Abstract
Purpose :
Myoepithelial cells (MECs) are an unique cell type known for its combined epithelial and smooth muscle phenotypes that are important components for their functions. They surround glandular secretory acini, express α-smooth muscle actin (SMA) and have a contractile function. Since acini contraction in the LG leads to tear release, it is important to evaluate function of MEC during aging and inflammation.
Methods :
The tamoxifen inducible SMA-CreErt2:Rosa26-Confetti, SMA-CreErt2:Rosa26-Tomato and TSP1-/-:SMA-CreErt2;Rosa26-Tomato (aqueous deficiency dry eye model) mice were used to study MEC function. MEC contraction and [Ca2+]i were determined using multiphoton microscopy. Gene and protein expression was studied by real-time RT PCR, and immunohistochemistry. The role of MECs in LG function was analyzed in vivo by genetic MEC lineage ablation.
Results :
We report that in adult mice MEC cell lineage contains slow proliferating long-lived MEC progenitors that upon LG injury could restore MEC and acinar compartments. The multiphoton imaging of acinar and MEC contraction and intracellular [Ca2+]i in whole LGs showed that acini contraction is driven by MECs. Using the TSP1−/− mouse strains we showed that acini contraction and [Ca2+]i signaling in response to oxytocin or ionomycin stimulation were substantially diminished in these mice. Similar to chronically inflamed LGs, contractile function of MECs becomes impaired in the process of aging, starting around 8-10 months of age. To better understand the role of MECs in LG function we performed MEC ablation using the SMACreErt2:TdTomato/DTA mouse. In this model, diphtheria toxin (DT) production is induced by tamoxifen administration in cells expressing SMA. The number of MECs was dramatically reduced in these mice upon tamoxifen administration compared to control mice. The remaining rare MEC had retracted cell processes and were no longer connected with each other. Moreover, in the control LGs a water channel protein aquaporin 5 (Aqp5) was localized on the apical membrane of acinar cells, whereas in the LGs with eliminated MECs it became rather diffused, suggesting loss of acinar cell polarity after MEC ablation. Ablation of MECs also perturbed acini contraction in response to oxytocin stimulation.
Conclusions :
Our study suggests that MECs are required for LG function and repair. Aging and inflammation substantially reduce MEC function and therefore tears discharge.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.