Proceedings of The Physiological Society
University of Edinburgh (2011) Proc Physiol Soc 25, C11 and PC11
The role of cGMP dependent protein kinase (PKG) in mediating the anticontractile function of perivascular fat
S. B. Withers1, L. Simpson1, M. E. Werner1, A. M. Heagerty1
1. Cardiovascular research group, University of Manchester, Manchester, United Kingdom.
INTRODUCTION: Obesity leads to a loss of adiponectin-mediated anticontractile function of perivascular fat (PVAT), thereby providing a link between obesity and subsequent hypertension. cGMP dependent protein kinase 1 (PKG) regulates smooth muscle relaxation and may be important in this vascular pathology, as high fat feeding is associated with downregulation of its expression in mice; furthermore overexpression of constitutively active PKG protects female mice from the effects of diet induced obesity. We aim to investigate the role of PKG in mediating the anticontractile property of PVAT. METHODS: PKG knockout mice (KO) and wildtype littermates (WT) were investigated for contractility and adiponectin expression. Arteries +/- PVAT were studied by wire myography under normoxia and experimental hypoxia +/- ANP (100nM). Contractile responses to noradrenaline (NA) were calculated as a percentage of KCl constriction. Solution transfer experiments were performed on arteries constricted with 10-5M NA, change in tension was measured following transfer to determine the role of PKG in the release of the anticontractile factor(s) or in mediating the downstream effects. Adiponectin expression in mesenteric fat samples was assessed using immunohistochemistry. Data are expressed as mean ± SEM and analysed by 2-way ANOVA or student’s t-test where appropriate. P<0.05 was deemed significant. RESULTS: PVAT conferred an anticontractile effect on WT arteries in normoxic conditions (n=7, P<0.001). PKG KO arteries + PVAT demonstrated increased contractility compared with WT littermates (n=5, P<0.001). Hypoxia increased contractility of WT arteries + PVAT alone but not KO arteries (WT normoxia vs. WT hypoxia: n=5, P<0.05; KO normoxia vs. KO hypoxia: n=5, P=NS). Incubation of arteries with ANP during hypoxia rescued the loss of PVAT function in WT arteries only (n=4, P<0.05) and was associated with an increase in adiponectin expression, although no effect was observed in arteries from KO mice (P=NS, n=4). Transfer of solution from WT + PVAT arteries to KO - PVAT and KO + PVAT to WT - PVAT caused a relaxation (Δ tension 0.21±0.03mN/mm and 0.17±0.03mM/mm respectively, n=4) , although significantly less than that observed between WT + PVAT to WT - PVAT arteries (0.3±mN/mm, n=4). CONCLUSION: PKG mediates the effects of healthy PVAT and is involved in the release and mediation of the downstream effect of factor(s) secreted by PVAT. ANP restores the anticontractile capacity of PVAT which is compromised following experimental hypoxia; this is mediated, at least in part, through a PKG dependent pathway as ANP does not have the same rescuing capacity in the absence of PKG. Furthermore, ANP increases the expression of adiponectin in these samples. The regulation of adiponectin by PKG remains to be fully understood.
Where applicable, experiments conform with Society ethical requirements