Schaaf KR, Buggs CJ, Putz ND, Langouet-Astrie CJ,. Influenza A Virus Causes Shedding of the Alveolar Epithelial Glycocalyx through Activation of Sheddases. FASEB J. 2022 May;36 Suppl 1
Hypothesis: We hypothesize that IAV causes glycocalyx shedding through induction of host sheddases.
Methods: We examined the literature and curated a list of sheddases associated with IAV with potential to cleave the glycocalyx (MMP-7, -2, -9 and their inhibitors TIMP-1 and -2). C57BL/6 mice were infected intranasally with A/PR/8/34 (H1N1) at 30,000 PFU/mouse and bronchoalveolar lavage and lung tissue were collected at day 1, 3, and 7 post infection. Sheddase expression was assessed by RT-qPCR and RNAscope was used to localize lung sheddase expression in infected and uninfected lungs. MLE-12 mouse lung epithelial cells were infected with viable or heat-inactivated (56C for 30 min) A/PR/8/34 (H1N1) at a MOI of 1 and sheddase expression measured by RT-qPCR.
Results: Mice infected with IAV develop significant lung inflammation (increased BAL inflammatory cells), lung permeability (increased BAL protein), and increased glycocalyx shedding. MMP-7 is upregulated in infected vs. uninfected lungs at day 1 and 3 post infection, then returns to baseline levels by day 7. MMP-7 is only expressed in cells that are directly infected by IAV. Expression of the MMP-7 inhibitor TIMP-1 is similar to uninfected lungs on day 1, but increases 50-fold on day 3. In contrast, MMP-2 and MMP-9, as well as their inhibitor TIMP-2 are not upregulated in the first 7 days after IAV infection. Preliminary studies in lung epithelial cells suggest that heat-inactivated IAV fails to upregulate MMP-7.
Conclusions: Together, these data suggest that localized IAV infection increases MMP-7 in a murine model of IAV infection, but has no effect on several other sheddases. This suggests that MMP-7 may modulate IAV-induced glycocalyx shedding. Future studies will explore the mechanisms of IAV induced glycocalyx shedding which could provide molecular targets for clinical intervention in IAV-ARDS pathogenesis.
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