Sodium-coupled neutral amino acid transporter SNAT2 – a regulatory hub of alveolar homeostasis and its critical role in acute lung injury/ARDS

• Applicant: Professor Dr. Wolfgang Kübler
• Subject Area: Anaesthesiology
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 441105380

Acute respiratory distress syndrome (ARDS), the most frequent cause of mortality in critical care medicine, is characterized by hyperinflammation, epithelial apoptosis, and a loss of alveolar-capillary barrier function with consecutive formation of a proteinaceous lung edema that ultimately results in respiratory failure. Despite numerous clinical trials, effective pharmacological treatments to improve overall survival in ARDS patients are still lacking. This unmet medical need stresses the necessity for a better understanding of the pathomechanisms underlying ARDS and the regulation of alveolar homeostasis and repair. In our project proposal, we postulate a key role for Na+-coupled neutral amino acid transporter SNAT2 in lung edema formation and alveolar epithelial apoptosis in ARDS. So far SNAT2 has not been implicated in any pulmonary pathologies. Yet, as SNAT2 mediates cellular uptake of neutral amino acids in cotransport with Na+, it may impact both Na+-driven alveolar fluid clearance (AFC) and amino acid-regulated cell signaling. In preliminary proof-of-concept data we show i) that SNAT2 expression is downregulated in response to inflammatory stimuli characteristic for ARDS, ii) that loss of SNAT2 inhibits AFC thus promoting edema formation, and iii) that SNAT2 loss aggravates ER-stress, ROS formation, and autophagy-mediated apoptosis through intracellular amino acid deprivation. SNAT2 may thus evolve as a novel master regulator of alveolar homeostasis, with SNAT2 loss promoting the classic hallmarks of ARDS.In the proposed work, we will first consolidate the relevance of SNAT2 in AFC and edema resolution in situ in isolated perfused mouse lungs, in vivo in a murine model of acute lung injury, and in vitro in a pulmonary epithelial cell culture system. Next, we will analyze SNAT2 regulation in the intact and injured alveolar epithelium. To this end, we will focus on changes in SNAT2 expression and function in response to inflammatory stimuli, bacterial toxins, or infection with live bacteria both in vitro and in situ, and dissect underlying regulatory mechanisms. Lastly, we will probe in depth for the regulatory role of SNAT2 on epithelial injury and repair processes. Specifically, we propose that in response to injury expression of ER stress markers, apoptotic and autophagic proteins, and ROS production will be increased in cells lacking functional SNAT2.We anticipate the results of our research to generate fundamental new knowledge, in that they will critically propel our understanding of dysregulated alveolar fluid transport and edema formation and generate important insights into the role of amino acids and their co-transporters in pro- and anti-apoptotic signaling pathways pertinent to alveolar epithelial injury. Our findings are expected to provide significant translational benefits by identifying SNAT2 as a potential target to improve edema resolution and maintain or restore epithelial barrier function in ARDS patients.

• DFG Programme: Research Grants