Serine Availability Influences Mitochondrial Dynamics and Function through Lipid Metabolism.

Cell proliferation can be dependent on the non-essential amino acid serine, and dietary restriction of serine inhibits tumor growth, but the underlying mechanisms remain incompletely understood. Using a metabolomics approach, we found that serine deprivation most predominantly impacts cellular acylcarnitine levels, a signature of altered mitochondrial function. Fuel utilization from fatty acid, glucose, and glutamine is affected by serine deprivation, as are mitochondrial morphological dynamics leading to increased fragmentation. Interestingly, these changes can occur independently of nucleotide and redox metabolism, two known major functions of serine. A lipidomics analysis revealed an overall decrease in ceramide levels. Importantly, supplementation of the lipid component of bovine serum or C16:0-ceramide could partially restore defects in cell proliferation and mitochondrial fragmentation induced by serine deprivation. Together, these data define a role for serine in supporting mitochondrial function and cell proliferation through ceramide metabolism.

Methionine metabolism is essential for SIRT1-regulated mouse embryonic stem cell maintenance and embryonic development.

Methionine metabolism is critical for epigenetic maintenance, redox homeostasis, and animal development. However, the regulation of methionine metabolism remains unclear. Here, we provide evidence that SIRT1, the most conserved mammalian NAD+-dependent protein deacetylase, is critically involved in modulating methionine metabolism, thereby impacting maintenance of mouse embryonic stem cells (mESCs) and subsequent embryogenesis. We demonstrate that SIRT1-deficient mESCs are hypersensitive to methionine restriction/depletion-induced differentiation and apoptosis, primarily due to a reduced conversion of methionine to S-adenosylmethionine. This reduction markedly decreases methylation levels of histones, resulting in dramatic alterations in gene expression profiles. Mechanistically, we discover that the enzyme converting methionine to S-adenosylmethionine in mESCs, methionine adenosyltransferase 2a (MAT2a), is under control of Myc and SIRT1. Consistently, SIRT1 KO embryos display reduced Mat2a expression and histone methylation and are sensitive to maternal methionine restriction-induced lethality, whereas maternal methionine supplementation increases the survival of SIRT1 KO newborn mice. Our findings uncover a novel regulatory mechanism for methionine metabolism and highlight the importance of methionine metabolism in SIRT1-mediated mESC maintenance and embryonic development.