Publications by Author: Lisa A. Freeburg

Background

Standardized exercise protocols have been shown to improve overall cardiovascular fitness, but direct effects on left ventricular (LV) function, particularly diastolic function and relation to post-transcriptional molecular pathways (microRNAs (miRs)) are poorly understood. This project tested the central hypothesis that adaptive LV remodeling resulting from a large animal exercise training protocol, would be directly associated with specific miRs responsible for regulating pathways relevant to LV myocardial stiffness and geometry.

Methods and results

Pigs (n = 9; 25 Kg) underwent a 4 week exercise training protocol (10 degrees elevation, 2.5 mph, 10 min, 5 days/week) whereby LV chamber stiffness (K_C) and regional myocardial stiffness (rK_m) were measured by Doppler/speckle tracking echocardiography. Age and weight matched non-exercise pigs (n = 6) served as controls. LV K_C fell by approximately 50% and rK_m by 30% following exercise (both p < 0.05). Using an 84 miR array, 34 (40%) miRs changed with exercise, whereby 8 of the changed miRs (miR-19a, miR-22, miR-30e, miR-99a, miR-142, miR-144, miR-199a, and miR-497) were correlated to the change in K_C (r ≥ 0.5 p < 0.05) and mapped to matrix and calcium handling processes. Additionally, miR-22 and miR-30e decreased with exercise and mapped to a localized inflammatory process, the inflammasome (NLRP-3, whereby a 2-fold decrease in NLRP-3 mRNA occurred with exercise (p < 0.05).

Conclusion

Chronic exercise reduced LV chamber and myocardial stiffness and was correlated to miRs that map to myocardial relaxation processes as well as local inflammatory pathways. These unique findings set the stage for utilization of myocardial miR profiling to identify underlying mechanisms by which exercise causes changes in LV myocardial structure and function.

Left ventricular pressure overload (LVPO) can lead to heart failure with a preserved ejection fraction (HFpEF) and LV chamber stiffness (LV K_c) is a hallmark. This project tested the hypothesis that the development of HFpEF due to an LVPO stimulus will alter posttranscriptional regulation, specifically microRNAs (miRs). LVPO was induced in pigs (n = 9) by sequential ascending aortic cuff and age- and weight-matched pigs (n = 6) served as controls. LV function was measured by echocardiography and LV K_c by speckle tracking. LV myocardial miRs were quantified using an 84-miR array. Treadmill testing and natriuretic peptide-A (NPPA) mRNA levels in controls and LVPO were performed (n = 10, n = 9, respectively). LV samples from LVPO and controls (n = 6, respectively) were subjected to RNA sequencing. LV mass and K_c increased by over 40% with LVPO (P < 0.05). A total of 30 miRs shifted with LVPO of which 11 miRs correlated to LV K_c (P < 0.05) that mapped to functional domains relevant to K_c such as fibrosis and calcium handling. LVPO resulted in reduced exercise tolerance (oxygen saturation, respiratory effort) and NPPA mRNA levels increased by fourfold (P < 0.05). RNA analysis identified several genes that mapped to specific miRs that were altered with LVPO. In conclusion, a specific set of miRs are changed in a large animal model consistent with the HFpEF phenotype, were related to LV stiffness properties, and several miRs mapped to molecular pathways that may hold relevance in terms of prognosis and therapeutic targets.

Strategic delivery of hydrogels to the newly formed myocardial infarction (MI) is an area of active investigation and offers high target specificity for releasing a small molecule therapeutic payload. This study examined the effects of delayed post-MI delivery (pigs, 3 days post-MI) of a shear-thinning hydrogel which encapsulated and released a small molecule matrix metalloproteinase inhibitor. The results demonstrated the feasibility and efficacy of targeted delivery of a shear-thinning injectable hydrogel containing a small molecule matrix metalloproteinase inhibitor to attenuate post-MI remodeling.