Colony Stimulating Factor-Induced Metabolic Changes Contribute to AM Proliferation via Akt/mTOR Pathway
Year: 2021
Type: conference-abstract
Abstract: Rationale: Alveolar macrophages (AMs), the resident phagocytic cells within the lung, are essential for maintenance of lung homeostasis. While at baseline AMs are metabolically quiescent and exhibit low levels of proliferation, alterations in AM numbers and/or metabolic capacities have been described and implicated in certain pulmonary disease states. Granulocyte macrophage colony stimulating factor (GM-CSF, or GM) and macrophage colony stimulating factor (M-CSF, or M) both exhibit mitogenic capacity for AMs. These CSFs also alter AM metabolism, yet a role for metabolism in AM proliferation has not been established. In this study, we examined mechanisms by which CSFs alter AM metabolism and how they contribute to AM proliferation. Methods: Primary AMs were obtained by lung lavage of C57BL/6 mice. AMs were stimulated with GM or M under glucose-sufficient or -deficient (i.e., galactose-containing) culture conditions. In vitro proliferation over 5 days was measured using an S3 Incucyte analyzer, and expression of cell cycle genes was determined by qRT-PCR. Expression of the glucose metabolism-associated genes glucose transporter 1 (Glut1) and phospho-fructokinase p (Pkfp) were likewise determined by qRT-PCR. CSF-induced AM glycolytic activity was determined by lactic acid assay. CSFinduced global gene expression was determined by RNA-seq. Activation of Akt was determined by Western blot for phospho-Akt, and pharmacologic inhibitors of Akt or mTOR were also employed. Results: Proliferation of AMs in response to GM or M was significantly attenuated when glycolytic activity was reduced via culture in galactosecontaining medium. However, only GM was capable of stimulating AM glycolytic activity, as evidenced by increased lactic acid production and increased expression of Glut1 and Pfkp. RNA-seq analysis revealed approximately 3,000 differentially expressed genes between GM-and M-stimulated AMs, including genes highly enriched for cell cycle, PI3K pathway and metabolism. Finally, stimulation with both GM and M resulted in phosphorylation and activation of Akt, and inhibition of both Akt and mTOR attenuated GM and M-induced proliferation and cell cycle gene expression. Conclusion: Our data reveal that GM, but not M, is capable of enhancing glycolytic activity in AMs, yet both GM and M require glucose to enhance proliferation in AMs. Additionally, both GM and M depend on Akt/mTOR signaling for their mitogenic activity. Overall, while glycolysis is necessary for AM proliferation, GM and M utilize glycolytic pathways differently. Further studies are required to better understand how these two mitogens program AMs for proliferation and engage distinct metabolic pathways to do so.
Institution: University of Michigan
Language: English
Topic: Immune cells in cancer
Subfield: Immunology
Field: Immunology and Microbiology
Domain: Life Sciences
Open Access status: bronze
OpenAlex ID: W4240929892