Regulator of calcineurin 1 deletion attenuates mitochondrial dysfunction and apoptosis in acute kidney injury through JNK/Mff signaling pathway.

Ischemia-reperfusion (I/R) induced acute kidney injury (AKI), characterized by excessive mitochondrial damage and cell apoptosis, remains a clinical challenge. Recent studies suggest that regulator of calcineurin 1 (RCAN1) regulates mitochondrial function in different cell types, but the underlying mechanisms require further investigation. Herein, we aim to explore whether RCAN1 involves in mitochondrial dysfunction in AKI and the exact mechanism. In present study, AKI was induced by I/R and cisplatin in RCAN1flox/flox mice and mice with renal tubular epithelial cells (TECs)-specific deletion of RCAN1. The role of RCAN1 in hypoxia-reoxygenation (HR) and cisplatin-induced injury in human renal proximal tubule epithelial cell line HK-2 was also examined by overexpression and knockdown of RCAN1. Mitochondrial function was assessed by transmission electron microscopy, JC-1 staining, MitoSOX staining, ATP production, mitochondrial fission and mitophagy. Apoptosis was detected by TUNEL assay, Annexin V-FITC staining and Western blotting analysis of apoptosis-related proteins. It was found that protein expression of RCAN1 was markedly upregulated in I/R- or cisplatin-induced AKI mouse models, as well as in HR models in HK-2 cells. RCAN1 deficiency significantly reduced kidney damage, mitochondrial dysfunction, and cell apoptosis, whereas RCAN1 overexpression led to the opposite phenotypes. Our in-depth mechanistic exploration demonstrated that RCAN1 increases the phosphorylation of mitochondrial fission factor (Mff) by binding to downstream c-Jun N-terminal kinase (JNK), then promotes dynamin related protein 1 (Drp1) migration to mitochondria, ultimately leads to excessive mitochondrial fission of renal TECs. In conclusion, our study suggests that RCAN1 could induce mitochondrial dysfunction and apoptosis by activating the downstream JNK/Mff signaling pathway. RCAN1 may be a potential therapeutic target for conferring protection against I/R- or cisplatin-AKI.

RCAN1.4 mediates high glucose-induced matrix production by stimulating mitochondrial fission in mesangial cells.

High glucose (HG)-induced mitochondrial dynamic changes and oxidative damage are closely related to the development and progression of diabetic kidney disease (DKD). Recent studies suggest that regulators of calcineurin 1 (RCAN1) is involved in the regulation of mitochondrial function in different cell types, so we investigate the role of RCAN1 in mitochondrial dynamics under HG ambience in rat glomerular mesangial cells (MCs). MCs subjected to HG exhibited an isoform-specific up-regulation of RCAN1.4 at both mRNA and protein levels. RCAN1.4 overexpression induced translocation of Dynamin related protein 1 (Drp1) to mitochondria, mitochondrial fragmentation and depolarization, accompanied by increased matrix production under normal glucose and HG ambience. In contrast, decreasing the expression of RCAN1.4 by siRNA inhibited HG-induced mitochondrial fragmentation and matrix protein up-regulation. Moreover, both mitochondrial fission inhibitor Mdivi-1 and Drp1 shRNA prevented RCAN1.4-induced fibronectin up-regulation, suggesting that RCAN1.4-induced matrix production is dependent on its modulation of mitochondrial fission. Although HG-induced RCAN1.4 up-regulation was achieved by activating calcineurin, RCAN1.4-mediated mitochondrial fragmentation and matrix production is independent of calcineurin activity. These results provide the first evidence for the HG-induced RCAN1.4 up-regulation involving increased mitochondrial fragmentation, leading to matrix protein up-regulation.

Parathyroid hormone-related protein induces fibronectin up-regulation in rat mesangial cells through reactive oxygen species/Src/EGFR signaling.

