Neuraminidase-1 (NEU1): Biological Roles and Therapeutic Relevance in Human Disease.

Neuraminidases catalyze the desialylation of cell-surface glycoconjugates and play crucial roles in the development and function of tissues and organs. In both physiological and pathophysiological contexts, neuraminidases mediate diverse biological activities via the catalytic hydrolysis of terminal neuraminic, or sialic acid residues in glycolipid and glycoprotein substrates. The selective modulation of neuraminidase activity constitutes a promising strategy for treating a broad spectrum of human pathologies, including sialidosis and galactosialidosis, neurodegenerative disorders, cancer, cardiovascular diseases, diabetes, and pulmonary disorders. Structurally distinct as a large family of mammalian proteins, neuraminidases (NEU1 through NEU4) possess dissimilar yet overlapping profiles of tissue expression, cellular/subcellular localization, and substrate specificity. NEU1 is well characterized for its lysosomal catabolic functions, with ubiquitous and abundant expression across such tissues as the kidney, pancreas, skeletal muscle, liver, lungs, placenta, and brain. NEU1 also exhibits a broad substrate range on the cell surface, where it plays hitherto underappreciated roles in modulating the structure and function of cellular receptors, providing a basis for it to be a potential drug target in various human diseases. This review seeks to summarize the recent progress in the research on NEU1-associated diseases and highlight the mechanistic implications of NEU1 in disease pathogenesis. An improved understanding of NEU1-associated diseases should help accelerate translational initiatives to develop novel or better therapeutics.

BMSC­derived exosome­mediated miR­25­3p delivery protects against myocardial ischemia/reperfusion injury by constraining M1­like macrophage polarization.

Myocardial ischemia/reperfusion injury (MIRI) is a significant challenge in the management of myocardial ischemic disease. Extensive evidence suggests that the macrophage­mediated inflammatory response may play a vital role in MIRI. Mesenchymal stem cells and, in particular, exosomes derived from these cells, may be key mediators of myocardial injury and repair. However, whether exosomes protect the heart by regulating the polarization of macrophages and the exact mechanisms involved are poorly understood. The present study aimed to determine whether exosomes secreted by bone marrow mesenchymal stem cells (BMSC­Exo) harboring miR­25­3p can alter the phenotype of macrophages by affecting the JAK2/STAT3 signaling pathway, which reduces the inflammatory response and protects against MIRI. An in vivo MIRI model was established in rats by ligating the anterior descending region of the left coronary artery for 30 min followed by reperfusion for 120 min, and BMSC­Exo carrying miR­25­3p (BMSC­Exo­25­3p) were administered through tail vein injection. A hypoxia­reoxygenation model of H9C2 cells was established, and the cells were cocultured with BMSC­Exo­25­3p in vitro. The results of the present study demonstrated that BMSC­Exo or BMSC­Exo­25­3p could be taken up by cardiomyocytes in vivo and H9C2 cells in vitro. BMSC­Exo­25­3p demonstrated powerful cardioprotective effects by decreasing the cardiac infarct size, reducing the incidence of malignant arrhythmias and attenuating myocardial enzyme activity, as indicated by lactate dehydrogenase and creatine kinase levels. It induced M1­like macrophage polarization after myocardial ischemia/reperfusion (I/R), as evidenced by the increase in iNOS expression through immunofluorescence staining and upregulation of proinflammatory cytokines through RT­qPCR, such as interleukin­1ß (IL­1ß) and interleukin­6 (IL­6). As hypothesized, BMSC­Exo­25­3p inhibited M1­like macrophage polarization and proinflammatory cytokine expression while promoting M2­like macrophage polarization. Mechanistically, the JAK2/STAT3 signaling pathway was activated after I/R in vivo and in LPS­stimulated macrophages in vitro, and BMSC­Exo­25­3p pretreatment inhibited this activation. The results of the present study indicate that the attenuation of MIRI by BMSC­Exo­25­3p may be related to JAK2/STAT3 signaling pathway inactivation and subsequent inhibition of M1­like macrophage polarization.

Pharmacological Activation of AMPK Prevents Drp1-mediated Mitochondrial Fission and Alleviates Hepatic Steatosis In vitro.

BACKGROUND: The incidence of non-alcoholic fatty liver disease (NAFLD) is increasing worldwide. Adenosine monophosphate-activated protein kinase (AMPK) activation is beneficial for NAFLD treatment. Recent studies show the excessive fission of mitochondria during NAFLD progression, so targeting mitochondria dynamics may be a possible target for NAFLD. Still, little is known about whether AMPK regulates mitochondrial dynamics in hepar. OBJECTIVE: This study investigated whether AMPK activation alleviates hepatic steatosis by regulating mitochondrial dynamics mediated by GTPase dynamin-related protein 1 (Drp1). METHODS: Human hepatocyte line L-02 cells were cultured and subjected to palmitic acid (PA) treatment for 24 h to establish a hepatic steatosis model in vitro, which was pre-treated with different tool drugs. Hepatocyte function, hepatocyte lipid content, mitochondrial reactive oxygen species (ROS) production, and mitochondrial membrane potential (MMP) were examined. The expression levels of genes and proteins associated with mitochondrial dynamics were assessed using reverse transcription-quantitative PCR and western blotting. RESULTS: The results indicated that 5-Aminoimidazole-4-carboxamide 1-ß-D-ribofuranoside (AICAR), an AMPK activator, improved hepatocyte function, as demonstrated by decreased alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activity (P＜0.05 or P＜0.01). In addition, AICAR decreased total cholesterol (TC) and triglyceride (TG) content and lipid deposition in hepatocytes (P＜0.01); decreased ROS production; improved MMP (P＜0.01); reduced fission-1 (Fis1) and mitochondrial fission factor (Mff) mRNA expression; and downregulated p-Drp1 (Ser 616) protein expression. In contrast, AICAR increased mitochondrial fusion factor mitofusin-1 (Mfn1) and mitofusin-2 (Mfn2) mRNA expression and upregulated p-Drp1 (Ser 637) protein expression. Mdivi-1, a Drp-1 inhibitor, was used to confirm whether mitochondrial dynamics regulated by Drp1-mediated the role of AICAR. Similar to AICAR, Mdivi-1 improved hepatocyte function and MMP significantly, decreased ROS production and lipid deposition, downregulated Fis1 and Mff mRNA expression, downregulated p-Drp1 (Ser 616) protein expression, and enhanced Mfn1 and Mfn2 mRNA and p-Drp1 (Ser 637) protein expression. However, Compound C, an AMPKspecific inhibitor, had less impact on the protective effect of Mdivi-1. CONCLUSION: The results demonstrated that AMPK activation has a protective effect on hepatic steatosis in vitro, largely dependent on the inhibition of Drp1-mediated mitochondrial fission.