Effect of ouabain on myocardial ultrastructure and cytoskeleton during the development of ventricular hypertrophy

Mouse N2a Neuroblastoma Assay: Uncertainties and Comparison with Alternative Cell-Based Assays for Ciguatoxin Detection

The growing concern about ciguatera fish poisoning (CF) due to the expansion of the microorganisms producing ciguatoxins (CTXs) increased the need to develop a reliable and fast method for ciguatoxin detection to guarantee food safety. Cytotoxicity assay on the N2a cells sensitized with ouabain (O) and veratridine (V) is routinely used in ciguatoxin detection; however, this method has not been standardized yet. This study demonstrated the low availability of sodium channels in the N2a cells, the great O/V damage to the cells and the cell detachment when the cell viability is evaluated by the classical cytotoxicity assay and confirmed the absence of toxic effects caused by CTXs alone when using the methods that do not require medium removal such as lactate dehydrogenase (LDH) and Alamar blue assays. Different cell lines were evaluated as alternatives, such as human neuroblastoma, which was not suitable for the CTX detection due to the greater sensitivity to O/V and low availability of sodium channels. However, the HEK293 Nav cell line expressing the α1.6 subunit of sodium channels was sensitive to the ciguatoxin without the sensitization with O/V due to its expression of sodium channels. In the case of sensitizing the cells with O/V, it was possible to detect the presence of the ciguatoxin by the classical cytotoxicity MTT method at concentrations as low as 0.0001 nM CTX3C, providing an alternative cell line for the detection of compounds that act on the sodium channels.

The role of profilin-1 in cardiovascular diseases

Dynamic remodeling of the actin cytoskeleton is an essential feature for virtually all actin-dependent cellular processes, including cell migration, cell cycle progression, chromatin remodeling and gene expression, and even the DNA damage response. An altered actin cytoskeleton is a structural hallmark associated with numerous pathologies ranging from cardiovascular diseases to immune disorders, neurological diseases and cancer. The actin cytoskeleton in cells is regulated through the orchestrated actions of a myriad of actin-binding proteins. In this Review, we provide a brief overview of the structure and functions of the actin-monomer-binding protein profilin-1 (Pfn1) and then discuss how dysregulated expression of Pfn1 contributes to diseases associated with the cardiovascular system.

Plectin protects podocytes from adriamycin-induced apoptosis and F-actin cytoskeletal disruption through the integrin α6β4/FAK/p38 MAPK pathway

Podocyte injury is an early pathological change characteristic of various glomerular diseases, and apoptosis and F‐actin cytoskeletal disruption are typical features of podocyte injury. In this study, we found that adriamycin (ADR) treatment resulted in typical podocyte injury and repressed plectin expression. Restoring plectin expression protected against ADR‐induced podocyte injury whereas siRNA‐mediated plectin silencing produced similar effects as ADR‐induced podocyte injury, suggesting that plectin plays a key role in preventing podocyte injury. Further analysis showed that plectin repression induced significant integrin α6β4, focal adhesion kinase (FAK) and p38 MAPK phosphorylation. Mutating Y1494, a key tyrosine residue in the integrin β4 subunit, blocked FAK and p38 phosphorylation, thereby alleviating podocyte injury. Inhibitor studies demonstrated that FAK Y397 phosphorylation promoted p38 activation, resulting in podocyte apoptosis and F‐actin cytoskeletal disruption. In vivo studies showed that administration of ADR to rats resulted in significantly increased 24‐hour urine protein levels along with decreased plectin expression and activated integrin α6β4, FAK, and p38. Taken together, these findings indicated that plectin protects podocytes from ADR‐induced apoptosis and F‐actin cytoskeletal disruption by inhibiting integrin α6β4/FAK/p38 pathway activation and that plectin may be a therapeutic target for podocyte injury‐related glomerular diseases.

Intravesicular administration of sodium hyaluronate ameliorates the inflammation and cell proliferation of cystitis cystica et glandularis involving interleukin-6/JAK2/Stat3 signaling pathway

Cystitis cystica et glandularis (CCEG) is a chronic cystitis that causes extreme agony in affected patients. However, there are lack of effective conservative treatments. In this study, it is evident that intravesicular sodium hyaluronate (SH) therapy significantly improved the clinical symptoms of CCEG patients and ameliorated the bladder mucosal inflammation and cell proliferation characteristics of the disease. Immunohistochemical staining showed that the staining intensities of hyaluronidase (HYAL 1/2), CD44, IL-6 and phosphorylated signal transducer and activator of transcription 3 (p-Stat3) in bladder mucosal tissue were significantly increased in CCEG patients compared with control patients and that intravesicular SH treatment suppressed these protein expression. We established a CCEG rat model by treating rats with E. coli intravesicularly, and we found that HYAL 1/2 and CD44 expression levels were significantly increased in the E. coli group compared with the NC group. Activation of the IL-6/JAK2/Stat3 pathway and the expression levels of the downstream pro-apoptotic proteins Mcl-1 and Bcl-xL were also significantly increased in the E. coli group compared with the NC group. The above changes were significantly mitigated by intravesicular SH treatment. Therefore, SH may serve as an effective therapy for CCEG by inhibiting bladder mucosal inflammation and proliferation.

