Constitutive adipocyte mTORC1 activation enhances mitochondrial activity and reduces visceral adiposity in mice

Area of Science:

• Metabolic research
• Obesity research
• Cellular metabolism

Background:

• Mechanistic target of rapamycin complex 1 (mTORC1) signaling plays a critical role in regulating adiposity.
• Previous studies show loss of mTORC1 function reduces adiposity, while partial inhibition enhances fat deposition.
• The precise role of constitutive mTORC1 activation specifically within adipocytes remains unclear.

Purpose of the Study:

• To investigate the in vivo effects of constitutive mTORC1 activation in adipocytes on overall adiposity.
• To elucidate the molecular mechanisms underlying changes in fat metabolism and energy expenditure.

Main Methods:

• Generated mice with adipocyte-specific constitutive mTORC1 activation via tuberous sclerosis complex (Tsc)1 deletion.
• Assessed body mass, energy expenditure, glucose and fatty acid metabolism, and mitochondrial function.
• Quantified mRNA and protein levels related to adipogenesis, lipolysis, browning, and mitochondrial biogenesis.

Main Results:

• Adipocyte-specific Tsc1 deletion reduced visceral fat mass, adipocyte size, and number.
• Observed increased lipolysis, enhanced mitochondrial oxidative activity, and induced 'browning' (UCP-1 expression) in visceral and subcutaneous fat.
• Improved glucose tolerance, insulin signaling in liver and muscle, and increased adiponectin secretion were noted, independent of diet composition.

Conclusions:

• Constitutive mTORC1 activation in adipocytes enhances mitochondrial function and promotes browning.
• This activation leads to a reduction in visceral adiposity and improves systemic metabolic parameters.
• Adipocyte mTORC1 signaling is a key regulator of fat mass and metabolic homeostasis.