signaling to direct nuclear specificity protein 1 and nuclear respiratory factor 1 transcription. Moreover, myeloid Phgdh deficiency reverses diet-induced obesity. Collectively, this study reveals that a mechanism involving de novo serine synthesis orchestrates mitochondrial biogenesis via mitochondrial-to-nuclear communication, and provides a potential therapeutic target for tackling inflammatory diseases and mitochondria-mediated diseases.

Pellino1 orchestrates gut-kidney axis to perpetuate septic acute kidney injury through activation of STING pathway and NLRP3 inflammasome

AIMS

Intestinal barrier dysfunction is the initial and propagable factor of sepsis in which acute kidney injury (AKI) has been considered as a common life-threatening complication. Our recent study identifies the regulatory role of Pellino1 in tubular death under inflammatory conditions in vitro. The objective of our current study is to explore the impact of Pellino1 on gut-kidney axis during septic AKI and uncover the molecular mechanism (s) underlying this process.

MATERIALS AND METHODS

Immunohistochemistry (IHC) was conducted to evaluate Pellino1 and NOD-like receptor thermal protein domain associated protein 3 (NLRP3) levels in renal biopsies from critically ill patients with a clinical diagnosis of sepsis. Functional and mechanistic studies were characterized in septic models of the Peli-knockout (Peli1-/-) mice by histopathological staining, enzyme-linked immunosorbent assay (ELISA), flow cytometry, immunofluorescence, biochemical detection, CRISPR/Cas9-mediated gene editing and intestinal organoid.

KEY FINDINGS

Pellino1, together with NLRP3, are highly expressed in renal biopsies from critically ill patients diagnosed with sepsis and kidney tissues of septic mice. The Peli1-/- mice with sepsis become less prone to develop AKI and have markedly compromised NLRP3 activation in kidney. Loss of Peli1 endows septic mice refractory to intestinal inflammation, barrier permeability and enterocyte apoptosis that requires stimulator of interferons genes (STING) pathway. Administration of STING agonist DMXAA deteriorates AKI and mortality of septic Peli1-/- mice in the presence of kidney-specific NLRP3 reconstitution.

SIGNIFICANCE

Our studies suggest that Pellino1 has a principal role in orchestrating gut homeostasis towards renal pathophysiology, thus providing a potential therapeutic target for septic AKI.

Qingfei xieding prescription ameliorates mitochondrial DNA-initiated inflammation in bleomycin-induced pulmonary fibrosis through activating autophagy

ETHNOPHARMACOLOGICAL RELEVANCE

Qingfei Xieding prescription was gradually refined and produced by Hangzhou Red Cross Hospital. The raw material includes Ephedra sinica Stapf, Morus alba L., Bombyx Batryticatus, Gypsum Fibrosum, Prunus armeniaca L. var. ansu Maxim., Houttuynia cordata Thunb. , Pueraria edulis Pamp. Paeonia L., Scutellaria baicalensis Georgi and Anemarrhena asphodeloides Bge. It is effective in clinical adjuvant treatment of patients with pulmonary diseases.

AIM OF THE STUDY

To explore the efficacy and underlying mechanism of Qingfei Xieding (QF) in the treatment of bleomycin-induced mouse model.

MATERIALS AND METHODS

TGF-β induced fibrotic phenotype in vitro. Bleomycin injection induced lung tissue fibrosis mouse model in vivo. Flow cytometry was used to detect apoptosis, cellular ROS and lipid oxidation. Mitochondria substructure was observed by transmission electron microscopy. Autophagolysosome and nuclear entry of P65 were monitored by immunofluorescence. Quantitative real-time PCR was performed to detect the transcription of genes associated with mtDNA-cGAS-STING pathway and subsequent inflammatory signaling activation.

RESULTS

TGF-β induced the expression of α-SMA and Collagen I, inhibited cell viability in lung epithelial MLE-12 cells that was reversed by QF-containing serum. TGF-β-mediated downregulation in autophagy, upregulation in lipid oxidation and ROS contents, and mitochondrial damage were rescued by QF-containing serum treatment, but CQ exposure, an autophagy inhibitor, prevented the protective role of QF. In addition to that, the decreased autophagolysosome in TGF-β-exposed MLE-12 cells was reversed by QF and restored to low level in the combination treatment of QF and CQ. Mechanistically, QF-containing serum treatment significantly inhibited mtDNA-cGAS-STING pathway and subsequent inflammatory signaling in TGF-β-challenged cells, which were abolished by CQ-mediated autophagy inhibition. In bleomycin-induced mouse model, QF ameliorated pulmonary fibrosis, reduced mortality, re-activated autophagy in lung tissues and restrained mtDNA-cGAS-STING inflammation pathway. However, the protective effects of QF in bleomycin-induced model mice were also abrogated by CQ.

