Analysis of Pathological Activities of CCN Proteins in Fibrotic Diseases: Liver Fibrosis

Expression and biological function of the cellular communication network factor 5 (CCN5) in primary liver cells

The cellular (centralized) communication network (CCN) factor protein family contains six small secreted cysteine-rich proteins sharing high structural similarity. These matricellular proteins have vital biological functions in cell adhesion, migration, cell cycle progression, and control of production and degradation of extracellular matrix. However, in liver the biological functions of CCN proteins become most visible during hepatic injury, disease, and remodeling. In particular, most of the hepatic functions of CCN proteins were derived from CCN2/CTGF, which becomes highly expressed in damaged hepatocytes and acts as a profibrogenic molecule. On the contrary, CCN1/CYR61 seems to have opposite effects, while the biological activity during hepatic fibrosis is somewhat controversially discussed for other CCN family members. In the present study, we analyzed the expression of CCN5/WISP2 in cultures of different types of primary liver cells and in an experimental model of hepatic fibrosis. We found that CCN5 is expressed in hepatic stellate cells, myofibroblasts and portal myofibroblasts, while CCN5 expression is virtually absent in hepatocytes. During hepatic fibrogenesis, CCN5 is significantly upregulated. Overexpression of CCN5 in portal myofibroblasts reduced expression of transforming growth factor-β receptor I (ALK5) and concomitant Smad2 activation, whereas JunB expression is upregulated. Moreover, elevated expression of CCN5 induces endoplasmic reticulum stress, unfolded protein response and apoptosis in portal myofibroblasts. We suggest that upregulated expression of CCN5 might be an intrinsic control mechanism that counteracts overshooting fibrotic responses in profibrogenic liver cells.

FN14 mRNA Expression Correlates with an Increased Number of Veins during Angiogenesis in the Process of Liver Fibrosis

In this study, we hypothesize that angiogenesis of special hepatic vessels such as sinusoid capillaries or veins is closely associated with increasing production of connective tissue in fibrogenesis. Thirty-six male Wistar rats were induced with hepatitis and cirrhosis of the liver using thioacetamide. The number of sinusoidal capillaries, veins, arteries and the area of connective tissue were counted and determined. Immunohistochemical study was performed on paraffin sections using monoclonal mouse anti-CD31. mRNA expression was determined using qPCR. We found a statistically significant reduction in the number of sinusoidal capillaries (p<0.0001) and an increase in the number of interlobular veins (p<0.0001) in the fibrosis and cirrhosis groups compared to the control group. There are no differences in the number of interlobular arteries (p=0.282) in the three groups. In our analysis, we found that the expression (mRNA) of Fn14 correlated with the number of veins in liver fibrosis (r=0.44, p=0.008). Our data shows that modulation of veins angiogenesis during fibrosis in chronic liver diseases may play an important role in increasing pathological changes of the liver.

Emerging role of CCN family proteins in fibrosis

Fibrosis is a common pathological change characterized by the excessive accumulation of fibrous connective tissue. Once uncontrolled, this pathological progress can lead to irreversible damage to the structure and function of organs, which is a serious threat to human health and life. Actually, the disability and death of patients caused by many chronic diseases have a closed relationship with fibrosis. The CCN protein family, including six members, is a small group of matrix proteins exhibiting structurally similar features. In the past 20 years, different biological functions of CCN proteins have been identified in various diseases. Of note, it has been recently shown that they are implicated in the key pathological process of fibrosis. In this review, we summarize the current status of knowledge regarding the role of CCN proteins involved in the pathogenesis of fibrosis diseases in detail. Furthermore, we highlight some of the underlying interaction mechanisms of CCN protein acting in fibrosis that helps to develop new drugs and determine appropriate clinical strategies for fibrotic diseases.

Paracrine effects of CCN3 from non-cancerous hepatic cells increase signaling and progression of hepatocellular carcinoma

BACKGROUND

The liver microenvironment plays a key role in the progression and metastasis of hepatocellular carcinoma (HCC). Gene expression profiling of non-cancerous hepatic tissues obtained from patients with metastatic HCC exhibit a unique immune response signature, including upregulation of CCN3. However, the role of CCN3 secreted from non-cancerous hepatic tissues in the progression of HCC remains unclear.

METHODS

Using tissue microarrays, we examined CCN3 in non-cancerous hepatic tissues of patients with HCC and correlated expression with clinical and pathological features. In addition, CCN3 localization and mechanisms of HCC progression were investigated in tissues and cell lines. Finally, correlations between CCN3 and cirrhosis were explored in patients.

RESULTS

CCN3 was primarily localized to hepatic cells of non-cancerous hepatic tissues and was associated with vascular invasion and poor prognosis in patients with HCC. CCN3 expression in non-cancerous hepatic tissues also correlated with the degree of liver fibrosis. Compared with conditioned media from wild-type LO2 cells, conditioned media from hepatic cell line LO2 activated by LX2 (aLO2-CM) induced CCN3 expression and HCC cell proliferation and metastasis. Further, aLO2-CM activated MAPK signaling and epithelial-mesenchymal transition in HCC cells. Finally, CCN3 was inversely related to cirrhosis in the prognosis of HCC and negatively regulated hepatic stellate cells (HSCs) in vitro with downregulation of α-SMA, TGF-β, and collagens.

CONCLUSIONS

CCN3 was secreted from hepatic cells activated by HSCs and increased MAPK signaling, EMT, proliferation and metastasis of HCC cells. CCN3 was also inversely related to cirrhosis, regulating HSCs through a negative feedback loop.