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Introduction
Oxidative stress is induced by an imbalance between the production and elimination of reactive oxygen species (ROS) and reactive nitrogen species (RNS) (1). Although ROS and RNS are generated under normal physiological conditions, numerous cellular functions are disturbed by the reaction of ROS/RNS with cellular components, including DNA, lipids and proteins (2–6). For example, sulfur-containing amino acids (methionine and cysteine) are sensitive to ROS (7). Mitochondria are a major source of ROS (8). The free radical ·O2- is produced by complex I and complex III of the electron transport chain (ETC) and released into the mitochondrial matrix (9). The mitochondrial dysfunction caused by oxidative stress and can result in cell loss leading to neurodegenerative diseases and ischemic brain injury (10). Thus, pro-oxidant antioxidant generation needs to be highly regulated (11).
Methionine sulfoxide reductase (Msr) A and B, which reduce free and protein-based methionine sulfoxides to methionine, are encoded by a single MsrA and three MsrB genes, respectively, in the mammalian genome (7,12). Mammalian MsrA is expressed in the mitochondria, cytosol and nucleus (13,14). Methionine oxidation and reduction serves an important role in cellular signaling, metabolism and oxidative stress under physiological and pathological conditions (15). MsrA repairs oxidatively-damaged proteins and functions as an antioxidant enzyme (16). MsrA has been identified to protect various cell types against oxidative stress-induced death (17,18).
Astragaloside IV (3-O-beta-D-xylopyranosyl-6-O-beta-D-glucopyrannosyl-cycloastragenol; AS-IV) is purified from the Chinese medicinal herb, Astragalus membranaceus (19). The molecular structure of AS-IV is illustrated in Fig. 1A. AS-IV has comprehensive pharmacological functions, including anti-inflammatory and antioxidative activity, and is able to reduce infarct size and improve post-ischemic brain function (20–22). However, few studies have investigated whether AS-IV prevents mitochondrial dysfunction via MsrA. The present study utilized a 1-methyl-4-phenylpyridinium (MPP+)-induced oxidative damage cell model to investigate this. MPP+ is toxic and acts by interfering with oxidative phosphorylation in the mitochondria through inhibiting complex I, which induces oxidative stress (23,24). MPP+ can reproduce the clinical and pathological features of Parkinson's disease (PD) in animal models (25–27). Therefore, present study aimed to investigate the protective effects of AS-IV against MPP+-induced oxidative damage and the potential molecular mechanisms underlying these effects.
Materials and methods
Antibodies and reagents
Anti-MsrA (cat. no. ab16803), anti-forkhead box protein...