CONCLUSION

QF alleviated bleomycin-induced pulmonary fibrosis by activating autophagy, inhibiting mtDNA-cGAS-STING pathway-mediated inflammation. This research recognizes the protection role of QF on bleomycin-induced mouse model, and offers evidence for the potentiality of QF in clinical application for pulmonary fibrosis treatment.

Mitochondrial DNA Stress-Mediated Health Risk to Dibutyl Phthalate Contamination on Zebrafish (Danio rerio) at Early Life Stage

Plastics contaminations are found globally and fit the exposure profile of the planetary boundary threat. The plasticizer of dibutyl phthalate (DBP) leaching has occurred and poses a great threat to human health and the ecosystem for decades, and its toxic mechanism needs further comprehensive elucidation. In this study, environmentally relevant levels of DBP were used for exposure, and the developmental process, oxidative stress, mitochondrial ultrastructure and function, mitochondrial DNA (mtDNA) instability and release, and mtDNA-cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) signaling pathway with inflammatory responses were measured in zebrafish at early life stage. Results showed that DBP exposure caused developmental impairments of heart rate, hatching rate, body length, and mortality in zebrafish embryo. Additionally, the elevated oxidative stress damaged mitochondrial ultrastructure and function and induced oxidative damage to the mtDNA with mutations and instability of replication, transcription, and DNA methylation. The stressed mtDNA leaked into the cytosol and activated the cGAS-STING signaling pathway and inflammation, which were ameliorated by co-treatment with DBP and mitochondrial reactive oxygen species (ROS) scavenger, inhibitors of cGAS or STING. Furthermore, the larval results suggest that DBP-induced mitochondrial toxicity of energy disorder and inflammation were involved in the developmental defects of impaired swimming capability. These results enhance the interpretation of mtDNA stress-mediated health risk to environmental contaminants and contribute to the scrutiny of mitochondrial toxicants.

The role of uterus mitochondrial function in high-fat diet-related adverse pregnancy outcomes and protection by resveratrol

This study elucidates the mechanism of obesity-related adverse pregnancy outcomes and further investigates the effect of resveratrol on reproductive performance in a short- or long-term HFD-induced obese mouse model. Results show that maternal weight had a significant positive correlation with litter mortality in mice. A long-term HFD increased body weight and litter mortality with decreased expression of uterine cytochrome oxidase 4 (COX4), which was recovered by resveratrol in mice. Moreover, HFD decreased the expression of peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), nuclear respiratory factors-1 (Nrf-1), and phosphorylated adenosine 5'-monophosphate (AMP)-activated protein kinase (p-AMPK) and increased the expression of phosphorylated extracellular regulated protein kinases (p-ERK) in the uterus. Resveratrol, a polyphenol that can directly bind to the ERK protein, suppressed the phosphorylation of ERK, increased the expression of p-AMPK, PGC-1α and Nrf-1, and decreased litter mortality in mice.

Role of mitochondrial dysfunction in kidney disease: Insights from the cGAS-STING signaling pathway

ABSTRACT

Over the past decade, mitochondrial dysfunction has been investigated as a key contributor to acute and chronic kidney disease. However, the precise molecular mechanisms linking mitochondrial damage to kidney disease remain elusive. The recent insights into the cyclic guanosine monophosphate-adenosine monophosphate (GMP-AMP) synthetase (cGAS)-stimulator of interferon gene (STING) signaling pathway have revealed its involvement in many renal diseases. One of these findings is that mitochondrial DNA (mtDNA) induces inflammatory responses via the cGAS-STING pathway. Herein, we provide an overview of the mechanisms underlying mtDNA release following mitochondrial damage, focusing specifically on the association between mtDNA release-activated cGAS-STING signaling and the development of kidney diseases. Furthermore, we summarize the latest findings of cGAS-STING signaling pathway in cell, with a particular emphasis on its downstream signaling related to kidney diseases. This review intends to enhance our understanding of the intricate relationship among the cGAS-STING pathway, kidney diseases, and mitochondrial dysfunction.

