The Role of the Vimentin Cytoskeleton in Lung Cancer, Platelet Mechanics, and Acute Lung InjuryPublic
Vimentin intermediate filaments (VIFs) provide mechanical integrity to cells and serve as markers of tissue origin and cell differentiation. Several non-mechanical roles for vimentin have recently been reported, including regulation of key pathways that control cell growth, cell signaling, and cell motility. Here, I present the role of vimentin in three different contexts. (1) Vimentin is highly expressed in metastatic cancers, and its expression correlates with poor patient prognoses. However, no causal in vivo studies linking vimentin and NSCLC progression existed until now. LSL-KrasG12D, Tp53fl/fl mice (KPV+/+) were crossed with vimentin-knockout mice (KPV–/–); KPV–/– mice have attenuated tumor growth and improved survival compared to KPV+/+ mice. KPV+/+ mice were treated with withaferin A (WFA), an agent that disrupts VIF formation. This treatment suppresses tumor growth and reduces tumor burden in the lung. Using an allograft tumor model, luciferase-expressing KPV+/+, KPV–/–, and KPVY117L cells were implanted into the flanks of nude mice to track cancer metastasis to the lung. KPVY117L cells form oligomers called unit-length filaments but cannot assemble into mature VIFs. KPV–/– and KPVY117L cells fail to metastasize, suggesting that cell-autonomous metastasis requires mature VIFs. Integrative metabolomic and transcriptomic analyses reveal that KPV–/– cells upregulate genes associated with ferroptosis, an iron-dependent form of regulated cell death. KPV–/– cells display reduced levels of the lipid repair enzyme glutathione peroxidase 4 (GPX4), leading to the accumulation of toxic lipid peroxides and increased ferroptosis in KPV–/– cells. I show that vimentin protects the cell from ferroptosis-mediated cell death, which contributes to tumor growth and metastasis in NSCLC. (2) Blood clots form after injury when platelets bind fibrin fibers and form thrombi. The mechanical properties of the clot are critical for proper wound healing and restoration of laminar blood flow. I found that platelet-rich plasma isolated from Vim–/– mice formed less contractile and viscoelastic thrombi than Vim+/+ platelet-rich plasma. In vivo, Vim–/– mice exhibit longer clotting times than Vim+/+ mice. I show that vimentin is required for efficient and mechanically robust blood clot formation through this work. (3) Acute lung injury is mediated by IL-1β signaling, which requires maturation via the NLRP3 inflammasome. Our group found that vimentin scaffolds the NLRP3 inflammasome and is required for IL-1β release. To target vimentin-mediated inflammasome signaling, we designed PEG-b-PPS micelles that contain Five1, a recently identified small molecule that causes VIF disassembly. Here, I provide proof-of-principle evidence that these nanoparticles decrease IL-1β release in vitro. Together, I show that vimentin is critical in NSCLC signaling by suppressing ferroptosis and promoting metastasis. Vimentin confers unique mechanical properties to blood clots which is required for efficient hemostasis. Finally, vimentin can be targeted in a cell-specific manner through nanoparticle delivery to disrupt pro-inflammatory signaling scaffolds and suppress inflammation. These studies ultimately advance understanding of intermediate filaments' mechanical and non-mechanical roles in cancer biology, hemostasis, and acute lung injury.