Biochemistry, Cyclic GMP

Excerpt

Second messengers are small, nonprotein intracellular molecules that amplify signals generated by cell-surface receptors. One such messenger, 3′,5′-cyclic guanosine monophosphate (cGMP), plays a central role in transducing extracellular signals into diverse physiological responses. Intracellular cGMP levels are tightly regulated by the opposing actions of guanylate cyclases, which synthesize cGMP from guanosine-5′-triphosphate, and phosphodiesterases (PDEs), which hydrolyze cGMP to inactive 5′-GMP and terminate signaling. Elevated cGMP activates protein kinase G and downstream effectors, thereby driving key physiological processes, including vasodilation.

cGMP signaling is essential for a broad range of functions, including synaptic transmission in vision, vascular homeostasis, and smooth muscle relaxation. Pharmacological targeting of the cGMP pathway has produced several successful therapies. Sildenafil (Viagra) enhances cGMP signaling by inhibiting cGMP-specific PDEs. More broadly, modulation of cGMP signaling underlies approved treatments for erectile dysfunction, pulmonary hypertension, heart failure, irritable bowel syndrome, coronary artery disease, and achondroplasia, highlighting the translational significance of this pathway.