Muscle inactivation of mTOR causes metabolic and dystrophin defects leading to severe myopathy

Area of Science:

• Cellular Biology
• Biochemistry
• Physiology

Background:

• Mammalian target of rapamycin (mTOR) is crucial for cell growth, forming mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2) with raptor and rictor, respectively.
• Raptor is essential for oxidative muscle integrity, while rictor is not.
• mTOR signaling pathways are vital in cellular processes and muscle function.

Purpose of the Study:

• To investigate the role of mTOR in muscle integrity and function.
• To determine the consequences of muscle-specific mTOR inactivation.
• To elucidate the relationship between mTOR, raptor, rictor, and dystrophin regulation.

Main Methods:

• Muscle-specific inactivation of mTOR in a mammalian model.
• Analysis of metabolic changes, mitochondrial function, and glucose uptake in mTOR-deficient muscles.
• Assessment of dystrophin content and transcriptional regulation.

Main Results:

• Muscle-specific mTOR inactivation leads to severe myopathy and premature death.
• mTOR-deficient muscles exhibit impaired oxidative metabolism, altered mitochondrial regulation, and glycogen accumulation, similar to raptor-deficient muscles.
• Loss of mTOR reduces dystrophin content independently of raptor and rictor, suggesting a distinct regulatory mechanism.

Conclusions:

• mTOR plays a critical role in maintaining muscle integrity and function, primarily through mTORC1.
• Regulation of dystrophin by mTOR is independent of raptor and rictor, and occurs in a cell-autonomous, rapamycin-resistant, and kinase-independent manner.
• These findings highlight mTOR's complex role in muscle physiology beyond its known functions in cell growth and metabolism.