Sieck, Gary C.

Abstract Background Heart failure (HF) is classified by ejection fraction: reduced EF (<40%) is HFrEF and preserved EF (>50%) is HFpEF. Unlike HFrEF, no therapeutic agent improves mortality in HFpEF. The molecular mechanism that produces HFpEF is not completely understood, but the cascade of pathology that produces HFpEF is thought to begin with changes in vascular reactivity, including a decrease in NO mediated vasodilatation, which coupled with subsequent changes in contractility, energetics and coronary blood flow produce HFpEF. If abnormal vascular reactivity is the initial step in the pathological cascade that produces HFpEF, restoring and/or improving vascular reactivity could represent a novel treatment strategy. Vascular reactivity is primarily regulated by myosin light chain phosphatase, which has catalytic, myosin targeting (MYPT1) and 20kDa subunits. Alternative mRNA splicing of exon24 (E24) of the MYPT1 transcript produces MYPT1 isoforms that differ by the presence or absence of a COOH-terminal leucine zipper (LZ+/LZ-); E24 exclusion produces an NO responsive LZ+ MYPT1, while E24 inclusion produces an NO unresponsive LZ- MYPT. Methods We used the mouse two-hit model of HFpEF (high fat diet and L-NAME) and treated mice with an anti-sense octo-guanidine targeting the 5’ splice site of E24 (ASO-E24) to increase the expression of the NO responsive, LZ+ MYPT1 isoform in vascular smooth muscle. Invasive and noninvasive hemodynamics were used to determine LV function. Results Compared to mice with HFpEF, ASO-E24 treatment maintains LZ+ MYPT1 expression (4.7±0.7au v 1.0±0.4au v 2.0±0.4au, control v HFpEF v ASO-E24 Rx, p<0.05), improves diastolic function; LVEDP (10±1mmHg v 20±4mmHg v 14±3mmHg, p<0.05), dP/dtmin (−8000±300mmHg/s v 6000±500mmHg/s v 8500±700mmHg/s, p<0.05), both early (E; 0.60±0.05m/s v 0.42±0.06m/s v 0.64±0.06m/s, p<0.05) and late diastolic filling (A; 0.38±0.03m/s v 0.24±0.02m/s v 0.47±0.04m/s, p<0.050 and also prevents the increase in lung weight (167±5g v 175±7g v 166±5g, p<0.05). Further, mice treated with ASO-E24 maintained normal relaxation to 8Br-cGMP (65±5% v 44±9% v 72±9%, p=0.05). Conclusion These data demonstrate that maintaining normal LZ+ MYPT1 expression and vascular reactivity prevent the development of HFpEF. These results are consistent with the hypothesis that abnormal vascular reactivity is the initial and primary step in the pathological cascade that produces HFpEF and ASO-E24, which is designed to preserve normal LZ+ MYPT1 expression and vascular reactivity, could represent a novel and effective treatment strategy for HFpEF. Clinical Prospective What is New? In HFpEF, an anti-sense octo-guanidine targeting the 5’ splice site of exon 24 (ASO-E24) of the MYPT1 transcript increases the expression of the NO responsive, LZ+ MYPT1 isoform in vascular smooth muscle. Preserving LZ+ MYPT1 expression and normal vascular reactivity prevents the development of HFpEF. A decrease in LZ+ MYPT1 expression contributes to the development of HFpEF. What are the Clinical Implications? The results of the study demonstrate that abnormal vascular reactivity is an important step in the pathological cascade that produces HFpEF Increasing LZ+ MYPT1 expression could represent a novel treatment strategy for HFpEF.