Corin protects against acute kidney injury in mice through anti-inflammatory effects

Corin is a type II transmembrane serine protease mainly expressed in the heart. Recently, corin was detected in the kidney and was reported to be associated with multiple kidney diseases. To date, its effect on acute kidney injury (AKI) has not been clarified. Here, we found that corin was constitutively expressed in renal tubules, especially in proximal and distal tubular epithelial cells. The expression of corin was dramatically reduced in ischemia/reperfusion injury (IRI)-induced AKI mouse model and oxygen-glucose deprivation (OGD)-induced human proximal tubular epithelial (HK-2) cells injury model, suggesting a potential role of corin in AKI. Corin deficient mice exhibited aggravated renal injury in AKI, as indicated by higher elevation of serum creatinine (SCr) and blood urea nitrogen (BUN), more severe tubular damage, and increased cell death versus wild type mice, demonstrating a protective effect of corin on AKI. In vitro overexpression of corin didn't directly alleviate hypoxia-induced HK-2 cells death, revealing that the protective effect of corin against AKI is not due to direct protection of tubular epithelial cells but may be through indirect protection. Microarray analysis showed enhanced inflammatory chemokines signaling and leukocyte chemotaxis in corin-/- mice after AKI, identifying an important role of corin in halting leukocyte chemotaxis and inflammatory response. Consistently, corin-/- mice after AKI displayed increased tubulointerstitial neutrophils and macrophages infiltration, as well as higher inflammatory mediators in kidneys. Taken together, our study indicates that tubular corin exerts a protective effect against AKI through negative regulation of chemotaxis signaling and inflammation in the kidney.

Sirt1 activation prevents high glucose-induced angiotensin converting enzyme 2 downregulation in renal tubular cells by regulating the TIMP3/ADAM17 pathway

BACKGROUND

Angiotensin converting enzyme 2 (ACE2) exerts renoprotective effects in diabetic kidney disease (DKD) by converting angiotensin (Ang) II into Ang (1-7). Previous studies have demonstrated that ACE2 expression in renal tubules is downregulated in DKD, but the mechanism is not fully understood. Sirtuin-1 (Sirt1) is a protein deacetylase that may regulate the activity of the renin-angiotensin system. The present study investigated the effects of Sirt1 on ACE2 expression under high glucose (HG) conditions and the underlying signaling pathway.

METHODS AND RESULTS

Rats with DKD and NRK-52E cells cultured with HG were employed in this study. Western blotting, immunohistochemistry detection and qRT-PCR were performed for protein and mRNA expression analyses. Rats subjected to DKD displayed downregulated expression of Sirt1 and ACE2 in kidneys. Resveratrol, an activator of Sirt1, restored ACE2 expression and ameliorated renal injuries. Similarly, pharmacological activation of Sirt1 with SRT1720 markedly upregulated ACE2 in NRK-52E cells cultured with HG, while Sirt1 small interfering RNA (siRNA) further suppressed ACE2 expression. In addition, A disintegrin and metalloproteinase (ADAM) 17 was observed to be upregulated, and its inhibitor, tissue inhibitor of metalloproteinase 3 (TIMP3), was downregulated in the kidneys of diabetic rats and NRK-52E cells incubated with HG. The TIMP3/ADAM17 pathway was involved in the regulation of ACE2 expression, as evidenced by decreased ACE2 expression levels after TIMP3-siRNA pretreatment. SRT1720 ameliorated the imbalance of TIMP3/ADAM17 induced by HG and consequently enhanced the expression of ACE2. Notably, the above effect of SRT1720 on ACE2 was interrupted by TIMP3-siRNA.

CONCLUSIONS

Our findings suggest that Sirt1 activation may prevent HG-induced downregulation of renal tubular ACE2 by modulating the TIMP3/ADAM17 pathway. Sirt1 stimulation might be a potential strategy for the treatment of DKD.

Proximal tubule-derived exosomes contribute to mesangial cell injury in diabetic nephropathy via miR-92a-1-5p transfer

BACKGROUND

Diabetic nephropathy (DN) is an increasing threat to human health and regarded to be the leading cause of end-stage renal disease worldwide. Exosomes delivery may play a key role in cross-talk among kidney cells and the progression of DN. However, the mechanisms underlying exosomes in DN remain unclear.

