Neutrophil Elastase Inhibits Activation of Adhesome Signaling Proteins and Promotes an Inflammatory Phenotype in Airway Smooth Muscle (ASM) Tissue
Authors: Lockett Angelia D , Wu Yidi , Gunst Susan 
Published: November 2023

Neutrophils release the serine protease, neutrophil elastase, at sites of airway inflammation, which is a central feature of asthma. Neutrophil elastase degrades elastin, an integral extracellular matrix (ECM) protein that binds to integrins on ASM to promote the elasticity and structural integrity of the tissue. We hypothesized that neutrophil elastase would modulate the activation of integrin associated adhesion complexes (adhesomes) that regulate cytoskeletal signaling pathways by degrading ECM proteins and disrupting their interactions with integrins. By severing connections between the ECM and integrins, elastase may alter the mechanical load on adhesion junctions and modulate phenotypic expression.

The adhesome proteins focal adhesion kinase (FAK) and paxillin are activated by mechanical tension and play a key role in ASM mechanotransduction. A decrease in mechanical load inhibits FAK and paxillin activation and increases the activation of Akt and the IL‐13‐induced secretion of eotaxin, indicators of the synthetic phenotype (Wu 2016). We evaluated the effect of neutrophil elastase on ASM tissues by incubating them with elastase for 2–3 hr and then stimulating them with ACh or IL‐13, followed by the analysis of FAK (Tyr 397), paxillin (Tyr 118) and Akt (Ser 473) phosphorylation and activation. Eotaxin secretion from the tissues was measured by ELISA after IL‐13 treatment for 20 hrs. Elastase treatment decreased activation of FAK and paxillin in ACh‐stimulated tissues and promoted the activation of Akt and the secretion of eotaxin, consistent with a decreased mechanical load and promotion of the synthetic inflammatory phenotype. Elastase treatment also reduced the contractile force in response to ACh by ~20% but did not reduce MLC phosphorylation, indicating that contractile protein activation was unaffected, which suggests that the force reduction resulted from decreased tension transmission at ASM cell – ECM junctions.

We hypothesized that the degradation of integrin‐ECM connections by elastase might alter mechanical load by causing the dissolution of cytosolic adhesome complexes that form complexes with integrin proteins. Talin binds directly to integrins and F‐actin filaments and provides a scaffold for the assembly of adhesome complexes. Talin can undergo cleavage leading to adhesome complex destabilization (Franco 2004). In the present study, treatment of ASM tissues with elastase for 3 hrs resulted in the cleavage of talin, suggesting that elastase treatment caused the disassembly of adhesome complexes.

In conclusion, our results suggest that elastase promotes an inflammatory phenotype in ASM tissues by disrupting the connections between the ECM and integrin proteins, resulting in decreased mechanical tension transmitted through adhesion junctions and in the disassembly of adhesome complexes. The reduction in mechanical load at adhesion junctions promotes the activation of signaling pathways involved in inflammation, chemokine synthesis and the synthetic phenotype. Elastase released into the airway tissue by neutrophils may promote the inflammatory synthetic phenotype in ASM.

Support or Funding Information

Funding: NIH grant numbers: R01 HL29289; R01 HL029289‐27S1; HL 109629; HL48522