TIMAP repression by TGFβ and HDAC3-associated Smad signaling regulates macrophage M2 phenotypic phagocytosis

Timap (tgfβ-inhibited membrane-associated protein) is an endothelium-enriched tgfβ downstream protein and structurally belongs to the targeting subunit of myosin phosphatase; however, the mechanism of tgfβ repressing timap and its functional relevance to tgfβ bioactivity remain largely unknown. here, we report that timap is reduced in tgfβ-elevated mouse fibrotic kidney and highly expressed in macrophages. tgfβ repression of timap is associated with hdac3 upregulation and its recruitment by smad2/3 at the smad binding element on timap promoter, whereas specific hdac3 inhibition reversed the timap repression, suggesting that tgfβ transcriptionally downregulates timap through hdac3-associated smad signaling. further investigation showed that timap over-expression interrupted tgfβ-associated smad signaling and timap repression by tgfβ correlated with tgfβ-induced macrophage m2 polarization markers, migration, and phagocytosis—the processes promoted by phosphorylation of the putative timap substrate myosin light chain (mlc). consistently, timap dephosphorylated mlc in macrophages and tgfβ induced macrophage migration and phagocytosis in timap- and mlc phosphorylation-dependent manners, suggesting that timap dephosphorylation of mlc constitutes an essential regulatory loop mitigating tgfβ-associated macrophage m2 phenotypic activities. given that hyperactive tgfβ often causes excessive macrophage phagocytic activities potentially leading to various chronic disorders, the strategies targeting hdac3/timap axis might improve tgfβ-associated pathological processes.