Nicotinamide phosphoribosyl transferase in mammary gland epithelial cells is required for nicotinamide mononucleotide production in mouse milk.

Tissue-specific deficiency of nicotinamide phosphoribosyl transferase (NAMPT), the rate-limiting enzyme of the nicotinamide adenine dinucleotide (NAD+)-salvage pathway, causes a decrease of NAD+ in the tissue, resulting in functional abnormalities. The NAD+-salvage pathway is drastically activated in the mammary gland during lactation, but the significance of this has not been established. To investigate the impact of NAD+ perturbation in the mammary gland, we generated two new lines of mammary gland epithelial-cell-specific Nampt-knockout mice (MGKO). LC-MS/MS analyses confirmed that the levels of NAD+ and its precursor nicotinamide mononucleotide (NMN) were significantly increased in lactating mammary glands. We found that murine milk contained a remarkably high level of NMN. MGKO exhibited a significant decrease in tissue NAD+ and milk NMN levels in the mammary gland during lactation periods. Despite the decline in NAD+ levels, the mammary glands of MGKO appeared to develop normally. Transcriptome analysis revealed that the gene profiles of MGKO were indistinguishable from those of their wild-type counterparts, except for Nampt. Although the NMN levels in milk from MGKO were decreased, the metabolomic profile of milk was otherwise unaltered. The mammary gland also contains adipocytes, but adipocyte-specific deficiency of Nampt did not affect mammary gland NAD+ metabolism or mammary gland development. These results demonstrate that the NAD+ -salvage pathway is activated in mammary epithelial cells during lactation and suggest that this activation is required for production of milk NMN rather than mammary gland development. Our MGKO mice could be a suitable model for exploring the potential roles of NMN in milk.

Feto-maternal cholesterol transport regulated by ß-Klotho-FGF15 axis is essential for fetal growth.

ß-Klotho (ß-KL) is indispensable to regulate lipid, glucose, and energy metabolism in adult animals. ß-KL is highly expressed in the yolk sac, but its role in the developmental stages has not been established. We hypothesized that ß-KL is required for metabolic regulation in the embryo and aimed to clarify the role of ß-KL during development. Here, we show that ß-KL regulates feto-maternal cholesterol transport through the yolk sac by mediating FGF 15 signaling, and also that impairment of the ß-KL-FGF15 axis causes fetal growth restriction (FGR). Embryos of ß- kl knockout (ß-kl-/-) mice were morphologically normal but exhibited FGR before placental maturation. The body weight of ß-kl-/- mice remained lower after birth. ß-KL deletion reduced cholesterol supply from the maternal blood and led to lipid shortage in the embryos. These phenotypes were similar to those of embryos lacking FGF15, indicating that ß-KL-FGF15 axis is essential for growth and lipid regulation in the embryonic stages. Our findings suggest that lipid abnormalities in early gestation provoke FGR, leading to reduced body size in later life.