Postdoc University of Groningen Groningen, Groningen, Netherlands
Abstract: Sjögren’s disease (SjD) is an autoimmune disease that involves the salivary glands amongst other tissues. Several different cell types together form the salivary gland tissue, including acinar cells, the luminal duct cells, and basal duct cells. In SjD, the function of the salivary glands is severely affected, which leads to symptoms ranging from dry mouth and swallowing problems to tooth decay and chronic inflammation. SjD is characterized by lymphocytic infiltration into the gland, predominantly around the ductal system, which is caused by triggers that are still unknown.1 The interplay between the ductal cells of the salivary gland and immune cells is crucial in the pathogenesis and disease progression. Therefore, novel disease models are necessary in which the interaction between the different cells of the salivary gland and immune cells can be studied together at the microscale. In this work, we present the development of a ‘healthy’ salivary gland that can be used to induce SjD at a later stage.
We have chosen to use an organ-on-a-chip2 approach, in which the patient-derived primary cells of the salivary gland are cultured inside microchannels.3 There were several challenges working with this particular organ-on-a-chip: 1) These primary gland cells grow and proliferate slowly; 2) the number of cells derived from biopsies is very low; and 3) it is not known which levels of shear stress are suited for these cells in vivo or in vitro. We have cultured biopsy-derived cells for up to 19 days in 10-mm-long microchannels of 360 µm width and 100 µm depth.4 Medium was continuously supplied by a syringe pump, at a relatively low target shear stress of 0.07 dyn/cm2 (or 10 µL/h). After 19 days, which is long due to the slow growing of cells, the cells were fixed with formaldehyde and stained for cytokeratin-7 (a marker for luminal duct cells) and cytokeratin-14 (a marker for basal duct cells). Our results show that 1) the cells in the microchannel were still alive after 19 days of incubation, indicated by calcein AM/propidium iodide staining. 2) While cell numbers were low initially, we studied the cells in the microchannel daily using microscopy and they proliferated slowly over time. Unexpectedly, cells had differentiated from their initial phenotype (basal duct) to become predominantly luminal duct cells, for reasons beyond our current understanding. One possible explanation may be that the shear stress inside the microchannels induced phenotypic changes. As to 3), the effects of different shear stress levels are now under investigation, using different combinations of geometries and flow rates to test this hypothesis. After establishing the conditions for this salivary gland on a chip in healthy conditions, we will induce disease to be able to study the cell-cell interactions of Sjögren’s disease.
[1] Verstappen, 2021, https://doi.org/10.1038/s41584-021-00605-2. [2] Leung, de Haan, 2022, https://doi.org/10.1038/s43586-022-00118-6. [3] Pringle, 2019, https://doi.org/10.1002/art.40659. [4] Grajewski. PhD thesis, University of Groningen, 2018.