METHODS

The cross-disciplinary study, including in vivo, in vitro, and human studies was conducted to explore the cross-talk between proximal tubular epithelial cells (PTECs) and mesangial cells (MCs) in DN. We purified exosome from PTECs treated with high glucose and db/db mice and assessed their influences in the pathologic change of MCs and downstream signal pathway. Healthy individuals and type 2 diabetic patients were enrolled to examine the role of exosomes in clinical applications.

RESULTS

High glucose stimulated PTECs to secrete exosomal miR-92a-1-5p, which was taken-up by glomerular MCs, inducing myofibroblast transdifferentiation (MFT) in vitro and in vivo. PTEC-released exosomal 92a-1-5p decreased reticulocalbin-3 expression, leading to endoplasmic reticulum (ER) stress by downregulating genes essential for ER homeostasis including calreticulin and mesencephalic astrocyte-derived neurotrophic factor. Treatment with miR-92a-1-5p inhibitor ameliorated kidney damage in db/db mice with DN. Urinary miR-92a-1-5p could predict kidney injury in type 2 diabetic patients.

CONCLUSIONS

PTEC-derived exosomal miR-92a-1-5p modulated the kidney microenvironment in vivo and in vitro models, which altered ER stress and MFT in MCs resulting in DN progression. Further blocking miR-92a-1-5p epigenetic regulatory network could be a potential therapeutic strategy to prevent the progression of DN. Video Abstract.

Sirtuin-1 attenuates cadmium-induced renal cell senescence through p53 deacetylation

Cadmium (Cd), the common environmental pollutant, primarily targets at renal proximal tubules and induces nephrotoxicity. Cellular senescence, a phenomenon of cell growth arrest and a characteristics of maladaptive cell self-repair, is associated with renal disease progression. However, whether and how Cd induces renal tubular cells premature senescence is unknown. In our study, we found that Cd induced kidney damage and dysfunctions, which correlated with exacerbated tubular cell senescence, evidenced by increased senescence-associated β-galactosidase activity, the upregulated protein expression of p53 and p21^Waf1/Cip1 proteins, and elevated expression and secretion of cytokines in human proximal tubular epithelial HK-2 cells in vitro and in Cd-treated mice in vivo. Moreover, a S-phase arrest and decrease in Edu positive rate were found in Cd-treated HK-2 cells. Mechanistically, Cd suppressed the expression and activity of Sirtuin-1 (SIRT1), an anti-senescence deacetylase, resulting in the accumulation of acetylated p53 and upregulation of p21^Waf1/Cip1. Activation of SIRT1 significantly abolished Cd-induced premature senescence and S-phase arrest. Finally, silencing p21^Waf1/Cip1 efficiently delayed premature senescence and recovered cell cycle progression. These findings indicate that Cd promotes tubular cells senescence and impairs tubular cells regeneration, resulting in kidney dysfunctions, which could be ameliorated by SIRT1 activation.

Proximal tubular epithelia-specific transcriptomics of diabetic mice treated with dapagliflozin

Based on recent clinical trials using sodium-glucose co-transporter 2 inhibitor (SGLT2i) demonstrating the significant improvement of outcomes of diabetic kidney disease (DKD), the paradigm shift from “glomerulocentric” to “tubule centric” pathophysiology in DKD progression has been highlighted. Several responsible mechanisms for renoprotective effects by SGLT2i have been proposed recently, but the changes in proximal tubule-specific gene expression by SGLT2i in diabetic mice have not been elucidated. We report the analysis of the proximal tubular-specific pathway, demonstrating the downregulation of oxidative phosphorylation in dapagliflozin-treated db/db mice, a type 2 diabetic model. After 8-week treatment of dapagliflozin for db/db mice having a proximal tubule-specific tdTomato reporter, tdTomato-positive cells were isolated by FACS. Pathway analysis of RNA sequencing of isolated tubular epithelia revealed that oxidative phosphorylation was downregulated in dapagliflozin-treated mice. However, depletion of renal tissue ATP content in db/db mice was ameliorated by dapagliflozin administration. Pimonidazole staining demonstrated renal cortical tissue hypoxia in db/db mice, which was improved by dapagliflozin administration. This study suggests that dapagliflozin can ameliorate the excessive oxygen and ATP consumption, and subsequent tissue hypoxia in the diabetic kidney, which may explain, in part, the responsible mechanisms of the renoprotective effects of dapagliflozin.

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Oxidative phosphorylation is downregulated by dapagliflozin in the proximal tubules of diabetic kidneys.

