Isoproterenol produces a rapid increase in sialidase activity in rat heart tissue and cardiomyocyte-derived H9c2 cells in culture

Gypensapogenin I Ameliorates Isoproterenol (ISO)-Induced Myocardial Damage through Regulating the TLR4/NF-κB/NLRP3 Pathway

Myocardial fibrosis (MF) is a common pathological feature of many heart diseases and seriously threatens the normal activity of the heart. Jiaogulan (Gynostemma pentaphyllum) tea is a functional food that is commercially available worldwide. Gypensapogenin I (Gyp I), which is a novel dammarane-type saponin, was obtained from the hydrolysates of total gypenosides. It has been reported to exert a beneficial anti-inflammatory effect. In our study, we attempted to investigate the efficiency and possible molecular mechanism of Gyp I in cardiac injury treatment induced by ISO. In vitro, Gyp I was found to increase the survival rate of H9c2 cells and inhibit apoptosis. Combined with molecular docking and Western blot analysis, Gyp I was confirmed to regulate the TLR4/NF-κB/NLRP3 signaling pathway. In vivo, C57BL6 mice were subcutaneously injected with 10 mg/kg ISO to induce heart failure. Mice were given a gavage of Gyp I (10, 20, or 40 mg/kg/d for three weeks). Pathological alterations, fibrosis-, inflammation-, and apoptosis-related molecules were examined. By means of cardiac function detection, biochemical index analysis, QRT-PCR monitoring, histopathological staining, immunohistochemistry, and Western blot analysis, it was elucidated that Gyp I could improve cardiac dysfunction, alleviate collagen deposition, and reduce myocardial fibrosis (MF). In summary, we reported for the first time that Gyp I showed good myocardial protective activity in vitro and in vivo, and its mechanism was related to the TLR4/NF-κB/NLRP3 signaling pathway.

Neuraminidase 1 deficiency attenuates cardiac dysfunction, oxidative stress, fibrosis, inflammatory via AMPK-SIRT3 pathway in diabetic cardiomyopathy mice

Diabetic cardiomyopathy (DCM) is associated with oxidative stress and augmented inflammation in the heart. Neuraminidases (NEU) 1 has initially been described as a lysosomal protein which plays a role in the catabolism of glycosylated proteins. We investigated the role of NEU1 in the myocardium in diabetic heart. Streptozotocin (STZ) was injected intraperitoneally to induce diabetes in mice. Neonatal rat ventricular myocytes (NRVMs) were used to verify the effect of shNEU1 in vitro. NEU1 is up-regulated in cardiomyocytes under diabetic conditions. NEU1 inhibition alleviated oxidative stress, inflammation and apoptosis, and improved cardiac function in STZ-induced diabetic mice. Furthermore, NEU1 inhibition also attenuated the high glucose-induced increased reactive oxygen species generation, inflammation and, cell death in vitro. ShNEU1 activated Sirtuin 3 (SIRT3) signaling pathway, and SIRT3 deficiency blocked shNEU1-mediated cardioprotective effects in vitro. More importantly, we found AMPKα was responsible for the elevation of SIRT3 expression via AMPKα-deficiency studies in vitro and in vivo. Knockdown of LKB1 reversed the effect elicited by shNEU1 in vitro. In conclusion, NEU1 inhibition activates AMPKα via LKB1, and subsequently activates sirt3, thereby regulating fibrosis, inflammation, apoptosis and oxidative stress in diabetic myocardial tissue.

Neuraminidase 1 is a driver of experimental cardiac hypertrophy

AIMS 

Despite considerable therapeutic advances, there is still a dearth of evidence on the molecular determinants of cardiac hypertrophy that culminate in heart failure. Neuraminidases are a family of enzymes that catalyze the cleavage of terminal sialic acids from glycoproteins or glycolipids. This study sought to characterize the role of neuraminidases in pathological cardiac hypertrophy and identify pharmacological inhibitors targeting mammalian neuraminidases.

METHODS AND RESULTS 

Neuraminidase 1 (NEU1) was highly expressed in hypertrophic hearts of mice and rats, and this elevation was confirmed in patients with hypertrophic cardiomyopathy (n = 7) compared with healthy controls (n = 7). The increased NEU1 was mainly localized in cardiomyocytes by co-localization with cardiac troponin T. Cardiomyocyte-specific NEU1 deficiency alleviated hypertrophic phenotypes in response to transverse aortic constriction or isoproterenol hydrochloride infusion, while NEU1 overexpression exacerbated the development of cardiac hypertrophy. Mechanistically, co-immunoprecipitation coupled with mass spectrometry, chromatin immunoprecipitation, and luciferase assays demonstrated that NEU1 translocated into the nucleus and interacted with GATA4, leading to Foetal gene (Nppa and Nppb) expression. Virtual screening and experimental validation identified a novel compound C-09 from millions of compounds that showed favourable binding affinity to human NEU1 (KD = 0.38 μM) and effectively prevented the development of cardiac remodelling in cellular and animal models. Interestingly, anti-influenza drugs zanamivir and oseltamivir effectively inhibited mammalian NEU1 and showed new indications of cardio-protection.

