Abstract
Background:
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. HFpEF is characteristically unresponsive to pharmacological intervention. Here, we tested the hypothesis that selective β
2
-Adrenoceptor (β
2
AR) modulation with salbutamol, a short-acting β
2
AR agonist, could alleviate symptoms of CKD and simultaneously augment cardiac function. Secondarily, we investigated the mechanism of actions of such β
2
AR-mediated therapeutics on cardiac and renal functions.
Methods:
Alport mice were injected intraperitoneally with salbutamol or DMSO vehicle as a single bolus of 200μg/dose in short-term studies or daily with 100 μg/dose for 2 weeks long-term. Cardiac and renal functions, cAMP levels,
in vivo
renal tubular LDL-C uptake and renal histology were evaluated post-injection.
In vitro
mechanistic studies were performed in HK-2, Alport dog smooth muscle and tubular epithelial cells differentiated from Alport patient-derived iPSCs. Protein-protein interactions were studied using co-immunoprecipitation experiments and LDL-C uptake was measured by live-cell imaging.
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 (IVRT), filling pressures (E/E’), and myocardial performance index, and systolic function reflected by ejection fraction, stroke volume and cardiac output improved significantly in parallel with increased cardiac cAMP. Mechanistically, in the kidney, salbutamol activated IDOL and hence lysosomal ubiquitination and degradation of LDLR via a novel β
2
AR-mediated, cAMP-independent pathway involving the Rac1/Cdc42 β
1
PixGEF. β
1
Pix reversibly sequesters IDOL into a complex with LDLR, thereby blocking the degradation pathway. β
2
AR stimulation dissipates the complex reactivating IDOL-mediated LDLR degradation thereby re-establishing LDL-C homeostasis and renal function. Using flow cytometry in HEK293T cells, ectopic expression of bPix stabilized membrane LDLR, sensitive to IDOL- but not PCSK-mediated degradation.
Conclusions:
β
2
AR agonism represents a potential treatment strategy to alleviate progression of CKD and heart failure associated with HFpEF phenogroup 3.
