Inflammation promotes adipocyte lipolysis via IRE1 kinase
Bibliographic record
Abstract
Abstract Obesity associates with inflammation, insulin resistance and higher blood lipids. It is unclear if immune responses facilitate lipolysis separate from hormone or adrenergic signals. We found that an ancient component of ER stress, inositol-requiring protein 1 (IRE1), discriminates inflammation-induced adipocyte lipolysis versus lipolysis regulated by adrenergic or hormonal stimuli. Inhibiting IRE1 kinase activity was sufficient to block adipocyte-autonomous lipolysis from multiple inflammatory ligands, including bacterial components, certain cytokines, and thapsigargin-induced ER stress. Adipocyte-specific deletion of IRE1 in mice prevented inflammatory ligand-induced lipolysis in adipose tissue. IRE1 kinase activity was dispensable for isoproterenol and cAMP-induced lipolysis in adipocytes and mouse adipose tissue. IRE1 RNase activity was not associated with inflammation-induced adipocyte lipolysis. We found no role for canonical unfolded protein responses (UPR) or ABL kinases in linking ER stress to lipolysis. Lipolysis was unchanged in adipose tissue from GRP78/BiP +/- compared to littermate mice. Tyrosine kinase inhibitors (TKIs) such as imatinib, which reduce ER stress and IRE1 RNase activity, did not alter lipolysis from inflammatory stimuli. Inhibiting IRE1 kinase activity blocked adipocyte NF-κB activation and Interleukin-6 (Il6) production due to inflammatory ligands. Inflammation-induced lipolysis mediated by IRE1 occurred independently from changes in insulin signalling in adipocytes. Therefore, inflammation can promote IRE1-mediated lipolysis independent of adipocyte insulin resistance. Our results show that IRE1 propagates an inflammation-specific lipolytic program independent from hormonal or adrenergic regulation, including insulin resistance. Targeting IRE1 kinase activity may benefit metabolic syndrome and inflammatory lipid disorders. Significance Adipocytes maintain metabolic homeostasis by storing nutrients and releasing lipids into the blood via lipolysis. Catecholamines stimulate adrenergic-mediated lipolysis, whereas insulin inhibits lipolysis. Obesity is associated with elevated blood lipids and inflammation, which can impair insulin-mediated suppression of lipolysis (i.e. insulin resistance). It is unclear if inflammatory triggers of lipolysis require insulin resistance or if specific lipolytic triggers engage distinct cell stress components. We found that a specific ER stress response was required for inflammation-mediated lipolysis, not adrenergic-mediated lipolysis. Bacterial and cytokine-induced lipolysis required adipocyte IRE1 kinase activity, but not IRE1 RNase activity typical of the ER stress-related unfolded protein response. We propose that inflammatory triggers of lipolysis engage IRE1 kinase independent of catecholamine and hormone responses, including insulin resistance. Graphical Abstract IRE1 kinase activity promotes an inflammation-specific adipocyte lipolytic program that is separate from hormonal or adrenergic regulation of lipolysis.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".