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Non-alcoholic fatty liver disease (NAFLD) is a significant public health concern, owing to its high prevalence, progressive nature and lack of effectivemedical therapies. NAFLD is a complex and multifactorial disease involving the progressive and concerted action of factors that contribute to the development of liver inflammation and eventually fibrosis. Here, we summarize fundamental molecular mechanisms underlying the pathogenesis of non-alcoholic steatohepatitis (NASH), how they are interrelated and possible translation to clinical applications. We focus on processes triggering and exacerbating apoptotic signalling in the liver of NAFLD patients and their metabolic and pathological implications. Indeed, liver injury and inflammation are cardinal histopathological features of NASH, a duo in which derailment of apoptosis is of paramount importance. In turn, the liver houses a very high number of mitochondria, crucial metabolic unifiers of both extrinsic and intrinsic signals that converge in apoptosis activation. The role of lifestyle options is also dissected, highlighting the management of modifiable risk factors, such as obesity and harmful alcohol consumption, influencing apoptosis signalling in the liver and ultimately NAFLD progression. Integrating NAFLD-associated pathologic mechanisms in the cell death context could provide clues for a more profound understating of the disease and pave the way for novel rational therapies. [ABSTRACT FROM AUTHOR]

p53 plays an important role in regulating expression of genes that mediate cell cycle progression and/or apoptosis. In addition, we have previously shown that the hydrophilic bile acid ursodeoxycholic acid (UDCA) prevents transforming growth factor β1-induced p53 stabilization and apoptosis in primary rat hepatocytes. Therefore, we hypothesized that p53 may represent an important target in bile acid-induced modulation of apoptosis and cell survival. In this study we demonstrated that UDCA reduces p53 transcriptional activity, thereby preventing its ability to induce Bax expression, mitochondrial translocation, cytochrome c release, and apoptosis in primary rat hepatocytes. More importantly, bile acid inhibition of p53-induced apoptosis was associated with decreased p53 DNA binding activity. Subcellular localization of p53 was also altered by UDCA. Both events appear to be related with increased association between p53 and its direct repressor, Mdm-2. In conclusion, these results further clarify the antiapoptotic mechanism of UDCA and suggest that modulation of Mdm-2/p53 interaction is a prime target for this bile acid. [ABSTRACT FROM AUTHOR]

OBJECTIVES: The increasing incidence of nonalcoholic (NASH) and alcoholic steatohepatitis (ASH), associated with lack of effective treatment, has prompted intensive studies on disease pathogenesis. Apoptosis is recognized as common in liver injury and may also contribute to tissue inflammation, fibrogenesis, and development of cirrhosis. In this study, we identified mechanisms of apoptosis induction in human steatohepatitis, and evaluated potential associations between apoptosis, liver pathology, and clinical presentation in NASH and ASH.METHODS: Hepatocyte apoptosis was evaluated by the TUNEL assay in 20 patients with NASH (all ambulatory), 40 with ASH (20 ambulatory, 20 hospitalized), and 20 controls. Liver biopsies were also graded for inflammation and fibrosis. Immunohistochemistry was performed for death receptors (Fas and TNF-R1), activated caspase-3, NF-κB p65, antiapoptotic Bcl-2 protein, and uncoupling protein 2 (UCP-2).RESULTS: TUNEL-positive hepatocytes were markedly increased in NASH (p<0.05) and ASH (p<0.01). Similar results were obtained for activated caspase-3, confirming the occurrence of apoptosis. The Fas receptor was upregulated in ASH, especially in hospitalized patients (p<0.01), whereas TNF-R1 was expressed both in NASH and ASH (p<0.01). In addition, patients with ASH showed a remarkable expression of active NF-κB, as compared to NASH and controls (p<0.01). Degrees of inflammation and fibrosis correlated with NF-κB p65 expression, which in turn coincided with apoptosis albeit Bcl-2 and UCP-2 expression.CONCLUSIONS: Liver injury in NASH and ASH is associated with increased hepatocyte apoptosis mediated by death receptors. Further, apoptosis correlates with active NF-κB expression, and disease severity. This potential mechanistic link might provide multiple interesting targets for therapeutic intervention.(Am J Gastroenterol 2004;99:1708-1717) [ABSTRACT FROM AUTHOR]

