Inhibition of G-protein-coupled Receptor Kinase 2 Prevents the Dysfunctional Cardiac Substrate Metabolism in Fatty Acid Synthase Transgenic Mice

Abstract

Impairment of myocardial fatty acid substrate metabolism is characteristic of late-stage heart failure and has limited treatment options. Here, we investigated whether inhibition of G-protein-coupled receptor kinase 2 (GRK2) could counteract the disturbed substrate metabolism of late-stage heart failure. The heart failure-like substrate metabolism was reproduced in a novel transgenic model of myocardium-specific expression of fatty acid synthase (FASN), the major palmitate-synthesizing enzyme. The increased fatty acid utilization of FASN transgenic neonatal cardiomyocytes rapidly switched to a heart failure phenotype in an adult-like lipogenic milieu. Similarly, adult FASN transgenic mice developed signs of heart failure. The development of disturbed substrate utilization of FASN transgenic cardiomyocytes and signs of heart failure were retarded by the transgenic expression of GRKInh, a peptide inhibitor of GRK2. Cardioprotective GRK2 inhibition required an intact ERK axis, which blunted the induction of cardiotoxic transcripts, in part by enhanced serine 273 phosphorylation of Pparg (peroxisome proliferator-activated receptor ␥). Conversely, the dual-specific GRK2 and ERK cascade inhibitor, RKIP (Raf kinase inhibitor protein), triggered dysfunctional cardiomyocyte energetics and the expression of heart failure-promoting Pparg-regulated genes. Thus, GRK2 inhibition is a novel approach that targets the dysfunctional substrate metabolism of the failing heart.Heart failure is a debilitating syndrome that involves insufficient cardiac performance. Multiple pathomechanisms have been elucidated, but treatment options remain insufficient, and hence the mortality of heart failure is high (1). The causes of heart failure are complex with ischemic heart disease being the most frequently associated condition (2). Co-existing disorders such as diabetes, hypertension, and obesity further deteriorate symptoms (3). Despite having a different etiology, late-stage heart failure is commonly characterized by severe changes in myocardial substrate metabolism, with a switch from fatty acid oxidation toward predominant glycolysis (4 -6). Conflicting evidence exists as to whether this substrate switch is beneficial or detrimental (7), but several previous studies have indicated that an increased availability of lipid substrates that counteract the substrate switch could improve cardiac function (7,8). Moreover, treatment options, which improve substrate availability, are attractive because the failing heart is often considered to be "an engine running out of fuel" (9).Following this concept, we aimed to investigate the impact of improved cardiac substrate availability by generating transgenic mice with myocardium-specific expression of fatty acid synthase (FASN), the major palmitate-synthesizing enzyme. Such an approach is also supported by data obtained for myocardium-specific Fasn deficiency, which have revealed the cardioprotective potential of Fasn (10). Moreover, hearts from patients with heart failure showed an increased express...

Obesity-induced cardiac lipid accumulation in adult mice is modulated by G protein-coupled receptor kinase 2 levels

“…Given the already mentioned role of GRK2 in fatty acid handling in white and brown adipose tissues [21, 25], it is tempting to suggest a similar direct effect of GRK2 downregulation in other organs such as the heart, where fatty acid oxidation is the main source of ATP. Notably, GRK2 inhibition has been shown to decrease lipid load in FASN transgenic mice [46]. In fact, both basal respiratory rate (oxygen consumption rate) and ATP-linked respiration, parameters that measure ATP production, were significantly increased when GRK2 was inhibited in mouse cardiomyocytes.…”

“…Interestingly, GRK2 hemizygous animals also show an increased activation of AMPK, an activator of mitochondrial fatty acid oxidation and of PGC-1α expression [45], also suggested to play a protective role in heart failure [48]. Thus, it is tempting to speculate that GRK2 downregulation may enhance AMPK stimulation downstream of several GPCR known to activate cardiac AMPK and to be modulated by GRK2, such as alpha-adrenergic, vasopressin (reviewed in [48]) or adiponectin receptors [46, 49]. An increased activation of AMPK signaling pathway in BAT and WAT of GRK2+/− mice upon cold exposure has also been reported [25].…”

The expanding GRK interactome: Implications in cardiovascular disease and potential for therapeutic development

“…These findings have been reaffirmed in a study wherein GRK2 levels were shown to be upregulated resulting in reduced fatty-acid oxidation in an in vivo model of perturbed energy substrate utilization and HF [74]. Further, GRK2 inhibition by GRKInh, a novel peptide inhibitor of GRK2, prevented the dysfunctional cardiac energetics present in this model [74]. Taken together, it is evident that GRK2 is a critical regulator of mitochondrial bioenergetics, and up-regulation of GRK2 within this cellular compartment leads to an altered redox state that appears to make the myocardium more susceptible to injury.…”

“…Conversely, βARKct expression can greatly enhance basal respiration rate and ATP production in myocytes [69]. These findings have been reaffirmed in a study wherein GRK2 levels were shown to be upregulated resulting in reduced fatty-acid oxidation in an in vivo model of perturbed energy substrate utilization and HF [74]. Further, GRK2 inhibition by GRKInh, a novel peptide inhibitor of GRK2, prevented the dysfunctional cardiac energetics present in this model [74].…”

G-Protein-Coupled Receptor Kinase 2 (GRK2) Inhibitors: Current Trends and Future Perspectives

“…These results indicated an enhanced substrate availability of cardiomyocytes with available energy for the heart muscle. 111 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 GLLRrHS (8a, KRX-683 107 ) and lauryl GLLRrHSI (8b, KRX-683 124 ), reduced blood glucose levels in animal models by inhibiting GRK2/3. 113 The peptide fragments of these inhibitors are quite similar to the catalytic fragment 383-390 KLLRGHSP of GRK2, which is the last part of an α-helix (residues 383-386) and the first part of a β-strand (residues 387-390).…”