Reticulon-1A mediates diabetic kidney disease progression through endoplasmic reticulum-mitochondrial contacts in tubular epithelial cells

Unfolded protein response-activated NLRP3 inflammasome contributes to pyroptotic and apoptotic podocyte injury in diabetic kidney disease via the CHOP-TXNIP axis

BACKGROUND

Diabetic kidney disease (DKD) is the leading cause of chronic kidney disease and end-stage renal disease worldwide. Podocyte injury and death is a key event in DKD progression. Emerging evidence has indicated that crosstalk between unfolded protein response (UPR) and NLR family pyrin domain containing 3 (NLRP3) inflammasome plays an essential role in DKD progression. However, the involvement of these pathways in podocyte injury and death during DKD remains unclear.

RESULTS

Here, we found that inositol-requiring enzyme 1 (IRE1) and protein kinase RNA-like ER kinase (PERK) branches of the UPR, NLRP3 inflammasome, and apoptosis were activated in podocytes under DKD and high glucose (HG) conditions. In vitro, inducing ER stress by thapsigargin, and IRE1 or PERK overexpression upon HG treatment stimulated NLRP3 inflammasome-mediated pyroptosis and apoptosis, whereas inhibiting IRE1 or PERK suppressed them. Importantly, we discovered that the newly identified NLRP3-binding partner, thioredoxin-interacting protein (TXNIP), upon activation by the transcription factor (TF) PERK/CCAAT-enhancer-binding protein homologous protein (CHOP), served as a link between IRE1 or PERK branches with NLRP3 inflammasome-mediated pyroptosis and apoptosis. TXNIP expression was promoted in podocytes from DKD patients and db/db mice, as well as in HG-exposed conditionally immortalized human podocyte (HPC). In HG-exposed HPC, IRE1 or PERK overexpression upregulated TXNIP expression, while IRE1 or PERK inhibition downregulated it. TXNIP or CHOP silencing both inhibited HG-upregulated TXNIP, further blocking NLRP3 inflammasome-mediated pyroptosis and apoptosis. Furthermore, NLRP3 overexpression aggravated HG-induced pyroptosis and apoptosis, whereas additional TXNIP silencing reversed them without affecting IRE1 or PERK branches.

CONCLUSION

In conclusion, our results suggested that UPR/NLRP3 inflammasome-mediated pyroptosis/apoptosis pathway was involved in diabetic podocyte injury, and that targeting the CHOP-TXNIP axis may serve as a promising therapeutic target for DKD.

The axis of miR-30a/AIF-1/TRPC6/calcineurin A/NFAT2 regulated the death modalities and inflammation of renal tubular epithelial cells in diabetic kidney disease via exosome

AIMS

Diabetic kidney disease (DKD) is a significant complication of diabetes, marked by inflammation, fibrosis, and cell death in renal tissues. This study aimed to elucidate the regulatory role of miR-30a in DKD, focusing on its impact on monocyte/macrophage activity, key protein expression, exosomes, and renal cell death modalities.

MATERIALS AND METHODS

Using db/db mice as a DKD model, miR-30a expression was manipulated through knockout and overexpression techniques. Macrophage activity was evaluated via F4/80 expression and the M1/M2 macrophage ratio. Key proteins (AIF-1, TRPC6, calcineurin A, NFAT2, and NLRP3) were measured in renal tissues and exosomes from blood and urine. In vitro, TCMK-1 cells under high-glucose conditions were used to assess cell death modalities, including autophagy, apoptosis, pyroptosis, and necrosis.

KEY FINDINGS

miR-30a inhibited macrophage activity, with increased F4/80 expression in knockout groups and decreased levels in overexpression groups. The M1/M2 macrophage ratio rose in knockout groups and fell in overexpression groups. miR-30a overexpression reduced key protein levels and urinary albumin (ALB), indicating a protective effect against DKD. Exosome concentration and protein content decreased in miR-30a-overexpressing mice. In vitro findings supported these results, highlighting miR-30a's regulatory effects on AIF-1, Caspase 3, TRPC6, Calcineurin A, NFAT2, and cell death modalities. Exosome secretion from TCMK-1 or RAW264.7 cells was affected by high-glucose conditions, influencing cell death modalities and functions of TCMK-1 cells.

SIGNIFICANCE

The axis of miR-30a/AIF-1/TRPC6/calcineurin A/NFAT2 regulated death modalities and inflammation of renal tubular epithelial cells in DKD via exosome. miR-30a might be a novel therapeutic target to slow DKD.

Elucidating the function of clusterin in the progression of diabetic kidney disease

Diabetic kidney disease (DKD) is a common microvascular complication and the main cause of death in diabetic patients. Metabolic disorders can accelerate the occurrence and development of DKD through a variety of ways, Recent studies have found that Clusterin (Clu) levels are associated with renal dysfunction and can be used as a biomarker of renal tubular injury, while preclinical studies reveal its renoprotective function. This article reviews the molecular mechanisms of Clu in the interaction between various cells in DKD. In addition, we discuss the latest research progress of Clu in the field of DKD. This review aims to explore Clu as a potential therapeutic target for DKD and provide some guidance for future clinical treatment.

Endoplasmic reticulum stress as a driver and therapeutic target for kidney disease

The endoplasmic reticulum (ER) has crucial roles in metabolically active cells, including protein translation, protein folding and quality control, lipid biosynthesis, and calcium homeostasis. Adverse metabolic conditions or pathogenic genetic variants that cause misfolding and accumulation of proteins within the ER of kidney cells initiate an injurious process known as ER stress that contributes to kidney disease and its cardiovascular complications. Initiation of ER stress activates the unfolded protein response (UPR), a cellular defence mechanism that functions to restore ER homeostasis. However, severe or chronic ER stress rewires the UPR to activate deleterious pathways that exacerbate inflammation, apoptosis and fibrosis, resulting in kidney injury. This insidious crosstalk between ER stress, UPR activation, oxidative stress and inflammation forms a vicious cycle that drives kidney disease and vascular damage. Furthermore, genetic variants that disrupt protein-folding mechanisms trigger ER stress, as evidenced in autosomal-dominant tubulointerstitial kidney disease and Fabry disease. Emerging therapeutic strategies that enhance protein-folding capacity and reduce the burden of ER stress have shown promising results in kidney diseases. Thus, integrating knowledge of how genetic variants cause protein misfolding and ER stress into clinical practice will enhance treatment strategies and potentially improve outcomes for various kidney diseases and their vascular complications.

Targeting mitochondrial dysfunction: an innovative strategy for treating renal fibrosis

The incidence and hospitalization rate of kidney disease, especially end-stage renal disease, have increased significantly, which seriously endangers the health of patients. Mitochondria are the core organelles of cellular energy metabolism, and their dysfunction can lead to kidney energy supply insufficiency and oxidative stress damage, which has become a global public health problem. Studies have shown that the disturbance of mitochondrial quality control mechanisms, including mitochondrial dynamics, autophagy, oxidative stress regulation and biosynthesis, is closely related to the occurrence and development of renal fibrosis (RF). As a multicellular pathological process, RF involves the injury and shedding of podocytes, the transdifferentiation of renal tubular epithelial cells, the activation of fibroblasts, and the infiltration of macrophages, among which the mitochondrial dysfunction plays an important role. This review systematically elaborates the molecular mechanisms of mitochondrial damage during RF progression, aiming to provide theoretical foundations for developing novel therapeutic strategies to delay RF advancement.

