Adrenal-targeted GRK2 gene deletion decreased circulating catecholamines and improved cardiac function and β-adrenergic reserve in mice at 4 weeks post-myocardial infarction.
Does adrenal-targeted GRK2 gene deletion improve cardiac function and reduce sympathetic activation in a post-MI heart failure mouse model?
Adrenal-targeted GRK2 gene deletion decreases circulating catecholamines and improves cardiac function and β-adrenergic reserve in a post-MI heart failure mouse model, suggesting a novel sympatholytic strategy.
Chronic heart failure (HF) is characterized by sympathetic overactivity and enhanced circulating catecholamines (CAs), which significantly increase HF morbidity and mortality. We recently reported that adrenal G protein-coupled receptor kinase 2 (GRK2) is up-regulated in chronic HF, leading to enhanced CA release via desensitization/down-regulation of the chromaffin cell α2-adrenergic receptors that normally inhibit CA secretion. We also showed that adrenal GRK2 inhibition decreases circulating CAs and improves cardiac inotropic reserve and function. Herein, we hypothesized that adrenal-targeted GRK2 gene deletion before the onset of HF might be beneficial by reducing sympathetic activation. To specifically delete GRK2 in the chromaffin cells of the adrenal gland, we crossed PNMTCre mice, expressing Cre recombinase under the chromaffin cell-specific phenylethanolamine N-methyltransferase (PNMT) gene promoter, with floxedGRK2 mice. After confirming a significant (∼50%) reduction of adrenal GRK2 mRNA and protein levels, the PNMT-driven GRK2 knock-out (KO) offspring underwent myocardial infarction (MI) to induce HF. At 4 weeks post-MI, plasma levels of both norepinephrine and epinephrine were reduced in PNMT-driven GRK2 KO, compared with control mice, suggesting markedly reduced post-MI sympathetic activation. This translated in PNMT-driven GRK2 KO mice into improved cardiac function and dimensions as well as amelioration of abnormal cardiac β-adrenergic receptor signaling at 4 weeks post-MI. Thus, adrenal-targeted GRK2 gene KO decreases circulating CAs, leading to improved cardiac function and β-adrenergic reserve in post-MI HF. GRK2 inhibition in the adrenal gland might represent a novel sympatholytic strategy that can aid in blocking HF progression. Chronic heart failure (HF) is characterized by sympathetic overactivity and enhanced circulating catecholamines (CAs), which significantly increase HF morbidity and mortality. We recently reported that adrenal G protein-coupled receptor kinase 2 (GRK2) is up-regulated in chronic HF, leading to enhanced CA release via desensitization/down-regulation of the chromaffin cell α2-adrenergic receptors that normally inhibit CA secretion. We also showed that adrenal GRK2 inhibition decreases circulating CAs and improves cardiac inotropic reserve and function. Herein, we hypothesized that adrenal-targeted GRK2 gene deletion before the onset of HF might be beneficial by reducing sympathetic activation. To specifically delete GRK2 in the chromaffin cells of the adrenal gland, we crossed PNMTCre mice, expressing Cre recombinase under the chromaffin cell-specific phenylethanolamine N-methyltransferase (PNMT) gene promoter, with floxedGRK2 mice. After confirming a significant (∼50%) reduction of adrenal GRK2 mRNA and protein levels, the PNMT-driven GRK2 knock-out (KO) offspring underwent myocardial infarction (MI) to induce HF. At 4 weeks post-MI, plasma levels of both norepinephrine and epinephrine were reduced in PNMT-driven GRK2 KO, compared with control mice, suggesting markedly reduced post-MI sympathetic activation. This translated in PNMT-driven GRK2 KO mice into improved cardiac function and dimensions as well as amelioration of abnormal