CONCLUSIONS 

This work identifies NEU1 as a critical driver of cardiac hypertrophy and inhibition of NEU1 opens up an entirely new field of treatment for cardiovascular diseases.

Neuraminidase 1 and its Inhibitors from Chinese Herbal Medicines: An Emerging Role for Cardiovascular Diseases

Neuraminidase, also known as sialidase, is ubiquitous in animals and microorganisms. It is predominantly distributed in the cell membrane, cytoplasmic vesicles, and lysosomes. Neuraminidase generally recognizes the sialic acid glycosidic bonds at the ends of glycoproteins or glycolipids and enzymatically removes sialic acid. There are four types of neuraminidases, named as Neu1, Neu2, Neu3, and Neu4. Among them, Neu1 is the most abundant in mammals. Recent studies have revealed the involvement of Neu1 in several diseases, including cardiovascular diseases, diabetes, cancers, and neurological disorders. In this review, we center the attention to the role of Neu1 in cardiovascular diseases, including atherosclerosis, ischemic myocardial injury, cerebrovascular disease, congenital heart disease, and pulmonary embolism. We also summarize inhibitors from Chinese herbal medicines (CHMs) in inhibiting virus neuraminidase or human Neu1. Many Chinese herbs and Chinese herb preparations, such as Lonicerae Japonicae Flos, Scutellariae Radix, Yupingfeng San, and Huanglian Jiedu Decoction, have neuraminidase inhibitory activity. We hope to highlight the emerging role of Neu1 in humans and potentially titillate interest for further studies in this area.

Calcium inhibitor inhibits high glucose‑induced hypertrophy of H9C2 cells

The aim of the present study was to explore whether the hypertrophy of H9C2 cardiomyocytes was induced by high glucose, to investigate whether the calcium channel inhibitor (Norvasc) could inhibit this process and to clarify the possible signaling pathways. The morphology of H9C2 cells was observed under an optical microscope, and the cell surface area was measured by Image Pro Plus 6.1 software. Furthermore, fluorescence spectrophotometry was used to detect intracellular calcium concentration ([Ca²⁺]i). ELISA was performed to detect calcineurin (CaN) activity; reverse transcription-quantitative PCR and western blotting were performed to detect the mRNA and protein expression levels of CaN Aβ subunit (CnAβ), nuclear factor of activated T cells 3 (NFAT3) and β type myosin heavy chain (β-MHC). Cell size was increased with the increase in glucose concentration of culture medium at 48 and 72 h, respectively, and decreased with the addition of Norvasc compared with those without Norvasc (P<0.05). There was no significant difference in cell size with the addition of Norvasc compared with cells cultured with 5 mM glucose (P>0.05). The average [Ca²⁺]i activity of single cells in the 48- and 72-h culture groups treated with 50 mM glucose was significantly higher than cells treated with 5 mM glucose (P<0.05); and the fluorescent value of average [Ca²⁺]i activity of single cells was lower, following the addition of Norvasc than that without Norvasc (P<0.05). CaN activity in the 48- and 72-h culture group treated with 50 mM glucose was markedly higher than that treated with 5 mM glucose, and the activity of CaN notably decreased with the addition of Norvasc compared with those without Norvasc. The mRNA and protein expression levels of CnAβ, NFAT3 and β-MHC in the 48- and 72-h culture groups treated with 50 mM glucose were all significantly higher than those treated with 5 mM glucose (P<0.05). The mRNA and protein expression of CnAβ, NFAT3 and β-MHC cultured with 50 mM glucose were significantly decreased following the addition of Norvasc (P<0.05). Thus, the calcium channel inhibitor Norvasc may inhibit high glucose-induced hypertrophy of H9C2 cardiomyocytes by inhibiting the Ca²⁺-CaN-NFAT3 signaling pathway.

