Chunyan Wu, Yuxing Wang, Quanchao Zhang, Chan Li, Yuanzhong Chen, Yong Wu
Background: Myeloproliferative neoplasms (MPNs) are frequently accompanied by bone marrow fibrosis and leukemic transformation, yet the cellular and molecular mechanisms that sustain apoptosis resistance and fibrotic progression remain unclear. Methods: Bone marrow mesenchymal stromal cells (BM-MSCs) from patients with polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF) were analyzed for fibrotic phenotype, apoptosis signaling, and pathway activation using cell counting kit-8, immunofluorescence, flow cytometry, western blotting, hydroxyproline and transmission electron microscopy. The cytotoxic and antifibrotic effects of the BCL-XL inhibitor ABT-263 (navitoclax), alone or combined with the JAK2 inhibitor ruxolitinib, were evaluated in stromal and hematopoietic contexts. Results: BCL-XL was markedly upregulated in JAK2-driven disease and predominated over other BCL-2 family members in both malignant hematopoietic cells and fibrotic stromal compartments. MSCs derived from MPN patients exhibited a myofibroblast-like phenotype characterized by increased α-smooth muscle actin (α-SMA) and fibronectin (FN) expression. Pharmacologic inhibition of BCL-XL with ABT-263 selectively induced mitochondrial apoptosis in PMF-derived MSCs and attenuated their profibrotic features. Mechanistically, transforming growth factor β (TGF-β) activated both SMAD3 and STAT3 signaling in MSCs, indicating cooperative engagement of TGF-β/SMAD3 and JAK2/STAT3 pathways in stromal fibrotic activation. Combined inhibition of BCL-XL and JAK2 produced synergistic antifibrotic and pro-apoptotic effects in MSCs, post-MPN acute myeloid leukemia (AML) cell lines, and patient-derived cells resistant to ruxolitinib. Conclusion: Collectively, these findings identified BCL-XL as a key mediator of MPN-associated fibrosis and therapeutic resistance, and confirmed dual targeting of BCL-XL and JAK2 as a rational strategy for advanced MPN.