cardiac β-adrenergic receptor signaling at 4 weeks post-MI. Thus, adrenal-targeted GRK2 gene KO decreases circulating CAs, leading to improved cardiac function and β-adrenergic reserve in post-MI HF. GRK2 inhibition in the adrenal gland might represent a novel sympatholytic strategy that can aid in blocking HF progression. IntroductionDespite recent advances in prevention and management of heart disease, death due to chronic heart failure (HF) 3The abbreviations used are: HFheart failureSNSsympathetic nervous systemCAcatecholamineβARβ-adrenergic receptorα2ARα2-adrenergic receptorNEnorepinephrineEpiepinephrineGRK2G protein-coupled receptor kinase 2KOknock-outPNMTphenylethanolamine N-methyltransferaseMImyocardial infarctionWTwild typeTHtyrosine hydroxylaseBNPbrain natriuretic peptideGAPDHglyceraldehyde 3-phosphate dehydrogenase. continues to rise and new and innovative treatments are needed (1Thomas S. Rich M.W. Heart Fail. Clin. 2007; 3: 381-387Abstract Full Text Full Text PDF PubMed Scopus (54) Google Scholar, 2Kaye D.M. Krum H. Nat. Rev. Drug Disc. 2007; 6: 127-139Crossref PubMed Scopus (101) Google Scholar). A salient feature of HF is elevated sympathetic nervous system (SNS) activity and outflow, reflected by increased circulating catecholamines (CAs). Initially an adaptive process to compensate for decreased function following cardiac injury through stimulation of β-adrenergic receptors (βARs), SNS activation becomes maladaptive, contributing significantly to disease morbidity and mortality (3Port J.D. Bristow M.R. J. Mol. Cell Cardiol. 2001; 33: 887-905Abstract Full Text PDF PubMed Scopus (234) Google Scholar, 4Rockman H.A. Koch W.J. Lefkowitz R.J. Nature. 2002; 415: 206-212Crossref PubMed Scopus (778) Google Scholar, 5Tilley D.G. Rockman H.A. Exp. Rev. Cardiovasc. Ther. 2006; 4: 417-432Crossref PubMed Scopus (64) Google Scholar). Levels of norepinephrine (NE) are associated with worsened prognosis in HF (6Cohn J.N. Levine T.B. Olivari M.T. Garberg V. Lura D. Francis G.S. Simon A.B. Rector T. N. Engl. J. Med. 1984; 311: 819-823Crossref PubMed Scopus (2751) Google Scholar). Epinephrine (Epi) and, to a lesser extent, NE secretion from the adrenal medulla provides essentially all circulating CAs and is a fundamental component of SNS outflow (7Hoffman B.B. Taylor P. Goodman 451: 919-928Crossref PubMed Scopus (341) Google Scholar). Included is the up-regulation of G protein-coupled receptor kinase 2 (GRK2 or βARK1), which contributes significantly to βAR and ventricular dysfunction (4Rockman H.A. Koch W.J. Lefkowitz R.J. Nature. 2002; 415: 206-212Crossref PubMed Scopus (778) Google Scholar, 5Tilley D.G. Rockman H.A. Exp. Rev. Cardiovasc. Ther. 2006; 4: 417-432Crossref PubMed Scopus (64) Google Scholar).α2ARs play a crucial role in autocrine feedback inhibition of CA release from cardiac sympathetic nerve terminals and from the adrenal medulla. In the latter tissue, they reside in membranes of chromaffin cells, which are responsible for adrenal CA production (10Brede M. Nagy G. Philipp M. Sorensen J.B. Lohse M.J. Hein L. Mol. Endocrinol. 2003; 17: 1640-1646Crossref PubMed Scopus (137) Google Scholar, 11Lymperopoulos A. Rengo G. Koch W.J. Trends Mol. Med. 2007; 13: 503-511Abstract Full Text Full Text PDF PubMed Scopus (108) Google Scholar). The importance of α2AR-mediated SNS activity regulation in cardiac disease has been well documented in a variety of knock-out (KO) mouse models (12Hein L. Altman J.D. Kobilka B.K. Nature. 1999; 402: 181-184Crossref PubMed Scopus (423) Google Scholar, 13Brede M. Wiesmann F. Jahns R. Hadamek K. Arnolt C. Neubauer S. Lohse M.J. Hein L. Circulation. 2002; 106: 2491-2496Crossref PubMed Scopus (169) Google Scholar, 14Brum P.C. Kosek J. Patterson A. Bernstein D. Kobilka B. Am. J. Physiol. Heart Circ. Physiol. 