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ABSTRACT Bone metastasis, the leading cause of breast cancer-related deaths, is characterized by bone degradation due to increased osteoclastic activity. In contrast, mechanical stimulation in healthy individuals upregulates osteoblastic activity, leading to new bone formation. However, the effect of mechanical loading on the development and progression of metastatic breast cancer in bone remains unclear. Here, we developed a new in vivo model to investigate the role of skeletal mechanical stimuli on the development and osteolytic capability of secondary breast tumors. Specifically, we applied compressive loading to the tibia following intratibial injection of metastatic breast cancer cells (MDA-MB231) into the proximal compartment of female immunocompromised (SCID) mice. In the absence of loading, tibiae developed histologically-detectable tumors with associated osteolysis and excessive degradation of the proximal bone tissue. In contrast, mechanical loading dramatically reduced osteolysis and tumor formation and increased tibial cancellous mass due to trabecular thickening. These loading effects were similar to the baseline response we observed in non-injected SCID mice. In vitro mechanical loading of MDA-MB231 in a pathologically relevant 3D culture model suggested that the observed effects were not due to loading-induced tumor cell death, but rather mediated via decreased expression of genes interfering with bone homeostasis. Collectively, our results suggest that mechanical loading inhibits the growth and osteolytic capability of secondary breast tumors after their homing to the bone, which may inform future treatment of breast cancer patients with advanced disease. © 2013 American Society for Bone and Mineral Research [ABSTRACT FROM AUTHOR]

Mesenchymal stem cells (MSCs) are capable of differentiating into a variety of lineages, including bone, cartilage, or fat, depending on the inducing stimuli and specific growth and differentiation factors. It is widely acknowledged that basic fibroblast growth factor (bFGF) modulates chondrogenic and osteogenic differentiation of MSCs, but thorough investigations of its effects on adipogenic differentiation are lacking. In this study, we demonstrate on the cellular and molecular level that supplementation of bFGF in different phases of cell culture leads to a strong enhancement of adipogenesis of MSCs, as induced by an adipogenic hormonal cocktail. In cultures receiving bFGF, mRNA expression of peroxisome proliferator-activated receptor γ2 (PPARγ2), a key transcription factor in adipogenesis, was upregulated even prior to adipogenic induction. In order to investigate the effects of bFGF on PPARγ ligand-induced adipogenic differentiation, the thiazolidinedione troglitazone was administered as a single adipogenic inducer. Basic FGF was demonstrated to also strongly increase adipogenesis induced by troglitazone, that is, bFGF clearly increased the responsiveness of MSCs to a PPARγ ligand. [Copyright &y& Elsevier]