MicroRNA-345-3p suppresses the Caspase-9/ transforming growth factor-β3 feedback axis to regulate homeostasis in goat...

Mammary gland involution in dairy goats critically governs subsequent lactation initiation and milk quality, with microRNAs (miRNAs) serving as pivotal molecular regulators. This study elucidates the mechanistic interplay among chi-miR-345-3p, caspase-9 (CASP9), and transforming growth factor-β3 (TGFβ3) in regulating the proliferation and apoptosis of goat mammary epithelial cells. Results showed that chi-miR-345-3p expression was significantly downregulated in mammary tissues during late-lactation and dry periods relative to late gestation, concurrently suppressing CASP9 and TGFβ3 through direct targeting. Functionally, chi-miR-345-3p promoted proliferation of GMECs and inhibited apoptosis, whereas CASP9/TGFβ3 exerted pro-apoptotic effects. Notably, a positive feedback loop was identified between TGFβ3 and CASP9, and this axis inhibits phosphorylation of the PI3K/AKT and p38-MAPK, thereby causing cell cycle arrest and promoting GMECs apoptosis. Chi-miR-345-3p targeted CASP9/TGFβ3 to alleviate their inhibition of these pathways, up-regulate cyclin D1 (CCND1) and down-regulate p53, thereby reducing cell cycle arrest and inhibiting apoptosis, and maintaining mammary epithelial cell homeostasis. This study reveals a bidirectional regulatory loop involving chi-miR-345-3p and CASP9/TGFβ3, which precisely regulates mammary involution by integrating the inhibitory action of chi-miR-345-3p with the positive feedback between CASP9 and TGFβ3. This discovery provides potential molecular targets for extending lactation persistency and improving milk production performance in dairy goats (or dairy livestock).