Regulation of activin receptor-interacting protein 2 expression in mouse hepatoma Hepa1-6 cells and its relationship with collagen type IV

The role of activin: the other side of chronic kidney disease-mineral bone disorder?

Chronic kidney disease-mineral bone disorder (CKD-MBD) plays a pivotal role in the excess of cardiovascular morbidity and mortality associated with CKD. There is now a growing awareness that pathways involved in CKD-MBD, like canonical Wnt signalling, are activated from the earliest stages of CKD, playing a role in the development of adynamic bone disease with unknown consequences on vasculature. These changes occur before the classic changes in mineral metabolism: secondary hyperparathyroidism, calcitriol deficiency and hyperphosphataemia. Furthermore, vascular calcification is frequently associated and evolves with decreased bone mineral density and deranged bone turnover, while bone and arterial mineralization share common pathways. Therefore, results of clinical trials focused on mineral bone disorder, aimed at preserving bone and cardiovascular health, are considered unsatisfactory. In order to identify more effective therapeutic strategies, it is necessary to clarify the pathways modulating the cross-talk between bone and vasculature and identify new mediators involved in the pathogenesis of CKD-MBD. Much attention has been paid recently to the role of the transforming growth factor-beta superfamily members in renal disease, and in particular of activin A (ActA). Preclinical studies demonstrate an upgrade of ActA signalling in kidney, skeleton, vasculature and heart during CKD. This supports the idea that an endocrine factor produced in the kidney during renal disease, in addition to promoting the progression of kidney damage, deranges other organs' homoeostasis and participates in CKD-MBD. In this review, we analyse the contribution of ActA to kidney fibrosis and inflammation as well as its role in the development of CKD-MBD.

Expression and anti-inflammatory role of activin receptor-interacting protein 2 in lipopolysaccharide-activated macrophages

The bacterial endotoxin lipopolysaccharide (LPS), a key pathogenic stimulator, can induce the activation of macrophages. Activin receptor-interacting protein 2 (ARIP2), an intracellular signaling protein, has a wide histological distribution, however, whether ARIP2 is involved in regulation of activation of macrophages was not well characterized. Here, by immunocytochemical staining, we found that ARIP2 protein existed in monocyte-macrophage cell line RAW264.7 cells and peritoneal macrophages of mouse, and ARIP2 expression in RAW264.7 cells was up-regulated by LPS. Furthermore, the results revealed that ARIP2 overexpression in the LPS-activated RAW264.7 cells inhibited the productions of IL-1β and TNFα, phagocytic activities and CD14 expression, whereas did not alter expressions of MyD88, TLR2 and TLR4. Additionally, in vivo ARIP2 overexpression also reduced the productions of IL-1β and TNFα from the LPS-stimulated peritoneal macrophages of mouse. These data suggest that ARIP2 may play an anti-inflammatory role in macrophages via inhibiting CD14 expression.

Ramipril attenuates left ventricular remodeling by regulating the expression of activin A-follistatin in a rat model of heart failure

Prior studies have shown that overexpression of ACT A can lead to ventricular remodeling in rat models of heart failure. Furthermore, recently work studying demonstrated that stimulation of activin An expression in rat aortic smooth muscle (RASM) cells by angiotensin II (Ang II). Ramipril is a recently developed angiotensin converting enzyme (ACE) inhibitor. To investigate the effects of Ramipril on expression of ACT A-FS, we established the rat model of heart failure after myocardial infarction (MI), and divided into either a sham operation (SO), MI, or MI-Ramipril group. We found that Ramipril significantly attenuates collagen-I and III deposition (col-I and III). Notably, we determined that expression of ACT A and II activin receptor (ActRII) were significantly down-regulated in the non-infarcted area of the left ventricle in the Ramipril group, whereas the mRNA and protein levels of FS were markedly up-regulated. Our data suggested that Ramipril benefited left ventricular remodeling by reducing fibrosis and collagen accumulation in the left ventricle of rats after myocardial infarction. This observation was also associated with down-regulation of ACT A expression. This study elucidated a new protective mechanism of Ramipril and suggests a novel strategy for treatment of post-infarct remodeling and subsequent heart failure.

