ADAMTS7 knockdown in context: emerging therapeutic targets in atherothrombosis

In recent years, the promise of leveraging genetic insights into atherosclerosis has begun to be realized in effective real-world therapies to prevent and treat atherosclerotic cardiovascular disease (ASCVD). The rapid translation from gene discovery to human therapy is perhaps best epitomized by the case of proprotein convertase subtilisin/kexin type 9 (PCSK9). Within little over a decade after genotyping analyses identified gain-of-function PCSK9 mutations as causing ASCVD,^1,2 monoclonal antibody inhibitors of PCSK9 were developed, proven to be efficacious in preventing cardiovascular events, and approved for clinical use. The scientific and practical success of these therapies have prompted development of PCSK9-targeting therapies with more sustained effects, including small interfering RNA (siRNA)-mediated gene knockdown lasting months³ and in vivo gene-editing (thus far in nonhuman primates) intended to last a lifetime.⁴ Other areas of active investigation targeting lipid mediators of atherosclerosis include vaccination to generate antigen-specific regulatory T cell responses against apolipoprotein B, the primary lipoprotein of low density lipoprotein (LDL).⁵

Sustained reduction of LDL cholesterol to near-fetal levels offers the potential to dramatically and perhaps permanently alter the natural history of ASCVD, the world’s leading cause of death; however, considerable scientific and practical barriers remain.⁶ Manifestations and proximate causes of ASCVD events– including coronary artery disease, peripheral arterial disease, aortic disease, and stroke – are heterogeneous. Certainly, subendothelial retention of lipid, resulting immune response, and inflammatory plaque destabilization and rupture remain important causes of ASCVD. Yet, atherosclerosis and related events may still occur in the absence of significant hyperlipidemia in the setting of vascular smooth muscle cell (VSMC) apoptosis, intimal hyperplasia and leukocytic infiltration, and superficial plaque erosion – all of which are implicated in vascular inflammation and thrombosis.⁷ These diverse, synergistic pathways of ASCVD and their related manifestations underscore the potential value of identifying non-lipid candidate genes and molecular targets implicated in atherosclerosis.

In this context, the work by Mizoguchi et al. in this issue of Circulation Research offers new scientific insights into a potentially important mediator of atherosclerosis that may have implications for therapeutic targeting.⁸ Building on previous studies identifying genetic regulators of VSMC migration in atherosclerosis^{9, 10} the authors probed the effects of ADAMTS7 catalytic function in VSMC migration and atherosclerosis. To investigate this, the authors purified full-length mouse ADAMTS7, experimentally tested effects of ADAMTS7 dosage and catalytic function (separately) on atherosclerosis, and subsequently determined effects of a human Adamts7 coding variant on secretion and migration of VSMCs. The catalytically mutant/inactivated mice (E373Q/E373Q homozygotes, with loss of ADAMTS7 catalytic function) and Adamts7 knockouts exhibited similar decreases in aortic arch (though not aortic root) atherosclerotic lesion formation vs. littermate controls, with significant reductions in intralesional smooth muscle cell (SMC) content observed in both the Adamts7 knockout and catalytically inactive mice (vs. controls). To investigate the role of ADAMTS7 catalytic function in VSMC migration, the authors then used a wound healing assay and observed that both the Adamts7 knockout and catalytically inactivated mice exhibited less VSMC migratory activity than wild type, whereas gain-of-function mice (Adamts7 overexpression) had increased VSMC migration. Finally, primary VSMCs from Adamts7 knockout mice were harvested to investigate migration induced by adenoviral-mediated expression of human ADAMTS7. The human Adamts7 gain-of-function allele (Ser214) led to the most VSMC migration whereas the loss-of-function allele (Pro214) led to reduced migration. Furthermore, the ADAMTS7 catalytic mutation made in the Ser214 allele led to similarly decreased VSMC migration as observed in the Pro214 allele.

Taken together, these thoughtfully designed and executed experiments indicate that ADAMTS7 dosage and catalytic activity promote VSMC migration into atherosclerotic lesions. Further, they suggest that therapeutically inhibiting ADAMTS7 catalytic activity may be one pathway by which to ameliorate atherosclerosis. These findings provide valuable scientific insights into novel mediators of atherosclerosis and raise several key questions related to therapeutic targets.

