Obesity supersizes the immune response to stroke

Please cite: Bradshaw K, Holsten J, Hahn O, Foltz A, Zera KA, Zhu L, Haarslev C, Wyss-Coray T, Peterson TC, Buckwalter M (in press). Obesity supersizes macrophage and neutrophil activation after stroke while lipid droplets play a protective role. Journal of Neuroinflammation. Obesity is a key risk factor for stroke and by 72 hours after stroke, obese mice have exacerbated stroke sizes, increased neuroinflammation, and motor deficits. To understand how obesity worsens outcomes, we performed single-cell RNA sequencing (scRNASeq) of immune cells in the blood (peripheral blood mononuclear cells, PBMCs) and brain (cortex) 72 hours after stroke or sham surgery in control or diet-induced obese mice. In the blood of obese mice compared to normal diet mice, myeloid cells exhibit the most transcriptional change in both sham and stroke mice. This includes two distinct chemotaxis neutrophil subtypes (enriched with neutrophil chemokine ligand Cxcl2 and receptor Cxcr2, respectively), interferon signaling neutrophils, and two macrophage subtypes enriched in the lipid droplet gene perilipin-2 (Plin2) with and without the foamy macrophage marker Cd36. In the brain, obesity did not induce major transcriptional changes in immune cells in sham mice, but after stroke there were dramatic changes in infiltrating Plin2+ and Plin2- macrophages, interferon-signaling dendritic cells, and 1 chemotaxis neutrophil subtypes. The immune changes induced by stroke in obese mice in brain macrophages and dendritic cells mirrored obesity-induced changes in blood macrophages, including amplification of lipid-related, interferon, and protein degradation genes and downregulation of protein synthesis genes. In neutrophils, obesity amplified interferon and TNF signaling in the blood while in addition enhancing oxidative stress, complement, and a robust pro-thrombotic transcriptional signature in brain neutrophils. Co-expression analysis revealed that Plin2 expression correlates with lipid-related, immune, stress, and coagulation genes, suggesting that lipid droplet accumulation, inflammation, oxidative stress, and coagulation are processes that amplify each other and are attractive candidates for therapies to ameliorate obesity-exacerbated stroke outcomes.