Inhibition of microtubule function prevents hypoxia-induced glycolysis

Abstract

In normoxic conditions where oxygen supply exceeds demand, mammalian cells produce 38 molecules of adenosine triphosphate (ATP) per molecule of glucose through cellular respiration which is primarily oxygen-dependent. In hypoxia where oxygen demand exceeds supply, the cell enters a bioenergetic crisis due to the decrease in oxygen-dependent ATP synthesis. The cell relies on overcoming this deficiency in ATP through upregulation of glycolytic gene expression via the hypoxia inducible factor 1-a (HIF-1a). However, it is highly unlikely, if not impossible, that the bioenergetic requirements of the hypoxic cell depend solely on the increased expression of glycolytic enzymes distributed randomly in the cytoplasm. We have recently shown that in response to hypoxia, glycolytic enzymes coalesce to form a glycolytic metabolon to effciently increase ATP production in response to this metabolic challenge (Kierans SJ, et al., 2023). While the function of this metabolon has been characterised, the mechanisms underpinning formation, scaffolding, and intracellular distribution remains poorly understood. Here we investigate the possible role of the cytoskeleton as a scaffold or transport system. Microtubules are a primary method of intracellular transport and may alter the energy distribution strategies of cells in bioenergetic crisis. It is hypothesized that the microtubular network transports glycolytic enzymes and/or facilitates increased glycolytic ATP production by promoting metabolon formation to induce glycolysis in hypoxia. Through western blots, it was successfully shown that upon exposure to 1% oxygen, caco2 intestinal epithelial cells induce a robust hypoxic response by stabilising HIF-1a. To investigate the role of the microtubules, two microtubule inhibitors were used: nocodazole, a microtubule assembly and disassembly inhibitor and dynarrestin, a dynein-1 motor transport protein inhibitor. Non-toxic concentrations of nocodazole and dynarrestin were determined using cell viability assays (trypan blue and resazurin assays). Upon exposure to 24 hours of hypoxia, caco2 cells elicit a statistically significant increase in intracellular lactate (185.9% ± 7.5% SEM, n = 3), which was then supressed when treated with nocodazole or dynarrestin (20.6% ± 10.2% SEM and 74.9% ± 8.87 SEM respectively, n = 3). These results thus implicate a role for the transport and structural capabilities of the microtubules in hypoxia-induced glycolysis. Kierans, S. J., Fagundes, R. R., Malkov, M. I., Sparkes, R., Dillon, E. T., Smolenski, A.,... & Taylor, C. T. (2023). Hypoxia induces a glycolytic complex in intestinal epithelial cells independent of HIF-1-driven glycolytic gene expression. Proceedings of the National Academy of Sciences, 120(35), e2208117120. University College Dublin, School of Medicine. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.