Oxaloacetate Restores HIF-1α-Mediated Mitochondrial Homeostasis to Counter Tubulointerstitial Injury in Diabetic Kidney Disease.

Quercetin ameliorates renal injury by promoting UCP1-mediated alleviation of lipid accumulation in diabetic kidney disease.

Mitochondrial dysfunction is a hallmark of diabetic kidney disease (DKD), yet its regulatory mechanisms remain poorly defined. Mitochondrial transcription factor A (TFAM), a central regulator of mitochondrial homeostasis, undergoes lysine 76 (K76) acetylation, but the functional significance of this modification in DKD has not been established. We collected kidney tissues from DKD patients and DKD mice, and assessed TFAM acetylation in HK-2 cells and primary renal tubular cells under high-glucose conditions. In addition, to investigate the potential mechanism of TFAM acetylation in mitochondrial damage within the kidney, we explored relevant pathways using proteomics and utilized streptozotocin (STZ)-induced DKD mouse models with tubular-specific expression of TFAM wild-type and mutant forms to examine kidney injury. Moreover, we identified TFAM K76 acetylation-specific inhibitors through high-throughput virtual screening and thoroughly validated them in HK-2 cells, primary cells, and DKD mice, confirming the critical role of TFAM acetylation in DKD-related kidney injury. Here, we identify TFAM K76 acetylation as a critical mediator of mitochondrial injury in DKD. TFAM K76 acetylation was markedly elevated in kidney tissues from DKD patients and diabetic mouse models, correlating with mitochondrial damage, inflammation, and fibrosis under hyperglycemic conditions. In vivo, overexpression of acetylation-mimetic TFAM K76Q in renal tubular epithelial cells aggravated renal injury and ultrastructural damage, whereas its deacetylation attenuated these effects. Mechanistically, TFAM K76 acetylation impaired oxidative phosphorylation and excessively activated autophagy, further exacerbating mitochondrial damage. We identified sirtuin 3 (SIRT3) as an upstream deacetylase that regulates this modification. Importantly, through high-throughput virtual screening, we discovered a novel small-molecule inhibitor (C14) that selectively reduces TFAM K76 acetylation and effectively alleviates hyperglycemia-induced mitochondrial dysfunction, inflammation, and fibrosis in both in vitro and in vivo models. Collectively, our findings define TFAM K76 acetylation as a pathogenic driver of DKD and propose C14 as a promising therapeutic candidate targeting mitochondrial metabolism.

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

Diabetic kidney disease (DKD) is the leading cause of chronic kidney disease (CKD) and end-stage renal disease (ESRD), but the pathogenesis is not completely understood. Tubulointerstitial injury plays critical roles in the development and progression of DKD. The present study aimed to investigate the profile of tubulointerstitial immune cell infiltration and reveal the underlying mechanisms between tubular cell injury and interstitial inflammation in DKD using bioinformatics strategies. First, xCell analysis identified immune cells displaying significant changes in the DKD tubulointerstitium, including upregulated CD4+ T cells, Th2 cells, CD8+ T cells, M1 macrophages, activated dendritic cells (DCs) and conventional DCs, as well as downregulated Tregs. Second, pyroptosis was identified as the main form of cell death compared with other forms of programmed cell death. Vascular cell adhesion protein 1 (VCAM1) was identified as the top ranked hub gene. The correlation analysis showed that VCAM1 was significantly positively correlated with pyroptosis and infiltrated immune cells in the tubulointerstitium. Upregulation of VCAM1 in the DKD tubulointerstitium was further verified in European Renal cDNA Bank cohort and was observed to negatively correlate with the glomerular filtration rate (GFR). Our in vitro study validated increased VCAM1 expression in HK-2 cells under diabetic conditions, and pyroptosis inhibition by disulfiram decreased VCAM1 expression, inflammatory cytokine release and fibrosis. In conclusion, our study identified upregulated VCAM1 expression in renal tubular cells, which might interact with infiltrated immune cells, thus promoting fibrosis. The FDA-approved drug disulfiram might improve fibrosis in DKD by targeting tubular pyroptosis and VCAM1 expression.

