DeVilbiss, A. | bioRxiv Science

bioRxiv2026

ACC1-Dependent De Novo Lipogenesis Sustains Hematopoietic Stem Cell Quiescence and Self-Renewal

Certain aspects of lipid metabolism are known to regulate hematopoietic stem cell (HSC) function, including fatty acid oxidation and lipid uptake, but there is a limited understanding of the contribution of de novo fatty acid synthesis to HSC homeostasis. Here, we show that endogenous fatty acid synthesis is essential for HSC function. Conditional deletion of Acaca, the gene that encodes the rate-limiting enzyme for de novo fatty acid synthesis, acetyl-CoA carboxylase 1 (ACC1), in hematopoietic cells profoundly reduces HSC function, marked by a reduced ability to reconstitute irradiated mice after competitive transplantation. ACC1 deficiency reduced quiescence, increased uptake of extracellular lipids, and increased reactive oxygen species in HSCs. The loss of HSC function is partly caused by increased fatty acid oxidation as deletion of CPT1a, which is required for long-chain fatty acid oxidation, partially rescued HSC function. A balance between fatty acid synthesis and fatty acid oxidation is thus critical for the maintenance of HSC function.

cell biology↗

bioRxiv2021

Adenylate Kinase 2 deficiency causes NAD+ depletion and impaired purine metabolism during myelopoiesis

Reticular Dysgenesis is a particularly grave form of severe combined immunodeficiency that affects the adaptive and innate immune system. Patients suffer from congenital neutropenia, lymphopenia, and deafness. The disease is caused by biallelic loss of function in mitochondrial Adenylate Kinase 2 (AK2). AK2 mediates the phosphorylation of AMP to ADP, as substrate for ATP synthesis. Accordingly, declining oxidative phosphorylation has been postulated as the driver of disease pathology. The mechanistic basis, however, remains incompletely understood. Single cell RNA-sequencing of patient bone marrow cells implicated altered RNA catabolism and ribonucleoprotein synthesis in the pathogenesis of Reticular Dysgenesis. To investigate these findings, we developed a disease model based on CRISPR-mediated disruption of the AK2 gene in primary human hematopoietic stem cells. We found that AK2-deficient myeloid progenitor cells not only have compromised mitochondrial energy metabolism and increased AMP levels, but also NAD+ and aspartate depletion, metabolites that rely on TCA-cycle activity for regeneration and synthesis. Furthermore, AK2-deficient cells exhibited strikingly increased levels of the purine nucleotide precursor IMP, decreased cellular RNA content, ribosome subunit expression, protein synthesis and a profoundly hypo-proliferative phenotype. The rise in IMP levels stemmed from increased AMP deamination. Pharmacologic inhibition of AMP deaminase normalized IMP levels in AK2-deficient cells, but further aggravated the disease phenotype, pointing to AMP catabolism as a possible metabolic adaptation to mitigate AMP-mediated toxicity. Inducing an adenosine disequilibrium in control cells produced a similar myeloid maturation defect. This study shows that AK2 deficiency globally curtailed mitochondrial metabolism resulting in NAD+ and aspartate deficiency and disordered purine metabolism. AMP accumulation and its detrimental effects on ribonucleotide synthesis capacity may contribute to the failure of myelopoiesis in Reticular Dysgenesis.

cell biology↗