Department of Aging Science and Medicine, Graduate School of Medicine, Kyoto University, Kyoto, 606-8507, Japan; Wellness Science Labs, Meiji Holdings Co., Ltd., Tokyo, 192-0919, Japan.
Department of Aging Science and Medicine, Graduate School of Medicine, Kyoto University, Kyoto, 606-8507, Japan.
Biochem Biophys Res Commun. 2024 Oct 8;728:150346. doi: 10.1016/j.bbrc.2024.150346. Epub 2024 Jul 2.
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.
组织特异性烟酰胺磷酸核糖转移酶（NAMPT）缺乏，烟酰胺腺嘌呤二核苷酸（NAD）补救途径的限速酶，导致组织中 NAD 减少，导致功能异常。NAD 补救途径在哺乳期乳腺中被剧烈激活，但这一意义尚未确定。为了研究 NAD 对乳腺的影响，我们生成了两种新的乳腺上皮细胞特异性 Nampt 敲除小鼠（MGKO）。LC-MS/MS 分析证实，哺乳期乳腺中 NAD 及其前体烟酰胺单核苷酸（NMN）的水平显著增加。我们发现鼠乳中含有非常高水平的 NMN。MGKO 在哺乳期乳腺中表现出组织 NAD 和乳汁 NMN 水平的显著下降。尽管 NAD 水平下降，但 MGKO 的乳腺似乎正常发育。转录组分析显示，MGKO 的基因谱与野生型对照没有区别，除了 Nampt。尽管 MGKO 乳汁中的 NMN 水平降低，但乳汁的代谢组谱没有改变。乳腺还含有脂肪细胞，但脂肪细胞特异性缺乏 Nampt 并不影响乳腺 NAD 代谢或乳腺发育。这些结果表明，NAD 补救途径在哺乳期乳腺上皮细胞中被激活，并表明这种激活是产生乳汁 NMN 所必需的，而不是乳腺发育所必需的。我们的 MGKO 小鼠可能是探索 NMN 在乳汁中潜在作用的合适模型。
