Inhibition of RhoA-mediated secretory autophagy in megakaryocytes mitigates myelofibrosis in mice.

Megakaryocytes (MKs) are polyploid cells that maintain bone marrow homeostasis by secreting cytokines, including transforming growth factor β1 (TGFβ1). During neoplastic transformation, MKs accumulate in the bone marrow, promoting fibrotic remodeling that leads to myelofibrosis. However, the therapeutic potential of targeting MK cytokine secretion remains poorly understood. Because unconventional secretion of TGFβ1 and interleukin 1β (IL1β) via secretory autophagy occurs in other cell types, we investigated whether MKs may utilize the same mechanism. Disrupting secretory autophagy, or inhibiting the small GTPase RhoA or its downstream effector Rho-associated kinase (ROCK), markedly reduced TGFβ1 and IL1β secretion in vitro. Conditional deletion of the autophagy gene Atg5 in the hematopoietic system limited megakaryocytosis and aberrant cytokine secretion in an MPLW515L-driven transplant model, while MK-specific deletion of Rhoa protected mice from fibrosis. Ultimately, ROCK inhibition, alone or combined with a JAK2 inhibitor, also attenuated disease hallmarks, identifying the RhoA-secretory autophagy axis as a promising therapeutic target in myelofibrosis.