2002; 283: H1838-H1845Crossref PubMed Scopus (75) Google Scholar), and in HF patients (15Small K.M. Wagoner L.E. Levin A.M. Kardia S.L. Liggett S.B. N. Engl. J. Med. 2002; 347: 1135-1142Crossref PubMed Scopus (488) Google Scholar, 16Small K.M. McGraw D.W. Liggett S.B. Annu. Rev. Pharmacol. Toxicol. 2003; 43: 381-411Crossref PubMed Scopus (286) Google Scholar). We recently reported that, in addition to myocardium, GRK2 is up-regulated in the adrenal gland in animal models of HF, leading to enhanced CA release via desensitization/down-regulation of the chromaffin cell α2ARs (17Lymperopoulos A. Rengo G. Funakoshi H. Eckhart A.D. Koch W.J. Nat. Med. 2007; 13: 315-323Crossref PubMed Scopus (200) Google Scholar). We also showed that adrenal GRK2 inhibition via adenoviral-mediated in vivo gene therapy using the βARKct (a GRK2 inhibitory peptide) (18Koch W.J. Rockman H.A. Samama P. Hamilton R.A. Bond R.A. Milano C.A. Lefkowitz R.J. Science. 1995; 268: 1350-1353Crossref PubMed Scopus (635) Google Scholar) acutely decreases circulating CAs and improves cardiac inotropic reserve and function (17Lymperopoulos A. Rengo G. Funakoshi H. Eckhart A.D. Koch W.J. Nat. Med. 2007; 13: 315-323Crossref PubMed Scopus (200) Google Scholar).In the present study, we posited that adrenal-targeted GRK2 gene deletion, before the onset of HF, might be beneficial by reducing sympathetic activation. To specifically delete GRK2 in the chromaffin cells of the adrenal gland, we took advantage of the Cre/loxP technology (19Wamhoff B.R. Sinha S. Owens G.K. Handb. Exp. Pharmacol. 2007; 178: 441-468Crossref Scopus (18) Google Scholar) and crossed PNMTCre mice, expressing Cre recombinase under the gene promoter of the chromaffin cell-specific enzyme phenylethanolamine N-methyl transferase (PNMT) (20Ebert S.N. Rong Q. Boe S. Thompson R.P. Grinberg A. Pfeifer K. Dev. Dyn. 2004; 231: 849-858Crossref PubMed Scopus (53) Google Scholar), with floxedGRK2+/+ mice (21Matkovich S.J. Diwan A. Klanke J.L. Hammer D.J. Marreez Y. Odley A.M. Brunskill E.W. Koch W.J. Schwartz R.J. Dorn 2nd, G.W. Circ. Res. 2006; 99: 996-1003Crossref PubMed Scopus (134) Google Scholar). To induce HF, resultant mice homozygous for the floxed allele (i.e. PNMTCre+/−/floxedGRK2+/+) and control mice with endogenous GRK2 expression underwent myocardial infarction (MI) and were studied at 4 weeks post-MI. Our data demonstrate that reduction of circulating CAs via adrenal-targeted GRK2 gene deletion can improve cardiac function and βAR signaling post-MI, and this sympatholysis is beneficial in HF.DISCUSSIONIn previous studies, we documented a crucial role for adrenal GRK2 in regulation of cardiac sympathetic stimulation, both under normal conditions and in the context of chronic HF (17Lymperopoulos A. Rengo G. Funakoshi H. Eckhart A.D. Koch W.J. Nat. Med. 2007; 13: 315-323Crossref PubMed Scopus (200) Google Scholar, 24Lymperopoulos A. Rengo G. Zincarelli C. Soltys S. Koch W.J. Mol. Ther. 2008; 16: 302-307Abstract Full Text Full Text PDF PubMed Scopus (74) Google Scholar; reviewed in Ref. 11Lymperopoulos A. Rengo G. Koch W.J. Trends Mol. Med. 2007; 13: 503-511Abstract Full Text Full Text PDF PubMed Scopus (108) Google Scholar). In the present study, we sought to investigate whether suppression of adrenal GRK2 before the onset of HF can confer any benefit in progressing post-MI HF by reducing cardiac sympathetic burden. To this end, we developed a new transgenic mouse model having the GRK2 gene specifically deleted in the chromaffin cells of the adrenal medulla (PNMT-driven GRK2 KO), by utilizing the well established Cre/loxP technology (19Wamhoff B.R. Sinha S. Owens G.K. Handb. Exp. Pharmacol. 