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ATRA, a retinoic acid isomer and the active metabolite of vitamin A, is known to restore the quiescent phenotype in PSCs as well as reduce concomitant ECM synthesis and pancreatic cancer cell invasion.It was recently shown to down-regulate cellular stiffness, contractility, and ECM remodelling by PSCs (unpublished data).Transforming growth factor β (TGF-β) is a potent activator of PSCs, and its activation requires spatiotemporal organisation of cellular and extracellular cues to liberate it from an inactive complex with latent TGF-β binding protein (LTBP).Here we study the mechanical activation of TGF-β by PSCs in vitro by investigating LTBP-1 organisation with fibrillar fibronectin and show that all trans-retinoic acid (ATRA), which induces PSC quiescence, down-regulates the ability of PSCs to mechanically organise LTBP-1 and activate TGF-β through a mechanism involving myosin II dependent contractility.
(b) Immunostaining images of non-targeting si RNA or fibronectin m RNA targeting si RNA treated control PSCs show that in the absence of fibronectin, LTBP-1 fibril alignment is significantly down-regulated.
As a result of fibronectin knockdown, LTBP-1/fibronectin co-localisation and fibril thickness were significantly decreased (Fig. Similarly, ATRA reduces expression of cell contractility marker vimentin in PSCs seeded on LTBP-1 rich matrices (Fig. Therefore, to understand the association between PSC contractility and LTBP-1 organisation in our system, control or ATRA treated PSCs were seeded on LTBP-1 rich matrices as previous.
PSCs were incubated for 16 hours to allow cell attachment and spreading after which, 20 μM blebbistatin (BBI), which blocks myosin II ATPase activity Fibronectin/LTBP-1 co-localisation and fibril density analysis of immunofluorescent images of BBI or DMSO only treatment of PSCs showed a significant difference between control and ATRA group in vehicle control condition; however, under BBI treatment control and ATRA groups establish similar fibronectin/LTBP-1 co-localisation levels and fibre thickness.
Interaction between LTBP-1 and fibronectin is analysed after 2 days of culture by immunofluorescent co-localisation.
(b) Colocalisation of LTBP-1 (red) and fibronectin (green) as a result of 10-day treated ATRA (1 μM) PSCs or control PSC incubation.