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Final Report Summary - NUVASCOG (NUtrition and microVAScular dynamics in COGnitive health)

NUVASCOG is the founding grant for the reintegration of the PI and the establishment of the Nutrition and Brain Health Laboratory at the Hebrew University. It has facilitated the PI's hiring as a tenure-track Senior Lecturer and has provided the foundation for the creation of a strong research group. Funding from the grant has provided the foundation for securing of additional grants from the Israel Science Foundation and other agencies, and expansion on the original grant aims to other areas of nutrition and brain health. Collectively, this has allowed for the recruitment and training of graduate students, has supported the assimilation of major experimental systems (for state-of the art evaluation of animal behavior, cerebrovascular physiology and neurovascular anatomy) and for the first series of experiments to be undertaken.

The specific objectives of this grant were to delineate the microvascular basis of age- and diet-related cognitive impairment, and to identify diet-responsive signaling pathways that can modulate microvascular plasticity, in two specific aims:

Aim 1: Test the hypothesis that impaired brain circulation and oxygen delivery due to aberrant microvascular plasticity is a mechanism of cognitive impairment in both folate-deficiency and aging.

Aim 2: Identify folate-responsive pathways that regulate microvascular plasticity in brain in young and old rats.

To achieve these aims we used a putative animal model of vascular cognitive impairment. We fed young and old rats control and folate deficient diets; providing folate deficient rats with supplemental methionine in an attempt to overcome at least one consequence of the deficiency; and repleting folate following deficiency in order to determine the extent to which deficiency-induced damage may be reversible The project was conducted in two phases. In the first 2 years young rats were subjected the experimental protocol and in the last two years the protocol was repeated in old rats. Preliminary findings over the course of the project have been disseminated at presentations by the PI and students at national and international conferences. The final analysis of comparing the effects and interactions of diet and age on cognitive, physiological, anatomical and molecular outcomes is now underway as are the manuscripts reporting on the full study design.

Key findings include the following:

1) In young rats, folate deficiency causes a reduction of brain blood volume (as detected by non-invasive absolute near infrared spectroscopy); The reduction in brain blood volume was partially mitigated by dietary supplementation with methionine, without changing plasma tHcy; The reduction of brain blood volume can be reversed upon repletion of folate-deficient rats with normal dietary folate (Aim1).

2) Folate-deficiency appears to induce qualitative histological abnormalities in brain microvessels in young rats, which may explain the functional changes described above . Aging appears to diminish the density of the brain microvascular bed irrespective of diet.

3) Folate- and methionine-responsive signaling pathways including vascular signaling, metabolic and inflammatory genes were identified in brain tissue (Aim2) by examining diet-induced changes in the expression of candidate pathways selected for their theoretical involvement in the regulation and maintenance of vascular plasticity as well as other important brain functions. The effects of aging were greater than the effects of diet. Of 101 genes assayed, a total of 60 responded to Age, 36 to Diet, and 19 showed a significant interactions between Age x Diet. Main effects of Diet and interactions effects were seen primarily in young rats.

4) No cognitive deficits were detected in the young animals as a result of diet. Aging resulted in a significant decrement in cognitive performance compared with the cognitive performance in the younger rats. However, as in the young rats, no cognitive deficits were identified in the old rats as a result of diet. While the dietary conditions used on our study did not appear to induce cognitive effects, the pattern of age related cognitive slowing were consistent with the reduction in brain blood volume indicated by near infrared spectroscopy and with the reduction with age in the expression of brain vascular genes. It is possible that these measures are more sensitive to early diet-induced brain changes than the behavioral measures of cognitive outcome.

These findings, pointing to diminished brain circulation with age as a potential cause of cognitive decline are consistent with cross-sectional findings in young and old adult humans. The potential of near infrared spectroscopy to detect early, potentially reversible, diet and age-induced changes in brain microvascular circulation bring us closer to the long term goal of using this technique as translational non-invasive biomarker of brain microvascular aging. The finding that methionine supplementation can mitigate the effects of folate-deficiency raises the possibility that this mitigation is the result of a secondary perturbation of liver lipid metabolism. Findings which identify the pathways that are affected by dietary and metabolic perturbation and aging will help to identify targets for diet and drug interventions to prevent cognitive decline. Thus in the long run this research provides important insight into the dietary (life-style) factors that confer risk of cognitive impairment and dementia in older adults, and point the way to interventions aimed at preventing or mitigating the heavy burden that these conditions place on individuals and society.

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