2007; 178: 441-468Crossref Scopus (18) Google Scholar), and we induced chronic HF by surgical MI in these mice. Our findings show that adrenal-restricted GRK2 deletion indeed leads to a significant reduction of circulating CAs in vivo in post-MI HF, thus proving the concept of the transgenic animal approach employed, and, importantly, this resultant reduction of both circulating CAs (NE and Epi) appears indeed to impede the deterioration of cardiac function and βAR signaling, which are hallmarks of the post-MI chronic HF progression.Previously, GRK2 was found, by tightly regulating the activity and function of the sympatho-inhibitory α2ARs of the adrenal gland and of the central SNS, to be a key regulator of the CA levels present at the heart at any given time and, hence, of the levels of cardiac catecholaminergic stimulation, which is an important factor affecting morbidity and mortality in HF (6Cohn J.N. Levine T.B. Olivari M.T. Garberg V. Lura D. Francis G.S. Simon A.B. Rector T. N. Engl. J. Med. 1984; 311: 819-823Crossref PubMed Scopus (2751) Google Scholar, 9Mudd J.O. Kass D.A. Nature. 2008; 451: 919-928Crossref PubMed Scopus (341) Google Scholar). Moreover, we have shown that adrenal GRK2 inhibition via adenoviral-mediated in vivo gene therapy acutely decreases circulating CAs and improves cardiac inotropic reserve and function in rats with already established HF (10 weeks post-MI) (17Lymperopoulos A. Rengo G. Funakoshi H. Eckhart A.D. Koch W.J. Nat. Med. 2007; 13: 315-323Crossref PubMed Scopus (200) Google Scholar). With the data from the current study, it is now even clearer that lowered GRK2 expression and activity in the adrenal gland can have a significant beneficial impact on the injured heart by imparting a sympatholytic effect on CA secretion from the adrenal medulla.Importantly, the PNMT-driven GRK2 KO mice appear viable and normal and present no gross phenotypic abnormalities. Interestingly, with regard to their adrenal phenotype, they appear to have significantly reduced CA biosynthetic activity, as reflected by the down-regulation of TH present in their adrenals. In addition, the size of their adrenals is reduced compared with WT animals at 2 months of age (Table 1), and, intriguingly, they also display significantly attenuated adrenal hypertrophy at 4 weeks post-MI (Table 2). Thus, adrenal GRK2 seems to be an important trophic factor for the adrenal gland in health, but also a major driving force behind adrenal hypertrophy and hyperfunctioning in HF. These findings are also consistent with the up-regulation of adrenal TH and the enhanced adrenal hypertrophy observed in HF rats, where adrenal GRK2 is also up-regulated, and also with the reduction of adrenal TH levels of HF rats observed when adrenal GRK2 is inhibited in vivo (17Lymperopoulos A. Rengo G. Funakoshi H. Eckhart A.D. Koch W.J. Nat. Med. 2007; 13: 315-323Crossref PubMed Scopus (200) Google Scholar). In addition, GRK2 emerges as a critical regulator of adrenal CA biosynthetic function in general, with its activity driving the organ toward increased production of CAs. The mechanisms for this are not clear at the moment. It could very well be an indirect mechanism, i.e. increased GRK2 leads to enhanced CA secretion, which in turn forces the adrenal medulla to produce more CAs to meet the growing demand, but GRK2 might also be more directly involved in adrenal CA biosynthesis, e.g. via regulation of specific biosynthetic enzymes. In any case, the mechanisms of this relationship of GRK2 with CA biosynthetic function in the adrenal gland will be of great interest to study and will be the focus of future studies.Perhaps the most important finding of the present study is that adrenal-targeted GRK2 deletion caused a substantial reduction in circulating CAs post-MI, although