Introduction: The recent development of new technologies such as single cell RNA sequencing (scRNAseq) has enabled identification of the mRNA transcripts expressed by single cells of many tissues including the airway. We analysed recent scRNAseq studies to investigate the expression of facilitative glucose transporters (GLUTs) and sodium coupled glucose transporters (SGLTs) in the epithelial cells of the airway epithelium from trachea to alveolus.

Methods: We used six studies that reported single cell data for the human airway for interrogation based on the basis of the data availability, the lung cell types included and the range glucose transporters reported (even if not detected) (1-6). The number of cells in a cluster in which RNA transcripts were detected (frequency, normally expressed as %) and the number of RNA transcripts recorded per cell (transcripts per million) were obtained.

Results: Not all studies reported the full range of transporters. Glucose transporter mRNA transcripts were expressed at lower levels than other epithelial marker genes and there were differences between cells freshly isolated from the airways and those grown in vitro. Nevertheless, these studies highlighted that there were differences in cellular expression of GLUTs and SGLTs.  GLUT1 was the most abundant of the broadly expressed transporters that included GLUT8, 10 and 13. GLUT9 transcripts were more common in basal cells and GLUT12 in ionocytes and ciliated cells.  SGLT1 transcripts were present in alveolar and secretory cells. GLUT3 mRNA transcripts were expressed in a cell cluster that expressed monocarboxylate (MCT2) transporters.

Conclusions: The differences in cellular transporter expression potentially underlie cell specific metabolic requirements to support proliferation, ion transport, mucous secretion, environment sensing and airway glucose homeostasis.  These studies also highlighted the role of glucose transporters in the movement of dehydroascorbic acid/vitamin C, myoinositol and urate which are factors important to the innate immune properties of the airways. Discrepancies in the reported detection of mRNAs, protein and function of glucose transporters in the lungs remains. Nevertheless, understanding which glucose transporters are present in the lung, their cellular location and how they change in respiratory disease will provide further insights into the function of airway cells and their contribution to cancer progression, the regulation of ASL glucose homeostasis and innate defence against infection.