Effect of SEPT6 on the biological behavior of hepatic stellate cells and liver fibrosis in rats and its mechanism

Abstract

Hepatic stellate cells (HSCs) are key effectors during the development of liver fibrosis. Septin 6 (SEPT6) is a highly evolutionarily conserved GTP-binding protein that regulates various cell biological behaviors. The expression and function of SEPT6 in HSCs remain unknown. Here we demonstrate that SEPT6 expression is significantly elevated following the activation of primary rat HSCs, the human hepatic stellate cell line LX-2 and the rat hepatic stellate cell line HSC-T6, as well as in both human and rat fibrotic liver tissue. In vitro, the overexpression of SEPT6 promoted HSCs activation, proliferation, cell cycle progression and migration and inhibited HSCs apoptosis. In contrast, knockdown of SEPT6 exerted the opposite effects on HSCs. Mechanistically, SEPT6 exerted its pro-fibrogenic effect by promoting the expression of TGF-β1 and the phosphorylation of Smad2, Smad3, extracellular-signal-regulated kinase, c-Jun NH2-terminal kinase, stress-activated protein kinase-2, and protein kinase B. However, in HSC-T6 cells, blockade of the TGF-β1/Smad signaling pathway by SB431542 significantly decreased the expression of α-smooth muscle actin, cyclin D1, BCL2, and matrix metalloproteinase-2 and-9, which had been enhanced by SEPT6 overexpression. In vivo, adenovirus-mediated SEPT6 inhibition attenuated thioacetamide (TAA)-induced liver fibrosis in rats by decreasing the deposition of the extracellular matrix (ECM). SEPT6 inhibition decreased the proliferation capacity of HSCs and induced apoptosis of HSCs. Collectively, our results reveal that SEPT6 regulates various biological behaviors in HSCs through TGF-β1/Smad, mitogen-activated protein kinases and phosphatidylinositol-3-kinase/protein kinase B signaling pathways, thus promoting liver fibrosis.

Novel Functions of the Septin Cytoskeleton

“…91 SEPT4 and SEPT6 were also found up-regulated in different rodent models of liver fibrosis, where they were associated with hepatic stellate cells (HSC). 90,104 However, given a recent report that shows down-regulation of SEPT9 expression in carbon tetrachlorideeinduced liver fibrosis, septin expression could be a subject of more complex regulation in fibrotic tissues. 105 Functional effects of selected septins on fibrogenesis were examined in a limited number of studies that utilized knockout mice models and adenovirus-mediated manipulation of septin expression in vivo.…”

“…32,106 In contrast to the reported antifibrotic functions of SEPT4, a recent study describes a profibrotic activity of SEPT6. 90 Indeed, shRNA-mediated depletion of SEPT6 in vivo attenuates thioacetamideinduced hepatic fibrosis in rats by inhibiting HSC activation and decreasing the excessive extracellular matrix deposition seen in fibrosis. 90 Finally, SEPT8-null mice do not show any differences in the development of kidney fibrosis as compared with wild-type controls, thereby suggesting dispensability of SEPT8 in this disease model.…”

“…90 Indeed, shRNA-mediated depletion of SEPT6 in vivo attenuates thioacetamideinduced hepatic fibrosis in rats by inhibiting HSC activation and decreasing the excessive extracellular matrix deposition seen in fibrosis. 90 Finally, SEPT8-null mice do not show any differences in the development of kidney fibrosis as compared with wild-type controls, thereby suggesting dispensability of SEPT8 in this disease model. 91 At present, it is unclear whether the conflicting evidence reflects peculiar roles of different members of the septin family in fibrosis, or tissue-specific effects of the septin cytoskeleton on fibrogenesis.…”

“…On a cellular level, septin-dependent regulation of tissue fibrosis is likely linked to the central profibrotic signaling pathway involving TGF-b. TGF-b is known to modulate septin expression and localization by up-regulating SEPT6 90,107 and down-regulating SEPT9 levels in the liver, 105 as well as triggering nuclear translocation of SEPT4/ ARTS in epithelial cells. 32 Septins themselves could act as positive regulators of TGF-b signaling by stimulating expression of this growth factor and promoting TGFbedriven Smad signaling, as was shown for SEPT6 and SEPT9 actions in HSC 90 and glioma cells, 108 respectively.…”

Tugging at the Heart Strings: The Septin Cytoskeleton in Heart Development and Disease

“…Together, these data provide insights into a septin-2 mediated anti-fibrotic response. On the other hand, septin-6 (SEPT6) promoted liver fibrosis through TGF-beta and MAP-kinase pathways [71]. It is unknown whether the other 10 septin proteins are involved in fibrosis.…”