Myoepithelial cells (MECs) are present in many exocrine glands including lacrimal, salivary, harderian, sweat, prostate, and mammary. MECs are a unique cell type that combines an epithelial and a smooth muscle phenotype. MECs express α-smooth muscle actin (SMA) and have a contractile function1,2. In addition to MECs, the lacrimal gland (LG) and the submandibular gland (SMG) contains SMA+ vascular cells called pericytes, which are cells of endodermal origin that envelop the surface of vascular tubes3. Although MECs and pericytes express many markers, SMA is the only marker that is not expressed in other LG and SMG cells1,3.
Within the last 40 years, several laboratories reported assays for dissociation of different exocrine gland tissues, in which non-enzymatic and enzymatic approaches were applied. In one of the first reports published in 1980, Fritz and coauthors described a protocol to isolate feline parotid acini using sequential digestion in a collagenase/trypsin solution4. In 1989, Hann and coauthors adjusted this protocol for acini isolation from rat LGs using a mixture of collagenase, hyaluronidase and DNase5. In 1990, Cripps and colleagues published the method of non-enzymatic dissociation of lacrimal gland acini6. Later, in 1998, Zoukhri and coauthors returned to an enzymatic dissociation protocol for following up Ca2+-imaging on LG and SMG isolated acini7. Within the last decade, researchers have turned their focus on isolation of stem/progenitor cells from exocrine glands. Pringle and coauthors described a protocol in 2011 for isolation of mouse SMG stem cells8. This method was based on isolation of stem cell-containing salispheres, which were maintained in culture. The authors claimed that proliferating cells expressing stem cell-associated markers could be isolated from these salispheres8. Shatos and coauthors published the protocol for progenitor cell isolation from uninjured adult rat LGs using enzymatic digestion and collecting “liberated” cells9. Later, in 2015, Ackermann and coauthors adjusted this procedure to isolate presumptive "murine lacrimal gland stem cells" ("mLGSCs") that could be propagated as a mono-layer culture over multiple passages10. However, none of the before mentioned procedures allowed for distinguishing cellular subtypes and individual populations of isolated epithelial cells. In 2016, Gromova and coauthors published a procedure for isolation of LG stem/progenitor cells from adult murine LGs using FACS11. However, this protocol was not intended to isolate MECs.
Recently, we have shown that we are able to isolate SMA+ cells from 3 week-old SMA-GFP mice12. However, at this time we have not separated different populations of SMA+ cells. Here we established a new procedure for the direct isolation of differentiated MECs and pericytes from adult LGs and SMGs.