Dicer deficiency in proximal tubules exacerbates renal injury and tubulointerstitial fibrosis and upregulates Smad2/3

Inducible deletion of microRNA activity in kidney mesenchymal cells exacerbates renal fibrosis

MicroRNAs (miRNAs) are sequence-specific inhibitors of post-transcriptional gene expression. However, the physiological functions of these non-coding RNAs in renal interstitial mesenchymal cells remain unclear. To conclusively evaluate the role of miRNAs, we generated conditional knockout (cKO) mice with platelet-derived growth factor receptor-β (PDGFR-β)-specific inactivation of the key miRNA pathway gene Dicer. The cKO mice were subjected to unilateral ureteral ligation, and renal interstitial fibrosis was quantitatively evaluated using real-time polymerase chain reaction and immunofluorescence staining. Compared with control mice, cKO mice had exacerbated interstitial fibrosis exhibited by immunofluorescence staining and mRNA expression of PDGFR-β. A microarray analysis showed decreased expressions of miR-9-5p, miR-344g-3p, and miR-7074-3p in cKO mice compared with those in control mice, suggesting an association with the increased expression of PDGFR-β. An analysis of the signaling pathways showed that the major transcriptional changes in cKO mice were related to smooth muscle cell differentiation, regulation of DNA metabolic processes and the actin cytoskeleton, positive regulation of fibroblast proliferation and Ras protein signal transduction, and focal adhesion-PI3K/Akt/mTOR signaling pathways. Depletion of Dicer in mesenchymal cells may downregulate the signaling pathway related to miR-9-5p, miR-344g-3p, and miR-7074-3p, which can lead to the progression of chronic kidney disease. These findings highlight the possibility for future diagnostic or therapeutic developments for renal fibrosis using miR-9-5p, miR-344g-3p, and miR-7074-3p.

SIRT2 alleviated renal fibrosis by deacetylating SMAD2 and SMAD3 in renal tubular epithelial cells

Transforming growth factor-β (TGF-β) is the primary factor that drives fibrosis in most, if not all, forms of chronic kidney disease. In kidneys that are obstructed, specific deletion of Sirt2 in renal tubule epithelial cells (TEC) has been shown to aggravate renal fibrosis, while renal tubule specific overexpression of Sirt2 has been shown to ameliorate renal fibrosis. Similarly, specific deletion of Sirt2 in hepatocyte aggravated CCl4-induced hepatic fibrosis. In addition, we have demonstrated that SIRT2 overexpression and knockdown restrain and enhance TGF-β-induced fibrotic gene expression, respectively, in TEC. Mechanistically, SIRT2 reduced the phosphorylation, acetylation, and nuclear localization levels of SMAD2 and SMAD3, leading to inhibition of the TGF-β signaling pathway. Further studies have revealed that that SIRT2 was able to directly interact with and deacetylate SMAD2 at lysine 451, promoting its ubiquitination and degradation. Notably, loss of SMAD specific E3 ubiquitin protein ligase 2 abolishes the ubiquitination and degradation of SMAD2 induced by SIRT2 in SMAD2. Regarding SMAD3, we have found that SIRT2 interact with and deacetylates SMAD3 at lysine 341 and 378 only in the presence of TGF-β, thereby reducing its activation. This study provides initial indication of the anti-fibrotic role of SIRT2 in renal tubules and hepatocytes, suggesting its therapeutic potential for fibrosis.

Epigenetic changes induced by pathogenic Chlamydia spp

Chlamydia trachomatis, C. pneumoniae, and C. psittaci, the three Chlamydia species known to cause human disease, have been collectively linked to several pathologies, including conjunctivitis, trachoma, respiratory disease, acute and chronic urogenital infections and their complications, and psittacosis. In vitro, animal, and human studies also established additional correlations, such as between C. pneumoniae and atherosclerosis and between C. trachomatis and ovarian cancer. As part of their survival and pathogenesis strategies as obligate intracellular bacteria, Chlamydia spp. modulate all three major types of epigenetic changes, which include deoxyribonucleic acid (DNA) methylation, histone post-translational modifications, and microRNA-mediated gene silencing. Some of these epigenetic changes may be implicated in key aspects of pathogenesis, such as the ability of the Chlamydia spp. to induce epithelial-to-mesenchymal transition, interfere with DNA damage repair, suppress cholesterol efflux from infected macrophages, act as a co-factor in human papillomavirus (HPV)-mediated cervical cancer, prevent apoptosis, and preserve the integrity of mitochondrial networks in infected host cells. A better understanding of the individual and collective contribution of epigenetic changes to pathogenesis will enhance our knowledge about the biology of Chlamydia spp. and facilitate the development of novel therapies and biomarkers. Pathogenic Chlamydia spp. contribute to epigenetically-mediated gene expression changes in host cells by multiple mechanisms.

