Sca-1 expression depicts pro-inflammatory murine neutrophils under steady state and pathological conditions
Authors: Nahiyera Milind , Sinha Supriya , Dhankani Priyanka , Singhal Apurwa , Singh Abhinav , Sharma Rakesh Kumar , Gond Ambalika , Gupta Kanchan , mitra Kalyan , Lahiri Amit , Jagavelu Kumarvelu , Filippi Marie-Dominique , Dikshit Madhu , Kumar Sachin 
Published: September 2024

AbstractNeutrophils play a crucial role in various pathophysiological conditions, yet targeting them for therapeutic intervention has been discouraged due to the associated risk of infections. Thus, identification of neutrophil subsets and their involvement in inflammatory conditions is warranted for targeted therapeutic strategies. This study, through screening of surface proteins on neutrophils isolated from different tissue microenvironments, identified a distinct neutrophil subset, CD11b+Ly6G+Sca1+neutrophils, expressing Stem cell antigen-1 (Sca-1). Interestingly, these Sca1posneutrophils were more abundant in the liver than BM, blood, and lungs. Further analysis revealed that Sca1pos neutrophils are mature and activated with enhanced effector functions, including superoxide generation, phagocytosis, degranulation, and NETosis. Tracing studies demonstrated ageing-independent characteristics of Sca1posneutrophils. Remarkably, Sca1pospro-inflammatory neutrophils promote T cell proliferation through ROS, while inhibition of Sca-1 restores T cell proliferation and ROS generation. Intriguingly, inflammatory as well as metabolic cues induce the transition of conventional neutrophils (Sca1neg) to Sca1posneutrophils and differentiation of progenitors (granulocyte monocyte progenitors, GMPs) into Sca1posneutrophils. Furthermore,in vivomodels of acute inflammation, peritonitis, and chronic inflammatory condition, non-alcoholic steatohepatitis (NASH), exhibit an increase of Sca1posneutrophils at inflammatory sites, while the pharmacological approach using NAC specifically mitigates the expansion of these pro-inflammatory neutrophils. Collectively, our findings unveil a novel subset of Sca1posneutrophils with implications for inflammation.Significance StatementNeutrophilic inflammation remains the leading driver in infectious and inflammatory diseases. Targeting neutrophil populations remained un-recommended due to hampering the immunological functions of neutrophils. The heterogeneity of neutrophils provides the perspective to target altered neutrophil subsets, but subtle changes defining neutrophil subsets make it complex and ambiguous. Our study identified abundant expression of Sca1on distinct neutrophils under steady state and inflammation. Thus, we reported previously undefined Sca1pospro-inflammatory neutrophil subsets and elucidated their regulation. This study further established their involvement in acute and chronic inflammatory conditions. This understanding may further pave the way toward targeting specific neutrophil subsets in pathologies characterized by neutrophilic inflammation.Graphical AbstractHighlightsCD11b+Ly6G+Sca1+neutrophil subset identified with <1% presence in BM and >40% frequency in the liver.These neutrophils are mature and activated, demonstrating enhanced effector functions.Sca1posneutrophils promote T cell proliferation and display pro-inflammatory characteristics.Conventional Sca1negneutrophils transition into Sca1posneutrophils in response to inflammatory signals, while progenitors undergo differentiation.Both acute and chronic inflammatory models show the expansion of CD11b+Ly6G+Sca1+neutrophils.