Macrophages Maintain Mammary Stem Cell Activity and Mammary Homeostasis via TNF-α-Cdk1/Cyclin B1 Axis

The study demonstrated that mammary resident macrophages played a crucial role in regulating mammary epithelium cell division and development through the TNF-α-Cdk1/Cyclin B1 axis. In vivo experiments showed that depleting macrophages led to a reduction in mammary basal and stem cells, while increasing luminal cells. In vitro, a 3D culture system revealed that co-culturing mammary basal cells with macrophages promoted the formation of branched functional mammary organoids. The TNF-α produced by macrophages activated the Cdk1/Cyclin B1 signaling in mammary cells, which was essential for maintaining mammary stem cell activity and homeostasis. These findings highlighted the importance of the macrophageal niche and the Cdk1/Cyclin B1 axis in mammary gland biology.