{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\nRecent findings indicate that the NPY4R gene—which encodes the pancreatic polypeptide receptor Y4—is intimately involved in the regulation of energy homeostasis and satiety. Genetic studies have identified copy number variations affecting this locus, including a CNV on chromosome 10q11.22 that encompasses PPYR1/NPY4R and accounts for a notable proportion of BMI variation. Additional work has posited that both genetic and structural variations in NPY4R might contribute to obesity pathogenesis, with increased copy numbers correlating with higher BMI and waist circumference particularly in women, underscoring a complex role in metabolic balance."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "3"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nPharmacologically, studies in isolated human colonic mucosa have demonstrated that the effects of pancreatic polypeptide (PP) on electrogenic ion transport are mediated predominantly by Y4 receptors, distinguishing them from other NPY receptor subtypes. Complementary reconstitution experiments in Sf9 insect cells have confirmed that hY4R couples efficiently to G(i/o) proteins, while comparative binding studies between rabbit and human receptors reveal subtle yet functionally relevant differences in pharmacological profiles."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "4", "end_ref": "6"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nAt the structural level, double-cycle mutagenesis and NMR analyses have shed light on the complex network of ionic, hydrophobic, and hydrogen-bond interactions that form the core peptide binding pocket of the receptor, delineating key residues in transmembrane segments that are critical for receptor activation by pancreatic polypeptide. Additionally, investigations into receptor desensitization have identified a specific carboxyl-terminal motif that regulates arrestin-3 recruitment and subsequent receptor internalization, processes vital for modulating signal duration and intensity."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "7"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nComputational studies further explore the interactions between NPY4R and related peptides such as peptide YY (PYY), highlighting the receptor’s potential as a therapeutic target for obesity and type 2 diabetes. This integrative body of evidence—from genetic associations and pharmacological profiling to structural characterization and in silico modeling—underscores the multifaceted role of NPY4R in satiety signaling and energy regulation, offering promising avenues for metabolic disease intervention."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "9"}]}, {"type": "t", "text": "\n"}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Bao-Yong Sha, Tie-Lin Yang, Lan-Juan Zhao, et al. 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