Hippo Signaling in the Lung: A Tale of Two Effectors—Yap Drives Airway Fate and Taz Drives Alveolar Differentiation

The mammalian lung operates under a biological paradox, requiring architectural fragility for gas exchange while maintaining robust regenerative plasticity to withstand injury. The Hippo signaling pathway has emerged as a central "rheostat" in orchestrating these opposing needs, yet the distinct roles of its downstream effectors remain underappreciated. This review synthesizes recent genetic and mechanobiological advances to propose a "Tale of Two Effectors" model, arguing for the functional non-redundancy of YAP and TAZ. We posit that YAP functions to drive airway progenitor expansion, mechanical force generation, and maladaptive remodeling. Conversely, TAZ-regulated uniquely via transcriptional mechanisms and mechanotransduction-acts as an obligate driver of alveolar differentiation and adaptive repair through an NKX2-1 feed-forward loop. Furthermore, we introduce the "See-Saw" model of tissue fitness, where mesenchymal niche collapse releases the mechanical brake on the epithelium, triggering the bronchiolization characteristic of pulmonary fibrosis. Finally, we extend this framework to malignancy, illustrating how Small Cell Lung Cancer (SCLC) subtypes mirror these developmental and regenerative states. This integrated framework offers new therapeutic distinct targets for modulating tissue fitness and resolving fibrosis.