Recent Update on Acute Kidney Injury-to-Chronic Kidney Disease Transition

Acute kidney injury (AKI) is characterized by an abrupt decline of excretory kidney function. The incidence of AKI has increased in the past decades. Patients diagnosed with AKI often undergo diverse clinical trajectories, such as early or late recovery, relapses, and even a potential transition from AKI to chronic kidney disease (CKD). Although recent clinical studies have demonstrated a strong association between AKI and progression of CKD, our understanding of the complex relationship between AKI and CKD is still evolving. No cohort study has succeeded in painting a comprehensive picture of these multi-faceted pathways. To address this lack of understanding, the idea of acute kidney disease (AKD) has recently been proposed. This presents a new perspective to pinpoint a period of heightened vulnerability following AKI, during which a patient could witness a substantial decline in glomerular filtration rate, ultimately leading to CKD transition. Although AKI is included in a range of kidney conditions collectively known as AKD, spanning from mild and self-limiting to severe and persistent, AKD can also occur without a rapid onset usually seen in AKI, such as when kidney dysfunction slowly evolves. In the present review, we summarize the most recent findings about AKD, explore the current state of biomarker discovery related to AKD, discuss the latest insights into pathophysiological underpinnings of AKI to CKD transition, and reflect on therapeutic challenges and opportunities that lie ahead.

The role of mitophagy in the development of chronic kidney disease

Chronic kidney disease (CKD) represents a significant global health concern, with renal fibrosis emerging as a prevalent and ultimate manifestation of this condition. The absence of targeted therapies presents an ongoing and substantial challenge. Accumulating evidence suggests that the integrity and functionality of mitochondria within renal tubular epithelial cells (RTECs) often become compromised during CKD development, playing a pivotal role in the progression of renal fibrosis. Mitophagy, a specific form of autophagy, assumes responsibility for eliminating damaged mitochondria to uphold mitochondrial equilibrium. Dysregulated mitophagy not only correlates with disrupted mitochondrial dynamics but also contributes to the advancement of renal fibrosis in CKD. While numerous studies have examined mitochondrial metabolism, ROS (reactive oxygen species) production, inflammation, and apoptosis in kidney diseases, the precise pathogenic mechanisms underlying mitophagy in CKD remain elusive. The exact mechanisms through which modulating mitophagy mitigates renal fibrosis, as well as its influence on CKD progression and prognosis, have not undergone systematic investigation. The role of mitophagy in AKI has been relatively clear, but the role of mitophagy in CKD is still rare. This article presents a comprehensive review of the current state of research on regulating mitophagy as a potential treatment for CKD. The objective is to provide fresh perspectives, viable strategies, and practical insights into CKD therapy, thereby contributing to the enhancement of human living conditions and patient well-being.

Exposure to polystyrene nanoplastics induces abnormal activation of innate immunity via the cGAS-STING pathway

Endogenous immune defenses provide an intrinsic barrier against external entity invasion. Microplastics in the environment, especially those at the nanoscale (nanoplastics or NPs), may pose latent health risks through direct exposure. While links between nanoplastics and inflammatory processes have been established, detailed insights into how they may perturb the innate immune mechanisms remain uncharted. Employing murine and macrophage (RAW264.7) cellular models subjected to polystyrene nanoplastics (PS-NPs), our investigative approach encompassed an array of techniques: Cell Counting Kit-8 assays, flow cytometric analysis, acridine orange/ethidium bromide (AO/EB) fluorescence staining, cell transfection, cell cycle scrutiny, genetic manipulation, messenger RNA expression profiling via quantitative real-time PCR, and protein expression evaluation through western blotting. The results showed that PS-NPs caused RAW264.7 cell apoptosis, leading to cell cycle arrest, and activated the cGAS-STING pathway. This resulted in NF-κB signaling activation and increased pro-inflammatory mediator expression. Importantly, PS-NPs-induced activation of NF-κB and its downstream inflammatory cascade were markedly diminished after the silencing of the STING gene. Our findings highlight the critical role of the cGAS-STING pathway in the immunotoxic effects induced by PS-NPs. We outline a new mechanism whereby nanoplastics may trigger dysregulated innate immune and inflammatory responses via the cGAS/STING pathway.

