Metamorphosing macrophages promote placental fibrosis by upregulating the transcription factor STAT5A.

BACKGROUND: Intrahepatic cholestasis of pregnancy (ICP) is an idiopathic disease that can lead to adverse pregnancy outcomes. However, the underlying mechanisms that lead to these adverse outcomes remain unclear. The objective of this study is to elucidate the specific mechanisms by which ICP results in adverse pregnancy outcomes by conducting a detailed analysis of the compositional and functional changes of various cell populations in ICP placentas compared to normal placentas using single-cell sequencing. Our findings may provide new targets to prevent and treat fetal complications associated with ICP. METHODS: Human placental tissues were collected for the following experiments. Masson staining was performed to assess collagen deposition and immunofluorescence was used to visualize the localization of fibrosis-related proteins, in order to confirm the presence and extent of placental fibrosis in ICP group compared with the control group. Single-cell sequencing was performed on placental tissues from both groups to evaluate changes in the compositional proportion and functional Features of macrophages in ICP compared to normal controls. Moreover, an ICP cell model established by TCA was utilized to detect the expression of transcription factor STAT5A, gene COL4A2, and the pro-fibrotic TGFβ1 pathway. Meanwhile other experiments such as siRNA transfection, chromatin immunoprecipitation-quantitative PCR(CHIP-qPCR) and dual-luciferase assays were also conducted to investigate the binding of STAT5A to COL4A2 in M2 macrophages. RESULTS: Masson staining and Immunofluorescence suggested the presence of fibrosis in the ICP placentas. Single-cell sequencing indicated changes in the proportions and functions of M2 macrophages in ICP placentas. Meanwhile, in the M2 macrophage model of ICP, the expression of pro-fibrotic signaling pathways was upregulated, with STAT5A being activated and COL4A2 expression increasing. siRNA transfection suggested that knockdown of STAT5A significantly reduced the mRNA and protein levels of COL4A2. CHIP-qPCR and Dual-luciferase assays indicated that STAT5A increased the activity of the COL4A2 cis-acting enhancer. CONCLUSIONS: M2 macrophages can induce villous basement membrane thickening and stromal collagen deposition through the activation of STAT5A and the upregulation of COL4A2 expression. This process is amplified by TGF-β1 autocrine signaling, which forms a self-reinforcing fibrotic cycle that decreases the placental function of material exchange through capillary compression and increased diffusion resistance, ultimately contributing to adverse fetal outcomes. GRAPHICAL ABSTRACT: [Image: see text] SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12967-026-07727-9.