Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCB374

Poster Communications

Platelet derived growth factor driven vascular smooth muscle cell remodelling potentiates abdominal aortic aneurysm

P. Kandavelu1, K. E. Porter1, D. J. Beech1, M. A. Bailey1

1. LICAMM, Faculty of Medicine and Health, University of Leeds, Leeds, WY, United Kingdom.

Abdominal aortic aneurysm (AAA) is a focal dilation of the abdominal aorta which typically occurs in hypertensive male patients and progresses to rupture. Patients undergo surveillance for many years until the threshold for intervention is reached. Repair poses risk to life in addition to significant morbidity. A better understanding of the mechanisms of disease progression would aid the development of novel medical treatments. The recent AAA Meta-GWAS identified potential enrichment of pathways linked to abnormal smooth muscle physiology in AAA. Platelet-derived growth factor (PDGF) is the major driver of vascular smooth muscle cell (VSMC) remodelling in physiology. We hypothesised that a transgenic mouse line with a tamoxifen inducible smooth muscle cell (SMC) specific constitutively active PDGFRβ (PDGF Receptor- β) mutant (PDGFRβD849V) would experience enhanced disease progression compared to wild-type littermates following elastase induced aneurysm induction. We first validated the spatial specificity of tamoxifen inducible SMC specific Cre (SM-MHC.CreERT2) by crossing the mice with Rosa26R.LacZ reporter mice. Upon tamoxifen administration, LacZ expression was observed only in SMC layers of aorta and bowel and not in other cells/tissue types like heart (cardiac) and skeletal muscle. Then, we generated PDGFRβD849V knock-in mice and induced the transgene in 8 weeks old adult male mice by injecting with 2 mg of tamoxifen for 5 consecutive days. Prior to Cre recombination, no expression of the constitutively active PDGFRβ mutant isoform was observed. Upon tamoxifen administration, the Cre-mediated recombination results in expression of mutant PDGFRβ and increased PDGFRβ signalling. The supra and infra-renal aortic diameters were measured by Vevo 2100 ultrasound and then the vessels were harvested at 12 weeks. Apart from a subtle but statistically significant increase (0.53±0.02 Vs 0.68±0.07; p=0.04; n≥9 for each group) in abdominal aortic diameter, we observed no difference in the basic phenotypic characteristics such as the body weights and organ weights between the PDGFRβWT and the PDGFRβD849V mice. The histological analysis of paraffin embedded thoracic and abdominal aortic sections showed no major architectural changes (n=6 each). Next we induced AAA by peri-adventitial application of elastase to the infra renal aorta. The size of the aneurysm was monitored at 2 & 4 weeks using 3D ultrasound volumetric measurement. In wild-type mice, the AAA was stable between 2 and 4 weeks. In the transgenic littermates however, there was evidence of progression of AAA between weeks 2 and 4 (10.70±0.99 Vs 17.72±1.76; p=0.017; n≥3 each). Thus our data show that PDGF driven VSMC proliferation may be important in the development and/or progression of AAA.

Where applicable, experiments conform with Society ethical requirements