Neuropeptide Y

Overview

Neuropeptide Y (NPY) is one of the most abundantly expressed neuropeptides in the mammalian nervous system. Discovered in 1982 by Tatemoto and colleagues, NPY is a 36-amino acid peptide belonging to the pancreatic polypeptide fold (PP-fold) family, which also includes peptide YY (PYY) and pancreatic polypeptide (PP). NPY is synthesized primarily in the arcuate nucleus of the hypothalamus and in sympathetic noradrenergic neurons throughout the peripheral nervous system.

Structure

NPY contains the conserved PP-fold structural motif characterized by an N-terminal tyrosine residue, an internal polyproline region, and a C-terminal alpha-helical segment. The C-terminal hexapeptide Tyr-X-X-X-X-Arg-CONH2 is essential for receptor binding and biological activity. The Y-X-X-X-X-R motif is shared among all PP-fold family members and is required for high-affinity interaction with NPY receptors.

Receptor System

NPY signals through at least five G-protein-coupled receptor subtypes (Y1, Y2, Y4, Y5, and Y6), each with distinct tissue distribution and functional roles:

• Y1 receptors: Expressed in the hypothalamus, cortex, and vasculature. They mediate appetite stimulation and vasoconstriction.
• Y2 receptors: Found on presynaptic terminals in the hypothalamus, hippocampus, and sympathetic neurons. They function as autoreceptors and mediate both orexigenic and anxiolytic effects.
• Y4 receptors: Preferentially bind pancreatic polypeptide and are expressed in the brainstem and intestinal mucosa.
• Y5 receptors: Highly expressed in the hypothalamus and are considered the principal mediators of NPY-induced feeding behavior.

Physiological Functions

NPY is the most potent endogenous orexigenic signal known. Injection into the paraventricular nucleus of the hypothalamus potently stimulates food intake, particularly carbohydrate-rich meals. NPY neurons in the arcuate nucleus integrate signals from peripheral metabolic hormones: they are activated by ghrelin and inhibited by leptin and insulin, positioning NPY as a key node in energy homeostasis.

Beyond appetite regulation, NPY modulates the stress response, anxiety, and circadian rhythms. NPY levels are altered in stress-related disorders, and NPY administration produces anxiolytic effects in animal models. In the periphery, NPY co-released with norepinephrine from sympathetic neurons enhances vasoconstriction and promotes angiogenesis.

Clinical Relevance

Dysregulation of NPY signaling has been implicated in obesity, anxiety disorders, depression, and substance abuse. NPY Y5 receptor antagonists were developed as potential anti-obesity agents, though clinical efficacy has been limited. Plasma NPY levels serve as a biomarker for sympathetic nervous system activity and have been evaluated in post-traumatic stress disorder and cardiovascular disease.