UC Davis

Background

Many patients with heart failure with preserved ejection fraction have metabolic syndrome and develop exercise-induced pulmonary hypertension (EIPH). Increases in pulmonary vascular resistance in patients with heart failure with preserved ejection fraction portend a poor prognosis; this phenotype is referred to as combined precapillary and postcapillary pulmonary hypertension (CpcPH). Therapeutic trials for EIPH and CpcPH have been disappointing, suggesting the need for strategies that target upstream mechanisms of disease. This work reports novel rat EIPH models and mechanisms of pulmonary vascular dysfunction centered around the transcriptional repression of the soluble guanylate cyclase (sGC) enzyme in pulmonary artery (PA) smooth muscle cells.

Methods

We used obese ZSF-1 leptin-receptor knockout rats (heart failure with preserved ejection fraction model), obese ZSF-1 rats treated with SU5416 to stimulate resting pulmonary hypertension (obese+sugen, CpcPH model), and lean ZSF-1 rats (controls). Right and left ventricular hemodynamics were evaluated using implanted catheters during treadmill exercise. PA function was evaluated with magnetic resonance imaging and myography. Overexpression of nuclear factor Y α subunit (NFYA), a transcriptional enhancer of sGC β1 subunit (sGCβ1), was performed by PA delivery of adeno-associated virus 6. Treatment groups received the SGLT2 inhibitor empagliflozin in drinking water. PA smooth muscle cells from rats and humans were cultured with palmitic acid, glucose, and insulin to induce metabolic stress.

Results

Obese rats showed normal resting right ventricular systolic pressures, which significantly increased during exercise, modeling EIPH. Obese+sugen rats showed anatomic PA remodeling and developed elevated right ventricular systolic pressure at rest, which was exacerbated with exercise, modeling CpcPH. Myography and magnetic resonance imaging during dobutamine challenge revealed PA functional impairment of both obese groups. PAs of obese rats produced reactive oxygen species and decreased sGCβ1 expression. Mechanistically, cultured PA smooth muscle cells from obese rats and humans with diabetes or treated with palmitic acid, glucose, and insulin showed increased mitochondrial reactive oxygen species, which enhanced miR-193b-dependent RNA degradation of nuclear factor Y α subunit (NFYA), resulting in decreased sGCβ1-cGMP signaling. Forced NYFA expression by adeno-associated virus 6 delivery increased sGCβ1 levels and improved exercise pulmonary hypertension in obese+sugen rats. Treatment of obese+sugen rats with empagliflozin improved metabolic syndrome, reduced mitochondrial reactive oxygen species and miR-193b levels, restored NFYA/sGC activity, and prevented EIPH.

Conclusions

In heart failure with preserved ejection fraction and CpcPH models, metabolic syndrome contributes to pulmonary vascular dysfunction and EIPH through enhanced reactive oxygen species and miR-193b expression, which downregulates NFYA-dependent sGCβ1 expression. Adeno-associated virus-mediated NFYA overexpression and SGLT2 inhibition restore NFYA-sGCβ1-cGMP signaling and ameliorate EIPH.