Cyclic AMP-guanine exchange factor activation inhibits JNK-dependent lipopolysaccharide-induced apoptosis in rat hepatocytes

The effects of ursodeoxycholic acid on sepsis-induced cholestasis management in an animal model

Objectives

Cholestasis refers to a reduction in bile flow from the liver into the biliary system. Ursodeoxycholic acid (UDCA) is commonly used for the treatment of hepatic cholestasis. This study aimed to explore the role of UDCA in the treatment and prevention of lipopolysaccharide (LPS)-induced cholestasis.

Methods

Sixty male albino rats were randomly classified into five groups of 12 rats each: the control group (received saline and water), UDCA group (received UDCA), LPS group (received LPS), treatment group (received LPS followed by UDCA), and prevention group (received UDCA followed by LPS). Changes in gamma-glutamyl transferase (GGT), plasma aspartate transferase (AST), plasma alkaline transferase (ALT), plasma alkaline phosphatase (ALP), total bilirubin (TBIL), hepatocyte apoptosis, immunomodulatory activity, plasma pro-inflammatory cytokines (TNF-α, IL-1α, and IL-4), and liver histology were assessed.

Results

UDCA improved serum liver chemical markers (GGT, ALP, and AST) in both the prevention and treatment groups (p < 0.05 and p < 0.05, respectively). CD3 count was higher in the UDCA treatment group compared to the LPS group (p < 0.001). UDCA caused a reduction in plasma TNF-α in the prevention group (P < 0.05); however, it had no effect on the treatment group, as compared to the LPS group. Similarly, UDCA had no effect on IL-1α or IL-4. UDCA treatment resulted in improved liver histological features and a significant reduction in liver tissue apoptosis in both the treatment and prevention groups, as compared to the LPS group (p = 0.013 and p = 0.002, respectively).

Conclusions

This study provides evidence of the effectiveness of UDCA for the treatment and prevention of sepsis-induced cholestasis.

Hepatic expression of lipopolysaccharide-binding protein (Lbp) is induced by the gut microbiota through Myd88 and impairs glucose tolerance in mice independent of obesity

Objective

Gut-derived inflammatory factors can impair glucose homeostasis, but the underlying mechanisms are not fully understood. In this study, we investigated how hepatic gene expression is regulated by gut colonization status through myeloid differentiation primary response 88 (MYD88) and how one of the regulated genes, lipopolysaccharide-binding protein (Lbp), affects insulin signaling and systemic glucose homeostasis.

Methods

Liver transcriptomics analysis was conducted on four groups of mice fed a chow diet: conventionally raised (CONV-R) wild-type, germ-free (GF) wild-type, CONV-R Myd88 KO, and GF Myd88 KO. Primary hepatocytes were exposed to combinations of lipopolysaccharide (LPS), LBP, and the LBP-blocking peptide LBPK95A, and the effect on insulin signaling was determined. To assess how LBP affects glucose metabolism in vivo, two mouse models were applied: treatment with LBPK95A and hepatic knockdown of Lbp using CRISPR-CAS9.

Results

We showed that the colonization status regulates gene expression in the liver and that a subset of these genes, including Lbp, is regulated through MYD88. Furthermore, we demonstrated that LBP impairs insulin signaling in hepatocytes in the presence of low levels of LPS and that the effect of LBP is abolished by LBPK95A. We showed that both systemic pharmacological blocking of LBP by LBPK95A and CRISPR-CAS9-mediated downregulation of hepatic Lbp improve glucose homeostasis.

Conclusions

Our results demonstrate that the gut microbiota regulates hepatic expression of Lbp through MYD88-dependent signaling. LBP potentiates LPS inhibition of insulin signaling in vitro and impairs systemic glucose homeostasis in vivo.

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Gut microbiota induces hepatic expression of Lbp through MYD88.

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LBP impairs insulin signalling in hepatocytes in the presence of low levels of LPS.

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Pharmacological blocking of LBP improves systemic glucose homeostasis.

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Knockdown of hepatic Lbp improves systemic glucose homeostasis.

Intracellular cAMP Sensor EPAC: Physiology, Pathophysiology, and Therapeutics Development

This review focuses on one family of the known cAMP receptors, the exchange proteins directly activated by cAMP (EPACs), also known as the cAMP-regulated guanine nucleotide exchange factors (cAMP-GEFs). Although EPAC proteins are fairly new additions to the growing list of cAMP effectors, and relatively "young" in the cAMP discovery timeline, the significance of an EPAC presence in different cell systems is extraordinary. The study of EPACs has considerably expanded the diversity and adaptive nature of cAMP signaling associated with numerous physiological and pathophysiological responses. This review comprehensively covers EPAC protein functions at the molecular, cellular, physiological, and pathophysiological levels; and in turn, the applications of employing EPAC-based biosensors as detection tools for dissecting cAMP signaling and the implications for targeting EPAC proteins for therapeutic development are also discussed.

