The role of folate in maintenance of mitochondrial DNA integrity and mitochondrial function.
Abstract
Adequate energy production through mitochondrial function is a key determinant of physical and cognitive performance. Mitochondrial function is strongly influenced by maintenance of the mitochondrial genome (mtDNA). mtDNA depletion disorders, resulting from inborn errors of metabolism (IEM) in mtDNA replication and repair enzymes, are characterized by impaired mtDNA synthesis, mitochondrial dysfunction, severe multi-organ dysfunction phenotypes, and often result in premature mortality. Similarly, deleterious mtDNA mutations, resulting from mutagenesis and/or mtDNA replication errors, accumulate with age and contribute to decline in mitochondrial function. Complete characterization of mtDNA maintenance mechanisms is required for the identification of targets to prevent and improve physical and cognitive performance of both active-duty military personnel and the aging veteran population. Maintenance of cellular thymidylate (dTMP) pools is essential for both accurate mtDNA replication and maintaining mtDNA integrity. dTMP is synthesized through either nucleotide salvage or folate-dependent de novo synthesis pathways. IEM in dTMP salvage pathway enzymes are associated with severe mtDNA depletion disorders. Our preliminary data indicate that folate-dependent de novo dTMP synthesis also contributes meaningfully to maintaining adequate mitochondrial dTMP levels. Folate and vitamin B12 are essential cofactors required for a metabolic network known as folate-mediated one-carbon metabolism (FOCM), which provides one-carbon groups for biosynthesis of nucleotides (including dTMP) and amino acids. Importantly, because DNA polymerases do not distinguish between dUTP and dTTP, inadequate dTMP (a dTTP precursor) synthesis leads loss of dTTP and subsequent misincorporation of uracil during DNA replication/repair. Base-excision repair mechanisms associated with removal of misincorporated uracil leads to DNA strand breaks and genome instability. Preliminary studies indicate that either decreased expression of the folate-dependent mitochondrial enzyme serine hydroxymethyltransferase 2 (SHMT2) or folate inadequacy depress mitochondrial de novo dTMP synthesis and lead to uracil accumulation in mtDNA. In cultured cells, these same insults to FOCM also lead to reduced both oxygen consumption rates and oxidative phosphorylation capacity, two hallmarks of mitochondrial function. Patients with IEM resulting from mutations in both SHMT2 alleles present with intellectual disability, motor dysfunction, and hypertrophic cardiomyopathyÑphenotypes also frequently associated with mitochondrial dysfunction. The molecular and physiological effects of more subtle genetic (i.e. individuals carrying one SHMT2 variant allele) and nutritional vulnerabilities on mtDNA maintenance are understudied. To date, most studies investigating the effects of perturbed FOCM on mtDNA integrity have been carried out in transformed (i.e. cancerous) or immortalized cell lines, which do not rely as heavily on mitochondrial function for energy production as do non-transformed tissues such as brain and muscle. The primary objective of the proposed work is to determine the genetic and nutritional factors that influence folate-dependent de novo mitochondrial dTMP synthesis to lead to changes in mtDNA integrity and mitochondrial function. These studies will also inform nutritional strategies that sustain mitochondrial function to meet the substantial energy demands of brain and muscle tissues to optimize physical and cognitive performance of military personnel. This is important because the increased metabolic/nutritional demands of combat troops have been shown to result in inadequate folate status.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 14, 2022
- Source ID
- W911NF2210119
Entities
People
- Martha S. Field
Organizations
- Army Contracting Command
- Cornell University
- United States Army