There are currently no FDA-approved treatments for heart failure with preserved ejection fraction (HFpEF). Here we compared the effects of exercise with and without α/β-adrenergic blockade with carvedilol in Col4a3-/- Alport mice, a model of the Phenogroup 3 subclass of HFpEF with underlying renal dysfunction. Alport mice were assigned to the following groups: no treatment control (n=29), carvedilol (n=11), voluntary exercise (n=9), combination carvedilol and exercise (n=8). Cardiac function was assessed by echocardiography after 4-week treatments. Running activity of Alport mice was similar to wild types at 1-month of age, but markedly reduced at 2 months (1.3±0.40 vs. 4.5±1.02 km/day, p<0.05). There was a non-significant trend for increased running activity at 2 months by carvedilol in the combination treatment group. Combination treatments conferred increased body weight of Col4a3-/- mice (22.0±1.18 vs. 17.8±0.29 g in untreated mice, p<0.01), suggesting improved physiology, and heart rates declined by similar increments in all carvedilol-treatment groups. The combination treatment improved systolic parameters; stroke volume (30.5±1.99 vs. 17.8±0.77 μL, p<0.0001) as well as ejection fraction and global longitudinal strain compared with controls. Myocardial Performance Index was normalized by all interventions (p<0.0001). Elevated osteopontin plasma levels in control Alport mice were significantly lowered only by combination treatment, and renal function of the Alport group assessed by urine albumin creatinine ratio was significantly improved by all treatments. The results support synergistic roles for exercise and carvedilol to augment cardiac systolic function of Alport mice with moderately improved renal functions but no change in diastole.
Background Heart transplant is the gold standard therapy for patients with advanced heart failure. Over 5,500 heart transplants are performed every year worldwide. Cardiac allograft vasculopathy (CAV) is a common complication post-heart transplant which reduces survival and often necessitates heart retransplantation. Post-transplant follow-up requires serial coronary angiography and endomyocardial biopsy (EMB) for CAV and allograft rejection screening, respectively; both of which are invasive procedures. This study aims to determine whether osteopontin (OPN) protein, a fibrosis marker often present in chronic heart disease, represents a novel biomarker for CAV. Methods Expression of OPN was analyzed in cardiac tissue obtained from patients undergoing heart retransplantation using immunofluorescence imaging ( n = 20). Tissues from native explanted hearts and three serial follow-up EMB samples of transplanted hearts were also analyzed in five of these patients. Results Fifteen out of 20 patients undergoing retransplantation had CAV. 13/15 patients with CAV expressed nuclear OPN. 5/5 patients with multiple tissue samples expressed nuclear OPN in both 1 st and 2 nd explanted hearts, while 0/5 expressed nuclear OPN in any of the follow-up EMBs. 4/5 of these patients had an initial diagnosis of dilated cardiomyopathy (DCM). Conclusion Nuclear localization of OPN in cardiomyocytes of patients with CAV was evident at the time of cardiac retransplant as well as in patients with DCM at the time of the 1 st transplant. The results implicate nuclear OPN as a novel biomarker for severe CAV and DCM.
Approximately 14 percent of the general population suffer from chronic kidney disease that can lead to acute kidney injury (AKI), a condition with up to 50% mortality for which there is no effective treatment. Hypertension, diabetes and cardiovascular disease are the main comorbidities, and more than 660,000 Americans have kidney failure. β2-Adrenergic Receptors (β2ARs) have been extensively studied in association with lung and cardiovascular disease, but with limited scope in kidney and renal diseases. β2ARs are expressed in multiple parts of the kidney including proximal and distal convoluted tubules, glomeruli, and podocytes. Classical and non-canonical β2AR signaling pathways interface with other intracellular mechanisms in the kidney to regulate important cellular functions including renal blood flow, electrolyte balance and salt handling, and tubular function that in turn exert control over critical physiology and pathology such as blood pressure and inflammatory responses. Nephroprotection through activation of β2ARs has surfaced as a promising field of investigation; however, there is limited data on the pharmacology and potential side effects of renal β2AR modulation. Here we provide updates on some of the major areas of preclinical kidney research involving β2AR signaling that have advanced to describe molecular pathways and identify potential drug targets some of which are currently under clinical development for the treatment of kidney-related disease.
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.
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