Macrophages Maintain Mammary Stem Cell Activity and Mammary Homeostasis via TNF-α-PI3K-Cdk1/Cyclin B1 Axis

This study investigates the role of macrophages in maintaining mammary stem cell activity and mammary homeostasis. The researchers found that macrophages regulate mammary epithelial cell division and development through the TNF-α-Cdk1/Cyclin B1 axis. In vivo experiments showed that depleting macrophages reduced the number of mammary basal and stem cells while increasing luminal cells. In vitro, a 3D culture system demonstrated that co-culturing mammary basal cells with macrophages promoted the formation of branched mammary organoids. The study highlights that TNF-α from macrophages activates the PI3K/Cdk1/Cyclin B1 signaling pathway in mammary cells, crucial for maintaining mammary stem cell activity and organoid formation, underscoring the importance of the macrophageal niche in mammary tissue homeostasis.