Activated hepatic stellate cells promote growth and inhibit apoptosis of hepatocellular carcinoma

Liver cirrhosis is the main risk factor for the development of hepatocellular carcinoma (HCC). Activated hepatic stellate cells (HSC)/myofibroblasts are the effector cells of hepatic fibrosis and secrete several growth factors known to be mitogenic. It has been shown previously that the stroma of HCC is infiltrated as well as encapsulated by activated HSC/ myofibroblasts. However, so far little is known about the interaction of activated HSC and HCC cells. Here we aimed to analyze the effects of activated HSC on the proliferation and growth of HCC cell lines in vitro and in vivo.

Methods: We analyzed the interaction of the HCC cell lines HepG2, Hep3B and PLC and human culture activated HSC, respectively, in vitro in monolayers as well as in 3-dimensional spheroid structures and in vivo after subcutaneous implantation into nude mice.

Results: Conditioned media (CM) of activated HSC significantly induced the proliferation of HCC cells in monolayers. Moreover, CM from activated HSC induced NFkB activity in HCC cell lines and inhibited apoptosis. In accordance, mixed spheroids from activated HSC and HCC-cells, respectively, revealed a significantly increased growth as compared to spheroids of HCC cells alone. Furthermore, mixed spheroids had smaller areas of central necrosis. After implantation of Hep3B or PLC cells in nude mice no tumor formation was detected during the observation interval of 12 weeks. In contrast, after implantation of a mixture of Hep3B cells and activated HSC formation of tumors was observed in all (10/10) mice after 4 weeks. HepG2 formed tumors also in the absence of activated HSC, however, mixed tumors of HepG2 and activated HSC grew significantly faster. Histological examination revealed smaller areas of central necrosis in mixed tumors as compared to tumors from HepG2 cells alone.

Conclusion: Activated HSC reveal a strong mitogenic effect on HCC cell lines in vitro and in vivo. In addition, activated HSC seem to protect HCC cells from apoptosis, potentially via NFkB activation. Herewith, stromal activated HSC/myofibroblasts might promote HCC progression. This interaction may be an interesting tumor cell differentiation-independent target for therapy.

Schlüsselwörter

Activated hepatic stellate cells; apoptosis; hepatocellular carcinoma