Importance of inhibitor of DNA binding/differentiation 2 in hepatic stellate cell differentiation and proliferation

Over-Expression of Inhibitor of Differentiation 2 Attenuates Post-Infarct Cardiac Fibrosis Through Inhibition of TGF-β1/Smad3/HIF-1α/IL-11 Signaling Pathway

Background: Cardiac fibrosis after myocardial infarction mainly causes cardiac diastolic and systolic dysfunction, which results in fatal arrhythmias or even sudden death. Id2, a transcriptional repressor, has been shown to play an important role in the development of fibrosis in various organs, but its effects on cardiac fibrosis remain unclear. This study aimed to explore the effects of Id2 on cardiac fibrosis after myocardial infarction and its possible mechanisms.

Methods: This study was performed in four experimental groups: control group, treatment group (including TGF-β1, hypoxia or MI), treatment+GFP group and treatment+Id2 group. In vitro anoxic and fibrotic models were established by subjecting CFs or NRVMs to a three-gas incubator or TGF-β1, respectively. An animal myocardial infarction model was established by ligating of the left anterior descending coronary artery followed by directly injecting of Id2 adenovirus into the myocardial infarct’s marginal zone.

Results: The results showed that Id2 significantly improved cardiac EF and attenuated cardiac hypertrophy. The mRNA and protein levels of α-SMA, Collagen I, Collagen III, MMP2 and TIMP1 were higher in treatment+Id2 group than those in treatment group as well as in treatment+GFP group both in vivo and in vitro. Immunofluorescence revealed that both α-SMA and vimentin were co-expressed in the treatment group and GFP group, but the co-expression were not detected in the control group and Id2 group. Additionally, our findings illustrated that Id2 had protective effects demonstrated by its ability to inhibit the TGF-β1/Smad3/HIF-1α/IL-11 signaling pathways. Besides, over-expression of Id2 reduced cardiomyocytes apoptosis.

Conclusion: In conclusion, this study demonstrated that over-expression of Id2 preserved cardiac function and ameliorated adverse cardiac remodeling, which might be a promising treatment target for cardiac fibrosis and apoptosis.

BMP-7/Smads-induced inhibitor of differentiation 2 (Id2) upregulation and Id2/Twist interaction was involved in attenuating diabetic renal tubulointerstitial fibrosis

Renal tubular epithelial-mesenchymal transition (EMT) is the main pathological change in diabetic renal tubulointerstitial fibrosis. Mounting evidence indicates that the inhibitor of differentiation 2 (Id2) protein acts as a negative regulatory factor in organ fibrosis and can inhibit or reverse the process of fibrosis. However, its specific regulatory mechanism is not clear. Diabetes mellitus (DM) rat models were established by injecting rats with streptozotocin and sacrificing them after 16 weeks. Rat renal tubular epithelial cells (NRK-52E) were cultured with normal and high glucose. Immunohistochemical analysis, double immunofluorescence staining, co-immunoprecipitation, Western blot analysis, and real-time polymerase chain reaction were used to determine the expression of Id2, Twist, Smad1/5/8, E-cadherin, α-smooth muscle actin (α-SMA), and collagen Ⅳ. The results showed that bone morphogenetic protein-7 (BMP-7) upregulated the expression of Id2 against high-glucose-induced EMT and extracellular matrix secretion. Moreover, only the simultaneous knockdown of Smad1, Smad5, and Smad8 downregulated the expression of Id2, which was not altered by the individual knockdown of Smad1, Smad5, and Smad8. Basic helix-loop-helix (bHLH) transcription factors were essential for Id2 to regulate the role of downstream target genes, and Twist was a bHLH transcription factor. Therefore, the expression of Twist was examined in this study. Twist was found to be highly expressed in the kidney of DM rats and renal tubular epithelial cells cultured with high glucose. The overexpression of Id2 did not alter the expression of Twist, but the interaction between Id2 and Twist was enhanced. In conclusion, the data showed the specific mechanism underlying Id2 negative regulation in diabetic renal tubulointerstitial fibrosis.

CD5L is a pleiotropic player in liver fibrosis controlling damage, fibrosis and immune cell content

BACKGROUND

Chronic hepatic inflammation leads to liver fibrosis, which may progress to cirrhosis, a condition with high morbidity. Our aim was to assess the as yet unknown role of innate immunity protein CD5L in liver fibrosis.

