Common polymorphisms in nitric oxide synthase (NOS) genes influence the quality of aging and longevity in humans. Alberto Montesanto, Paolina Crocco, Federica Tallaro, Francesca Pisani, Bruno Mazzei, Vincenzo Mari, Andrea Corsonello, Fabrizia Lattanzio, Giuseppe Passarino and Giuseppina Rose conducted a study of 763 individuals aged 19-107 years to examine the variability of three human genes (NOS1, NOS2, NOS3) responsible for NO synthesis. Their study aimed to determine if gene variation in NOS genes was associated with longevity and geriatric parameters. The results showed that NOS1 and NOS2 were associated with longevity. Additionally, NOS1 rs1879417 was associated with lower cognitive performance while NOS2 rs2297518 polymorphism was associated with physical performance. SNPs in the NOS1 and NOS3 genes were also found to be respectively associated with depression symptoms and disability, two factors affecting quality of life in older individuals. Overall, the study showed that genetic variability of NOS genes has an effect on common age-related phenotypes and longevity in humans as well as previously reported for model organisms. 

Nitric oxide (NO) is a signaling molecule that interacts with different intracellular targets to trigger multiple signal transduction pathways. It contributes to the control of almost every cellular function. NO is produced by NADPH-dependent enzymes named NO synthases (NOS), encoded by three distinct NOS genes named neuronal (nNOS or NOS1), inducible (iNOS or NOS2), and endothelial (eNOS or NOS3). Although all isoforms share a similar function, their modes of action are quite different. While NOS1 and NOS3 are constitutively expressed and Ca2+/calmodulin-dependent, the inducible form (NOS2) is induced by inflammatory stimuli and is Ca2+/calmodulin-independent. Although all three isoforms can be found in numerous tissues, the specific cell type where NOS enzymes are located determines the specific outcomes of the NO signaling pathways.

NO produced by NOS1 functions as a regulator of neuronal transmission, cerebral blood flow and synaptic plasticity thus acting as a neuromodulator and neuroprotective agent. In endothelial cells, NO mainly produced by NOS3 acts as a regulator of vascular homeostasis being involved in the regulation of smooth muscle relaxation and in the inhibition of platelet aggregation. NO produced by NOS2 particularly in macrophages is mainly involved in the maintenance of the immune-inflammatory response. The biological effects of NO largely depend on the amount of NO produced. High amounts of NO or its derivative reactive nitrogen species (RNS) can trigger nitrosative modifications of proteins, lipids and nucleic acids, which may lead to cytotoxicity, neurodegeneration, and apoptotic cell death.

Supportive evidence for a role of NOSs in healthy aging and lifespan extension has come from studies with knockout models. In mice lacking all three NOS isoforms, the survival rate is reduced by 80%. Moreover, a reduction in survival rate of about 50%, and an attenuation of caloric restriction-induced life extension has been observed in nos3 knockout mice.

The study analyzed common and potentially functional NOS SNPs in a sample group of 763 individuals ranging from 19 to 107 years old. The sample was collected during several campaigns of recruitment. Subjects with dementia and/or neurological disorders were not included. The variability of genes that were tested for association with longevity was also investigated in relation to accepted biomarkers of the aging process that evaluate physical, cognitive, and psychological status in the elderly population. The management of activities of daily living, physical performance and cognitive function were assessed. 

All the subjects gave their written informed consent to use their anonymous genetic and phenotypic data for genetic studies on aging and longevity. The recruitment campaigns received the approval of the Ethical committee of the University of Calabria.Values used in the analyses were corrected for age, sex, and height since hand grip strength (HG) is affected by these factors. The reason for a test not being carried out was specified, whether due to physical disabilities or refusal to participate. SNPs were selected based on minor allele frequency (MAF) [10% in Caucasians], putative functional significance (non-synonymous SNPs, SNPs located in the 50- and 30-UTR regions), and SNPs previously investigated in association studies. The selected SNPs for each gene are reported in Table 1.

The Geriatric Depression Scale (GDS) was used to measure depression in the elderly. A score above five suggests moderate depression, while a score above ten suggests severe depression. GDS scores were dichotomized as one if the subject showed depression symptoms (GDS [5) and zero otherwise.

Regression models were applied to estimate how the variability of genes analyzed influences the predisposition to human longevity and functional parameters including cognitive function, functional performance, and depression status. In the regression models, sex was used as a covariate when testing the association between the variability of analyzed genes and human longevity. Covariate adjustment included sex, age, and height when analyzing HG scores, only age and sex when investigating disability and depression status. MMSE scores were normalized for age and educational status according to a standardized procedure reported in Grigoletto et al. (1999).

The Mini Mental State Examination (MMSE) test was used to evaluate cognitive performance. MMSE scores were dichotomized as 1 if the subject showed normal cognitive function (MMSE C 23) and zero otherwise.

The Model-based multifactor dimensionality reduction (MB-MDR) algorithm was applied to explore interaction effects between analyzed polymorphisms on phenotypes.