The role of l -serine and l -threonine in the energy metabolism and nutritional stress response of Trypanosoma cruzi

Abstract

l -Serine and l- threonine have versatile roles in metabolism. In addition to their use in protein synthesis, these amino acids participate in the biosynthesis pathways of other amino acids and even phospholipids. Furthermore, l -serine and l- threonine can be substrates for a serine/threonine dehydratase (Ser/ThrDH), resulting in pyruvate and 2-oxobutyrate, respectively, thus being amino acids with anaplerotic potential. Trypanosoma cruzi , the etiological agent of Chagas disease, uses amino acids in several biological processes: metacyclogenesis, infection, resistance to nutritional and oxidative stress, osmotic control, etc. This study investigated the import and metabolism of l -serine, l- threonine, and glycine in T. cruzi . Our results demonstrate that these amino acids are transported from the extracellular environment into T. cruzi cells through a saturable transport system that fits the Michaelis-Menten model. Our results show that l -serine and l- threonine can sustain epimastigote cell viability under nutritional stress conditions and stimulate oxygen consumption, maintaining intracellular ATP levels. Additionally, our findings indicate that serine plays a role in establishing the mitochondrial membrane potential in T. cruzi . Serine is also involved in energy metabolism via the serine-pyruvate pathway, which stimulates the production and subsequent excretion of acetate and alanine. Our results demonstrate the importance of l -serine and l -threonine in the energy metabolism of T. cruzi and provide new insights into the metabolic adaptations of this parasite during its life cycle. IMPORTANCE Trypanosoma cruzi , the parasite responsible for Chagas disease, impacts 5–6 million individuals in the Americas and is rapidly spreading globally due to significant human migration. This parasitic organism undergoes a complex life cycle involving triatomine insects and mammalian hosts, thriving in diverse environments, such as various regions within the insect’s digestive tract and mammalian cell cytoplasm. Crucially, its transmission hinges on its adaptive capabilities to varying environments. One of the most challenging environments is the insect’s digestive tract, marked by nutrient scarcity between blood meals, redox imbalance, and osmotic stresses induced by the triatomine’s metabolism. To endure these conditions, T. cruzi has developed a remarkably versatile metabolic network enabling it to metabolize sugars, lipids, and amino acids efficiently. However, the full extent of metabolites this parasite can thrive on remains incompletely understood. This study reveals that, beyond conventional carbon and energy sources (glucose, palmitic acids, proline, histidine, glutamine, and alanine), three additional metabolites (serine, threonine, and glycine) play vital roles in the parasite’s survival during starvation. Remarkably, serine and threonine directly contribute to ATP production through a serine/threonine dehydratase enzyme not previously described in T. cruzi . The significance of this metabolic pathway for the parasite’s survival sheds light on how metabolic networks aid in its endurance under extreme conditions and its ability to thrive in diverse metabolic settings.

Nutritional deficiency suppresses reproduction in Serangium japonicum through vitellogenin down‐regulation

“…From an energy economics perspective, this reflects an energy-saving strategy involving the shutdown of non-essential functions. 45 Under nutritional stress, organisms tend to prioritize maintenance of core physiological functions such as basal metabolism and stress responses, 46,47 while down-regulating physiological processes that are noncritical for immediate survival, including reproductive potential and immune defense. 48 Notably, among identified reproduction-related DEGs, a significant majority were downregulated, suggesting that alternative prey may impair insect reproductive potential through the suppression of key gene expression.…”

Nutritional deficiency suppresses reproduction in Serangium japonicum through vitellogenin down‐regulation

“…From an energy economics perspective, this reflects an energy-saving strategy involving the shutdown of non-essential functions. 45 Under nutritional stress, organisms tend to prioritize maintenance of core physiological functions such as basal metabolism and stress responses, 46,47 while down-regulating physiological processes that are noncritical for immediate survival, including reproductive potential and immune defense. 48 Notably, among identified reproduction-related DEGs, a significant majority were downregulated, suggesting that alternative prey may impair insect reproductive potential through the suppression of key gene expression.…”

