Possible mechanisms of autophagy-dependent regulation of airway fibrosis: Autophagy may regulate airway fibrosis via two different mechanisms: Hypothesis (A) Autophagy is required for airway fibrosis by serving as a backup energy reserve providing the cellular resources needed during ECM protein biosynthesis. Hypothesis (B) Autophagy inhibits airway fibrosis via degradation of ECM proteins and their precursors. ASM = airway smooth muscle, ECM = extracellular matrix, Baf A1 = bafilomycin A1, CQ = chloroquine, 3- MA = 3-methyladenine, MΦ = macrophage, TGFβ = transforming growth factor-beta, mTOR = mammalian target of rapamycin.