ADAMTS7 cleavage and vascular smooth muscle cell migration is affected by a coronary-artery-disease-associated variant

Abstract

Recent genome-wide association studies have revealed an association between variation at the ADAMTS7 locus and susceptibility to coronary artery disease (CAD). Furthermore, in a population-based study cohort, we observed an inverse association between atherosclerosis prevalence and rs3825807, a nonsynonymous SNP (A to G) leading to a Ser-to-Pro substitution in the prodomain of the protease ADAMTS7. In light of these data, we sought a mechanistic explanation for this association. We found that ADAMTS7 accumulated in smooth muscle cells in coronary and carotid atherosclerotic plaques. Vascular smooth muscle cells (VSMCs) of the G/G genotype for rs3825807 had reduced migratory ability, and conditioned media of VSMCs of the G/G genotype contained less of the cleaved form of thrombospondin-5, an ADAMTS7 substrate that had been shown to be produced by VSMCs and inhibit VSMC migration. Furthermore, we found that there was a reduction in the amount of cleaved ADAMTS7 prodomain in media conditioned by VSMCs of the G/G genotype and that the Ser-to-Pro substitution affected ADAMTS7 prodomain cleavage. The results of our study indicate that rs3825807 has an effect on ADAMTS7 maturation, thrombospondin-5 cleavage, and VSMC migration, with the variant associated with protection from atherosclerosis and CAD rendering a reduction in ADAMTS7 function.

Figure 1

ADAMTS7 Colocalizes with Smooth Muscle Cells in Human Atherosclerotic Plaques (A) Atherosclerotic coronary artery sections were subjected to double immunostaining of smooth muscle α-actin (SMA) and ADAMTS7. Purple color (NBT/BCIP) indicates SMA staining, and dark brown color with DAB indicates ADAMTS7 staining. Black arrow indicates cell positive for both SMA and ADAMTS7. Green arrow indicates extracellular ADAMTS7 staining. Negative controls are shown in Figure S1. (B) Atherosclerotic carotid artery sections were subjected to double immunostaining of SMA with Fast red and ADAMTS7 with DAB (brown color). Negative controls are shown in Figure S1. (C) Atherosclerotic carotid artery sections were subjected to double fluorescent immunostaining for SMA (red) and ADAMTS7 (green) and DAPI fluorescent staining for nuclei (blue), followed by confocal microscopy examination. Upper left panel shows SMA staining; upper right panel shows ADAMTS7 staining; lower left panel shows nuclear staining; lower right panel shows merged image from SMA, ADAMTS7, and nuclear staining.

Figure 2

Effect of ADAMTS7 Genotype on VSMC Migration (A) Primary cultures of VSMCs were subjected to double fluorescent immunostaining for the smooth muscle α-actin (SMA, red) and ADAMTS7 (green) and nucleus staining with propidium iodide (blue). Representative images are shown. (B) Primary cultures of VSMCs of the A/A, A/G, or G/G genotype for rs3825807 were subjected to scratch assay by a commonly used method. Column chart shows migration distances (mean ± SEM) of VSMCs of the A/A, A/G, or G/G genotype for rs3825807 (n = 5 different donor cell preparations for each genotype). ^∗p < 0.05 comparing A/A and G/G genotype group. (C and D) Primary cultures of VSMCs of the A/A or G/G genotype were subjected to scratch (C) and migration (D) assays, without or with medium swapping at the outset of the assay (i.e., at hour 0 of the assay, the culture medium of G/G genotype cells was replaced by A/A genotype cell conditioned medium, and vice versa). Column chart shows migration distances or migrated cell numbers (mean ± SEM) (n = 3 different donor cell preparations for each genotype). ^∗p < 0.05 comparing A/A genotype cells without medium swapping and G/G genotype cells without medium swapping; #p < 0.05 comparing G/G genotype cells with A/A genotype cell conditioned medium versus G/G genotype cells without medium swapping.

