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S64 Alveolar epithelial type II cell expression of VEGF-Axxxa is critical for development of Idiopathic Pulmonary Fibrosis (IPF): an anti-fibrotic role for VEGF-Axxxb anti-angiogenic isoforms?
  1. SL Barratt1,
  2. T Blythe1,
  3. C Jarrett1,
  4. K Ourradi1,
  5. GI Welsh1,
  6. C Scotton2,
  7. DO Bates3,
  8. AB Millar1
  1. 1University of Bristol, Bristol, UK
  2. 2University of Exeter, Exeter, UK
  3. 3University of Nottingham, Nottingham, UK

Abstract

Introduction VEGF has been implicated in the development of IPF. Alternative splicing of the VEGF-A gene generates numerous isoforms. The differential effects of these isoforms, in particular the VEGF-Axxxb family, thought to have several opposing functions to the conventional family of isoforms (VEGF-Axxxa), have not been considered.

Hypothesis

  • The balance of VEGF-Axxxa:VEGF-Axxxb isoform expression is important in the pathogenesis of IPF.

  • VEGF-Axxxb isoforms may be protective against the formation of pulmonary fibrosis (PF).

Methods Normal and IPF lung lysates (n = 5) were analysed by western blotting (WB), and ELISA using an antibodies specific for PanVEGF-A and VEGF-Axxxb isoforms.

The Bleomycin (BLM)-induced model of PF was used in conjunction with two transgenic (TG) mouse models, developed to explore the role of ATII-derived VEGF in the development of PF: 1) a conditionally inducible, ATII-specific, VEGF knock-out mouse (STCLL mice) and 2) a TG mouse over-expressing VEGF-Axxxb in ATII cells (MMTV-VEGF165b).

To explore the therapeutic potential of VEGF-Axxxb in PF, wild-type mice were administered intraperitoneal (IP) injections of VEGF-A165b, commencing 10 days after BLM challenge.

In all experiments fibrosis was assessed histologically using Masson’s Trichrome, with blinded scoring of tissue sections.

Results By WB (n = 3) and ELISA (n = 5) there was no significant difference in PanVEGF-A expression between normal and IPF lung homogenates (t-test, p > 0.05). In contrast, VEGF-Axxxb expression was significantly increased in these same IPF samples compared to control, by ELISA (t-test, ****p < 0.0001) and WB (Densitometry: t-test, *p < 0.05).

Specific deletion of VEGF-A from ATII cells of mice ameliorated the development of BLM-induced pulmonary fibrosis (n = 5, Lung fibrosis score: ANOVA with Holm’s Sidak **p < 0.01). Over-expression of VEGF-Axxxb in ATII cells also ameliorated the development of pulmonary fibrosis (n = 6, Lung fibrosis score: ANOVA with Holm’s Sidak ***p < 0.001). Furthermore, delivery of VEGF-A165b, specifically during the fibrotic phase of the BLM model, also attenuated lung fibrosis development (n = 6, Lung fibrosis score: ANOVA with Holm’s Sidak *p < 0.05).

Conclusion Changes in the bioavailability of ATII cell-derived VEGF-A, namely the ratio of VEGF-Axxxa:VEGF-Axxxb, appear critical to the development of pulmonary fibrosis. This data suggests that more a targeted approach to anti-VEGF-A therapy in IPF should be explored.

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