Parathyroid hormone-related protein (PTHrP) is known to be up-regulated in both glomeruli and tubules in patients with diabetic kidney disease (DKD), but its role remains unclear. Previous studies show that PTHrP-induced hypertrophic response in mesangial cells (MCs) and epithelial-mesenchymal transition (EMT) in tubuloepithelial cells can be mediated by TGF-ß1. In the present study, although long-term PHTrP (1-34) treatment increased the mRNA and protein level of TGF-ß1 in primary rat MCs, fibronectin up-regulation occurred earlier, suggesting that fibronectin induction is independent of TGF-ß1/Smad signaling. We thus evaluated the involvement of epidermal growth factor receptor (EGFR) signaling and found that nicotinamide adenine dinucleotide phosphate oxidase-derived reactive oxygen species mediates PTHrP (1-34)-induced Src kinase activation. Src phosphorylates EGFR at tyrosine 845 and then transactive EGFR. Subsequent PI3K activation mediates Akt and ERK1/2 activation. Akt and ERK1/2 discretely lead to excessive protein synthesis of fibronectin. Our study thus demonstrates the new role of PTHrP in fibronectin up-regulation for the first time in glomerular MCs. These data also provided new insights to guide development of therapy for glomerular sclerosis.

Src-mediated ligand release-independent EGFR transactivation involves TGF-ß-induced Smad3 activation in mesangial cells.

A great deal of evidence highlighted the pathophysiologic importance of TGF-ß1/Smad3 pathway in masangial extracellular matrix (ECM) accumulation, but some alternative signaling pathways are also involved. TGF-ß was shown recently to induce rapid and transient epidermal-like growth factor receptor (EGFR) transactivation and subsequent fibronectin expression via heparin-binding epidermal-like growth factors (HB-EGF) release and binding in mesangial cells, which is independent of Smad2 activation. However, whether TGF-ß could induce persistent EGFR transactivation remains to be identified. The present study demonstrates that in addition to transient EGFR transactivation, TGF-ß1 can also induce continuous EGFR transactivation by a non-ligand-dependent pathway in rat mesangial cells. This sustained EGFR transactivation is mainly due to Src kinase-mediated persistent EGFR tyrosine phosphorylation at Y845 rather than Y1173. TGF-ß1-induced early Smad3 phosphorylation is independent of transient EGFR transactivation and ERK1/2 activation initiated by HB-EGF release, whereas Src-mediated chronic EGFR transactivation and ERK1/2 activation participate in Smad3 activation in a relatively modest and delayed manner. Therefore, the present study further clarifies the mechanisms of EGFR transactivation in the TGF-ß-initiated ECM upregulation and raises the possibility that targeting EGFR may provide a viable alternative strategy for inhibiting TGF-ß in chronic kidney disease.

Dual roles of parathyroid hormone related protein in TGF-ß1 signaling and fibronectin up-regulation in mesangial cells.

Little is known about the cross-talk between parathyroid hormone (PTH) related protein (PTHrP) and TGF-ß1 in mesangial cells (MCs). Our results showed that PTHrP treatment (≤3 h) induced internalization of PTH1R (PTH/PTHrP receptor)-TßRII (TGF-ß type 2 receptor) complex and suppressed TGF-ß1-mediated Smad2/3 activation and fibronectin (FN) up-regulation. However, prolonged PTHrP treatment (12-48 h) failed to induce PTH1R-TßRII association and internalization. Total protein levels of PTH1R and TßRII were unaffected by PTHrP treatment. These results suggest that internalization of PTH1R and TßRII after short PTHrP treatment might not lead to their proteolytic destruction, allowing the receptors to be recycled back to the plasma membrane during prolonged PTHrP exposure. Receptor re-expression at the cell surface allows PTHrP to switch from its initial inhibitory effect to promote induction of FN. Our study thus demonstrates the dual roles of PTHrP on TGF-ß1 signaling and FN up-regulation for the first time in glomerular MCs. These data also provided new insights to guide development of therapy for diabetic kidney disease (DKD).

Parathyroid hormone-related peptide (1-34) reduces alveolar bone loss in type 1 diabetic rats.

OBJECTIVE: To investigate the role of parathyroid hormone related protein (PTHrP) in diabetic periodontitis. METHODS: After injected with 55mg/kg streptozotocin, diabetic rats were treated subcutaneously with low-dose (40µg/kg, once daily for 5days per week), middle-dose (80µg/kg) or high-dose (160µg/kg) PTHrP(1-34) peptide. Treatment continued for 12 weeks. Changes in periodontal tissues were confirmed by micro-computerized tomography assay and H&E analysis. We used tartrate resistant acid phosphatase (TRAP) staining to identify osteoclast cells. The expression of TNF-α, IL-1ß and IL-6 was assessed by immunohistochemistry and Western blot. RESULTS: Tooth-supporting structure loss was observed in periodontal tissues of diabetic rats. PTHrP (1-34) attenuated alveolar bone loss, especially in the middle-dose and high-dose group. Whereas TNF-α, IL-1ß and IL-6 protein levels were increased in the diabetic gingival tissues, PTHrP (1-34) treatment inhibited the increase of IL-1ß and IL-6, but had no effect on TNF-α. CONCLUSION: Type 1 diabetes increased the susceptibility to periodontal disease. Intermittent administration of PTHrP (1-34) exhibited an inhibitory effect on alveolar bone resorption and the gingival inflammation in periodontal tissues of diabetic rats.

