Role of ghrelin system in neuroprotection and cognitive functions: implications in Alzheimer's disease.

Alzheimer's disease (AD) is a multifactorial progressive neurodegenerative disorder characterized by loss of memory and cognitive deficits, strongly influenced by the metabolic status, in which the impairment of neuropeptides/neurotransmitters systems has been previously observed. Ghrelin is a multifunctional hormone produced in a wide variety of tissues, which has been associated with the progression of obesity and metabolic syndrome, but has been also linked to neuromodulation, neuroprotection and memory and learning processes. In addition, ghrelin system also acts in an autocrine/paracrine fashion where the majority of its components [ghrelin variants (native ghrelin, In1-ghrelin), acylation enzyme (GOAT) and receptors (GHS-Rs)] are expressed in the different regions of central nervous system. In spite of all these pieces of information strongly suggesting a close association between ghrelin system and AD, which could be of pathophysiological relevance, few studies have been addressed to clarify this relationship. In this work, the role of ghrelin system in neuroprotection, memory consolidation and learning is reviewed, and its influence in AD, as well as the regulation of its expression in the brain of AD patients, is discussed.