METHODS

CD5L was measured by ELISA in plasma samples from cirrhotic (n = 63) and hepatitis (n = 39) patients, and healthy controls (n = 7), by immunohistochemistry in cirrhotic tissue (n = 12), and by quantitative RT-PCR in mouse liver cell subsets isolated by cell sorting. Recombinant CD5L (rCD5L) was administered into a murine model of CCl₄-induced fibrosis, and damage, fibrosis and hepatic immune cell infiltration, including the LyC6^hi (pro-fibrotic)-LyC6^low (pro-resolutive) monocyte ratio were determined. Moreover, rCD5L was added into primary human hepatic stellate cells to study transforming growth factor β (TGFβ) activation responses.

FINDINGS

Cirrhotic patients showed elevated plasma CD5L concentrations as compared to patients with hepatitis and healthy controls (Mann-Whitney test p < 0·0001). Moreover, plasma CD5L correlated with disease progression, FIB4 fibrosis score (r:0·25, p < 0·0001) and tissue expression (r = 0·649; p = 0·022). Accordingly, CCl₄-induced damage increased CD5L levels in total liver, particularly in hepatocytes and macrophages. rCD5L administration attenuated CCl₄-induced injury and fibrosis as determined by reduced serum transaminase and collagen content. Moreover, rCD5L inhibited immune cell infiltration and promoted a phenotypic shift in monocytes from LyC6^hi to LyC6^low. Interestingly, rCD5L also had a direct effect on primary human hepatic stellate cells promoting SMAD7 expression, thus repressing TGFβ signalling.

INTERPRETATION

Our study identifies CD5L as a key pleiotropic inhibitor of chronic liver injury. FUND: Fundació Marató TV3, AGAUR and the ISCIII-EDRF.

BMP-7/TGF-β1 signalling in myoblasts: components involved in signalling and BMP-7-dependent blockage of TGF-β-mediated CTGF expression

We and others have recently described the antagonistic role of Bone morphogenetic protein-7 (BMP-7) in TGF-β signalling and myogenic differentiation. To specify the underlying mechanism(s), we here analysed the expression and function of the individual components mediating TGF-β1 and BMP-7 responses. We found that BMP-7 at a concentration of 25 ng/ml induces signalling exclusively via ALK2 and ALK3 leading to the activation of Smad1 and Smad5 and subsequent expression of Id proteins. In contrast, low doses of TGF-β1 (0.1 ng/ml) lead to an exclusive activation of ALK5 and phosphorylation of Smad2 and Smad3 that regulate specific target genes including connective tissue growth factor (CTGF). CTGF is rapidly induced by TGF-β1 already 1h after stimulation and reduced by BMP-7 application. Smad1/Smad5 or Id1/2 overexpression reduced the TGF-β1-mediated expression of CTGF. However, although siRNA-mediated knock down of Alk2/3 or Smad1/5 counteracts the BMP-7 effect on basal CTGF expression there was no consistent reversion of the observed BMP-7 effect on TGF-β1-mediated CTGF expression. Moreover, ALK5 inhibition using the SB431542 inhibitor significantly affected CTGF expression only at later time points whereas ERK1/2 inhibition completely abrogated CTGF expression. These findings point towards a regulatory role of BMP-7 that relies on modulation of Mitogen-activated protein kinases rather than mechanisms that are exclusively driven by differential Smad activation.

Splenectomy reduces fibrosis and preneoplastic lesions with increased triglycerides and essential fatty acids in rat liver cirrhosis induced by a choline-deficient L-amino acid-defined diet

AIM

  This study investigated whether splenectomy is of significance in non-alcoholic steatohepatitis (NASH).

METHODS

  Five-week-old Wistar rats were fed a choline-deficient diet for 8 weeks to create a NASH model. A sham-operation or splenectomy was then performed, and rats were killed 4 weeks later.

RESULTS

  Liver fibrosis and liver preneoplastic lesions were significantly reduced in the splenectomy group compared to the sham-operation group, and α-smooth muscle actin (SMA) expression was significantly inhibited (liver fibrosis area: sham 8.63 ± 4.09%, splenectomy 5.45 ± 3.69%, P < 0.01; preneoplastic lesion size: sham 6.56 ± 3.68 ×10(6)  µm(2) /cm(2) , splenectomy 4.63 ± 3.27 ×10(6)  µm(2) /cm(2) , P < 0.05; the number of preneoplastic lesions: sham 8.33 ± 3.96/cm(2) , splenectomy 5.17 ± 1.80/cm(2) , P < 0.01; α-smooth muscle actin-positive area: sham 4.41 ± 2.48%, splenectomy 2.75 ± 1.66%, P < 0.01) On the other hand, liver triglycerides and essential fatty acids were significantly increased in the splenectomy group (liver triglycerides: sham 182 ± 35.0 mg/g, splenectomy 230 ± 35.0 mg/g, P < 0.05; liver linoleic acid: sham 17.2 ± 4.9 mg/g, splenectomy 23.3 ± 6.9 mg/g, P < 0.05; liver α-linolenic acid: sham 118 ± 36.6 µg/g, splenectomy 162 ± 51.4 µg/g, P < 0.05). In addition, expressions of hepatic fatty acid metabolism-related genes (e.g. acyl-CoA oxidase, liver carnitine palmitoyl-CoA transferase I, cytochrome P450 4A, long-chain acyl-CoA dehydrogenase and medium-chain acyl-CoA dehydrogenase) were significantly inhibited in the splenectomy group.

