Discovery of a potential therapeutic target of severe congenital neutropenia

Drs. Jose Cancelas Perez, MD, PhD, and Carolyn Lutzko, PhD, led a team of Cancer and Blood Diseases Institute (CBDI) investigators tackling a long standing question on how severe congenital neutropenia (SCN) may come arise. An article on this is featured in The Journal of Clinical Investigation. 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 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. Their 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.

Novel epigenetic regulation of oligodendrocyte and astrocyte fate switch

Dr. Quing Lu, PhD, and collaborators defined, and reported in Developmental Cell, a novel mechanism of oligodendrocyte and astrocyte lineage determination by Hdac3 interaction with p300 histone acetyltransferase. Establishment, and maintenance, of central nervous system glial cell identity ensures proper brain development and function, yet the epigenetic mechanisms underlying glial fate control remain poorly understood. They found that the histone deacetylase Hdac3 controls oligodendrocyte-specification gene Olig2 expression and functions as a molecular switch for oligodendrocyte and astrocyte lineage determination. Hdac3 ablation leads to a significant increase of astrocytes with a concomitant loss of oligodendrocytes. Lineage tracing indicates that the ectopic astrocytes originate from oligodendrocyte progenitors. Genome-wide occupancy analysis reveals that Hdac3 interacts with p300 to activate oligodendroglial lineage-specific genes, while suppressing astroglial differentiation genes including NFIA. Furthermore, we find that Hdac3 modulates the acetylation state of Stat3 and competes with Stat3 for p300 binding to antagonize astrogliogenesis. Their studies suggest that Hdac3 cooperates with p300 to prime and maintain oligodendrocyte identity while inhibiting NFIA and Stat3-mediated astrogliogenesis, and thereby regulates phenotypic commitment at the point of oligodendrocyte-astrocytic fate decision.

Discovery of a new molecular pathway of airway hyperresponsiveness in sickle cell disease

Dr. Punam Malik, MD, led a team of collaborators who determined, and reported in The Journal of Clinical Investigations, the placenta growth factor pathway as a key augmenting component in airway hyperresponsiveness and asthma. Airway hyperresponsiveness (AHR) affects 55%-77% of children with sickle cell disease (SCD) and occurs even in the absence of asthma. While asthma increases SCD morbidity and mortality, the mechanisms underlying the high AHR prevalence in a hemoglobinopathy remain unknown. In allergen-exposed mice, loss of Plgf dampened AHR, reduced inflammation and eosinophilia, and decreased expression of the Th2 cytokine IL-13 and the leukotriene-synthesizing enzymes 5-lipoxygenase and leukotriene-C4-synthase. Plgf-/- mice treated with leukotrienes phenocopied the WT response to allergen exposure; conversely, anti-PlGF Ab administration in WT animals blunted the AHR. Notably, Th2-mediated STAT6 activation further increased PlGF expression from lung epithelium, eosinophils, and macrophages, creating a PlGF/leukotriene/Th2-response positive feedback loop. Similarly, they found that the Th2 response in asthma patients associates with increased expression of PlGF and its downstream genes in respiratory epithelial cells. In an SCD mouse model, they observed increased AHR and higher leukotriene levels abrogated by anti-PlGF Ab or the 5-lipoxygenase inhibitor zileuton. Their findings indicate that PlGF exacerbates AHR and uniquely links the leukotriene and Th2 pathways in asthma, and suggest that zileuton and anti-PlGF Ab could be promising therapies to reduce pulmonary morbidity in SCD.