Objective To investigate the impact of Sca-1 bone marrow derived stem cells on apoptosis in murine cardiac fibroblasts and the molecular mechanisms of young(Y)Sca-1 bone marrow stem cell(BMSC)on old(O)cardiac fibroblast cell(CFC)apoptosis.Methods The apoptosis and survival of Y and O CFC were assessed under hypoxic conditions.Co-cultures of Y and O Sca-1 bone marrow-derived mesenchymal stem cells(BMSC)with O CFC were established to investigate the impact of Sca-1 BMSC on the apoptotic response and viability of O CFC,employing TUNEL staining,qRT-PCR,Western Blot,and CCK8 assays.Furthermore,differential secretion profiles of growth factors by Y and O Sca-1 BMSC were compared using qRT-PCR and ELISA analysis.Results Compared to Y CFC,O CFC exhibited an increased rate of apoptosis and a decreased rate of cell survival.However,when compared to O cells,Y Sca-1 BMC significantly reduced apoptosis in O CFC and enhanced cell survival.Moreover,Y Sca-1 BMSC demonstrated a higher secretion of GDF5(Growth Differentiation Factor 5)than O cells(P<0.05).Importantly,the protective effects of Y Sca-1 BMSC on apoptosis and survival in O CFC were abolished upon neutral-ization of GDF5 expression.Conclusion Y Sca-1 BMSC decreases O CFC apoptosis through GDF5.