| Abstract: | NAD biosynthesis is of substantial interest because of its important roles in regulating various biological processes. Nicotinamide mononucleotide adenylyltransferase 3 (Nmnat3) is considered a mitochondria-localized NAD synthesis enzyme involved in de novo and salvage pathways. Although the biochemical properties of Nmnat3 are well documented, its physiological function in vivo remains unclear. In this study, we demonstrated that Nmnat3 was localized in the cytoplasm of mature erythrocytes and critically regulated their NAD pool. Deficiency of Nmnat3 in mice caused splenomegaly and hemolytic anemia, which was associated with the findings that Nmnat3-deficient erythrocytes had markedly lower ATP levels and shortened lifespans. However, the NAD level in other tissues were not apparently affected by the deficiency of Nmnat3. LC-MS/MS-based metabolomics revealed that the glycolysis pathway in Nmnat3-deficient erythrocytes was blocked at a glyceraldehyde 3-phosphate dehydrogenase (GAPDH) step because of the shortage of the coenzyme NAD. Stable isotope tracer analysis further demonstrated that deficiency of Nmnat3 resulted in glycolysis stall and a shift to the pentose phosphate pathway. Our findings indicate the critical roles of Nmnat3 in maintenance of the NAD pool in mature erythrocytes and the physiological impacts at its absence in mice. |
