Background Adequate cellular thymidylate (dTMP) pools are essential for preservation of nuclear and mitochondrial genome stability. Previous studies have indicated that disruption in nuclear dTMP synthesis leads to increased uracil misincorporation into DNA, affecting genome stability. To date, the effects of impaired mitochondrial dTMP synthesis in nontransformed tissues have been understudied. Objectives This study aimed to determine the effects of decreased serine hydroxymethyltransferase 2 (Shmt2) expression and dietary folate deficiency on mitochondrial DNA (mtDNA) integrity and mitochondrial function in mouse tissues. Methods Liver mtDNA content, and uracil content in liver mtDNA, were measured in Shmt2+/− and Shmt2+/+ mice weaned onto either a folate-sufficient control diet (2 mg/kg folic acid; C) or a modified diet lacking folic acid (0 mg/kg folic acid) for 7 wk. Shmt2+/− and Shmt2+/+ mouse embryonic fibroblast (MEF) cells were cultured in defined culture medium containing either 0 or 25 nM folate (6S-5-formyl-tetrahydrofolate, folinate) to assess proliferative capacity and mitochondrial function. Chi-square tests, linear mixed models, and 2-factor ANOVA with Tukey post hoc analyses were used to analyze data. Results Shmt2 +/− mice exhibited a 48%–67% reduction in SHMT2 protein concentrations in tissues. Interestingly, Shmt2+/− mice consuming the folate-sufficient C diet exhibited a 25% reduction in total folate in liver mitochondria. There was also a >20-fold increase in uracil in liver mtDNA in Shmt2+/− mice consuming the C diet, and dietary folate deficiency also increased uracil content in mouse liver mtDNA from both Shmt2+/+ and Shmt2+/− mice. Furthermore, decreased Shmt2 expression in MEF cells reduced cell proliferation, mitochondrial membrane potential, and oxygen consumption rate. Conclusions This study demonstrates that Shmt2 heterozygosity and dietary folate deficiency impair mitochondrial dTMP synthesis in mice, as evidenced by the increased uracil in mtDNA. In addition, Shmt2 heterozygosity impairs mitochondrial function in MEF cells. These findings suggest that elevated uracil in mtDNA may impair mitochondrial function.
Many countries in sub-Saharan Africa have experienced lower COVID-19 caseloads and fewer deaths than countries in other regions worldwide. Under-reporting of cases and a younger population could partly account for these differences, but pre-existing immunity to coronaviruses is another potential factor. Blood samples from Sierra Leonean Lassa fever and Ebola survivors and their contacts collected before the first reported COVID-19 cases were assessed using enzyme-linked immunosorbent assays for the presence of antibodies binding to proteins of coronaviruses that infect humans. Results were compared to COVID-19 subjects and healthy blood donors from the United States. Prior to the pandemic, Sierra Leoneans had more frequent exposures than Americans to coronaviruses with epitopes that cross-react with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), SARS-CoV, and Middle Eastern respiratory syndrome coronavirus (MERS-CoV). The percentage of Sierra Leoneans with antibodies reacting to seasonal coronaviruses was also higher than for American blood donors. Serological responses to coronaviruses by Sierra Leoneans did not differ by age or sex. Approximately a quarter of Sierra Leonian pre-pandemic blood samples had neutralizing antibodies against SARS-CoV-2 pseudovirus, while about a third neutralized MERS-CoV pseudovirus. Prior exposures to coronaviruses that induce cross-protective immunity may contribute to reduced COVID-19 cases and deaths in Sierra Leone.
Classical cystathionine β‐synthase‐deficient homocystinuria (HCU) is a life‐threatening inborn error of sulfur metabolism. Treatment for pyridoxine‐nonresponsive HCU involves lowering homocysteine (Hcy) with a methionine (Met)‐restricted diet and betaine supplementation. Betaine treatment efficacy diminishes significantly over time due to impairment of betaine‐Hcy S‐methyltransferase (BHMT) function. Little is known regarding the regulation of BHMT in HCU. Using a betaine‐responsive preclinical mouse model of HCU, we observed that this condition induces a 75% repression of BHMT mRNA, protein and enzyme activity, and significant depletion of hepatic betaine levels. BHMT repression was proportional to plasma Hcy levels but was not observed in mouse models of homocystinuria due to either methylenetetrahydrofolate reductase or Met synthase deficiency. Both Met supplementation and chemically induced glutathione depletion exacerbated hepatic BHMT repression in HCU mice but not wild‐type (WT) controls. Conversely, cysteine treatment normalized hepatic BHMT expression in HCU mice but had no effect in WT control animals. Taurine treatment induced BHMT expression in HCU mice by 5‐fold and restored maximal lowering of Hcy levels during long‐term betaine treatment with a concomitant normalization of inflammatory cytokine expression and a significantly improved coagulative phenotype. Collectively, our findings indicate that adjuvantial taurine treatment has the potential to significantly improve clinical outcomes in HCU.—Maclean, K. N., Jiang, H, Phinney, W. N., Keating, A. K., Hurt, K. J., Stabler, S. P. Taurine alleviates repression of betaine‐homocysteine S‐methyltransferase and significantly improves the efficacy of long‐term betaine treatment in a mouse model of cystathionine β‐synthase‐deficient homocystinuria. FASEB J. 33, 6339–6353 (2019). http://www.fasebj.org
Background. Adequate cellular thymidylate (dTMP) pools are essential for preservation of nuclear and mitochondrial genome stability. Previous studies have indicated that disruption in dTMP synthesis in the nucleus leads to increased uracil misincorporation into DNA affecting genome stability. To date, the effects of impaired mitochondrial dTMP synthesis in non-transformed tissues have been understudied. Objective. This study aimed to determine the effects of decreased serine hydroxymethyltransferase 2 (Shmt2) expression and dietary folate deficiency on mitochondrial DNA integrity and mitochondrial function in mouse tissues. Methods. Liver mitochondrial DNA (mtDNA) content, and uracil content in liver mtDNA was measured in Shmt2+/- and Shmt2+/+ mice weaned onto either a folate-sufficient control diet (2 mg/kg folic acid, C) or a modified diet lacking folic acid (0 mg/kg folic acid, FD) for 7 wks. Shmt2+/- and Shmt2+/+ mouse embryonic fibroblasts (MEF cells) were cultured in defined culture medium containing either 0 or 25 nM folate to assess proliferative capacity and mitochondrial function. Results. Shmt2+/- mice exhibited 48-67% reduction in SHMT2 protein levels in tissues. Interestingly, Shmt2+/- mice consuming the folate-sufficient C diet exhibited a 25% reduction in total folate in liver mitochondria. There was also a >20-fold increase in uracil in liver mtDNA in Shmt2+/- mice consuming the C diet, and dietary folate deficiency also increased uracil content in mouse liver mtDNA from both Shmt2+/+ and Shmt2+/- mice. Furthermore, decreased Shmt2 expression in MEF cells reduced cell proliferation, mitochondrial membrane potential, and oxygen consumption rate. Conclusions. This study demonstrates that Shmt2 heterozygosity and dietary folate deficiency impair mitochondrial dTMP synthesis, as evidenced by the increased uracil in mtDNA. In addition, Shmt2 heterozygosity impairs mitochondrial function in MEF cells. These findings suggest that elevated uracil in mtDNA may impair mitochondrial function.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.