Figure 3

Effect of ADAMTS7 Genotype on Thrombospondin-5 Cleavage (A) A representative image of immunoblot (IB) analysis of cleaved TSP5 in media conditioned by VSMCs of the A/A, A/G, or G/G genotype for rs3825807. The same amount (20 μg) of proteins for each genotype was loaded. Data shown in column chart are mean (±SEM) values of cleaved TSP5 band intensity in immunoblots (n = 5 different donor cell preparations for each genotype). ^∗p < 0.05 comparing A/A and G/G genotypes. (B) A representative image and quantifications of immunoblot analysis of products from in vitro TSP5 cleavage assays. Recombinant TSP5 (2 μg) was incubated with or without 5 μl concentrated media conditioned by VSMCs of the A/A or G/G genotype, in a digestion buffer at 37°C for 8 hr. The digests, along with undigested TSP5, were subjected to immunoblot analysis with an anti-TSP5 antibody. Data shown in graph are mean (±SEM) values (n = 4 for each genotype). ^∗p < 0.05 comparing A/A (second column) and – (first column) or comparing A/A with G/G (third column). (C) A representative image and quantifications of immunoblot analysis of products from in vitro TSP5 cleavage assays. Recombinant TSP5 (2 μg) was incubated with 1, 2, or 4 μl concentrated media (1 μg total proteins/μl) conditioned by HEK293 cells transfected with a plasmid to produce the ADAMTS7 prodomain-metalloproteinase-domain of either ADAMTS7-214Ser or ADAMTS7-214Pro, in a digestion buffer at 37°C for 8 hr. The digests, along with undigested TSP5 and concentrated conditioned media, were subjected to immunoblot analysis with an anti-TSP5 antibody. Data shown in graph are mean (±SEM) values (n = 3 for each genotype). ^∗p < 0.05 comparing ADAMTS7-214Ser and ADAMTS7-214Pro.

Figure 4

Effect of ADAMTS7 Genotype on the Amount of Cleaved ADAMTS7 Prodomain in VSMC Conditioned Media (A) A representative image of immunoblot (IB) analysis of cleaved ADAMTS7 prodomain in media conditioned by VSMCs of the A/A, A/G, or G/G genotype for rs3825807. The same amount (20 μg) of proteins for each genotype was loaded. Data shown in column chart are mean (±SEM) values of cleaved ADAMTS7 prodomain band intensity in immunoblots (n = 5 different donor cell preparations for each genotype). ^∗p < 0.05 comparing A/A and G/G genotypes. (B) A representative image of immunoblot analysis of cleaved ADAMTS7 prodomain in lysates of VSMCs of the A/A or G/G genotype for rs3825807. The same amount (20 μg) of proteins for each genotype was loaded. Data shown in column chart are mean (±SEM) values of full-length ADAMTS7 band intensity in immunoblots (n = 3 different donor cell preparations for each genotype).

Figure 5

Effect of ADAMTS7 Genotype on ADAMTS7 Prodomain Processing Cultured HEK293 cells were transfected with a plasmid to produce a recombinant protein containing the ADAMTS7 prodomain and metalloproteinase domain followed by a c-Myc epitope tag, with either serine (Ser) or proline (Pro) at residue 214 in the ADAMTS7 prodomain. Conditioned media, cell surface washes (with 0.5M NaCl), and cell lysates were subjected to immunoblot analyses with an anti-cMyc antibody or an anti-ADAMTS7 prodomain antibody. The same amount (40 μg) of proteins for each allele was loaded. (A) A schematic diagram for the produced recombinant protein. P1, Pint, and M indicate the previously reported initially processed form, intermediately processing form, and fully processed form, respectively; CP indicates a cleaved ADAMTS7 prodomain fragment. (B to G) Representative images of the immunoblot (IB) analyses and column chart presentations of mean (±SEM) values (n = 4 for each allele). ^∗p < 0.05 comparing ADAMTS7-214Ser and ADAMTS7-214Pro.