One set of questions relates to the tissue targets: Does the finding that ADAMTS7 catalytic inactivation and knockout affected aortic arch but not root lesions reflect meaningful vascular location-specific differences? Or is this simply the result of the experimental model and timing at which lesions were assessed? Indeed, if effects of ADAMTS7 differ significantly by vascular site (perhaps in accordance with known location-specific differences in plaque composition¹¹), related effects on clinical coronary artery disease vs. stroke (and underlying carotid disease) vs. peripheral arterial disease might likewise differ accordingly.

A separate set of questions relates to the mechanistic target: What is the overall role of VSMC maturation and migration in the pathogenesis of atherosclerosis and clinical ASCVD? Given evolving mechanistic knowledge on inflammation, plaque erosion, and thrombosis as (at times) key mediators of ASCVD – coupled with GWAS data finding similar CAD-associated effect sizes for the Adamts7 gain-of-function allele (Ser214) as established lipid-related risk variants for CAD (including a PCSK9 gain-of-function variant)¹² – it is certainly plausible that ADAMTS7-related pro-inflammatory VSMC phenotype switching, intralesional migration, and related leukocyte infiltration represent a central pathway of some atherosclerotic phenotypes.

If this is the case, how does this pathway fit in the context of other known (and potentially targetable) mediators of atherosclerosis (Figure)? Could targeting ADAMTS7 be performed in conjunction with targeting the hematopoietic niche¹³ and/or inflammasome? Broadening further, how do these potential targets fit in the context of known lipid-focused targets such as PCSK9? Given the heterogeneity of atherosclerosis and its mechanistic mediators as well as related therapeutic targets, targeting several of these key pathways simultaneously may provide a particularly comprehensive means of arresting atherosclerosis (Figure). Yet, each additional target and intervention brings its own set of potential risks, which may be particularly noteworthy for less lipid-focused targets: whereas excess LDL cholesterol appears to fulfill little in the way of physiologic needs and genetic interventions on cholesterol pathways therefore may be comparatively low risk, less is known regarding potential off-target effects of intervening on targets such as ADAMTS7. These considerations are perhaps even more pronounced for interventions targeting immune response¹⁴ given the clear off-target toxicity that would result from complete/permanent ablation of certain components of immune response, making molecular rather than genetic targets perhaps more desirable for immunomodulatory interventions (Figure).

Figure. Novel and emerging genetic and molecular targets in atherothrombosis.

Several potential therapeutic targets related to atherosclerosis and thrombosis have emerged in recent years, including both lipid-focused and less lipid-focused targets. These include genetic and molecular targets and correspond to known key mediators of athero-thrombosis. Selected emerging targets are depicted in the figure. ADAMTS7 indicates the gene ADAM Metallopeptidase with Thrombospondin Type 1 Motif 7; ANGPTL4, the gene for angiopoietin like 4; ApoB, apolipoprotein B; ASGR1, the gene for asialogycoprotein receptor 1; CCR5, the gene for C-C chemokine receptor 5; CD47, for cluster of differentiation 47; IL-1B, interleukin 1-beta; IL-6, interleukin-6; LDL, low density lipoprotein; Mcp1, the gene for monocyte chemoattractant protein 1; MIA3, the gene for melanoma inhibitory protein 3; PCSK9, the gene for proprotein convertase subtilisin/kexin type 9; TMAO, trimethylamine N-oxide; TREM-1, triggering receptor expressed on myeloid cells 1; vLDL, very low density lipoprotein; VSMC, vascular smooth muscle cell.

Ultimately, these concerns are inevitable outgrowths following the discovery of new mechanistic targets and pathways for intervention. Whether ADAMTS7 will be a key target (and/or one of several targets) for clinically viable and scalable therapies for atherosclerosis remains to be seen. Nevertheless, the fact that this is even a discussion is a testament to the depth of recent scientific advances and therapeutic potential derived from leveraging genetic insights to alter the natural history of atherosclerosis.