Macrophage-fibroblast interaction is required for asbestos-induced toxicity

All organ tissues contain fibroblasts and macrophages. Emerging evidence indicates that direct interaction between fibroblasts and macrophages occur to maintain homeostasis as well as determining disease outcomes, such as asbestos-induced toxicity. The interaction, or communication, between these cells have a role in

changing the phenotype of each cell. Activated fibroblasts express sonic hedgehog, and macrophages express proteins in the Hedgehog pathway, including patched, smoothened, and glioma-associated oncogene. Our preliminary data show that macrophages from human subjects have increased expression of Gli1, Smo, and

Ptch. Subjects with asbestos-induced toxicity also express significantly more PGC-1a and CPT1A in lung macrophages than normal subjects. Mice harboring a conditional deletion of Shh in fibroblasts blocked Gli1 expression in macrophages, whereas asbestos-exposed WT mice had increased expression of Gli1, PGC-1a,

Cpt1a, and increased OXPHOS in macrophages. Recombinant Shh induced expression of acyl carnitines necessary for FAO. These data strongly suggest that fibroblast-macrophage interaction has an important role in asbestos-induced toxicity. We hypothesize that fibroblast-macrophage interactions via Hh signaling mediate

macrophage metabolic reprogramming and progressive asbestos-induced toxicity. In Aim 1, we will co-culture human lung fibroblasts (HLF) with resident alveolar macrophages (RAMs) or monocyte-derived macrophages (MDMs) from human subjects to determine which cell subset has Hh signaling. We will also determine

mitochondrial bioenergetics to confirm FAO in lung macrophages from subjects with asbestos-induced toxicity with and without silencing Smo. Aim 2 we will determine the fibroblast cell type that is responsible for production of Shh utilizing Cthrc1creER mice. We will also determine the mechanism(s) by which Hh signaling in macrophages

mediates metabolic reprogramming to FAO utilizing mice harboring a conditional deletion of Smo in macrophages. In Aim 3, we will determine if constitutive activation of hedgehog signaling in macrophages mediates progression of established asbestos-induced toxicity. We will also determine if disruption of fibroblast-

macrophage communication will abrogate this progression. By using innovative techniques, transgenic mice, and human tissue, the studies in this proposal will provide: (a) new insights into fibroblast-macrophage interaction via Hh signaling; (b) an understanding of the molecular mechanism(s) by which fibroblast-macrophage

interaction mediate metabolic reprogramming; and (c) proof-of-concept by targeting the Hh pathway genetically and pharmacologically to disrupt fibroblast-macrophage interaction and halt or reverse asbestos-induced toxicity.