it did not affect CA levels in normal, sham-operated mice. This finding confirms that the genetic perturbations employed to create this PNMT-driven GRK2 KO line did not have any nonspecific, non-adrenal GRK2-related effects on circulating CAs. More importantly, it also strongly suggests that adrenal GRK2 is absolutely crucial for the elevation of CA levels in post-MI HF, and thus, inhibition/suppression of adrenal GRK2 activity early on after the occurrence of an MI can have a powerful sympatholytic effect, which is very beneficial in the post-MI HF setting (9Mudd J.O. Kass D.A. Nature. 2008; 451: 919-928Crossref PubMed Scopus (341) Google Scholar, 25Floras J.S. Circulation. 2002; 105: 1753-1755Crossref PubMed Scopus (42) Google the reduction in circulating CAs by GRK2 deletion in the present study appears might have been circulating CA levels the normal this can be by the that, in the PNMT-driven GRK2 KO model GRK2 is deleted in cells and not in sympathetic in the (20Ebert S.N. Rong Q. Boe S. Thompson R.P. Grinberg A. Pfeifer K. Dev. Dyn. 2004; 231: 849-858Crossref PubMed Scopus (53) Google Scholar). sympathetic can produce and release NE the NE can normally βARs present in central which NE release G. Pharmacol. Rev. 2004; PubMed Scopus Google thus, even might not be reduced by the GRK2 deletion in adrenal chromaffin when all these are into the to CA levels in normal PNMT-driven GRK2 KO mice and the CA in these mice observed post-MI are not all that even in the catecholaminergic of the heart can have beneficial effects on cardiac function and of the HF S.B. J. S. D. B. J. M.J. Wagoner L.E. J.L. J.D. Bristow M.R. 2006; PubMed Scopus Google Scholar). In plasma CA reduction has been to be beneficial in HF patients S.B. J. S. D. B. J. M.J. Wagoner L.E. J.L. J.D. Bristow M.R. 2006; PubMed Scopus Google Scholar, M.R. H. R. J. B. L. S. S. M.J. R. P. Circulation. 2004; PubMed Scopus Google Scholar). Thus, it is absolutely that the in circulating CAs we observed in the PNMT-driven GRK2 KO mice can significantly impact cardiac function and βAR signaling post-MI in a beneficial finding of the present study is the observed down-regulation of GRK2 in the of PNMT-driven GRK2 KO mice. myocardial GRK2 cardiac βAR signaling and function and cardiac and its up-regulation post-MI is a major to the of the heart (3Port J.D. Bristow M.R. J. Mol. Cell Cardiol. 2001; 33: 887-905Abstract Full Text PDF PubMed Scopus (234) Google Scholar, 4Rockman H.A. Koch W.J. Lefkowitz R.J. Nature. 2002; 415: 206-212Crossref PubMed Scopus (778) Google Scholar, 5Tilley D.G. Rockman H.A. Exp. Rev. Cardiovasc. Ther. 2006; 4: 417-432Crossref PubMed Scopus (64) Google Scholar, G. A. Zincarelli C. M. Soltys S. Koch W.J. Circulation. PubMed Scopus Google Scholar), this finding is of the improved cardiac βAR signaling and function induced by CA reduction in the HF PNMT-driven GRK2 KO mice. it suggests a regulation of myocardial GRK2 activity by the levels of cardiac catecholaminergic activation G. A. Zincarelli C. M. Soltys S. Koch W.J. Circulation. PubMed Scopus Google Scholar, G. Lefkowitz R.J. Koch W.J. Circulation. PubMed Scopus Google Scholar), which in turn are tightly by GRK2 activity in the adrenal and in the central SNS A. Rengo G. Koch W.J. Trends Mol. Med. 2007; 13: 503-511Abstract Full Text Full Text PDF PubMed Scopus (108) Google Scholar, A. Rengo G. Funakoshi H. Eckhart A.D. Koch W.J. Nat. Med. 2007; 13: 315-323Crossref PubMed Scopus (200) Google Scholar). Thus, the findings of the present study the that GRK2 is a key in cardiac both and after sympathetic stimulation, and in in where this function is as in the chronic HF setting A. Rengo G. Koch W.J. Trends Mol. Med. 2007; 13: 503-511Abstract Full Text Full Text PDF PubMed Scopus (108) Google the present study that adrenal-targeted GRK2 gene deletion of cardiac dysfunction and and the abnormalities of cardiac βAR signaling in post-MI chronic HF by significantly reducing circulating levels after cardiac which are for the heart (6Cohn J.N. Levine T.B. Olivari M.T. Garberg V. Lura D. Francis G.S. Simon A.B. Rector T. N. Engl. J. Med. 1984; 311: 819-823Crossref PubMed Scopus (2751) Google Scholar, 25Floras J.S. Circulation. 