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A human APOC3 missense variant and monoclonal antibody accelerate apoC-III clearance and lower triglyceride-rich lipoprotein levels

Abstract

Recent large-scale genetic sequencing efforts have identified rare coding variants in genes in the triglyceride-rich lipoprotein (TRL) clearance pathway that are protective against coronary heart disease (CHD), independently of LDL cholesterol (LDL-C) levels1. Insight into the mechanisms of protection of these variants may facilitate the development of new therapies for lowering TRL levels. The gene APOC3 encodes apoC-III, a critical inhibitor of triglyceride (TG) lipolysis and remnant TRL clearance2. Here we report a detailed interrogation of the mechanism of TRL lowering by the APOC3 Ala43Thr (A43T) variant, the only missense (rather than protein-truncating) variant in APOC3 reported to be TG lowering and protective against CHD3,4,5. We found that both human APOC3 A43T heterozygotes and mice expressing human APOC3 A43T display markedly reduced circulating apoC-III levels. In mice, this reduction is due to impaired binding of A43T apoC-III to lipoproteins and accelerated renal catabolism of free apoC-III. Moreover, the reduced content of apoC-III in TRLs resulted in accelerated clearance of circulating TRLs. On the basis of this protective mechanism, we developed a monoclonal antibody targeting lipoprotein-bound human apoC-III that promotes circulating apoC-III clearance in mice expressing human APOC3 and enhances TRL catabolism in vivo. These data reveal the molecular mechanism by which a missense variant in APOC3 causes reduced circulating TG levels and, hence, protects from CHD. This protective mechanism has the potential to be exploited as a new therapeutic approach to reduce apoC-III levels and circulating TRL burden.

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Figure 1: Human APOC3 A43T carriers exhibit lower apoC-III levels than non-carriers.
Figure 2: Mice expressing APOC3 A43T have reduced TRL and circulating apoC-III levels.
Figure 3: The A43T substitution promotes circulating apoC-III clearance and renal uptake by perturbing apoC-III binding to lipoproteins.
Figure 4: Anti-human-apoC-III monoclonal antibodies STT505 and STT5058 lower circulating apoC-III levels and promote TRL clearance.

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Gene Expression Omnibus

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NCBI Reference Sequence

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Acknowledgements

The authors thank A. Wilson, E. Edouard, J. McParland, M. McCoy, K. Trindade, S. DerOrhannessian, M. Risman, K. Burton, and M. Sun for technical expertise and M. Lazar, M. Bucan, Z. Arany, B. Garcia, N. Hand, D. Marchadier, D. Conlon, and R. Bauer for helpful discussions. This work was supported in part by NIH grants R01HL133502 and R37HL055323 and a grant from the Foundation Leducq CVGeneF(x) Transatlantic Network of Excellence to D.J.R. and by NIH grant F30HL124967 to S.A.K. This project also used the UPCI Cancer Proteomics Facility, which is supported in part by NIH award P30CA047904. Recruitment to the Penn Medicine BioBank was supported by the Penn Cardiovascular Institute, the Perelman School of Medicine of the University of Pennsylvania, and a gift from the Smilow family.

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S.A.K., J.S.M., C.V., A.V.H.S., and P.Z. performed experiments on the A43T variant. S.A.K., X.Z., Z.S., and N.A.Y. performed selective reaction monitoring measurements from human plasma samples. S.A.K., P.D.-J., J.A.L., N.B., W.J.Z., I.T., and H.d.H. designed and performed experiments on anti-apoC-III monoclonal antibodies. G.M.P., P.N., M.C., S.L.-K., M.C.P., A.R.T., and S.K. provided guidance with study design. S.A.K. and D.J.R. secured funding, conceived and designed experiments, interpreted all results, and wrote the manuscript. All authors provided input on the manuscript.

Corresponding author

Correspondence to Daniel J Rader.

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Competing interests

D.J.R. has previously been paid as a consultant for the following companies: Aegerion, Alnylam, Eli Lily, Pfizer, and Novartis. P.D.J., A.R.T., and D.J.R. are cofounders of Staten Biotechnology BV. In addition, J.A.L., N.B., and W.J.Z. are employees of and hold equity in Staten Biotechnology BV. I.T. is an employee of FairJourney Biologics. H.d.H. is an employee of and holds equity in argenX BVBA. The other authors declare no competing financial interests.

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Khetarpal, S., Zeng, X., Millar, J. et al. A human APOC3 missense variant and monoclonal antibody accelerate apoC-III clearance and lower triglyceride-rich lipoprotein levels. Nat Med 23, 1086–1094 (2017). https://doi.org/10.1038/nm.4390

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