Human MC4R variants affect endocytosis, trafficking and dimerization revealing multiple cellular mechanisms involved in weight regulation

Abstract

Summary The Melanocortin-4 Receptor (MC4R) plays a pivotal role in energy homeostasis. We used human MC4R mutations associated with an increased or decreased risk of obesity to dissect mechanisms that regulate MC4R function. Most obesity-associated mutations impair trafficking to the plasma membrane (PM), whereas obesity-protecting mutations either accelerate recycling to the PM or decrease internalization, resulting in enhanced signaling. MC4R mutations that do not affect canonical Gα s protein-mediated signaling, previously considered to be non-pathogenic, nonetheless disrupt agonist-induced internalization, β-arrestin recruitment, and/or coupling to Gα s , establishing their causal role in severe obesity. Structural mapping reveals ligand-accessible sites by which MC4R couples to effectors and residues involved in the homodimerization of MC4R, which is disrupted by multiple obesity-associated mutations. Human genetic studies reveal that endocytosis, intracellular trafficking, and homodimerization regulate MC4R function to a level that is physiologically relevant, supporting the development of chaperones, agonists, and allosteric modulators of MC4R for weight loss therapy.

Obesity, POMC, and POMC-processing Enzymes: Surprising Results From Animal Models

“…The primary effects of POMC-derived peptides on feeding/body weight are thought to be mediated by MSH peptides acting on the melanocortin 4 receptor (MC4R) ( 18 , 29 , 30 ). Mouse studies show that intracerebroventricular (i.c.v.)…”

Identification of p.Met215Ile mutation of the MC4R gene in a Moroccan woman with obesity

“… 6 The α‐MSH also increases energy expenditure by regulating intracellular concentrations cyclic adenosine monophosphate (cAMP) production by increasing adenylyl cyclase (AC) activity through Gαs signaling, 7 followed by activation of protein kinase A (PKA), exchange protein activated by cAMP (EPAC), extracellular signal‐regulated kinase 1/2 (ERK1/2), C‐AMP Response Element‐binding protein (CREB), and increased transcription of c‐Fos and decreased AMP‐activated protein kinase (AMPK). 8 , 9 The α‐MSH signaling also increases firing in MC4R neurons by activity regulation of the potassium channels. 10 The ligand binding results in closure of Kir7.1 leading to depolarization of MC4R neurons and playing a central role in the regulation of energy homeostasis.…”

“… 5 In fact, its endocytosis and targeting to early endosomes followed by rapidly recycling to the cell membrane or translocate to lysosomes for degradation. 8 The arrestin could also contribute to melanocortin signaling. It induces activation of the MAPK pathway leading to phosphorylation of ERK1/2.…”

“…Classically, the receptor coupling results in the activation of phospholipase C (PLC) and increased cytosolic calcium concentration through Gαq which results in decreased food intake 6 . The α‐MSH also increases energy expenditure by regulating intracellular concentrations cyclic adenosine monophosphate (cAMP) production by increasing adenylyl cyclase (AC) activity through Gαs signaling, 7 followed by activation of protein kinase A (PKA), exchange protein activated by cAMP (EPAC), extracellular signal‐regulated kinase 1/2 (ERK1/2), C‐AMP Response Element‐binding protein (CREB), and increased transcription of c‐Fos and decreased AMP‐activated protein kinase (AMPK) 8,9 . The α‐MSH signaling also increases firing in MC4R neurons by activity regulation of the potassium channels 10 .…”

“…The Gαs mediated also the recruitment of β‐arrestin resulting in the internalization and desensitization of the receptor 5 . In fact, its endocytosis and targeting to early endosomes followed by rapidly recycling to the cell membrane or translocate to lysosomes for degradation 8 . The arrestin could also contribute to melanocortin signaling.…”