The Emerging Roles of the Gaseous Signaling Molecules NO, H₂S, and CO in the Regulation of Stem Cells

Stem cell technology can be used in tissue engineering and regenerative medicine to transplant stem cells of somatic, embryonic, or induced pluripotent origin, which have tremendous potential for the treatment of currently incurable diseases. Stem cells can maintain their stemness through their self-renewal capability while promoting tissue repair and regeneration through differentiation into various target tissue cells. These two major processes of stem cell biology are precisely regulated via extracellular and intracellular signals. Gaseous signaling molecules have recently been identified to play important roles in both physiology and pathophysiology, and inhalable nitric oxide (iNO) has even been applied as a therapeutic agent. Compared with chemical formulations, these molecules have lower molecular weights and are more likely to pass through the blood-brain barrier and between cells. Nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S), three major gaseous signaling molecules involved in biological functions, are emerging as regulators of stem cell processes such as self-renewal, differentiation, survival, anti-apoptotic effects, proliferation, and immune rejection. Although many reviews concerning the roles of gaseous signaling molecules in different diseases or systems are available, few have focused on the roles of these molecules in the regulation of stem cells. Therefore, the aim of this paper is to systematically review the current literature on the functions and mechanisms of the gaseous signaling molecules NO, H₂S, and CO in different types of stem cells and to summarize the effects of these molecules on stem cell biology and in therapy.