Knockdown of FSTL1 attenuates sepsis-induced acute lung injury by inhibiting inflammation and ferroptosis

Sepsis is a life-threatening condition characterized by high morbidity and mortality, with acute lung injury being the earliest and most severe complication. The damage to pulmonary microvascular endothelial cells (HPMECs) resulting from excessive inflammation plays a critical role in sepsis-induced acute lung injury (si-ALI). This study aimed to elucidate the role of Follistatin-like protein 1 (FSTL1) in si-ALI and its underlying pathophysiological mechanisms. We established an in vitro model of HPMECs stimulated by lipopolysaccharide (LPS), revealing a significant upregulation of FSTL1 at both mRNA and protein levels. Knockdown of FSTL1 mitigated inflammation by inhibiting the secretion of interleukin-1β (IL-1β) and interleukin-6 (IL-6), reducing reactive oxygen species (ROS) production, malondialdehyde (MDA) and ferrous ion (Fe^2 +) levels, while simultaneously increasing glutathione (GSH) levels. Moreover, western blot showed that the knockdown of FSTL1 effectively suppresses cellular ferroptosis through the upregulation of SLC7A11, GPX4, and FTH. Conversely, FSTL1 overexpression exacerbated inflammation and ferroptosis, an effect reversible partly by the ferroptosis inhibitor Ferrostatin-1 (Fer-1). Furthermore, utilizing cecal ligation and puncture (CLP) method to establish sepsis mice model demonstrated that silencing of FSTL1 alleviated lung tissue damage associated with sepsis-induced pulmonary injury while inhibiting IL-1β and IL-6, ROS production, and ferroptosis. In conclusion, our findings indicated that knockdown of FSTL1 significantly improved si-ALI both in vitro and in vivo, suggesting it as a potential therapeutic target for managing sepsis-induced acute lung injury.