Summer Undergraduate Research Internship

Mentor: Mirella L Meyer-Ficca, Ph.D.

Background: Vitamin B3 (Niacin, nicotinic acid and nicotinamide) is an essential human micronutrient. A diet deficient in niacin results in the debilitating disease Pellagra. Vitamin B3 is a dietary precursor required for the synthesis of NAD and NADP, two cofactors that participate in many metabolic processes in the body. NAD is also a coenzyme for several epigenetic regulator proteins (e.g. sirtuins) that regulate energy and fat metabolism related gene expression, and activity of all these enzymes directly depends on NAD availability.

In humans, niacin deficiency in the diet directly results in the diminished availability of NAD, changing the activities of NAD dependent-enzymes and presumably NAD-dependent epigenetic gene expression control. Blood and tissue NAD levels decline with increasing age in humans, even despite adequate dietary niacin intake. This decline presumably is due to increased NAD consumption by NAD-degrading enzymes such as poly(ADP-ribose) polymerases (with PARP1 as main NAD-consumer in this group), CD38, and several sirtuin enzymes. Enzymes with the highest affinity for NAD are PARP1 and CD38, and CD38 is currently thought to be the major NAD-consumer responsible for the aging-related NAD decline, but the impact of PARP1-mediated NAD depletion during aging is currently unknown NAD dynamics has been difficult to investigate due to a lack of appropriate animal models. In contrast to humans, rodents, which otherwise provide excellent epigenetic and metabolic animal models, unfortunately do not require Vitamin B3 as an essential vitamin for NAD synthesis. Our lab therefore has developed a transgenic mouse model with a “human-like” pathway of NAD synthesis. Those mice have acquired niacin dependency (ANDY) and, if maintained on a niacin-deficient diet, become NAD-deficient in a manner comparable to humans. To test the hypothesis that both CD38 and PARP1 contribute to the age-related NAD decline, we have generated ANDY mice that lack the genes encoding PARP1, CD38, or both, (designated ANDY-PARP1 KO, ANDY-CD38 KO, or ANDY-double KO, respectively).

Project Description:

The objective of the project is to characterize the NAD-decline in ANDY, ANDY-PARP1 KO, ANDY-CD38 KO and ANDY-double KO on a niacin-deficient diet. To this end, cohorts of the different mouse lines will be kept on niacin-deficient or complete control diet for a period of several weeks. Blood samples will be collected at regular intervals, and metabolic parameters and body composition with be assessed using EchoMRI and metabolic chambers. At the conclusion of the feeding trial, blood and tissues will be collected. Blood NAD and NADP will be quantified using an enzymatic cycling assay to determine the dynamics of NAD decline. Tissue NAD content will be quantified to determine to which extend the individual enzymes contribute to declining tissue NAD levels.

Duties and Responsibilities: The students will learn basic laboratory methods (buffer preparation), basic animal husbandry, use of rodent metabolic chambers and EchoMRI, blood and tissue extraction methods, enzymatic cycling assays for NAD and NADP, data collection and analysis.

Principal Investigator: Dr. Jeffrey Mason

Research Area: Physiology of Reproductive Senescence

Background: Young, reproductively-cycling women hold a significant health advantage over similarly aged men. As reproductive cycling continues, both ovarian germ and somatic cells are continually depleted until the time of menopause, when a large proportion of these cells are lost, along with the female health advantage. At the time of menopause, disease rates in women begin to exceed those of men. Current treatment in the form of hormone replacement therapy is often unpredictable and comes with several limitations and adverse effects, and is focused on replacing only a portion of the ovarian function lost at menopause. Research from our lab shows that replacement of senescent ovaries in post-reproductive mice with young, cycling ovaries extends longevity and ameliorates age-associated dyslipidemia and chronic inflammation. In a pilot study, depletion of germ cells prior to transplantation enhanced the longevity-extending effects of the young, transplanted ovaries and, as with germ cell-containing ovaries, decreased the severity of inflammation, but did so independent of germ cells. In germ cell-depleted primitive species, longevity extension is dependent on the up-regulation of Foxo signaling. In mammals, Foxo suppresses the de novo methyltransferase Dnmt3b and reduces the age-associated erosion of methylation patterns and epigenetic reprogramming. Foxo signaling is also linked to gender-specific longevity in centenarians. Ovarian Foxo signaling is significantly reduced at menopause due to the loss of Foxo-producing ovarian tissue.

Project Description: Determine how young intact and germ cell-depleted ovaries affect age-related changes in health, lipid metabolism, transcription, dyslipidemia and chronic inflammation in post-reproductive mice. Based on our preliminary data, we hypothesize that transplantation of young ovaries will improve health and slow/avert the age-related epigenetic reprogramming of metabolism- and immune-regulating genes in post-reproductive female mice. We expect to quantify differences in exosomal miRNA trafficking and profiles and transcription profiles of metabolism and immune function genes in post-reproductive female mice and that these age-related differences will be mitigated by transplantation of young ovaries both with and without germ cells.

Duties and Responsibilities: The intern student will learn to assess health with in vivo health span assays, miRNA trafficking/profiling, gene expression, exosomal tracking/processing, immune function changes by T-cell, cytokine and pathological analyses and dyslipidemia by in vivo lipid tolerance and circulating lipoprotein levels in post-reproductive mice and in vitro.