Inhibition of P-Selectin Rescues the Phenotype of a Novel Genetic Animal Model for Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic inflammatory disorder which leads to progressive fibrosis and lung failure within 2-5 years1,2. Approximately 30% of IPF patients develop Chronic Kidney Disease (CKD) with renal dysfunction and fibrosis3. The treatment options for IPF are still limited and the disease is an unmet clinical need. The only animal model for IPF is represented by mice treated with bleomycin, a compound used for chemotherapy which has lung toxicity as its major adverse effect, that develop progressive fibrosis. Recent data indicate that bleomycin triggers lung fibrosis by increasing the release of the pro-inflammatory cytokine TGF-β by the resident megakaryocytes (MK)4. Using these observations as foundation, we investigated whetherGata1lowmice, a model for myelofibrosis induced by a TGF-β/P-selectin (P-sel) circuitry established by the abnormal MK5, includes fibrosis in lungs and kidney and whether these traits are rescued by genetic ablation (P-selnullmutation) and antibody neutralization (by RB40.34) of P-sel. MK were observed in lungs from wild-type (WT, n=9),Gata1low(n=22),P-selnull(n=4) andP-selnullGata1low(n=10) littermates. In frequency, MK were significantly lower inGata1low andP-selnullGata1lowthan in WT andP-selnulllittermates (median=1.3-1.5 vs 3-3.7/0.144mm2, p<0.003) and mostly immature. In addition, lungs and kidney fromGata1low mice, but not those from the other experimental groups, contained great levels of TGF- β (Fig.1). Interstitial pneumonia was observed in lungs from WT (n=12, age=3-13 months, males=8, females=4),P-selnull(n=9, age=3-16 months, males=4, females=5),Gata1low(n=29, age=2-24 months, males=16, females=13) andGata1lowP-selnull(n=18, age=3-16 months, males=7, females=11) mice while nephritis was observed only in kidneys fromGata1low mice. Controlling for the effects of sex, there are statistically significant differences in severity of inflammation in kidney (p=0.001) but not in lungs (p=0.86) betweenGata1low and WT mice. These results indicate that lung inflammation is a baseline condition of the CD1 background used for the study while kidney inflammation is a trait exclusive toGata1low mutants independently from their gender. Great levels of fibrosis were observed in lungs and kidney fromGata1low mice but not in those from WT littermates. There are statistically significant differences in lung (p=0.01) and kidney (p<0.001) fibrosis between the two groups; these differences remained after adjusting for age or sex. By contrast, there is insufficient evidence to conclude there exists a relationship between age and fibrosis grade in the other experimental groups. Age was found to be a statistically significant effect modifier on the relationship between genotype and fibrosis in lung (p=0.024) and kidney (0.004). In addition, although there is insufficient evidence for a relationship between sex and fibrosis grade in lung (p=0.62), there is a statistically significant effect of gender in kidney fibrosis inGata1low mice (p<0.001). These results indicate that fibrosis in lung and nephritis and fibrosis in kidney are novel traits ofGata1low mice developed independently from the underlying state of inflammation and which are rescued by ablation ofP-sel. To further clarify the role of P-sel in lung and kidney fibrosis, 14Gata1lowmice (7 males, 7 females) were treated with either vehicle (8 mice) or RB40.34 (30 μg/mouse/day per 3 days/week by tail vein injection as described6). Mice were sacrificed on day 5 (males) and 12 (females) and histopathology, inflammation, fibrosis and TGF-β content in lungs and kidney analyzed. Treatment with RB40.34 restored the morphology and reduced inflammation, fibrosis and TGF-β content in the lungs and in kidney with respect to vehicle (Fig.1). In conclusion, Gata1low mice are a novel animal model for IPF with CKD. The phenotype is associated with highTGF-βcontent in lung and kidney and is rescued by targeting P-sel, suggesting that treatment with antibodies against P-sel may cure IPF in man. REF: 1Richeldi et al.Lancet389: 1941, 2017; 2Hutchinson et al.EurRespirJ46, 795, 2015; 3Ikezoeet al.Respiration94: 346, 2017; 4Zhouet al.CellDeathDis10:648, 2019: 5Spangrudeet al.StemCells34: 67, 2016; 6Emburyet al.Blood104: 3378, 2004. Disclosures Migliaccio: Novartis:Research Funding.