TRAIL and EGFR Pathways Targeting microRNAs are Predominantly Regulated in Human Diabetic Nephropathy

BACKGROUND

Unbiased microRNA profiling of renal tissue and urinary extracellular vesicles (uEVs) from diabetic nephropathy (DN) subjects may unravel novel targets with diagnostic and therapeutic potential. Here we used the miRNA profile of uEVs and renal biopsies from DN subjects available on the GEO database.

METHODS

The miR expression profiles of kidney tissue (GSE51674) and urinary exosomes (GSE48318) from DN and control subjects were obtained by GEO2R tools from Gene Expression Omnibus (GEO) databases. Differentially expressed miRNAs in DN samples, relative to controls, were identified using a bioinformatic pipeline. Targets of miRs commonly regulated in both sample types were predicted by miRWalk, followed by functional gene enrichment analysis. Gene targets were identified by MiRTarBase, TargetScan and MiRDB.

RESULTS

Eight miRs, including let-7c, miR-10a, miR-10b and miR-181c, were significantly regulated in kidney tissue and uEVs in DN subjects versus controls. The top 10 significant pathways targeted by these miRs included TRAIL, EGFR, Proteoglycan syndecan, VEGF and Integrin Pathway. Gene target analysis by miRwalk upon validation using ShinyGO 70 targets with significant miRNA-mRNA interaction.

CONCLUSION

In silico analysis showed that miRs targeting TRAIL and EGFR signaling are predominately regulated in uEVs and renal tissue of DN subjects. After wet-lab validation, the identified miRstarget pairs may be explored for their diagnostic and/or therapeutic potential in diabetic nephropathy.

Formononetin Attenuates Renal Tubular Injury and Mitochondrial Damage in Diabetic Nephropathy Partly via Regulating Sirt1/PGC-1α Pathway

Mitochondrial abnormality is one of the main factors of tubular injury in diabetic nephropathy (DN). Formononetin (FMN), a novel isoflavonoid isolated from Astragalus membranaceus, has diverse pharmacological activities. However, the beneficial effects of FMN on renal tubular impairment and mitochondrial dysfunction in DN have yet to be studied. In this study, we performed in vivo tests in Streptozotocin (STZ) -induced diabetic rats to explore the therapeutic effects of FMN on DN. We demonstrated that FMN could ameliorate albuminuria and renal histopathology. FMN attenuated renal tubular cells apoptosis, mitochondrial fragmentation and restored expression of mitochondrial dynamics-associated proteins, such as Drp1, Fis1 and Mfn2, as well as apoptosis-related proteins, such as Bax, Bcl-2 and cleaved-caspase-3. Moreover, FMN upregulated the protein expression of Sirt1 and PGC-1α in diabetic kidneys. In vitro studies further demonstrated that FMN could inhibit high glucose-induced apoptosis of HK-2 cells. FMN also reduced the production of mitochondrial superoxide and alleviated mitochondrial membrane potential (MMP) loss. Furthermore, FMN partially restored the protein expression of Drp1, Fis1 and Mfn2, Bax, Bcl-2, cleaved-caspase-3, Sirt1 and PGC-1α in HK-2 cells exposure to high glucose. In conclusion, FMN could attenuate renal tubular injury and mitochondrial damage in DN partly by regulating Sirt1/PGC-1α pathway.

