NRASQ61R Expression in Lymphatic Endothelial Cells Causes Enlarged Vessels, Hemorrhagic Chylous Effusions, and High Mortality in a Mouse Model of Kaposiform Lymphangiomatosis.

BACKGROUND: Kaposiform lymphangiomatosis (KLA) is an aggressive complex lymphatic anomaly. Patients exhibit malformed lymphatic vessels and often develop hemorrhagic effusions and elevated angiopoietin-2 (Ang-2) levels. A somatic NRAS p.Q61R (NRASQ61R) mutation has been associated with KLA. Existing preclinical models do not recapitulate the thoracic effusions that drive morbidity and mortality in patients. The goal of this study was to develop a genetic mouse model that more closely mimics the clinical phenotype of KLA.

PROCEDURE: A tamoxifen-inducible Cre-loxP system was used to conditionally express NRASQ61R in lymphatic endothelial cells in postnatal mice. Prox1-CreERT2 mice were mated to Lox-STOP-Lox-NRASQ61R mice. Tamoxifen (100 or 75 µg) was administered to litters on postnatal days (P) 1-3 to induce Cre-mediated recombination and NRASQ61R expression. Survival, effusion incidence, and plasma Ang-2 levels were assessed at 3 weeks. Recombination efficiency and lymphatic vessel structure in the lungs and whole-mounts of the diaphragm and ear were determined.

RESULTS: NRASQ61R mice treated with 100 µg tamoxifen P1-P3 died within 5 weeks. NRASQ61R mice treated with 75 µg tamoxifen P1-P3 had increased mortality, severe hemorrhagic and chylous effusions, and approximately three-fold higher angiopoietin-2 levels. NRASQ61R recombination was 93% in the pulmonary lymphatics, which were enlarged and abnormal. Lymphatic vessel diameters were increased in the diaphragm (193%) and ears (152%).

CONCLUSIONS: NRASQ61R mutant mice closely resemble KLA patients with high mortality, hemorrhagic chylothorax, elevated Ang-2 levels, and enlarged lymphatic vessels. Future studies can utilize this model to elucidate the mechanisms underlying KLA pathogenesis and test novel therapeutics.