Kinetin inhibits hepatic stellate cell activation and induces apoptosis via interactions with the TGF-ß1/Smad signaling pathway.

Hepatic fibrosis is the pathological repair response of the liver to chronic injury; hepatic stellate cell (HSC) activation is the central link in the pathogenesis of hepatic fibrosis. Previously, we showed that kinetin, a plant cytokinin hormone, has a protective effect on CCl4-induced liver injury in mice. However, the role of kinetin in liver fibrosis remains unclear. We aimed to study these protective effects and to determine the mechanisms by which kinetin mediates HSC activation and apoptosis. For this purpose, the human HSC line LX-2 was treated with 10 ng/ml transforming growth factor-ß1 (TGF-ß1) for 24 h to stimulate activation. We found that treatment with kinetin at the sub-cytotoxic dose of 40 µg/ml for 48 h reduced the expression of the HSC activation marker α-SMA and inhibited the secretion of extracellular matrix proteins. In addition, kinetin was found to inhibit the proliferation and migration of LX-2 cells. We found that kinetin induced apoptosis in LX-2 cells by increasing the level of cleaved-caspase 3 and the Bax-to-Bcl-2 ratio. Interestingly, these effect were not observed in quiescent HSCs, suggesting that they are activation-dependent. Further study showed that kinetin attenuates activation and promotes apoptosis of LX-2 cells in vitro in part by suppressing the TGF-ß1/Smad signaling pathway.

Intraflagellar transport 20 cilia-dependent and cilia-independent signaling pathways in cell development and tissue homeostasis.

Intraflagellar transport (IFT) is an essential condition for ciliogenesis. The primary cilia protrude like antennae and act as chemical or mechanical sensory organelles that coordinate specific receptor localization and signal transduction. IFT20 is the smallest molecule in IFT complex B, which is located in both the cilia and the Golgi complex. Recent studies have shown that IFT20 is a key molecule in multiple signaling pathways. Importantly, in the function of IFT20, signal transduction is not restricted to cilia, but is also involved in non-ciliary functions. Here we summarize current knowledge regarding IFT20-mediated signaling pathways and their relationship with cell development and tissue homeostasis, and analyse the cilia-dependent and cilia-independent mechanisms of IFT20 coordinated signaling pathways and potential crosstalk between the mechanisms. This review provides a comprehensive perspective on IFT20 coordinates signaling mechanisms in cell development and tissue homeostasis.