Abstract
Mesenchymal stem cells (MSCs) play important roles in tissue repair and cancer progression. Our recent work suggests that some mesenchymal cells, notably myofibroblasts exhibit regulated exocytosis resembling that seen in neuroendocrine cells. We now report that MSCs also exhibit regulated exocytosis. Both a G-protein coupled receptor agonist, chemerin, and a receptor tyrosine kinase stimulant, IGF-II, evoked rapid increases in secretion of a marker protein, TGFβig-h3. The calcium ionophore, ionomycin, also rapidly increased secretion of TGFβig-h3 while inhibitors of translation (cycloheximide) or secretory protein transport (brefeldin A) had no effect, indicating secretion from preformed secretory vesicles. Inhibitors of the chemerin and IGF receptors specifically reduced the secretory response. Confocal microscopy of MSCs loaded with Fluo-4 revealed chemerin and IGF-II triggered intracellular Ca2+ oscillations requiring extracellular calcium. Immunocytochemistry showed co-localisation of TGFβig-h3 and MMP-2 to secretory vesicles, and transmission electron-microscopy showed dense-core secretory vesicles in proximity to the Golgi apparatus. Proteomic studies on the MSC secretome identified 64 proteins including TGFβig-h3 and MMP-2 that exhibited increased secretion in response to IGF-II treatment for 30min and western blot of selected proteins confirmed these data. Gene ontology analysis of proteins exhibiting regulated secretion indicated functions primarily associated with cell adhesion and in bioassays chemerin increased adhesion of MSCs and adhesion, proliferation and migration of myofibroblasts. Thus, MSCs exhibit regulated exocytosis that is compatible with an early role in tissue remodelling.
Highlights
The recruitment by peripheral tissues of bone marrow derived mesenchymal stem cells (MSCs) is a crucial component in tissue responses to damage, inflammation and progression to cancer [1,2,3]
We report that insulin-like growth factor (IGF) and chemerin stimulate calcium-dependent release of a range of proteins from preformed secretory vesicles in MSCs, that they stimulate increased intracellular calcium albeit with different timecourses, and that increased secretion leads to an altered microenvironment capable of changing adhesion of MSC themselves and adhesion and migration of other cell types
The calcium ionophore, ionomycin, stimulated TGFβig-h3 secretion from MSCs that was comparable to that IGF-I and IGF-II indicative of a response via Ca2+ dependent exocytosis (Fig 1C), while the response to IGF-II was attenuated in the absence of extracellular calcium (Fig 1D)
Summary
The recruitment by peripheral tissues of bone marrow derived mesenchymal stem cells (MSCs) is a crucial component in tissue responses to damage, inflammation and progression to cancer [1,2,3]. The tissue microenvironment in turn provides the conditions required for differentiation of MSCs into different cell types. All cells possess the capacity for secretion, and the secretomes of MSCs have attracted increasing attention [10,11,12,13]. Endocrine and exocrine cells can occur via either the constitutive pathway or the regulated pathway where exocytosis of storage (usually dense cored) vesicles occurs in response to secretagogues following an increase in intracellular calcium [14,15]. In other cell types including mesenchymal cells, protein secretion is often considered to be constitutive, it is recognised that there is capacity for regulated secretion in these cells [16]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