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

To investigate the role of histone deacetylase 6 (HDAC6) in podocyte injury in diabetic kidney disease (DKD) in mice. 1) The 8-week-old male CD-1 mice were selected to construct the model of DKD with streptozocin (STZ). After the model was established, the mice were intraperitoneally injected with HDAC6 inhibitor CAY10603 (5mg/kg/daily) or same volume vehicle as control. The mice were divided into four groups, control (CTL)+vehicle (Veh) (n=5), CLT+CAY10603 (n=3), STZ+Veh (n=9), and STZ+CAY10603 (n=7). Mice in STZ+Veh and STZ+CAY10603 groups developed DKD, while mice in the CTL+Veh and CTL+CAY10603 groups were served as normal controls. The therapeutic effect was evaluated through urine albumin-to-creatinine ratio (uACR) and renal pathology after the 2-week treatment with CAY10603. 2) Human podocytes were cultured in vitro and were divided into four groups as follows: CTL, transforming growth factor-β (TGFβ), TGFβ+CAY10603 (250 nmol/L), and TGFβ+CAY10603 (500 nmol/L) groups. The control group did not receive any treatment, the last three groups were given 36-h TGFβ treatment at 5 ng/µL, with or without CAY10603 as indicated for an additional 12 h. Western blot was performed to determine the inhibitory effect of CAY10603 on NLRP3 inflammasome. 3) HDAC6 knockout (KO) mice were generated and used to create STZ-induced model of DKD. The mice were divided into four groups: C57BL/6J wild type (WT) (n=6), HDAC6 KO (n=6), WT+STZ (n=10), and HDAC6 KO+STZ (n=9). Samples were collected 16 weeks after successful modeling and changes in uACR and renal pathology were evaluated accordingly. After 2 weeks of treatment, mice in the STZ+CAY10603 group exhibited reduction in uACR (P<0.05) and inhibition of glomerular mesangium expansion (P<0.05) compared with those of the mice in the STZ+Veh group. There was no statistically significant difference in the indicators between the CTL+Veh group and the CTL+CAY10603 group. In vitro cultured podocytes, compared with the control group, NLRP3 inflammasome activation was seen in the TGFβ group. CAY10603 treatment significantly inhibited the activation of NLRP3 in the dosage-dependent manner (P<0.05). Compared with those of the WT group, the WT+STZ group showed increased uACR (P<0.05), obvious glomerulosclerosis and loss of podocytes numbers. Compared with those of the WT+STZ group, the HDAC6 KO+STZ group showed effectively reduction of uACR (P<0.05) and improvement in the renal pathological changes in mice. There was no significant difference in these aspects between the WT and HDAC6 KO groups. Inhibition of HDAC6 alleviates proteinuria and podocyte injury in the mouse model of DKD by suppressing the activation of NLRP3 inflammasome.

BackgroundThe senescence of renal tubular epithelial cells (RTECs) is crucial in the progression of diabetic kidney disease (DKD). Accumulating evidence suggests a close association between insufficient mitophagy and RTEC senescence. Yeast mitochondrial escape 1-like 1 (YME1L), an inner mitochondrial membrane metalloprotease, maintains mitochondrial integrity. Its functions in DKD remain unclear. Here, we investigated whether YME1L can prevent the progression of DKD by regulating mitophagy and cellular senescence.MethodsWe analyzed YME1L expression in renal tubules of DKD patients and mice, explored transcriptomic changes associated with YME1L overexpression in RTECs, and assessed its impact on RTEC senescence and renal dysfunction using an HFD/STZ-induced DKD mouse model. Tubule-specific overexpression of YME1L was achieved through the use of recombinant adeno-associated virus 2/9 (rAAV 2/9). We conducted both in vivo and in vitro experiments to evaluate the effects of YME1L overexpression on mitophagy and mitochondrial function. Furthermore, we performed LC–MS/MS analysis to identify potential protein interactions involving YME1L and elucidate the underlying mechanisms.ResultsOur findings revealed a significant decrease in YME1L expression in the renal tubules of DKD patients and mice. However, tubule-specific overexpression of YME1L significantly alleviated RTEC senescence and renal dysfunction in the HFD/STZ-induced DKD mouse model. Moreover, YME1L overexpression exhibited positive effects on enhancing mitophagy and improving mitochondrial function both in vivo and in vitro. Mechanistically, our LC–MS/MS analysis uncovered a crucial mitophagy receptor, BCL2-like 13 (BCL2L13), as an interacting partner of YME1L. Furthermore, YME1L was found to promote the phosphorylation of BCL2L13, highlighting its role in regulating mitophagy.ConclusionsThis study provides compelling evidence that YME1L plays a critical role in protecting RTECs from cellular senescence and impeding the progression of DKD. Overexpression of YME1L demonstrated significant therapeutic potential by ameliorating both RTEC senescence and renal dysfunction in the DKD mice. Moreover, our findings indicate that YME1L enhances mitophagy and improves mitochondrial function, potentially through its interaction with BCL2L13 and subsequent phosphorylation. These novel insights into the protective mechanisms of YME1L offer a promising strategy for developing therapies targeting DKD.