Downregulation of Profilin-1 Expression Attenuates Cardiomyocytes Hypertrophy and Apoptosis Induced by Advanced Glycation End Products in H9c2 Cells

Cardiomyocytes hypertrophy and apoptosis induced by advanced glycation end products (AGEs) is the crucial pathological foundation contributing to the onset and development of diabetic cardiomyopathy (DCM). However, the mechanism remains poorly understood. Here, we report that profilin-1 (PFN-1), a well-known actin-binding protein, serves as a potent regulator in AGEs-induced cardiomyocytes hypertrophy and apoptosis. PFN-1 was upregulated in AGEs-treated H9c2 cells, which was associated with increased cardiomyocytes hypertrophy and apoptosis. Silencing PFN-1 expression remarkably attenuated AGEs-induced H9c2 cell hypertrophy and apoptosis. Mechanistically, AGEs increased PFN-1 expression through elevating ROS production and RhoA and ROCK2 expression. Consequently, elevated PFN-1 promoted actin cytoskeleton disorganization. When either ROS production/ROCK activation was blocked or cells were treated with Cytochalasin D (actin depolymerizer), H9c2 cells were protected against AGEs-induced cardiac myocyte abnormalities, concomitantly with downregulated expression of PFN-1 and improved actin cytoskeleton alteration. Collectively, these data suggest that PFN-1 may play an important role in AGEs-induced hypertrophy and apoptosis in H9c2 cells.

Profilin‑1 contributes to cardiac injury induced by advanced glycation end‑products in rats

Cardiac injury, including hypertrophy and fibrosis, induced by advanced glycation end products (AGEs) has an important function in the onset and development of diabetic cardiomyopathy. Profilin-1, a ubiquitously expressed and multifunctional actin-binding protein, has been reported to be an important mediator in cardiac hypertrophy and fibrosis. However, whether profilin-1 is involved in AGE-induced cardiac hypertrophy and fibrosis remains to be determined. Therefore, the present study aimed to investigate the function of profilin-1 in cardiac injury induced by AGEs. The model of cardiac injury was established by chronic tail vein injection of AGEs (50 mg/kg/day for 8 weeks) in Sprague-Dawley rats. Rats were randomly assigned to control, AGEs, AGEs + profilin-1 shRNA adenovirus vectors (AGEs + S)or AGEs + control adenovirus vectors (AGEs + V) groups. Profilin-1 shRNA adenovirus vectors were injected via the tail vein to knockdown profilin-1 expression at a dose of 3×10⁹ plaque forming units every 4 weeks. Echocardiography was performed to measure cardiac contractile function. Cardiac tissues were stained with Masson's trichrome stain to evaluate ventricular remodeling. The serum levels of procollagen type III N-terminal peptide were detected by ELISA. The expression of profilin-1, receptor for AGEs (RAGE), Rho, p65, atrial natriuretic peptide, β-myosin heavy chain, matrix metalloproteinase (MMP)-2 and MMP-9 were determined using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and/or western blot analysis and immunohistochemistry staining. The results demonstrated that chronic injection of exogenous AGEs led to cardiac dysfunction, hypertrophy and fibrosis, as determined by echocardiography, Masson trichrome staining and the expression of associated genes. The expression of profilin-1 was markedly increased in heart tissue at the mRNA and protein level following AGE administration, as determined by RT-qPCR and western blotting, which was further confirmed by immunohistochemistry staining. Furthermore, the expression of RAGE, Rho and p65 was also increased at the protein level. Notably, knockdown of profilin-1 expression ameliorated AGE-induced cardiac injury and reduced the expression of RAGE, Rho and p65. These results indicate an important role for profilin-1 in AGE-induced cardiac injury, which may provide a novel therapeutic target for patients with diabetic heart failure.

