Extracellular matrix maintenance by hypodermal macrophages modulates Staphylococcus aureus skin infection
VOISIN B. 1,2, NADELLA V. 2, DOEBEL T. 2, GOEL S. 2, SAKAMOTO K. 2, AYUSH O. 2, JO J. 2, KELLY M. 3, KOBAYASHI T. 2, JIANG J. 4, HU Y. 5, YAN C. 5, NAGAO K. 2
1 CNRS, UPR3572, I2CT, Strasbourg, France; 2 National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, United States; 3 Single-Cell Analysis Facility, Frederick National Laboratory for Cancer Research, Frederick, United States; 4 University of Texas Health Science Center, San Antionio, United States; 5 National Cancer Institute, National Institutes of Health, Rockville, United States
Macrophages play essential roles in tissue homeostasis but their functions in skin remains incompletely understood. Particularly, the biology of macrophages of the hypodermis (HDM), the deepest layer of the skin and a common site of Staphylococcus aureus (S. aureus) infection, remains largely unexplored. By using a combination of flow-cytometry, bulk RNA-seq and single-cell RNA-seq, we uncovered two populations of HDM with distinct transcriptomes and tissue-residency. Both populations relied on the colony stimulating factor 1 (CSF1) receptor signaling for their tissue homeostasis. Single-cell RNA-seq of stromal cell compartment identified fibroblasts as a major source of hypodermal CSF1, depletion of which, in Tek-cre x Csf1-floxed mice, resulted into a layer-specific depletion of macrophages. Strikingly, HDM depletion was spatially and temporally associated with an alteration of fibrillar collagen network and increased accumulation of hyaluronic acid (HA). HDM control over HA tissue accumulation was dependent on insulin growth factor 1 (IGF1), whose cell-autonomous production tuned HDM transcription factor circuitry and expression of the HA-receptor LYVE1 through MAPK signaling cascade. Interestingly, HA accumulation in the hypodermis was associated with a significant decrease of cellulitis, triggered by local injection of S. aureus in vivo in different mouse models. Particularly, in-vitro culture of S. aureus in presence of HA demonstrated a dose-dependent bacteriostatic effect, suggesting that deposition of hyaluronic acid in the absence of HDM or HDM-derived IGF1 conferred host protection against S. aureus. These findings extend macrophage functions to the regulation of hyaluronic acid with a crucial anti-microbial role, which may be harnessed to limit the establishment of infection in the hypodermal niche.