Wogonoside ameliorates oxidative damage in tubular epithelial cells of diabetic nephropathy by modulating the HNF4A-NRF2 axis

Diabetic nephropathy (DN), a leading cause of end-stage renal disease, presents significant challenges due to its complex pathophysiology and limited effective treatment options. Increasing evidence suggests that tubular injury is an early event preceding glomerular damage in DN. Wogonoside, a natural flavonoid derived from Scutellaria baicalensis, has not been previously reported for DN treatment. This study aims to investigate the protective effects and underlying mechanisms of wogonoside on renal tubular epithelial cells (TECs) in DN. The results showed that wogonoside mitigates high glucose (HG)-induced oxidative stress in TCMK-1 cells. Additionally, wogonoside protects renal function, reduces renal tubular damage, and modulates the oxidative stress response in HFD/STZ-induced DN mouse model. Importantly, our results indicated that hepatocyte nuclear factor 4 alpha (HNF4A) expression is downregulated in the kidneys of DN mice and HG-induced TCMK-1 cells. Wogonoside can bind to HNF4A, upregulate its expression, and promote nuclear translocation. Bioinformatic analysis suggested that NRF2 might be a downstream signaling of HNF4A. This was confirmed by Co-IP and experiments involving HNF4A overexpression and NRF2 knockdown, which demonstrated that wogonoside regulates the HNF4A-NRF2 axis to alleviate oxidative stress in TECs. Collectively, these findings identify wogonoside as a possible therapeutic agent for DN, highlighting HNF4A as a promising target for intervention.

Exploring a novel mechanism for targeting β-arrestin-2 in the management of diabetic nephropathy

Diabetic nephropathy (DN) is a well-known microvascular complication in patients with diabetes mellitus, which is characterized by the accumulation of extracellular matrix in the glomerular and tubulointerstitial compartments, along with the hyalinization of intrarenal vasculature. DN has recently emerged as a leading cause of chronic and end-stage renal disease. While the pathobiology of other diabetic microvascular complications, such as retinopathy, is largely understood and has reasonable therapeutic options, the mechanisms and management strategies for DN remain incompletely elucidated. In this editorial, we comment on the article by Liu et al, focusing on the mechanisms underlying the detrimental impact of β-arrestin-2 on the kidneys in the context of DN. The authors suggest that inhibiting β-arrestin-2 could alleviate renal damage through suppressing apoptosis of glomerular endothelial cells (GENCs), highlighting β-arrestin-2 as a promising therapeutic target for DN. The study proposed that β-arrestin-2 triggers endoplasmic reticulum (ER) stress via the ATF6 signaling pathway, thereby promoting GENC apoptosis and exacerbating DN progression. Given the novel and crucial role of β-arrestin-2 in ER stress-related DN, it is imperative to further explore β-arrestin-2, its roles in ER stress and the potential therapeutic implications in DN.

Tangshenning formula alleviates tubular injury in diabetic kidney disease via the Sestrin2/AMPK/PGC-1α axis: Restoration of mitochondrial function and inhibition of ferroptosis

ETHNOPHARMACOLOGICAL RELEVANCE

Tangshenning (TSN) is a traditional Chinese medicinal formula developed on principles of kidney tonification and collateral unblocking. TSN, formulated from Astragalus mongholicus Bunge, Rheum palmatum L., Ligusticum chuanxiong Hort., and Rosa laevigata Michx., has demonstrated significant clinical efficacy in the treatment of diabetic kidney disease (DKD). Our previous studies have suggested that TSN mitigates tubular injury in DKD by inhibiting ferroptosis, however, the precise molecular targets and mechanistic pathways underlying these effects remain to be fully elucidated.

AIM OF THE STUDY

We investigated whether the Sestrin2/AMPK/PGC-1α axis serves as a key pathway mediating TSN's protective effects against tubular injury in DKD.

METHODS

In vivo, a spontaneous DKD mouse model was developed using KK-Ay mice. In vitro, human tubular epithelial cells (TECs) were used to establish high glucose and ferroptosis models, as well as a Sestrin2 knockdown model for further analysis. Molecular docking was utilized to examine the binding interactions between TSN's key active components and Sestrin2. Colocalization of Sestrin2 and GPX4 was assessed using dual fluorescence staining. Protein expression levels related to the Sestrin2/AMPK/PGC-1α pathway, ferroptosis markers (SLC7A11 and GPX4), and the tubular injury marker KIM-1 were quantified via Western blot analysis. In vivo, DHE staining, TUNEL staining, and ferrous ion content measurement were performed to evaluate ferroptosis levels in renal tissue. In vitro, the BODIPY 581/591 C11 probe and ferrous ion assay were used to assess ferroptosis levels in TECs. MitoSOX staining, JC-1 assay, and ATP level measurements were conducted to evaluate mitochondrial function in TECs.

RESULTS

In vivo, our results demonstrated that TSN improved renal function, alleviated tubular injury, and reduced pathological damage in DKD mice. Furthermore, TSN upregulated the protein expression of the Sestrin2/AMPK/PGC-1α axis and decreased ferroptosis-related markers in the DKD mouse model. Similarly, in vitro, TSN enhanced the expression of the Sestrin2/AMPK/PGC-1α pathway, restored mitochondrial function, and inhibited ferroptosis in TECs under high glucose and ferroptosis-inducing conditions. Additionally, downregulation of Sestrin2 impaired the therapeutic effects of TSN.

CONCLUSION

TSN alleviates tubular injury in DKD by activating the Sestrin2/AMPK/PGC-1α pathway, restoring mitochondrial function, and inhibiting ferroptosis in TECs.

RTN3 regulates collagen biosynthesis and profibrotic macrophage differentiation to promote pulmonary fibrosis via interacting with CRTH2

BACKGROUND

As an endoplasmic reticulum (ER) protein, Reticulum 3 (RTN3) has been reported to play a crucial role in neurodegenerative diseases, lipid metabolism, and chronic kidney disease. The involvement of RTN3 in idiopathic pulmonary fibrosis (IPF), a progressive and fatal interstitial lung disease, remains unexplored.

METHODS

In this study, we explored the role of RTN3 in pulmonary fibrosis using public datasets, IPF patient samples, and animal models. We investigated its pathogenic mechanisms in lung fibroblasts and alveolar macrophages.

RESULTS

We found decreased levels of RTN3 in IPF patients, bleomycin-induced mice, and TGFβ-treated cell lines. RTN3-null mice exhibited more severe pulmonary fibrosis phenotypes in old age or after bleomycin treatment. Collagen synthesis was significantly increased in RTN3-null mice lung tissues and lung fibroblasts. Mechanistic studies revealed that RTN3 deficiency reduced the ER-anchored CRTH2 in lung fibroblasts, which serves as an antifibrotic molecule via antagonizing collagen biosynthesis. Simultaneously, RTN3 deficiency reduced the autophagy degradation of CRTH2 which acts as an activator of profibrotic macrophage differentiation. Both effects of RTN3 and CRTH2 in lung fibroblasts and alveolar macrophages aggravated age-or bleomycin-induced pulmonary fibrosis. Additionally, we also identified a mutation of RTN3 in patients with ILD.

CONCLUSIONS

Our research demonstrated that RTN3 plays a significant role in the lung, and reduction of RTN3 levels may be a risk factor for IPF and related diseases.

