How do quiescent cells maintain their viability?

Quiescent adult stem cells maintain their viability through using cyclin dependent kinase inhibitors and Rb tumor suppressor. More specifically, at the G1 checkpoint mitogens lead to cyclin D expression, which activates CDKs and inactivates Rb. Adult stem cells also use cyclin dependent kinase inhibitors and Rb to maintain the restriction point and enable cells to exit the cell cycle. Quiescent cells also activate autophagy, to help remove damaged or unnecessary toxins and maintain cellular homeostasis. Additionally, these cells exhibit increased resistance to apoptosis. They activate anti-apoptotic signaling pathways to survive under conditions where dividing cells would be undergoing cell death.