Objective To investigate the effects of insulin-like growth factor 1 receptor (IGF-1R) inhibitor on tubulopathy in diabetic kidney disease (DKD) mice. Methods C57BL/6J male mice were randomly divided into normal control group (n=10) and DKD model group (n=30), by giving a single intraperitoneal injection of STZ 150 mg/kg to establish a DKD model. After established successfully, the mice in DKD model group were randomly divided into DKD group (n=10), benazepril group (n=10) and IGF-1R inhibitor group (n=10). IGF-1R inhibitor group was given intraperitoneal injection of IGF-1R inhibitor (30 mg·kg-1·d-1) and benazepril group was given intraperitoneal injection of benazepril (30 mg·kg-1·d-1). Normal control group and DKD group were given an equal amount of normal saline. After 8 weeks of feeding, mice were euthanatized. Body weight and kidney weight were recorded. Blood, urine and kidney samples were collected. Biochemical tests such as blood glucose and urine albumin were measured by automatic biochemical instruments and albumin excretion rate was calculated. Pathological changes of mice were observed by hematoxylin-eosin staining (HE) and periodic acid-schiff staining (PAS). Phosph (p) IGF-1R expression level was determined by immunohistochemistry and Western blotting. Results Compared with the normal control group, blood glucose, kidney weight/body weight and urinary albumin excretion rate were significantly higher in DKD group (all P<0.01). In DKD mice, glomerular expansion, tubular stenosis, tubular swelling and tubular atrophy were significantly detected. Meanwhile, the number of proximal tubular epithelial (PTE) cells was decreased, and the renal tubular injury scores, the average glomerular volume, and pIGF-1R protein expression were increased (all P<0.05). Compared with the DKD group, albumin excretion rate was significantly reduced (P<0.01), the above pathological changes were alleviated and the effect of IGF-1R inhibitor was more significant. Compared with the DKD group, the pIGF-1R protein expression was reduced in IGF-1R inhibitor group (P<0.05). Compared with the benazepril group, the pIGF-1R protein expression was reduced in IGF-1R inhibitor group (P<0.05). Conclusion IGF-1R inhibitor has better effect than benazepril on alleviating the tubulopathy of DKD mice. Key words: Diabetic nephropathies; Receptor, IGF type 1; Kidney tubules

Autophagy protects podocytes from injury in diabetic kidney disease (DKD). Restoring glomerular autophagy is a promising approach to limit DKD. This study demonstrates a novel regulatory mechanism of autophagy that blocks this critical protection of the glomerular filtration barrier. We demonstrated that TRPC6 induced in podocytes in mouse models of diabetes mediates calpain activation, thereby impairing podocyte autophagy, causing injury and accelerating DKD. Furthermore, this study provides proof of principle for druggable targets for DKD because restoration of podocyte autophagy by calpain inhibitors effectively limits glomerular destruction. Diabetic kidney disease is associated with impaired podocyte autophagy and subsequent podocyte injury. The regulation of podocyte autophagy is unique because it minimally uses the mTOR and AMPK pathways. Thus, the molecular mechanisms underlying the impaired autophagy in podocytes in diabetic kidney disease remain largely elusive. This study investigated how the calcium channel TRPC6 and the cysteine protease calpains deleteriously affect podocyte autophagy in diabetic kidney disease in mice. We demonstrated that TRPC6 knockdown in podocytes increased the autophagic flux because of decreased cysteine protease calpain activity. Diabetic kidney disease was induced in vivo using streptozotocin with unilateral nephrectomy and the BTBR ob/ob mouse models. Diabetes increased TRPC6 expression in podocytes in vivo with decreased podocyte autophagic flux. Transgenic overexpression of the endogenous calpain inhibitor calpastatin, as well as pharmacologic inhibition of calpain activity, normalized podocyte autophagic flux, reduced nephrin loss, and prevented the development of albuminuria in diabetic mice. In kidney biopsies from patients with diabetes, we further confirmed that TRPC6 overexpression in podocytes correlates with decreased calpastatin expression, autophagy blockade, and podocyte injury. Overall, we discovered a new mechanism that connects TRPC6 and calpain activity to impaired podocyte autophagy, increased podocyte injury, and development of proteinuria in the context of diabetic kidney disease. Therefore, targeting TRPC6 and/or calpain to restore podocyte autophagy might be a promising therapeutic strategy for diabetic kidney disease.