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Renal tissue ATP content increased in dapagliflozin-treated diabetic mice.

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Dapagliflozin improved renal cortical hypoxia in type 2 diabetic mice.

Inhibition of fibroblast growth factor-inducible 14 attenuates experimental tubulointerstitial fibrosis and profibrotic factor expression of proximal tubular epithelial cells

BACKGROUND AND AIM

As a proinflammatory cytokine, tumor necrosis factor-like weak inducer of apoptosis (TWEAK) participates in the progression of renal fibrosis by binding to its receptor, fibroblast growth factor-inducible 14 (Fn14). However, the effect of Fn14 inhibition on tubular epithelial cell-mediated tubulointerstitial fibrosis remains unclear. This study aimed to elucidate the role of TWEAK/Fn14 interaction in the development of experimental tubulointerstitial fibrosis as well as the protective effect of Fn14 knockdown on proximal tubular epithelial cells.

METHODS

A murine model of unilateral ureteral obstruction was constructed in both wild-type and Fn14-deficient BALB/c mice, followed by observation of the tubulointerstitial pathologies.

RESULTS

Fn14 deficiency ameliorated the pathological changes, including inflammatory cell infiltration and cell proliferation, accompanied by reduced production of profibrotic factors and extracellular matrix deposition. In vitro experiments showed that TWEAK dose-dependently enhanced the expression of collagen I, fibronectin, and α-smooth muscle actin in proximal tubular epithelial cells. Interestingly, TWEAK also upregulated the expression levels of Notch1/Jagged1. Fn14 knockdown and Notch1/Jagged1 inhibition also mitigated the effect of TWEAK on these cells.

CONCLUSIONS

In conclusion, TWEAK/Fn14 signals contributed to tubulointerstitial fibrosis by acting on proximal tubular epithelial cells. Fn14 inhibition might be a therapeutic strategy for protecting against renal interstitial fibrosis.

Baicalin attenuates fibrogenic process in human renal proximal tubular cells (HK-2) exposed to diabetic milieu

AIMS

Baicalin, a flavonoid glycoside substance extracted from Scutellaria baicalensis Georgi, has been shown to exhibit multiple therapeutic properties owing to its anti-inflammatory effect. Diabetes is characterized by chronic hyperglycemia, inflammation and oxidative stress, which promote renal fibrosis and kidney failure. Although anti-fibrogenic effects of baicalin in lung and liver have been reported previously, no study has investigated its roles in renal fibrosis. Here, we demonstrated protective effects of baicalin against fibrogenic process in human kidney proximal tubular epithelial cells (HK-2) exposed to diabetic milieu.

MAIN METHODS

To investigate the effects of baicalin on oxidative stress- and inflammation-induced fibrosis in HK-2 cells, protein and gene expressions of NF-κB- and STAT3-associated inflammatory molecules and TGFβ-associated extracellular matrix proteins were examined by western blotting, immunocytochemistry and qRT-PCR. To determine physiological changes of HK-2 exposed to diabetic milieu in response to baicalin, production of cAMP and cGMP and Ca2+ influx were measured.

KEY FINDINGS

Baicalin attenuated oxidative stress- and inflammation-inudced IκB and JAK2 phosphorylations and, subsequent, NF-κB nuclear translocation and STAT3 phosphorylation. Consequently, it markedly reduced transactivation of NF-κB- and STAT3-associated inflammatory genes such as ICAM1, VCAM1, TGFβ, IL1β and MCP1, and protein expression of TGFβ-associated extracellular matrix proteins, such as fibronectin and collagen IV. These effects are, partially, attributed to its regulatory function of intracellular concentration of Ca2+ via interaction with type A γ-aminobutyric acid receptor.

SIGNIFICANCE

This is the first study which investigated anti-fibrogenic effect of baicalin in human kidney cells, and our results highlight a potential therapeutic application of baicalin for diabetic nephropathy.

