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Caveolin-3 regulates compartmentation of cardiomyocyte beta2-adrenergic receptor-mediated cAMP signaling.

ABSTRACT: The purpose of this study was to investigate whether caveolin-3 (Cav3) regulates localization of ?2-adrenergic receptor (?2AR) and its cAMP signaling in healthy or failing cardiomyocytes. We co-expressed wildtype Cav3 or its dominant-negative mutant (Cav3DN) together with the Förster resonance energy transfer (FRET)-based cAMP sensor Epac2-camps in adult rat ventricular myocytes (ARVMs). FRET and scanning ion conductance microscopy were used to locally stimulate ?2AR and to measure cytosolic cAMP. Cav3 overexpression increased the number of caveolae and decreased the magnitude of ?2AR-cAMP signal. Conversely, Cav3DN expression resulted in an increased ?2AR-cAMP response without altering the whole-cell L-type calcium current. Following local stimulation of Cav3DN-expressing ARVMs, ?2AR response could only be generated in T-tubules. However, the normally compartmentalized ?2AR-cAMP signal became diffuse, similar to the situation observed in heart failure. Finally, overexpression of Cav3 in failing myocytes led to partial ?2AR redistribution back into the T-tubules. In conclusion, Cav3 plays a crucial role for the localization of ?2AR and compartmentation of ?2AR-cAMP signaling to the T-tubules of healthy ARVMs, and overexpression of Cav3 in failing myocytes can partially restore the disrupted localization of these receptors.

SUBMITTER: Wright PT

PROVIDER: S-EPMC4266930 | biostudies-literature | 2014 Feb

REPOSITORIES: biostudies-literature

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Caveolin-3 regulates compartmentation of cardiomyocyte beta2-adrenergic receptor-mediated cAMP signaling.

Wright Peter T PT Nikolaev Viacheslav O VO O'Hara Thomas T Diakonov Ivan I Bhargava Anamika A Tokar Sergiy S Schobesberger Sophie S Shevchuk Andrew I AI Sikkel Markus B MB Wilkinson Ross R Trayanova Natalia A NA Lyon Alexander R AR Harding Sian E SE Gorelik Julia J

Journal of molecular and cellular cardiology 20131215

The purpose of this study was to investigate whether caveolin-3 (Cav3) regulates localization of β2-adrenergic receptor (β2AR) and its cAMP signaling in healthy or failing cardiomyocytes. We co-expressed wildtype Cav3 or its dominant-negative mutant (Cav3DN) together with the Förster resonance energy transfer (FRET)-based cAMP sensor Epac2-camps in adult rat ventricular myocytes (ARVMs). FRET and scanning ion conductance microscopy were used to locally stimulate β2AR and to measure cytosolic cAM ...[more]

PMID: 24345421

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Project description:Angiotensin-II (Ang-II) from extracardiac sources and intracardiac synthesis regulates cardiac homeostasis, with mitogenic and growth-promoting effects largely due to altered gene expression. Here, we assessed the possibility that angiotensin-1 (AT1R) or angiotensin-2 (AT2R) receptors on the nuclear envelope mediate effects on cardiomyocyte gene expression. Immunoblots of nucleus-enriched fractions from isolated cardiomyocytes indicated the presence of AT1R and AT2R proteins that copurified with the nuclear membrane marker nucleoporin-62 and histone-3, but not markers of plasma (calpactin-I), Golgi (GRP-78), or endoplasmic reticulum (GM130) membranes. Confocal microscopy revealed AT1R and AT2R proteins on nuclear membranes. Microinjected Ang-II preferentially bound to nuclear sites of isolated cardiomyocytes. AT1R and AT2R ligands enhanced de novo RNA synthesis in isolated cardiomyocyte nuclei incubated with [alpha-(32)P]UTP (e.g. 36.0 +/- 6.0 cpm/ng of DNA control versus 246.4 +/- 15.4 cpm/ng of DNA Ang-II, 390.1 +/- 15.5 cpm/ng of DNA L-162313 (AT1), 180.9 +/- 7.2 cpm/ng of DNA CGP42112A (AT2), p < 0.001). Ang-II application to cardiomyocyte nuclei enhanced NFkappaB mRNA expression, a response that was suppressed by co-administration of AT1R (valsartan) and/or AT2R (PD123177) blockers. Dose-response experiments with Ang-II applied to purified cardiomyocyte nuclei versus intact cardiomyocytes showed greater increases in NFkappaB mRNA levels at saturating concentrations with approximately 2-fold greater affinity upon nuclear application, suggesting preferential nuclear signaling. AT1R, but not AT2R, stimulation increased [Ca(2+)] in isolated cardiomyocyte nuclei. Inositol 1,4,5-trisphosphate receptor blockade by 2-aminoethoxydiphenyl borate prevented AT1R-mediated Ca(2+) release and attenuated AT1R-mediated transcription initiation responses. We conclude that cardiomyocyte nuclear membranes possess angiotensin receptors that couple to nuclear signaling pathways and regulate transcription. Signaling within the nuclear envelope (e.g. from intracellularly synthesized Ang-II) may play a role in Ang-II-mediated changes in cardiac gene expression, with potentially important mechanistic and therapeutic implications.

Project description:Appropriate glucagon secretion from pancreatic alpha cells in response to hypoglycemia is an important component of maintaining glucose homeostasis. Dysregulated glucagon secretion leads to the delayed recovery from a hypoglycemic attack in type 1 diabetes patients which can be lethal. Although elucidating the precise mechanism of glucagon secretion in hypoglycemia is warranted, the underlying mechanism remains poorly understood.The present study provides evidence of the role of autophagy in glucagon secretion in hypoglycemia by demonstrating that autophagy regulates adrenergic stimulation of glucagon secretion downstream of beta2 adrenergic receptor. First, from the analyses of T1D human islets and the published database of scRNA-seq of T1D human alpha cells, we described autophagy pathways altered in T1D alpha cells. Second, we generated alpha cell-specific Atg7KO mice (alphaAtg7KO) and clarified that the lack of autophagy in alpha cells impairs the reactive glucagon secretion in acute hypoglycemia. Third, to interrogate the molecular mechanism of autophagy-mediated glucagon regulation, we analyzed top genes downregulated inT1D and T2D alpha cells and found the expression of beta2 adrenergic receptor showed significant down-regulation in T1D alpha cells. We confirmed the decreased expression of beta2 adrenergic receptor in alpha cells of the T1D pancreas section, the islets of alphaAtg7KO mice, and a murine alpha cell line with stable knockdown of Atg7. Furthermore, in vivo and ex vivo studies of alphaAtg7KO mice exhibited that lack of autophagy led to the loss of stimulatory effect of beta2-adrenergic signaling on glucagon secretion. Finally, we established the Atg7 knockdown model in sorted human alpha cells and confirmed the effect of autophagy on the expression of the beta2 adrenergic receptor. Together, our study provides novel insights into the regulatory role of autophagy in glucagon secretion in response to hypoglycemia and provides therapeutic options to achieve stable glycemic control in T1D patients.

Dataset Information

Caveolin-3 regulates compartmentation of cardiomyocyte beta2-adrenergic receptor-mediated cAMP signaling.

Publications

Caveolin-3 regulates compartmentation of cardiomyocyte beta2-adrenergic receptor-mediated cAMP signaling.

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