The cGAS/STING-mediated inflammatory response plays a key role in diabetic kidney disease (DKD) pathogenesis. However, effective anti-inflammatory therapies to halt disease its progression remain unavailable. The Qihuang Yishen (QHYS) formula has been demonstrated to reduce proteinuria and halt the course of DKD. However, the underlying mechanism of QHYS remains unclear. The purpose of this study was to determine whether QHYS had anti-inflammatory effects on DKD by targeting the cGAS/STING pathway both in vitro and in vivo. In vivo, DKD models were established in KK-Ay mice using a high-fat diet. In vitro, human renal tubular epithelial cells (HK-2) were exposed to high glucose (HG) and palmitic acid (PA) for 24 h to simulate renal tubular injury. Both experimental settings received interventions with QHYS or canagliflozin (positive control drug). Bioactive components in QHYS-containing serum were characterized by HPLC-ESI/MS. Body weight, random blood glucose, renal function markers, urinary protein levels, renal tubular injury indicators, and renal histological lesions were evaluated. Mitochondrial ultrastructure was analyzed by transmission electron microscopy (TEM). Western blotting quantified mitochondrial proteins TFAM and TOM20. Cell viability was assessed via CCK-8 assay, while ELISA kits measured IL-6 and TNF-α levels in cell supernatant. Quantitative PCR assessed expression of mtDNA and inflammatory mediators (IL-6, TNF-α, IFN-γ and CXCL10 mRNA). For cGAS/STING pathway analysis, key proteins were evaluated through western blotting, immunofluorescence, and immunohistochemistry. Additionally, mtDNA transfection experiments in HK-2 cells elucidated QHYS's regulatory mechanism on this pathway. HPLC-ESI/MS identified 32 principal bioactive components in QHYS. In vivo experiments showed that QHYS significantly reduced Scr and UREA levels (p < 0.05), decreased UACR, 24 h UTP and renal tubular injury markers NAG and NGAL levels (p < 0.01), and alleviated renal histopathological damage in KK-Ay mice, including glomerular hypertrophy, mesangial matrix expansion, tubular vacuolar degeneration, and tubulointerstitial inflammation. Moreover, QHYS ameliorated mitochondrial structural damage, upregulated the expression of TFAM and TOM20 (p < 0.05), and suppressed cGAS/STING pathway activation (p < 0.01). In vitro experiments demonstrated that QHYS alleviated mitochondrial damage (p < 0.05) and mtDNA leakage (p < 0.01), and inhibited cGAS/STING signaling and downstream inflammation (p < 0.05). More importantly, transfecting mtDNA into the cytoplasm to mimic the leakage process demonstrated that QHYS-containing serum directly inhibits cGAS/STING pathway activation (p < 0.05), and this mechanism also alleviated renal tubular injury in DKD. QHYS attenuates renal tubular inflammatory damage via cGAS/STING pathway regulation. This pioneering study provides the first evidence that herbal medicine exerts renal tubule protection through multi-target regulation of innate immune-mediated inflammatory injury in metabolic nephropathy, offering novel scientific evidence for DKD intervention.

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.

FABP4 inhibition protects renal tubular cells and ameliorates renal inflammation in diabetic kidney disease.

