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Wu et al. Mast cells and vein graft remodelling

INTRODUCTION cells also regulate vascular matrix remodelling after
resolution of acute inflammation. This is particularly
Mast cells are versatile innate immune cells, well- important under pro-atherosclerotic conditions as
known for their role in inflammation and innate vascular smooth muscle cells from pro-atherosclerotic
immunity. [1,2] Despite the wide distribution of mast animals are more susceptible to chronic proliferation in
cells in arterial adventitia and perivascular connective response to mitogenic stimuli. In the present study,
[17]
tissue, our understanding of the influence of mast we performed interpositional vein grafting in mast cell
cells in vascular disease is limited. In recent years, deficient mouse lines bred on both a normolipidaemic
accumulating evidence suggests that mast cells and hyperlipidaemic genetic background (Kit W-sh/W-sh
promote vascular inflammation and contribute to the and apoE Kit W-sh/W-sh ) to address this question.
-/-
progression of a number of vascular diseases including
atherosclerosis, aortic aneurysm and vein graft METHODS
neointima hyperplasia. [3-6] Systemic activation of mast
cells using dinitrophenyl-albumin increased plaque size in Animals
apoE mice, whilst selective stimulation of perivascular All experiments which involved animals conformed
-/-
mast cells had no impact on plaque formation but to Directive 2010/63/EU of the European Parliament
destabilised established plaque with increased intra- and also to the UK Home Office Animal (Scientific
plaque haemorrhage. Compound 48/80, another Procedures) Act 1986 and were performed under
[7]
mast cell activator, demonstrated a similar effect to Project Licence PPL 60/4114. In addition, ethical
promote atherosclerosis development, which was permission for the study had been granted by the
inhibited by the mast cell stabiliser cromolyn. [8,9] In University of Strathclyde ethical review committee.
addition to pharmacological manipulation of mast cell
function, studies using genetic mast cell deficiency Mice carrying the Kit W-sh/W-sh mutation were used in
(as a consequence of spontaneous mutation in the this study as a mast cell deficiency model. Kit W-sh/W-sh
promoter region of the c-kit gene ) also confirmed is a spontaneous mutation in the promoter region of
[10]
the detrimental effect of mast cells in atherosclerosis. the c-kit gene which is critical for mast cell survival.
[3]
[10]
Mechanistic studies revealed that activated mast As the c-kit gene itself is intact, c-kit expression is
cells synthesised and released a wide range of pro- preserved to some extent in the early life of these mice.
inflammatory factors including interleukin (IL)-6 and Consequently, systemic mast cell deficiency does
IL-8, interferon gamma, tumournecrosis factor alpha, not develop until 4 weeks old. Jackson Laboratories
histamine, chymase and tryptase. Consequently, mast (USA) was the original supplier of both the Kit W-sh/W-sh
cells exacerbated vascular inflammation with increased and apoE mice and these were subsequently bred in-
-/-
intra-plaque leukocyte infiltration, lipid uptake, vascular house. Both strains were on a C57BL/6J background.
matrix degradation and subsequent plaque expansion In order to generate a hyperlipidaemic mouse line
-/-
and destabilisation. [6] lacking mast cells, apoE and Kit W-sh/W-sh mice were
cross-bred. For the normolipidaemic Kit W-sh/W-sh mice,
In vein graft disease, neointimal hyperplasia is the congenic control was C57BL/6J while for the
the major cause of restenosis. [11,12] The neointima hyperlipidaemic apoE Kit W-sh/W-sh mice, the apoE was
-/-
-/-
formation in vein grafts is mainly driven by acute the congenic control. All mice were maintained on a
vascular inflammation. In a mouse vein graft model, the cycle of 12-h periods of light and dark and allowed
acute inflammation usually lasts less than two weeks access to normal chow diet and water ad libitum. Male
following grafting surgery. [13,14] The neointima thereafter mice (about 10 to 20 weeks old) were used in this
undergoes a remodelling stage where neointimal study.
cells differentiate into smooth muscle-like cells and
synthesise large amount of vascular matrix including Surgery
collagen and elastin as a process of arterialisation. [12,15] The mouse vein graft model is a well-established
The remodelling process stabilises neointimal cells and model for studying neointimal hyperplasia. [13,14] Briefly,
prevents chronic neointimal thickening. We and others i.p. injection of sodium pentobarbital (60 mg/kg) was
have found that perivascular mast cells boost acute used as an anaesthetic agent with top-up doses
vein graft inflammation via an increase in cytokine administered as appropriate and depending on the
secretion and activation of the complement system. [14,16] depth of anaesthesia demonstrated by the pedal
This leads to a significant rise in cell proliferation in withdrawal reflex. All animals received perioperative
the acute inflammation stage (one week after vein analgesic cover (buprenorphine; 0.05 mg/kg body
graft implantation) and more neointima formation. weight, s.c.). From a donor mouse, the thoracic inferior
However, it is not clear whether perivascular mast vena cava was carefully harvested. In all experiments
138 Vessel Plus ¦ Volume 1 ¦ September 26, 2017