Chronic inflammation of the lacrimal gland (LG), as occurs in Sjgren?s syndrome, is the leading cause of aqueous-? deficientdryeyedisease(DED).ThemechanismsleadingtoinsufficientLGsecretionarestillnotcompletelyunderstood. The LG is composed of acinar, myoepithelial, and ductal cells, with acini and myoepithelial cells (MEC) forming the secretory units. MECs express several muscle proteins, such as alpha smooth muscle actin (SMA) and calponin, and are thereforeabletocontract.MECsarebeststudiedinthemammaryglandwheretheircontractionisshowntobecrucial for milk production and contraction is mainly controlled by the neuropeptide oxytocin. Despite their potential critical role in LG secretion, very little is known about MEC contraction in this tissue, nor is the impact of chronic inflammation of the LG on these cells. One of goals of the current proposal is to fill this gap in knowledge. Our preliminary studies show that murine and human LG MECs express the oxytocin receptor (OXTR) and contract in response to oxytocin stimulation. Furthermore, we show that MECs in chronically inflamed LG are atrophied, with down-?regulation of contractile proteins SMA and calponin and the OXTR and MECs from these glands do not contract in response to oxytocinstimulation.Wepreviouslyreportedthatinterleukin-?1(IL-?1)inhibitsneurotransmitterreleasefromLGefferent nerves leading to DED. We also reported activation of the stress activated c-?Jun N-?terminal kinase (JNK) and metalloproteinases 2 (MMP2) in chronically inflamed LGs and that inhibition of either pathway restored LG secretion andtearsoutputinanimalmodelsofDED.Numerousstudiesshowedthatdenervationofmuscletissuesleadstotissue atrophyanddegradationofmusclecontractileproteinsviatheubiquitin/proteasomepathways.Basedonthesefindings, wehypothesizethatinchronicDED,proinflammatorycytokinesinhibitneurotransmitterreleasefromLGefferentnerves creating a denervated-?like tissue and that they trigger degradation of the OXTR and MEC myofilament proteins. This degradation translates into a loss of contractibility of MECs thus further exacerbating the effect of the loss of neural inputonthesecretoryunitsoftheLG.WefurtherhypothesizethattheJNK,MMP2,andubiquitin/proteasomepathways mediate the effects of proinflammatory cytokines on MEC functions. We will use both in vitro (sorted MEC cells) as well as animal models of DED to investigate how proinflammatory cytokines interfere with oxytocin-?induced contraction of LGMECs.WewilluseunbiasedRNA-?seqandquantitativeglobalproteomicstechniquestoidentifynovelpathwaysthat are altered in MECs in chronically inflamed LGs. At the completion of these studies, we will have established a role for the MEC, an important and yet understudied cell in the LG, and the oxytocin signaling system in the pathogenesis of aqueous-?deficientDEDandidentifiedpotentialnoveltherapeutictargets.
Chronic inflammation of the lacrimal gland as occurs in autoimmune dry eye disease, lead to loss of the moisture producing cells and decreased tear production. In the lacrimal gland, one type of cells, the myoepithelial cells that are known to be important in other secreting tissues, such the mammary gland, are understudied. The proposal will study the role of myoepithelial cells in health and disease and unravel new strategies to restore lacrimal gland secretion and adequate aqueous tear production.