Targeting programmed cell death in diabetic kidney disease: from molecular mechanisms to pharmacotherapy

Diabetic kidney disease (DKD), one of the most prevalent microvascular complications of diabetes, arises from dysregulated glucose and lipid metabolism induced by hyperglycemia, resulting in the deterioration of renal cells such as podocytes and tubular epithelial cells. Programmed cell death (PCD), comprising apoptosis, autophagy, ferroptosis, pyroptosis, and necroptosis, represents a spectrum of cell demise processes intricately governed by genetic mechanisms in vivo. Under physiological conditions, PCD facilitates the turnover of cellular populations and serves as a protective mechanism to eliminate impaired podocytes or tubular epithelial cells, thereby preserving renal tissue homeostasis amidst hyperglycemic stress. However, existing research predominantly elucidates individual modes of cell death, neglecting the intricate interplay and mutual modulation observed among various forms of PCD. In this comprehensive review, we delineate the diverse regulatory mechanisms governing PCD and elucidate the intricate crosstalk dynamics among distinct PCD pathways. Furthermore, we review recent advancements in understanding the pathogenesis of PCD and explore their implications in DKD. Additionally, we explore the potential of natural products derived primarily from botanical sources as therapeutic agents, highlighting their multifaceted effects on modulating PCD crosstalk, thereby proposing novel strategies for DKD treatment.

RTN1A mediates diabetes-induced AKI-to-CKD transition

Diabetic patients have increased susceptibility to acute kidney injury (AKI), and AKI could progress to chronic tubulointerstitial injury and fibrosis, referred to as AKI-to-chronic kidney disease (AKI-to-CKD) transition. However, whether diabetes directly promotes AKI-to-CKD transition is not known. We previously showed that reticulon-1A (RTN1A), a gene highly upregulated in injured renal tubular epithelial cells (RTECs), promotes AKI-to-CKD transition in nondiabetic settings. Therefore, we also examined whether reducing RTN1A expression could attenuate diabetes-induced AKI-to-CKD transition. Diabetes was induced by a high-fat diet and streptozotocin injections, and unilateral ischemic reperfusion injury was created as an AKI model in control, diabetic, and RTEC-specific Rtn1a-knockdown diabetic mice. AKI induced greater renal function decline, tubulointerstitial injury, and fibrosis in diabetic mice than in nondiabetic mice. Reduction of RTN1A markedly reduced the CKD development following AKI in diabetic mice, which was associated with reduced ER stress and mitochondrial dysfunction in RTECs. These findings indicate that diabetes markedly accelerates AKI-to-CKD transition and that RTN1A is a crucial mediator of diabetes-induced AKI-to-CKD transition. The development of RTN1A inhibitors could potentially attenuate AKI-to-CKD transition in diabetic patients.

β-Arrestin-2 enhances endoplasmic reticulum stress-induced glomerular endothelial cell injury by activating transcription factor 6 in diabetic nephropathy

BACKGROUND

Glomerular endothelial cell (GENC) injury is a characteristic of early-stage diabetic nephropathy (DN), and the investigation of potential therapeutic targets for preventing GENC injury is of clinical importance.

AIM

To investigate the role of β-arrestin-2 in GENCs under DN conditions.

METHODS

Eight-week-old C57BL/6J mice were intraperitoneally injected with streptozotocin to induce DN. GENCs were transfected with plasmids containing siRNA-β-arrestin-2, shRNA-activating transcription factor 6 (ATF6), pCDNA-β-arrestin-2, or pCDNA-ATF6. Additionally, adeno-associated virus (AAV) containing shRNA-β-arrestin-2 was administered via a tail vein injection in DN mice.

RESULTS

The upregulation of β-arrestin-2 was observed in patients with DN as well as in GENCs from DN mice. Knockdown of β-arrestin-2 reduced apoptosis in high glucose-treated GENCs, which was reversed by the overexpression of ATF6. Moreover, overexpression of β-arrestin-2 Led to the activation of endoplasmic reticulum (ER) stress and the apoptosis of GENCs which could be mitigated by silencing of ATF6. Furthermore, knockdown of β-arrestin-2 by the administration of AAV-shRNA-β-arrestin-2 alleviated renal injury in DN mice.

CONCLUSION

Knockdown of β-arrestin-2 prevents GENC apoptosis by inhibiting ATF6-mediated ER stress in vivo and in vitro. Consequently, β-arrestin-2 may represent a promising therapeutic target for the clinical management of patients with DN.

RBBP6-Mediated ERRα Degradation Contributes to Mitochondrial Injury in Renal Tubular Cells in Diabetic Kidney Disease

Diabetic Kidney Disease (DKD), a major precursor to end-stage renal disease, involves mitochondrial dysfunction in proximal renal tubular cells (PTCs), contributing to its pathogenesis. Estrogen-related receptor α (ERRα) is essential for mitochondrial integrity in PTCs, yet its regulation in DKD is poorly understood. This study investigates ERRα expression and its regulatory mechanisms in DKD, assessing its therapeutic potential. Using genetic, biochemical, and cellular approaches, ERRα expression Was examined in human DKD specimens and DKD mouse models. We identified the E3 ubiquitin ligase retinoblastoma binding protein 6 (RBBP6) as a regulator of ERRα, promoting its degradation through K48-linked polyubiquitination at the K100 residue. This degradation pathway significantly contributed to mitochondrial injury in PTCs of DKD models. Notably, conditional ERRα overexpression or RBBP6 inhibition markedly reduced mitochondrial damage in diabetic mice, highlighting ERRα's protective role in maintaining mitochondrial integrity. The interaction between RBBP6 and ERRα opens new therapeutic avenues, suggesting that modulating RBBP6-ERRα interactions could be a strategy for preserving mitochondrial function and slowing DKD progression.

Dihydrolipoamide S-acetyltransferase activation alleviates diabetic kidney disease via AMPK-autophagy axis and mitochondrial protection

Diabetic kidney disease (DKD), a severe complication of diabetes marked by deregulated glucose metabolism, remains enigmatic in its pathogenesis. Herein, we delved into the functional role of Dihydrolipoamide S-acetyltransferase (DLAT), a pivotal E2 component of the pyruvate dehydrogenase complex (PDC), in the context of DKD. Our findings revealed a downregulation of DLAT in the kidneys of diabetic patients, correlating inversely with kidney function. Parallel downregulation was observed in both high-fat diet/streptozotocin (HFD/STZ) and db/db mouse models, as well as in human proximal tubular epithelial cells (HK-2) cultured under hyperglycemic conditions. To further elucidate the role of endogenous DLAT in DKD, we employed genetic ablation of Dlat in mouse models. Dlat haploinsufficient mice exhibited exacerbated renal dysfunction, structural damage, fibrosis, and mitochondrial dysfunction under DKD conditions. Consistent with these findings, modulation of DLAT expression in HK-2 cells highlighted its influence on fibrosis, with overexpression attenuating Fibronectin and Collagen I levels, while downregulation exacerbated fibrosis. Mechanistically, we discovered that DLAT activates mitochondria autophagy through the Adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) signaling pathway, thereby mitigating mitochondrial dysfunction associated with DKD progression. Inhibition of AMPK abrogated the protective effects of DLAT against mitochondrial dysfunction and DKD. Notably, we identified Hyperforin (HPF), a phytochemical, as a potential therapeutic agent. HPF activates DLAT and AMPK, subsequently ameliorating renal dysfunction, injuries, and fibrosis in both in vivo and in vitro models. In summary, our study underscores the pivotal role of DLAT and AMPK in kidney health and highlights the therapeutic potential of HPF in treating DKD.

