GDF3 induces inflammation through the activation of SMAD2/3 signaling in adipose tissue macrophages from aged mice.

NLRP3 inflammasome-induced inflammation in aging is linked to visceral adiposity and increased inflammatory adipose tissue macrophages (ATMs) and aged adipose B cells (AABs). However, additional pathways supporting this process are unclear. Transcriptome analysis revealed significant age- and NLRP3-dependent upregulation of Gdf3 in ATMs. Here, we investigate the impact of GDF3-SMAD2/3 axis on adipose tissue (AT) inflammation in old mice. We report that inflammatory ATMs increase with elevated phospho-SMAD2/3 level during aging. Similarly, rGDF3 treatment to cultured macrophages of old mice reduces CD206 while increasing pSMAD2/3 and CD9. Lifelong Gdf3 deletion protects 22-months-old mice from LPS-induced hypothermia. Furthermore, old Gdf3-/- mice exhibit reductions in CD11c+/CD9+ ATMs, PDL1+/CD73+ AABs with decreased pSMAD2/3 and Il1b, Il6, Tnfa in AT. Single-cell RNA-seq of CD45+ AT cells from old mice supports the presence of distinct inflammatory ATM populations (Il1b+ and Cd9+), regulated by Gdf3. Old myeloid cell-specific Gdf3-deficient mice phenocopies Gdf3-/- mice, indicating that these results are due to myeloid-driven GDF3. Moreover, pharmaceutical SMAD2/3 inhibition (SIS3) mimics the Gdf3 deletion. SIS3-injected old mice, but not young, show a reduction in inflammation with fewer CD11c+/CD9+ ATMs and PDL1+ AABs. Overall, our study demonstrates that GDF3-SMAD2/3 axis may offer a new approach to target inflammatory ATMs and AABs, reducing inflammation in the aged.