BACKGROUND:
Cellular senescence is linked to aging and tumorigenesis. The senescence of mesenchymal stem cells (MSCs) may influence the tumor growth, metastasis, and angiogenesis by secreting a variety of cytokines and growth factors.

RESULTS:
The conditioned media of adipose derived MSCs (AD-MSCs) stimulated the proliferation of human LoVo colorectal-cancer cells, and the replicative senescent MSCs had the more obvious effects in comparison to that of premature AD-MSCs. Analysis of the factors secreted in the MSCs culture media determined that senescent MSCs expressed and secreted high levels of galectin-3. Galectin-3 expression correlated with the stimulatory effect of senescent AD-MSCs on LoVo cells proliferation, as knockdown of galectin-3 in senescent AD-MSCs significantly reversed the effect of MSCs-mediated growth stimulation of LoVo cells. Furthermore, the simultaneous addition of recombinant galectin-3 to the co-culture systems partially restored the tumor-promoting effect of the senescent AD-MSCs. Analysis of the mechanisms of senescent MSCs and galectin-3 on LoVo cells signal transduction determined that senescent MSCs and exogenous galectin-3 promoted cell growth by activating the mitogen-activated protein kinase (MAPK) (extracellular signal-regulated kinase [ERK]1/2) pathway.

CONCLUSIONS:
Senescent MSCs may alter the tissue microenvironment and affect nearby malignant cells via cytokine secretion, and galectin-3 is an important mediator of senescent AD-MSC-mediated stimulation of colon cancer cell growth. Therefore, thorough assessment of AD-MSCs prior to their implementation in clinical practice is warranted.