Hirudin, a thrombin inhibitor, attenuates TGF-β-induced fibrosis in renal proximal tubular epithelial cells by inhibition of protease-activated receptor 1 expression via S1P/S1PR2/S1PR3 signaling

Renal interstitial fibrosis (RIF) is the final common outcome of numerous chronic kidney diseases, contributing to end-stage renal disease. Hirudin, a thrombin inhibitor, has attracted increased attention as a potential treatment approach for renal fibrosis. The present study aimed to investigate the molecular mechanism underlying the effect of hirudin on fibrosis in renal proximal tubular epithelial cells. An in vivo mouse RIF model established using unilateral ureteral obstruction (UUO) and an in vitro of RIF using the renal tubular epithelial cell line HK-2 treated with TGF-β were used. Expressions of sphingosine-1-phosphate (S1P) receptors (S1PR)1-4 and protease-activated receptor 1 (PAR1) were measured by reverse transcription-quantitative PCR and western blotting in mice with UUO and TGF-β induced HK-2 cells. Western blotting was used to detect the expression of N-cadherin, Slug, E-cadherin, Collagen IV, fibronectin, MMP9 and monocyte chemoattractant protein-1. Immunofluorescence staining was conducted to measure α-SMA level expression. The results demonstrated that the expression levels of S1PR1, S1PR2, S1PR3, S1PR4 and PAR1 were upregulated in both TGF-β-induced HK-2 cells and renal tissues from mice with unilateral ureteral ligation. Notably, hirudin inhibited TGF-β-induced PAR1, S1PR2 and S1PR3 upregulation in both HK-2 cells and renal tissues. Additionally, the inhibition of S1PR2 and S1PR3 resulted in PAR1 downregulation. Furthermore, treatment with S1P and PAR1 agonists abolished the effect of hirudin on the expression of EMT, fibrosis-related proteins and monocyte chemoattractant protein 1. In conclusion, hirudin attenuated TGF-β-induced fibrosis in proximal renal tubular epithelial HK-2 cells by inhibiting PAR1 expression via the S1P/S1PR2/S1PR3 signaling pathway. Therefore, hirudin may be considered as a promising therapeutic agent for RIF.

FOXO1-Mediated Downregulation of RAB27B Leads to Decreased Exosome Secretion in Diabetic Kidneys

Exosomes have been implicated in diabetic kidney disease (DKD), but the regulation of exosomes in DKD is largely unknown. Here, we have verified the decrease of exosome secretion in DKD and unveiled the underlying mechanism. In Boston University mouse proximal tubule (BUMPT) cells, high-glucose (HG) treatment led to a significant decrease in exosome secretion, which was associated with specific downregulation of RAB27B, a key guanosine-5'-triphosphatase in exosome secretion. Overexpression of RAB27B restored exosome secretion in HG-treated cells, suggesting a role of RAB27B downregulation in the decrease of exosome secretion in DKD. To understand the mechanism of RAB27B downregulation, we conducted bioinformatics analysis that identified FOXO1 binding sites in the Rab27b gene promoter. Consistently, HG induced phosphorylation of FOXO1 in BUMPT cells, preventing FOXO1 accumulation and activation in the nucleus. Overexpression of nonphosphorylatable, constitutively active FOXO1 led to the upregulation of RAB27B and an increase in exosome secretion in HG-treated cells. In vivo, compared with normal mice, diabetic mice showed increased FOXO1 phosphorylation, decreased RAB27B expression, and reduced exosome secretion. Collectively, these results unveil the mechanism of exosome dysfunction in DKD where FOXO1 is phosphorylated and inactivated in DKD, resulting in RAB27B downregulation and the decrease of exosome secretion.

Cilomilast Ameliorates Renal Tubulointerstitial Fibrosis by Inhibiting the TGF-β1-Smad2/3 Signaling Pathway

Background: Renal tubulointerstitial fibrosis is the key pathological feature in chronic kidney diseases (CKDs) with no satisfactory therapies in clinic. Cilomilast is a second-generation, selective phosphodiesterase-4 inhibitor, but its role in renal tubulointerstitial fibrosis in CKD remains unclear.

Material and Methods: Cilomilast was applied to the mice with unilateral ureteric obstruction (UUO) and renal fibroblast cells (NRK-49F) stimulated by TGF-β1. Renal tubulointerstitial fibrosis and inflammation after UUO or TGF-β1 stimulation were examined by histology, Western blotting, real-time PCR and immunohistochemistry. KIM-1 and NGAL were detected to evaluate tubular injury in UUO mice.

Results:In vivo, immunohistochemistry and western blot data demonstrated that cilomilast treatment inhibited extracellular matrix deposition, profibrotic gene expression, and the inflammatory response. Furthermore, cilomilast prevented tubular injury in UUO mice, as manifested by reduced expression of KIM-1 and NGAL in the kidney. In vitro, cilomilast attenuated the activation of fibroblast cells stimulated by TGF-β1, as shown by the reduced expression of fibronectin, α-SMA, collagen I, and collagen III. Cilomilast also inhibited the activation of TGF-β1-Smad2/3 signaling in TGF-β1-treated fibroblast cells.

