The association between mitochondrial DNA copy number, low-density lipoprotein cholesterol, and cardiovascular disease risk

Mitochondria are the primary organelle to generate cellular energy. Our group and others have reported that lower mitochondrial DNA copy number (mtDNA CN) is associated with higher risk of cardiovascular disease outcomes (CVD) and higher LDL levels. However, the causal relationship between mtDNA CN and CVD remains to be studied. Here we performed cross-sectional and prospective association analyses of blood-derived mtDNA CN and CVD outcomes in up to 27,316 participants from different racial/ethnic groups with whole genome sequencing. We validated most of the previously reported associations but effect sizes were smaller in this study. For example, one SD unit decrease in mtDNA CN was significantly associated with 1.08-fold (95% CI, 1.04, 1.12; P =1.7E-04) hazard for developing incident coronary heart disease (CHD) adjusting for age, sex and race/ethnicity. We conducted Mendelian randomization (MR) to explore causal relationships between mtDNA CN, LDL, and CHD. Bi-directional univariable MR analyses provided strong evidence indicating higher LDL level is causally associated with lower mtDNA CN, and CHD was weakly associated with lower mtDNA CN. We found no evidence supporting a causal association for lower mtDNA CN with higher CHD risk or higher LDL. In multivariable MR, no associations were observed between mtDNA CN and CHD controlling for LDL level (P =0.92), whereas strong evidence for a direct causal effect was found for higher LDL on lower mtDNA CN, adjusting for CHD status (P =8.3E-10). Findings from this study indicate high LDL underlies the complex relationships between vascular atherosclerosis and lower mtDNA CN. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement Cohort acknowledgement/support: The Atherosclerosis Risk in Communities study has been funded in whole or in part with Federal funds from the National Heart, Lung, and Blood Institute, National Institutes of Health, Department of Health and Human Services, under Contract nos. (75N92022D00001, 75N92022D00002, 75N92022D00003, 75N92022D00004, 75N92022D00005). The authors thank the staff and participants of the ARIC study for their important contributions. WGS for NHLBI TOPMed: Atherosclerosis Risk in Communities (phs001211.v3.p2.c1) was performed at the Baylor College of Medicine Human Genome Sequencing Center (3U54HG003273-12S2 / HHSN268201500015C). Core support including centralized genomic read mapping and genotype calling, along with variant quality metrics and filtering were provided by the TOPMed Informatics Research Center (3R01HL-117626-02S1; contract HHSN268201800002I). Core support including phenotype harmonization, data management, sample-identity QC, and general program coordination were provided by the TOPMed Data Coordinating Center (R01HL-120393; U01HL-120393; contract HHSN268201800001I). We gratefully acknowledge the study participants who provided biological samples and data for TOPMed. Cohort acknowledgement/support: Cohort acknowledgement/support: WGS for the NHLBI TOPMed program: CARDIA (phs001612) was performed at the Baylor Human Genome Sequencing Center (HHSN268201600033I). Centralized read mapping and genotype calling, along with variant quality metrics and filtering were provided by the TOPMed Informatics Research Center (3R01HL-117626-02S1). Phenotype harmonization, data management, sample-identity QC, and general study coordination, were provided by the TOPMed Data Coordinating Center (3R01HL-120393-02S1). The CARDIA study is conducted and supported by the National Heart, Lung, and Blood Institute (NHLBI) in collaboration with the University of Alabama at Birmingham (HHSN268201800005I & HHSN268201800007I), Northwestern University (HHSN268201800003I), University of Minnesota (HHSN268201800006I), and Kaiser Foundation Research Institute (HHSN268201800004I). We gratefully acknowledge the study participants who provided biological samples and data for TOPMed. We also wish to thank the staff of the CARDIA study. Cohort acknowledgement/support: Cardiovascular Health Study: This research was supported by contracts HHSN268201200036C, HHSN268200800007C, HHSN268201800001C, N01HC55222, N01HC85079, N01HC85080, N01HC85081, N01HC85082, N01HC85083, N01HC85086, 75N92021D00006, and grants U01HL080295, U01HL130114, and R01HL105756 from the National Heart, Lung, and Blood Institute (NHLBI), with additional contribution from the National Institute of Neurological Disorders and Stroke (NINDS). Additional support was provided by R01AG023629 from the National Institute on Aging (NIA). A full list of principal CHS investigators and institutions can be found at CHS-NHLBI.org. