Phosphodiesterase 4 (PDE4) is an enzyme that breaks down cyclic adenosine monophosphate (cAMP). cAMP is a signalling molecule that is involved in many cellular processes, including inflammation, pain, and smooth muscle contraction. PDE4 is expressed in a variety of tissues, including the lungs, skin, immune cells, and brain. The different PDE4 subtypes have distinct tissue distributions and functions. The main functions of PDE4 include: Regulating inflammation: PDE4 inhibitors are being studied as potential treatments for inflammatory diseases such as asthma, chronic obstructive pulmonary disease (COPD), and rheumatoid arthritis. Regulating pain: PDE4 inhibitors are also being studied as potential treatments for pain conditions such as migraine and chronic pain. Regulating smooth muscle contraction: PDE4 inhibitors are being studied as potential treatments for conditions that involve smooth muscle contraction, such as asthma and urinary incontinence. Regulating cell growth and di...