Wnt/β-catenin Pathway Aggravates Renal Fibrosis by Activating PUM2 Transcription to Repress YME1L-mediated Mitochondrial Homeostasis

Chronic kidney disease (CKD) affects more than 10% of people worldwide and is a leading cause of death. However, the pathogenesis of CKD remains elusive. The oxidative stress and mitochondrial membrane potential were detected using Enzyme-linked immunosorbent assay and JC-1 assay. Co-immunoprecipitation, dual-luciferase assay, chromatin IP, RNA IP and RNA pull-down were used to validate the interactions among genes. Exploiting a H2O2-induced fibrosis model in vitro, PUM2 expression was upregulated in Human kidney 2 cell (HK-2) cells, along with reduced cell viability, enhanced oxidative stress, impaired mitochondrial potential, and upregulated expressions of fibrosis-associated proteins. While PUM2 knockdown reversed the H2O2-induced injury in HK-2 cells. Mechanically, Wnt/β-catenin pathway activated PUM2 transcription via TCF4. It was further identified that Wnt/β-catenin pathway inhibited YME1L expression through PUM2-mediated destabilizing of its mRNA. PUM2 aggravated H2O2-induced oxidative stress, mitochondrial dysfunction, and renal fibrosis in HK-2 cell via suppressing YME1L expression. Our study revealed that Wnt/β-catenin aggravated renal fibrosis by activating PUM2 transcription to repress YME1L-mediated mitochondrial homeostasis, providing novel insights and potential therapeutic targets for the treatment of kidney fibrosis.

STING deficiency alleviates ferroptosis through FPN1 stabilization in diabetic kidney disease

Ferroptosis, a form of cell death driven by iron-dependent lipid peroxidation, has known as one of the most significant pathological processes involved in diabetic kidney disease (DKD). Stimulator of interferon genes (STING) has been demonstrated its potential in regulating ferroptosis, but the regulatory role in DKD mice and underlying mechanisms haven't been illustrated. To elucidate whether and how STING regulates ferroptosis in DKD, we detected the influence of STING on diabetic-related ferroptosis in a diabetic model and in erastin-induced renal tubular epithelial cells (RTECs). Our study demonstrated that STING was abnormally activated and promoted ferroptosis in DKD. STING deficiency alleviated renal pathologic damages and disfunction in diabetic mice via alleviating ferroptosis and reducing oxidative stress. Mechanismly, STING inhibition was shown to improve ferroptosis and reduce oxidative stress in erastin-induced RTECs. The disruption of ferroportin1 (FPN1) on the basis of STING inhibition abolished the improvements in ferroptosis and promoted reactive oxygen species (ROS) generation. Further, STING inhibition alleviated ferroptosis via stabilizing FPN1 protein level by decreasing ubiquitinated FPN1 for proteasomal degradation. In conclusion, STING deficiency protected against diabetic renal injury via alleviating ferroptosis through stabilizing FPN1 and reducing oxidative stress, providing a possible potential approach for the treatment of DKD.

cGAS-STING, an important signaling pathway in diseases and their therapy

Since cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway was discovered in 2013, great progress has been made to elucidate the origin, function, and regulating mechanism of cGAS-STING signaling pathway in the past decade. Meanwhile, the triggering and transduction mechanisms have been continuously illuminated. cGAS-STING plays a key role in human diseases, particularly DNA-triggered inflammatory diseases, making it a potentially effective therapeutic target for inflammation-related diseases. Here, we aim to summarize the ancient origin of the cGAS-STING defense mechanism, as well as the triggers, transduction, and regulating mechanisms of the cGAS-STING. We will also focus on the important roles of cGAS-STING signal under pathological conditions, such as infections, cancers, autoimmune diseases, neurological diseases, and visceral inflammations, and review the progress in drug development targeting cGAS-STING signaling pathway. The main directions and potential obstacles in the regulating mechanism research and therapeutic drug development of the cGAS-STING signaling pathway for inflammatory diseases and cancers will be discussed. These research advancements expand our understanding of cGAS-STING, provide a theoretical basis for further exploration of the roles of cGAS-STING in diseases, and open up new strategies for targeting cGAS-STING as a promising therapeutic intervention in multiple diseases.