Abstract:

G protein coupled receptors (GPCRs) are developed for organisms to uptake enough foods during evolution. As
a primary nutrition sensor system, GPCRs are expressed in endocrine cells within the gut mucosa, and absorb nutrients and
quantitate them with voltage-gated calcium channels, sodium potassium pump and vegetative nervous system. These signals
are transmitted to brain for appetite control. GPCRs also coordinate with other chemosensory signaling elements. The release
of hormones can regulate energy and glucose homeostasis. The malfunction of GCPRs may be responsible for a variety of
metabolic dysfunctions associated with overfeeding or obesity. In addition, another nutrient sensor system, mammalian target
of rapamycin (mTOR) has been implicated as a sensor of nutrient sufficiency for dividing cells and is activated by essential
amino acids, glucose and lipids. mTOR is also involved in the mechanisms for efficient transition between anabolic states
and catabolic states. When nutrients are absorbed, the glucose will be transformed into liver glycogen or muscle glycogen
for future utilization, and the lipids will be stored in adipose tissue. The glycogen will be used in pyrophosphorolysis and the
lipids will be consumed by β-oxidation when energy is needed. When the nutrition storage exceeds some limits, mTOR will
activate many processes that generate or use a large amount of energy and glycogen. It is increasingly apparent that mTORactivated
metabolism impacts most major cellular functions, thus playing an oversized role in regulating basic cell behaviors
such as growth and proliferation, and many disease including cancer, obesity, and type 2 diabetes. Furthermore, there is
a ubiquitous natural phenomenon that the lifespan of an organism is closely related to its metabolic activity. The higher
the metabolism speed, the shorter the lifespan, and vice versa. In recent years, multiple studies have shown that calorie
restriction can prolong lifespan, so overnutrition may not only induce multiple diseases but also shorten lifespan. This review
describes recent findings regarding overnutrition-related diseases. The main purpose is to attract extensive attention and
broaden academic interest.

Key words: G proteincoupled receptors, mTOR, nutrition, signaling pathway, metabolic syndrome