SPP1 exacerbates ARDS via elevating Th17/Treg and M1/M2 ratios through suppression of ubiquitination-dependent HIF-1α degradation

Abstract

Background: Acute respiratory distress syndrome (ARDS) is a severe inflammatory pulmonary condition that leads to respiratory failure. The imbalance of Th17/Treg and M1/M2 is implicated in ARDS. A better understanding of the regulation of the balance of Th17/Treg and M1/M2 may provide novel therapeutic targets for ARDS.

Methods: Plasma and BALF samples were collected from ARDS patients. Inflammatory cytokines were examined by ELISA. Th17, Treg, M1 and M2 were identified via immunofluorescence staining of RORγt, Foxp3, iNOS and Arg-1. H&E and Masson's trichrome staining were applied for evaluating pulmonary damage and fibrosis. A mouse model of ARDS was established through LPS administration. HIF-1α was immunoprecipitated and subjected to ubiquitination analysis via western blotting. The expression of SPP1, VHL and HIF-1α was examined by RT-qPCR and western blotting.

Results: ARDS patients showed elevated levels of inflammatory cytokines and ratios of Th17/Treg and M1/M2. SPP1 was upregulated in ARDS mice, and silencing of SPP1 alleviated lung injury and fibrosis. SPP1 inhibited VHL expression to reduce the ubiquitination and degradation of HIF-1α in ARDS. Overexpression of SPP1 facilitated Th17, Treg and M1 polarization but inhibited M2 polarization through upregulation of HIF-1α.

Conclusion: SPP1 elevates Th17/Treg and M1/M2 ratio by suppressing VHL expression and ubiquitination-dependent HIF-1α degradation, thus exacerbating ARDS. Our study provides novel mechanistic insights into ARDS pathogenesis and promising therapeutic targets.

Keywords: ARDS; Degradation; HIF-1α; Macrophage; SPP1; Th17; Treg.