Effect of Danggui Buxue decoction on hypoxia-induced injury of retinal Müller cells in vitro

Retinopathy is a common complication of diabetes mellitus and the leading cause of visual impairment. Danggui Buxue decoction (RRP) has been used as a traditional drug for the treatment of diabetic nephropathy for many years. The aim of this study was to investigate the effects of RRP on hypoxia-induced retinal Müller cell injury. A model of retinal Müller cell damage was created using high glucose levels (25 mmol/L) and/or exposure to low oxygen conditions (1% O2). RRP was given to rats by continuous gavage for 7 days to obtain drug-containing serum. After sterilization, the serum was added to the culture medium at a ratio of 10%. Cell viability, apoptosis, and cell proliferation were assessed using the CCK-8 kit, Annexin V-FITC/propidium iodide apoptosis kit, and EdU kit. The mRNA levels of angiogenesis factors (ANGPTL4, VEGF) and inflammatory factors (IL-1B, ICAM-1) were detected by RT-qPCR. Western blot analysis was employed to assess the levels of proteins related to the ATF4/CHOP pathway. Following hypoxia for 48 h and 72 h, there was a significant decrease in cell viability and proliferation, as well as a notable increase in apoptosis compared to the control group (21% O2). However, high glucose stimulation had no significant effect, and high glucose combined with hypoxia had no further damage to cells. After 48 h of exposure to low oxygen levels, the mRNA expression levels of ANGPTL4, VEGF, IL-1B, and ICAM-1 in retinal Müller cells were significantly higher than in the control group (21% O2). RRP treatment significantly alleviated the increase of cell apoptosis and the upregulation of IL-1B and-1 in retinal Müller cells induced by hypoxia. RRP has the potential to reduce the suppression of the ATF4/CHOP pathway in hypoxia-induced retinal Müller cells, and it significantly alleviates cell apoptosis through regulating inflammatory factors and the ATF4/CHOP pathway.

Astragaloside IV attenuates fatty acid-induced renal tubular injury in diabetic kidney disease by inhibiting fatty acid transport protein-2

BACKGROUND

Renal tubular injury induced by free fatty acid bound to albumin is the key pathological basis for the progression of diabetic kidney disease. However, effective interventions are limited. Astragaloside IV, as a major bioactive component purified from Astragalus membranaceus (Fisch.) Bunge, possesses pharmacological properties of lowering blood glucose and proteinuria, and renal tubular protection in diabetic kidney disease. Further work is needed to understand the underlying molecular mechanisms.

PURPOSE

This study was designed to investigate the mechanism of renal tubular protection by astragaloside IV in diabetic kidney disease.

METHODS

Rats receiving high-fat diet combined with streptozotocin (30 mg/kg, i.p.) were gavaged with astragaloside IV (10 mg/kg/d or 20 mg/kg/d) or empagliflozin (1.72 mg/kg/d) for 8 weeks. In vitro, the NRK-52E cells were treated with free fatty acid-deleted BSA or palmitic acid-bound BSA in the presence or absence of astragaloside IV (5 μM, 10 μM, 20 μM) or 5 μM of mcc950. The effects of astragaloside IV on mitochondrial function, NLRP3/ASC/IL-18/IL-1β inflammatory cascade, and renal tubular injury were detected by pathological staining, immunoblotting, MitoSOX Red staining. Next, to investigate the mechanism of renal tubular protection by astragaloside IV, we transfected Fatp2 siRNA into BSA-PA-treated NRK-52E cells and injected lipofermata (a FATP2 inhibitor) intraperitoneally into free fatty acid-bound BSA overloaded rats with concomitant astragaloside IV treatment.

RESULTS

Treatment with astragaloside IV for 8 weeks dose-dependently attenuated the blood glucose, ratio of urinary albumin to creatinine, disorder of lipid metabolism, and pathological injury in diabetic kidney disease rats. In addition, astragaloside IV dose-dependently attenuated mitochondrial-derived reactive oxygen species and subsequent inhibiting NLRP3-mediated inflammatory cascade in diabetic kidney disease rats and palmitic acid-bound BSA-treated NRK-52E cells, thereby exerting renal tubular protection. More importantly, the effects of astragaloside IV on restoration of mitochondrial function, inhibition of inflammatory response and amelioration of renal tubular injury in vivo and in vitro were further enhanced when used in combination with Fatp2 siRNA or lipofermata.

CONCLUSION

Astragaloside IV exerts antioxidant and anti-inflammatory effects in diabetic kidney disease by inhibiting FATP2-mediated fatty acid transport, thereby attenuating renal tubular injury.

Tubulointerstitial injury in proteinuric chronic kidney diseases

Proteinuria is an independent risk factor for chronic kidney disease progression and cardiovascular diseases. Apart from its prognostic role, the load of proteins that pass across the disrupted glomerular capillary wall trigger multiple pathophysiologic processes. These include, among others, intratubular complement activation and excessive proximal tubular reabsorption of filtered proteins, especially albumin and albumin-bound free fatty acids, which can set off several pathways of cellular damage. The activation of these pathways can cause apoptosis of proximal tubular cells and paracrine effects that incite the development of interstitial inflammation and fibrosis, ultimately leading to irreversible kidney injury. In this review, we provide a comprehensive overview of the current understanding on the mechanisms underlying the tubular toxicity of ultrafiltered proteins in the setting of proteinuric chronic kidney diseases. The acquired knowledge is expected to be instrumental for the development of novel therapeutic classes of medications to be tested on top of standard of care with optimized renin-angiotensin-aldosterone blockade and sodium-glucose cotransporter-2 inhibition, in order to further improve the clinical outcomes of patients with proteinuric chronic kidney diseases.

Podocyte-specific KLF6 primes proximal tubule CaMK1D signaling to attenuate diabetic kidney disease

Diabetic kidney disease (DKD) is the main cause of chronic kidney disease worldwide. While injury to the podocytes, visceral epithelial cells that comprise the glomerular filtration barrier, drives albuminuria, proximal tubule (PT) dysfunction is the critical mediator of DKD progression. Here, we report that the podocyte-specific induction of human KLF6, a zinc-finger binding transcription factor, attenuates podocyte loss, PT dysfunction, and eventual interstitial fibrosis in a male murine model of DKD. Utilizing combination of snRNA-seq, snATAC-seq, and tandem mass spectrometry, we demonstrate that podocyte-specific KLF6 triggers the release of secretory ApoJ to activate calcium/calmodulin dependent protein kinase 1D (CaMK1D) signaling in neighboring PT cells. CaMK1D is enriched in the first segment of the PT, proximal to the podocytes, and is critical to attenuating mitochondrial fission and restoring mitochondrial function under diabetic conditions. Targeting podocyte-PT signaling by enhancing ApoJ-CaMK1D might be a key therapeutic strategy in attenuating the progression of DKD.