On the Many Actions of Ouabain: Pro-Cystogenic Effects in Autosomal Dominant Polycystic Kidney Disease

Ouabain and other cardenolides are steroidal compounds originally discovered in plants. Cardenolides were first used as poisons, but after finding their beneficial cardiotonic effects, they were rapidly included in the medical pharmacopeia. The use of cardenolides to treat congestive heart failure remained empirical for centuries and only relatively recently, their mechanisms of action became better understood. A breakthrough came with the discovery that ouabain and other cardenolides exist as endogenous compounds that circulate in the bloodstream of mammals. This elevated these compounds to the category of hormones and opened new lines of investigation directed to further study their biological role. Another important discovery was the finding that the effect of ouabain was mediated not only by inhibition of the activity of the Na,K-ATPase (NKA), but by the unexpected role of NKA as a receptor and a signal transducer, which activates a complex cascade of intracellular second messengers in the cell. This broadened the interest for ouabain and showed that it exerts actions that go beyond its cardiotonic effect. It is now clear that ouabain regulates multiple cell functions, including cell proliferation and hypertrophy, apoptosis, cell adhesion, cell migration, and cell metabolism in a cell and tissue type specific manner. This review article focuses on the cardenolide ouabain and discusses its various in vitro and in vivo effects, its role as an endogenous compound, its mechanisms of action, and its potential use as a therapeutic agent; placing especial emphasis on our findings of ouabain as a pro-cystogenic agent in autosomal dominant polycystic kidney disease (ADPKD).

Ibutilide protects against cardiomyocytes injury via inhibiting endoplasmic reticulum and mitochondrial stress pathways

Atrial fibrillation (AF) is a complex disease with multiple inter-relating causes culminating in rapid atrial activation and atrial structural remodeling. The contribution of endoplasmic reticulum and mitochondria stress to AF has been highlighted. As the class III antiarrhythmic agent, ibutilide are widely used to AF. This study was designed to explore whether ibutilide could treat AF by inhibiting endoplasmic reticulum stress pathways and mitochondria stress. The neonatal rat cardiomyocytes were isolated and exposed to H₂O₂, ibutilide was add to the culture medium 12 h. Then the cell viability, oxidative stress levels and apoptotic rate were analyzed. In addition, endoplasmic reticulum stress related protein (GRP78, GRP94, CHOP), mitochondria-dependent protein (Bax, Bcl-2) and caspase-3/9/12 were identified by real-time PCR and western blot analysis. In our results, remarkable decreased cell viability and oxidative stress levels were detected in cardiomyocytes after treating with H₂O₂. The apoptotic rate and the expression of proteins involved in mitochondrial stress and endoplasmic reticulum stress pathways increased. While ibutilide significantly inhibited these changes. These data suggested that ibutilide serves a protective role against H₂O₂-induced apoptosis of neonatal rat cardiomyocytes, and the mechanism is related to suppression of mitochondrial stress and endoplasmic reticulum stress.

Cofilin1 is involved in hypertension-induced renal damage via the regulation of NF-κB in renal tubular epithelial cells

BACKGROUND

Inflammation mediated by nuclear factor-κB (NF-κB) plays a critical role in the pathogenesis of hypertensive nephropathy (HN). Cytoskeletal remodelling is necessary for the activation of NF-κB. An actin-binding protein, cofilin-1 promotes dynamic alterations to the cytoskeleton by severing actin filaments. However, whether cofilin1 modulates NF-κB activity via cytoskeletal remodelling in the setting of hypertensive renal damage and what mechanisms underlie this phenomenon, remain unknown.

METHODS

Twenty-one-week old spontaneously hypertensive rats (SHRs) were treated with an antioxidant (100 or 250 mg kg(-1) day(-1)), grape seed proanthocyanidins extract (GSPE), for 22 weeks. Twenty-four-hour urinary protein, serum creatinine and urea nitrogen levels were measured. Haematoxylin and eosin (HE) staining was performed, and the expression levels of renal cortex cofilin1, monocyte chemotactic protein 1 (MCP1), interleukin-1β (IL1β) and NF-κB were evaluated via either Western blotting or immunohistochemistry. In vitro, human proximal renal tubular epithelial cells (HK-2 cells) were pre-incubated either with or without GSPE and subsequently treated with angiotensinII (AngII). Furthermore, a lentiviral shRNA-vector was utilized to knockdown cofilin1 expression in the HK-2 cells, which were stimulated with AngII. Actin filaments, NF-κB activity and several downstream inflammatory factors, including MCP1 and IL-1β, were investigated.

RESULTS

In addition to elevated blood pressure and 24 h urinary protein levels, NF-κB activity and the expression levels of MCP1 and IL-1β were significantly increased, resulting in tubulointerstitial inflammatory infiltration in SHRs. The phosphorylation (inactivation) of cofilin1 was increased in the kidneys of the SHRs. In vitro, AngII stimulation resulted in the phosphorylation of cofilin1, the formation of actin stress fibres and nuclear translocation of NF-κB p65 in the HK2 cells. Both GSPE pretreatment and the shRNA knockdown of cofilin1 inhibited Rel/p65 nuclear translocation, as well as the expression of both MCP-1 and IL-1β in the AngII-induced HK2 cells.

CONCLUSION

These results demonstrate that cofilin1 is involved in hypertensive nephropathy by modulating the nuclear translocation of NF-κB and the expression of its downstream inflammatory factors in renal tubular epithelial cells.