Effect of tauroursodeoxycholic acid on endoplasmic reticulum stress-induced caspase-12 activation

Abstract

Activation of death receptors and mitochondrial damage are well-described common apoptotic pathways. Recently, a novel pathway via endoplasmic reticulum (ER) stress has been reported. We assessed the role of tauroursodeoxycholic acid (TUDCA) in inhibition of caspase-12 activation and its effect on calcium homeostasis in an ER stress-induced model of apoptosis. The human liver-derived cell line, Huh7, was treated with thapsigargin (TG) to induce ER stress. Typical morphologic changes of ER stress preceded development of apoptotic changes, including DNA fragmentation and cleavage of poly (adenosine diphosphateribose) polymerase (PARP), as well as activation of caspase-3 and -7. Elevation of intracellular calcium levels without loss of mitochondrial membrane potential (MMP) was shown using Fluo-3/Fura-red labeling and flow cytometry, and confirmed by induction of Bip/GRP78, a calcium-dependent chaperon of ER lumen. These changes were accompanied by procaspase-12 processing. TUDCA abolished TG-induced markers of ER stress; reduced calcium efflux, induction of Bip/GRP78, and caspase-12 activation; and subsequently inhibited activation of effector caspases and apoptosis. In conclusion, we propose that mitochondria play a secondary role in ER-mediated apoptosis and that TUDCA prevents apoptosis by blocking a calcium-mediated apoptotic pathway as well as caspase-12 activation. This novel mechanism of TUDCA action suggests new intervention methods for ER stress-induced liver disease. (HEPATOLOGY 2002;36:592-601.)

Tauroursodeoxycholic acid reduces apoptosis and protects against neurological injury after acute hemorrhagic stroke in rats

“…Membrane stability inhibits cytochrome c release, thereby reducing downstream events such as caspase activation and substrate cleavage (43). In addition, TUDCA can inhibit endoplasmic reticulum stress-induced cell death by blocking a calciummediated apoptotic pathway (44).…”

Molecular mechanisms of apoptosis in the liver of rats after portal branch ligation with and without retrorsine

“…Schematically, three main initiation pathways leading to the activation of effector proteases called caspases are found in the liver: 11,12,21 the first one involves activation of death receptors, the second one is triggered by mitochondrial dysfunction and the last one by endoplasmic reticulum stress.…”

“…Retrorsine was dissolved in HCl (pH 2.5) followed by neutralization by NaOH 0.1 N, as described. 14,15 At 4 weeks after the second injection, PBL was performed as described 3 and four to eight animals per group were killed at 0, 30 min, 3,5,12,24,48,72 and 168 h after PBL. Livers were excised and samples of anterior and posterior lobes were immersed in 4% buffered formaldehyde for histological and immunohistochemical analysis.…”

“…The death receptor-mediated pathway leads to caspase 8 activation. The mitochondrial dysfunction-mediated pathway, through cytochrome c release into the cytosol, and the endoplasmic reticulum stress-triggered pathway, through caspase 12 activation, 11,12 both lead to caspase 9 activation.…”

Caspase-12: an overview

“…Nevertheless, many of the different reports on the ER localization of caspase-12 and on the molecular mechanisms of its activation during ER-stress-induced apoptosis have been proposed on the basis of studies in human cells and cell lines. 10,[21][22][23][24][25][26] A biocomputational analysis of the human genome reveals that the human caspase-12 gene on chromosome 11q22.3 has acquired several nonsense mutations, leading to a premature translational stop or to a loss-offunction mutation (Figure 1b). The premature stop may lead to the production of a CARD-only protein 27 (and Lamkanfi et al, unpublished results).…”