Metabolic Profile Associated With Encystation in Acanthamoeba

“…In the targeted study by Tsai et al (2023), this same pathway was implicated in amino acid homeostasis achievement after long-term exposure of Acanthamoeba to the coculture media. Another recent study on Trypanosoma cruzi demonstrated that serine and threonine act as critical carbon sources during nutritional stress, sustaining mitochondrial membrane potential (ΔΨm) and ATP production via oxidative phosphorylation (Alencar et al 2025). Regulation of this pathway in Acanthamoeba may represent a strategy to repurpose these amino acids for energy maintenance and stress resilience during dormancy.…”

Energy metabolism in Trypanosoma cruzi : the validated and putative bioenergetic and carbon sources

“…In the mammalian host-cell cytoplasm, the parasite competes for resources with the metabolic machinery and systems that sequester them into organelles. As a consequence, most metabolites are present at low concentrations ( 65 ) when compared with the K M values for most of the parasite nutrient transporters characterized so far ( 66 ). In the insect midgut, T. cruzi faces rapid nutrient absorption by insect gut epithelial cells after blood meals ( 67 – 69 ).…”

“…T. cruzi acquires amino acids through proteolytic activities, transport systems, or biosynthesis pathways. Amino acid transport systems for l -proline (Pro) ( 24 ), l -aspartate (Asp) ( 115 ), l -arginine (Arg) ( 116 ), l -glutamate (Glu) ( 117 ), l- glutamine ( 27 ), l -histidine (His) ( 28 ), l -leucine (Leu), l -isoleucine (Ile), l -valine (Val) ( 118 ), l -serine (Ser), l -threonine (Thr), and glycine (Gly) ( 66 ) among others, have been characterized in recent years (reviewed in reference 119 ). Except for His, transport occurs via active processes, dependent on the plasma membrane H + gradient (reviewed in reference 119 ).…”

“…It has been proposed that T. cruzi , like T. brucei , might synthesize Thr from homoserine and acyl-homoserine lactones, bypassing the homoserine kinase step ( 158 ). Due to these biosynthetic deficiencies, T. cruzi depends on the extracellular uptake of Ser and Thr ( 66 ). Recent studies show that Ser and Thr are important carbon and energy sources for T. cruzi during starvation, directly contributing to ATP production ( 66 ).…”

Nutritional deficiency suppresses reproduction in Serangium japonicum through vitellogenin down‐regulation

“…From an energy economics perspective, this reflects an energy-saving strategy involving the shutdown of non-essential functions. 45 Under nutritional stress, organisms tend to prioritize maintenance of core physiological functions such as basal metabolism and stress responses, 46,47 while down-regulating physiological processes that are noncritical for immediate survival, including reproductive potential and immune defense. 48 Notably, among identified reproduction-related DEGs, a significant majority were downregulated, suggesting that alternative prey may impair insect reproductive potential through the suppression of key gene expression.…”

Metabolic Profile Associated With Encystation in Acanthamoeba

“…In the targeted study by Tsai et al (2023), this same pathway was implicated in amino acid homeostasis achievement after long-term exposure of Acanthamoeba to the coculture media. Another recent study on Trypanosoma cruzi demonstrated that serine and threonine act as critical carbon sources during nutritional stress, sustaining mitochondrial membrane potential (ΔΨm) and ATP production via oxidative phosphorylation (Alencar et al 2025). Regulation of this pathway in Acanthamoeba may represent a strategy to repurpose these amino acids for energy maintenance and stress resilience during dormancy.…”

Energy metabolism in Trypanosoma cruzi : the validated and putative bioenergetic and carbon sources

“…In the mammalian host-cell cytoplasm, the parasite competes for resources with the metabolic machinery and systems that sequester them into organelles. As a consequence, most metabolites are present at low concentrations ( 65 ) when compared with the K M values for most of the parasite nutrient transporters characterized so far ( 66 ). In the insect midgut, T. cruzi faces rapid nutrient absorption by insect gut epithelial cells after blood meals ( 67 – 69 ).…”

