Heme oxygenase-1 regulates cell proliferation via carbon monoxide-mediated inhibition of T-type Ca2+ channels

Hayley Duckles,Moza M Al-Owais,Hannah E Boycott,John P Boyle,Karen E Porter,Mark L Dallas,Emily Johnson,Jacobo Elies,Chris Peers,Jason L Scragg,Francesca Giuntini

doi:10.1007/s00424-014-1503-5

Abstract

Induction of the antioxidant enzyme heme oxygenase-1 (HO-1) affords cellular protection and suppresses proliferation of vascular smooth muscle cells (VSMCs) associated with a variety of pathological cardiovascular conditions including myocardial infarction and vascular injury. However, the underlying mechanisms are not fully understood. Over-expression of Cav3.2 T-type Ca2+ channels in HEK293 cells raised basal [Ca2+]i and increased proliferation as compared with non-transfected cells. Proliferation and [Ca2+]i levels were reduced to levels seen in non-transfected cells either by induction of HO-1 or exposure of cells to the HO-1 product, carbon monoxide (CO) (applied as the CO releasing molecule, CORM-3). In the aortic VSMC line A7r5, proliferation was also inhibited by induction of HO-1 or by exposure of cells to CO, and patch-clamp recordings indicated that CO inhibited T-type (as well as L-type) Ca2+ currents in these cells. Finally, in human saphenous vein smooth muscle cells, proliferation was reduced by T-type channel inhibition or by HO-1 induction or CO exposure. The effects of T-type channel blockade and HO-1 induction were non-additive. Collectively, these data indicate that HO-1 regulates proliferation via CO-mediated inhibition of T-type Ca2+ channels. This signalling pathway provides a novel means by which proliferation of VSMCs (and other cells) may be regulated therapeutically.

Highlights

Vascular smooth muscle cells (VSMCs) control vascular tone through regulated contraction which is highly dependent on Ca2+ influx, primarily via voltage-dependent L-type Ca2+ channels [4, 21, 33, 48, 50, 54]
The known role of T-type Ca2+ channels in proliferation, together with our recent study indicating that carbon monoxide (CO) can directly modulate T-type Ca2+ channels [5], indicates that heme oxygenase-1 (HO-1)-derived CO can limit proliferation via inhibition of T-type Ca2+ channels
To examine whether the Heme oxygenase (HO)-1/CO pathway was able to modify proliferation in human VSMCs, we studied cells cultured from human saphenous vein

Summary

Introduction

Vascular smooth muscle cells (VSMCs) control vascular tone (and blood flow and distribution) through regulated contraction which is highly dependent on Ca2+ influx, primarily via voltage-dependent L-type Ca2+ channels [4, 21, 33, 48, 50, 54]. VSMCs are not terminally differentiated and can undergo adaptive phenotypic changes: their ability to become non-contractile, proliferative cells is an important factor in both developmental vasculogenesis and vascular repair [35, 36, 52]. This switch to a proliferative state is important in pathological situations such as atherosclerosis, restenosis, neointimal hyperplasia and hypertension [19, 36]. T-type Ca2+ channels are expressed in VSMCs, their role in vasoconstriction is unclear (see [10]).

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