Enhanced expression of membrane-associated sialidase Neu3 decreases GD3 and increases GM3 on the surface of Jurkat cells during etoposide-induced apoptosis

We previously reported that, in Jurkat human T cells, the topoisomerase II inhibitor etoposide enhances sialidase activity and reduces cell surface sialic acid levels at an early stage of apoptosis and that the decreases in sialic acid are suppressed by the sialidase inhibitor 2,3-dehydro-2-deoxy-N-acetylneuraminic acid [Azuma Y., et al., Glycoconj. J., 17, 301-306 (2000)]. In the current studies, we treated Jurkat cells with etoposide and examined the changes in the cell surface levels of gangliosides GM1, GM2, GM3, GD1a, and GD3 at physiological pH using anti-ganglioside antibodies. We also examined the sialidase activity on the cell surface using 4-methylumbelliferyl N-acetylneuraminic acid and measured the mRNA expression of the plasma membrane-associated sialidase Neu3 and the lysozomal Neu1 using real-time PCR. We found an increase in GM3 and a decrease in GD3 during the early stage (4 h) of etoposide-induced apoptosis that preceded the increase in cell surface exposure of phosphatidylserine (4 to 6 h). The caspase 3 inhibitor acetyl-Asp-Glu-Val-Asp-aldehyde significantly suppressed changes in GM3 and GD3 and blocked the enhanced cell surface sialidase activity. Furthermore, etoposide caused a gradual up-regulation of Neu3 mRNA expression but not Neu1 mRNA expression. Enhanced Neu3 mRNA expression was suppressed in the presence of caspase 3 inhibitor. These results indicate that Neu3 is up-regulated in Jurkat cells undergoing etoposide-induced apoptosis through intracellular signaling events downstream of caspase 3 activation and that enhanced Neu3 activity is closely related to the changes of cell surface ganglioside composition.

Chronic ethanol consumption upregulates the cytosolic and plasma membrane sialidase genes, but down regulates lysosomal membrane sialidase gene in rat liver

We have previously shown that chronic ethanol feeding stimulates liver cytosolic sialidase (CS) and plasma membrane sialidase (PMS), whereas it decreases lysosomal membrane sialidase (LMS) activities with concomitant alterations in their relative synthetic rate in rat. To understand the molecular mechanism(s) for these changes, we have evaluated the effect of ethanol administration in male Wistar rats as a function of increasing dietary ethanol concentration after 8 weeks of pair-feeding on (i) the expression of CS, PMS, and LMS genes by real-time quantitative polymerase chain reaction method; (ii) their relative transcription rates by nuclear run-on assay; and (iii) the actual amount of these sialidase proteins in the liver fractions of the respective groups by Western blot method. We have demonstrated that the animals fed with 10.6%, 20.8%, and 36% of total calories as ethanol showed a 20% (P<.05), 34% (P<.01), and 69% (P<.01) increase in CS mRNA level, and 22% (P<.05), 26% (P<.01), and 47% (P<.01) increase in PMS mRNA level, but a decrease in LMS mRNA level by 35% (P<.05), 50% (P<.01), and 80% (P<.01), respectively, as compared to controls. Western blot analyses of CS, PMS, and LMS in the liver subfractions showed that changes in protein levels of CS, LMS, and PMS were consistent with the corresponding changes in the respective mRNA levels. Thus, the upregulation of CS and PMS, but not LMS which is down regulated by chronic ethanol, may account for the appearance of asialoconjugates in alcoholics.

Chronic ethanol feeding controls the activities of various sialidases by regulating their relative synthetic rates in the rat liver

We have determined the concentration effects of feeding for 8 weeks 10.8%, 21.6%, and 36% dietary ethanol calories on the activities and relative synthetic rates (RSRs) of various subcellular sialidases of rat liver. The hepatic RSRs of each species of sialidase was determined based on the ratio of 1-hour incorporation of [35S]-methionine into immunoprecipitable sialidase as percent of the incorporation into total protein in each subcellular fraction. Ganglioside sialidase activities in the hepatic subcellular fractions were also determined. Ethanol feeding at 36% dietary calories caused an increase in the ganglioside sialidase activity of the plasma membrane sialidase (PMS) by 232% (P < .01) and that of cytosolic sialidase (CS) by 184% (P < .05), but decreased the lysosomal membrane sialidase (LMS) by 54% (P < .01) when compared with the control animals. The specificity of each antisialidase antibody was verified by immunoblots. The RSR of PMS was increased by 40% (P < .01), 67% (P < .01), and 220% (P < .01) in the 10.8%, 21.6%, and 36% ethanol groups, respectively. Similarly, the RSR of CS was increased by 17% (P < .01), 19% (P < .01), and 63% (P < .01), respectively, in these ethanol groups. In contrast, the RSR of LMS was inhibited by 36% (P < .01), 34% (P < .01), and 69% (P < .01), respectively, in these ethanol groups. Intralysosomal sialidase failed to hydrolyze gangliosides. Thus, PMS and CS, but not LMS or intralysosomal sialidase, may play important roles in ethanol-modulated desialylation of gangliosides and consequent liver injury and behavioral alterations.