Abstract Rationale Acute Respiratory Distress Syndrome (ARDS) is the most frequent cause of death in intensive care units, yet effective pharmacological treatments are still lacking. Dysregulation of alveolar fluid clearance (AFC) and loss of alveolar-capillary barrier function due to alveolar epithelial cell (AEC) death are hallmarks of ARDS. The Na+-coupled neutral amino acid (AA) transporter SNAT2 belongs to the SLC38 gene family and transports one neutral AA along with one Na+. We previously demonstrated that SNAT2 is expressed in AEC and promotes AFC in isolated perfused lungs via its function as Na+ transporter. Here, we investigated the role of SNAT2 as AA transporter and its relevance in the regulation of AEC homeostasis. We hypothesized that SNAT2 might be a central regulator of AEC metabolism and fate in acute lung injury (ALI)/ARDS, and could thus represent a novel therapeutic target. Methods In human primary AEC, SNAT2 was either inhibited by α-methylaminoisobutyric acid (MeAIB), knocked down (KD) by siRNA, or overexpressed (OE) by transfection with a SLC38A2-Myc-DDK-tagged plasmid. AEC were stimulated with a mix of LPS, IFN-γ, TNF-α and IL-1β (cytomix). After 24h, apoptosis, autophagy and ER-stress markers (ATF4, CHOP) were evaluated by qPCR, Western blot, and flow cytometry. Cell proliferation and migration were assessed by Ki67 staining, BrdU incorporation and scratch assay. Changes in cell metabolism were evaluated by Seahorse assay. In vivo, LPS (5 mg/kg BW intranasally)-induced ALI was assessed in Slc38a2+/- and corresponding wildtype (WT) mice. Results Stimulation of AEC with cytomix downregulated SNAT2 expression (protein and mRNA). After 24h of MeAIB treatment, intracellular levels of glutamine (Gln) were reduced, and Seahorse assays revealed a metabolic shift towards glycolysis. In parallel, both MeAIB treatment and SNAT2 KD promoted AEC apoptosis, upregulated ATF4 and CHOP, and induced excessive autophagy. In addition, SNAT2 loss markedly impaired AEC proliferation and migration. Conversely, SNAT2 OE in AEC reversed the cytomix-induced upregulation of ATF4 and CHOP, and restored their proliferation capacity. Upon LPS treatment Slc38a2+/- mice showed increased barrier permeability (protein in bronchoalveolar lavage), and increased ATF4 and CHOP expression in lung tissue relative to WT mice. Conclusions SNAT2 loss is caused by inflammatory stimuli and promotes a glycolytic shift, ER-stress, excessive autophagy and cell death in AEC. As such, SNAT2 loss may contribute relevantly to the pathogenesis of ALI and impair epithelial repair and regeneration. These effects are likely mediated by impaired Gln uptake and dysregulation of AEC metabolic homeostasis. This abstract is funded by: Deutsche Forschungsgemeinschaft
Li et al. (2026) studied this question.