Amyloid β-peptide (Aβ)-induced cell death may involve activation of the E2F-1 transcription factor and other cell cycle-related proteins. In previous studies, we have shown that tauroursodeoxycholic acid (TUDCA), an endogenous bile acid, modulates Aβ-induced apoptosis by interfering with crucial events of the mitochondrial pathway. In this study, we examined the role of E2F and p53 activation in the induction of apoptosis by Aβ, and investigated novel molecular targets for TUDCA. The results showed that despite Bcl-2 up-regulation, PC12 neuronal cells underwent significant apoptosis after incubation with the active fragment Aβ (25–35), as assessed by DNA fragmentation, nuclear morphology and caspase-3-like activation. In addition, transcription through the E2F-1 promoter was significantly induced and associated with loss of the retinoblastoma protein. In contrast, levels of E2F-1, p53 and Bax proteins were markedly increased. Overexpression of E2F-1 in PC12 cells was sufficient to induce p53 and Bax proteins, as well as nuclear fragmentation. Notably, TUDCA modulated Aβ-induced apoptosis, E2F-1 induction, p53 stabilization and Bax expression. Further, TUDCA protected PC12 cells against p53- and Bax-dependent apoptosis induced by E2F-1 and p53 overexpression, respectively. In conclusion, the results demonstrate that Aβ-induced apoptosis of PC12 cells proceeds through an E2F-1/p53/Bax pathway, which, in turn, can be specifically inhibited by TUDCA, thus underscoring its potential therapeutic use. [ABSTRACT FROM AUTHOR]

The rTg4510 mouse is a tauopathy model, characterized by massive neurodegeneration in Alzheimer's disease (AD)-relevant cortical and limbic structures, deficits in spatial reference memory, and progression of neurofibrillary tangles (NFT). In this study, we examined the role of apoptosis in neuronal loss and associated tau pathology. The results showed that DNA fragmentation and caspase-3 activation are common in the hippocampus and frontal cortex of young rTg4510 mice. These changes were associated with cleavage of tau into smaller intermediate fragments, which persist with age. Interestingly, active caspase-3 was often co-localized with cleaved tau. In vitro, fibrillar Aβ1-42 resulted in nuclear fragmentation, caspase activation, and caspase-3-induced cleavage of tau. Notably, incubation with the antiapoptotic molecule tauroursodeoxycholic acid abrogated apoptosis-mediated cleavage of tau in rat cortical neurons. In conclusion, caspase-3-cleaved intermediate tau species occurred early in rTg54510 brains and preceded cell loss in Aβ-exposed cultured neurons. These results suggest a potential role of apoptosis in neurodegeneration. [ABSTRACT FROM AUTHOR]

Necroptosis is a highly immunogenic regulated cell death routine that depends on receptor-interacting protein 3 (RIP3) kinase activity. We aimed to evaluate the role of necroptosis in the pathogenesis of nonalcoholic fatty liver disease (NAFLD)-driven carcinogenesis. C57BL/6 wild-type (WT) or RIP3-deficient (RIP3-/-) mice were fed a choline-deficient L-amino acid-defined diet (CDAA; n= 14) or an isocaloric control diet (CSAA; n= 14) diet for 66 weeks. RIP3 deficiency ameliorated CDAA-induced inflammation and fibrosis and decreased the NAFLD activity score. Intriguingly, RIP3-/- mice displayed increased body weight, as well as insulin resistance at 66 weeks. RIP3-/- mice tended to show reduced incidence of macroscopic preneoplasic nodules, accompanied by significantly reduced Ki67 positive hepatocytes. Microarray analysis and subsequent validation studies showed that absence of RIP3 hampered the expression of oncogenes and signaling pathways controlling tumour microenvironment and protected against oxidative stress. Overall, targeting RIP3-dependent signaling might be a promising approach to arrest NAFLD progression to HCC, although complementary approaches may be required to control insulin resistance in obese patients. [ABSTRACT FROM AUTHOR]