Abstract
The mechanistic target of rapamycin (mTOR) is a central regulator of cellular homeostasis that integrates environmental and nutrient signals to control cell growth and survival. Over the past two decades, extensive studies of mTOR have implicated the importance of this protein complex in regulating a broad range of metabolic functions, as well as its role in the progression of various human diseases. Recently, mTOR has emerged as a key signaling molecule in regulating animal entry into a hypometabolic state as a survival strategy in response to environmental stress. Here, we review current knowledge of the role that mTOR plays in contributing to natural hypometabolic states such as hibernation, estivation, hypoxia/anoxia tolerance, and dauer diapause. Studies across a diverse range of animal species reveal that mTOR exhibits unique regulatory patterns in an environmental stressor-dependent manner. We discuss how key signaling proteins within the mTOR signaling pathways are regulated in different animal models of stress, and describe how each of these regulations uniquely contribute to promoting animal survival in a hypometabolic state.
Highlights
It was determined that rapamycin inhibited the activity of an immunosuppressive compound called FK506 in part by competing for its binding towards FKBP (FK506 binding protein), and this interaction facilitated the inhibition of T cell activation [4]
Consistent with Akt acting upstream of mechanistic target of rapamycin (mTOR), p-Akt levels were significantly reduced in M. leucogaster during torpor. For both mTOR and Akt, the total protein levels did not fluctuate in bats during hibernation, suggesting that post-translational phosphorylation was the primary mechanism of regulation [15]
A recent study that examined the regulation of the insulin signaling pathway across six different lemur tissues during torpor showed that were no changes to the levels of p-Akt (Ser-473) and only one out of six tissues displayed a slight reduction in p-mTOR
Summary
For both mTOR and Akt, the total protein levels did not fluctuate in bats during hibernation (as seen in ground squirrels), suggesting that post-translational phosphorylation was the primary mechanism of regulation [15]. A recent study that examined the regulation of the insulin signaling pathway across six different lemur tissues during torpor showed that were no changes to the levels of p-Akt (Ser-473) and only one out of six tissues (kidney) displayed a slight reduction in p-mTOR
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