Renal tubular epithelial cells response to injury in acute kidney injury

Acute kidney injury (AKI) is a clinical syndrome characterized by a rapid and significant decrease in renal function that can arise from various etiologies, and is associated with high morbidity and mortality. The renal tubular epithelial cells (TECs) represent the central cell type affected by AKI, and their notable regenerative capacity is critical for the recovery of renal function in afflicted patients. The adaptive repair process initiated by surviving TECs following mild AKI facilitates full renal recovery. Conversely, when injury is severe or persistent, it allows the TECs to undergo pathological responses, abnormal adaptive repair and phenotypic transformation, which will lead to the development of renal fibrosis. Given the implications of TECs fate after injury in renal outcomes, a deeper understanding of these mechanisms is necessary to identify promising therapeutic targets and biomarkers of the repair process in the human kidney.

Organelle communication maintains mitochondrial and endosomal homeostasis during podocyte lipotoxicity

Organelle stress exacerbates podocyte injury, contributing to perturbed lipid metabolism. Simultaneous organelle stresses can occur in the kidney in the diseased state; therefore, a thorough analysis of organelle communication is crucial for understanding the progression of kidney diseases. Although organelles closely interact with one another at membrane contact sites, limited studies have explored their involvement in kidney homeostasis. The endoplasmic reticulum (ER) protein, PDZ domain-containing 8 (PDZD8), is implicated in multiple-organelle-tethering processes and cellular lipid homeostasis. In this study, we aimed to elucidate the role of organelle communication in podocyte injury using podocyte-specific Pdzd8-knockout mice. Our findings demonstrated that Pdzd8 deletion exacerbated podocyte injury in an accelerated obesity-related kidney disease model. Proteomic analysis of isolated glomeruli revealed that Pdzd8 deletion exacerbated mitochondrial and endosomal dysfunction during podocyte lipotoxicity. Additionally, electron microscopy revealed the accumulation of abnormal, fatty endosomes in Pdzd8-deficient podocytes during obesity-related kidney diseases. Lipidomic analysis indicated that glucosylceramide accumulated in Pdzd8-deficient podocytes, owing to accelerated production and decelerated degradation. Thus, the organelle-tethering factor, PDZD8, plays a crucial role in maintaining mitochondrial and endosomal homeostasis during podocyte lipotoxicity. Collectively, our findings highlight the importance of organelle communication at the 3-way junction among the ER, mitochondria, and endosomes in preserving podocyte homeostasis.

LncRNA KIFAP3-5:1 inhibits epithelial-mesenchymal transition of renal tubular cell through PRRX1 in diabetic nephropathy

Long noncoding RNAs play an important role in several pathogenic processes in diabetic nephropathy, but the relationship with epithelial-mesenchymal transition in DN is unclear. Herein, we found that KIFAP3-5:1 expression was significantly down-regulated in DN plasma samples, db/db mouse kidney tissues and high glucose treated renal tubular epithelial cells compared to normal healthy samples and untreated cells. Overexpression of KIFAP3-5:1 improved renal fibrosis in db/db mice and rescued epithelial-mesenchymal transition of high glucose cultured renal tubular epithelial cells. The silence of KIFAP3-5:1 will exacerbate the progression of EMT. Mechanistically, KIFAP3-5:1 was confirmed to directly target to the -488 to -609 element of the PRRX1 promoter and negatively modulate PRRX1 mRNA and protein expressions. Furthermore, rescue assays demonstrated that the knockdown of PRRX1 counteracted the KIFAP3-5:1 low expression-mediated effects on EMT in hRPTECs cultured under high glucose. The plasma KIFAP3-5:1 of DN patients is highly correlated with the severity of renal dysfunction and plays an important role in the prediction model of DN diseases. These findings suggested that KIFAP3-5:1 plays a critical role in regulation of renal EMT and fibrosis through suppress PRRX1, and highlight the clinical potential of KIFAP3-5:1 to assist in the diagnosis of diabetic nephropathy.

High-Performance Hydrogel-Encapsulated Engineered Exosomes for Supporting Endoplasmic Reticulum Homeostasis and Boosting Diabetic Bone Regeneration

The regeneration of bone defects in diabetic patients still faces challenges, as the intrinsic healing process is impaired by hyperglycemia. Inspired by the discovery that the endoplasmic reticulum (ER) is in a state of excessive stress and dysfunction under hyperglycemia, leading to osteogenic disorder, a novel engineered exosome is proposed to modulate ER homeostasis for restoring the function of mesenchymal stem cells (MSCs). The results indicate that the constructed engineered exosomes efficiently regulate ER homeostasis and dramatically facilitate the function of MSCs in the hyperglycemic niche. Additionally, the underlying therapeutic mechanism of exosomes is elucidated. The results reveal that exosomes can directly provide recipient cells with SHP2 for the activation of mitophagy and elimination of mtROS, which is the immediate cause of ER dysfunction. To maximize the therapeutic effect of engineered exosomes, a high-performance hydrogel with self-healing, bioadhesive, and exosome-conjugating properties is applied to encapsulate the engineered exosomes for in vivo application. In vivo, evaluation in diabetic bone defect repair models demonstrates that the engineered exosomes delivering hydrogel system intensively enhance osteogenesis. These findings provide crucial insight into the design and biological mechanism of ER homeostasis-based tissue-engineering strategies for diabetic bone regeneration.

Autophagy, Pyroptosis and Ferroptosis are Rising Stars in the Pathogenesis of Diabetic Nephropathy

Diabetic nephropathy (DN) is one of the most common microvascular complications in diabetes and can potentially develop into end-stage renal disease. Its pathogenesis is complex and not fully understood. Podocytes, glomerular endothelial cells (GECs), glomerular mesangial cells (GMCs) and renal tubular epithelial cells (TECs) play important roles in the normal function of glomerulus and renal tubules, and their injury is involved in the progression of DN. Although our understanding of the mechanisms leading to DN has substantially improved, we still need to find more effective therapeutic targets. Autophagy, pyroptosis and ferroptosis are programmed cell death processes that are associated with inflammation and are closely related to a variety of diseases. Recently, a growing number of studies have reported that autophagy, pyroptosis and ferroptosis regulate the function of podocytes, GECs, GMCs and TECs. This review highlights the contributions of autophagy, pyroptosis, and ferroptosis to DN injury in these cells, offering potential therapeutic targets for DN treatment.

NDUFS4 regulates cristae remodeling in diabetic kidney disease

The mitochondrial electron transport chain (ETC) is a highly adaptive process to meet metabolic demands of the cell, and its dysregulation has been associated with diverse clinical pathologies. However, the role and nature of impaired ETC in kidney diseases remains poorly understood. Here, we generate diabetic mice with podocyte-specific overexpression of Ndufs4, an accessory subunit of mitochondrial complex I, as a model investigate the role of ETC integrity in diabetic kidney disease (DKD). We find that conditional male mice with genetic overexpression of Ndufs4 exhibit significant improvements in cristae morphology, mitochondrial dynamics, and albuminuria. By coupling proximity labeling with super-resolution imaging, we also identify the role of cristae shaping protein STOML2 in linking NDUFS4 with improved cristae morphology. Together, we provide the evidence on the central role of NDUFS4 as a regulator of cristae remodeling and mitochondrial function in kidney podocytes. We propose that targeting NDUFS4 represents a promising approach to slow the progression of DKD.

