Abstract 8859: Hematopoietic Calr Frameshift Mutation Exacerbates Hypoxia-Induced Pulmonary Hypertension in Mice

Abstract

Introduction: Calreticulin ( CALR ) frameshift is the second frequent driving mutation in myeloproliferative neoplasms (MPNs). MPNs are complicated with pulmonary hypertension (PH), but the mechanistic relevance of the CALR mutations on PH has not yet been clarified. Methods and Results: We generated a 10-bp deletion knock-in mice with murine Calr exon 9 mimicking the human CALR mutations. To investigate whether the hematopoietic CALR mutation contributes to PH, a bone marrow transplantation (BMT) was applied using the donor BM cells from Calr knock-in mice or control wild-type (WT) mice. Four weeks after BMT, the recipient mice transplanted with BM cells from Calr knock-in mice (Del-R) and WT mice (WT-R) were exposed to chronic hypoxia. Three weeks after starting chronic hypoxia exposure, the right ventricular systolic pressure and right ventricle/left ventricle-plus-septum weight ratio in the Del-R mice were significantly increased compared to the WT-R mice. Lung histology showed an acceleration of pulmonary arterial muscularization and medial wall thickness in Del-R mice after chronic hypoxia. Increases in macrophage infiltration was similarly observed in both WT-R and Del-R mice after chronic hypoxia. Endothelin-1 expression and STAT3 phosphorylation were significantly upregulated in the lung of Del-R mice compared to the WT-R mice in response to chronic hypoxia. Using Calr Del/CAG-EGFP double transgenic mice, we visualized the accumulations of donor-derived macrophages in pulmonary arterial regions. BM-derived macrophages carrying the Calr mutation showed increases in endothelin-1 expression, indicating that BM-derived macrophages with the Calr mutation played important roles in the pulmonary arterial remodeling. Conclusion: The frameshifted Calr mutations presented a novel mechanism of PH through BM-derived macrophages accompanied by upregulation of endothelin-1.