Kwon, Y. Y. | bioRxiv Science

bioRxiv2025

Sustained Glucose Turnover Flux Distinguishes Cancer Cachexia from Nutrient Limitation

Cancer cachexia is an involuntary weight loss condition characterized by systemic metabolic disorder. A comprehensive flux characterization of this condition however is lacking. Here, we systematically isotope traced eight major circulating nutrients in mice bearing cachectic C26 tumors (cxC26) and food intake-matched mice bearing non-cachectic C26 tumors (ncxC26). We found no difference in whole-body lipolysis and proteolysis, ketogenesis, or fatty acid and ketone oxidation by tissues between the two groups. In contrast, compared to ncxC26 mice ad libitum, glucose turnover flux decreased in food intake-controlled ncxC26 mice but not in cxC26 mice. Similarly, sustained glucose turnover flux was observed in two autochthonous cancer cachexia models despite reduced food intake. We identified glutamine and alanine as responsible for sustained glucose production and tissues with altered use of glucose and lactate in cxC26 mice. We provide a comprehensive view of metabolic alterations in cancer cachexia revealing those distinct from decreased nutrient intake. HighlightsO_LIQuantitative fluxomics of cancer cachexia under matched food intake and body weight C_LIO_LIIntact lipolysis, proteolysis, ketogenesis, and lipid oxidation in cachectic mice C_LIO_LISustained glucose consumption in cachectic mice despite reduced food intake C_LIO_LIIncreased glucose production from glutamine and alanine in cachectic mice C_LI

cancer biology↗

bioRxiv2023

Ongoing evolution of the Mycobacterium tuberculosis lactate dehydrogenase reveals the pleiotropic effects of bacterial adaption to host pressure

The bacterial determinants that facilitate Mycobacterium tuberculosis (Mtb) adaptation to the human host environment are poorly characterized. We have sought to decipher the pressures facing the bacterium in vivo by assessing Mtb genes that are under positive selection in clinical isolates. One of the strongest targets of selection in the Mtb genome is lldD2, which encodes a quinone-dependent L-lactate dehydrogenase (LldD2) that catalyzes the oxidation of lactate to pyruvate. Lactate accumulation is a salient feature of the intracellular environment during infection and lldD2 is essential for Mtb growth in macrophages. We determined the extent of lldD2 variation across a set of global clinical isolates and defined how prevalent mutations modulates Mtb fitness. We show the stepwise nature of lldD2 evolution that occurs as a result of ongoing lldD2 selection in the background of ancestral lineage defining mutations and demonstrate that the genetic evolution of lldD2 additively augments Mtb growth in lactate. Using quinone-dependent antibiotic susceptibility as a functional reporter, we also find that the evolved lldD2 mutations functionally increase the quinone-dependent activity of LldD2. Using 13C-lactate metabolic flux tracing, we find that lldD2 is necessary for robust incorporation of lactate into central carbon metabolism. In the absence of lldD2, label preferentially accumulates in methylglyoxal precursors dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (G3P) and is associated with a discernible growth defect, providing experimental evidence for accumulated lactate toxicity via a methylglyoxal pathway that has been proposed previously. The evolved lldD2 variants increase lactate incorporation to pyruvate but also alter flux in the methylglyoxal pathway, suggesting both an anaplerotic and detoxification benefit to lldD2 evolution. We further show that the mycobacterial cell is transcriptionally sensitive to the changes associated with altered lldD2 activity which affect the expression of genes involved in cell wall lipid metabolism and the ESX-1 virulence system. Together, these data illustrate a multifunctional role of LldD2 that provide context for the selective advantage of lldD2 mutations in adapting to host stress.

microbiology↗