Fig. 8
Schematic illustration for the working hypothesis of the functional role of the TLR2 system in regulating early embryo development. Toll-like receptor 2 (TLR2) is expressed in bovine early embryos. Activation of TLR2 with its specific agonist (Pam3Cys) increases the developmental competence of IVP bovine embryos. (1) Activation of bovine TLR2 accelerates embryo development, possibly via inducing weak innate immune responses (TNFA, IFNT), and lowering apoptosis-related genes to improve the quality of the embryo. (2) Increased cytosolic Ca2+ which subsequently accelerates the developmental process and blastocyst formation in IVP bovine embryos. (3) Meanwhile, TLR2 activation induced the autophagic activity of embryos. (4) Also, TLR2 activation suppressed apoptosis-related genes, cathepsin B activity and DNA damage thereby decreasing the apoptosis levels in IVP embryos. Together, these findings indicate that activation of early embryonic TLR2 enhances cytosolic calcium, and autophagy and reduces apoptosis levels thereby supporting embryo development and survival under in vitro culture conditions.