Diabetic kidney disease (DKD) is a microvascular complication of diabetes accompanied by inflammation and tubular fibrosis. Berberine (BBR), a plant alkaloid and traditional Chinese medicine, has been shown to have beneficial effects on DKD. However, its mechanism underlying its therapeutic effects in DKD remain to be fully elucidated. Herein, we investigated the protective effects of BBR on STZ/HFD-induced DKD mice and high glucose (HG)-treated renal tubular epithelial cells (TECs). Results showed that BBR reduced inflammation and tubular fibrosis in DKD mice. Meanwhile, BBR also reversed HG-induced inflammation and fibrosis in TECs. Mechanistically, qPCR and western blotting assays revealed that BBR abolished the HG-induced upregulation of ISG15 and the changes in the expression of pyroptosis-related proteins. Furthermore, overexpression of ISG15 in kidney and TECs significantly exacerbated renal tubular cell injury and abolished the protective effect of BBR against DKD. In conclusion, these results demonstrated that BBR can attenuate inflammation and tubular fibrosis in DKD by inhibiting ISG15 and pyroptosis, providing a new potential strategy for the treatment of DKD and highlighting the therapeutic potential of BBR in mitigating renal injury and fibrosis.

Renal tubule cells act as a primary site of injury in diabetic kidney disease (DKD), with dysfunctional mitochondrial quality control (MQC) closely associated with progressive kidney dysfunction in this context. Our investigation delves into the observed inactivation of yes-associated protein 1 (YAP1) and consequential dysregulation of MQC within renal tubule cells among DKD subjects through bioinformatic analysis of transcriptomics data from the Gene Expression Omnibus (GEO) dataset. Receiver operating characteristic curve analysis unequivocally underscores the robust diagnostic accuracy of YAP1 and MQC-related genes for DKD. Furthermore, we observed YAP1 inactivation, accompanied by perturbed MQC, within cultured tubule cells exposed to high glucose (HG) and palmitic acid (PA). This pattern was also evident in the tubulointerstitial compartment of kidney sections from biopsy-approved DKD patients. Additionally, renal tubule cell-specific Yap1 deletion exacerbated kidney injury in diabetic mice. Mechanistically, Yap1 deletion disrupted MQC, leading to mitochondrial aberrations in mitobiogenesis and mitophagy within tubule cells, ultimately culminating in histologic tubular injury. Notably, Yap1 deletion-induced renal tubule injury promoted the secretion of C-X-C motif chemokine ligand 1 (CXCL1), potentially augmenting M1 macrophage infiltration within the renal microenvironment. These multifaceted events were significantly ameliorated by administrating the YAP1 activator XMU-MP-1 in DKD mice. Consistently, bioinformatic analysis of transcriptomics data from the GEO dataset revealed a noteworthy upregulation of tubule cells-derived chemokine CXCL1 associated with macrophage infiltration among DKD patients. Crucially, overexpression of YAP1 via adenovirus transfection sustained mitochondrial membrane potential, mtDNA copy number, oxygen consumption rate, and activity of mitochondrial respiratory chain complex, but attenuated mitochondrial ROS production, thereby maintaining MQC and subsequently suppressing CXCL1 generation within cultured tubule cells exposed to HG and PA. Collectively, our study establishes a pivotal role of tubule YAP1 inactivation-mediated MQC dysfunction in driving DKD progression, at least in part, facilitated by promoting M1 macrophage polarization through a paracrine-dependent mechanism.

One of the main characteristics of diabetic kidney disease (DKD) is abnormal renal tubular fatty acid metabolism, especially defective fatty acid oxidation (FAO), accelerating tubular injury and tubulointerstitial fibrosis. Thiosulfate sulfurtransferase (TST), a mitochondrial enzyme essential for sulfur transfer, is reduced in metabolic diseases like diabetes and obesity. However, the potential role of TST in regulating fatty acid metabolic abnormalities in DKD remains unclear. Here, our data revealed decreased TST expression in the renal cortex of DKD patients. TST deficiency exacerbated tubular impairment in both diabetic and renal fibrosis mouse models, while sodium thiosulfate treatment or TST overexpression mitigated renal tubular injury with high-glucose exposure. TST downregulation mediated the decrease in S-sulfhydration of very long-chain specific acyl-CoA dehydrogenase, resulting in mitochondrial FAO dysfunction. This sequence of events exacerbates the progression of tubulointerstitial injury in DKD. Together, our findings demonstrate TST as a regulator of renal tubular injury in DKD.