The Desmosome-Keratin Intermediate Filament Network in Lung Epithelial Injury, Repair and Regeneration - The normal structure and function of the lung are maintained in homeostasis, and repaired and regenerated following diverse injuries by region-specific stem and progenitor cells. Dysfunction or loss of lung stem cells is believed to contribute to human idiopathic pulmonary fibrosis (IPF). Desmoplakin (DSP) is the most abundant component of desmosomes, which are intercellular adhesive junctions found in epithelia. Previous genome- wide association studies (GWAS) have identified a single nucleotide polymorphism (SNP), rs2076295 in DSP intron 5, as a significant genetic variant associated with IPF. Recent studies revealed a transitional state in alveolar type II progenitor cells (AT2) that is persistent in pulmonary fibrosis, including IPF. This transitional state of AT2 is marked by elevated expression of Keratin 8 (K8), an essential component of the intermediate filament (IF) cytoskeleton. The keratin IF cytoskeleton anchors to the desmosome through DSP binding, forming a robust transcellular network that enhances mechanical resilience of epithelial tissues. Given the critical roles of DSP and K8 in the desmosome-keratin IF network and their association with IPF, we seek to explore the role of this network in lung injury and fibrosis. Preliminary data suggest that the desmosome-K8 IF network serves dual functions in regulating apoptosis and differentiation of AT2, contextually linked to lung injury and the niche stiffness. This model could resolve the contradictory results from earlier GWAS. Specifically, low baseline DSP expression may predispose individuals to IPF by increasing AT2 susceptibility to apoptosis post-injury. In contrast, higher DSP expression, triggered by increased niche stiffness, might induce the transitional state of AT2 and inhibit their differentiation into alveolar type I cells (AT1), impeding lung regeneration and promoting fibrosis. In this proposal, we hypothesize that the desmosome-keratin intermediate filament network functions as a signaling platform, dynamically regulating the fate and state of AT2 cells in response to lung injury and the mechanical properties of their niche. Specific aims are: (1) to determine the mechanisms by which rs2076295 genetic variants regulate DSP gene expression and how reduced baseline DSP expression increases the susceptibility of AT2 to apoptosis after lung injury; (2) to determine whether matrix stiffness-dependent remodeling of the desmosome-K8 IF network regulates the transitional AT2 state and the mechanisms involved; and (3) to test the therapeutic potential of targeting the mechanosensitive desmosome-K8 IF network to reinstate AT2 regenerative capabilities and reverse persistent lung fibrosis in mice.
