su min (violet) hong

read_status: annotated
type: paper
title: Tirzepatide modulates the regulation of adipocyte nutrient metabolism through long-acting activation of the GIP receptor
year: 2024
authors:
  - Regmi, Ajit
  - Aihara, Eitaro
  - Christe, Michael E.
  - Varga, Gabor
  - Beyer, Thomas P.
  - Ruan, Xiaoping
  - Beebe, Emily
  - O’Farrell, Libbey S.
  - Bellinger, Melissa A.
  - Austin, Aaron K.
  - Lin, Yanzhu
  - Hu, Haitao
  - Konkol, Debra L.
  - Wojnicki, Samantha
  - Holland, Adrienne K.
  - Friedrich, Jessica L.
  - Brown, Robert A.
  - Estelle, Amanda S.
  - Badger, Hannah S.
  - Gaidosh, Gabriel S.
  - Kooijman, Sander
  - Rensen, Patrick C.N.
  - Coskun, Tamer
  - Thomas, Melissa K.
  - Roell, William
journal: Cell Metabolism
doi: 10.1016/j.cmet.2024.05.010
url: https://linkinghub.elsevier.com/retrieve/pii/S1550413124001864
project:
  - IGP
system:
  - adipose_tissue
  - adipocytes
  - white_adipose_tissue
disease:
  - type_2_diabetes
  - obesity
  - dyslipidemia
genes:
  - gipr
  - insulin_receptor
  - lpl
processes:
  - gipr_signaling
  - insulin_sensitization
  - glucose_uptake
  - lipid_clearance
  - lipolysis
  - glycerogenesis
methods:
  - primary_human_adipocyte_culture
  - hyperinsulinemic_euglycemic_clamp
  - stable_isotope_tracing
  - radiolabeled_substrate_uptake
  - in_vivo_lipid_challenge
key_findings:
  - gipr_agonism_enhances_insulin_action
  - insulin_dependent_metabolic_switching
  - bias_toward_glycerol_over_dnl
  - lpl_mediated_lipid_clearance
  - fasting_state_lipolysis_activation
limitations:
  - indirect_systemic_effects
  - limited_human_in_vivo_validation
  - cell_type_specific_contributions_unclear
relevance:
  - mechanistic_basis_for_dual_incretin_therapy
  - adipose_specific_metabolic_control
  - therapeutic_metabolic_partitioning
concepts:
  - Insulin_Context_Dependent_GPCR_Signaling
  - Adipose_Macronutrient_Partitioning
  - Long_Acting_GPCR_Agonism
tags:
  - gipr
  - incretin
  - adipocyte_metabolism
  - metabolic_partitioning

Abstract

Tirzepatide, a glucose-dependent insulinotropic polypeptide/glucagon-like peptide 1 receptor (GIPR/GLP1R) agonist, has, in clinical trials, demonstrated greater reductions in glucose, body weight, and triglyceride levels compared with selective GLP-1R agonists in people with type 2 diabetes (T2D). However, cellular mechanisms by which GIPR agonism may contribute to these improved efficacy outcomes have not been fully defined. Using human adipocyte and mouse models, we investigated how long-acting GIPR agonists regulate fasted and fed adipocyte functions. In functional assays, GIPR agonism enhanced insulin signaling, augmented glucose uptake, and increased the conversion of glucose to glycerol in a cooperative manner with insulin; however, in the absence of insulin, GIPR agonists increased lipolysis. In diet-induced obese mice treated with a long-acting GIPR agonist, circulating triglyceride levels were reduced during oral lipid challenge, and lipoprotein-derived fatty acid uptake into adipose tissue was increased. Our findings support a model for long-acting GIPR agonists to modulate both fasted and fed adipose tissue function differentially by cooperating with insulin to augment glucose and lipid clearance in the fed state while enhancing lipid release when insulin levels are reduced in the fasted state.

Key Findings

• GIPR is functionally expressed on human and mouse adipocytes

• Long-acting GIPR agonism enhances insulin-stimulated glucose uptake

• GIPR signaling biases glucose carbons toward glycerol rather than de novo lipogenesis

• Insulin presence switches GIPR output from lipolysis to storage

• Chronic GIPR agonism improves lipid clearance without increasing adiposity

• Fasted-state GIPR activation promotes lipolysis and lipid oxidation

Methods

• Differentiated primary human adipocyte cultures

• Fluorescent ligand tracing in intact adipose tissue

• cAMP signaling assays for GPCR activation

• Radiolabeled glucose and fatty acid uptake assays

• Stable isotope tracing with NMR

• Hyperinsulinemic–euglycemic clamps

• In vivo oral lipid challenge and TRL particle uptake

Notes

• Demonstrates direct adipocyte-autonomous effects of GIPR signaling

• Reframes GIPR as a context-dependent metabolic switch

• Separates insulin secretion effects from adipocyte insulin action

• Provides a mechanistic explanation for superior lipid lowering with tirzepatide

• Adipose tissue acts as a regulated metabolic buffer rather than passive storage

Figures / Data

• Figure 1: Direct binding and signaling of GIPR agonists in adipocytes

• Figure 2: Transcriptional overlap and divergence between GIPR and insulin signaling

• Figure 3: Enhanced insulin-stimulated glucose uptake and glycerol production

• Figure 4: LPL-dependent lipid clearance into adipose tissue

• Figure 5: Insulin-suppressed, fasting-specific GIPR-driven lipolysis

• Figure 6: Integrated fed vs fasted adipose metabolic model

Limitations

• Systemic endocrine and CNS effects not fully isolated

• Non-adipocyte GIPR-expressing cells may contribute

• Limited direct human metabolic flux data

• Long-term adipose remodeling not assessed