The insulin receptor family and protein kinase B (Akt) are activated in the heart by alkaline pH and α1-adrenergic receptors

Abstract

Insulin and insulin-like growth factor stimulate protein synthesis and cardioprotection in the heart, acting through their receptors (INSRs, IGF1Rs) and signalling via protein kinase B (PKB, also known as Akt). Protein synthesis is increased in hearts perfused at alkaline pHo to the same extent as with insulin. Moreover, α1-adrenergic receptor (α1-AR) agonists (e.g. phenylephrine) increase protein synthesis in cardiomyocytes, activating PKB/Akt. In both cases, the mechanisms are not understood. Our aim was to determine if insulin receptor-related receptors (INSRRs, activated in kidney by alkaline pH) may account for the effects of alkaline pHo on cardiac protein synthesis, and establish if α1-ARs signal through the insulin receptor family. Alkaline pHo activated PKB/Akt signalling to the same degree as insulin in perfused adult male rat hearts. INSRRs were expressed in rat hearts and, by immunoblotting for phosphorylation (activation) of INSRRs/INSRs/IGF1Rs, we established that INSRRs, together with INSRs/IGF1Rs, are activated by alkaline pHo. The INSRR/INSR/IGF1R kinase inhibitor, linsitinib prevented PKB/Akt activation by alkaline pHo, indicating that INSRRs/INSRs/IGF1Rs are required. Activation of PKB/Akt in cardiomyocytes by α1-AR agonists was also inhibited by linsitinib. Furthermore, linsitinib inhibited cardiomyocyte hypertrophy induced by α1-ARs in cultured cells, reduced the initial cardiac adaptation (24 h) to phenylephrine in vivo (assessed by echocardiography) and increased cardiac fibrosis over 4 d. We conclude that INSRRs are expressed in the heart and, together with INSRs/IGF1Rs, the insulin receptor family provide a potent system for promoting protein synthesis and cardioprotection. Moreover, this system is required for adaptive hypertrophy induced by α1-ARs.

Cardiomyocyte BRAF and type 1 RAF inhibitors promote cardiomyocyte and cardiac hypertrophy in mice in vivo

“…The chest cavity was opened and the heart and lungs were removed into modified ice-cold KHBBS (25 mM NaHCO 3 , 119 mM NaCl, 35 mM KCl, 2.5 mM CaCl 2 , 1.2 mM MgSO 4 , 1.2 mM KH 2 PO 4 equilibrated with 95% O 2 /5% CO 2 ) whilst the heart was still beating. Hearts were perfused retrogradely (37°C at 70 mm Hg) as described previously [ 27 ] with a 15 min equilibration period. SB590885 was added at the end of the equilibration period and all perfusions continued for a further 15 min.…”

The anti-cancer drug dabrafenib is not cardiotoxic and inhibits cardiac remodelling and fibrosis in a murine model of hypertension

“…C57Bl/6J mice, Sprague-Dawley rats and Alzet osmotic minipumps were from Charles River U.K. Details of animal housing, husbandry and welfare are provided in [ 21 ].…”

“…Adult male (300–350 g) Sprague-Dawley rats were used for heart perfusions. Hearts were prepared and perfused in the Langendorff mode as described in [ 21 ]. Hearts were perfused for 15 min with Krebs-Henseleit bicarbonate-buffered saline (25 mM NaHCO 3 , 119 mM NaCl, 4.7 mM KCl, 2.5 mM CaCl 2 , 1.2 mM MgSO 4 , 1.2 mM KH 2 PO 4 , pH 7.4, containing 10 mM glucose and equilibrated with 95% O 2 /5% CO 2 ) without or with dabrafenib (5 µM) or trametinib (1 µM).…”

Of Mouse and Man: Cross-Species Characterization of Hypertensive Cardiac Remodeling

“…Total RNA was prepared by homogenizing frozen murine heart tissue with 1 mL TRIzol followed by 200 μL chloroform. RNA was prepared and reverse transcribed to cDNA as previously described [ 42 ]. Reverse Quantitative PCR (qPCR) was performed as previously described [ 13 ].…”