A groundbreaking study reveals that changes in protein interactions, rather than protein amounts, underpin insulin resistance in skeletal muscle, highlighting new potential therapeutic targets.
A new study published in Molecular Systems Biology suggests that insulin resistance in skeletal muscle is driven less by changes in protein amounts than by a wholesale reshaping of the way proteins interact with one another.
Led by Benjamin L. Parker at the University of Melbourne, the research combines two mass spectrometry approaches to map the muscle cell’s interactome, the network of physical contacts that underpins signalling, folding and energy use. According to the paper, more than 7,000 unique protein interactions were identified among 5,346 proteins, with the biggest disruptions centred on the endoplasmic or sarcoplasmic reticulum, the compartment where proteins are folded and quality-checked. The findings point to a disorder in protein processing machinery as a defining feature of insulin-resistant muscle.
The team used cultured mouse muscle cells treated with palmitate to induce insulin resistance, then paired protein correlation profiling with quantitative cross-linking mass spectrometry to track which proteins stayed together, separated or reassembled under stress. The study found that thousands of cross-linked peptides changed in abundance, but most of those shifts occurred without any corresponding change in the amount of the proteins themselves. In other words, the architecture of the protein network changed even when the parts did not, strengthening the argument that interactome remodelling is a core part of the disease process.
One protein stood out in particular: PDIA6, an endoplasmic reticulum enzyme involved in disulphide bond formation and rearrangement. The researchers report that PDIA6 formed many altered interactions, including a marked reduction in links with BiP, a key stress-response chaperone. They also found that PDIA6 moved into larger protein assemblies under insulin-resistant conditions. When they overexpressed PDIA6 in mice fed a high-fat diet, insulin-stimulated glucose uptake fell rather than improved, alongside weaker activation of Akt and AS160, two important markers of insulin signalling.
The study also extended cross-linking analysis into intact skeletal muscle tissue, where it found further changes in pathways linked to glycolysis, calcium handling and contraction. Those results included altered interactions around the calcium-release machinery and contractile proteins such as myosin heavy chain 7. The authors say the work shows that quantitative interactome mapping can be done in whole tissue and may reveal disease mechanisms that are invisible to protein-abundance measurements alone.
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