Conclusion: The findings of this study suggest that cilomilast is protective against renal tubulointerstitial fibrosis in CKD, possibly through the inhibition of TGF-β1-Smad2/3 signaling, indicating the translational potential of this drug in treating CKD.

Inhibition of ROCK2 alleviates renal fibrosis and the metabolic disorders in the proximal tubular epithelial cells

Non-specific inhibition of Rho-associated kinases (ROCKs) alleviated renal fibrosis in the unilateral ureteral obstruction (UUO) model, while genetic deletion of ROCK1 did not affect renal pathology in mice. Thus, whether ROCK2 plays a role in renal tubulointerstitial fibrosis needs to be clarified. In the present study, a selective inhibitor against ROCK2 or genetic approach was used to investigate the role of ROCK2 in renal tubulointerstitial fibrosis. In the fibrotic kidneys of chronic kidney diseases (CKDs) patients, we observed an enhanced expression of ROCK2 with a positive correlation with interstitial fibrosis. In mice, the ROCK2 protein level was time-dependently increased in the UUO model. By treating CKD animals with KD025 at the dosage of 50 mg/kg/day via intraperitoneal injection, the renal fibrosis shown by Masson's trichrome staining was significantly alleviated along with the reduced expression of fibrotic genes. In vitro, inhibiting ROCK2 by KD025 or ROCK2 knockdown/knockout significantly blunted the pro-fibrotic response in transforming growth factor-β1 (TGF-β1)-stimulated mouse renal proximal tubular epithelial cells (mPTCs). Moreover, impaired cellular metabolism was reported as a crucial pathogenic factor in CKD. By metabolomics analysis, we found that KD025 restored the metabolic disturbance, including the impaired glutathione metabolism in TGF-β1-stimulated tubular epithelial cells. Consistently, KD025 increased antioxidative stress enzymes and nuclear erythroid 2-related factor 2 (Nrf2) in fibrotic models. In addition, KD025 decreased the infiltration of macrophages and inflammatory response in fibrotic kidneys and blunted the activation of macrophages in vitro. In conclusion, inhibition of ROCK2 may serve as a potential novel therapy for renal tubulointerstitial fibrosis in CKD.

DsbA-L mediated renal tubulointerstitial fibrosis in UUO mice

Recent studies have reported that upregulation of disulfide-bond A oxidoreductase-like protein (DsbA-L) prevented lipid-induced renal injury in diabetic nephropathy (DN). However, the role and regulation of proximal tubular DsbA-L for renal tubulointerstitial fibrosis (TIF) remains unclear. In current study, we found that a proximal tubules-specific DsbA-L knockout mouse (PT-DsbA-L-KO) attenuated UUO-induced TIF, renal cell apoptosis and inflammation. Mechanistically, the DsbA-L interacted with Hsp90 in mitochondria of BUMPT cells which activated the signaling of Smad3 and p53 to produce connective tissue growth factor (CTGF) and then resulted in accumulation of ECM of BUMPT cells and mouse kidney fibroblasts. In addition, the progression of TIF caused by UUO, ischemic/reperfusion (I/R), aristolochic acid, and repeated acute low-dose cisplatin was also alleviated in PT-DsbA-L-KO mice via the activation of Hsp90 /Smad3 and p53/CTGF axis. Finally, the above molecular changes were verified in the kidney biopsies from patients with obstructive nephropathy (Ob). Together, these results suggest that DsbA-L in proximal tubular cells promotes TIF via activation of the Hsp90 /Smad3 and p53/CTGF axis.

DsbA-L upregulation prevents lipid-induced renal injury in diabetic nephropathy. Here, the authors show that DsbA-L knockout attenuates tubulointerstitial fibrosis in mice, and show that this occurs via activation of Smad3 and p53, which result in modulation of CTGF, a regulator of kidney fibrosis.