Localisation and role of activin receptor-interacting protein 1 in mouse brain

Activin A, a stimulator of follicle-stimulating hormone secretion from the pituitary, acts as a neurotrophic and neuroprotective factor in the central nervous system. Activin receptor-interacting protein 1 (ARIP1) has been identified as a cytoplasmic protein that interacts with the type II receptor of activin (ActRII). However, the distribution pattern and function of ARIP1 are not well characterised in the brain. In the present study, we confirmed the existence of mRNA and protein of ARIP1 in the mouse brain, and found that ARIP1 was mainly localised at the hippocampus and hypothalamus in the cerebrum, granular layers in the cerebellum (especially in Purkinje cells of the cerebellum) and choroid epithelial cells by immunohistochemical staining. Furthermore, in contrast to the significant increase of activin A mRNA, ARIP1 mRNA and protein expression decreased in the mechanically lesioned brain of the mouse. Using neuroblastoma-derived Neuro-2a cells to investigate the function of ARIP1, we found that overexpression of ARIP1 down-regulated the activin A-induced signal transduction and significantly decreased the voltage-gated Na(+) current (I(Na) ). These data indicate that ARIP1 is a key molecule for the regulation of the action of activin in neurones, and also that decreased ARIP1 expression in the lesioned brain may be beneficial to the neurotrophic and neuroprotective roles of activin A in recovery after brain injury.

Expression and localization of activin receptor-interacting protein 2 in mouse tissues

Activin plays important roles in reproductive tissues as a stimulator of follicle-stimulating hormone (FSH) secretion. Activin receptor-interacting protein 2 (ARIP2) has been recently identified in mouse tissues as a regulatory protein of activin signal transduction. However, the localization and function of ARIP2 are not well characterized. In this study, we found that ARIP2 mRNA and protein were widely expressed in mouse tissues by reverse transcription-PCR (RT-PCR) and Western blotting. The immunoreactivities of ARIP2 were mainly localized at myocardial cells of heart, Leydig cells in testis, macrophages and epithelial cells of bronchus in lung, renal tubule and collecting tubule, pancreatic islet, adrenal gland, adenohypophysis and hypothalamus by immunohistochemical staining. Furthermore, ARIP2 overexpression down-regulated signal transduction induced by activin A in pituitary gonadotroph LbetaT2 cells and inhibited FSH secretion from primary cultured anterior pituitary cells induced by activin A. These findings suggest that ARIP2 is widely distributed in various tissues and may be a negative regulator of activin action in pituitary cells.

Activins and activin antagonists in hepatocellular carcinoma

In many parts of the world hepatocellular carcinoma (HCC) is among the leading causes of cancer-related mortality but the underlying molecular pathology is still insufficiently understood. There is increasing evidence that activins, which are members of the transforming growth factor β (TGFβ) superfamily of growth and differentiation factors, could play important roles in liver carcinogenesis. Activins are disulphide-linked homo- or heterodimers formed from four different β subunits termed βA, βB, βC, and βE, respectively. Activin A, the dimer of two βA subunits, is critically involved in the regulation of cell growth, apoptosis, and tissue architecture in the liver, while the hepatic function of other activins is largely unexplored so far. Negative regulators of activin signals include antagonists in the extracellular space like the binding proteins follistatin and FLRG, and at the cell membrane antagonistic co-receptors like Cripto or BAMBI. Additionally, in the intracellular space inhibitory Smads can modulate and control activin activity. Accumulating data suggest that deregulation of activin signals contributes to pathologic conditions such as chronic inflammation, fibrosis and development of cancer. The current article reviews the alterations in components of the activin signaling pathway that have been observed in HCC and discusses their potential significance for liver tumorigenesis.

Activin receptor-interacting protein 2 expression and its biological function in mouse hepatocytes

AIM: To investigate the activin receptor-interacting protein 2 (ARIP2) expression and its biological function in hepatocytes.

METHODS: Expression of ARIP2 in mouse liver tissue and hepatoma cell line Hepal-6 cells was detected by Western blot, immunohistochemistry and cytochemical staining. Effect of ARIP2 on activin-induced gene transcription was analyzed using CAGA-lux plasmid. Effect of over-expression of ARIP2 on the proliferation of Hepal-6 cells was assayed with MTT method.

RESULTS: ARIP2 was expressed in mouse liver tissue and Hepal-6 cells. The expression of ARIP2 in activin A-stimulated Hepal-6 cells was increased in a time-dependent manner, and peaked at 24 h. There was a significant difference in the expression level of ARIP2 on Hepal-6 cells at 12 and 24 h in contrast with the control group (1.01 ± 0.16, 1.62 ± 0.26 vs 0.82 ± 0.11, P < 0.05, P < 0.01). pcDNA3-ARIP2-transfected Hepal-6 cells obviously suppressed the gene transcription induced by activin A. MTT assay displayed that activin A (5 μg/L and 10 μg/L) remarkably inhibited the proliferation of Hepal-6 cells, the A₅₇₀ nm value was 1.59 ± 0.03 and 1.49 ± 0.04 vs 1.79±0.07, respectively (P < 0.05, P < 0.01). ARIP2 over-expression in Hepal-6 cells significantly blocked the inhibitory effects of activin A (5 μg/L and 10 μg/L) on the proliferation of Hepal-6 cells.

CONCLUSION: ARIP2 can be expected to become a regulation target of genes in treatment of liver injury induced by activin.