Proceedings of The Physiological Society
University of Edinburgh (2011) Proc Physiol Soc 25, PC34
Vascular smooth muscle proliferation is regulated by an increase in mitochondrial motility
S. Chalmers1, P. Coats1, J. G. McCarron1
1. University of Strathclyde, Glasgow, United Kingdom.
Mitochondrial function is critical for multiple facets of cellular function including ATP production and Ca2+ handling. Subcellular location of the organelle is important for function. In smooth muscle, mitochondria modulate Ca2+ signals arising from InsP3 receptors, even localised Ca2+ puffs, revealing a close physical relationship between the sarcoplasmic reticulum and mitochondria. This seems incompatible with the free movement of mitochondria observed in several cell types. An in vitro study of intact cerebral resistance arteries at physiological pressure, individual mitochondria within smooth muscle were largely stationary (0.00159 ± 0.00004 moving mitochondria μm-2min-1, n=23); however in a small number of cells mitochondria displayed large-scale directed movements (0.00104 ± 0.00003 cells containing moving mitochondria μm-2min-1, n=23). When arteries were maintained in organ culture for up to 4 days to promote proliferation, an increased number of cells showing moving mitochondria (0.00341 ± 0.00008 cells μm-2min-1; n=16, p<0.01) and an increase in the extent of movement occurred (0.01043 ± 0.00027 moving mitochondria μm-2min-1, n=16, p<0.01). Expression of the mitochondrial tether mitofusin-2 decreased and the proliferative marker proliferating cell nuclear antigen (PCNA) increased, by western blotting and immunocytochemistry of fixed, pressurised arteries (n≥3 for each). Maintenance of arteries with the small molecule inhibitor of mitochondrial fission Mdivi-1 (50 μM) for the duration of the 4 days organ culture restricted mitochondrial dynamics (0.00228 ± 0.00024 mitochondria moving μm-2min-1 in 0.00145 ± 0.00015 cells μm-2min-1; n=6, p<0.01 for each, compared to untreated arteries maintained in culture for 4 days) and reduced the extent of proliferation as shown by PCNA staining (7.69 ± 2.87 compared to 15.70 ± 2.23 RFU/pixel corrected for non-specific staining of secondary antibody only, n=7, p<0.05), 3H-thymidine incorporation and fluorescence-activated cell sorting by propidium iodide incorporation (n≥3 for each). Thus, when smooth muscle is allowed to proliferate, mitochondria switch from being static to highly mobile, which may contribute to the altered Ca2+ signalling observed in proliferative smooth muscle. Inhibiting mitochondrial mobility decreases proliferation and may be a novel target for the prevention of proliferative vascular disease. Values are expressed as mean ± S.E.M. for n cells or regions of intact artery, significance calculated using Student’s t-tests.
Where applicable, experiments conform with Society ethical requirements