Analysis of Axin2 expression and function in murine models for pancreatic cancer

Abstract

Background: The involvement of Wnt in carcinogenesis and progression of pancreatic cancer is currently intensely discussed. We evaluated activation of the Wnt signaling pathway by using a Wnt reporter mouse strain expressing β-galactosidase under the control of the Axin2 promotor during pancreatitis induced formation of precancerous lesions. We also evaluated activation of Wnt signaling during interaction of pancreatic cancer with the tumor stroma.

Results: Activation of Wnt signaling was observed during acinar-to-ductal metaplasia after chronic as well as acute pancreatitis. Activation of Wnt signaling was also noticed during growth of pancreatic cancer in an orthotopic syngeneic pancreas cancer model. Activation of Wnt signaling was, however, not observed in carcinoma associated fibroblasts, but was detected in few cell clusters inside the tumor. Genetic ablation of Axin2 significantly reduced body weight without having a major impact on blood glucose concentration. However, ablation of Axin2 had no influence on the observed β-galactosidase positive cell clusters or on tumor weight.

Conclusion: These data demonstrate that the Wnt signaling pathway is activated during acinar-to-ductal metaplasia after injury to the pancreas. However these data do not support a major role of Wnt signaling or of Axin2 in carcinoma associated fibroblasts and tumor growth.

Keywords: Acinar cell carcinoma; Cancer immunology; Diabetes; Founder mutations; Hyperglycemia; Solid-pseudopapillary neoplasms.

Fig. 1

Characterization of the animal model for chronic pancreatitis. a Hyperglycemia was induced in two cohorts (STZ, STZ+Cer) by ip injection of 50 mg/kg streptozotocin on day 1–5 and chronic pancreatitis was then induced in two cohorts (Cer, STZ+Cer) by administration of three ip injections of cerulein (50 µg/kg) on the indicated days; the control group (Cer) was treated with the appropriate vehicle solution instead of STZ. b β-galactosidase staining in tubular complexes of the pancreas in normoglycemic and hyperglycemic Axin2^+/lacZ mice was observed after pancreatitis, whereas no β-galactosidase staining was observed in Axin2^+/+ mice. Bars 50 μm

Fig. 2

Characterization of the animal model for acute pancreatitis. a Hyperglycemia was induced in two cohorts (STZ, STZ+Cer) by ip injection of 50 mg/kg streptozotocin on day 1–5 and chronic pancreatitis was then induced in two cohorts (Cer, STZ+Cer) by administration of eight ip injections of cerulein (50 µg/kg) on day 22 and 23; the control groups (Sham, Cer) were treated with the appropriate vehicle solutions. b β-galactosidase staining in tubular complexes of the pancreas in normoglycemic and hyperglycemic Axin2^+/lacZ mice was observed after pancreatitis, whereas no β-galactosidase staining was observed in Axin2^+/+ mice. Bars 50 μm

Fig. 3

Characterization of the animal model for studying desmoplasia. a 6606PDA cells were injected on day 0 into the pancreas of C57BL6-Tg^{ACTB-eGFP1Osb/J}, Axin2^+/+, Axin2^+/lacZ or Axin2^lacZ/lacZ mice and the tumors were analyzed on day 20 or 21. b Desmoplastic reaction visualized by anti-GFP immunohistochemistry in a C57BL6-Tg^{ACTB-eGFP1Osb/J} mouse, which ubiquitously expresses GFP, shows strong GFP expression in fibroblast like cells surrounding the carcinoma (arrow), and few GFP expressing cells within the carcinoma (arrowhead). c Characteristic images of tumors in Axin2^+/lacZ mice showing no β-galactosidase staining in fibroblast like cells surrounding the carcinoma (arrow), but few clusters of β-galactosidase⁺ cells within the carcinoma (arrowhead). Bars 50 µm

Fig. 4

Analysis of body weight, blood glucose and tumor weight in Axin2^+/lacZ or Axin2^lacZ/lacZ mice. a Axin2^lacZ/lacZ mice have a significantly decreased body weight. b No major influence of Axin2 genotype on blood glucose concentration was observed. c No significant influence of Axin2 genotype on tumor weight could be demonstrated. Significant difference: *P = 0.006