Quantitative proteomic analysis of hepatocyte-secreted extracellular vesicles reveals candidate markers for liver toxicity

Extracellular vesicles have created great interest as possible source of biomarkers for different biological processes and diseases. Although the biological function of these vesicles is not fully understood, it is clear that they participate in the removal of unnecessary cellular material and act as carriers of various macromolecules and signals between the cells. In this report, we analyzed the proteome of extracellular vesicles secreted by primary hepatocytes. We used one- and two-dimensional liquid chromatography combined with data-independent mass spectrometry. Employing label-free quantitative proteomics, we detected significant changes in vesicle protein expression levels in this in vitro model after exposure to well-known liver toxins (galactosamine and Escherichia coli-derived lipopolysaccharide). The results allowed us to identify candidate markers for liver injury. We validated a number of these markers in vivo, providing the basis for the development of novel methods to evaluate drug toxicity. This report strongly supports the application of proteomics in the study of extracellular vesicles released by well-controlled in vitro cellular systems. Analysis of such systems should help to identify specific markers for various biological processes and pathological conditions.

BIOLOGICAL SIGNIFICANCE

Identification of low invasive candidate marker for hepatotoxicity. Support to apply proteomics in the study of extracellular vesicles released by well-controlled in vitro cellular systems to identify low invasive markers for diseases.

8-Chloroadenosine 3',5'-monophosphate induces cell cycle arrest and apoptosis in multiple myeloma cells through multiple mechanisms

The aim of this study was to investigate the molecular mechanism of 8-chloroadenosine 3',5'-monophosphate (8-Cl-cAMP) in the inhibition of the growth and induction of apoptosis of multiple myeloma (MM) cells. Two MM-derived cell lines, RPMI-8226 and U266, were used. Cell viability, apoptosis induction and mitochondrial transmembrane potential were determined and the expression levels of cell cycle regulatory proteins (Cdk2, cyclin E, p27 and c-myc) and p38 mitogen-activated protein kinase (MAPK) protein were detected. Following treatment with 8-Cl-cAMP, the percentage of apoptotic cells increased in a concentration- and time-dependent manner and the mitochondrial transmembrane potential collapsed to reveal typical apoptotic features. Our data further demonstrated that 8-Cl-cAMP induced progressive phosphorylation of p38 MAPK and that the expression levels of p27 proteins in the MM cells were increased whereas those of c-myc were significantly decreased. Notably, the proapoptotic effect of 8-Cl-cAMP was largely prevented by a p38 MAPK inhibitor. Furthermore, knockdown of p27 was able to decrease the 8-Cl-cAMP-induced apoptosis in the MM cells. These results indicate that 8-Cl-cAMP induced p27-dependent cell cycle arrest and apoptosis in the MM cells, which demonstrates the potential of cAMP-modulating agents for use in the treatment of MM.

cAMP-guanine exchange factor protection from bile acid-induced hepatocyte apoptosis involves glycogen synthase kinase regulation of c-Jun NH2-terminal kinase

Cholestatic liver disorders are accompanied by the hepatic accumulation of cytotoxic bile acids that induce cell death. Increases in cAMP protect hepatocytes from bile acid-induced apoptosis by a cAMP-guanine exchange factor (cAMP-GEF)/phosphoinositide-3-kinase (PI3K)/Akt pathway. The aim of these studies was to identify the downstream substrate in this pathway and to determine at what level in the apoptotic cascade cytoprotection occurs. Since inhibitory phosphorylation of glycogen synthase kinase-3 (GSK) occurs downstream of PI3K/Akt and this phosphorylation has been implicated in cell survival, we conducted studies to determine whether GSK was downstream in cAMP-GEF/PI3K/Akt-mediated cytoprotection. Our results show that treatment of hepatocytes with the cAMP-GEF-specific analog, 4-(4-chlorophenylthio)-2'-O-methyladenosine-3',5'-cAMP, results in PI3K-dependent phosphorylation of GSK. Direct chemical inhibition of GSK in rat hepatocytes or human HUH7-NTCP cells with several structurally and functionally distinct inhibitors including bromoindirubin-3'-oxime (BIO), maleimides (SB216763, SB415286), thiadiazolidine derivatives, and LiCl attenuates apoptosis induced by glycochenodeoxycholate (GCDC). In addition, genetic silencing of the GSK β isoform with small interfering RNA attenuates GCDC apoptosis in HUH7-NTCP cells. Adenoviral inhibition of the Rap1 blocks both cAMP-GEF-mediated cytoprotection against GCDC-induced apoptosis and Akt/GSK3β phosphorylation. GCDC-induced phosphorylation of the proapoptotic kinase, c-Jun NH(2)-terminal kinase (JNK) is inhibited by GSK inhibition or cAMP-GEF activation. GCDC-induced apoptosis is accompanied by phosphorylation of the endoplasmic reticulum stress markers pIEF2α and IRE-1, and pretreatment with the cAMP-GEF analog or GSK inhibitors prevents this phosphorylation. Collectively, our results support the presence of a cAMP/cAMP-GEF/Rap1/PI3K/Akt/GSKβ survival pathway in hepatocytes that inhibits bile acid-induced JNK phosphorylation.