2002; 105: 1753-1755Crossref PubMed Scopus (42) Google Scholar). the beneficial effects of GRK2 deletion also include down-regulation of cardiac an important of cardiac dysfunction in HF, and are even a reduction in CA levels, which could be for cardiac of the and with S.B. J. S. D. B. J. M.J. Wagoner L.E. J.L. J.D. Bristow M.R. 2006; PubMed Scopus Google Scholar, M.R. H. R. J. B. L. S. S. M.J. R. P. Circulation. 2004; PubMed Scopus Google Scholar). Thus, reduction of sympathetic via adrenal GRK2 inhibition as early as in the of post-MI HF emerges as an strategy in the management of IntroductionDespite recent advances in prevention and management of heart disease, death due to chronic heart failure (HF) 3The abbreviations used are: HFheart failureSNSsympathetic nervous systemCAcatecholamineβARβ-adrenergic receptorα2ARα2-adrenergic receptorNEnorepinephrineEpiepinephrineGRK2G protein-coupled receptor kinase 2KOknock-outPNMTphenylethanolamine N-methyltransferaseMImyocardial infarctionWTwild typeTHtyrosine hydroxylaseBNPbrain natriuretic peptideGAPDHglyceraldehyde 3-phosphate dehydrogenase. continues to rise and new and innovative treatments are needed (1Thomas S. Rich M.W. Heart Fail. Clin. 2007; 3: 381-387Abstract Full Text Full Text PDF PubMed Scopus (54) Google Scholar, 2Kaye D.M. Krum H. Nat. Rev. Drug Disc. 2007; 6: 127-139Crossref PubMed Scopus (101) Google Scholar). A salient feature of HF is elevated sympathetic nervous system (SNS) activity and outflow, reflected by increased circulating catecholamines (CAs). Initially an adaptive process to compensate for decreased function following cardiac injury through stimulation of β-adrenergic receptors (βARs), SNS activation becomes maladaptive, contributing significantly to disease morbidity and mortality (3Port J.D. Bristow M.R. J. Mol. Cell Cardiol. 2001; 33: 887-905Abstract Full Text PDF PubMed Scopus (234) Google Scholar, 4Rockman H.A. Koch W.J. Lefkowitz R.J. Nature. 2002; 415: 206-212Crossref PubMed Scopus (778) Google Scholar, 5Tilley D.G. Rockman H.A. Exp. Rev. Cardiovasc. Ther. 2006; 4: 417-432Crossref PubMed Scopus (64) Google Scholar). Levels of norepinephrine (NE) are associated with worsened prognosis in HF (6Cohn J.N. Levine T.B. Olivari M.T. Garberg V. Lura D. Francis G.S. Simon A.B. Rector T. N. Engl. J. Med. 1984; 311: 819-823Crossref PubMed Scopus (2751) Google Scholar). Epinephrine (Epi) and, to a lesser extent, NE secretion from the adrenal medulla provides essentially all circulating CAs and is a fundamental component of SNS outflow (7Hoffman B.B. Taylor P. Goodman 451: 919-928Crossref PubMed Scopus (341) Google Scholar). Included is the up-regulation of G protein-coupled receptor kinase 2 (GRK2 or βARK1), which contributes significantly to βAR and ventricular dysfunction (4Rockman H.A. Koch W.J. Lefkowitz R.J. Nature. 2002; 415: 206-212Crossref PubMed Scopus (778) Google Scholar, 5Tilley D.G. Rockman H.A. Exp. Rev. Cardiovasc. Ther. 2006; 4: 417-432Crossref PubMed Scopus (64) Google Scholar).α2ARs play a crucial role in autocrine feedback inhibition of CA release from cardiac sympathetic nerve terminals and from the adrenal medulla. In the latter tissue, they reside in membranes of chromaffin cells, which are responsible for adrenal CA production (10Brede M. Nagy G. Philipp M. Sorensen J.B. Lohse M.J. Hein L. Mol. Endocrinol. 