GDF15 and posterior cortical atrophy: Although CM from parental PCa cells (C4-2B and LNCaP C-81) did not alter osteoblastic OPG expression, it did increase the RANKL/OPG ratio compared to that achieved with CM from GDF15-KO PCa cells in the bone microenvironment, reflecting increased resorption and decreased bone mass (Fig. 6b and S6a).