The study findings have implications for the identification of novel pathways with which to selectively target folate-metabolism blood cancers.
Throughout the world, folic acid (folate) status varies greatly based on factors such as nutritional intake, common genetic polymorphisms, and widespread supplementation, explained Anna E Beaudin, PhD, during a session at the 65th American Society of Hematology (ASH) Annual Meeting and Exposition. Beaudin, associate professor, Division of Hematology and Hematologic Malignancies, Department of Internal Medicine at the University of Utah School of Medicine, explained further that folate-derived one-carbon metabolism (OCM) is known to regulate cellular methylation, de novo nucleotide biosynthesis, and mitochondrial metabolism, which are processes that are essential to hematopoietic stem cell (HSC) function and establishment.
During fetal development, it is known that varying prenatal folate status can metabolically program HSCs and can affect adult HSC self-renewal and engraftment potential. However, Beaudin noted that there remains a limited understanding of the driving force behind HSC developmental programming.
“The idea behind this work really initiates from a historic observation during World War II referred to as the Dutch Hunger Winter, [during which] the Axis powers cut the food supply off to the Dutch for a limited period of time, [forcing the population to eat] about 500 calories a day, and this is for the entire population, including pregnant women,” Beaudin said during the session. “Afterwards, the food supply was rapidly reestablished. But much later, the babies [born to these pregnant women] were found to have a much higher incidence of many chronic diseases associated with inflammation, including type 2 diabetes, obesity, cardiovascular disease, and even premature death.”
Beaudin explained further that following the observation of the impact of fetal nutrition on development from the Dutch Hunger Winter, David Barker, MD, PhD, FRS, established the developmental origins of health and disease hypothesis. Barker theorized that increasing risk of chronic disease throughout the lifespan is triggered by adverse events (AEs) during early life, such as microbial exposure, toxic exposure, and early life nutrition.
“We don't often intervene for these types of diseases until adulthood, when there's really only a minimal reduction in risk from disease,” Beaudin said. “My lab’s goal is to try to understand how these [AEs] during early life are associated with risk for disease and drivers for chronic disease, so we can apply interventions much earlier and thereby have a much greater impact on mitigating risk for disease across the lifespan.”
Beaudin and her colleagues approached this by studying folate, which is not only a critical nutrient during development, but it's also thought to be a critical driver in the disease susceptibility phenotype driven by Barker’s hypothesis of the developmental origins of disease. Folate, an essential water soluble vitamin found in many nutrients, is often advised for pregnant women to supplement their nutrition during fetal development.
“This is because it [sic] very strongly prevents a neural tube defect, which is a very common birth defect. In fact, just taking folate during development can prevent up to 70% of neural tube defects in the general population,” Beaudin said. “It's for this reason that we fortify the entire population with folate in the United States since 1998, and in many industrialized countries. [Further], we do this despite not having a handle on the mechanism by which folate supplementation prevents neural tube defects.”
Beaudin explained further that there is also a lack of understanding regarding how folate supplementation impacts other developing organ systems. For this reason, Beaudin and her colleagues sought to investigate the effects of early folate nutrition on developing hematopoietic or blood systems.
“During development, [folate] is a critical regulator of metabolism, including mitochondrial metabolism. It is [also] a critical regulator of epigenetics, as it provides one-carbons for all cellular methylation reactions,” Beaudin said. “[Additionally], it is also a critical regulator of both DNA synthesis and DNA stability because it provides one-carbons for nucleotide synthesis and metabolism.”
Within the hematopoietic system, HSCs form the foundation of the immune system, Beaudin explained. Additionally, HSCs make all blood and immune cells across an individual’s lifespan. Further, HSCs are established very early during development, which makes them amenable to the developmental origins of health and disease hypothesis.
“Importantly, [HSCs] are heavily regulated during development by both epigenetics and by mitochondrial metabolism,” Beaudin said. “In this study, we sought to directly investigate the effects of prenatal folate nutrition on developing [HSCs]. To do this, we put female mice on 3 diets that modeled human population–wide folate consumption.”
The 3 diets included folate at 0 mg/kg (deficient folate), 2 mg/kg (control), and 8 mg/kg (supplemented folate). The female mice were placed on the diet for a few weeks before mating and after becoming pregnant. Once the mice gave birth, the offspring were weaned onto a normal child-equivalent diet.
“This is modeling something similar to the Dutch Hunger Winter study, where they were on these 3 different folate-controlled diets only during this developmental window, and then went on to normal diets for the rest of their lifespan,” Beaudin said. “The first thing we noticed is when we looked into the adult bone marrow, which is where all your [HSCs] reside for the rest of your lifespan, [there were] fundamental changes to adult hematopoiesis, increases in the number of stem cells and progenitor cells in the bone marrow and in bone response to folate deficiency and folate supplementation, and fundamental changes to output downstream of that.”
Additionally, the investigators observed that the whole adult bone marrow hematopoietic system was remodeled in response to the very limited change during development.
“We reasoned that these changes were being driven by fundamental alterations to [HSCs], since these are the cells that are present and remodeled during early development in response to changes to bone nutrition.” Beaudin said.
To test this, Beaudin and her colleagues isolated the stem cells out of the bone marrow of adult offspring during development and transplanted them into adult recipients to test their output. Beaudin noted that the results of this showed that the stem cells from the folate deficient bone marrow were completely unprepared and unable to produce blood cells in the transplant setting, whereas the stem cells from the supplemented offspring were overpowered and able to produce significantly more blood and immune cells upon transplantation.
“We were interested in investigating how this was programmed during development metabolically, and we were surprised to see the opposite pattern in output from the hematopoietic system during development, where our folate deficient offspring were producing way more blood cells during development and the supplemented were producing less,” Beaudin said. “When we looked at the metabolic correlates of these changes, we observed fundamental metabolic differences between folate deficient and folate supplemented in [HSCs], and this was associated with an increase in metabolic activity in our folate deficient stem cells during development.”
Further, when tracked into adulthood, the investigators observed that there was a strong metabolic phenotype in the HSCs of the folate deficient offspring. These offspring exhibited a robust impairment in mitochondrial metabolism that had been programmed from development in response to folate deficiency, according to Beaudin.
“We also examined transcriptional differences underlying this effect, and observed the most robust impairments and effects on mitochondrial metabolism that we believe is underwritten by epigenetic rewiring during development,” Beaudin said. “To summarize, our data suggest that adult [HSCs] can be programmed by manipulating prenatal folate during development. Maternal nutrition, including folate nutrition, has critical implications for both adult [HSC] function and metabolic function. We believe that this initiates during fetal development by metabolic programming of mitochondrial metabolism.”
Further, Beaudin noted that her research team believes that this mitochondrial metabolism involves transcriptional remodeling that implicates epigenetic underpinnings. According to Beaudin, this nutritional metabolic programming of adult HSC function has critical implications for hematologic and immune function across the lifespan.
“These [HSCs] are giving rise to all adult immune cells and blood cells across the lifespan,” Beaudin said during the session. “[Now], we're working on leveraging this understanding of metabolic mechanisms by which folate nutrition programs [HSCs] to identify novel pathways with which to selectively target folate-metabolism blood cancers, as antifolates have been a mainstay of leukemic treatment for many decades.”
Beaudin AE. Metabolic Programming of Hematopoietic Stem Cell Function By Prenatal Folate. Presented at: 65th ASH Annual Meeting and Exposition in San Diego, California; December 9, 2023.