PB-2

Lipogenic and catabolic processes constitute fundamental metabolic pathways that govern energy homeostasis during oocyte maturation and subsequent embryonic development. Although emerging evidence has highlighted the regulatory potential of Procyanidin B2 (PB2) in modulating meiotic progression and developmental competence of mammalian oocytes, the underlying mechanisms remain elusive, particularly in porcine oocytes. The present study was designed to systematically evaluate the therapeutic potential of PB2 in porcine oocyte in vitro maturation (IVM) and delineate its underlying mechanisms. Our findings reveal that supplementation with 5 μg/mL PB2 during IVM significantly improves meiotic competence, as evidenced by enhanced polar body extrusion rates, while concurrently boosting the developmental capacity of subsequent parthenogenetic embryos. PB2 reduced the incorrect distribution of cortical granules and improved the cytoplasmic maturation rate of the oocytes. Further analysis revealed that this treatment significantly enhanced the efficiency of lipid catabolism and fatty acid β-oxidation, increased the mitochondrial content and ATP levels, while reducing intra-oocyte ROS production. Notably, PB2 supplementation significantly increased the phosphorylation of AMP-activated protein kinase (AMPK); the inhibition of AMPK activity (Compound C, AMPK inhibitor) suppressed the ability of PB2 to promote lipid metabolism and increase mitochondrial content in oocytes. Besides, inhibition of AMPK lowered the oocyte maturation rate and the subsequent zygote cleavage and blastocyst formation rate when compared to that of the PB2 treatment. These results suggest that PB2 can promote lipid catabolism by activating AMPK, thereby enhancing the developmental potential of porcine oocytes.

Vascular smooth muscle cell (VSMC) proliferation contributes to intimal thickening in atherosclerosis and restenosis diseases. As a proanthocyanidin type B, procyanidin B2 (PB2) is abundantly found in cocoa, apples, and grapes and is reported to have vascular protective effects. However, the mechanisms by which PB2 inhibits proliferation of VSMCs are not clearly understood. Therefore, the purpose of this study was to investigate the underlying mechanism of PB2-induced inhibition of cell proliferation in VSMCs. We found that PB2 dose- and time-dependently increased phosphorylation of liver kinase B1 (LKB1) and AMP-activated protein kinase (AMPK) in VSMCs. AMPK is a serine-threonine kinase and serves as a key sensor of cellular energy. PB2 induced LKB1 translocation from nucleus to cytosol which led to AMPK activation. In addition, PB2-induced AMPK activation decreased cell proliferation and cell cycle progression by inhibiting mammalian target of rapamycin signaling pathway. Transfection with LKB1 or AMPK siRNA and transduction of dominant-negative isoforms of the α1 and α2 subunits of AMPK eliminated anti-proliferative effects of PB2. These results demonstrate that PB2 might be a preventive agent for cardiovascular disorders such as atherosclerosis and hypertension.