Induction of apoptotic cell death is emerging as a promising strategy for prevention and treatment of obesity because removing of adipocytes via apoptosis may result in reducing body fat and a long-lasting maintenance of weight loss. However, the mechanisms controlling adipocyte apoptosis are unknown and even the ability of adipocytes to undergo apoptosis has not been conclusively demonstrated. We have shown previously that the specific Ca2+ Signal, Sustained increase in intracellular Ca2+, triggers apoptotic cell death via activation of Ca2+-dependent proteases and that the apoptosis-inducing effect of the hormone 1,25-dixydroxyvitamin D-3 (1,25(OH)(2)D-3) is mediated through Ca2+ signaling. Here, we report that 1,25(OH)(2)D-3 induces apoptosis in mature mouse 3T3-L1 adipocytes via activation of Ca2+-dependent calpain and Ca2+/calpain-dependent caspase-12. Treatment of adipocytes with 1,25(OH)2D3 induced, in concentration- and time-dependent fashion, a sustained increase in the basal level of intracellular Ca2+. The increase in Ca2+ was associated with induction of apoptosis and activation of p-calpain and caspase-12. Our results demonstrate that Ca2+-mediated apoptosis can be induced in mature adipocytes and that the apoptotic molecular targets activated by 1,25(OH)(2)D-3 in these cells are Ca2+-dependent calpain and caspase-12. These findings provide rationale for evaluating the role of vitamin D in prevention and treatment of obesity. (C) 2009 Elsevier Inc. All rights reserved.