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Updated: Nov 11, 2025
Analysis of Cardiac Contractile Dysfunction and Ca2+ Transients in Rodent Myocytes
Published on: May 25, 2022
mTOR-mediated calcium transients affect cardiac function in ex vivo ischemia-reperfusion injury
Briana K Shimada1, Naaiko Yorichika1, Jason K Higa1
1Department of Anatomy, Biochemistry, and Physiology, Center for Cardiovascular Research, John A. Burns School of Medicine, University of Hawai'i at Manoa, Honolulu, Hawai'i, USA.
Abstract:
The mechanistic target of rapamycin (mTOR) is a key mediator of energy metabolism, cell growth, and survival. While previous studies using transgenic mice with cardiac-specific overexpression of mTOR (mTOR-Tg) demonstrated the protective effects of cardiac mTOR against ischemia-reperfusion (I/R) injury in both ex vivo and in vivo models, the mechanisms underlying the role of cardiac mTOR in cardiac function following I/R injury are not well-understood. Torin1, a pharmacological inhibitor of mTOR complex (mTORC) 1 and mTORC2, significantly decreased functional recovery of LV developed pressure in ex vivo I/R models (p < 0.05). To confirm the role of mTOR complexes in I/R injury, we generated cardiac-specific mTOR-knockout (CKO) mice. In contrast to the effects of Torin1, CKO hearts recovered better after I/R injury than control hearts (p < 0.05). Interestingly, the CKO hearts had exhibited irregular contractions during the reperfusion phase. Calcium is a major factor in Excitation-Contraction (EC) coupling via Sarcoplasmic Reticulum (SR) calcium release. Calcium is also key in opening the mitochondrial permeability transition pore (mPTP) and cell death following I/R injury. Caffeine-induced SR calcium release in isolated CMs showed that total SR calcium content was lower in CKO than in control CMs. Western blotting showed that a significant amount of mTOR localizes to the SR/mitochondria and that GSK3-β phosphorylation, a key factor in SR calcium mobilization, was decreased. These findings suggest that cardiac mTOR located to the SR/mitochondria plays a vital role in EC coupling and cell survival in I/R injury.
Insights
Cardiac mechanistic target of rapamycin (mTOR) protects against ischemia-reperfusion (I/R) injury by regulating calcium handling and cell survival. Inhibiting mTOR worsens I/R injury, while its cardiac-specific knockout improves recovery.
Area of Science:
- Cardiovascular Biology
- Cellular Metabolism
- Molecular Cardiology
Background:
- Mechanistic target of rapamycin (mTOR) is crucial for cell growth and survival.
- Cardiac-specific mTOR overexpression protects against ischemia-reperfusion (I/R) injury.
- Mechanisms of cardiac mTOR in I/R injury remain unclear.
Purpose of the Study:
- Investigate the role of cardiac mTOR complexes in cardiac function following I/R injury.
- Elucidate the mechanisms by which cardiac mTOR influences I/R injury outcomes.
Main Methods:
- Utilized pharmacological inhibition of mTOR complexes (mTORC1/2) with Torin1.
- Generated cardiac-specific mTOR-knockout (CKO) mice.
- Assessed cardiac function ex vivo and in vivo.
- Analyzed sarcoplasmic reticulum (SR) calcium handling and western blotting for protein localization and phosphorylation.
Main Results:
- Torin1 treatment impaired functional recovery after I/R injury.
- CKO hearts showed improved recovery from I/R injury compared to controls.
- CKO hearts exhibited irregular contractions and reduced SR calcium content.
- mTOR localized to SR/mitochondria, and GSK3-β phosphorylation was decreased in CKO hearts.
Conclusions:
- Cardiac mTOR plays a vital role in excitation-contraction coupling and cell survival during I/R injury.
- mTOR's localization to SR/mitochondria is critical for its protective functions.
- Targeting cardiac mTOR may offer therapeutic strategies for I/R injury.
