This work employed a mouse model of liver specific depletion of the gene Cdh1 and its respective protein E cadherin to study the role of this protein in liver homeostasis and pathophysiology. The experiment was done with specific focus on the effects concerning hepatocellular carcinoma (HCC) development.
Background: Cadherins are present in all higher organisms, and have been studied rigorously in the past. The cadherin family is huge, encompassing more than 400 (known) members. E cadherin is the name-giver of that family and is considered to be of great importance to a broad range of physiological and pathophysiological functions. Known functions include cell-cell adhesion and deregulation of E-cadherin (in almost all cases a down-regulation) is associated with increased aggressiveness in both human and animal tumors. Aside from that, E-cadherin is of great importance during embryogenesis.
Worldwide, HCC is an important disease in humans, especially in certain countries (mostly developing countries). While females are only occasionally affected by HCC, it ranks among the top 3 tumor-related death causes in males. The difficulties in treating this tumor curatively make research of genes or proteins relevant to HCC important for human medicine improvement. The existence of a connection between Cdh1 or E Cadherin and HCC has been suggested, but more research is still required.
Methods: Employing Cre/loxP technology, a mouse model of liver specific E cadherin depletion was created (L Cdh1del/del). The mice were compared to littermates with normal Ecadherin levels (L Control). Mice body and organ weight was documented at different ages, and liver tissue was analyzed using qRT-PCR (cDNA), Western blot, histochemistry and immunohistochemistry.
To test effects of the reduced E-cadherin on tumor development, a cohort of male mice was injected with a chemical carcinogen (DEN) at two weeks of age to induce HCC, and mice were analyzed 4, 8 or 12 months later.
Results: Aside from a slight retardation in weight gain, L Cdh1del/del did not suffer from severe health effects or spontaneous tumor development. Histology showed some alterations around the small bile ducts in the liver (in the periportal fields) and RNA analysis showed that mice underwent a phase of considerably altered RNA activity (429 significantly regulated genes at 3 weeks of age), but later only a few up/down-regulated genes remained (28 genes at 6 weeks of age). Aside from Cdh1, no genes considered cadherin family members were regulated. Western blot analysis, qRT-PCR and IHC confirmed that E cadherin was down regulated on RNA level and on protein level in this animal model.
All mice injected with DEN developed tumors, but L Cdh1del/del were affected more heavily, with tumors reaching large diameters faster. If mice were kept longer than 8 months, L Cdh1del/del had to be euthanized significantly earlier than L Control.
A spin-off of the model was the establishment of a permanent cell line, developed from a liver tumor of a L Cdh1del/del mouse. PCR requiring a functional primer binding site on exon 10 of Cdh1 could not produce DNA product, indicating that the cell line was a derivative of an E-cadherin negative liver cell.
Conclusion: Liver specific E cadherin reduction had a surprisingly small effect in the present mouse model (compared to the effects of E cadherin loss in organs like the skin or intestine, as documented in the literature) if mice were not challenged with a chemical carcinogen.
If mice were challenged with experimental HCC induction, lack of E cadherin had a strong effect on the tumor growth. These findings attest, by an experimental animal model, the importance of E cadherin for tumor development in the liver. This data reinforces previous observations concerning E cadherin effects on tumors in studies working with resected human tumors of the liver or with conditional organ specific mouse models studying carcinoma in other organs (like