Unfolded protein response induced by Brefeldin A increases collagen type I levels in hepatic stellate cells through an IRE1α, p38 MAPK and Smad-dependent pathway

Abstract

Unfolded protein response (UPR) triggered as a consequence of ER stress has been shown to be involved in the development of different pathologies, including fibrotic disorders. In the present paper we explore the role played by UPR on a key fibrogenic parameter in the liver: collagen type I levels in activated hepatic stellate cells (HSC). Using Brefeldin A (BFA) as an ER stress inducer we found that UPR correlated with enhanced mRNA and protein levels of collagen type I in a cell line of immortalized non-tumoral rat HSC. Analysis of the three branches of UPR revealed the activation of IRE1α, PERK and ATF6 in response to BFA, although PERK activation was shown not to be involved in the fibrogenic action of BFA. BFA also activated p38 MAPK in an IRE1α-dependent way and the p38 MAPK inhibitor SB203580 prevented the increase in collagen type I mRNA and protein levels caused by BFA, suggesting the involvement of this kinase on this effect. Analysis of Smad activation showed that phosphorylated nuclear levels of Smad2 and 3 were increased in response to BFA treatment. Inhibition of Smad3 phosphorylation by SIS3 prevented the enhancement of collagen type I levels caused by BFA. Pretreatment with IRE1α and p38 MAPK inhibitors also prevented the increased p-Smad3 accumulation in the nucleus, suggesting an IRE1α-p38 MAPK-Smad pathway to be responsible for the fibrogenic action of BFA on HSC.

Emodin suppresses activation of hepatic stellate cells through p38 mitogen‐activated protein kinase and Smad signaling pathways in vitro

“…Several recent studies have demonstrated that both p38 MAPK and Smad signaling independently and additively regulate α1(I) collagen gene expression by transcriptional activation (de Galarreta et al, ; Tsukada, Westwick, Ikejima, Sato, & Rippe, ). In contrast, other studies have reported TGFβ1 regulation of collagenase expression in osteoblastic cells by cross talk between the Smad and p38 MAPK signaling pathways (Selvamurugan et al, ).…”

Angiotensin II-induced podocyte apoptosis is mediated by endoplasmic reticulum stress/PKC-δ/p38 MAPK pathway activation and trough increased Na+/H+ exchanger isoform 1 activity

“…Although these mechanisms have not been thoroughly explored, previous studies have indicated that the effects of Ang II via AT1R activation on podocyte injury are related to reactive oxygen species (ROS) overproduction mediated by nicotinamide adenine dinucleotide phosphate (NADPH) oxidase [ 16 , 17 ]. In other cell types, ROS production is closely related to ER stress, protein kinase C delta (PKC-δ) and p38 mitogen-activated protein kinase (p38 MAPK) activation, and together, these events are associated with apoptotic responses [ 18 – 21 ].…”

Transforming growth factor β (TGFβ) cross-talk with the unfolded protein response is critical for hepatic stellate cell activation

“…First, IRE1␣ signaling has been implicated in HSC fibrogenic gene expression through both its endonuclease domain and through p38 signaling; however, we find that neither of these mechanisms are critical for HSC activation in our inducible IRE1␣ system or necessary for C/EBP␤ phosphorylation. p38 activation was previously associated with SMAD3 phosphorylation and collagen I expression in response to chemically induced ER stress (11), whereas activation of the transcription factor XBP1 downstream of IRE1␣ endonuclease activity is associated with ER dilation and up-regulation of genes involved in protein trafficking and secretion (5,6,8). Furthermore, we show that overexpression of either the K907A or K599A IRE1␣ mutant still led to up-regulation of total C/EBP␤ expression, implicating a kinase-and endonuclease-independent mechanism of C/EBP␤ regulation.…”

“…Less is known regarding ATF6␣ in HSCs. Inhibition of ATF6␣ reduced HSC activation in response to chemically induced ER stress, but no direct mechanisms for ATF6␣ signaling during HSC activation have been identified (11). Further studies are needed to fully understand the integration of IRE1␣, PERK, and ATF6␣ signaling during HSC activation and how crosstalk between activation signals (such as TGF␤) and UPR signaling influences HSC activation and survival.…”

“…This kinase activity is necessary for activation of its endonuclease domain as well as mediating downstream signaling cascades involving apoptosis-signaling kinase 1 (ASK1) (15)(16)(17)(18)(19). Both the kinase and endonuclease domains of IRE1␣ are associated with HSC activation (5,8,11), but the mechanisms that regulate and propagate IRE1␣ signaling during HSC activation and fibrogenesis are not completely understood.…”