The Spleen Promotes Liver Sinusoidal Endothelial Cell Angiogenesis by Stimulating the TGFβ/Smad2/3 Pathway Through GDF15

Background and Aims: Liver sinusoidal endothelial cells (LSECs) are crucial nonparenchymal cells involved in liver fibrosis progression. Liver fibrosis develops from various chronic liver diseases, with pathological progression associated with the spleen. However, the precise mechanism by which the spleen influences LSECs during fibrosis is not fully understood. This study investigated the spleen's effect on LSEC angiogenesis and its underlying mechanisms using animal and cellular experiments. Methods: Splenectomy or sham operations were performed on carbon tetrachloride (CCl₄)–induced liver fibrosis mice and oil-treated control mice. Intraoperative spleen serum, peripheral serum from hepatitis B cirrhosis patients pre- and post-splenectomy, and normal human peripheral serum were collected and used to treat cultured LSECs. LSEC proliferation, migration, and tubule formation were then assessed. Active serum cytokines were identified by cytokine array analysis, and activated signaling pathways in LSECs were investigated through functional experiments. Results: The spleen promoted LSEC angiogenesis in fibrotic mice. Compared to peripheral serum, spleen serum from cirrhotic patients significantly enhanced LSEC proliferation, migration, and tubule formation. Growth differentiation factor 15 (GDF15) was elevated in spleen serum and promoted LSEC angiogenesis. In vitro, GDF15 induced Smad2/3 phosphorylation in LSECs. Furthermore, inhibition of Smad3 phosphorylation attenuated the pro-angiogenic effects of spleen serum or GDF15 on LSECs. Conclusion: The spleen promotes LSEC angiogenesis by activating the TGFβ/Smad2/3 pathway through GDF15 in serum.