P42 (RA6425)
Differential Effects of Statins on Calcium Deposition in Sub-populations of
Bovine Aortic Smooth Muscle Cell: Possible Modulation by Effects on Growth
Factor Signalling
KW Siddals1, S Sinha1, J Mcloughlin1, CM Cheung1, RJ Middleton1, J Hegarty1, AE
Canfield2, JM Gibson1 and PA Kalra1
1
Vascular Research, Clinical Sciences Building, Hope Hosptial, Stott Lane, Salford,
M6 8HD, United Kingdom and 2Wellcome Trust Centre for Cell-Matrix Research,
University of Manchester, Michael Smith Building, Oxford Road, Manchester, M13
9PT, United Kingdom
Calcification of arteries in patients with chronic kidney disease (CKD) is associated
with increased cardiovascular risk. Vascular calcification is an active, highly
regulated, process involving the osteogenic conversion of a distinct population of
vascular smooth muscle cells (VSMCs). When cultured in vitro, some populations of
VSMCs spontaneously form calcified vessels. Other populations of VSMCs deposit a
diffuse mineralised matrix in vitro when they are cultured in the presence of βglycerophosphate (βGP). Statins stimulate bone formation in vitro and in vivo, yet the
effect of statins on vascular calcification in vivo is still not understood. Some studies
show no effect while others show decreased progression. Therefore, the purpose of
this study was to investigate the effect of statins on growth, differentiation and
mineral deposition by VSMCs.
Using two calcifying subtypes of bovine aortic smooth muscle cells, one that lays
down a diffuse calcified matrix, the other forming calcified ridges, we have shown
that the HMG-CoA Reductase inhibitors cerivastatin (10-200nM) and atorvastatin
(250-1000nM) significantly decreased IGF-stimulated proliferation of both population
of VSMCs (p<0.05). In the diffuse calcifying cells both statins increased calcium
deposition (ceriv 50nM p<0.01, atorv 250nM p<0.01) and alkaline phosphatase (AP)
activity (ceriv 10nM, atorv 250nM p<0.05), a marker of the osteogenic conversion of
VSMCs, induced by βGP. Interestingly in the ridge forming cells both statins had the
opposite effect, decreasing both calcium deposition (ceriv at 10-100nM, atorv at 1001000nM, p<0.01) and AP activity (ceriv at 25-100nM, atorv at 100-1000nM, p<0.05)
In the diffuse cells statins may mediate their effects on vascular calcification by
modulating insulin-like growth factor (IGF) signalling, as IGF-I (25-100ng/ml)
inhibits the rise in AP activity associated with the osteogenic conversion of VSMCs
(p<0.005) and cerivastatin (100nM) reverses the IGF effect on both mineralization
(p<0.005) and AP activity (p<0.05).
These results demonstrate that statins exert different effects on different VSMC
subtypes. Effects seen in diffuse calcifying cells may be partially explained by the
removal of an IGF signal preventing osteoblastic conversion of VSMCs. Therefore,
the exact mechanisms underlying statin effects in both diffuse and ridge forming cells
clearly warrant further investigation.