Genetic Analysis of TOR Complex Gene Variation With Human Longevity: A Nested Case–Control Study of American Men of Japanese Ancestry

Brian J. Morris,1,2,3 Timothy A. Donlon,1 Qimei He,1 John S. Grove,1,4 Kamal H. Masaki,1,2 Ayako Elliott,1 D. Craig Willcox,1,2,5 Richard Allsopp,6 and Bradley J. Willcox1,2

1Honolulu Heart Program (HHP)/Honolulu-Asia Aging Study (HAAS), Department of Research, Kuakini Medical Center,

2Department of Geriatric Medicine, John A. Burns School of Medicine, University of Hawaii, Honolulu, Hawaii. & Clinical Genomics Laboratory, School of Medical Sciences, University of Sydney, Sydney, New South Wales, Australia. 4Public Health Sciences, John A. Burns School of Medicine, University of Hawaii at Manoa, Honolulu, Hawaii. 5Department of Human Welfare, Okinawa International University, Ginowan, Okinawa, Japan. 6Institute for Biogenesis Research, University of Hawaii, Honolulu, Hawaii.

Address correspondence to Brian J. Morris, DSc, PhD, Honolulu Heart Program/Honolulu-Asia Aging Study, Department of Research, Kuakini Medical Center, HPM-9, 347 North Kuakini Street, Honolulu, Hawaii 96817. Email: brian.morris@sydney.edu.au

The mechanistic target of rapamycin (mTOR) pathway is crucial for life span determination in model organisms. The aim of the present study was to test tagging single-nucleotide polymorphisms that captured most of the genetic varia- tion across key TOR complex 1 (TORC1) and TOR complex 2 (TORC2) genes MToR, RPToR, and RicToR and the important downstream effector gene RPS6Ka1 for association with human longevity (defined as attainment of at least 95 years of age) as well as health span phenotypes. Subjects comprised a homogeneous population of American men of Japanese ancestry, well characterized for aging phenotypes and who have been followed for 48 years. The study used a nested case–control design involving 440 subjects aged 95 years and older and 374 controls. It found no association of 6 tagging single-nucleotide polymorphisms for MToR, 61 for RPToR, 7 for RicToR, or 5 for RPS6Ka1 with longevity. Of 40 aging-related phenotypes, no significant association with genotype was seen. Thus common genetic variation (minor allele frequency ≥10%) in MToR, RPToR, RicToR, and RPS6Ka1 is not associated with extreme old age or aging phe- notypes in this population. Further research is needed to assess the potential genetic contribution of other mTOR pathway genes to human longevity, gene expression, upstream and downstream targets, and clinically relevant aging phenotypes.

Key Words: Genetic association analysis—Health span—Life span—Longevity—Target of rapamycin.

Received november 13, 2013; accepted January 20, 2014

Decision editor: Rafael de cabo, PhD

nutrient-sensing pathways (7,8) and is pivotal to life span extension in response to caloric restriction (9,10). Despite good evidence showing that insulin/insulin-like growth fac- tor-1 and mTOR pathways are critical for life span regula- tion of model organisms (6,11,12), to date, attainment of extreme old age in humans has been consistently replicated only for variation in one gene in these pathways, the fork- head box O transcription factor 3 gene (FoXo3) (5,6).

major causes of death in developed countries. The rate of aging is influenced by environmental and genetic factors. Identification of the molecular mechanisms responsible for this complex polygenic phenotype represents a major cur- rent challenge. Because the genetic component becomes paramount for the attainment of extreme old age (1–3) and caloric restriction is the most effective means of extending life span in diverse species (4), studies of polymorphisms in genes belonging to intracellular pathways that are modu- lated by caloric restriction have been conducted in nonage- narian and centenarian populations (4,5). These pathways affect insulin/insulin-like growth factor-1 signaling and growth responses. The hyperfunction theory of aging postu- lates that in later life, the once-beneficial processes contrib- uting to growth become deleterious by causing hypertrophic and hyperplastic pathologies (6).

mTOR is an evolutionarily conserved serine/threonine phosphoinositide 3-kinase-related kinase with crucial roles in cell growth and metabolism in response to nutri- ents, growth factors, cellular energy, and stress (6,8,13,14). Rapamycin forms a stoichiometric complex with mTOR to inhibit its kinase activity (15,16) and can thus extend mean and maximum life span of middle-aged male and female mice, with no adverse health consequences, only benefits

The mechanistic (formerly “mammalian”) target of rapamycin (mTOR) is positioned at a central hub of

mTOR is a component of two structurally and func- tionally distinct multiprotein complexes—TOR complex

1 (TORC1) and TOR complex 2 (TORC2). In mammals, two accessory proteins—regulatory-associated protein of mTOR (raptor or RPTOR) and rapamycin-insensitive com- panion of mTOR (rictor or RICTOR)—distinguish TORC1 from TORC2, respectively (19,20). mTORC1 exerts its effects on temporal control of cell growth by regulating sev- eral cellular processes, including translation, transcription, ribosome biogenesis, nutrient transport, and autophagy (14). The two TOR complexes constitute an evolutionar- ily conserved ancestral signaling network that responds to energy levels and sources of energy in order to control the fundamental process of cell growth and maintenance. In addition to its key role in aging, mTOR has been implicated in cancer, cardiovascular disease, obesity, and diabetes (21).