Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC246
The effects of zinc deficiency on vascular smooth muscle cell function
K. Allen-Redpath1, O. Ou2, J. H. Beattie2, I. Kwun3, G. F. Nixon1
1. School of Medical Sciences, University of Aberdeen, Aberdeen, United Kingdom. 2. Rowett Institute of Nutrition and Health, University of Aberdeen, Aberdeen, United Kingdom. 3. Department of Food Science, Andong National University, Andong, Korea, Republic of.
Recently dietary zinc deficiency has been associated with a potential role in cardiovascular diseases and changes have been observed in the expression of proteins associated with vascular smooth muscle cell (VSMC) differentiation (Beattie et al. 2008). The aim of this study is to elucidate the effect of a zinc deficient environment on vascular smooth muscle cell function using both in vivo and in vitro models. Male Lister hooded rats (8 weeks old) were maintained on a 2 week zinc adequate diet (35 mg/kg) or zinc deficient diets (3mg/kg or <1mg/kg). There was a significant reduction in plasma zinc levels in rats fed a zinc deficient diet compared to the zinc adequate diet as assessed by atomic absorption spectrophotometry (35mg/kg zinc diet - 150 ± 4 µg/ml, 3mg/kg zinc diet - 80 ± 4 µg/ml, <1mg/kg zinc diet - 60 ± 4 µg/ml; n=10 for each diet group, mean ± s.e.m., ANOVA p<0.05). Carotid arteries were dissected and stimulated for 15 mins with either 50 ng/ml platelet-derived growth factor (PDGF) or 1 µM sphingosine 1-phosphate (S1P), both of which have been previously shown to activate intracellular growth pathways in VSMC. Activation of extracellular signal-regulated kinase (ERK1/2) was measured by immunoblotting in arterial homogenates as an indicator of cell growth and survival. In arteries from zinc deficient rats, S1P-stimulated ERK1/2 activation was significantly decreased compared to rats fed a zinc adequate diet (densitometry; 35mg/kg zinc diet - 5.3 ± 2.0 fold increase, 3mg/kg zinc diet - 1.4 ± 0.5 fold increase, <1mg/kg zinc diet - 1.3 ± 0.4 fold increase; n=5 for each group, mean ± s.e.m., ANOVA p<0.05). PDGF-induced activation of ERK1/2 was also reduced (35mg/kg zinc diet - 5 ± 1.4 fold increase, 3mg/kg zinc diet - 1.3 ± 0.1 fold increase, <1mg/kg zinc diet - 1.3 ± 0.3 fold increase; n=4 for each group, mean ± s.e.m., ANOVA p<0.05). The total ERK1/2 expression was unaltered in arteries from rats on zinc deficient compared to zinc adequate diets. To determine if these changes in ERK1/2 activation were reflected in changes to VSMC phenotype, the expression of protein markers for smooth muscle differentiation was examined. Expression of calponin and smooth muscle α-actin were unchanged in arteries from rats with zinc deficient diets. In parallel in vitro experiments, primary cultured rat aorta VSMC were maintained for 24 hours in zinc-deficient or zinc-supplemented medium and stimulated with either PDGF or S1P for 15 mins. ERK1/2 activation was unaffected in zinc deficient compared to zinc-supplemented conditions. Also, markers of smooth muscle differentiation were unaltered. In conclusion, dietary zinc deficiency in vivo reduces activation of the growth and pro-survival pathways in arteries suggesting a change towards an apoptotic phenotype. This is probably not a direct effect of zinc deficiency on VSMC.
Where applicable, experiments conform with Society ethical requirements