CONCLUSION

  These findings suggest that spleen plays an important regulatory role in the fibrosis, preneoplastic lesion and lipid metabolism of liver in a rat choline-deficient L-amino acid model.

Pathogenesis of liver fibrosis

Liver fibrosis is a major cause of morbidity and mortality worldwide due to chronic viral hepatitis and, more recently, from fatty liver disease associated with obesity. Hepatic stellate cell activation represents a critical event in fibrosis because these cells become the primary source of extracellular matrix in liver upon injury. Use of cell-culture and animal models has expanded our understanding of the mechanisms underlying stellate cell activation and has shed new light on genetic regulation, the contribution of immune signaling, and the potential reversibility of the disease. As pathways of fibrogenesis are increasingly clarified, the key challenge will be translating new advances into the development of antifibrotic therapies for patients with chronic liver disease.

Emodin protects rat liver from CCl4-induced fibrogenesis via inhibition of hepatic stellate cells activation

AIM: To investigate the role of emodin in protecting the liver against fibrogenesis caused by carbon tetrachloride (CCl₄) in rats and to further explore the underlying mechanisms.

METHODS: Rat models of experimental hepatic fibrosis were established by injection with CCl₄; the treated rats received emodin via oral administration at a dosage of 20 mg/kg twice a week at the same time. Rats injected with olive oil served as a normal group. Histopathological changes were observed by hematoxylin and eosin staining. The activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in serum and hepatic hydroxyproline content were assayed by biochemical analyses. The mRNA and protein relevant to hepatic stellate cell (HSC) activation in the liver were assessed using real-time reverse transcription-polymerase chain reaction (RT-PCR), immunohistochemistry, western blotting and enzyme-linked immunosorbent assay.

RESULTS: The degree of hepatic fibrosis increased markedly in the CCl₄ group compared to the normal group (P < 0.01), and decreased markedly in the emodin group compared to the CCl₄ group according to METAVIR scale (P < 0.01) compared with those in the normal control group (51.02 ± 10.64 IU/L and 132.28 ± 18.14 IU/L). The activities of serum ALT and AST were significantly higher in rats injected with CCl₄ (289.25 ± 68.84 IU/L and 423.89 ± 35.67 IU/L, both P < 0.05). The activities of serum ALT and AST were significantly reduced by administration of emodin (176.34 ± 47.29 IU/L and 226.1 ± 44.52 IU/L, both P < 0.05). Compared with the normal controls (54.53 ± 13.46 mg/g), hepatic hydroxyproline content was significantly higher in rats injected with CCl₄ (120.27 ± 28.47 mg/g, P < 0.05). Hepatic hydroxyproline content was significantly reduced in the rats treated with emodin at 20 mg/kg (71.25 ± 17.02 mg/g, P < 0.05). Emodin significantly protected the liver from injury by reducing serum AST and ALT activities and reducing hepatic hydroxyproline content. The mRNA levels of transforming growth factor-β1 (TGF-β1), Smad4 and α-SMA in liver tissues were significantly down-regulated in SD rats that received emodin treatment. Furthermore, significant down-regulation of serum TGF-β1 protein levels and protein expression of Smad4 and α-SMA in liver tissues was also observed in the rats. Emodin inhibited HSC activation by reducing the abundance of TGF-β1 and Smad4.

CONCLUSION: Emodin protects the rat liver from CCl₄-induced fibrogenesis by inhibiting HSC activation. Emodin might be a therapeutic antifibrotic agent for the treatment of hepatic fibrosis.

Transcriptional regulation of hepatic stellate cells

Hepatic stellate cell (HSC) activation is a process of cellular transdifferentiation in which, upon liver injury, the quiescent vitamin A storing perisinusoidal HSC is converted into a wound-healing myofibroblast and acquires potent pro-inflammatory and pro-fibrogenic activities. This remarkable phenotypic transformation is underpinned by changes in the expression of a vast number of genes. In this review we survey current knowledge of the transcription factors that either control HSC activation or which regulate specific fibrogenic functions of the activated HSC such as collagen expression, proliferation and resistance to apoptosis.