Ca2+/calmodulin-dependent protein kinase II function in vascular remodelling

Abstract

Vascular smooth muscle (VSM) undergoes a phenotypic switch in response to injury, a process that contributes to pathophysiological vascular wall remodelling. VSM phenotype switching is a consequence of changes in gene expression, including an array of ion channels and pumps affecting spatiotemporal features of intracellular Ca(2+) signals. Ca(2+) signalling promotes vascular wall remodelling by regulating cell proliferation, motility, and/or VSM gene transcription, although the mechanisms are not clear. In this review, the functions of multifunctional Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) in VSM phenotype switching and synthetic phenotype function are considered. CaMKII isozymes have complex structural and autoregulatory properties. Vascular injury in vivo results in rapid changes in CaMKII isoform expression with reduced expression of CaMKIIγ and upregulation of CaMKIIδ in medial wall VSM. SiRNA-mediated suppression of CaMKIIδ or gene deletion attenuates VSM proliferation and consequent neointimal formation. In vitro studies support functions for CaMKII in the regulation of cell proliferation, motility and gene expression via phosphorylation of CREB1 and HDACIIa/MEF2 complexes. These studies support the concept, and provide potential mechanisms, whereby Ca(2+) signalling through CaMKIIδ promotes VSM phenotype transitions and vascular remodelling.

Figure 1. SiRNA mediated suppression of CaMKIIδ inhibits vascular wall remodelling in response to injury

Neointima and medial layer areas were quantified 14 days following balloon angioplasty injury of the rat common carotid artery. Shown are representative sections from a sham control and arteries transduced with adenoviral short hairpin RNA constructs targeting CaMKIIδ mRNA or luciferase RNA as a negative control. The red tracings outline neointima regions in these phase contrast images. Reprinted from House & Singer, 2008.

Figure 2. Localization of activated CaMKII to the leading edge in migrating VSM cells

A monolayer of cultured rat aortic VSM cells was scrape-wounded and fixed after 6 h for indirect confocal immunofluorescence microscopy. A, image of cells stained with a primary antibody targeting threonine 287-phosphorylated CaMKII (P-CaMKIIThr287), as an index of activated CaMKII. B, cells were stained with a primary antibody specific for total CaMKIIδ₂, the predominant isoform in these cells. Nuclei are counterstained with DAPI. Scale bar = 10 μm. Reprinted from Mercure et al. 2008.

Figure 3. Model of CaMKII function in vascular smooth muscle phenotype switching

Differentiated VSM express primarily CaMKII γ isoforms that participate in Ca²⁺ homeostasis and modulation of contractile function in response to ligands such as angiotensin II (AII), noradrenaline (NA), or endothelin -1 (ET-1) (House et al. 2008b; Kim et al. 2008). Upon cell culture or injury, VSM cells transition to a synthetic phenotype, a process that includes changes in expression of diverse Ca²⁺ signalling proteins, including voltage gated Ca²⁺ channels (VGCC), STIM1/Orai1 store operated channels, and specific TRPC channels including TRPC6. Up-regulation of CaMKIIδ is proposed to couple growth factor-initiated Ca²⁺ signals to VSM cell proliferation and motility, as well as gene transcription, promoting the synthetic phenotype and vascular remodelling.