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. Sequencing was supported and conducted in collaboration with Baylor University (HHSN268201600033I, 3U54HG003273-12S2, HHSN268201500015C) and Broad Genomics (HHSN268201600034I) contracts from NHLBI. Cohort acknowledgement/support: The WGS for FHS (phs000974) was performed at the Broad Institute of MIT and Harvard (3R01HL092577-06S1 and 3U54HG003067-12S2). The FHS acknowledges the support of contracts NO1-HC-25195, HHSN268201500001I and 75N92019D00031 from the National Heart, Lung and Blood Institute and grant supplement R01 HL092577-06S1 for this research. We also acknowledge the dedication of the FHS study participants without whom this research would not be possible. Dr. Vasan is supported in part by the Evans Medical Foundation and the Jay and Louis Coffman Endowment from the Department of Medicine, Boston University School of Medicine. X.L., S.S., C.L.S, and C.L. are also supported by R01AG059727. C.L.S and S.S are also supported by AG052409, AG054076 and AG059421. Cohort acknowledgement/support: Support for GENOA was provided by the National Heart, Lung and Blood Institute (HL054457, HL054464, HL054481, HL141292, HL119443, and HL087660) of the National Institutes of Health. Sequencing for the GENOA (phs001345.v1.p1) was performed by the University of Washington Northwest Genomics Center (3R01HL055673-18S1 from the NHLBI and at the Broad Institute of MIT and Harvard (HHSN268201500014C)). The authors also wish to thank the staff and participants of GENOA. Cohort acknowledgement/support: The Jackson Heart Study (JHS) is supported and conducted in collaboration with Jackson State University (HHSN268201800013I), Tougaloo College (HHSN268201800014I), the Mississippi State Department of Health (HHSN268201800015I) and the University of Mississippi Medical Center (HHSN268201800010I, HHSN268201800011I and HHSN268201800012I) contracts from the National Heart, Lung, and Blood Institute (NHLBI) and the National Institute on Minority Health and Health Disparities (NIMHD). The authors also wish to thank the staffs and participants of the JHS. Molecular data for the Trans-Omics in Precision Medicine (TOPMed) program was supported by the National Heart, Lung and Blood Institute (NHLBI). Genome sequencing for NHLBI TOPMed: The Jackson Heart Study (phs000964.v1.p1) was performed at the Northwest Genomics Center (HHSN268201100037C). Core support including centralized genomic read mapping and genotype calling, along with variant quality metrics and filtering were provided by the TOPMed Informatics Research Center (3R01HL-117626-02S1; contract HHSN268201800002I). Core support including phenotype harmonization, data management, sample-identity QC, and general program coordination were provided by the TOPMed Data Coordinating Center (R01HL-120393; U01HL-120393; contract HHSN268201800001I). Laura Raffield was also supported by the National Center for Advancing Translational Sciences, National Institutes of Health, through Grant KL2TR002490 (LMR). We gratefully acknowledge the studies and participants who provided biological samples and data for TOPMed. Cohort acknowledgement/support: The WHI program is funded by the National Heart, Lung, and Blood Institute, National Institutes of Health, U.S. Department of Health and Human Services through contracts 75N92021D00001, 75N92021D00002, 75N92021D00003, 75N92021D00004, 75N92021D00005. We thank all WHI participants for their dedications and contributions. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Ethics committee/IRB of Boston University gave ethical approval for this work All participants have provided written informed consent for genetic studies. The study protocols and consent forms were reviewed and approved by respective institutional review board I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data produced are available online at TOPMed