The involvement of Akt, mTOR, and S6K in the in vivo effect of IGF-1 on the regulation of rat cardiac Na+/K+-ATPase

IGF-1 contributes to cardiovascular protection in obesity by upregulating Na+/K+-ATPase activity and modulating key signaling pathways in rats on a high-fat diet

This study examined the ability of insulin-like growth factor-1 (IGF-1) to improve the expression and function of cardiac sodium/potassium adenosine triphosphatase (Na+/K+-ATPase) and reduce heart hypertrophy in obese rats. Adult male Wistar rats received a standard diet or a high-fat (HF) diet for 12 weeks. A bolus injection of IGF-1 (50 μg/kg, i.p.) was administered to half of the HF rats 24 hours before euthanasia. IGF-1 treatment increased: the activity of Na+/K+-ATPase and expression of phosphorylated and total Na+/K+-ATPase α1 subunit, the phosphorylation of IGF-1 receptor β /insulin receptor β at Tyr1131/Tyr1146, insulin receptor substrate-1 (IRS-1) at Tyr1222, mammalian target of rapamycin (mTOR) at Ser2481, protein kinase B (Akt) at Ser473 and the expression of type-2 angiotensin II (AngII) receptor (AT2R). Conversely, IGF-1 reduced the levels of IRS-1 phosphorylated at Ser307, mTOR at Ser2448, ribosomal protein p70 S6 kinase (S6K) at Thr421/Ser424, and the expression of type-1 Ang II receptor (AT1R) in the heart, as well as the serum levels of Ang II in obese rats. IGF-1 treatment reduced cardiac mass and elevated mRNA expression of the α-myosin heavy chain (MHC), and the α/β MHC ratio in the hearts of obese rats. The results of this study suggest that the administration of IGF-1 to obese rats reduces the adverse effects of HF diet, potentially by lowering Ang II-mediated activation of mTOR/S6K and enhancing the IRS-1/Akt pathway, which promotes Na+/K+-ATPase activity in the heart and diminishes cardiac hypertrophy.

Cardiac-Specific Suppression of Valosin-Containing Protein Induces Progressive Heart Failure and Premature Mortality Correlating with Temporal Dysregulations in mTOR Complex 2 and Protein Phosphatase 1

Valosin-containing protein (VCP), an ATPase-associated protein, is emerging as a crucial regulator in cardiac pathologies. However, the pivotal role of VCP in the heart under physiological conditions remains undetermined. In this study, we tested a hypothesis that sufficient VCP expression is required for cardiac development and physiological cardiac function. Thus, we generated a cardiac-specific VCP knockout (KO) mouse model and assessed the consequences of VCP suppression on the heart through physiological and molecular studies at baseline. Our results reveal that homozygous KO mice are embryonically lethal, whereas heterozygous KO mice with a reduction in VCP by ~40% in the heart are viable at birth but progressively develop heart failure and succumb to mortality at the age of 10 to 12 months. The suppression of VCP induced a selective activation of the mammalian target of rapamycin complex 1 (mTORC1) but not mTORC2 at the early age of 12 weeks. The prolonged suppression of VCP increased the expression (by ~2 folds) and nuclear translocation (by >4 folds) of protein phosphatase 1 (PP1), a key mediator of protein dephosphorylation, accompanied by a remarked reduction (~80%) in AKTSer473 phosphorylation in VCP KO mouse hearts at a later age but not the early stage. These temporal molecular alterations were highly associated with the progressive decline in cardiac function. Overall, our findings shed light on the essential role of VCP in the heart under physiological conditions, providing new insights into molecular mechanisms in the development of heart failure.