Parathyroid hormone inhibits TGF-ß/Smad signaling and extracellular matrix proteins upregulation in rat mesangial cells.

Accumulation of glomerular matrix is a hallmark of diabetic nephropathy. TGF-ß1 is a major cytokine mediating the production of various extracellular matrix (ECM) proteins. The aim of this study is to elucidate the effect of parathyroid hormone (PTH) on TGF-ß1 and high glucose-induced upregulation of ECM proteins in primary mesangial cells from Sprague-Dawley rat. The results showed that PTH pretreatment prevented TGF-ß1 and high glucose-induced Smad2/3 phosphorylation and consequent upregulation of fibronectin and type IV collagen within 4 h. The inhibitory effect of PTH is due to PTH1R activation, because knocking down PTH 1 receptor (PTH1R) by RNA interference reversed the inhibitory effect of PTH on TGF-ß1 and high glucose-induced Smad2/3 phosphorylation and ECM upregulation. Furthermore, it is found that PTH1R associated with TGF-ß type II receptor (TßR II) and both receptors internalized into the cytoplasm when mesangial cells were stimulated with PTH alone. The internalization of TßR II might reduce the amount of membrane TßR II, attenuate the sensitivity of mesangial cells to TGF-ß1, and therefore inhibit Smad activation and ECM upregulation induced by TGF-ß1 and high glucose. Further studies are needed to know whether the endocytic receptors are to be degraded or recycled, and evaluate the role of PTH in TGF-ß1 signaling more comprehensively.

Akt and RhoA activation in response to high glucose require caveolin-1 phosphorylation in mesangial cells.

Glomerular matrix accumulation is a hallmark of diabetic renal disease. Serine/threonine kinase PKC-ß1 mediates glucose-induced Akt S473 phosphorylation, RhoA activation, and transforming growth factor (TGF)-ß1 upregulation and finally leads to matrix upregulation in mesangial cells (MCs). It has been reported that glucose-induced PKC-ß1 activation is dependent on caveolin-1 and the presence of intact caveolae in MCs; however, whether activated PKC-ß1 regulates caveolin-1 expression and phosphorylation are unknown. Here, we showed that, although the caveolin-1 protein level had no significant change, the PKC-ß-specific inhibitor LY-333531 blocked caveolin-1 Y14 phosphorylation in high glucose (HG)-treated MCs and in the renal cortex of diabetic rats. The Src-specific inhibitor SU-6656 prevented the HG-induced association between PKC-ß1 and caveolin-1 and PKC-ß1 membrane translocation, whereas PKC-ß1 small interfering RNA failed to block Src activation, indicating that Src kinase is upstream of PKC-ß1 activation. Although LY-333531 blocked PKC-ß1 membrane translocation, it had no effect on the PKC-ß1/caveolin-1 association, suggesting that PKC-ß1 activation requires the interaction of caveolin-1 and PKC-ß1. PKC-ß1-mediated Akt S473 phosphorylation, RhoA activation, and fibronectin upregulation in response to HG were prevented by SU-6656 and nonphosphorylatable mutant caveolin-1 Y14A. In conclusion, Src activation by HG mediates the PKC-ß1/caveolin-1 association and PKC-ß1 activation, which assists in caveolin-1 Y14 phosphorylation by Src kinase. The downstream effects, including Akt S473 phosphorylation, RhoA activation, and fibronectin upregulation, require caveolin-1 Y14 phosphorylation. Caveolin-1 is thus an important mediator of the profibrogenic process in diabetic renal disease.

Involvement of cyclin dependent kinase 5 and its activator p35 in staurosporine-induced apoptosis of cortical neurons.