“…T. cruzi acquires amino acids through proteolytic activities, transport systems, or biosynthesis pathways. Amino acid transport systems for l -proline (Pro) ( 24 ), l -aspartate (Asp) ( 115 ), l -arginine (Arg) ( 116 ), l -glutamate (Glu) ( 117 ), l- glutamine ( 27 ), l -histidine (His) ( 28 ), l -leucine (Leu), l -isoleucine (Ile), l -valine (Val) ( 118 ), l -serine (Ser), l -threonine (Thr), and glycine (Gly) ( 66 ) among others, have been characterized in recent years (reviewed in reference 119 ). Except for His, transport occurs via active processes, dependent on the plasma membrane H + gradient (reviewed in reference 119 ).…”

“…It has been proposed that T. cruzi , like T. brucei , might synthesize Thr from homoserine and acyl-homoserine lactones, bypassing the homoserine kinase step ( 158 ). Due to these biosynthetic deficiencies, T. cruzi depends on the extracellular uptake of Ser and Thr ( 66 ). Recent studies show that Ser and Thr are important carbon and energy sources for T. cruzi during starvation, directly contributing to ATP production ( 66 ).…”

Nutritional deficiency suppresses reproduction in Serangium japonicum through vitellogenin down‐regulation

“…From an energy economics perspective, this reflects an energy-saving strategy involving the shutdown of non-essential functions. 45 Under nutritional stress, organisms tend to prioritize maintenance of core physiological functions such as basal metabolism and stress responses, 46,47 while down-regulating physiological processes that are noncritical for immediate survival, including reproductive potential and immune defense. 48 Notably, among identified reproduction-related DEGs, a significant majority were downregulated, suggesting that alternative prey may impair insect reproductive potential through the suppression of key gene expression.…”

Metabolic Profile Associated With Encystation in Acanthamoeba

“…In the targeted study by Tsai et al (2023), this same pathway was implicated in amino acid homeostasis achievement after long-term exposure of Acanthamoeba to the coculture media. Another recent study on Trypanosoma cruzi demonstrated that serine and threonine act as critical carbon sources during nutritional stress, sustaining mitochondrial membrane potential (ΔΨm) and ATP production via oxidative phosphorylation (Alencar et al 2025). Regulation of this pathway in Acanthamoeba may represent a strategy to repurpose these amino acids for energy maintenance and stress resilience during dormancy.…”

Energy metabolism in Trypanosoma cruzi : the validated and putative bioenergetic and carbon sources

“…In the mammalian host-cell cytoplasm, the parasite competes for resources with the metabolic machinery and systems that sequester them into organelles. As a consequence, most metabolites are present at low concentrations ( 65 ) when compared with the K M values for most of the parasite nutrient transporters characterized so far ( 66 ). In the insect midgut, T. cruzi faces rapid nutrient absorption by insect gut epithelial cells after blood meals ( 67 – 69 ).…”

“…T. cruzi acquires amino acids through proteolytic activities, transport systems, or biosynthesis pathways. Amino acid transport systems for l -proline (Pro) ( 24 ), l -aspartate (Asp) ( 115 ), l -arginine (Arg) ( 116 ), l -glutamate (Glu) ( 117 ), l- glutamine ( 27 ), l -histidine (His) ( 28 ), l -leucine (Leu), l -isoleucine (Ile), l -valine (Val) ( 118 ), l -serine (Ser), l -threonine (Thr), and glycine (Gly) ( 66 ) among others, have been characterized in recent years (reviewed in reference 119 ). Except for His, transport occurs via active processes, dependent on the plasma membrane H + gradient (reviewed in reference 119 ).…”

“…It has been proposed that T. cruzi , like T. brucei , might synthesize Thr from homoserine and acyl-homoserine lactones, bypassing the homoserine kinase step ( 158 ). Due to these biosynthetic deficiencies, T. cruzi depends on the extracellular uptake of Ser and Thr ( 66 ). Recent studies show that Ser and Thr are important carbon and energy sources for T. cruzi during starvation, directly contributing to ATP production ( 66 ).…”