Abstract
Introduction:
Col4a3-/- Alport mice present a model of heart failure with preserved ejection fraction (HFpEF) secondary to chronic kidney disease(CKD) wherein etiological relationships have been established between hypertension, pulmonary edema, inflammation, cardiac hypertrophy and fibrosis, diastolic dysfunction and underlying abnormalities of elevated low-density lipoprotein receptor (LDLR) expression, excess LDL-cholesterol(LDL-C) accumulation, and mitochondrial dysfunction in renal tubules.
Hypothesis:
We tested the hypothesis that selective β2-Adrenoceptor (β2AR) modulation with salbutamol, a short-acting β2AR agonist, could alleviate symptoms of CKD and simultaneously augment cardiac function.
Methods:
Alport mice were injected i.p.with salbutamol or DMSO vehicle as a single bolus of 200μg/dose in short-term studies or daily with 100 μg/dose for 2 wks long-term. Cardiac and renal functions, cAMP levels, in vivo renal tubular LDL-C uptake and renal histology were evaluated post-injection. N=3-8 for all experiments.
Results:
Short-term, salbutamol improved renal function in parallel with decreased LDLR levels and reduced uptake of LDL-C into renal tubules. Long-term, cardiac diastolic function assessed by isovolumetric relaxation time, filling pressures, and myocardial performance index, and systolic function reflected by ejection fraction, stroke volume and cardiac output improved significantly in parallel with increased cardiac cAMP (p<.05). Mechanistically, in the kidney, salbutamol activated IDOL and hence lysosomal ubiquitination and degradation of LDLR via a novel β2AR-mediated, cAMP-independent pathway involving the Rac1/Cdc42 β1PixGEF. β1Pix reversibly sequesters IDOL into a complex with LDLR, thereby blocking the degradation pathway. β2AR stimulation dissipates the complex reactivating IDOL-mediated LDLR degradation thereby re-establishing LDL-C homeostasis and renal function. Using flow cytometry in 293T cells, ectopic expression of bPix stabilized membrane LDLR, sensitive to IDOL- but not PCSK-mediated degradation.
Conclusions:
β2AR agonism represents a potential treatment strategy to alleviate progression of CKD and HF associated with HFpEF phenogroup 3.