AIM: To investigate whether cyclin-dependent kinase 5 and its regulatory protein p35 was involved in staurosporine-induced apoptosis of cortical neuronal cultures. METHODS: Primary cerebral cortical neurons were exposed to 300 nmol/L staurosporine. After incubation for different time, morphological alterations were observed with phase-contrast microscopy, fluorescence microscopy, and transmission electron microscopy. DNA fragmentation was detected by agarose gel electrophoresis. The protein levels of Cdk4, p53, Cdk5, and its regulatory protein p35 following staurosporine treatment were measured by Western blotting. The Cdk5 activity was assayed for histone H1 kinase activity by autoradiography. RESULTS: The typical morphological changes of apoptosis were observed and the nuclear DNA fragmentation showed the characteristic "ladder" pattern after the cells were treated by staurosporine. The Cdk5 protein level increased markedly at 3 h and continued to 24 h. The p35 level increased at 3 h after being exposed to staurosporine, and decreased at 12 h. The cleavage of p35 to p25 was also detected at 12 h and increased at 24 h. There was no increase in Cdk5 kinase activity despite the increased cleavage of p35. The protein level of Cdk4 protein increased at 3 h and then decreased gradually from 6 h, but it was still higher than that in the vehicle cultures at 12 h. The p53 level decreased obviously at 3 h after staurosporine treatment and then seemed to increase at 12 h, but remained lower than that of vehicle cultures. CONCLUSION: Staurosporine-induced increase in Cdk5 protein levels and the cleavage of p35 to p25 may contribute to neuronal apoptosis.

Staurosporine induces apoptosis in NG108-15 cells.

AIM: To observe if staurosporine induced apoptosis in NG108-15 cells and its effect on protein expression level of several genes related to apoptosis. METHODS: Phase-contrast microscopy, fluorescence microscopy, and transmission electron microscopy were used to observe staurosporine-induced morphological changes. Agarose gel electrophoresis was used to detect DNA fragmentation. Western blots were used to measure protein expression level of several genes related to apoptosis. RESULTS: Cells treated with staurosporine 0.1 micromol/L showed typical morphological changes of apoptosis. A "ladder" pattern representing fragmentation of DNA into oligonucleosome length fragments was observed after 6 h of staurosporine treatment and sustained until 24 h. The Bax expression increased significantly at 6 h after exposure to staurosporine, peaked at 12 h compared with vehicle cultures, and decreased at 24 h. The Bcl-2 expression increased and reached the highest level at 3 h. It was then decreased gradually but still higher than normal expression level. There was an obvious caspase-3 cleavage at 6 h after exposing the cells to staurosporine. Treatment with staurosporine for 12 h markedly decreased the expression of p53 protein. Cdk5 protein expression did not have obvious changes after the cells were exposed to staurosporine. CONCLUSION: Staurosporine induced apoptotic death in NG108-15 cells. Cells might die via a pathway that is dependent on Bax expression but independent of p53, and caspase-3 cleavage was involved.

[Protective effects of tacrine and donepezil against staurosporine-induced apoptotic death].

AIM: To study whether tacrine and donepezil can prevent cell apoptosis induced by staurosporine in NG108-15 and Hela cell lines. METHODS: MTT assay was used to examine if staurosporine impairs cell metabolism. Phase-contrast and fluorescence microscope were used to examine cell morphological changes. DNA was isolated and electrophoretically separated on 1% agarose gel to observe if there were DNA fragments. Western blot was made to analyse protein levels of anti-apoptotic Bcl-2 and proapoptotic Bax. RESULTS: NG108-15 cells treated with 0.1 mumol.L-1 staurosporine for 12-24 hours exhibited marked cell death and DNA fragmentation. Pre-treatment with 0.1 mmol.L-1 tacrine provided approximately 40% protective effect and resulted in obvious inhibition or delay of DNA fragmentation. Moreover, NG108-15 cells treated with tacrine became elongated and polarized, and showed longer processes than control cells. Pretreatment with 0.1 mmol.L-1 tacrine significantly increased the expression of Bcl-2 protein level and delayed the staurosporine-induced increase of Bax protein expression. However, donepezil did not show any protective effect on the cell impairment induced by staurosporine in NG108-15 cells. In Hela cells 0.1 mumol.L-1 staurosporine also induced significant cell injury, but pretreatment with tacrine and donepezil did not provide any obvious protective effect against this cell damage. CONCLUSION: Donepezil did not provide obvious protective effect against apoptosis, and protective effects of tacrine might not be mediated through AChE inhibition. Protective effects of tacrine against staurosporine-induced injury might be selective to different cells.