Exosomal FBLN7 from Senescent Adipocytes Reprograms PDGFRβ+ ASPCs to Drive Age‑Exacerbated Adipose Fibrosis
In obese, aged adipose tissue senescent adipocytes release extracellular vesicles enriched in FBLN7 mRNA and miR‑30a antagonists. These vesicles are preferentially taken up by PDGFRβ+ adipogenic stem and precursor cells (ASPCs), overriding TGF‑β/Smad2/3‑independent fibrotic programming and amplifying collagen I/VI deposition. Blocking exosome secretion or neutralizing vesicular FBLN7 restores ASPB adipogenic potential, reduces fibrosis, and improves metabolic health even when TGF‑β signaling remains active.
Mechanistic Rationale
The current model places FBLN7 as a cell‑autonomous profibrotic factor induced in PDGFRα+ ASPC2 by palmitate‑stressed adipocyte signals (see [1]). Aging, however, adds a layer of senescence‑associated secretory phenotype (SASP) that includes elevated extracellular vesicle (EV) release ([5]). We propose that senescent hypertrophic adipocytes load EVs with FBLN7 transcripts and with endogenous inhibitors of miR‑30a (a known antifibrotic miR that predicts metabolically healthy obesity ([4])). PDGFRβ+ ASPCs, a subset distinct from the PDGFRα+CD9high collagen‑producing progenitors ([2]), express high levels of EV uptake machinery (e.g., syndecan‑4) and, upon EV internalization, translate FBLN7 protein intracellularly. FBLN7 then acts as a scaffold that stabilizes latent TGF‑β complexes and simultaneously sequesters miR‑30a, creating a double‑hit: enhanced TGF‑β signaling and loss of miR‑30a‑mediated repression of COL1A1/ COL6A1 transcription. This mechanism can operate even when canonical TGF‑β ligands are neutralized, explaining why fibrosis persists in some anti‑TGF‑β trials.
Testable Predictions
- EV isolates from visceral fat of aged, obese mice will contain higher FBLN7 mRNA and lower miR‑30a levels than EVs from young, obese counterparts.
- In vitro, PDGFRβ+ ASPCs treated with aged‑adipocyte EVs will show increased COL1A1/ COL6A1 expression and α‑SMA staining, an effect abolished by GW4869 (exosome release inhibitor) or by anti‑FBLN7 antibodies added to the EV preparation.
- In vivo, aged obese mice administered GW4869 or fed with FBLN7‑targeted antisense oligonucleotides packaged in EVs will exhibit reduced collagen deposition (hydroxyproline assay), improved glucose tolerance, and unchanged circulating TGF‑β1 levels compared with vehicle controls.
- Single‑cell RNA‑sequencing of stromal vascular fraction from treated mice will reveal a shift of PDGFRβ+ ASPCs from a myofibroblast transcriptional signature (Postn+, Acta2+) toward adipogenic regulators (Pparg+, Cebpa+).
Potential Experimental Approaches
- EV characterization: Ultracentrifugation of fat‑pad lysates, western blot for FBLN7, qPCR for miR‑30a, nanoparticle tracking for size/concentration.
- Cellular uptake: Label EVs with DiD, incubate with sorted PDGFRβ+ ASPCs, quantify fluorescence by flow cytometry; block with heparan sulfate or dynasore to confirm endocytosis.
- Functional assays: Treat ASPCs with EVs ± GW4869 or anti‑FBLN7, measure collagen gel contraction, Smad2/3 phosphorylation (Western), and luciferase activity of COL1A1 promoter.
- In vivo validation: Use aged (18‑month) C57BL/6J mice fed HFD for 12 weeks; administer GW4869 (intraperitoneal, 5 mg/kg twice weekly) or EVs loaded with FBLN7‑ASO; assess fibrosis (picrosirius red staining), metabolic phenotypes (GTT/ITT), and adipocyte size.
- Controls: Include young obese mice, TGF‑β neutralizing antibody treatment, and PDGFRα+ ASPC2‑specific FBLN7 knockout to distinguish vesicle‑mediated effects from cell‑autonomous pathways.
If these predictions hold, the hypothesis would reposition FBLN7 as a paracrine, EV‑borne effector that links adipocyte senescence to pathogenic ASPC reprogramming, offering a novel therapeutic avenue that complements existing TGF‑β or miR‑30a strategies.