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Insulin Signaling Cascade in the Hearts of Long-Lived Growth Hormone Receptor Knockout Mice: Effects of Calorie Restriction

¹ Instituto de Química y Fisicoquímica Biológicas (IQUIFIB), Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Argentina.
² Geriatrics Research, Departments of Internal Medicine and Physiology, and ³ Department of Pharmacology, School of Medicine, Southern Illinois University, Springfield.

Address correspondence to Fernando Pablo Dominici, PhD, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Instituto de Química y Fisicoquímica Biológicas (IQUIFIB), Junin 956, sexto piso, Buenos Aires, Buenos Aires 1113, Argentina. E-mail: dominici{at}qb.ffyb.uba.ar

Calorie restriction (CR) improves insulin sensitivity and increases life span in normal but not in long-lived growth hormone-resistant knockout (GHRKO) mice. In this study, we examined interactive effects of GH resistance and long-term CR on cardiac insulin action. GHRKO mice exhibited marked increases in the insulin-induced phosphorylation of the insulin receptor (IR), insulin receptor substrate-1 (IRS-1), Akt, and ERK1/2 along with elevated insulin-stimulated IRS-1-associated regulatory subunit of phosphatidylinositol 3-kinase in the heart. These changes were associated with elevated protein levels of IR, IRS-1, and Akt and with a down-regulation of cardiac glucose transporter 4 (GLUT4). In normal mice, CR induced an important increase in the phosphorylation of cardiac Akt without elevation of Akt protein, reaching activation levels similar to those seen in GHRKO mice. This change may be cardioprotective and thus contribute to increased longevity in response to CR. Interestingly, the insulin signaling cascade in the heart of GHRKO mice was unaffected by CR.

Key Words: GHRKO mice • Calorie restriction • Heart • Insulin signaling