Sitagliptin ameliorates renal tubular injury in diabetic kidney disease via STAT3-dependent mitochondrial homeostasis through SDF-1α/CXCR4 pathway

Mitochondrial abnormalities play critical roles in diabetic tubular injury progression. Dipeptidyl peptidase-4 (DPP4) inhibitors are widely used antihyperglycemic agents that exert renal protective and positive effects against mitochondrial dysfunction in diabetic kidney disease (DKD). However, their underlying mechanism remains unclear. In this study, DPP4 upregulation, mitochondrial fragmentation, and altered mitochondrial dynamics-associated protein expression were observed in the tubules of DBA2/J (D2) diabetic mice with unilateral nephrectomy and in albumin-stimulated tubular cells. The inhibition of DPP4 by sitagliptin (Sita) ameliorated these mitochondrial perturbations both in vivo and in vitro, whereas DPP4 overexpression aggravated mitochondrial fusion-fission disorder and tubular cell injury in albumin-treated HK-2 cells. Downstream of DPP4, the SDF-1α/CXCR4 pathway was significantly suppressed in diabetic tubules. After Sita treatment, this signaling pathway was restored, and the mitochondrial dynamics was improved. Furthermore, a direct interaction between STAT3 and OPA1 was found in the mitochondria of tubular cells, and this effect was weakened by overloading albumin and by CXCR4 siRNA treatment, suggesting a possible link between DPP4-mediated SDF-1α/CXCR4/STAT3 signaling and mitochondrial dysfunction in diabetic tubular cells. The results suggest that a novel mechanism links the DPP4 enzyme to impaired mitochondrial dynamics homeostasis during tubular injury in DKD and highlight that the SDF-1α/CXCR4/STAT3 signaling pathway could become a potential target for managing DKD.

miR-214 represses mitofusin-2 to promote renal tubular apoptosis in ischemic acute kidney injury

Disruption of mitochondrial dynamics is an important pathogenic event in both acute and chronic kidney diseases, but the underlying mechanism remains poorly understood. Here, we report the regulation of mitofusin-2 (Mfn2; a key mitochondrial fusion protein) by microRNA-214 (miR-214) in renal ischemia-reperfusion that contributes to mitochondrial fragmentation, renal tubular cell death, and ischemic acute kidney injury (AKI). miR-214 was induced, whereas Mfn2 expression was decreased, in mouse ischemic AKI and cultured rat kidney proximal tubular cells (RPTCs) following ATP depletion treatment. Overexpression of miR-214 decreased Mfn2. Conversely, inhibition of miR-214 with anti-miR-214 prevented Mfn2 downregulation in RPTCs following ATP depletion. Anti-miR-214 further ameliorated mitochondrial fragmentation and apoptosis, whereas overexpression of miR-214 increased apoptosis, in ATP-depleted RPTCs. To test regulation in vivo, we established a mouse model with miR-214 specifically deleted from kidney proximal tubular cells (PT-miR-214-/-). Compared with wild-type mice, PT-miR-214-/- mice had less severe tissue damage, fewer apoptotic cells, and better renal function after ischemic AKI. miR-214 induction in ischemic AKI was suppressed in PT-miR-214-/- mice, accompanied by partial preservation of Mfn2 in kidneys. These results unveil the miR-214/Mfn2 axis that contributes to the disruption of mitochondrial dynamics and tubular cell death in ischemic AKI, offering new therapeutic targets.

Nicotinamide reduces renal interstitial fibrosis by suppressing tubular injury and inflammation

Renal interstitial fibrosis is a common pathological feature in progressive kidney diseases currently lacking effective treatment. Nicotinamide (NAM), a member of water‐soluble vitamin B family, was recently suggested to have a therapeutic potential for acute kidney injury (AKI) in mice and humans. The effect of NAM on chronic kidney pathologies, including renal fibrosis, is unknown. Here we have tested the effects of NAM on renal interstitial fibrosis using in vivo and in vitro models. In vivo, unilateral urethral obstruction (UUO) induced renal interstitial fibrosis as indicated Masson trichrome staining and expression of pro‐fibrotic proteins, which was inhibited by NAM. In UUO, NAM suppressed tubular atrophy and apoptosis. In addition, NAM suppressed UUO‐associated T cell and macrophage infiltration and induction of pro‐inflammatory cytokines, such as TNF‐α and IL‐1β. In cultured mouse proximal tubule cells, NAM blocked TGF–β‐induced expression of fibrotic proteins, while it marginally suppressed the morphological changes induced by TGF‐β. NAM also suppressed the expression of pro‐inflammatory cytokines (eg MCP‐1 and IL‐1β) during TGF‐β treatment of these cells. Collectively, the results demonstrate an anti‐fibrotic effect of NAM in kidneys, which may involve the suppression of tubular injury and inflammation.