Iron uptake by ZIP8 and ZIP14 in human proximal tubular epithelial cells

In patients with iron overload disorders, increasing number of reports of renal dysfunction and renal iron deposition support an association between increased iron exposure and renal injury. In systemic iron overload, elevated circulating levels of transferrin-bound (TBI) and non-transferrin-bound iron (NTBI) are filtered to the renal proximal tubules, where they may cause injury. However, the mechanisms of tubular iron handling remain elusive. To unravel molecular renal proximal tubular NTBI and TBI handling, human conditionally immortalized proximal tubular epithelial cells (ciPTECs) were incubated with ⁵⁵Fe as NTBI and fluorescently labeled holo-transferrin as TBI. Ferrous iron importers ZIP8 and ZIP14 were localized in the ciPTEC plasma membrane. Whereas silencing of either ZIP8 or ZIP14 alone did not affect ⁵⁵Fe uptake, combined silencing significantly reduced ⁵⁵Fe uptake compared to control (p < 0.05). Furthermore, transferrin receptor 1 (TfR1) and ZIP14, but not ZIP8, colocalized with early endosome antigen 1 (EEA1). TfR1 and ZIP14 also colocalized with uptake of fluorescently labeled transferrin. Furthermore, ZIP14 silencing decreased ⁵⁵Fe uptake after ⁵⁵Fe-Transferrin exposure (p < 0.05), suggesting ZIP14 could be involved in early endosomal transport of TBI-derived iron into the cytosol. Our data suggest that human proximal tubular epithelial cells take up TBI and NTBI, where ZIP8 and ZIP14 are both involved in NTBI uptake, but ZIP14, not ZIP8, mediates TBI-derived iron uptake. This knowledge provides more insights in the mechanisms of renal iron handling and suggests that ZIP8 and ZIP14 could be potential targets for limiting renal iron reabsorption and enhancing urinary iron excretion in systemic iron overload disorders.

Paricalcitol attenuates indoxyl sulfate-induced apoptosis through the inhibition of MAPK, Akt, and NF-kB activation in HK-2 cells

BACKGROUND/AIMS

Indoxyl sulfate (IS) is a uremic toxin and an important causative factor in the progression of chronic kidney disease. Recently, paricalcitol (19-nor-1,25-dihydroxyvitamin D2) was shown to exhibit protective effects in kidney injury. Here, we investigated the effects of paricalcitol treatment on IS-induced renal tubular injury.

METHODS

The fluorescent dye 2',7'-dichlorofluorescein diacetate was used to measure intracellular reactive oxygen species (ROS) following IS administration in human renal proximal tubular epithelial (HK-2) cells. The effects of IS on cell viability were determined using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assays and levels of apoptosis-related proteins (Bcl-2-associated protein X [Bax] and B-cell lymphoma 2 [Bcl-2]), nuclear factor-κB (NF- κB) p65, and phosphorylation of mitogen-activated protein kinase (MAPK) and protein kinase B (Akt) were determined by semiquantitative immunoblotting. The promoter activity of NF-κB was measured by luciferase assays and apoptosis was determined by f low cytometry of cells stained with f luorescein isothiocyanate-conjugated Annexin V protein.

RESULTS

IS treatment increased ROS production, decreased cell viability and induced apoptosis in HK-2 cells. IS treatment increased the expression of apoptosis-related protein Bax, decreased Bcl-2 expression, and activated phosphorylation of MAPK, NF-κB p65, and Akt. In contrast, paricalcitol treatment decreased Bax expression, increased Bcl-2 expression, and inhibited phosphorylation of MAPK, NF-κB p65, and Akt in HK-2 cells. NF-κB promoter activity was increased following IS, administration and was counteracted by pretreatment with paricalcitol. Additionally, flow cytometry analysis revealed that IS-induced apoptosis was attenuated by paricalcitol treatment, which resulted in decreased numbers of fluorescein isothiocyanate-conjugated Annexin V positive cells.

CONCLUSION

Treatment with paricalcitol inhibited IS-induced apoptosis by regulating MAPK, NF-κB, and Akt signaling pathway in HK-2 cells.

Protective Effects of Pistacia lentiscus L. fruit extract against calcium oxalate monohydrate induced proximal tubular injury

ETHNOPHARMACOLOGICAL RELEVANCE

The world prevalence of kidney stones is increasing and plants are frequently used to treat urolithiasis. Pistacia lentiscus L, a plant which freely grows around the Mediterranean basin areas, is widely used for various pathologies. P. lentiscus has an important impact as it has economical value on top of its pharmacological interest. Decoctions of its aerial parts and/or resin are used to treat kidney stones.

AIM OF THE STUDY

To in vitro assess the potential nephroprotective effect of Pistacia lentiscus ethanolic fruit extract (PLEF) on proximal tubular cells in response to the adhesion of calcium oxalate monohydrate (COM) crystals.