RTN3 deficiency exacerbates cisplatin-induced acute kidney injury through the disruption of mitochondrial stability

Reticulum 3 (RTN3) is an endoplasmic reticulum (ER) protein that has been reported to act in neurodegenerative diseases and lipid metabolism. However, the role of RTN3 in acute kidney injury (AKI) has not been explored. Here, we employed public datasets, patient data, and animal models to explore the role of RTN3 in AKI. The underlying mechanisms were studied in primary renal tubular epithelial cells and in the HK2 cell line. We found reduced expression of RTN3 in AKI patients, cisplatin-induced mice, and cisplatin-treated HK2 cells. RTN3-null mice exhibit more severe AKI symptoms and kidney fibrosis after cisplatin treatment. Mitochondrial dysfunction was also found in cells with RTN3 knockdown or knockout. A mechanistic study revealed that RTN3 can interact with HSPA9 in kidney cells. RTN3 deficiency may disrupt the RTN3-HSPA9-VDAC2 complex and affect MAMs during ER-mitochondrion contact, which further leads to mitochondrial dysfunction and exacerbates cisplatin-induced AKI. Our study indicated that RTN3 was important in the kidney and that a decrease in RTN3 in the kidney might be a risk factor for the aggravation of AKI.

MicroRNA-26a alleviates tubulointerstitial fibrosis in diabetic kidney disease by targeting PAR4

Our previous study found that miR-26a alleviates aldosterone-induced tubulointerstitial fibrosis (TIF). However, the effect of miR-26a on TIF in diabetic kidney disease (DKD) remains unclear. This study clarifies the role and possible mechanism of exogenous miR-26a in controlling the progression of TIF in DKD models. Firstly, we showed that miR-26a was markedly decreased in type 2 diabetic db/db mice and mouse tubular epithelial cells (mTECs) treated with high glucose (HG, 30 mM) using RT-qPCR. We then used adeno-associated virus carrying miR-26a and adenovirus miR-26a to enhance the expression of miR-26a in vivo and in vitro. Overexpressing miR-26a alleviated the TIF in db/db mice and the extracellular matrix (ECM) deposition in HG-stimulated mTECs. These protective effects were caused by reducing expression of protease-activated receptor 4 (PAR4), which involved in multiple pro-fibrotic pathways. The rescue of PAR4 expression reversed the anti-fibrosis activity of miR-26a. We conclude that miR-26a alleviates TIF in DKD models by directly targeting PAR4, which may provide a novel molecular strategy for DKD therapy.

MAPK1 Mediates MAM Disruption and Mitochondrial Dysfunction in Diabetic Kidney Disease via the PACS-2-Dependent Mechanism

Diabetic kidney disease (DKD) is a leading cause of end-stage renal disease (ESRD). Mitochondrial dysfunction in renal tubules, occurring early in the disease, is linked to the development of DKD, although the underlying pathways remain unclear. Here, we examine diabetic human and mouse kidneys, and HK-2 cells exposed to high glucose, to show that high glucose disrupts mitochondria-associated endoplasmic reticulum membrane (MAM) and causes mitochondrial fragmentation. We find that high glucose conditions increase mitogen-activated protein kinase 1(MAPK1), a member of the MAP kinase signal transduction pathway, which in turn lowers the level of phosphofurin acidic cluster sorting protein 2 (PACS-2), a key component of MAM that tethers mitochondria to the ER. MAPK1-induced disruption of MAM leads to mitochondrial fragmentation but this can be rescued in HK-2 cells by increasing PACS-2 levels. Functional studies in diabetic mice show that inhibition of MAPK1 increases PACS-2 and protects against the loss of MAM and the mitochondrial fragmentation. Taken together, these results identify the MAPK1-PACS-2 axis as a key pathway to therapeutically target as well as provide new insights into the pathogenesis of DKD.

EIF2α/ATF4 pathway enhances proliferation of mesangial cell via cyclin D1 during endoplasmic reticulum stress in IgA nephropathy

IgA nephropathy (IgAN) is an essential cause of kidney failure and end-stage kidney disease worldwide. Mesangial hypercellularity is an important characteristic of IgAN, but the underlying mechanism remains unclear. Endoplasmic reticulum (ER) stress is a series of stress responses to restore the function of endoplasmic reticulum. We aimed to explore how ER stress functioned in kidneys of IgAN. We first examined ER stress in IgAN kidneys in vivo and in vitro, by testing the levels of ER stress associated proteins (BIP, p-eIF2α and ATF4). Our results showed that ER stress was activated in IgAN patients, mice and cell model. ER stress activation was related to the distribution of IgA deposition and the degree of mesangial proliferation. To determine the role of ER stress in mesangial cell (MC) proliferation of IgAN, we then tested the levels of ER stress and MC proliferation (cyclin D1, cell viability and cell cycle) through inhibiting ER stress associated proteins. After inhibiting ER stress associated proteins, ER stress was inactivated and cell proliferation was inhibited in MCs. We also explored the correlation between ER stress in the glomerulus and the clinical outcomes of IgAN patients in a prospective study. Patients with lower expression of p-eIF2α or ATF4 had higher rates of hematuria remission, proteinuria remission and clinical remission. In summary, our work outlines that in IgAN, ER stress mediated by eIF2α/ATF4 pathway promotes MC proliferation via up-regulating the expression of cyclin D1. Furthermore, p-eIF2α and ATF4 in the glomerulus negatively correlate with the clinical remission of IgAN patients.

Non-steroidal mineralocorticoid receptor antagonist finerenone ameliorates mitochondrial dysfunction via PI3K/Akt/eNOS signaling pathway in diabetic tubulopathy

Diabetic tubulopathy (DT) is a recently recognized key pathology of diabetic kidney disease (DKD). The mitochondria-centric view of DT is emerging as a vital pathological factor in different types of metabolic diseases, such as DKD. Finerenone (FIN), a novel non-steroidal mineralocorticoid receptor antagonist, attenuates kidney inflammation and fibrosis in DKD, but the precise pathomechanisms remain unclear. The role of mineralocorticoid receptor (MR) in perturbing mitochondrial function via the PI3K/Akt/eNOS signaling pathway, including mitochondrial dynamics and mitophagy, was investigated under a diabetic state and high glucose (HG) ambiance. To elucidate how the activation of MR provokes mitochondrial dysfunction in DT, human kidney proximal tubular epithelial (HK-2) cells were exposed to HG, and then mitochondrial dynamics, mitophagy, mitochondrial ROS (mitoROS), signaling molecules PI3K, Akt, Akt phosphorylation and eNOS were probed. The above molecules or proteins were also explored in the kidneys of diabetic and FIN-treated mice. FIN treatment reduced oxidative stress, mitochondrial fragmentation, and apoptosis while restoring the mitophagy via PI3K/Akt/eNOS signaling pathway in HK-2 cells exposed to HG ambiance and tubular cells of DM mice. These findings linked MR activation to mitochondrial dysfunction via PI3K/Akt/eNOS signaling pathway in DT and highlight a pivotal but previously undiscovered role of FIN in alleviating renal tubule injury for the treatment of DKD.

