Key Points
- For the first time, researchers measured age-related waning levels of the essential molecule nicotinamide adenine dinucleotide (NAD+) in the hypothalamus of mice.
- Nicotinamide mononucleotide (NMN) supplementation doubles NAD+ levels in this brain structure.
- Injecting aged mice with microscopic vesicles from young mice containing an enzyme that synthesizes NMN – NAMPT – increased hypothalamic NAD+ by ~50%.
An important structure in the lower region of the brain called the hypothalamus regulates a myriad of physiological functions that are essential for our survival. These tasks include the control of body temperature, hunger, thirst, parenting behaviors, fatigue, and the sleep-wakefulness cycle (circadian rhythm). Due to its crucial roles in regulating physiological homeostasis, some researchers consider the hypothalamus a high-order control center for aging in mammals. Since NAD+ levels fall with age in other organs contributing to their functional decline, it seems the same would be true for the hypothalamus, however, this had never been measured before.
Published in NPJ Aging, Imai and colleagues from Washington University use a newly-devised method to measure NAD+ levels in the hypothalamus of mice. They found that NAD+ levels significantly decline in older mice in three of four subregions of the hypothalamus. Moreover, a single 300 mg/kg injection of NMN approximately doubled NAD+ levels at 30 minutes following the injection in all four hypothalamic subregions. Injecting aged mice with microscopic vesicles from young mice containing an NMN-synthesizing enzyme (NAMPT) increased NAD+ levels by ~50% in the hypothalamus. These findings provide the first evidence for an age-related decline in hypothalamic NAD+ levels and show that NMN can replete NAD+ to potentially improve sleep, physical activity, and cognitive function.
Hypothalamic NAD+ Levels Fall with Age and NMN Replenishes Them
Imai and colleagues utilized their new procedure that incorporates laser-based dissections of tissue to measure hypothalamic NAD+ levels in aged mice. Compared to young mice, NAD+ levels fell significantly in three out of four subregions of the hypothalamus. These findings provide the first confirmation that, like most other tissues, NAD+ levels fall in the hypothalamus with age.
Since NMN restores NAD+ levels in most other tissues, Imai and colleagues examined whether it would do so in the hypothalamus. After a single NMN injection into the bloodstream, they noticed that NAD+ levels about doubled in all four of the hypothalamus subregions. These findings show that NMN restores hypothalamic NAD+ levels in mice.
Previous research has shown that vesicles containing the NAMPT enzyme, which synthesizes NMN, regulate hypothalamic NAD+ levels. For this reason, Imai and colleagues tested whether injecting NAMPT-containing vesicles from young mice into older mice would raise NAD+ levels in the hypothalamus. After injecting the vesicles derived from younger mice filled with NMN-synthesizing NAMPT enzymes, older mice showed ~50% increase in hypothalamic NAD+ levels. These results confirm that the hypothalamus utilizes NAMPT-containing vesicles to synthesize NAD+.
“Our results demonstrated that supplementation of [NAMPT vesicles] purified from young mice significantly increased the NAD+ levels in the whole hypothalamus … in aged mice,” said Imai and colleagues.
NMN Potentially Rejuvenates Physiological Homeostasis via the Hypothalamus
The study’s importance rests on being the first to confirm that NAD+ levels fall with age in the hypothalamus. Since NAD+ plays essential roles in repairing DNA, cell energy generation, and eliminating cell stress-inducing molecules, NAD+ repletion in the hypothalamus may help maintain its function with age.
Increasing NAD+ levels with NMN or NAMPT vesicles may stave off age-related changes in sensory and emotional processing associated with the hypothalamus. Moreover, preserving hypothalamic function could help with sleep and other hypothalamus-associated functions pertaining to physiological homeostasis.
The study’s biggest limitation was that it didn’t measure whether NAD+ repletion improves hypothalamic function in aged mice. This endeavor isn’t easily executed since the hypothalamus mediates nervous system responses along with the release of multiple hormones. A more comprehensive study of NAD+ repletion’s effects on the hypothalamus could examine blood levels of hormones associated with the hypothalamus such as gonadotropin-releasing hormone and/or follicle-stimulating hormone.
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