GDF9 and ovarian dysfunction: Ovarian treatment with MSCs cultured under low-O2 tension could improve ovarian failure caused by malnutrition in female rats based on increased HSP70 expression and decreased caspase-3 expression as apoptotic inhibitors, increased VEGF1 and GDF-9 expression as markers of viability and differentiation, regeneration of ovarian tissue, and improved count of Graafian follicle.