Exosomal SPRY4 from adipogenic BMSCs impairs angiogenesis via the PTPRB/TIE2/PI3K axis in Steroid-induced osteonecrosis of the femoral head.

Abstract

Background: Steroid-induced osteonecrosis of the femoral head (SONFH) drives irreversible bone collapse, yet current therapies inadequately target the disrupted angiogenic-osteogenic coupling central to its pathogenesis. Although pathological adipocyte hyperplasia is a hallmark of SONFH, the mechanisms by which adipogenic bone marrow mesenchymal stem cells (BMSCs) suppress angiogenesis remain unresolved. Emerging evidence implicates exosomes as mediators of adipose-vascular crosstalk, yet their role in SONFH-associated vasculopathy remains unexplored. Here, we elucidate how adipogenic BMSCs impair angiogenesis in SONFH through exosomal delivery of SPRY4.

Methods: Adipogenic BMSCs and human umbilical vein endothelial cells (HUVECs) were co-cultured in vitro. RT-PCR was employed to assess the expression of angiogenic genes. Transwell and wound healing assays were conducted to evaluate the migratory capacity of HUVECs. Tube formation assays were performed to investigate HUVEC angiogenesis. RNA sequencing (RNAseq) was utilized to identify potential regulatory factors within exosomes derived from adipogenic BMSCs. The target relationship between SPRY4 and PTPRB was predicted and validated through co-immunoprecipitation and mass spectrometry. Western blotting (WB) was used to confirm the signaling pathway involved in SPRY4-mediated angiogenesis disorders. Hematoxylin and eosin (HE) staining and immunohistochemistry (IHC) were employed to examine the in vivo effects of exosomes derived from adipogenic BMSCs.

Results: This study demonstrates that adipogenic BMSCs impair angiogenesis in SONFH through exosome-mediated delivery of SPRY4. Key findings reveal: (1) exosomes derived from adipogenic BMSCs suppressed endothelial cell migration, impaired angiogenesis, and downregulated angiogenic gene expression. (2) SPRY4 as a key exosomal effector, which enhanced phosphatase activity of PTPRB through direct interaction. This SPRY4-PTPRB axis inhibited TIE2 receptor autophosphorylation and downstream PI3K/AKT signaling. (3) In vivo, SPRY4 overexpression exacerbated the impairment of bone mass and microvascular density in SD rat model with SONFH, whereas shSPRY4 lentiviral intervention or pharmacological modulation of PTPRB and PI3K signaling using AKB9778 and YS-49 effectively reversing pathological manifestations.

Conclusion: Exosomes derived from adipogenic BMSCs containing SPRY4 can induce SONFH-like injury by targeting PTPRB to suppress the TIE2/PI3K/AKT pathway, proposing targeted disruption of adipose-endothelial crosstalk as a novel therapeutic strategy for osteonecrosis.