Hypothesis

Endotrophin (COL6a3) released from dysfunctional adipocytes binds integrin αvβ3 on the adipocyte surface, activating focal adhesion kinase (FAK) and downstream YAP/TAZ nuclear translocation. This mechanotransductive signal cooperates with IL‑17A–STAT3 signaling from adipose‑resident γδ T cells to push mature adipocytes toward a PDGFRα+ preadipocyte state and subsequent transdifferentiation into collagen‑producing myofibroblasts. Blocking integrin αvβ3 or FAK will break this feed‑forward loop, reducing fibrosis even when TGF‑β, hypoxia, and senescent cell burdens remain high.

Mechanistic Rationale

• Endotrophin is a known pro‑fibrotic matricellular fragment that accumulates in obese adipose tissue [3].
• Integrin αvβ3 is a mechanosensitive receptor that links extracellular matrix rigidity to intracellular FAK‑YAP/TAZ signaling, a pathway shown to regulate cell fate in fibroblasts and epithelial cells.
• In adipose tissue, elevated ECM stiffness promotes actin stress‑fiber formation; inhibiting actin contractility rescues adipocytes from a fibrotic phenotype [3], suggesting that upstream mechanosensors integrate stiffness cues.
• Aging visceral adipose tissue accumulates IL‑17A‑producing γδ T cells that drive chronic inflammation independent of obesity [2]; IL‑17A activates STAT3, which can cooperate with YAP/TAZ to transcriptionally induce PDGFRα and myofibroblast markers.
• TGF‑β/Smad2/3 signaling remains the master regulator of ECM deposition [1], but our model places endotrophin‑integrin signaling upstream of the adipocyte dedifferentiation step, providing a mechanistic link between matrix fragment accumulation and cellular transdifferentiation.
• Senescent adipocytes secrete ECM‑remodeling factors that exacerbate the pro‑fibrotic milieu [6]; however, the integrin‑FAK‑YAP/TAZ axis may operate independently of senescence, offering a therapeutic window.

Testable Predictions

1. In visceral adipose tissue from aged, obese mice, adipocyte‑specific loss of integrin αvβ3 will reduce PDGFRα+ preadipocyte accumulation and α‑SMA+ myofibroblast numbers despite high endotrophin levels.
2. Pharmacological inhibition of FAK (e.g., with 'defactinib') will decrease YAP/TAZ nuclear localization in isolated adipocytes exposed to recombinant endotrophin, and will attenuate collagen‑I secretion in vitro.
3. Co‑culture of adipocytes with IL‑17A‑producing γδ T cells will synergistically increase PDGFRα expression; this effect will be abolished by either integrin αvβ3 blockade or STAT3 inhibition.
4. Treating aged, obese mice with an integrin αvβ3‑blocking antibody will lower pericellular fibrosis and improve glucose tolerance without altering TGF‑β levels or senescent cell burden.

Potential Experimental Approaches

• Generate adipocyte‑specific Itgav (integrin αv) knockout mice crossed with leptin‑deficient (ob/ob) background; assess VAT fibrosis via hydroxyproline content, immunofluorescence for PDGFRα and α‑SMA, and metabolic readouts (GTT, ITT).
• Isolate primary murine adipocytes, treat with recombinant endotrophin ± FAK inhibitor, measure phospho‑FAK, nuclear YAP/TAZ (Western blot/IF), and qPCR for Pdgfrα, Acta2.
• Flow cytometry of stromal vascular fraction to quantify γδ T cell IL‑17A production; co‑culture experiments with neutralizing anti‑IL‑17A or STAT3 inhibitor (Stattic).
• Pharmacological studies: administer integrin αvβ3‑blocking antibody or oral FAK inhibitor to aged, obese wild‑type mice for 8 weeks; compare to vehicle and to dapagliflozin as a positive control.

If these experiments confirm the predictions, the integrin αvβ3‑FAK‑YAP/TAZ axis would emerge as a mechanosensitive conduit that translates endotrophin‑rich matrix changes into adipocyte‑to‑myofibroblast conversion, offering a novel anti‑fibrotic target distinct from TGF‑β or senolytic strategies.