Metformin is still being investigated due to its potential use as a therapeutic agent for managing overweight or obesity. However, the underlying mechanisms are not fully understood. Inhibiting the adipogenesis of adipocyte precursors may be a new therapeutic opportunity for obesity treatments. It is still not fully elucidated whether adipogenesis is also involved in the weight loss mechanisms by metformin. We therefore used adipose-derived stem cells (ADSCs) from inguinal and epididymal fat pads to investigate the effects and mechanisms of metformin on adipogenesis in vitro. Our results demonstrate the similar effect of metformin inhibition on lipid accumulation, lipid droplets fusion, and growth in adipose-derived stem cells from epididymal fat pads (Epi-ADSCs) and adipose-derived stem cells from inguinal fat pads (Ing-ADSCs) cultures. We identified that cell death-inducing DFFA-like effector c (Cidec), Perilipin1, and ras-related protein 8a (Rab8a) expression increased ADSCs differentiation. In addition, we found that metformin inhibits lipid droplets fusion and growth by decreasing the expression of Cidec, Perilipin1, and Rab8a. Activation of AMPK pathway signaling in part involves metformin inhibition on Cidec, Perilipin1, and Rab8a expression. Collectively, our study reveals that metformin inhibits lipid storage, fusion, and growth of lipid droplets via reduction in Cidec and its regulatory factors in ADSCs cultures. Our study supports the development of clinical trials on metformin-based therapy for patients with overweight and obesity.

Immune cell infiltration into the tumor microenvironment is associated with cancer prognosis. Tumor-associated macrophages play essential roles in tumor initiation, progression, and metastasis. Follistatin-like protein 1 (FSTL1), a widely expressed glycoprotein in human and mouse tissues, is a tumor suppressor in various cancers and a regulator of macrophage polarization. However, the mechanism by which FSTL1 affects crosstalk between breast cancer cells and macrophages remains unclear. By analyzing public data, we found that FSTL1 expression was significantly low in breast cancer tissues compared to normal breast tissues, and high expression of FSTL1 in patients indicated prolonged survival. Using flow cytometry, we found that total and M2-like macrophages dramatically increased in the metastatic lung tissues during breast cancer lung metastasis in Fstl1^+/− mice. Transwell assay in vitro and q-PCR experimental results showed that FSTL1 inhibited macrophage migration toward 4T1 cells by decreasing CSF1, VEGF-α, and TGF-β secretion in 4T1 cells. We demonstrated that FSTL1 inhibited M2-like tumor-associated macrophage recruitment toward the lungs by suppressing CSF1, VEGF-α, and TGF-β secretion in 4T1 cells. Therefore, we identified a potential therapeutic strategy for triple-negative breast cancer.

Immune cell infiltration in the tumor microenvironment is associated with cancer prognosis. Tumor-associated macrophages (TAMs) play an essential role in tumor initiation, progression, and metastasis. Follistatin-like protein 1 (Fstl1), a glycoprotein widely expressed in human and mouse tissues, is a tumor suppressor in various cancers and a regulator in macrophage polarization. However, how Fstl1 affects the crosstalk between breast cancer cells and macrophages remains unclear. Analyzing the public data, we found that Fstl1 expression significantly decreases in breast cancer tissues compared with normal breast tissues, and high expression of Fstl1 in patients means prolonged survival. Using flow cytometry, we found that total macrophages and M2-like macrophages increased in the metastatic lung tissues during breast cancer lung metastasis of Fstl1+/- mice. Cellular experiments in vitro showed that Fstl1 inhibited macrophage migration towards 4T1 cells via decreasing colony stimulating factor 1 (CSF-1), transforming growth factor-β1 (TGFB1) and vascular endothelial growth factor-α (VEGF-α) expression of 4T1 cells. We demonstrated that Fstl1 inhibited M2-like tumor-associated macrophages recruitment towards the lung and suppressed TGFB1/Smad2/3 pathway and relevant cytokines expression of 4T1 cells. Thereby we find a potential therapeutic strategy contributing to breast cancer.