2003; 17: 1640-1646Crossref PubMed Scopus (137) Google Scholar, 11Lymperopoulos A. Rengo G. Koch W.J. Trends Mol. Med. 2007; 13: 503-511Abstract Full Text Full Text PDF PubMed Scopus (108) Google Scholar). The importance of α2AR-mediated SNS activity regulation in cardiac disease has been well documented in a variety of knock-out (KO) mouse models (12Hein L. Altman J.D. Kobilka B.K. Nature. 1999; 402: 181-184Crossref PubMed Scopus (423) Google Scholar, 13Brede M. Wiesmann F. Jahns R. Hadamek K. Arnolt C. Neubauer S. Lohse M.J. Hein L. Circulation. 2002; 106: 2491-2496Crossref PubMed Scopus (169) Google Scholar, 14Brum P.C. Kosek J. Patterson A. Bernstein D. Kobilka B. Am. J. Physiol. Heart Circ. Physiol. 2002; 283: H1838-H1845Crossref PubMed Scopus (75) Google Scholar), and in HF patients (15Small K.M. Wagoner L.E. Levin A.M. Kardia S.L. Liggett S.B. N. Engl. J. Med. 2002; 347: 1135-1142Crossref PubMed Scopus (488) Google Scholar, 16Small K.M. McGraw D.W. Liggett S.B. Annu. Rev. Pharmacol. Toxicol. 2003; 43: 381-411Crossref PubMed Scopus (286) Google Scholar). We recently reported that, in addition to myocardium, GRK2 is up-regulated in the adrenal gland in animal models of HF, leading to enhanced CA release via desensitization/down-regulation of the chromaffin cell α2ARs (17Lymperopoulos A. Rengo G. Funakoshi H. Eckhart A.D. Koch W.J. Nat. Med. 2007; 13: 315-323Crossref PubMed Scopus (200) Google Scholar). We also showed that adrenal GRK2 inhibition via adenoviral-mediated in vivo gene therapy using the βARKct (a GRK2 inhibitory peptide) (18Koch W.J. Rockman H.A. Samama P. Hamilton R.A. Bond R.A. Milano C.A. Lefkowitz R.J. Science. 1995; 268: 1350-1353Crossref PubMed Scopus (635) Google Scholar) acutely decreases circulating CAs and improves cardiac inotropic reserve and function (17Lymperopoulos A. Rengo G. Funakoshi H. Eckhart A.D. Koch W.J. Nat. Med. 2007; 13: 315-323Crossref PubMed Scopus (200) Google Scholar).In the present study, we posited that adrenal-targeted GRK2 gene deletion, before the onset of HF, might be beneficial by reducing sympathetic activation. To specifically delete GRK2 in the chromaffin cells of the adrenal gland, we took advantage of the Cre/loxP technology (19Wamhoff B.R. Sinha S. Owens G.K. Handb. Exp. Pharmacol. 2007; 178: 441-468Crossref Scopus (18) Google Scholar) and crossed PNMTCre mice, expressing Cre recombinase under the gene promoter of the chromaffin cell-specific enzyme phenylethanolamine N-methyl transferase (PNMT) (20Ebert S.N. Rong Q. Boe S. Thompson R.P. Grinberg A. Pfeifer K. Dev. Dyn. 2004; 231: 849-858Crossref PubMed Scopus (53) Google Scholar), with floxedGRK2+/+ mice (21Matkovich S.J. Diwan A. Klanke J.L. Hammer D.J. Marreez Y. Odley A.M. Brunskill E.W. Koch W.J. Schwartz R.J. Dorn 2nd, G.W. Circ. Res. 2006; 99: 996-1003Crossref PubMed Scopus (134) Google Scholar). To induce HF, resultant mice homozygous for the floxed allele (i.e. PNMTCre+/−/floxedGRK2+/+) and control mice with endogenous GRK2 expression underwent myocardial infarction (MI) and were studied at 4 weeks post-MI. Our data demonstrate that reduction of circulating CAs via adrenal-targeted GRK2 gene deletion can improve cardiac function and βAR signaling post-MI, and this sympatholysis is beneficial in HF.
Lymperopoulos et al. (Tue,) conducted a other in Heart failure post-myocardial infarction. Adrenal-targeted GRK2 gene deletion vs. Control mice was evaluated on Plasma levels of norepinephrine and epinephrine, cardiac function, and β-adrenergic receptor signaling. Adrenal-targeted GRK2 gene deletion decreased circulating catecholamines and improved cardiac function and β-adrenergic reserve in mice at 4 weeks post-myocardial infarction.