Tubular TMEM16A promotes tubulointerstitial fibrosis by suppressing PGC-1α-mediated mitochondrial homeostasis in diabetic kidney disease

Tubulointerstitial fibrosis (TIF) plays a crucial role in the progression of diabetic kidney disease (DKD). However, the underlying molecular mechanisms remain obscure. The present study aimed to examine whether transmembrane member 16A (TMEM16A), a Ca2+-activated chloride channel, contributes to the development of TIF in DKD. Interestingly, we found that TMEM16A expression was significantly up-regulated in tubule of murine model of DKD, which was associated with development of TIF. In vivo inhibition of TMEM16A channel activity with specific inhibitors Ani9 effectively protects against TIF. Then, we found that TMEM16A activation induces tubular mitochondrial dysfunction in in vivo and in vitro models, with the evidence of the TMEM16A inhibition with specific inhibitor. Mechanically, TMEM16A mediated tubular mitochondrial dysfunction through inhibiting PGC-1α, whereas overexpression of PGC-1α could rescue the changes. In addition, TMEM16A-induced fibrogenesis was dependent on increased intracellular Cl-, and reducing intracellular Cl- significantly blunted high glucose-induced PGC-1α and profibrotic factors expression. Taken together, our studies demonstrated that tubular TMEM16A promotes TIF by suppressing PGC-1α-mediated mitochondrial homeostasis in DKD. Blockade of TMEM16A may serve as a novel therapeutic approach to ameliorate TIF.

YTHDF1 mitigates acute kidney injury via safeguarding m6A-methylated mRNAs in stress granules of renal tubules

Acute kidney injury (AKI) presents a daunting challenge with limited therapeutic options. To explore the contribution of N6-methyladenosine (m6A) in AKI development, we have investigated m6A-modified mRNAs within renal tubular cells subjected to injuries induced by diverse stressors. Notably, while the overall level of m6A-modified RNA remains unaltered in renal tubular cells facing stress, a distinct phenomenon emerges-mRNAs bearing m6A methylation exhibit a pronounced tendency to accumulate within stress granules (SGs), structures induced in response to these challenges. Cumulation of m6A-modified mRNA in SGs is orchestrated by YTHDF1, a m6A 'reader' closely associated with SGs. Strikingly, AKI patients and various mouse AKI models showcase elevated levels of renal tubular YTHDF1. Depleting YTHDF1 within renal tubular cells leads to a marked reduction in m6A-modified mRNA accumulation within SGs, accompanied by an escalation in cell apoptosis under stress challenges. The significance of YTHDF1's protective role is further underscored by findings in AKI mouse models triggered by cisplatin or renal ischemia-reperfusion treatments. In particular, renal tubular-specific YTHDF1 knockout mice exhibit heightened AKI severity when contrasted with their wild-type counterparts. Mechanistic insights reveal that YTHDF1 fulfills a crucial function by safeguarding m6A-modified mRNAs that favor cell survival-exemplified by SHPK1-within SGs amid stress-challenged renal tubular cells. Our findings collectively shed light on the pivotal role of YTHDF1 in shielding renal tubules against AKI, through its adeptness in recruiting and preserving m6A-modified mRNAs within stress-induced SGs.

LRRK2 Gly2019Ser Mutation Promotes ER Stress via Interacting with THBS1/TGF-β1 in Parkinson's Disease

The gene mutations of LRRK2, which encodes leucine-rich repeat kinase 2 (LRRK2), are associated with one of the most prevalent monogenic forms of Parkinson's disease (PD). However, the potential effectors of the Gly2019Ser (G2019S) mutation remain unknown. In this study, the authors investigate the effects of LRRK2 G2019S on endoplasmic reticulum (ER) stress in induced pluripotent stem cell (iPSC)-induced dopamine neurons and explore potential therapeutic targets in mice model. These findings demonstrate that LRRK2 G2019S significantly promotes ER stress in neurons and mice. Interestingly, inhibiting LRRK2 activity can ameliorate ER stress induced by the mutation. Moreover, LRRK2 mutation can induce ER stress by directly interacting with thrombospondin-1/transforming growth factor beta1 (THBS1/TGF-β1). Inhibition of LRRK2 kinase activity can effectively suppress ER stress and the expression of THBS1/TGF-β1. Knocking down THBS1 can rescue ER stress by interacting with TGF-β1 and behavior burden caused by the LRRK2 mutation, while suppression of TGF-β1 has a similar effect. Overall, it is demonstrated that the LRRK2 mutation promotes ER stress by directly interacting with THBS1/TGF-β1, leading to neural death in PD. These findings provide valuable insights into the pathogenesis of PD, highlighting potential diagnostic markers and therapeutic targets.

Broadening horizons: the contribution of mitochondria-associated endoplasmic reticulum membrane (MAM) dysfunction in diabetic kidney disease

Diabetic kidney disease (DKD) is a global health issue that presents a complex pathogenesis and limited treatment options. To provide guidance for precise therapies, it is crucial to accurately identify the pathogenesis of DKD. Several studies have recognized that mitochondrial and endoplasmic reticulum (ER) dysfunction are key drivers of the pathogenesis of DKD. The mitochondria-associated ER membrane (MAM) is a dynamic membrane contact site (MSC) that connects the ER and mitochondria and is essential in maintaining the normal function of the two organelles. MAM is involved in various cellular processes, including lipid synthesis and transport, calcium homeostasis, mitochondrial fusion and fission, and ER stress. Meanwhile, recent studies confirm that MAM plays a significant role in the pathogenesis of DKD by regulating glucose metabolism, lipid metabolism, inflammation, ER stress, mitochondrial fission and fusion, and autophagy. Herein, this review aims to provide a comprehensive summary of the physiological function of MAMs and their impact on the progression of DKD. Subsequently, we discuss the trend of pharmaceutical studies that target MAM resident proteins for treating DKD. Furthermore, we also explore the future development prospects of MAM in DKD research, thereby providing a new perspective for basic studies and clinical treatment of DKD.

Tubular injury in diabetic kidney disease: molecular mechanisms and potential therapeutic perspectives

Diabetic kidney disease (DKD) is a chronic complication of diabetes and the leading cause of end-stage renal disease (ESRD) worldwide. Currently, there are limited therapeutic drugs available for DKD. While previous research has primarily focused on glomerular injury, recent studies have increasingly emphasized the role of renal tubular injury in the pathogenesis of DKD. Various factors, including hyperglycemia, lipid accumulation, oxidative stress, hypoxia, RAAS, ER stress, inflammation, EMT and programmed cell death, have been shown to induce renal tubular injury and contribute to the progression of DKD. Additionally, traditional hypoglycemic drugs, anti-inflammation therapies, anti-senescence therapies, mineralocorticoid receptor antagonists, and stem cell therapies have demonstrated their potential to alleviate renal tubular injury in DKD. This review will provide insights into the latest research on the mechanisms and treatments of renal tubular injury in DKD.

Epigenetic regulation of mitochondrial-endoplasmic reticulum dynamics in kidney diseases

Kidney diseases are serious health problems affecting >800 million individuals worldwide. The high number of affected individuals and the severe consequences of kidney dysfunction demand an intensified effort toward more effective prevention and treatment. The pathophysiology of kidney diseases is complex and comprises diverse organelle dysfunctions including mitochondria and endoplasmic reticulum (ER). The recent findings prove interactions between the ER membrane and nearly all cell compartments and give new insights into molecular events involved in cellular mechanisms in health and disease. Interactions between the ER and mitochondrial membranes, known as the mitochondria-ER contacts regulate kidney physiology by interacting with each other via membrane contact sites (MCS). ER controls mitochondrial dynamics through ER stress sensor proteins or by direct communication via mitochondria-associated ER membrane to activate signaling pathways such as apoptosis, calcium transport, and autophagy. More importantly, these organelle dynamics are found to be regulated by several epigenetic mechanisms such as DNA methylation, histone modifications, and noncoding RNAs and can be a potential therapeutic target against kidney diseases. However, a thorough understanding of the role of epigenetic regulation of organelle dynamics and their functions is not well understood. Therefore, this review will unveil the role of epigenetic mechanisms in regulating organelle dynamics during various types of kidney diseases. Moreover, we will also shed light on different stress origins in organelles leading to kidney disease. Henceforth, by understanding this we can target epigenetic mechanisms to maintain/control organelle dynamics and serve them as a novel therapeutic approach against kidney diseases.