MATERIALS AND METHODS

Human Kidney [HK]-2 cells were incubated with and without COM in the presence or absence of PLEF. Cell viability was measured by the resazurin assay. The expression of E-cadherin was analyzed by PCR. The extracellular production of H₂O₂ was measured by Amplex® Red H₂O₂ Assay. The numbers of detached or non-adherent COM crystals in the presence of PLEF were microscopically captured and counted using ImageJ software. The interaction of PLEF with COM and the effect of PLEF on crystal size were analyzed by flow cytometry. The spectrophotometric measurement of turbidity was performed for assessing the COM concentration.

RESULTS

PLEF incubated with COM was able to increase the cell viability. The decrease of E-cadherin expression after incubation with COM was counteracted by PLEF. Overproduction of H₂O₂ induced by COM was also inhibited by PLEF. Observations using flow cytometry showed that interactions between PLEF and the COM crystals occurred. PLEF was also effective in reducing the particles size and in lowering COM concentration.

CONCLUSION

Our data show that COM tubulotoxicity can be significantly reversed by PLEF -at least in part- via an inhibition of COM crystals adhesion onto the apical membrane. This early beneficial effect of PLEF needs to be further investigated as a useful strategy in nephrolithiasis prevention.

Novel findings of secreted cyclophilin A in diabetic nephropathy and its association with renal protection of dipeptidyl peptidase 4 inhibitor

BACKGROUND

Our previous clinical indicated that urinary cyclophilin A was a good marker for diabetic nephropathy.

METHODS

We used animal and cell models of diabetic nephropathy to examine the role of cyclophilin A in disease progression.

RESULTS

Significantly increased urinary cyclophilin A could be detected in db/db at the 8th week. Linagliptin (3mg/kg/day and 15mg/kg/day) could suppress urinary 8-hydroxy-2'-deoxyguanosine at the 8th and 16th week but only the high dose Linagliption could suppress cyclophilin A at the 8th week. Compared to 8-hydroxy-2'-deoxyguanosine, cyclophilin A was a stronger, earlier, and more sensitive marker. Immunohistochemical staining for cyclophilin A was also positive for db/db. In cell studies, oxidative stress and hyperglycemia could stimulate MES-13 and HK-2 cells to secrete cyclophilin A. Hyperglycemia stimulated HK-2 cells to secrete TGFβ1, which caused secretion of cyclophilin A. The secreted cyclophilin A further stimulated CD 147 to move outward from cytosol onto cell membrane in confocal microscopy, which was associated with the p38 MAPK pathway in the downstream.

CONCLUSIONS

Secreted cyclophilin A may play an important role in diabetic nephropathy in the mouse model and is associated with TGFβ1, CD 147, and the p38 MAPK pathway.

Activation of the Nlrp3 inflammasome by mitochondrial reactive oxygen species: a novel mechanism of albumin-induced tubulointerstitial inflammation

Albuminuria is not only an important marker of chronic kidney disease but also a crucial contributor to tubulointerstitial inflammation (TIF). In this study, we determined whether activation of the Nlrp3 inflammasome is involved in albuminuria induced-TIF and the underlying mechanisms of inflammasome activation by mitochondrial reactive oxygen species (mROS). We established an albumin-overload induced rat nephropathy model characterised by albuminuria, renal infiltration of inflammatory cells, tubular dilation and atrophy. The renal expression levels of the Nlrp3 inflammasome, IL-1β and IL-18 were significantly increased in this animal model. In vitro, albumin time- and dose-dependently increased the expression levels of the Nlrp3 inflammasome, IL-1β and IL18. Moreover, the silencing of the Nlrp3 gene or the use of the caspase-1 inhibitor Z-VAD-fmk significantly attenuated the albumin-induced increase in IL-1β and IL-18 expression in HK2 cells. In addition, mROS generation was elevated by albumin stimulation, whereas the ROS scavenger N-acetyl-l-cysteine (NAC) inhibited Nlrp3 expression and the release of IL-1β and IL-18. In kidney biopsy specimens obtained from patients with IgA nephropathy, Nlrp3 expression was localised to the proximal tubular epithelial cells, and this result is closely correlated with the extent of proteinuria and TIF. In summary, this study demonstrates that albuminuria may serve as an endogenous danger-associated molecular pattern (DAMP) that stimulates TIF via the mROS-mediated activation of the cytoplasmic Nlrp3 inflammasome.