GHSR suppression in neurons protects against aging-associated metabolic and cognitive impairments

Aging is accompanied by progressive declines in metabolic and cognitive functions. Growth hormone secretagogue receptor (GHSR), a receptor for the gut hormone ghrelin, is highly expressed in neurons and plays a crucial role in metabolic regulation. We previously reported that aged global GHSR-ablated mice are lean and insulin-sensitive, and that neuronal GHSR-deleted mice (Syn1-cre;Ghsr^f/f) completely prevent diet-induced obesity. However, the role of neuronal GHSR in metabolic and cognitive aging has not been elucidated. The current study aims to determine the roles of neuronal GHSR in aging metabolism and cognitive dysfunction. Syn1-cre;Ghsr^f/f mice were subjected to cold stress, glucose- and insulin-tolerance tests, behavioral tests, and tissue analysis. Aging is accompanied by glycemic dysregulation and insulin resistance; old Syn1-cre;Ghsr^f/f mice showed improved glucose tolerance and insulin sensitivity. Aging is associated with thermogenic impairment and cognitive decline; old Syn1-cre;Ghsr^f/f mice showed better cold resistance and retained better recognition memory. Noticeably, there were increased expression of thermogenic makers (PGC1α and UCP1) and elevated sympathetic innervation markers (tyrosine hydroxylase and synaptophysin) in brown adipose tissue of old Syn1-cre;Ghsr^f/f mice. Lastly, old Syn1-cre;Ghsr^f/f mice exhibited decreased pro-inflammatory cytokines and increased neural plasticity-related markers (brain-derived neurotrophic factor, synaptophysin, and tyrosine hydroxylase) in metabolic and cognitive-relevant brain regions such as hypothalamus, cortex, and hippocampus. In conclusion, neuronal inhibition of GHSR promotes a healthy aging phenotype showing improved energy metabolism and cognitive function, which is likely contributed to the improved thermogenesis and insulin sensitivity, reduced inflammation, and restored neuronal plasticity.