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.

NDUFS4 Regulates Cristae Remodeling in Diabetic Kidney Disease

The mitochondrial electron transport chain (ETC) is a highly adaptive process to meet metabolic demands of the cell, and its dysregulation has been associated with diverse clinical pathologies. However, the role and nature of impaired ETC in kidney diseases remains poorly understood. Here, we generated diabetic mice with podocyte-specific overexpression of Ndufs4, an accessory subunit of mitochondrial complex I, as a model to investigate the role of ETC integrity in diabetic kidney disease (DKD). We find that these conditional mice exhibit significant improvements in cristae morphology, mitochondrial dynamics, and albuminuria. By coupling proximity labeling with super-resolution imaging, we also identify the role of cristae shaping proteins in linking NDUFS4 with improved cristae morphology. Taken together, we discover the central role of NDUFS4 as a powerful regulator of cristae remodeling, respiratory supercomplexes assembly, and mitochondrial ultrastructure in vitro and in vivo. We propose that targeting NDUFS4 represents a promising approach to slow the progression of DKD.

The Interplay between Immune and Metabolic Pathways in Kidney Disease

Kidney disease is a significant health problem worldwide, affecting an estimated 10% of the global population. Kidney disease encompasses a diverse group of disorders that vary in their underlying pathophysiology, clinical presentation, and outcomes. These disorders include acute kidney injury (AKI), chronic kidney disease (CKD), glomerulonephritis, nephrotic syndrome, polycystic kidney disease, diabetic kidney disease, and many others. Despite their distinct etiologies, these disorders share a common feature of immune system dysregulation and metabolic disturbances. The immune system and metabolic pathways are intimately connected and interact to modulate the pathogenesis of kidney diseases. The dysregulation of immune responses in kidney diseases includes a complex interplay between various immune cell types, including resident and infiltrating immune cells, cytokines, chemokines, and complement factors. These immune factors can trigger and perpetuate kidney inflammation, causing renal tissue injury and progressive fibrosis. In addition, metabolic pathways play critical roles in the pathogenesis of kidney diseases, including glucose and lipid metabolism, oxidative stress, mitochondrial dysfunction, and altered nutrient sensing. Dysregulation of these metabolic pathways contributes to the progression of kidney disease by inducing renal tubular injury, apoptosis, and fibrosis. Recent studies have provided insights into the intricate interplay between immune and metabolic pathways in kidney diseases, revealing novel therapeutic targets for the prevention and treatment of kidney diseases. Potential therapeutic strategies include modulating immune responses through targeting key immune factors or inhibiting pro-inflammatory signaling pathways, improving mitochondrial function, and targeting nutrient-sensing pathways, such as mTOR, AMPK, and SIRT1. This review highlights the importance of the interplay between immune and metabolic pathways in kidney diseases and the potential therapeutic implications of targeting these pathways.

O-GlcNAcylation enhances Reticulon 2 protein stability and its promotive effects on gastric cancer progression

Our previous study indicated that Reticulon 2 (RTN2) was upregulated and facilitated the progression of gastric cancer. Protein O-linked β-N-acetylglucosaminylation (O-GlcNAcylation) is a general feature during tumorigenesis, and regulates protein activity and stability through post-translational modification on serine/threonine. However, the relationship between RTN2 and O-GlcNAcylation have never been determined. In this study, we explored the influence of O-GlcNAcylation on RTN2 expression and its promotive role in gastric cancer. We found that RTN2 interacted with O-GlcNAc transferase (OGT) and was modified by O-GlcNAc. O-GlcNAcylation enhanced RTN2 protein stability via attenuating its lysosomal degradation in gastric cancer cells. Furthermore, our results demonstrated that RTN2-induced activation of ERK signalling was dependent on O-GlcNAcylation. Consistently, the stimulative effects of RTN2 on cellular proliferation and migration were abrogated by OGT inhibition. Tissue microarray with immumohistochemical staining also confirmed that the expression of RTN2 was positively correlated with the level of total O-GlcNAcylation as well as the phosphorylation level of ERK. Besides, combined RTN2 and O-GlcNAc staining intensity could improve predictive accuracy for gastric cancer patients' survival compared with each alone. Altogether, these findings suggest that O-GlcNAcylation on RTN2 was pivotal for its oncogenic functions in gastric cancer. Targeting RTN2 O-GlcNAcylation might provide new ideas for gastric cancer therapies.

Sodium-glucose cotransporter inhibitors and kidney fibrosis: review of the current evidence and related mechanisms

Sodium-glucose cotransporter inhibitors (SGLT2i) are a new class of anti-diabetic drugs that have beneficial cardiovascular and renal effects. These drugs decrease proximal tubular glucose reabsorption and decrease blood glucose levels as a main anti-diabetic action. Furthermore, SGLT2i decreases glomerular hyperfiltration by a tubuloglomerular feedback mechanism. However, the renal benefits of these agents are independent of glucose-lowering and hemodynamic factors, and SGLT2i also impacts the kidney structure including kidney fibrosis. Renal fibrosis is a common pathway and pathological marker of virtually every type of chronic kidney disease (CKD), and amelioration of renal fibrosis is of utmost importance to reduce the progression of CKD. Recent studies have shown that SGLT2i impact many cellular processes including inflammation, hypoxia, oxidative stress, metabolic functions, and renin-angiotensin system (RAS) which all are related with kidney fibrosis. Indeed, most but not all studies showed that renal fibrosis was ameliorated by SGLT2i through the reduction of inflammation, hypoxia, oxidative stress, and RAS activation. In addition, less known effects on SGLT2i on klotho expression, capillary rarefaction, signal transducer and activator of transcription signaling and peptidylprolyl cis/trans isomerase (Pin1) levels may partly explain the anti-fibrotic effects of SGLT2i in kidneys. It is important to remember that some studies have not shown any beneficial effects of SGLT2i on kidney fibrosis. Given this background, in the current review, we have summarized the studies and pathophysiologic aspects of SGL2 inhibition on renal fibrosis in various CKD models and tried to explain the potential reasons for contrasting findings.

Mitochondria-associated endoplasmic reticulum membranes: A promising toxicity regulation target

Mitochondria-associated endoplasmic reticulum membranes (MAMs) are dynamic suborganelle membranes that physically couple endoplasmic reticulum (ER) and mitochondria to provide a platform for exchange of intracellular molecules and crosstalk between the two organelles. Dysfunctions of mitochondria and ER and imbalance of intracellular homeostasis have been discovered in the research of toxics. Cellular activities such as oxidative stress, ER stress, Ca²⁺ transport, autophagy, mitochondrial fusion and fission, and apoptosis mediated by MAMs are closely related to the toxicological effects of various toxicants. These cellular activities mediated by MAMs crosstalk with each other. Regulating the structure and function of MAMs can alleviate the damage caused by toxicants to some extent. In this review, we discuss the relationships between MAMs and the mechanisms of toxicological effects, and highlight MAMs as a potential target for protection against toxicants.