Circ_0021205: a key player in modulating inflammatory responses and mitigating acute lung injury in sepsis

Circular RNAs (circRNAs) have been increasingly proven to regulate the progression of various diseases, including sepsis-related acute lung injury (ALI). In the current study, we detected the role of circ_0021205 in sepsis-related ALI and its potential value in the treatment of sepsis-related ALI. RAW264.7 cell line was co-cultured with lipopolysaccharide (LPS) to construct sepsis-related ALI cell. The expression levels of RNA and protein were valued using qRT-PCR and Western blot (WB), respectively. Cell viability and cell apoptosis were estimated by CCK-8 and flow cytometry, respectively. The targeting relationship between circ_0021205, miR-545-3p and PIK3C3 were analyzed using dual-luciferase reporter experiment or RNA pull-down assay. HE staining, wet/dry (W/D) weight ratio, myeloperoxidase (MPO) level and TUNEL staining of lung tissues and inflammatory cells in BALF were detected in the sepsis model. In LPS-induced RAW264.7 cell, the expression levels of circ_0021205 and PIK3C3 were down-regulated, while miR-545-3p was up-regulated in LPS-induced RAW264.7 cell line. Overexpression of circ_0021205 decreased the levels of IL-1β, IL-6 and TNF-α, reduced the expression of iNOS and CD86 and elevated the expression of CD206 and Arg1 both in vitro and in vivo. Compared with the LPS+vector-NC, the viability of TC-1 cells co-cultured with the cell supernatant of overexpressed circ_0021205 was increased, but apoptosis level was decreased compared with LPS+vector-NC. Circ_0021205 could target miR-545-3p, thereby regulating the expression of PIK3C3. PIK3C3 was the downstream targets of miR-545-3p. Up-regulation of circ_0021205 could decrease injury score, W/D ratio, MPO level and apoptosis level in lung tissue, and the total protein, neutrophils and macrophages in BALF. Collectively, our research confirmed that circ_0021205 could regulate macrophage polarization via sponging miR-545-3p to affect the expression of PIK3C3, and then influence sepsis-related ALI. However, given that classic autophagy markers (LC3-II/I, p62, and Beclin-1) were not detected in the present study, the regulatory role of PIK3C3 may not be exclusively dependent on autophagy activation. PIK3C3-mediated non-autophagic signaling pathways may also contribute to the phenotypic and functional alterations of macrophages observed in this work.