Patients in organ failure of vascular origin have increased circulating hematopoietic stem cells and
progenitors (HSC/P). Plasma levels of angiotensin II (Ang-II), are commonly increased in
vasculopathies. Hyperangiotensinemia results in activation of a very distinct Ang-II receptor set,
Rho-family GTPase members, and actin in bone marrow endothelial cells (BMEC) and HSC/P,
which results in decreased membrane integrin activation in both BMEC and HSC/P, and in HSC/P
de-adhesion and mobilization. The Ang-II effect can be reversed pharmacologically and
genetically by inhibiting Ang-II production or signaling through BMEC AT2R, HSCP AT1R/
AT2R or HSC/P RhoA, but not by interfering with other vascular tone mediators.
Hyperangiotensinemia and high counts of circulating HSC/P seen in sickle cell disease (SCD) as a
result of vascular damage, is significantly decreased by Ang-II inhibitors. Our data define for the
first time the role of Ang-II HSC/P traffic regulation and redefine the hematopoietic consequences
of anti-angiotensin therapy in SCD.
Severe congenital neutropenia (SCN) is often associated with inherited heterozygous point mutations in ELANE, which
encodes neutrophil elastase (NE). However, a lack of appropriate models to recapitulate SCN has substantially hampered
the understanding of the genetic etiology and pathobiology of this disease. To this end, we generated both normal and SCN
patient–derived induced pluripotent stem cells (iPSCs), and performed genome editing and differentiation protocols that
recapitulate the major features of granulopoiesis. Pathogenesis of ELANE point mutations was the result of promyelocyte
death and differentiation arrest, and was associated with NE mislocalization and activation of the unfolded protein
response/ER stress (UPR/ER stress). Similarly, high-dose G-CSF (or downstream signaling through AKT/BCL2) rescues
the dysgranulopoietic defect in SCN patient–derived iPSCs through C/EBPβ-dependent emergency granulopoiesis. In
contrast, sivelestat, an NE-specific small-molecule inhibitor, corrected dysgranulopoiesis by restoring normal intracellular
NE localization in primary granules; ameliorating UPR/ER stress; increasing expression of CEBPA, but not CEBPB; and
promoting promyelocyte survival and differentiation. Together, these data suggest that SCN disease pathogenesis includes
NE mislocalization, which in turn triggers dysfunctional survival signaling and UPR/ER stress. This paradigm has the
potential to be clinically exploited to achieve therapeutic responses using lower doses of G-CSF combined with targeting to
correct NE mislocalization.