(8) The Impact of miR-17~92 Haploinsufficiency on Cardiac and Pulmonary Vascular Development

Ashley Kimble, Northwestern University, Ann and Robert H. Lurie Children's Hospital of Chicago, CHICAGO, IL, United States; Gregory B. Waypa, Northwestern University, United States; Mary E. Robbins, Northwestern University, Ann and Robert H. Lurie Children's Hospital of Chicago, United States; Joann M. Taylor, Stanley Manne Research Institute at Ann and Robert H Lurie Children's Hospital of Chicago, United States

Background: Bronchopulmonary dysplasia causes significant morbidity and mortality in premature infants. Pulmonary hypertension (PH) is often associated with BPD. Underlying mechanisms are not well understood. We previously reported severe attenuation of microRNA (miR)-17~92 expression in human infants who died with BPD and in a murine model of BPD. Murine global deletion of miR-17~92 results in lethal pulmonary hypoplasia and heart defects. The effect of miR-17~92 haploinsufficiency (HI) on cardiac and pulmonary vascular development during murine aging has not been characterized.

Objectives: The following studies test the hypothesis that miR-17~92 HI causes PH reminiscent of a BPD-like phenotype.

Design/Methods: miR-17~92flox/flox and Tg-Sox2Cre mice were mated to produce HI (Tg-Sox2Cre/miR-17~92+/flox) and littermate controls (C: miR-17~92+/flox). Mice and hearts were weighed (n=1-7/group). The right ventricle (RV) was separated from the left ventricle and septum (LV+S; n=14/group). RV systolic pressure (RVSP) is measured by Millar (n=4-8/group). Small non-muscular vessel counts were analyzed with ImageQuant Pro (n=3-6/group). Medial wall thickness of small pulmonary arterioles were measured with ImageJ (n=3/group). Cardiomyocytes were counted and measured (n=3/group). Data analyzed by ANOVA. Significance at p< 0.05.

Results: Heart: body weight ratios are similar between groups. RVSP is increased in HI vs C at P60 (26.8 vs 17.8, p=0.01) but not P28 (18.5 vs 17.1, [mmHg], p=0.9). Fulton’s index (RV/LV+S) is increased in HI vs C at P14 (0.26 vs 0.23, p=0.03). LV+S is lower in HI vs C at P14 (25.0 vs 31.5) and P28 (44.4 vs 51.5; p=0.001). There is no difference in vessel count (P14: HI 5.9, C 6.2; P28: HI 8.0, C 10.5; P60: HI 7.7, C 7.7 [vessels/HPF]) or MWT (P14: HI 0.44, C 0.45; P28 HI 0.12, C 0.18; P60 HI 0.28, C 0.22). Cardiomyocyte counts (P14: HI 6.2, C 5.8, P28: HI 8.8, C 10.5, P60: HI 7.7, C 7.7 [100,000 cells/g]), length (P14: HI 69.2, C 72.9, P28 HI70.4, C 65.6), and width (P14: HI 17.6, C 17.7; P28: HI 19.4, C 17.7[um]) are similar for HI and C.

Conclusion: Our data reveals a progressive PH as miR-17~92 HI causes increased RVSP at P60 but not P28. A secondary sign of PH, RV hypertrophy, is present at P14. Other mechanisms of PH by changes in the pulmonary vasculature, including decreased pulmonary vessel counts, MWT proliferation, or changes in cardiomyocyte morphology are not present. Therefore, miR-17~92 HI may impact cardiac and pulmonary vascular development differently than mechanisms reported in other PH models.