Dynamic ’omics redefines how insulin signalling choreographs glucose metabolism

Krycer J1, Yugi K2,4, Fazakerley D1, Humphrey S1, Quek L1, Hirayama A3, Soga T3, Kuroda S4 and James D1

  1. University of Sydney, Sydney, Australia.
  2. RIKEN IMS, Yokohama, Japan.
  3. Keio University, Tsuruoka, Japan.
  4. University of Tokyo, Kashiwa, Japan.

Adipose (fat) tissue plays a crucial role in energy storage and release. Accordingly, adipose metabolism responds to fluctuating nutrient availability and hormonal cues. For instance, after a meal, insulin triggers a phosphorylation cascade to stimulate glucose uptake. This is considered insulin’s primary role, with subsequent energy storage activated by allostery as substrates accumulate. However, our recent phosphoproteomics screen in insulin-treated adipocytes identified hundreds of metabolic proteins - could insulin signalling play a role beyond glucose uptake, coercing glucose down specific metabolic routes? We addressed this by measuring acute, temporal metabolomic changes upon insulin exposure, taking a dynamic approach to traditional steady-state 13C-tracer-experiments. We found three exciting results: (1) Insulin rapidly stimulated glucose uptake (t1/2=4 min), with its kinetics explaining 48% of metabolomic changes in response to insulin. Indeed, glucose was necessary for insulin-stimulated lipogenesis and suppression of fatty-acid oxidation, suggesting glucose facilitates insulin action. (2) Despite this, flux analysis revealed glucose was primarily converted to lactate and favoured NADPH-generating pathways (e.g., pyruvate anaplerosis, pentose phosphate pathway). This is reminiscent of cancer metabolism. We believe this allows glucose to facilitate anabolism beyond being a mere carbon source in (terminally-differentiated) adipocytes. (3) Overlaying metabolomic and phosphoproteomic data (’transomic analysis’) revealed protein phosphorylation changed rapidly (<5 min), activating anabolism before substrates accumulated. Thus, insulin creates a demand-driven system to ’drag’ glucose down specific pathways. This complements supply-driven regulation of anabolism by substrate accumulation. Overall, this redefines how signalling coordinates metabolism, with implications for metabolic dysregulation in overactive signalling (cancer) or nutrient oversupply (diabetes).